ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V008T00A001. doi:10.1115/OMAE2017-NS8.

This online compilation of papers from the ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2017) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Arctic Sea Transportation

2017;():V008T07A001. doi:10.1115/OMAE2017-61211.

Challenges when operating offshore systems in the Arctic were addressed and analyzed from general data communications systems to distress communications systems. Two methodologies were developed with tools for estimating: a) Rainfall rate in the worst case as well as the degradation due to the highest rainfall rate to link budget of typical satellite links; b) Performance of any service at a given geographical area or location. The evaluations were for diversified inputs such as geographical locations were ranging from further south to high North; the most typical satellite communications systems in the region; and an abundant list of services dedicated to offshore Oil and Gas industry, the paper has provided a wide range list of results and recommendations when analyzing services performances from low to high latitudes and west to east longitudes. An important conclusion was that voice-relevant services were not working fine for both Inmarsat and VSAT from the latitude of 73.5 degree North regardless of the bandwidth of the satellite when assuming the deadline for these voice packets was one second. These services can be partially of fully satisfied by Inmarsat or VSAT depends on the bandwidth provided if working below that latitude. For file transfer services, it is possible to guarantee a certain satisfactory ratio at high latitude provided a compensation for bandwidth. The paper1 also provides other numerical results in regarding of link compensation that can be used for new satellite link purpose.

Topics: Arctic region
Commentary by Dr. Valentin Fuster
2017;():V008T07A002. doi:10.1115/OMAE2017-61814.

It is inevitable that commercial shipping and oil and gas resource exploitation activities in the Arctic will increase due to decreasing sea ice extent caused by global climate changes. Significantly more demanding and at the same time less well known environmental conditions create a need for reliable methods to assess icebreaking performance guaranteeing safe performance of the ships operating in this area subjected to various ice conditions. The classic approach of assessing ice-going performance, which combines class rules, experience and model tests, may not be applicable for the Arctic region in full. Furthermore, ship yards experience difficulties due to decreasing time frames and financial restrictions. Therefore this paper seeks to introduce a new development for a realistic and validated direct simulation approach for prediction of the hull load and icebreaking resistance that covers all aspects of the industrial design process and allows a more comprehensive analysis. The breaking model will provide a variable breaking pattern and is able to mimic the influence of the vessel speed and the environment on the ice loading and the predicted breaking length. In order to predict the extreme representative conditions to be simulated, a reverse extreme load prediction methodology is incorporated. An efficient, time dependent dynamic coupling between broken ice fragments, ice features, the 3D flow field and the ship’s hull provides resistance values for performance calculations. The computational model will be validated against full-scale data and class rules using deterministic and probabilistic measures. This simulation approach is developed within international research collaboration between Pella Sietas, Rolls Royce Marine, TUHH and NTNU. An overview of the project together with the current status of the ongoing work including first results is presented.

Topics: Ice , Ships
Commentary by Dr. Valentin Fuster
2017;():V008T07A003. doi:10.1115/OMAE2017-61816.

Increased competition and low oil prices coupled with promising prospects for new oil and gas (O&G) reserves in the Arctic region has led to expansion of activities into the offshore Arctic. This brings along new challenges for the offshore logistics that need to be addressed. These challenges impose more stringent requirements for the logistics system setup, especially on the design and operation of vessels. Copying the logistics system and vessels designed for the North Sea operations is not a sustainable way forward. The few existing studies related to Arctic logistics mainly focus on ship technology solutions for cold and ice infested areas or solutions to the area-specific operational challenges for shipping companies. However, there is a need to understand how these solutions are connected and impact each other in a larger offshore supply logistics system, and thus address the challenges of Arctic logistics as a whole. A methodology for quick evaluation of the feasibility and costs of the logistics system in the early stages of offshore supply planning was developed and presented in previous research [1]. It allows for testing the effects of using alternative ship designs and the overall supply fleet composition on system’s cost and performance while satisfying prospective campaign requirements. Safety standards and requirements for emergency preparedness and environmental performance are taken into account while cost effectiveness of the logistics system as a whole is the main quantifiable measure. Building on the new methodology a simulation tool for remote offshore operations has been developed and is presented in current work. Simulation models allow us to consider the dynamic and uncertain nature of variables, such as variation in weekly transport demand, weather impact on sailing times and fuel consumption, and schedule deviations. The evaluation of the performance of a logistic system is done by simulating the logistic operation over a large number of scenarios. Input parameters are weather data generated from historical observations and probability distributions for transport demand. Output from the tool are key performance indicators for: system costs, logistic robustness and emergency preparedness. The tool consists of three main components: simulation of a regular supply logistics operation, simulation of emergency situations, and visualization of the simulated operations. The proposed methodology and tool are tested on real-life cases for offshore supply planning of drilling campaigns in remote areas for one of the major international O&G operators.

Commentary by Dr. Valentin Fuster
2017;():V008T07A004. doi:10.1115/OMAE2017-61841.

The subsurface transport of ice along the underwater body of a ship hull or a structure may cause damages to appendages. In order to investigate the conditions under which the ice accumulation occurs, a series of model tests was carried out in the ice basin of Aalto University. The used ship model was towed laterally against the ice with one side breaking level ice. The transport of broken ice floes broken off from the intact ice sheet has been has been monitored with underwater cameras. Both the model drift speed, respectively the ice drift speed, and the ice thickness are found to affect ice accumulation process. The Densimetric Froude number is introduced as measured to determine whether ice floes will accumulate on the upstream of the hull. It is found that ice accumulation is triggered at relatively low Froude number.

Topics: Ice , Ships
Commentary by Dr. Valentin Fuster
2017;():V008T07A005. doi:10.1115/OMAE2017-61951.

Basic principles of the multidisciplinary approach to arctic marine transport systems (MTS) design and analysis are described in the article. The main idea of the approach is to synthesize geographic information system (GIS) technologies, different shipbuilding disciplines, fleet planning instruments and agent-based dynamic simulation models in an integrated software framework on the basis of object-oriented programming. Vessel operation is described as the movement and interaction of independent ships in GIS environment within the framework of the simulation model. MTS operation combines vessel operation itself (routing, determination of speed and fuel consumption, icebreaker escort, etc.) with plenty of external entities (port infrastructure, ice channel freezing process, offshore platform operation, etc.) that could be described as systems with comprehensive logic and physical behavior. Such integration provides a new quality of MTS simulation that allows considering complex interconnection of various subsystems and all the important details of each MTS project. The outline of the program framework to realize such an approach is given, and two case studies are described to demonstrate its capabilities and feasibility.

Commentary by Dr. Valentin Fuster
2017;():V008T07A006. doi:10.1115/OMAE2017-62191.

Rapid freezing of sea water on a cold substrate of spongy ice is investigated. The mechanism of transient ice accretion on cold substrates is different than slow freezing of salt water. An investigation of rapid freezing in this paper fills a gap of knowledge related to periodic icing of salt water on marine and offshore structures. The equation of transient heat conduction through brine-spongy ice is analyzed. Rapid freezing causes complete salt trapping, which makes the salinity constant and stable at the phase interface during the solidification. A thin layer of salt water is considered in contact with a spongy substrate. A finite difference method is employed to calculate the rate of solidification of the brine layer and consequently the thickness of ice accumulated. The discretization is based on the Method of Lines (MOL) which is a useful numerical-iterative method for boundary moving problems. Numerical results show that colder substrates and brine layers have the potential to create a thicker layer of new ice.

Topics: Freezing , Seawater
Commentary by Dr. Valentin Fuster
2017;():V008T07A007. doi:10.1115/OMAE2017-62240.

Ice loads time series should be treated in the other way than separate independent ice loads observations. The stochastic process approach can provide information about such important characteristic as mean length of signal’s outcome beyond some critical level and expected number of such outcomes.

The paper considers global ice loads registered in an ice tank experiment with a cylindrical indenter of 100 mm width. The autocorrelation function is fitted in a manner that the observed load process is differentiable. The study conducted in the paper demonstrates that characteristics, such as the number outcomes beyond some critical level and the time spent off this level, are governed in the same way as parameters of a stationary differentiable normal process.

Normal stationary model of ice loads process allows its simulation, if autocorrelation function is given. In the paper, such simulation is performed.

Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Full Scale Measurements in Ice

2017;():V008T07A008. doi:10.1115/OMAE2017-61353.

Co-occurrence probability analysis of sea ice between adjacent areas is very helpful for the hazard prevention and protection strategy making of coastal and offshore engineering. Yingkou and Huludao with similar latitudes are located on the opposite sides of Liaodong Bay of China. Their sea ice conditions are both apparent in winter and early spring, so it is useful to study on the co-occurrence situations of sea ice conditions between these two areas. Based on the annual maximum sea ice thickness of Yingkou and Huludao observation stations, the co-occurrence probability analysis of sea ice thickness is conducted. The joint probability distributions of sea ice thickness between these adjacent areas are constructed by using univariate maximum entropy distributions and four bivariate copulas. Both marginal curve fittings are very well, and the model determined by Gumbel-Hougaard copula describes the bivariate sea ice thickness data best. Then different cases of co-occurrence probabilities of sea ice thickness between Yingkou and Huludao are presented, and they can provide references to the hazard protection of the coastal and offshore structures between these two areas.

Topics: China , Probability , Sea ice
Commentary by Dr. Valentin Fuster
2017;():V008T07A009. doi:10.1115/OMAE2017-62000.

In recent years, there has been unprecedented interest shown in the Arctic region by the industry, as it has become increasingly accessible for oil and gas exploration, shipping, and tourism. The decrease in ice extent in the Arctic has renewed the interest in the Northern Sea route, necessitating further research to evaluate the adequacy of the equipment and appliances used on vessels traversing in polar waters. In the oil and gas industry, exploration and production vessels and platforms are highly dependent on the piping facilities for rendering their intended function, and therefore, flow assurance is extremely crucial. If the winterization of pipes is not done properly, this could lead to massive cost overruns due to unplanned production shutdowns or even worse, accidents. A temperature drop between the different areas of the production facilities will change the thermodynamic properties of the fluids, and could cause the processing of the crude oil to become inefficient.

The introduction of the Polar Code by the International Maritime Organization (IMO) attempts to mitigate some of the risks endangering the vessels in polar waters. The Polar Code is scheduled to take effect on 01.01.2017, and applies to all vessels traversing in polar waters. The Polar Code requires that all machinery installations and associated equipment required for the safe operation of ships shall be protected against the effect of freezing and increased viscosity of liquids, and that working liquids shall be maintained in a viscosity range that ensures the operation of the machinery. To account for this, the heat loss of pipes carrying liquid (water for fire extinguishing and hydraulic fluid amongst others) needs to be estimated and mitigating measures must be taken.

In this study, methodology from the refrigeration industry is applied to calculate the estimated time to freeze for liquids in pipes. The methodology is adapted for use in the maritime industry, and results are presented in this study. The methodology used was found to be quite flexible, allowing for the calculation of complex scenarios and shapes, including the effect of varying degrees of insulation on pipes, and can easily be applied for approximating the best suitable method of insulating pipes to ensure flow assurance and maintain fluid properties at desired levels. Tables estimating the time-to-freeze for insulated pipes of different diameters and insulation thicknesses exposed to cross-winds of varying speeds are provided. The methodology is found to have great potential, and should be investigated further with experiments. The objective of the paper is thus to introduce the methodology for cold-climate engineering and use it for practical analysis of realistic estimates of insulated and non-insulated piping.

Topics: Pipes
Commentary by Dr. Valentin Fuster
2017;():V008T07A010. doi:10.1115/OMAE2017-62253.

Sets of measurements of underwater ridge parts usually contain a limited amount of data. Outcomes need to be made while relying on small sample sizes. In this event, the chance of making inaccurate estimations increases.

This paper proposes to use stochastic confidence regions in the estimation of the unknown parameters of keel depths. A model for a random variable with a lognormal distribution for keel depths is assumed. Regions for the mean and standard deviation of keel depths are obtained from Mood’s and minimum-area confidence regions for parameters of the normally distributed random variable. Conservative safety probability of non-exceeding the critical keel depth in one random interaction of the ridge with structure is estimated.

An algorithm for statistically assessment of ice ridge keel data by means of confidence region building is here offered. The assessment of a set of ridge keel depths for the Gulf of Bothnia (Baltic Sea) is performed.

Topics: Ice ridges , Keel
Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Ice Management

2017;():V008T07A011. doi:10.1115/OMAE2017-61639.

Using autonomous underwater vehicles (AUVs) for mapping the underwater topography of sea-ice and icebergs, or detecting keels of ice ridges, is foreseen as an enabling technology in future Arctic offshore operations. This paper presents a method for online iceberg drift estimation using a Simultaneous Localization and Mapping (SLAM) approach using an AUV with a multi-beam echosounder (MBE) during such survey/monitoring operations. Iceberg drift is affected by wind, current, and Coriolis forces. This can be hard to predict, making automated mapping of icebergs difficult. The method proposed in this paper estimates the iceberg’s pose using a particle filter, where each particle uses extended information filters to estimate the topography of the iceberg. A grid map is used to store the iceberg topography, and distributed particle mapping is used to avoid expensive copy operations during particle resampling. The proposed method is verified through a simulation study, using a 6 DOF AUV model, an MBE sensor model, and an iceberg topography taken from the PERD iceberg sightings database. The method is able to provide a georeferenced iceberg position, thus, estimating the iceberg’s drift trajectory. A topography estimate of the iceberg, corrected for iceberg drift, is also generated. Furthermore, the algorithm estimates the iceberg drift velocity, as well as the relative iceberg-AUV pose, for use in future iceberg mapping guidance algorithms. The simulation study illustrates the performance of the method, and a short execution time analysis is presented to illustrate the method’s real-time potential.

Commentary by Dr. Valentin Fuster
2017;():V008T07A012. doi:10.1115/OMAE2017-61822.

This paper presents a ship-mounted multi-lens camera system for sea-ice monitoring and algorithms to automatically evaluate the sea-ice concentration and to indicate the floe-sizes in a radius of 100 meter around the vessel. During the SWEDARCTIC Arctic Ocean 2016 expedition, 11 camera lenses recorded the sea-ice conditions around the Swedish icebreaker Oden. As an example of the possible use of this image system, the images of six lenses are combined into one 360° panoramic image. To distinguish between water and sea-ice in the images, and thus to evaluate the sea-ice concentration around the vessel, a direct thresholding, the k-means, and a novel adaptive thresholding method are applied. Moreover, an edge detector gives the number of pixels that either form the boundary between sea-ice and water or are part of a visible ice fracture. The ratio between these edge pixels and the total number of pixels containing sea-ice gives an indication of the floe size distribution (FSD) in the image.

Commentary by Dr. Valentin Fuster
2017;():V008T07A013. doi:10.1115/OMAE2017-62021.

Ice management is one of the ways to achieve a more efficient operation of marine ice-resistant platforms in winter, to secure oil offloading operations and, if necessary, to support rescue and evacuation operations. Since 2012, Krylov State Research Centre, St. Petersburg, Russia, runs a training complex for navigational simulation of ship movement in ice conditions, developed with participation of TRANSAS, a global leader in the field of marine navigation simulators. The core functional elements of this training complex are the models of interaction between marine technology (ships and platforms) and ice in given water areas. One of the completed Russian Projects, Prirazlomnaya offshore ice-resistant platform, is taken as a case study to illustrate a stage-by-stage process of working out a tactic of ice management near the platform, including:

1) analysis of ice conditions in the area of Prirazlomnoye oil field, with consideration of environmental variability;

2) development of maneuvering procedures for the ice-breaking vessels to ensure safe oil offload to tankers;

3) polishing these maneuvers by means of a training complex;

4) analysis of the real maneuvers performed near the platform.

This approach allowed a deeper understanding of the developed maneuvering layouts for supply vessels, with respect to specific ice conditions and given operational circumstances.

Topics: Simulation , Ice
Commentary by Dr. Valentin Fuster
2017;():V008T07A014. doi:10.1115/OMAE2017-62509.

Satellite remote sensing technology plays an important role in ice monitoring and characterization in support of ice management operations for Arctic floating drilling that previously have been described by industry to include three stages: (1) far-field reconnaissance for potentially unmanageable ice features (2) mid-field verification of ice breakability and (3) near-field ice floe size reduction.

The paper discusses the application of satellite remote sensing methods for identification of Potentially Unmanageable Ice Features (PUIF) as well as challenges associated with satellite data interpretation and feature tracking. Examples of PUIF identification using both publicly and commercially available satellite imagery and other remote sensing data collected during the Oden Arctic Technology Research Cruise 2015 (OATRC 2015) are presented and the challenges with the PUIF detection and monitoring are discussed.

In addition, airborne remote sensing systems for PUIF identification, both existing (such as Electromagnetic Induction (EMI)) and under development (such as dual frequency radar, multi-band synthetic aperture radar), are discussed and their capabilities contrasted and compared to satellite-based methods. Furthermore, potential ways of optimally combining airborne and satellite remote sensing are proposed.

Topics: Ice
Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Ice Model Tests

2017;():V008T07A015. doi:10.1115/OMAE2017-61248.

The marginal ice zone (MIZ) is the outer part of the sea-ice covered ocean, where ice can be found in the form of large floating chucks better known as floes. Since it is the area where the most part of the interaction between ice cover and ocean waves takes place, it requires careful modelling. However existing mathematical models, based on the traditional thin-plate theory, underestimate waves attenuation for the most energetic waves, since the energy dissipation occurring during the process is not taken into account. New laboratory experimental and direct numerical models are presented here. In the experimental model a thin plastic plate is tested under the action of incident waves with varying amplitudes and periods. The same experimental set-up was reproduced using a numerical model, which was developed by coupling a High Order Spectral Numerical Wave Tank with the Navier-Stokes solver IHFOAM. Data from the experiments and numerical models confirm that non-linear effects lead to a decrease of wave transmission.

Commentary by Dr. Valentin Fuster
2017;():V008T07A016. doi:10.1115/OMAE2017-61548.

Waves penetrate deep into the ice covered seas, inducing breakup of the ice cover. Concomitantly, the ice cover attenuates the wave energy over distance, so that wave impacts die out eventually. Observations of wave attenuation and concurrent wave-induced breakup in the literature are serendipitous due to difficulties in making measurements in ice covered seas. Hence understanding of wave-ice interactions remain uncertain. Here we present measurements of wave propagation through ice covered waters in the new experimental wave-ice facility at the University of Melbourne. The facility comprises of a 14m long and 0.76m wide flume in a refrigerated chamber, where temperatures can be lowered down to −12 degrees Celsius to generate a continuous ice cover on the water surface. A wave maker, installed at one end, is used to generate regular waves, ranging from gently-sloping to storm-like conditions. Wave attenuation rates are determined from video-camera images of the displacements of markers embedded in the ice cover. The experiments investigated wave propagation through the continuous ice cover, breakup, and propagation through the broken ice cover. Spatial evolution of the breakup and geometrical properties of floes are monitored and correlated with incident wave properties. Wave attenuation over broken ice is investigated and compared against the continuous ice case.

Topics: Waves , Flumes , Ice
Commentary by Dr. Valentin Fuster
2017;():V008T07A017. doi:10.1115/OMAE2017-61808.

This paper presents a review of the state of the art of model-scale ice with a focus on mechanical behavior, mechanical testing and scaling. The goal of the model-scale ice production is the generation of a material that can represent sea ice in as many aspects as possible. The question therefore is, to what extent model-scale ice complies with this high level requirement and what possible limitations of model-scale ice are encountered. A part of the answer lies in the history of model-scale testing in ice as model ice was originally designed to test ships in ice. The interaction of ships with ice, when breaking level ice, differs from other interaction scenarios in terms of triggered failure processes and consequently in the relevant mechanical properties of the ice. The significance of the forces in particular interaction scenarios is reflected in the applied scaling laws. The standard scaling laws are presented together with published alternatives and their limitation and practicality is evaluated. The relevant interaction forces and ice properties are compiled for level ice breaking, ships in brash ice and offshore structures in slow ice drift. In the production of model-scale ice, the mechanical properties and their measurements play a significant role, as they determine how well the full-scale scenario is scaled. However, latest research in context with earlier published findings indicates that state of the art measurement procedures may not be able to capture the actual ice properties, as the mechanical behavior of model-scale ice might be different than generally presumed. Consequently, this paper presents alternative measurement procedures and highlights existing knowledge gaps which are worthwhile to be addressed in future.

Topics: Ice
Commentary by Dr. Valentin Fuster
2017;():V008T07A018. doi:10.1115/OMAE2017-62248.

One of the aims of the German national funded research project ProEis is to develop a methodology for determination of ice loads on model propellers which will then aid in improving and developing software tools for their prediction. For this purpose, a prototype device has been designed at HSVA within this project which is used to guide defined ice floes with one degree of freedom into a model propeller where they are milled and the resulting forces and moments are measured. This paper focuses on the description of the ice feeding device and presents some first results with respect to the physical process as well as measured load characteristics. For now, experiments are conducted in absence of water in order to exclude all hydrodynamic effects. A podded propeller is used which allows measuring of shaft torque and shaft thrust. A high speed video camera is also employed to record the propeller-ice interaction process at 5000 frames per second, allowing to observe the milling process in detail. Two basic impact patterns are observed with respect to their relative load levels. When the greater part of the leading edge of the propeller strikes the ice from the top, i.e. it crushes the granular layer and cuts off a relatively large chunk of ice, the maximum shaft thrust is approximately 1.5 times as high as when the leading edge of the propeller makes contact at the front face of a floe, scraping off a thin layer of ice. Shaft torque is mostly unaffected by the type of impact. The performance of the ice feeding device and the findings of the first tests presented here are reviewed and discussed critically. Recommendations for the planning of such tests and possible improvements of the device are given.

Topics: Ice , Propellers
Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Numerical Ice Modeling

2017;():V008T07A019. doi:10.1115/OMAE2017-61012.

This paper investigates the iceberg impact force to fixed structures in multi-planar space (3D). The global and local impact mechanics are discussed in details. The global impact energy is calculated by considering the eccentricities of iceberg in multi-planar space considering the tangential impact momentum. Thus, the impact phenomenon in a detailed manner could be assessed, such as the influences of friction and structural inclination to impact loads et.al.. It is found that the dissipated energy during an impact does not depend on the local stiffness within the contact area. Meanwhile, the impact force and duration are linked to the local stiffness. A semi-integrated analysis has been demonstrated to approach the local deformations of structure and iceberg. The structure and ice deformation could be simplified as linear/nonlinear springs. The ice pressure-area relationship and the force-deformation curve are used respectively to approach the local deformation. The methodology proposed here shows excellent agreement with previous work in planar case (2D). Sensitivity studies have been performed both to global and local mechanics. Conclusions and summaries have been included.

Topics: Stress , Icebergs
Commentary by Dr. Valentin Fuster
2017;():V008T07A020. doi:10.1115/OMAE2017-61903.

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches.

This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). It can simulate the ice loadings of a drifting ice-sheet (including ridge or not) on predefined structures such as conical, cylindrical, sloping & vertical wall, artificial islands or more complex geometry by user input file like semi-submersible floaters with pontoon and columns allowing to obtain the detailed results on the different parts of the structure.

This paper presents the overall functionalities of Ice-MAS and the different possibilities to model a semi-submersible floater. It will focus on the results obtained for different geometries subject to ice sheet loading through different incidence angles. The issues related to the anchoring of the platform are addressed in a simplified way.

Commentary by Dr. Valentin Fuster
2017;():V008T07A021. doi:10.1115/OMAE2017-61939.

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches.

This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). The current development phase consists of the determination of the forces generated by an iceberg during an impact on an offshore structure.

This paper will provide an overview of the latest Ice-MAS development. It will introduce the main functionalities of the simulation tool and the different options for modelling an offshore structure. It will then focus on the modelling approach used for an iceberg, the calculation of the different hydrodynamic coefficients and their variability according to the separation distance from the structure. The model used to compute the impact load will be detailed, including the local crushing behavior which is simulated by a pressure-area correlation.

Commentary by Dr. Valentin Fuster
2017;():V008T07A022. doi:10.1115/OMAE2017-62479.

A three-dimensional discrete element model is under development to simulate a number of different keel-gouge and subsea interaction scenarios. The model is being validated against controlled tests conducted in the National Research Council’s ice tank facility under the Pipeline Ice Risk and Mitigation (PIRAM) Joint Industry Project, which was led by C-CORE on behalf of a number of oil and gas companies. To investigate the influence of certain key parameters on the failure behaviour of the keel, a sensitivity analysis has been carried out. Best results were achieved when Young’s modulus of the keel was 5 MPa, the shear-to-tensile ratio of the freeze bonds was set to 1.2, the internal friction angle of the ice was 9°, the bond breakage ratio 0.8 % and Young’s modulus of the gravel 0.01 MPa. A low modulus for the gravel was needed to prevent premature failure of the keel, a consequence of the model not accounting for soil deformations. Using these parameters the model was able to accurately reproduce the loads on the soil tray during peak loading. Future developments in the model include using ‘clumps’ to give more representative ice block shapes, which will allow interlocking between ice pieces and the development of force chains.

Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Structure-Ice-Interactions

2017;():V008T07A023. doi:10.1115/OMAE2017-61018.

This article deals with Short Wave Infra-Red (SWIR) and Long Wave Infra-Red (LWIR) imaging sensors for detecting icebergs in harsh metocean conditions. Field data acquired during the Statoil Offshore Newfoundland Research Expedition 2015 (ONRE15) is analyzed. The analysis is supported by a numerical modelling study which aims at simulating the optical properties of ice and water combined with the radiation transfer in the Infra Red.

Topics: Sensors , Modeling , Icebergs
Commentary by Dr. Valentin Fuster
2017;():V008T07A024. doi:10.1115/OMAE2017-61392.

The process of ice-structure interaction is a complex problem which is influenced by the properties of both ice and the structure. In this paper, the material point method (MPM) is introduced to simulate the interaction between an ice sheet and a cylinder structure. MPM is efficient in solving history dependent and large deformation problems and has shown advantage in hyper-velocity impact and landslide issues, etc..

The constitutive relation of ice is based on elasto-viscous-plastic model with the Drucker-Pragers yield criterion. Ice follows the Maxwell elasto-viscous model before the yield criterion is reached and fails when the plastic strain surpasses the failure strain. Meanwhile, the constitutive model used in this work considers the effect of the Young’s modulus, Poisson’s ratio, density, temperature, cohesive force and internal friction angle of ice.

A series of simulations are conducted and the results are in accord with existing theories. According to the comparison, the influences of ice temperature and penetration speed of the structure on the global ice load are testified. The numerical tests have proven the feasibility of MPM in simulating the interaction between an ice sheet and a cylinder structure. Future work in ice-structure interaction problems with MPM is also discussed.

Commentary by Dr. Valentin Fuster
2017;():V008T07A025. doi:10.1115/OMAE2017-61491.

IMO has developed the functionally based Polar Code, which entered into force 01.01.2017. The code requires marine operators to provide lifesaving equipment that ensures a minimum of 5 days survival time. This requirement puts additional strain on the existing life-saving appliances.

To identify the key elements for compliance of the IMO Polar Code, a full-scale exercise (SARex, (April 2016)) was initiated and organized by University of Stavanger, the Norwegian Coast Guard and GMC Maritime. The object of the SARex full scale exercise was to identify the gaps between the functionality provided by existing SOLAS approved safety equipment and the functionality required by the Polar Code. The exercise was conducted with the help of the vessel KV Svalbard (Norwegian Coast Guard), and participated by leading experts from industry, governmental organizations and academia.

The following topics were specifically addressed in the exercise that took place in the marginal ice zone of the coast of Svalbard late April 2016:

1. Functionality of survival craft and PPE (Personal Protective Equipment) polar conditions.

2. Coast Guard’s search and rescue procedures, including handling of mass evacuations in Polar Regions.

3. Functionality of Personal/Group survival gear according to the requirements defined in the IMO Polar Code.

Survival for 5 days according to the requirements defined in the IMO Polar Code in a life raft represents a large challenge with regard to design of rescue craft, design of PPE (Personal Protective Equipment), rations and on-board organization. As the IMO Polar Code is functional based, a holistic approach has to be utilized when assessing the survival chain. For an assessment of the survival chain to be conducted in a sustainable manner, key elements essential for survival in a life raft have to be identified and prioritized.

Designing a survival chain applicable to maritime industry also involves considering commercial, economic and operational restrictions.

The paper will elaborate on the key elements essential for a minimum of 5 days survival in a life raft based on the findings identified in the Phase 1, Functionality of survival craft and PPE (Personal Protective Equipment) polar conditions, of the SARex exercise. The findings will be assessed and evaluated based on industry limitations.

Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Structures in Ice

2017;():V008T07A026. doi:10.1115/OMAE2017-61097.

In this paper, a theoretical approach is employed to analyze the thermal behaviour and study the cooling process of water droplets in cold regions. Additionally, the effect of several parameters, such as air temperature, droplet size, initial droplet temperature, relative humidity and droplet salinity on the cooling process is investigated. The model contains convection, evaporation, and radiation heat transfer from the droplet’s surface and a uniform temperature across the droplet. The results illustrate a good agreement between the theoretical predictions and previously measured data. Furthermore, droplet size, air temperature, initial droplet temperature, and droplet flight time have a substantial effect on the droplet cooling process. This model is a useful tool to investigate the thermal behaviour and the cooling process of water droplets.

Commentary by Dr. Valentin Fuster
2017;():V008T07A027. doi:10.1115/OMAE2017-61588.

In recent years, there has been unprecedented interest shown in the Arctic region by the industry, as it has become increasingly accessible for oil and gas exploration, shipping, and tourism. The decrease in ice extent in the Arctic has renewed the interest in the Northern Sea route, necessitating further research to evaluate the adequacy of the equipment and appliances used on vessels traversing in polar waters.

The introduction of the Polar Code by the International Maritime Organization (IMO) attempts to mitigate some of the risks endangering the vessels in Polar waters. The Polar Code is scheduled to take effect on 01.01.2017, and applies to all vessels traversing in polar waters. One of the requirements in the Polar Code is that means shall be provided to remove or prevent accretion of snow and/or ice from escape routes, embarkation areas and access points. Even though, prior to the formulation of Polar Code, the requirement for de-icing the deck surfaces on vessels already exists, the suitability of the equipment currently in use is debatable. Large amounts of energy is required to maintain an ice-free surface, which is not desirable economically or environmentally, due to the substantial increase in fuel consumption.

In this study, a heated deck element manufactured by GMC Maritime AS is subjected to cross flow wind of 5 m/s, 10 m/s and 15 m/s at various sub-zero temperatures in GMC Maritime AS’s climate laboratory in Stavanger, Norway. The deck element is rated to 1400 W / m2, and is one of the designs provided by GMC Maritime AS. The power consumption of the deck element is measured and compared to theoretical heat loss calculations. Large discrepancies between the measured power consumption and the theoretical heat loss were discovered, indicating the need for further studies on the matter.

As part of SARex Spitzbergen 2016, a search and rescue exercise conducted off North Spitzbergen, heated deck elements on board the Norwegian Coast Guard Vessel KV Svalbard were studied and are discussed in this paper. The heating elements in the deck elements were designed to specifications at the time of commissioning, but proves insufficient when the vessel is in transit or exposed to slight winds, allowing snow and ice to accumulate on the surface.

Finally, suggestions for a more energy efficient design of deck elements are made, as the current designs are found to have potential for improvement, especially due to the lack of insulation between the deck elements and the hull of the vessel.

Commentary by Dr. Valentin Fuster
2017;():V008T07A028. doi:10.1115/OMAE2017-61735.

Sea ice can interact with offshore structures in regions with at least seasonal ice coverage. Therefore the prediction of ice loads on offshore structures is required by many standards or classification rules and guidelines. In order to do this, empirical formulas are often prescribed. These are based on assumptions in combination with model or full scale tests. Yet there are very few publications where the results of the formulas are actually compared to measurements.

A case study is made for ice loads on the Norströmsgrund lighthouse. First of all current empirical formulas given by standards bodies or classification societies are reviewed with focus on applicability. Secondly, the ice loads predicted by the empirical formulas are compared to measurements. It was found that for the given case most methods significantly overestimate the load. The applicability of some methods is disputable.

Topics: Stress , Ice
Commentary by Dr. Valentin Fuster
2017;():V008T07A029. doi:10.1115/OMAE2017-62159.

Iceberg drift forecast is a challenging process. Large uncertainties in iceberg geometry and in the driving forces — current, wind and waves — make accurate forecasts difficult. This article illustrates from a data set that even if the uncertainties in current, wind and waves are reduced the forecast using a dynamic iceberg models stays difficult, because of the sensitivity of the model to different parameters and inputs. Nevertheless, if the uncertainty of the current driving force on the iceberg is reduced by measuring the current at the iceberg location, it is possible under specific conditions to estimate the approximate iceberg shape. This iceberg shape geometry can be used directly in the dynamic iceberg model.

Commentary by Dr. Valentin Fuster
2017;():V008T07A030. doi:10.1115/OMAE2017-62403.

The metocean conditions in the Barents Sea entail lower temperatures, and more snow and icing on offshore structures than what can be expected further south on the Norwegian Continental Shelf. The conditions are not considered extreme compared with other Arctic waters, but low temperatures, accumulation of snow and icing on structures and equipment may affect operations and equipment functionality. To manage these issues and ensure a safe working environment, winterization of installations is necessary. This article describes some results from a winterization study executed for the Petroleum Safety Authority Norway. The study objective was to provide an overview of known solutions and measures for winterization related to low temperatures, snow and icing for drilling rigs and production platforms operating in the Norwegian part of the Barents Sea. The study also describes solutions and measures that may be applicable at different locations in the Barents Sea, and available standards and guidelines related to winterization. Issues related to sea ice, bergy bits and icebergs have not been addressed.

As a part of the study, winterization standards and manuals for drilling rigs and production platforms were reviewed, along with available experience from previous and ongoing projects. The information was systematized, and a high level summary produced. The results showed that the main issues related to low temperatures, snow and icing for rigs and platforms operating in the Barents Sea can be simplified and summarized as follow: 1) Snow and icing on exposed surfaces. 2) Freezing of fluids in piping/equipment/tanks. 3) Personnel exposure to low temperatures and weather. These issues were further categorized to include typical areas and equipment types. Several solutions and measures were identified for each of them. The study showed that most of the identified solutions and measures are applicable for most locations in the area open for petroleum activities. However, more permanent and robust solutions should be selected for the coldest areas, as icing rates increases, and wind chill temperature decreases with lower temperatures.

The review of winterization manuals also showed the importance of implementing organizational and operational measures related to winterization. Education and training in proper use of winter technology, and defensive behaviour with respect to falling ice and slippery surfaces were identified as some of the most important measures to avoid incidents. Checklists for inspections, before and during the winter season, are important measures to secure areas and equipment when temperatures fall towards freezing point.

The study results show a large variety in available solutions and measures for each issue. These shall, combined with organizational and operational measures, ensure safe operations in the Barents Sea. The study shows that the challenge is not whether solutions and measures exist, but in finding the right combination of them for different conditions at specific locations.

Topics: Low temperature , Seas
Commentary by Dr. Valentin Fuster
2017;():V008T07A031. doi:10.1115/OMAE2017-62416.

It is believed that ice loading can be a stationary process at least sometimes during the state of continuous brittle crushing. Confidence in the distribution law, stationarity in time, and autocorrelation function of local ice loads is the key factor for assessment of such loads and their successful simulation. Good understanding of the load process on the level of a single transducer record can be helpful in future analysis and simulation of loads on wider contact areas.

In this paper local loads, simultaneously measured by two middle subpanels at the Norströmsgrund lighthouse in March 2001, are studied. Stationary time series of lognormal origin of 50 seconds duration are extracted from both of the subpanel records. From the studied data, stationarity was not observed simultaneously at different subpanels. The correlation of one stationary subpanel record with simultaneous record of the other subpanel found to be weak.

A simple function with good fit to the observed autocorrelation curve of stationary load fragments is suggested. The findings are compared with parameters obtained for local loads in previous studies. A transition from autocorrelation function for raw lognormal data to autocorrelation function of logarithmic normal data is performed.

Topics: Stress , Ice
Commentary by Dr. Valentin Fuster

Polar and Arctic Sciences and Technology: Vessels in Ice

2017;():V008T07A032. doi:10.1115/OMAE2017-61583.

A 2D numerical model was proposed to predict the repetitive icebreaking pattern and ice force of an advancing ship in level ice are presented. The numerical model focuses on the icebreaking at the waterline and neglects the broken ice rotating and sliding underwater hull. The repeated ship-ice contact and bending failure of a floating ice along the waterline are evaluated numerically. The computed ice channel width and icebreaking resistance are compared with measured values in the model test. Numerical results show moderately good agreement with the model test data. The effects of ice thickness and ship speed on the icebreaking resistance are investigated numerically. The icebreaking resistance depends on both the ice thickness and ship speed. The ice channel, however, depends on ice thickness, but there is little difference in ship speed.

Topics: Simulation , Ice , Ships
Commentary by Dr. Valentin Fuster
2017;():V008T07A033. doi:10.1115/OMAE2017-61717.

Ship navigation performance in the Arctic ice-covered sea was investigated from various kinds of satellite data and a numerical model of sea ice. The effect of dynamical processes of ice on the performance was especially examined, for it was not focused enough in previous studies. As a result, it was found that ice stress can explain some parts of the navigation when high amount of speed reduction occurred in thin ice area, and vice versa. The result indicates an importance of considering dynamical processes of ice in addition to static condition of ice, to improve an accuracy of an ice navigation performance estimation.

Commentary by Dr. Valentin Fuster
2017;():V008T07A034. doi:10.1115/OMAE2017-62545.

During ship ice interaction events (i.e. rams with multi-year ice), the occurrence of local pressures vary in time and space. A link between local pressures and global forces is the sum of the local forces from n High Pressure Zones (HPZs) across the interaction face equals the total force transmitted into the structure.

In this paper, a model for HPZ density, and force during ship ram events is presented. The occurrence and intensity of HPZs on panel areas were simulated using a Poisson process and an exponential distribution for HPZ force. The model is extended to consider HPZ occurrence in time through a ramming event, modeling HPZ rate. Such a model allows the designer to determine baseline ‘parent’ local pressure design parameters based on vessel size and expected operational speed. The faster a ship operates through an ice regime, the greater the HPZ rate. Larger and faster ships will penetrate further, having longer interaction durations and hence a greater number of HPZs forming (unless, for example, the ship passes through a ridge). Rates too will vary along the vessel being greater on the bow and least from mid-body to stern. For design, we are interested in the maximum local pressure on a single panel area through the ram duration.

The results are compared with previous local pressure models for design.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Drilling Fluids: Improving State of the Art

2017;():V008T11A001. doi:10.1115/OMAE2017-61108.

Modern rheological analyses provide good possibilities to understand the deformation and flow of fluids under different conditions. These methods used so far in the food industry as well as in the paints and coatings industry should transferred to the oil and gas industry, especially to the drilling fluid sector, to understand the drilling fluid behavior under borehole conditions. Traditionally, the rheology of drilling fluids is based on measurements under atmospheric conditions. The present study describes a new HT/HP measuring system by Anton Paar GmbH consisting of a modern rheometer including a high-pressure cell. This new system allows rheological analyses under a pressure up to 1000 bar and a temperature up to 300 °C. In consequence it is possible to observe conventional challenges within the drilling fluid sector under new points of view. Within the present study different drilling fluid systems were analyzed under common as well as under new rheological aspects. The results of both measuring systems were compared to each other. Furthermore, drilling fluid properties such as density, filtration and settling behavior were determined under different temperature regimes. Regarding to the operating principle of the electric impulse drilling (EID) technique the electric conductivity plays an important role and has to be taken into account. The results of these tests are also presented shortly.

Commentary by Dr. Valentin Fuster
2017;():V008T11A002. doi:10.1115/OMAE2017-61276.

About 75% of all formations drilled worldwide are shale formations and 90% of all wellbore instability problems occur in shale formations. This increases the overall cost of drilling. Therefore, drilling through shale formations, which have nanosized pores with nanodarcy permeability still need better solutions since the additives used in the conventional drilling fluids are too large to plug them. One of the solutions to drilling problems can be adjusting drilling fluid properties by adding nanoparticles. Drilling mud with nanoparticles can physically plug nanosized pores in shale formations and thus reduce the shale permeability, which results in reducing the pressure transmission and improving wellbore stability. Furthermore, the drilling fluid with nanoparticles, creates a very thin, low permeability filter cake resulting in the reduction of the filtrate penetration into the shale. This thin filter cake implies high potential for reducing the differential pressure sticking. In addition, borehole problems such as too high drag and torque can be reduced by adding nanoparticles to drilling fluids.

This paper presents the results of laboratory examination of the influence of commercially available nanoparticles of SiO2 (dry SiO2 and water-based dispersion of 30 wt% of silica), and TiO2 (water-based dispersion of 40 wt% of titania) in concentrations of 0.5 wt% and 1 wt% on the properties of water-based fluids. Special emphasis is put on the determination of lubricating properties of the water-based drilling fluids. Nanoparticles added to the base mud without any lubricant do not improve its lubricity performance, regardless of their concentrations and type. However, by adding 0.5 wt% SiO2-disp to the base mud with lubricant, its lubricity coefficient is reduced by 4.6%, and by adding 1 wt% TiO2-disp to the base mud with lubricant, its lubricity coefficient is reduced by 14.3%.

Topics: Nanoparticles , Water
Commentary by Dr. Valentin Fuster
2017;():V008T11A003. doi:10.1115/OMAE2017-61476.

The paper describes studies on the development of the new formulas of water-based drilling mud for drilling in clays and shales. The research were undertaken as a part of the OPTIDRILTEC project. First stage of the project included studies related to selection of ionic inhibitors of hydration. The tests of inorganic agents with various concentrations influence on technological parameters of the developed drilling muds was undertaken. The disintegration and linear swelling tests under influence of developed muds with different ionic inhibitors were conducted on the rock samples. Miocene shale was used as the model rocks. Within a framework of the project, it was conducted selection of the polymeric inhibitors of hydration. Subsequently, different polymers were tested for the influence on technological parameters of drilling muds as well as on disintegration and linear swelling of model rocks. Studies also consists of synthesis of short-chained cationic polymers (with primary amine groups in the side chains) and cationic-anionic polymers (with, apart amine groups, sulfonic amine groups). Synthesized polymers are characterized by low molecular masses (about 10.000 – 20.000 atomic mass unit) and small steric hindrance of side chains. The studies allowed development of new water-based mud formulas for drilling in clay rocks. Developed drilling muds are characterized by good technological parameters, resistance to temperature and to salts along with effective preservation against disintegration and swelling of clay rocks. Moreover, based on the research results it can be observed that synthesized cationic polymers are efficient inhibitors of clay rocks hydration. Newly developed drilling muds could be successfully applied in the oil and gas industry causing improved drilling conditions and decreased drilling costs.

Topics: Drilling , Rocks
Commentary by Dr. Valentin Fuster
2017;():V008T11A004. doi:10.1115/OMAE2017-62329.

In view of the increasing scarcity of energy resources, wells are being drilled to progressively greater depths for the production of liquid and gaseous hydrocarbons. Economical exploitation of these HT/HP reservoirs is possible only with the application of drilling and completion methods which do not damage the formation. Here, the reservoir-saving exposure of these deposits is an essential contribution.

The damage potential of drilling fluids and treatment fluids is usually assessed on the basis of return permeability (RP) tests. An impairment of the effective rock permeability through appropriate candidate fluids (drill in fluids, etc.) can be measured with special laboratory tests. In addition to the RP-Tests further investigations should be made to estimate the formation damage such as high-resolution digital photography, mercury porosimetry, scanning electron microscopy as well as microsection analyses.

Within the framework of the German Society for Petroleum and Coal Science and Technology a project was carried out to evaluate common formation damage test facilities and to define the “best practice” meeting the requirements of RP-measurements under borehole-like conditions. After a thorough evaluation an advanced HT/HP facility for formation damage testing was designed and built. By using of this set-up, systematic return-permeability tests were performed under dynamic conditions for temperatures up to 180 °C, for a flow pressure up to 250 bar, and a mantle pressure up to 350 bar.

This paper presents results from a study on the filtration and formation damage behaviour of drilling fluids under variation of the concentration and of the weighting material particle size distribution. Furthermore, promising results from changing dynamic and static filtration experiments are discussed.

Commentary by Dr. Valentin Fuster
2017;():V008T11A005. doi:10.1115/OMAE2017-62669.

Shales instability is a result of its mineralogical composition (especially content of different water sensitive clay) and its physico-chemical properties. In different laboratory research of shale/drilling fluid interaction conducted until now, researcher used different shale samples (original rock samples taken by the coring process, drilling cuttings, outcrop samples and artificial rock samples), different laboratory equipment and various inhibitive muds. There are two main problems related to the laboratory testing of shale samples’ quantity and quality. The main task of this paper was to examine the applicability of outcrop rock (shale) samples for laboratory research of shale/drilling fluid interaction. Rock samples were taken at natural shale outcrop on different locations in Croatia. In the first stage of the laboratory research, mineralogical composition and petrophysical properties of used shale samples were tested. In the second stage, shale samples’ swelling in different fluid were examined. After getting results of the shale swelling, new quantity of outcrop shale samples was taken, crushed to drilling cuttings size and placed in roller oven cells previous charged with different fluids. In the last stage, a dried (hot rolled) shale sample was used for preparation of the artificial shale samples. Generated artificial samples were used in further laboratory research.

Topics: Fluids , Drilling , Rocks , Shales
Commentary by Dr. Valentin Fuster

Petroleum Technology: Drilling Geomechanics, Circulation Loss and Wellbore Stability

2017;():V008T11A006. doi:10.1115/OMAE2017-61597.

Drilling new infill wells in depleted reservoirs is extremely problematic and costly due to low formation fracture pressure and narrow mud window resulting from in-situ stress changes due to fluid extraction. This is of paramount importance especially for drilling operations in deep-water reservoirs, which requires precise prediction of formation fracture pressure. In turn, this entails accurate prediction of reservoir stress changes with pore pressure depletion, i.e., the stress path. Currently-used models assume a transient flow regime with reservoir depletion. However, flow regime in depleted reservoirs is dominantly pseudo-steady state (PSS). Shahri and Miska (2013) proposed a model under plane-strain assumption. However, subsea subsidence measurements confirm that depletion-induced reservoir deformation mainly occurs in axial direction. We provide analytical solutions for stress path prediction under different deformational conditions namely, plane strain-traction and displacement boundary conditions, generalized-plane-stress, generalized uniaxial strain, and uniaxial-strain. For this purpose, constitutive relations of poroelasticity are combined with equilibrium equations, and pore pressure profile is described by PSS flow regime. In a numerical example, we examine the effects of different deformational conditions on depletion-induced in-situ stress changes. Interestingly, results indicates that stress path in reservoir is significantly affected by reservoir’s boundary conditions. The stress path under plane strain-displacement assumption overestimates the stress path predicted under uniaxial strain state by almost a factor of two. However, the generalized plane stress and traction plane strain conditions underestimates the results of uniaxial strain assumption. The order of stress path values for different boundary conditions can be summarized as: SPps-disp > SPuniaxial > SPps-trac > SPgps.

Topics: Stress
Commentary by Dr. Valentin Fuster
2017;():V008T11A007. doi:10.1115/OMAE2017-61858.

An important problem during drilling operation is wellbore instability; a complex problem caused by mechanical and chemical related factors. Even the best drilling practice could evade small instability problems that later may become irreparable. The risk of wellbore stability is mostly related to drilling, tripping and reaming activity with, including lost circulation, sloughing repair and loss of penetration. In this paper, the impact of historical and state of diagenesis and compaction on borehole instability has been studied, systematized, and used for general modelling. All the concepts are presented as symbolic concepts in a hierarchical order and linked in a chain of cause-effect relationships to wellbore failures. Through surveillance of drilling parameters, diagenesis and compaction were identified through formation hardness, well depth, shale type, and cuttings/cavings characteristic. From the analysis, kaolinite, which normally exists in intermediate diagenesis, is most likely to cause bit balling when hydrated. Smectite, which is water-sensitive clay, would cause chemical wellbore instability in water-based mud. Carbonates formation such as dolomite and limestone is more likely to result in lost circulation as compared to shale. Our work demonstrates how state of diagenesis and compaction could influence wellbore instability condition. This knowledge could be applied to understand the behavior of rock formation being drilled and would influence the prediction of probable failures as an end result. The method presented here integrates theoretical knowledge and real-time drilling data to envisage the most likely failure.

Commentary by Dr. Valentin Fuster
2017;():V008T11A008. doi:10.1115/OMAE2017-61868.

The arctic region hold abundant oil & gas resources according to the assessment by United States Geological Survey (USGS) in 2009. While, the thaw of permafrost during drilling operation can lead to the instability of wellhead. A coupled thermal model between wellbore and formation is given considering the latent heat of fusing and migration of water during the thaw of permafrost, and the thawed permafrost zone can be estimated. A wellhead stability analysis method considering heat transferred from wellbore is also proposed in this paper. FLAC3D software is applied to analyze the wellhead stability. Some conclusions are made through a case study: Flow in the wellbore delivers heat from deep part of formation to the shallow part of the formation, which leads to the permafrost thaws. Thawed permafrost losses most of the shear strength compared to that of the frozen permafrost which leads to the settlement of wellhead. The calculated results using FLAC3D software shows that the wellhead settles as deep as 0.66 m resulting from the permafrost thaw. In addition, the installation of anti-sinking pad is suggested to reduce the wellhead settlement. According to our simulation, the anti-sinking pad with radius of 8 times the wellhead radius is suggested, which can reduce the wellhead settlement to 0.1 m.

Commentary by Dr. Valentin Fuster
2017;():V008T11A009. doi:10.1115/OMAE2017-62519.

Lost circulation events during drilling are associated with the initiation of new fractures or the reopening of pre-existing fractures from the wellbore. Practices frequently implemented to combat lost circulation, including wellbore strengthening (WBS), are employed by plugging and propping the newly induced and pre-existing fractures to limit further propagation from the wellbore. One observation that was noted is that there is a discrepancy in the performance of lost circulation prevention methods for different temperatures between the fluids used and the surrounding formation. However, it is not yet fully understood how temperature affects pre-existing fractures and newly initiated fractures during these practices.

This study discusses how the stress state around fractures is influenced by a change in temperature considering fluid flow into a formation through drilling induced fractures. A finite element analysis with a coupled thermal-hydrologic-mechanical processes simulation was established to demonstrate how the stress redistributes around the fractures while considering fluid invasion and heat transmission. The results of the changing thermal stress around the fractures under various scenarios have been investigated. Included in our analysis is the potential risk of reinitiating fractures. The conclusions from this study indicate that a large temperature difference between the formation rock and fluid flow into the fractures could be a major concern when trying to prevent fracture propagation and control lost circulation events. It could potentially diminish the effect of enhanced hoop stress provided by WBS and fracture plugging by lost circulation materials. Such information is important to facilitate a successful management of lost circulation by taking into accounts the thermal impact of different lost circulation prevention approaches. The results from this paper are particularly important when a large temperature difference exists between circulating fluids and surrounding rock as commonly seen in HPHT and deep water wells.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Drilling Mechanics

2017;():V008T11A010. doi:10.1115/OMAE2017-61230.

Wellbore friction represents one of the biggest limitations for drilling and completion of long 3-dimensional wells. Traditionally, wellbore friction forces calculation is performed using soft-string torque and drag models, which assume tubular to be in contact with the wellbore at any point along its length. However, precise results are needed for wells with complex geometry and high doglegs.

This paper presents a novel way regarding wellbore friction forces calculation, which takes into account both wellbore deviation and wellbore tortuosity. To locate contact points of the string and the wellbore, a Dogleg Severity filter, or DLS-filter is proposed. The DLS-filter is integrated into soft-string torque and drag models by taking into account dogleg, wellbore geometry and depth. Such simple implementation of DLS-filter makes it applicable for any case only if survey data is available.

Fundamental understanding of drillstring mechanics and drilling fluids properties is essentially required in planning phase and drilling operations. To enhance the accuracy of torque and drag calculation, thermal effects on buoyancy forces and viscous forces have been studied. Experiments using one oil-based mud (OBM) recipe and one water-based mud (WBM) recipe have been conducted to measure viscosity and density of fluids in different pressure and temperature conditions. Based on the obtained results, viscosity model and density model as functions of pressure and temperature have been developed for better model interpretation of fluids thermal effects in HPHT conditions. Friction factor is a critical parameter to affect wellbore friction, which depends on fluids composition, contact surface, rotary speed, temperature, etc. Conventionally it is set constant for friction forces calculation. Experimental results show that the friction factor is heavily dependent on the temperature. In this study, friction factor was assumed to increase linearly with temperature for torque and drag calculation.

The new approach provides more correct values for torque and drag, and gives a better understanding of the downhole environment, as cuttings transport and drillstring dynamics. The study can be further used for the evaluation and recommendation of drilling muds for HPHT wells. Such analysis will aid in the design of appropriate drilling mud in the integrated well planning phase.

Commentary by Dr. Valentin Fuster
2017;():V008T11A011. doi:10.1115/OMAE2017-62071.

The influence of shale anisotropy orientation on shale drilling performance has been studied using a new laboratory procedure. This procedure includes drilling and testing three sets of shale samples in different orientations from a single rock sample. Shale samples of different types were collected from outcrops located at Conception Bay South (CBS) in Newfoundland, Canada. For predrilling tests, oriented physical and mechanical measurements on each type of shale were conducted on the same rocks that will be drilled later. For drilling tests, three sets of tests were conducted. Each set was in a different orientation, corresponding to those in the physical and mechanical measurements. Each set was conducted under the same drilling parameters of pressure, flow rate (FR), and weight on bit (WOB) using a fully instrumented laboratory scale drilling rig. Two different types of drill bits were used, including a 35 mm dual cutter PDC bit and a 25.4 mm diamond coring bit. The drilling data was analyzed by constructing relationships between drilling rate of penetration (ROP) versus orientation (i.e. 0°, 45°, or 90°). The analysis also included relationships between WOB and bit cutter Depth of Cut (DOC), Revolution Per Minute (RPM), and Torque (TRQ). All the above relations were evaluated as a function of shale bedding orientation. This evaluation can assist in understanding the influence of shale anisotropy on oriented drilling. Details of the conducted tests and results are reported.

Topics: Drilling , Anisotropy , Shales
Commentary by Dr. Valentin Fuster
2017;():V008T11A012. doi:10.1115/OMAE2017-62088.

A laboratory procedure has been developed to evaluate the anisotropy of Rock Like Material (RLM), granite, red shale, and green shale. This procedure involves detailed anisotropy evaluation steps through implementing circular ultrasonic wave velocity measurements, representing physical measurement and multiple drilling parameters (MDP), representing drilling performance. The physical tests involved circular pattern measurements of compressional and shear wave velocities, VP and VS, respectively. The drilling tests involved drilling samples of each rock in different a 25.4 mm Diamond Coring bit. The MDP included the study of the variations of Rate of Penetration (ROP), bit cutter Depth of Cut (DOC), Revolution Per Minute (RPM), and Torque (TRQ). The MPD were studied as function of orientations under atmospheric pressure. In addition to the physical and drilling evaluation, mechanical tests, such as Oriented Unconfined Compressive Strength (OUCS) were also used in rock anisotropy evaluation. Concrete with fine aggregate and Portland cement is used as RLM for much of the laboratory work. This material was cast into cylinders measuring 101.6 mm by 152.4 mm and 203.2 mm by 203.2 mm, from which NQ; 47.6mm core samples were taken. Coring was performed in three main orientations including 0°, 45°, and 90°. Characterization tests were performed on the RLM cores as they were conducted on the natural rock that included granite and red shale as isotropic and vertical transverse isotropic rocks, respectively. A fully instrumented lab-scale rotary drilling rig was used in conducting the drilling experiments. Details on the strategy for the tests on the anisotropy evaluation with results from laboratory work on natural rocks and RLM are reported. Result of the effect of shale anisotropy orientation on the drilling parameters that influence ROP as means of anisotropy evaluation are also, reported.

Topics: Drilling , Anisotropy , Waves , Rocks
Commentary by Dr. Valentin Fuster
2017;():V008T11A013. doi:10.1115/OMAE2017-62158.

Stick-slip is one of the typical phenomenon which is observed in offshore drilling and considered as a critical problem for the drilling operation. The stick-slip makes a large fluctuation of drill bit rotation, even though the top of the drill pipe is rotating at a steady velocity and sometimes causes the damage of the drill bit. Additionally, it leads a crushing of the sediment layer which is a big problem especially for the scientific drilling [1][2][3]. The main purpose of the scientific drilling is to correct high quality core samples of sediment layers under the seabed. However, once the stick-slip occurs, it makes difficult to recover a high-quality sediment layer core sample. Therefore, it is necessary to detect the occurrence of stick-slip and its fundamental characteristics such as oscillation periods and amplitudes by simulation with the aid of surface drilling data, which can be monitored during the drilling operation to mitigate or prevent stick-slip. It would be advantageous to identify the characteristics of the stick-slip from the surface drilling data.

The past study [4][5][6] investigated a numerical method to analyze the stick-slip by solving the NDDE (Neutral Delay Differential Equation) which is derived from torsional vibration equation. A small-scale model experiment was conducted in a water tank to observe the stick-slip phenomenon, and the result from the analytical model is evaluated with that obtained from the experiments.

In this study, the numerical model is applied for the stick-slip analysis not only of the drill pipe model but also the actual drill pipe in operation. The solutions of the NDDE is depend on not the initial value but the initial history of the solution, because NDDE contains a delayed function term. Especially, the initial history settings have much effect on the numerical solution of NDDE in case of the actual drill pipe. Additionally, to solve the NDDE for stick-slip analysis, we must set some model parameters concerned with the frictional torque on drill bit. The present study investigated the effects of the initial history and the model parameters settings on numerical solutions in detail and presented an procedure to determine the appropriate settings of the initial history and the model parameters by reference to the measured top drive torque.

Commentary by Dr. Valentin Fuster
2017;():V008T11A014. doi:10.1115/OMAE2017-62327.

During riserless drilling operations, which are carried out in some scientific drillings and in the initial stages of all drilling operations in oil and gas exploration, a lifting force is generated in addition to a drag forces in ocean current environment owing to the ocean current and the rotation of the drill pipe. This is called the Magnus effect, and it is a critical phenomenon during such operations.

First, the lifting and drag forces are calculated using the computational fluid dynamic (CFD), and the lift and drag coefficients are calculated for several rotational velocities of the drill pipe and the velocities of the ocean current. It can be observed through the calculations that the lifting force increases as the rotational velocity of the drill pipe increases, and it reaches a level of approximately several times that of the drag force. The force reaches such a considerably high magnitude that it can induce the motions of the drill pipe, resulting in the generation of a high bending moment.

An analytical model of a drill pipe has been established by applying an absolute nodal coordinate formulation (ANCF), which can express a relatively flexible and long pipe, such as a drill pipe. ANCF is a finite element method, and was basically developed to analyze deformable linear objects such as the cable. With ANCF, the absolute slopes of elements are defined based on the absolute nodal coordinate. Finally, the drill pipe motions are simulated using the established model by applying the results of CFD simulations for sample cases and referencing the operation of the Chikyu.

Commentary by Dr. Valentin Fuster
2017;():V008T11A015. doi:10.1115/OMAE2017-62337.

In both of scientific and industrial drilling, it is not desirable to any have accompanying vibrations, large fluctuations, or other unexpected dynamics disturbing a steady and stable drilling process. One of the origins of such disturbances can be the flexibility of the drill pile; drill pipe is easily deformed by external perturbations because it is very long and slender. To specify the stable range of parameters of drill pipe, we theoretically and numerically analyzed a Cosserat-type mathematical model of drill pile. The values of the parameters of this model were set to appropriate values representing actual riserless drilling situations adopted in the operations of the scientific deep-sea drilling vessel Chikyu owned by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We concluded that the buckling of pipe should be treated as a possible accident, but buckling does not happen in the normal operations of the Chikyu.

Commentary by Dr. Valentin Fuster
2017;():V008T11A016. doi:10.1115/OMAE2017-62427.

Petroleum engineers are aware of the advantages of directional and horizontal wells. In case of intermediate deep wells, the preference is the customary solution, in which a well is drilled vertically to the kick off point, and then moved directionally to the reservoir level. Nowadays, due to the advent of extended reach drilling, this approach does not satisfy the meant goal anymore. In extended reach drilling, the concern lies on the drill pipe’s strength. Because of the great depth of the borehole, the torque and tension below the drill floor increase and could reach the drill pipe’s strength. Therefore, in order to extend the wellbore reach, it is necessary to minimize the torque and drag. Several authors have mentioned that catenary profile may help reduce torque and drag.

The purpose of the paper is to analyze the mechanics of the drill string, and to understand the stress distribution along the drill string and the geometry of the well configurations while bringing the borehole from a vertical to a horizontal position. . This will be achieved by means of an analytical comparison between the catenary profiles and the conventional well configurations.

A novel catenary profile which improves the previous models is also presented in this paper. The modified catenary has a larger curvature of the drill string; particularly in the upper parts of the borehole the bending stresses are small. The modified catenary profile, which resembles a free hanging cable, can be a novel method in directional drilling of deep and extended reach wells. Thus, the build rate in the modified catenary is being continuously increased until it reaches the desired position. It is different from conventional methods used especially in horizontal drilling to connect the vertical and the horizontal section, where the build rate is kept constant.

The focus of this paper lies on the study of catenary’s geometry as a complex well path and the induced stress. Different approaches are used and compared.

Commentary by Dr. Valentin Fuster

Petroleum Technology: General Petroleum Engineering

2017;():V008T11A017. doi:10.1115/OMAE2017-61573.

This paper presents a backstepping approach for an active heave compensator actuated by a double acting cylinder. For practical applications, is desired to stabilize the system around the equilibrium point when subjected to unknown external disturbances. Knowing the governing equations, a robust backstepping control design is proposed by introducing a well-defined smooth function and using a Nussbaum function together with a Kalman filter-based disturbance estimator. The efficiency of the proposed control scheme is demonstrated through numerical simulations and compared with related works.

Commentary by Dr. Valentin Fuster
2017;():V008T11A018. doi:10.1115/OMAE2017-62310.

Accurate pressure drop estimation is vital in the hydraulic design of annular drillholes in Petroleum Industry. The present study investigates the effects of fluid velocity, fluid type, fluid rheology, drillpipe rotation speed, drillpipe eccentricity and drillhole inclinationon on pressure losses with the presence of cuttings using both experiments and computational fluid dynamics (CFD). The eccentricity of the drillpipe is varied in the range of 0 – 100% and it rotates about its own axis at 0 – 150 rpm. The diameter ratio of the simulated drillhole is 0.56 and it is inclined in the range of 0 – 15°. The effects of fluid rheology are addressed by testing power law and yield power law fluids. Both of the laminar and turbulent conditions are experimentally tested and numerically simulated. Experimental data confirmed the validity of current CFD model developed using ANSYS 16.2 platform. The goal of the current work is to develop a comprehensive CFD tool that can be used for modeling the hydraulic conditions associated with hole cleaning in extended reach drilling.

Topics: Pressure , Annulus
Commentary by Dr. Valentin Fuster
2017;():V008T11A019. doi:10.1115/OMAE2017-62366.

Serious operational problems caused by asphaltene deposition during oil production have driven the ongoing effort to understand this phenomenon. Many studies have focused on related asphaltene precipitation flocculation and deposition in oil reservoirs and flow assurance in the wellbores. Experimental techniques and theoretical models have been developed trying to understand and predict asphaltene behavior. Nevertheless, some ambiguities still remain with regard to the characterization of asphaltene in crude oil and its stability during the primary, secondary, and tertiary recovery stages within the near-wellbore regions.

The paper will review asphaltene in crude oil systems: asphaltene properties and their impact on oil production, including the effects of pressure, temperature, and composition. Asphaltene content is an important factor in determining the properties of a crude oil. Three main methods are used to measure the asphaltene content in laboratory: the first method called SARA, which separates dead oil into saturates, aromatics, resins, and asphaltenes depending on their solubility and polarity. The second is aliphatic hydrocarbon titration using dead oil; in this method the asphaltene precipitation point is detected by the asphaltene precipitation detection unit (APDU). The third method is the depressurization of a live oil bottomhole sample, this method depends on monitoring the flocculation point due to light transmittance caused by the infrared laser [3].

Solubility and density parameters trends are proportional to the pressure depletion until the pressure reaches the bubble point. Below the bubble point pressure (Pb), the solubility and density are inversely proportional to the pressure. The solubility increases linearly with temperature until the reservoir temperature, after that, it decreases linearly as the temperature increases. These advanced measurements facilitate an understanding of petroleum heavy constituents. Anew research field called “Petroleomics” has started receiving more attention; it is based on integrating the different knowledge of chemical composition of petroleum to develop correlation studies and improve the prediction of asphaltene phase behavior.

Commentary by Dr. Valentin Fuster
2017;():V008T11A020. doi:10.1115/OMAE2017-62472.

Decline curve analysis is one of the most widely used production data analysis technique for forecasting whilst type curve analysis is a graphical representation technique for history matching and forecasting. The combination of both methods can estimate the reserves and the well/reservoir parameters simultaneously. The purpose of this study is to construct the new production decline curves to analyze the pressure and production data. These curves are constructed by combining decline curve and a type curve analysis technique that can estimate the existing reserves and determine the other well/reservoir parameters for gas wells. The accuracy of these parameter estimations depends on the quality and type of the pressure and production data available. This study illustrates the conventional decline curve that can be used to analyze the gas well performance data with type curves based on pseudo time function. On the other hand, log-log plots are used as a diagnostic tool to identify the appropriate reservoir model and analogous data trend. Pressure derivative and type curves are used to construct a radial model of the reservoir. In addition, Blasingame and Fetkovich type curves analysis are also presented in a convenient way. The decline curve analysis shows steady state production for a long time, then a decline is observed which indicates a boundary dominated flow. The Blasingame type curve matching points is going downward, which indicate the influence of another nearby well. The reservoir parameters that are obtained by using the decline curve and type curves analysis show a similar trend and close match for different approaches. These observations closely match results of different analysis. This analysis improves the likelihood of the results being satisfactory and reliable, though it changes with time until the end of the production period. This analysis technique can be extended to other type of well/reservoir system, including horizontal wells and fractured reservoirs.

Topics: Pressure
Commentary by Dr. Valentin Fuster

Petroleum Technology: Inflow Control Technology in Reservoir Management

2017;():V008T11A021. doi:10.1115/OMAE2017-62301.

Breakthroughs of water and/or gas in production wells may have direct consequences for the production rates and overall field recovery. Multiple technologies have recently been developed to autonomously control inflow from the reservoir. Common to all these technologies is that new limitations are introduced which may have a negative impact on the well. This paper presents the design process for the next generation inflow control system and introduces new requirements for such completions.

Traditional Passive Inflow Control Devices (ICD) are designed to act in a preventive manner by setting up a somewhat more even inflow profile along the reservoir section and thereby delay the breakthrough of gas or water. More recently, several new initiatives have been presented which will operate autonomously, with an ambition to choke back unwanted production. Common to these technologies is that they are primarily dependent on viscosity differences between the reservoir fluids.

In the work presented in the following, the design process has identified the following requirements for the next generation autonomous inflow control system:

• easy to install completion

• robust in design and functionality

• Improve clean-up of mud and completion fluids

• independent of fluid viscosity

• negligible pressure drop during normal production

• allows back-flow of fluids

In this paper the results from an ongoing development of a new design inflow control system, independent on differences in fluid viscosities is presented, which fulfills above requirements. This system is based on a valve, which blocks, or restricts, production of unwanted water or gas, and re-opens for production if oil comes back. It can be designed to stop water/gas production at a predetermined WC/GOR. Furthermore, it ensures efficient clean-up along the full length of the reservoir section and is insensitive to exposure to mud, particles and filter cake. The installation of this system will not restrict any future well operations and it can be designed with a fail-safe option.

The new system represents a great technological improvement which will ensure a robust, economical and fail safe design as well as a simplification of inflow design process, since it will work irrespective of local productivity, pressure and flow rate. Hence, removing the operational envelopes on which other technologies must be designed for to be able to work properly.

Topics: Inflow
Commentary by Dr. Valentin Fuster
2017;():V008T11A022. doi:10.1115/OMAE2017-62441.

A new tool to stop, control and manage water production in oil wells is presented. The tool is simple and robust and can be installed blindly with no concern for orientation. The tool is fully autonomous and does not require external signal or power. The water stop tool has a high potential for effective reservoir management as it can stop water locally, reopen if oil again enters the tool, and also reroute water to surface or to a water bearing formation through a separate conduit.

Commentary by Dr. Valentin Fuster
2017;():V008T11A023. doi:10.1115/OMAE2017-62587.

The functions of the various wellbore completion components and their impact on the given well performance should be fully understood to achieve the full potential of advanced wells completions (AWCs).

Inflow control technology has been a success when installed in many fields. Field trials of the more recently developed Autonomous Flow Control Completions (AFCC) have shown their potential to further improve well performance. However, such (autonomous) discrimination and control of the different fluid phases, presents new modelling challenges that require extension of today’s wellbore/reservoir models and workflows for optimizing the completion design. The modelling challenges associated with this new technology requires more research to correctly quantify their added-value and guide future design improvements in AFCC technology.

This paper discusses how the currently available modelling tools can best designed when only single-phase flow performance data is available. Methods and workflows to improve the modelling accuracy, as well as, to understand the performance of an AFCC in a horizontal well in comparison with passive inflow control technology are presented. Novel methods to visualize and optimize the AFCC are presented and used to optimize the equipment design and identify the technology’s added-value.

Finally, this paper presents a modelling workflow for reservoir and well engineering studies by providing optimal AFCC selection guidelines together with a brief summary of an extension of the work reported here to multi-phase flow in typical AFCCs. Incorrect modelling of the devices Multi-Phase Flow Performance was found to effect the economic evaluation of this promising technology; forming an extra barrier to its early adoption.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Innovations in Drilling, Production and Transport

2017;():V008T11A024. doi:10.1115/OMAE2017-61105.

The Electric Impulse Drilling (EID) uses high voltage impulses to destroy the rock. Without any mechanical interaction between a bit and the rock, it works with almost no wear. Because of that, there is a big potential for reducing roundtrips and non-productive time. In a current R&D project, an EID system is built up and will be tested in a shallow well. A very difficult task during the development is the adjustment of the process to high-pressure conditions.

Commentary by Dr. Valentin Fuster
2017;():V008T11A025. doi:10.1115/OMAE2017-62205.

The undisturbed geothermal gradient is a key thermal boundary that drives heat transfer processes occurring in oil and gas wells throughout their lifetime. However, the temperature distribution with depth is somewhat uncertain, and this is often assumed to be a linear approximation from the mudline to the bottom of the well. During drilling, the circulating temperature may significantly affect the rheology of the drilling fluids and the cement setting processes. Therefore, erroneous estimates of the wellbore temperature may affect the overall performance of the drilling phase and subsequent well operations. Further, it is important to know the accurate temperature distribution within the formation for assessment of the petroleum prospectivity through source rock maturation and reservoir quality.

This paper presents a numerical methodology to estimate the undisturbed geothermal gradient while drilling in offshore wells. This methodology may also be applied to onshore wells by simplification.

The new approach is based on an in-house axisymmetric wellbore transient thermal model, in which the equations are solved using the finite difference method. The model computes the heat transfer between the well and riser system with the surroundings. However, other computational codes may also be used following the framework presented in this study. The computer code should provide a detailed representation of the geometry of the wellbore, the physical properties of the drilling fluid and formation, the suitable thermal boundary conditions and temporal discretization. The temperatures of the fluid at the inlet of the drillstring and at the bottom hole assembly (BHA), in the annulus A, are used as input to the numerical model that iteratively adjusts the undisturbed geothermal gradient, which generated the temperature recordings while drilling.

The paper comprises cases studies of hypothetical wells drilled in relevant offshore areas in the world, each with their distinctive and variable geothermal gradient, defined by the different rock formations encountered. Uncertainties regarding the thermal properties of the rock were also considered to ascertain the robustness of the code. The water depth of the drilling site was also observed to impact the convergence of the algorithm. The results obtained by the numerical approach are in good agreement with the expected values of the undisturbed formation temperatures.

The novelty of the numerical framework is the ability to provide reliable and satisfactory estimates of the undisturbed geothermal gradient for wellbores with any configuration, lithology and rock properties. These estimates are based on temperature measurements of the circulating drilling fluid at the BHA and account for uncertainty in rock thermal properties; in reasonable time using standard engineering computers.

Commentary by Dr. Valentin Fuster
2017;():V008T11A026. doi:10.1115/OMAE2017-62395.

One of the limiting factors for maximizing drilling performance is drillstring vibration/dynamics. With the development of in-bit, at bit or near bit vibration monitoring sensors, it has been reported that while drilling with PDC bits in hard formations, stick-slip is mostly observed before other types of vibration. Commonly, stick slip is a mathematical problem that can be resolved using various technics (like analytical, numerical, etc.). To compliment this theoretical effort, experimental measurements are required to verify mathematical models under controlled conditions and assess their range of applicability. This is why a large number of laboratory setups around the world exist. A comprehensive literature research has shown that most of the known experimental setups are smaller than 10 m length and focused mainly on vertical wells. Building a setup that reproduces real hydrocarbon wells, including the drill string inertia and the delayed response between bit and surface, as well as the complex friction transfer process taking place between the wellbore and the drillstring, is not feasible. Thus, downscaling the typical drillstring parameters is necessary for the study of vibrations and vibration suppression at laboratory conditions. Vibration suppression modeling and validation require a particular, dedicated laboratory setup. The design of such an installation will be presented in the following paper. The newly proposed experimental setup will exceed all existing stick-slip or lateral vibration experimental setups on the market by size, while adding new features like axial movement (mimicking ROP or heave compensation) and curved sections. This new facility will be the first to integrate the hardware in the loop capabilities and can be connected with any drilling simulator that supports such an option. This design will account not only for torsional vibrations, but will also allow the string to move axially while RPM, WOB and flow rates may be directly linked to a drilling simulator. Because of its design, to resemble medium to small radius of curvature, the stick slip process can be captured and highlighted for a wide range of directional well situations. Once the range in operating conditions was defined, the equipment and mechanical components for the facility were selected and designed. The new facility will significantly improve our ability to reproduce the physics of drill string vibrations and will lead to better optimization of downhole vibration suppression. The incorporated link to drilling simulators can improve the development of the next generation of vibration suppressing models and hardware.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Integrity of Well Cement Barriers

2017;():V008T11A027. doi:10.1115/OMAE2017-61106.

Wellbore irregularities can cause excessive mechanical friction forces while attempting to land casing strings, and unfavorable conditions for primary cementing of casing strings. In an eccentric annulus, the fluid velocity is largest in the wide section of the annulus. The drilling fluid on the narrow side of the annulus may be immobilized due to the lower wall shear stress in this section of the annulus. A direct consequence for the primary cementing operation is the potential for having residual drilling fluid between casing and formation, and thereby failing to achieve zonal isolation and adequate mechanical support for the casing.

Casing strings are usually fitted with centralizers at predetermined intervals in order to achieve a minimum degree of centralization in the wellbore and efficient fluid displacement during primary cementing. Centralizer distribution and design are based on assumptions of regular wellbore geometries and often analytical models for estimating lateral casing string displacement in the well. The latter assumption implies that bending moments are not transmitted across centralizers, and may lead to nonconservative centralizer designs. To investigate the effect of irregularity and casing string stiffness, we consider a stiff string model that approximates the casing string as finite beam elements with bending and axial degrees of freedom at each end, thereby accounting for transmission of both axial and bending stresses between elements. In this work, we evaluate wellbore irregularity by inspecting a six-arm caliper log and estimate the cross-sectional shape of the wellbore by cubic spline interpolation between the arms of the caliper tool.

Analyses of the caliper logs indicate that long, continuous strecthes conform to the nominal wellbore size, and that local hole enlargements may be significant. Irregularities are found to be largely symmetric about the wellbore axis, although some examples exhibit elliptic or oval shapes that may conform with local in-situ stress directions. We detail the stiff string model assumptions and implementation for evaluating casing centralization, and demonstrate the approach on model irregularities and on selected caliper log sections. Calculations suggest that bow spring centralizers result in better casing centralization in vertical parts of the wellbore, while large bow spring compression favour rigid centralizers in more inclined parts of the well. Axial compression close to the bottom of the wellbore section leads to a geometric softening effect of the casing, which affects transverse displacement and centralization between centralizers. Higher in the well where the casing is in tension, a geometric stiffening effect reduces transverse displacement. In proximity of washed out and irregular sections, centralization is affected both by placement of the centralizers and a reduction in the restoring capability of bow spring centralizers.

Commentary by Dr. Valentin Fuster
2017;():V008T11A028. doi:10.1115/OMAE2017-61209.

The annuli between two casings can be closed or open to formation. After completion, the temperature of the annular fluids will be close to the formation temperature. This is because it will take some time for the well to begin to exchange heat with the produced fluids from the reservoir. If the well is located in deep water, the wellhead temperature will be equal to the bottom seawater temperature.

At the start of production, warm reservoir fluids will be transported upward to the surface. This will transport heat to the upper part of the well and heat up fluids in the closed annuli. Because of the space limitation, the fluids are not allowed to expand. As a result, the pressure in each annulus will build up with time. In the worst case, this can lead to casing failures. A similar situation may occur when a high pressure, high temperature (HPHT) well is shut in and the well temperature approaches the formation temperature. If there is a net heating of the well, a pressure buildup will be exerted on the blowout preventer (BOP) system.

An example well consists of several casings and producing tubing. Each annulus is filled with a fluid, which can be a water-based or an oil-based fluid. In this study, a simple fluid, which comprises water and barite with no additives, is considered. The monodisperse suspension will be used to investigate the barite settling in a closed A-annulus. It is expected that the settling process will be much faster than it would have been if the fluid is a gel. The production casing and packers serve as barrier elements in the well.

This paper gives an overview and challenges associated with temperature-induced pressure increase in closed annuli. The paper also considers barite settling — another effect responsible for annular pressure buildup (APB) in closed annuli. In addition, remedies for APB will be reviewed.

The dynamic density and volume behavior of a fluid depend on pressure and temperature. To predict APB, a transient flow model is required. The main objective is to demonstrate that the AUSMV scheme can simulate APB due to barite settling and temperature increase. The AUSMV is a hybrid explicit numerical scheme that combines advection upstream splitting method (AUSM) and flux vector splitting (FVS) method.

A transient hydraulic model should be able to capture the dynamics of the settling process where settling particles force compressible liquid upward, resulting in pressure buildup in a sealed annular space. The proposed model captures these effects and takes the compressibility of the annular fluid into account. Another advantage of the transient model is that it can also predict the local concentration of barite in the annulus. This is important for a closer integration of the scheme with a temperature model, because heat flux depends on the spatial and time-varying compositions of the fluid in the annulus.

The AUMSV scheme is one out of many numerical methods that can be used for solving mass transport problems. It has been chosen due to its simplicity with respect to implementation. In the present work, the annular temperatures predicted by a separate transient temperature model will serve as inputs to the numerical scheme.

Commentary by Dr. Valentin Fuster
2017;():V008T11A029. doi:10.1115/OMAE2017-61227.

Geopolymers, being inorganic polymers created from rock sources, were evaluated as an alternative to Portland cement. To evaluate their usability some properties of a selected geopolymer were measured and compared with those from a neat class G Portland cement. The geopolymeric slurries showed a non-Newtonian viscosity behavior with a measurable, albeit low, yield stress. The pumpability measurements using atmospheric and pressurized consistometer showed an adequate set profile for both the geopolymer and cement sample. Static fluid loss test show that the geopolymeric slurries experienced a lower fluid loss compared to that of the Portland cement. The shrinkage factor for the geopolymers was reduced (expanded) as the downhole temperature was ramped up. The shrinkage of the Portland cement sample proceeded only with a lower rate. Tensile strength of the geopolymers was approximately 5% of their compressive strength; however, this value for Portland cement was approximately 10% of its compressive strength. Finally, shear bond strength of geopolymers would benefit from improvement.

Commentary by Dr. Valentin Fuster
2017;():V008T11A030. doi:10.1115/OMAE2017-62028.

One of the most critical operations during well construction is the cementing procedure. Due to the curing nature of the cement slurry there will be only one opportunity to cement the well properly. Although one for top hole cases can fill cement in from the top in a remedial operation, this possibility cannot fully compensate for a non-optimal initial cement job. Furthermore, it cannot be applied to other well sections. In those sections, complex squeeze cementing operations may be necessary. Consequences of improper annular cement can be leakage during production phase and extensive costs when the well is to be plugged for abandonment after the production phase. To ensure that the risk of poor cement is minimised it is important to use the best procedures to place the cement properly. To be able to select the optimum procedures, it is necessary to improve the understanding of the displacement in the wellbore annulus. All wells will be cemented in several sections. Findings and improvements that can reduce risk of poor cementing results are thus highly relevant for a large number of operations every year.

The article is based on analysing experimental results that illustrates a drilling fluid being displaced by a cement slurry. These fluids are represented by realistic model fluids and circulated through a transparent annular section. The geometry used is a 6,5″outer diameter with an inner string of 5″that also can rotate. The selected pipe sizes may normally be found in the lower parts of a well and often in deviated sections where the inner pipe cannot be assumed concentric at all times. Both concentric and eccentric inner pipe positions have therefore been selected. The test section was run both in horizontal and in inclined position. The test section was 10 meters long and instrumented with conductivity probes in an array around the perimeter at 4 separate positions along the pipe. Together with cameras along the test section the fluid interphases was observed along the test section.

Results presented in the article show that inner string rotation provides a steeper displacement front, On the other hand such rotation will also cause more mixing at the interphase. Results also show that the displacement front in a concentric annulus is significantly affected by gravity. While for an eccentric annulus, with the low side at the bottom, the narrow gap is poorly displaced when realistic fluids are applied. It was also observed that the displacement front in concentric annulus was more stable when the test section was inclined than in horizontal position.

Commentary by Dr. Valentin Fuster
2017;():V008T11A031. doi:10.1115/OMAE2017-62351.

Previous research on application of geopolymers in oil/gas wells is mainly unsuccessful due to failure to achieve a reasonable thickening time. This study presents geopolymer composite mixtures that have high compressive and shear bond strength, enhanceed thickening time, high durability, and reasonable shrinkage. Class F fly ash geopolymers are used for developing samples with different mix designs in this work. Class H Portland cement is used as a controller on all the tests conducted in this work. Tests conducted in this research include: unconfined compressive strength (UCS), shear bond strength, thickening time, and durability tests. Results indicate temperature as a crucial factor affecting the thickening time of geopolymer mix slurry. More than four hours thickening time is achieved by optimizing mix design and applying a developed mix of superplasticizer and retarder. UCS testing indicates a high compressive strength after one and fourteen days of curing for geopolymer mixtures. More than 6000 psi strength is achieved in long term (28 days curing). This indicates strength gained over time, for geopolymer mixture, where strength retrogression effects are observed for Portland cements. Results also reveal higher shear bond strength for Geopolymer mix, which can better tolerate de-bonding issues. Additionally, more ductile material behavior and higher fracture toughness, were observed for optimum geopolymer mixes. Final observations confirm applicability of these materials for oil and gas well cementing with circulating temperatures up to 300°F.

Commentary by Dr. Valentin Fuster
2017;():V008T11A032. doi:10.1115/OMAE2017-62444.

The annular cement sheath is one of the most important well barrier elements, both during production and after well abandonment. It is however well-known that repeated pressure and temperature variations in the wellbore during production and injection can have a detrimental effect on the integrity of the cement sheath. Degradation of cement sheaths result in formation of cracks and microannuli, which leads to loss of zonal isolation and subsequent pressure build-up in the annulus.

A unique laboratory set-up with downscaled samples of rock, cement and pipe has been constructed to study cement sheath failure mechanisms such as debonding and crack formation during thermal cycling. Cement integrity before and after thermal cycling is visualized in 3D by X-ray computed tomography (CT). However, this previous set-up had some significant limitations such as lack of direct physical confinement around the rock. This lack of direct confinement created unrealistic outer boundary conditions around the rocks during experiments as opposed to field conditions, which influenced the obtained experimental results.

This paper describes in detail an improved version of this laboratory set-up, where the set-up has been redesigned to include direct physical confinement around the rock as well as improved cement placement, while retaining all the advantages of the previous set-up.

Commentary by Dr. Valentin Fuster
2017;():V008T11A033. doi:10.1115/OMAE2017-62523.

The automatization of the drilling process opens the opportunity to faster reactions in case of unexpected drilling conditions, therefore reducing the risk that a drilling incident escalates to a serious situation. It also allows to push the drilling performance to be as close as possible to the limits of drillability as a function of the varying drilling conditions. But to achieve high level of drilling process automation, it is necessary to have access to accurate mathematical models of the complex physical system that is composed of the drilling rig, the drill-string, the drilling fluid and the borehole itself.

As the development of accurate heat transfer, mechanical and hydraulic models and their utilization in full scale drilling applications is a huge and complex task, it is tempting to recreate drilling automatization problems in a laboratory scale setup.

Because of sudden variations of the downhole drilling conditions, like when transitioning from soft to hard rock or when the bit is subject to large torque variations induced by interbedded rock layers, the boundary conditions at the bit change suddenly and require quick response from the automatic top-drive and hoisting system controllers. At a small laboratory scale, the necessary reaction times are of the order of milliseconds and therefore exclude any manual intervention. It is therefore crucial that the automatic control methods utilize precise mathematical models of the physical system to accurately estimate the limits by which the drilling process can be managed under safe conditions. For that reason, a general purpose mathematical model of small-scale drilling rigs has been developed.

First, the Rayleigh-Ritz method is used to determine the deflection of the drill-string and to estimate the side forces at the contact points along the drill-string and BHA (Bottom Hole Assembly). Then the dynamic response of the power transmission system is modelled for both variable frequency drive controlled tri-phase motors and for stepper motors, including friction effects at the contact points. Friction is modelled using Stribeck theory rather than the classical Coulomb laws of friction. Finally, the expected response of 3D accelerometers, that could be placed on the outside of a BHA component, is modelled to retrieve possible inclination variations and potential vibration modes such as torsional oscillations, forward or backward whirl.

The generality of the model is such that it can be used for many small-scale drilling rig designs.

Commentary by Dr. Valentin Fuster
2017;():V008T11A034. doi:10.1115/OMAE2017-62600.

Sustained Casing Pressure (SCP) is a well integrity problem and its removal is required. Techniques that involve replacing the fluid inside the annulus with a heavier fluid (kill fluid, KF) to stop gas migration have so far failed due to issues resulting from fluid incompatibility. This study aims to develop an intervention fluid compatible with water-based annular fluids. Based on the theory of buoyant slippage, brominated organic fluids have been produced and tested to assess compatibility and performance with multiple physical models. Results showed that the KF was able to settle down in water-based fluids, build up and exert pressure at the bottom. Experiments also exposed the formation of a mixture zone just above the building-up KF column. Lower injection rates and/or larger nozzle sizes decrease KF dispersion, prevent mixture zone formation and increase KF recovery. Intervention fluids developed in this study may revive the defunct bleed-and-lube (B&L) technique that would dramatically reduce the cost of SCP removal or may be used in an alternative process of continuous displacement that would significantly reduce the time of well intervention. Presented in the paper is also a road map for testing the SCP removal process that would lead to development of this technology.

Topics: Pressure , Fluids
Commentary by Dr. Valentin Fuster
2017;():V008T11A035. doi:10.1115/OMAE2017-62645.

Verification of annular barriers is essential for well integrity, with ultrasonic methods being central in well integrity testing for many decades. By doing ultrasonic pitch-catch measurements on a bench top laboratory setup developed to replicate an oil well casing, we were able to show that the beam width, −6dB, of the leaky Lamb wave propagating in the pipe widens only from 14 to 20.4 mm after 140mm of propagation in the pipe. This indicates that the excited Lamb wave has beam-like features, with litle spreading perpendicular to the propagation direction, hence, can be used to evaluate a limited area of the pipe. When introducing two pipes in the experimental setup, as an extension of a previously conducted simulation study by Viggen et al. [1], we could observe multiple Lamb wave packets being excited in the pipes. By adjusting the setup to replicate casing eccentricity, the effects of this could be observed in the measurements.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Multiphase Equilibria in Petroleum Engineering

2017;():V008T11A036. doi:10.1115/OMAE2017-61193.

Multiphase isenthalpic flash calculations are often required in compositional simulations of steam-based enhanced oil recovery methods. These flash calculations are challenging in the narrow-boiling regions and in the determination of the correct number of existing phases. Based on the free-water assumption that the aqueous phase is pure water, a robust and efficient algorithm is proposed to perform isenthalpic three-phase flash calculations in this work. Multiphase equilibria can be considered by this algorithm, including single-phase equilibria, two-phase equilibria, and three-phase vapor-liquid-aqueous equilibria.

Isenthalpic flash is a type of flash calculation conducted at given pressure and enthalpy for a feed mixture. In the proposed algorithm, assuming the feed is stable, the temperature is first determined by solving the energy conservation equation. Then the stability test on the feed mixture is conducted at the calculated temperature and the given pressure. If the mixture is found unstable, the two-phase and three-phase vapor-liquid-aqueous isenthalpic flash calculations can be simultaneously initiated without resorting to stability tests. To achieve simultaneous flashes, the outer loop is used to update the temperature by solving the energy conservation equation. The inner loop is used to obtain phase fractions and compositions by performing a three-phase free-water isothermal flash. Note that a two-phase isothermal flash will be initiated if an open feasible region in the phase fractions appears in any iteration during the three-phase isothermal flash or any of the ultimately calculated phase fractions from the three-phase flash do not belong to [0,1]. Negative flash is allowed in the three-phase free-water isothermal flash.

A number of example calculations for water/hydrocarbon mixtures are carried out to test the robustness of the proposed algorithm. At low to medium pressures, a good agreement can be achieved between the results obtained by this algorithm and those obtained by the conventional algorithm. This algorithm performs well for the narrow-boiling regions, for example, the three-phase vapor-liquid-aqueous equilibrium region encountered for the water/hydrocarbon mixtures. During the iteration, the new algorithm can readily handle the appearance and disappearance of phases in the inner loop as temperature updates in the outer loop. The number of stability tests involved in the new algorithm is significantly reduced, helping to boost its computational efficiency.

Topics: Algorithms , Water
Commentary by Dr. Valentin Fuster
2017;():V008T11A037. doi:10.1115/OMAE2017-61581.

The phase distributions and mechanical properties of annular flow are constantly fluctuating, so they can be regarded as random states. The probability analysis of annular flow is an appropriate method to research the formation, development and evolution of the flow pattern. In the present work, the atomization and deposition rates of fully developed annular flow are investigated in detail by the method of a probability analysis. First, the basic equations of the probability model are applied to solve some important intermediate parameters of annular flow. Second, the atomization and deposition rates of any size droplets are closely related to the probabilities of droplet generation and disappearance. Third, the interchange rate of the whole liquid phase can be obtained by summing the generation and disappearance probabilities of arbitrary size droplets. The predictions of atomization rate are well verified by comparing with the experimental date of 71 cases from three sets of tests. It is demonstrated that the probability model can accurately calculate the atomization rate of the fully developed annular flow for most cases. The predicted deviation for some cases may be caused by the neglect of droplet breakup process. Furthermore, the effects on the atomization rate of seven parameters of annular flow are discussed in detail.

Commentary by Dr. Valentin Fuster
2017;():V008T11A038. doi:10.1115/OMAE2017-62194.

A novel and pragmatic technique has been proposed to quantify the non-equilibrium phase behaviour together with physical properties of foamy oil under reservoir conditions. Experimentally, constant-composition expansion (CCE) experiments at various constant pressure decline rates are conducted to examine the non-equilibrium phase behaviour of solvent-CO2-heavy oil systems. Theoretically, the amount of evolved gas is firstly formulated as a function of time, and then incorporated into the real gas equation to quantify the non-equilibrium phase behaviour of the aforementioned systems. Meanwhile, theoretical models have been developed to determine the time-dependent compressibility and density of foamy oil. Good agreements between the experimentally measured volume-pressure profiles and calculated ones have been achieved, while both amounts of evolved gas and entrained gas as well as compressibility and density of foamy oil were determined. The time-dependent effects of entrained gas on physical properties of oleic phase were quantitatively analyzed and evaluated. A larger pressure decline rate and a lower temperature are found to result in a lower pseudo-bubblepoint pressure and a higher expansion rate of the evolved gas volume in the solvent-CO2-heavy oil systems. Apparent critical supersaturation pressure increases with either an increase in pressure decline rate or a decrease in system temperature. Physical properties of the oleic phase under non-equilibrium conditions follow the same trends as those of conventionally undersaturated oil under equilibrium conditions when pressure is higher than the pseudo-bubblepoint pressure. However, there is an abrupt increase of compressibility and decrease of density associated with pseudo-bubblepoint pressure instead of bubblepoint pressure due to the initialization of gas bubble growth. The amount of dispersed gas in the oleic phase is found to impose a dominant impact on physical properties of the foamy oil. Compared with CCE experiment at constant volume expansion rate, a rebound pressure and its corresponding effects on physical properties cannot be observed in the CCE experiments at constant pressure decline rate.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Oilwell Cement Technology

2017;():V008T11A039. doi:10.1115/OMAE2017-62015.

Drilling through low pressure formations, either offshore or through depleted formations, requires the use of low density fluids to prevent lost circulation and as well as to properly place cement during cementing applications. Achieving these densities in cements can be done through foaming the cement, increasing water content, or through the addition of silica based microspheres. Each of these methods have individual limitations, and in the case of silica based microspheres, their specific fallback is a chemical instability with the microsphere itself reacting with the cement pore fluid.

This chemical instability creates a hydrophilic gel that is expansive and creates fractures in the cement as it expands, which is more formally referred to as alkali-silica reactivity (ASR). Prevention of ASR involves the application of additives to the cement that acts as a sink for the alkalinity in which prevents the expansion of ASR. A specific application that this paper investigates for this prevention is the use of Lithium nitrate.

This study looks at the effects of a high alkalinity environment onto the microspheres by visualizing the reactions that are occurring using Scanning Electron Microscopy (SEM), and confirming the presence of ASR when silica based microspheres encounter a high pH environment. Then cement samples were created to compare the effects lithium nitrate has on cements created with silica based microspheres. SEM and micro indentation was conducted on these samples, which showed that lithium nitrate prevents reactions, but after 28-day hydration a loss of mechanical properties is present.

Commentary by Dr. Valentin Fuster
2017;():V008T11A040. doi:10.1115/OMAE2017-62393.

Well cements are an important aspect of wellbore integrity and recent investigations focus on describing the cement lifetime using, when possible, non-destructive tests like ultrasonic measurements. However, the original API and ASTM testing standards were based on destructive mechanical testing of cements, leading to the decision to investigate the backward and forward compatibility between ultrasonic measurements and mechanical testing, which makes the subject of this work.

Ultrasonic cement measurement became a very popular method to assess the mechanical properties of the cement in a non-destructive manner. Since various measurement systems exist on the market, the development of an accurate reference data base that can be used to calibrate such measurements becomes very important. Two major systems have therefore been compared: the ultrasonic compressive strength, using the ultrasonic pulse velocity (UPV) principle, and the unconfined compressive strength (UCS), using the standard testing frame according to API and ASTM standards. The tests have been performed at different curing times, using both devices, on class G API cements with bentonite and other additives.

This paper presents the results of over two hundred experiments that have displayed a different UPV response as a function of the additive content. These allow us to expand the existing UPV vs. UCS correlations. Moreover, it was observed that after a given curing time, depending on the additive and its concentration, the UPV response is not as sensitive as the results yielded by the UCS method. The outcomes are an important step forward to improve and understand the wellbore integrity.

Commentary by Dr. Valentin Fuster
2017;():V008T11A041. doi:10.1115/OMAE2017-62455.

Cementation of casing string depends on composition and properties of cement slurry. The properties of Portland cements must often be modified to meet the demands of a particular well application. These modifications are accomplished by the admixing of additives that effectively alter the hydration chemistry. Silica (SiO2) is used most frequently for the prevention of strength retrogression. It can have a different particle size (“silica sand”, with an average particle size of about 100 μm; “silica flour”, with an average particle size of about 15 μm; and “silica fume”, with mean particle size between 0,1 μm and 0,2 μm). Commercially available additive “Microblock” was used in lab tests. It is a liquid cement additive made from a finely divided, high surface-area silica (D50: cca 0.15 μm; D90: cca 0.75 μm). “Microblock” can help prevent high-temperature strength retrogression, control lost circulation as well as gas migration and can provide a degree of fluid-loss control. The Portland cement slurries with 10%, 20%, 30% and 40% of “Microblock” have been tested. Results of laboratory tests have shown that silica fume (also known as microsilica) affects the slurry properties such as thickening time, rheology, fluid loss, free water, slurry stability, and set cement compressive strength. The development of high early compressive strength is important to ensure structural support to casing and hydraulic/mechanical isolation of downhole intervals. The development of compressive strength of Portland cement slurries with and without “Microblock” at different curing temperature (90 °C, 120 °C and 150 °C) has been determined by Ultrasonic cement analyzer. Results have shown that “Microblock” affects the properties of cement slurry and set cement. The compressive strength has been higher with the addition of “Microblock” than compressive strength of neat PC slurry, but negative effect has been exhibited on slurry rheology and early strength development at elevated temperatures.

Commentary by Dr. Valentin Fuster
2017;():V008T11A042. doi:10.1115/OMAE2017-62456.

Various authors have pointed out the importance of cement mixing process and its effect on cement properties. From all cement properties, two are extremely important: the mechanical cement strength (unconfined compressive strength or UCS) and the rheology. The first is critically impacting the well integrity whereas the latter is affecting the pumping ability and displacement in the well, which will also have effects on the well integrity.

A previously performed literature survey has pointed out that mixing energy alone may not be sufficient to describe the cement slurry changes, and inferred that shear rate can also impact the final cement properties, such as thickening time or cement strength. Starting from the existing investigations, our goal is to quantify the source of maximum energy input during a conventional cement job and estimate its effect on final cement properties.

This paper is showing theoretical and experimental investigations on selected API cements with respect to their properties as a function of mixing energy. The first part of the paper is focusing on the estimation of mixing energy in different section of the cement pathway to the annulus. The second part will show some experimental results and the new way ahead, based on our findings.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Petroleum Production Systems Design and Operation

2017;():V008T11A043. doi:10.1115/OMAE2017-61865.

Despite the common presence of water in oil production, just recently, the scientific community has devoted efforts to studying the influence of emulsion phenomena effects related to oil production using pumps. In the context of this study of phase inversion phenomena, the influence of viscosities and rotational speeds in Electrical Submersible Pumps (ESPs) are evaluated as part of this effort. This study is aimed at investigating the influence of viscosity in phase inversion phenomena. An 8-stage ESP was tested with three different rotational speeds and two different oil viscosities for the best efficiency point (BEP) flow rates. Initially, the total flow rate was obtained in relation to BEP using ESP performance curves for pure oil at 52 cP and 298 cP and rotational speeds of 800 rpm, 1200 rpm and 2400 rpm. The total flow rate was kept constant and the water cut was increased from zero to a hundred percent. The inversion phase phenomenon was detected by the performance improvement when the water cut increased. The factors analyzed were the head and efficiency of the ESP as a function of the water cut. The phase inversion experimental data obtained in this study was compared with literature models for horizontal pipes. The results of this comparison presented satisfactory agreement. The phase inversion phenomena occur in all 8-stage at same time. Hysteresis was observed in ESPs for oil viscosity of 52 cP and rotating speed of 800 rpm and 1200 rpm.

Commentary by Dr. Valentin Fuster
2017;():V008T11A044. doi:10.1115/OMAE2017-62118.

In offshore operations, wind, waves and currents cause motions on Floating Production Storage and Offloading (FPSO) platforms that can induce effects on equipment at the topside processing plant, such as on an oilfield separator. The purpose of this work is to propose a procedure to evaluate the quality of the emulsion separated in a horizontal Free Water Knockout separator (FWKO) under the influence of the FPSO motions in ocean waves. In this paper, a software named WAMIT© was used to obtain FPSO motions. Time series of roll and pitch motions are calculated considering regular and irregular waves and through these results the emulsion quality indicator is obtained to evaluate the separator performance. The main contribution from the present study is the estimation of the quality of the emulsion separated on the FWKO, which can contribute to improve the operational criteria for three-phase separators commonly used in offshore applications.

Topics: FPSO , Ocean waves , Water
Commentary by Dr. Valentin Fuster
2017;():V008T11A045. doi:10.1115/OMAE2017-62176.

In this work, the Flow Performance Index (FPI) is introduced to guide the analysis of the performance of well systems for petroleum production. For some time now, the oil industry has been investing in the technological advancement of the instrumentation of its wells and flow lines; therefore, the volume of acquired data is quite substantial. Nevertheless, these data are still scantly used and stored in isolated databases where sharing the data is difficult, forcing the professionals to waste time, searching and organizing information, rather than spending time on decision-making processes. Consequently, there is a need to organize and integrate the available data from the different sources and areas of petroleum engineering. The FPI may be employed to handle large amounts of field data (measured periodically) in a rational approach to integrate the data. The FPI allows the assessment of the technologies used in wells for completion and artificial lift, and the performance of wells and flow lines; it may be used for monitoring production and to aid in the diagnosis of flow assurance problems; it could also be employed for benchmark studies and comparison of field production systems. A few examples of applications of the FPI are presented here, comparing the performance of vertical, directional and horizontal wells, sand control technologies, and monitoring of production. Further, the concept of the FPI is extended for gas-lift wells, and a more general formulation is proposed to include mechanical-lift systems. The examples given herein have proven the usefulness of the FPI, in different areas of an upstream business unity in Brazil.

Commentary by Dr. Valentin Fuster
2017;():V008T11A046. doi:10.1115/OMAE2017-62407.

Recent advances on the modeling of two-phase flows in pipes have shown that the accurate modeling of Two-Fluid equations allow the dynamic simulation of various regimes within a single numerical framework, diminishing the empiricism associated with the flow-pattern dependent closure relations. Such “Regime-Capturing” approaches have been traditionally called “Slug-Capturing”, as a reference to dynamic simulations of stratified-to-slug transition. In this paper, we will outline several examples of applications, ranging from horizontal stratified wavy, slug and annular flows, to vertical annular and intermittent flows. Vertical flow has been a bottleneck in Slug Capturing due to ill-posedness of the Two-Fluid Model. Ill-posedness of the model equations will be briefly addressed along with different regularization methods and stabilizing terms based on physical behavior, such as shape profile factors and dynamic pressure contributions. In order to numerically solve the governing system of equations, the finite volume method is employed with Upwind and second order TVD spatial discretization schemes, along with first order time discretization.

Flow parameters such as temperature and pressure drop are determined as well as film thickness and wave characteristics of both annular and stratified flow, and slug velocity, length and frequency in slugging cases. Comparison with experimental data for annular, slug and stratified flows, with different fluids and pipeline configurations are presented, illustrating the good performance of the methodology.

Commentary by Dr. Valentin Fuster
2017;():V008T11A047. doi:10.1115/OMAE2017-62409.

This work consists of an experimental analysis of the liquid-liquid two-phase flow of water-kerosene through a vertical bend. The duct has diameter of 0.026 m, the bend radius is 0.125 m and the superficial velocities of the water and kerosene ranged from 0.1 to 1.0 m/s. The pressures drops were measured by differential pressure transducers SMAR LD301, the holdups were determined by the method of trapping fluid using quick-closing valves and the flow patterns was determined using a high-speed camera. The bend pressure gradient is increased with the superficial velocities of both phases. The bend coefficient has no correlation with the mixture Reynolds number, such as in single-flows. The modified Reynolds number proposed by [1] described accurately the bend flow pattern.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2017;():V008T11A048. doi:10.1115/OMAE2017-62410.

The finite volume techniques for solving fluid flow problems can be broadly classified in cell center and cell vertex methodologies. The conventional finite volume techniques belong to the former class, since the elements coming from the grid generator are used as control volumes for performing the balances of the physical quantities, like mass, momentum and energy. The majority of the available methods in the literature uses this type of approach for solving multiphase flows of oil, water and gas in porous media. In petroleum reservoir simulation it is common for the conventional finite volume method to be linked to corner-point grids. This paper presents an Element-based Finite Volume Method (EbFVM), whereby the control volumes are constructed using parts of the elements, generating polygonal meshes in which mass, momentum and energy conservation are enforced. Polygonal meshes considerably reduce the number of unknowns of the linear system when compared with conventional finite volume methods. Three-dimensional hybrid grids are employed for the solution of oil-water flows in a porous media resembling a petroleum reservoir using the IMPES, sequential and fully implicit approaches. The analytical solution of the 1D Buckley-Leverett problem is used for evaluation purposes, and numerical solutions for 2D and 3D problems using unstructured grids are carried out to demonstrate the generality of the method and for comparing the robustness, convergence rate and CPU time of the IMPES and Fully Implicit solutions. Memory usage and convergence rate are also presented for the solution of 3D problems using tetrahedral grids in a cell-center and cell-vertex methodologies.

Commentary by Dr. Valentin Fuster
2017;():V008T11A049. doi:10.1115/OMAE2017-62424.

The objective of this research is to investigate the path of oil drops within an Electrical Submersible Pump (ESP) impeller, to evaluate its size and velocity as function of water flow rate and the ESP rotation speed. An experimental study was conducted at University of Campinas - Brazil with an ESP prototype designed to allow flow visualization within the impeller through a transparent shell. A high-speed camera with lighting set captures images of the oil droplets at a rate of 1000 frames per second. The set of data was performed at three rotational speeds — 600 rpm, 900 rpm and 1200 rpm — for three water flow rates — 80%, 100% and 120% of the best efficiency point (BEP). The results reveal that the oil drops become smaller when the rotational speed increases. The same behavior is noticed when the water flow rate increases. Generally, the oil droplets have spherical and elliptical shapes that change as function of their position inside the impeller channel. Furthermore, the drops have random trajectories, but a pattern can be detected in three cases: droplets near the pressure blade, droplets near the suction blade and droplets that move from the suction blade to the pressure blade. The average velocity of the oil droplets that move near the suction blade is significantly higher than the average velocity of the droplets that move near the pressure blade. Velocity changes as function of the impeller radius suggest different accelerations that may be caused by drag forces and pressure forces. The size of the oil drops has no significant influence on their velocities.

Commentary by Dr. Valentin Fuster
2017;():V008T11A050. doi:10.1115/OMAE2017-62438.

The current study concerns a recurrent problem in the oil industry when dealing with waxy crude oils in offshore fields. When a waxy crude stays static in the seabed for any reason, it cools down below the wax appearance temperature (WAT). Hence, crystals of wax appear in the fluid. These wax crystals form a crystalline structure. The strength of a crystalline structure rises with time. What also rises with time is the minimum pressure necessary to restart the flow.

When designing subsea structures, engineers assume that flow restart will occur when the pressure is sufficient to overcome a threshold stress. This threshold stress is related to what the literature calls apparent yield stress. Considerable evidence suggests, however, that a simplified momentum equation considering only this rheological parameter and the necessary pressure will provide an overestimated value. What this study aims to accomplish is a better understanding of the phenomenon involved in this process.

To do so, we build an experimental apparatus that allows us to represent the condition of the temperature close to bottom of the sea, and a pressurization system that allows us to precisely control the inlet pressure. The apparatus is composed of a one-inch pipeline that is submerged in a water bath (5°C) and a nitrogen system with controlled valves to pressurize the inlet of the pipeline.

Much discussion in the literature concerns the restart of a flow of gelled waxy crude. Many studies have suggested that the most important phenomena involved are the following aspects of the oil: its rheological behaviour, its compressibility, and its shrinkage. The current study contributes to the literature by demonstrating that the behaviour of a gelled waxy crude oil having a high percentage of wax that builds up a strong crystalline structure is impacted by rheological behaviour, time, and aging time.

To be able to provide the industry a reliable prediction of the gelled waxy restart pressure, it is necessary for engineers to carry out a great deal of experimentation and improvement in the models. In this paper, we compare the experimental data with the prediction of a model consisting of a weakly compressible fluid with an elasto-viscoplastic thixotropic behaviour. The comparison advances our knowledge in the phenomena involved in restart of gelled crudes and, in fact, shows the model capable of approaching the results expected by the industry.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Recent Developments in Artificial Lift and Gas Well Deliquification

2017;():V008T11A051. doi:10.1115/OMAE2017-62459.

This paper presents an alternative form of IPR, called in this study “Gas Dynamic IPR” (GDIPR), and compares it with the performance of conventional Inflow Performance Relationships (IPR) for gas reservoirs. The main objective of the GDIPR is to provide a simple but robust IPR solution for gas wells under transient conditions for the early and late life of gas reservoirs. Conventional IPR models are often not able to capture transient effects for the late life of gas reservoirs. The GDIPR solution, on the other hand, can be used for the cases of buildup and drawdown tests (early life), and for the modeling of transient liquid loading phenomena in gas wells (late life). The GDIPR is compared to conventional IPR models in two case studies. The comparison analysis show that the conventional IPR models do not provide reliable results, while the GDIPR is in agreement with the solution from discretized reservoir models. The GDIPR technique is computationally less expensive than discretized reservoir models, and is able to capture both the transient well behavior and the steady-state solution, for early and late life of gas reservoirs.

Commentary by Dr. Valentin Fuster
2017;():V008T11A052. doi:10.1115/OMAE2017-62460.

This study presents an experimental and numerical investigation on the effect of fluid properties on the performance curves for Gas-Lift Valves (GLV). Nitrogen and natural gas are used as the working fluids at pressure up to 66.2 and 45.5 bar respectively (960 and 660 psig). The performance of GLVs can be obtained theoretically or experimentally. However, it has been proved in the literature that the theoretical performance curves for such valves may not work appropriately for a wide range of fluids, pressure and temperature conditions.

The objective of this study is to investigate experimentally and numerically the applicability of using air instead of natural gas and how it would impact the performance of GLVs. The experimental results have been obtained using a high-pressure gas-lift testing facility located at the Louisiana State University. The GLV evaluated in the experiments is an orifice valve with 12.7 mm (32/64 in.) opening diameter. The experimental data results is compared with results obtained using a commercial simulator using a mechanistic model, and the Thornhill-Craver empirical model, which is often used to predict the gas flow through an orifice.

The results showed a significant difference between using natural gas and nitrogen as a working with respect to flow rate mainly due to the large difference in the specific gravity. Moreover, both theoretical and mechanistic models over predicted flow rates for both gases probably due to the inaccurate estimation of the specific discharge Cd of the GLV, as this value is not constant and changes with the valve and fluid types.

Topics: Fluids , Valves
Commentary by Dr. Valentin Fuster
2017;():V008T11A053. doi:10.1115/OMAE2017-62508.

Liquid loading is the mechanism that is associated with increased liquid hold-up and liquid back flow at lower gas flow rates in gas production wells. In laboratory, most liquid loading experiments are performed at fixed gas and liquid rates (mass flow controlled). In the field, the well behavior is a coupled well-reservoir system in which the reservoir results in a pressure or mass flow controlled inflow, depending on the reservoir characteristics. In this paper results are presented which have been performed with a pressure controlled vessel attached to a vertical pipe. The pressure drop between the vessel was varied to represent reservoir characteristics from tight to prolific. The goal of the experiments was to evaluate the relation and the time ‘trajectory’ between the minimum in the pressure drop curve and the actual flooding point. From these experiments it was concluded that the stability is determined by the overall pressure drop curve. That is the pressure drop from vessel to separator and not the tubing pressure drop curve. This stability point can be at a higher or lower velocity than the actual loading/flooding point and therefore, loading is not the cause of the production decrease. That also means stable production is possible below the flooding point in slugging conditions. In future, the distinction between stable flow and loading/flooding must be made more strict.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Simulation of Petroleum Engineering Systems

2017;():V008T11A054. doi:10.1115/OMAE2017-62536.

One of the critical factors in the deepwater exploration and development is the temperature during the drilling process. Temperature in the wellbore will induce the wellbore instability, which means the bottom hole pressure will change according to the accumulated thermal effects on the density, viscosity of the fluid during the circulation. Unpredicted bottom hole pressure will lead to unknown well control risks, which make the deepwater drilling is in great danger and unacceptable for the engineers.

In the casing design, the thermal effects were ignored in the past but with drilling deeper subsea wells, the thermal effects will exist inevitably. The extreme values observed at the seafloor could be as low as 40°F and as high as 150∼200°F at the wellbore annulus. Unfortunately, deepwater environments combine low temperatures, high pressures, gas and water that can induce hydrate formation. Hydrates can lead to drillpipe blockages and affect BOP operation. The low temperatures due to the hydrate or ocean current affect the properties of cement, which indicates to redesign cement slurry composition required.

Except the effects on the density and viscosity of fluid, the rising temperature in the annulus between the drill pipe and casing will make the trapped pressure increase in the annulus between outside casings. If the annulus build-up pressure can’t be released without rapture disks, otherwise the trapped pressure is beyond the initial design pressure, and the potential damage will happen.

This paper provides a simplified method to predict the circulation temperature under steady-state heat transfer in the deepwater rissssserswellbore, and a simulator is developed.

Commentary by Dr. Valentin Fuster
2017;():V008T11A055. doi:10.1115/OMAE2017-62537.

Producing hydrocarbon from deep water assets is extremely challenging and expensive. A good estimate of rates from multiple pay zones is essential for well monitoring, surveillance, and workover decisions. Such information can be gleaned from flowing fluid pressure and temperature; deep-water wells are often well instrumented that offers such data on a continuous basis. In this study a model is presented that estimates zonal flow contributions based on energy and momentum balances. Kinetic and heat energy coming from the reservoir fluid to the production tubing is accounted for in the model. The momentum balance for wellbore takes into account differing flow profile in laminar and turbulent flows.

In addition, when sandface temperature data are not available, a recently developed analytical model to estimate the effect of Joule-Thompson expansion on sandface temperature was used to estimate sandface temperature from reservoir temperature. The model developed can be applied to any reservoir with multiple pay zones and is especially useful for deep-water assets where production logging is practically impossible. Available field data for multiphase flow was used to validate the model. Sensitivity analyses were performed that showed accurate temperature data is essential for the model to estimate zonal contribution accurately.

Commentary by Dr. Valentin Fuster
2017;():V008T11A056. doi:10.1115/OMAE2017-62538.

The usual assumption of isothermal flow may be unsuitable in low-conductivity formations where large drawdowns occur. The increase in oil temperature associated with Joule-Thompson (J-T) heating triggers the consequent changes in oil viscosity and density. This paper presents an analytical 1D radial-flow model for estimating the transient flowing-fluid temperature in a single-phase oil reservoir. The model allows oil density, viscosity, and the J-T coefficient to vary with pressure and temperature. A rigorous thermodynamic expression based on fluid PVT behavior underpins the proposed model.

A detailed sensitivity analysis has shown the effect of oil production rate on reservoir heating and consequent changes in fluid properties. Specifically, we observed that fluid temperature increase above the original formation temperature occurs with a decrease in formation permeability, an increase in oil viscosity, and a decrease in overall heat-transfer coefficient. Of course, J-T heating increases with increasing flow rate.

Changes in reservoir temperature occur within about 100 ft. from the wellbore. Overall, the lessons learned from this study illuminates the need for reevaluating tubular design, flow-assurance issues related to dissolved solids, and assessment of well productivity index arising from J-T heating.

Commentary by Dr. Valentin Fuster

Petroleum Technology: Well Drilling Fluids and Hydraulics

2017;():V008T11A057. doi:10.1115/OMAE2017-61026.

Magnetic shielding of the Measurement While Drilling (MWD) directional tools and damages to mud pumps, down-hole tools and casing/drill-pipe and difficulties in understanding logging results are some of the main problems caused by steel and magnetic contaminated drilling fluids. In order to have these problems significantly reduced, all the magnetic contaminants should ideally be removed from the drilling fluid by the use of ditch magnets. Hence, the magnets and their ability to remove magnetic waste from the drilling fluid was evaluated by field evaluations.

Data from a field test of a new ditch magnet system where all the drilling fluid is forced to flow into an area with a strong magnetic fields have been compared with data from an operation with a traditional ditch magnet system in order to see if there are any significant differences in the total amount of magnetic waste material collected from the two systems. It is shown how drilling length, inclination and casing size may affect the production of magnetic debris entering the drilling fluid, and hence, show the well construction dependence of the ditch magnet performance.

Topics: Magnets , Ditches
Commentary by Dr. Valentin Fuster
2017;():V008T11A058. doi:10.1115/OMAE2017-61030.

Displacement processes are part of several drilling fluid operations. These operations include non-trivial items like changing from water based drilling fluid to oil based or opposite, casing cleaning operations, change to completion fluids or displacement operations during cementing. Among these operations, cementing is the most important and difficult because the scope is to create a permanent barrier and permanent zonal isolation in operations involving only limited volumes of fluids and slurries.

Empirical guidelines have been implemented to improve displacement processes in wells. Analytical and numerical models are frequently used. The models seem to be efficient in predicting pressure losses. However, they seem to be incapable of accurately predict the displacement efficiency. Laboratory experimental results have been evaluated and have been scaled up to for field application with variable success rate. These difficulties are caused by the presence of too many length scales or other dimensional scales.

Topics: Fluids , Drilling , Annulus
Commentary by Dr. Valentin Fuster
2017;():V008T11A059. doi:10.1115/OMAE2017-61125.

It is of high potential and risk to form gas hydrate along the wellbore in deepwater drilled-kick scenarios. Considering the transient mass transfer process that appears as the hydrate shell renewal at gas-liquid interface, we build a fully coupled hydrodynamic-hydrate model to describe the interaction of hydrate phase transition characteristics and wellbore multiphase flow behaviors. Through comparison with experimental data, the performance of proposed model is validated and evaluated. The simulation results show that the hydrate formation region is mainly near the seafloor affected by the fluid temperature and pressure distributions along the wellbore. The volume change and mass transfer over a hydrate coated moving bubble, vary complicatedly, because of the hydrate formation, hydrate decomposition and bubble dissolution (both gas and hydrate). Overall, hydrate phase transition can significantly alter the void fraction and migration velocity of free gas in two aspects: (1) when gas enters the hydrate stability field, a solid hydrate shell will form around the gas bubble, and thereby the velocity and void fraction of free gas can be considerably decreased; (2) the free gas will separate from solid hydrate and expand rapidly near the sea surface (out of hydrate stability field), which can lead to an abrupt hydrostatic pressure loss and explosive development of kick accident. These two phenomena generated by hydrate phase transition can make deepwater gas kick to be “hidden” and “abrupt” successively, and present challenges to early kick detection and wellbore pressure management.

Commentary by Dr. Valentin Fuster
2017;():V008T11A060. doi:10.1115/OMAE2017-61131.

For a particle on a wall or cuttings bed in a multiphase flow in confined geometries a condition for onset and lift-off is very important. In this case, a fundamental problem of hydrodynamic forces and torque acting on a particle moving near and on the wall in a viscous fluid needs to be solved.

In this paper, systematical simulation of a flow was performed around a perfect rolling or sliding spherical particle near the wall. A shear flow of Newtonian and Herschel-Bulkley fluids was investigated. The simulation was conducted for Reynolds numbers up to 200 and the dimensionless positive particle velocity Vp < 1.4. The relative particle velocity was made dimensionless by dividing it by the incoming flow velocity in front of the particle. The simulation was performed using the open-source CFD package OpenFOAM. The simulation results for Newtonian fluid agree with data presented in the literature.

For the particle’s low translational velocity the drag force coefficient in the non-Newtonian fluid is lower than in Newtonian fluid, but for increasing translational velocity the drag force coefficient increases.

The lift force coefficient behavior is non-monotonic versus rheology parameters. Lift and drag force show a sudden drop for very small translational velocities.

Our simulation shows that in the case of large Bingham numbers the particle’s lift force can be negative for steady perfect particle rolling. Thus, friction between particle and surface prevents particle’s take-off in some cases.

Knowing the dependence of the lift force on Reynolds number and rheological parameters allows one to determine incipient motion and take-off conditions for a spherical particle.

Topics: Shear flow
Commentary by Dr. Valentin Fuster
2017;():V008T11A061. doi:10.1115/OMAE2017-61192.

An experimental study was performed to investigate the influence of fluid elastic properties on the settling velocity of spherical particles in viscoelastic polymer fluids. The Particle Image Shadowgraph (PIS) technique was used to measure the settling velocity of the spherical particles (with average diameter of 2mm) in the hydrolyzed poly acrylamide (HPAM) polymer test fluids.

Test fluids were prepared by mixing 3 different grades of HPAM (with molecular weights of; 500,000; 8,000,000; and 20,000,000) at polymer concentrations of 0.09 and 0.1% by weight. Shear viscosity and oscillatory measurements were carried out to characterize the test fluids.

The test fluids were formulated in such a way that they had almost identical shear viscosity characteristics while showing significantly different elastic properties. The relaxation time was used to quantify the elastic characteristics of the fluids.

To quantify the impact of elasticity, the experimentally measured settling velocities were compared to the values calculated by using the model developed for predicting settling velocity of spherical particles in power law (visco-inelastic) fluids [1]. Experimental results indicated that the settling velocity of spherical particles in visco-elastic fluids decreased significantly with the increasing elasticity (measured in terms of relaxation times) of the fluids.

Commentary by Dr. Valentin Fuster
2017;():V008T11A062. doi:10.1115/OMAE2017-61391.

During drilling, there must be an evaluation of the maximum pressure that the formation can handle during a well kill scenario. This will depend on various parameters like fracture pressure, pore pressure, kick volume and several other factors. The depth of the next planned hole section will depend on if a kick of a certain size can be handled safely. This evaluation is often referred to as performing kick tolerances. When starting to drill a section, one will take a leak off test to get an indication of the fracture pressure at the last set casing shoe and this will be important information for the kick tolerance results.

For HPHT wells the margin between pore and fracture pressures will be small, and one often has to resort to using transient flow models to perform the kick tolerances. However, there are many uncertain parameters that are affecting the results. Some examples here are pore pressure, type of kick and kick distribution. There is a need for trying to incorporate the uncertainty in the calculation process to give a better overview of possible outcomes. This approach has become more and more popular, and one example here is reliability based casing design.

This paper will first describe the kick tolerance concept and its role in well design planning and operational follow up. An overview of all parameters that can affect the results will be given. In water based mud, the gas kick will be in free form yielding higher maximum casing shoe pressures compared to the situation when oil based mud is used where the kick can be fully dissolved.

Then it will be shown how both an analytical and a transient flow model can be used in combination with the use of Monte Carlo simulations to generate a probabilistic kick tolerance calculation showing possible outcomes for maximum casing shoe pressure for different kick volumes. Here uncertain input parameters that can affect the calculation result will be drawn from statistical distributions and propagated through the flow model to estimate the casing shoe pressure. Multiple runs will be needed in the Monte Carlo simulation process to generate a distribution of the maximum casing shoe pressure. This will demand a rapid and robust flow model.

The resulting maximum casing shoe pressure distribution will then be compared against the uncertainty in the fracture pressure at the last set casing shoe to yield a probability for inducing losses. The numerical approach for predicting well pressures and a schematic of the total calculation process will be given.

Emphasis will also be put on discussing how this should be presented to the engineer with respect to visualization and communication. It will also be shown that one of the strengths of the probabilistic approach is that it is very useful for performing sensitivity analysis such that the most dominating factors affecting the calculation results can be identified. In that way, it can help in interpreting and improving the reliability of the kick tolerance simulation results.

Commentary by Dr. Valentin Fuster
2017;():V008T11A063. doi:10.1115/OMAE2017-61449.

Drilling fluid is the mixture of base fluid and special chemicals. The system is designed to meet operational requirements. These complex fluids can carry drilled cuttings to surface, provide enough force or pressure to the formation and have adequate holding capacity in pump-off period to prevent particle precipitation. These necessities are controlled by fluid rheology. The art of flow or flow science, i.e. rheology, examines the deformation and flow behavior of the fluid. Ideal viscous flow through ideal elastic deformation is analyzed in this branch.

Increase in energy demand and depletion of shallow hydrocarbon reserves has driven the industry to explore deeper reservoirs. Thanks to the technical developments in the drilling industry, operations can go further, especially in offshore wells. Non-aqueous conventional drilling fluid systems (NAS), synthetic based mud (SBM) or oil based mud (OBM), are favorable due to lubricity effect, high inhibitive characteristic and temperature-rheological stability in deep formations. Despite the advantages of NAS over the water based systems (WBM), their flow characteristics vary with pressure due to compressibility. Mezger stated that “For most liquids, the viscosity values are increasing with increasing pressure since the amount of free volume within the internal structure is decreasing due to compression, therefore the molecules are more and more limited in their mobility. This increases the internal frictional forces and the flow resistance”1. By considering the primary well control requirements, drilling fluid equivalent pressure in both static and dynamic conditions can overbalance the fluid pressure in the rock pores and cannot exceed the inelastic strength of the medium in conventional, over-balanced operations. Mud playing pressure window shrinks as the depth is increased and is even not tolerable in ultra-deep offshore wells. Incompetent fluid formulation and hydraulic design led to detrimental and vital problems. In literature, limited research on high pressure fluid deformation behavior and rheological experimental data are found to understand the flow behavior and rheological changes in down hole conditions2. Generally rheological measurements are taken at the surface conditions and extrapolated to the down hole conditions that cause the perversity in real high pressure deformation behavior.

This study is conducted to examine the high pressure effect on NAS rheology and to compare the experimental results to the conventional WBM. High Pressure, High Temperature (HPHT) Anton Paar MCR-302 compact rheometer (1,000 bar–14,500 psi, 300°C capacity) is preferred rather than using HPHT viscometers due to exact frictionless air bearings in the laboratory experiments. Controlled shear rate (CSR) and rate sweep test methodologies are used in the rheological tests. Tests are performed from ambient surface conditions to 12,000 psi pressure at constant temperature. To get a better understanding of flow properties and to have a more accurate hydraulic design, rheological characterization is simulated under in-situ conditions. Test results are analyzed to understand the compressibility and pressure effects on rheological parameters in constitutive equation (yield stress, apparent viscosity, and flow behavior index) and deformation behavior.

Commentary by Dr. Valentin Fuster
2017;():V008T11A064. doi:10.1115/OMAE2017-62024.

Borehole hydraulics, hole cleaning and mechanical friction are important factors for well planning and drilling operations. Many studies aim to exploit and optimize the effect of different operational parameters. The effect of wellbore geometry on hole cleaning and mechanical friction has so far not received much attention. This paper presents results from experimental laboratory tests where hydraulics, hole cleaning and mechanical friction have been investigated for circular and non-circular wellbore geometries with a relevant oil-based field drilling fluid (OBM). The non-circular wellbore geometry was made by adding spiral grooves to the wellbore walls in order to investigate the effects on cuttings transport and mechanical friction. The study contributes to describe the function and ability of deliberately induced non-circular geometry in wellbores as means to achieve a more efficient drilling and well construction. Improving hole cleaning will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells. Reduced mechanical friction may improve the drilling process and many operations during the completion phase.

The laboratory experiments were performed in an advanced flow loop setup reproducing field-relevant flow conditions. The flow loop consists of a 10 m long 4” inner diameter borehole made of concrete. A free whirling rotational string with 2” diameter provides a realistic down hole annular geometry. A field-relevant oil based drilling fluid (OBM) was circulated through the test section at different flow rates. To represent the effect of rate of penetration, synthetic drilling cuttings (quartz sand particles) were injected at different rates through the annulus in the horizontal test section. The test results show that borehole hydraulics and cutting transport properties are significantly improved in the non-circular wellbore relative to the circular wellbore. The effect of the mechanical friction is more complex, yet significantly different for the two geometries.

Commentary by Dr. Valentin Fuster
2017;():V008T11A065. doi:10.1115/OMAE2017-62129.

Inaccurate calculation of settling and slip velocities of cuttings leads to inaccurate determination of cuttings concentration and, hence, borehole pressure, as well as inaccurate lag times. To minimize these problems, an understanding of the relation between drilling fluid characteristics and the cuttings transport process is essential. It is desirable for drilling fluids to form a gel structure to help cuttings transportation and suspension of solids. The gel structure development is proportional to increase in aging time. The increase in aging time yields higher shear stress responses at a constant rate of deformation to the drilling fluid sample. The gel structure development helps keep cuttings in suspension and shows a viscoelastic response to small deformations. Understanding these viscoelastic responses is important in rheological characterization and settling velocity prediction. Thus, viscoelastic drilling fluid characteristics should be investigated in depth to better estimate settling and slip velocities of cuttings and to increase cutting transport efficiency.

The main focus of this project is to work on viscoelastic and time-dependent fluid characterization to identify the relation between rheological properties and settling velocities of cuttings. Rheological experiments were conducted using an Anton Paar Physica MCR 301 Rheometer. Three different drilling fluids, Water Based Mud (WBM), Oil Based Mud (OBM) and Synthetic Based Mud (SBM), are used for rheological and settling velocity experiments. Stress Overshoot Tests (SOTs) and Steady-Shear experiments were performed to investigate viscoelastic properties and gel structure of the fluids, and to examine time and temperature dependence of WBM, OBM and SBM. Information obtained from the viscoelastic and time-dependent fluid characterization tests was coupled with settling velocity data using both arbitrary shape of cuttings and spherical particles. A mathematical model that considers viscoelastic properties and time dependency of drilling fluids was developed to estimate settling and slip velocities of the cuttings. Comparisons between the proposed models and existing models based on standard rheological measurements were also done. The results show that the proposed model has good agreement with the experimental data.

Commentary by Dr. Valentin Fuster
2017;():V008T11A066. doi:10.1115/OMAE2017-62132.

The objective of this study is to investigate flow behavior and survival ratio of different fluids with Hollow Glass Microspheres (HGM) as they pass through jet nozzles under various flow conditions. Three types of HGM with different compressive strengths (5,000 – 19,000 psi) and specific gravities (0.38 – 0.46) for 10% and 30% volumetric concentrations were tested under 196 – 345 ft/s average fluid velocities from 0.5 – 1.5 inch standoff distances during impact tests using a new High Shear Rate Facility (HSRF). Density measurements before and after each circulation cycle were used for calculating survival ratio of the HGM. Particle size analysis was carried out to see the change in the size distribution of HGM after impact experiments. A scanning electron microscope (SEM) was used to view samples of HGM from before and after impact tests to define breakage behavior. The Hertz Impact Law was used to build a mechanistic model to estimate survival ratio under several assumptions. An empirical equation was developed and compared with experimental results. Breakage type is the result of cyclic fatigue because breakage does not occur in one circulation. Standoff distance, concentration of HGM and velocity of the fluid are strong parameters of the survival ratio function. Size distribution analysis and SEM microphotographs show that larger HGM break first.

Commentary by Dr. Valentin Fuster
2017;():V008T11A067. doi:10.1115/OMAE2017-62244.

Particle dynamics within Newtonian and viscoelastic shear thinning flows were investigated with a self-confined cloud of particles around an obstacle. Water and three aqueous Poly-Anionic Cellulose (PAC) solutions were test fluids. An experimental study of an upward vertical pipe was carried out using particle image velocimetry (PIV) techniques to measure the particle and liquid velocity profiles. The fluidized cloud height was measured for better assessing rheological and particle loading effects on particle interactions within liquid flows. It was observed that the dynamics of particles were closely associated with local shear rate, fluid rheology and particle loading. Additionally, it was noted that the slip velocity of particles was relative to the surrounding liquid and was high in regions with a high shear rate and depended significantly on the liquid rheological parameters. The experimental findings were compared against three-dimensional numerical CFD simulations. In the case of particle dynamics in the water sample, it was noted that the simulation results were comparable to the experimental observations. However, for PAC solutions, particles were completely flushed out from the computational domain. This was considered a consequence of inadequate drag and settling velocity formulation within the CFD model. These shortcomings of the drag model were rendered, as Newtonian drag laws were applied to a non-Newtonian fluid, and only used background shear rates of the fluid flow field in estimating the local viscosity experienced by these particles.

Commentary by Dr. Valentin Fuster
2017;():V008T11A068. doi:10.1115/OMAE2017-62544.

Modern drill strings for the exploration of oil and gas are equipped with a variety of sensor carrying devices such as Measurement While Drilling (MWD), Logging While Drilling (LWD), and Formation Testing While Drilling (FTWD). These devices generate a large amount of downhole data, such as the orientation of the well, drilling parameters e.g. weight on bit and torque, and formation properties. Appropriate telemetry systems are included in the drill string to transfer relevant downhole data in real time to the surface. Other data is stored in memories downhole for subsequent evaluation. However, drilling fluid properties are still monitored at the surface and their behavior under borehole conditions is predicted with hydraulic models. Commercial solutions for a direct downhole measurement of various drilling fluid parameters are rare, though they would increase drilling process safety and the knowledge about the behavior of drilling fluids under real bottomhole conditions.

The pH has a significant influence on the properties of water-based muds and plays a role in the chemistry of oil-based muds as the water cut in the emulsion increases. Commercial pH-sensing devices, such as the glass electrode, and optical sensors are not appropriate for the pH measurement under bottomhole conditions. Fragility, the insufficient degree of miniaturization, the low temperature and pressure resistance due to the liquid reference electrolyte, and phenomena such as the alkaline error are certain drawbacks of glass electrodes. Often optical sensors often will not capture the whole pH scale and require the medium to be at least slightly transparent for light. The usage of pH-sensors based on EIS (electrolyte-isolator-semiconductor) structures is a possible application of chemical sensors for drilling fluid monitoring under in situ borehole conditions.

This paper presents results from a study on the behavior of an EIS structure as a pH sensitive electrode measured vs. a commercial Ag/AgCl reference electrode in comparison with a commercial glass electrode. EIS structures are capacitive pH sensors where the sensing layer is generally a metal oxide on a semiconductor substrate.

Measurements in basic drilling muds were conducted under constant temperature and atmospheric pressure while the drilling mud was steadily stirred. The mud was titrated from alkaline to acidic conditions with hydrochloric acid and the pH was measured after potential equilibration at the electrodes. The results show a general feasibility for the usage of the proposed sensor. There are still certain challenges to be overcome in the development of a robust and reliable pH-sensing device for complex fluids, such as drilling muds under high pressure/high temperature (HP/HT) conditions.

Topics: Fluids , Sensors , Drilling
Commentary by Dr. Valentin Fuster

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