bluuebunny/crossref_metadata_2025 huggingface dataset:
CFD Hydrodynamic Performance Comparison between Conventional and VIV-Mitigating Buoyancy Modules
Authors: Lai L. S.
Published: February 2018

Vortex-induced vibration (VIV) is a significant factor in causing cyclic stress and fatigue damage in drilling risers. A new design of drill riser buoyancy is introduced with tri-helical grooves formed into the module to mitigate against VIV. The focus of this work is to characterize the hydrodynamic performance improvement of this new design helically grooved buoyancy over the conventional buoyancy design.

Computational fluid dynamics (CFD) is employed to simulate the buoyancy module hydrodynamic behavior in 3-d space. A current speed representative of offshore environment corresponding to Re = 106 is considered using a Reynolds-averaged (k-epsilon) turbulence model. This methodology is based on previously validated domain, mesh and temporal independence studies for a circular cylinder that also showed agreement with published literature. The hydrodynamic performance is characterized primarily by the in-line and cross-flow drag coefficients Cdx and Cdy.

For the helical buoyancy, Cdx is benchmarked between CFD simulation and physical town tank testing which showed similar results. Direct comparison of Cdx for the static buoyancy module (bluff body) sees Cdx being higher for the helical form compared to the circular form due to the circular form's inherent drag crisis characteristic. However simply comparing Cdx would be erroneous. A complete hydrodynamic performance representation requires the consideration of the full flow field and Cdy. This exposes that periodic vortex shedding occurs for the circular form but is mitigated for the helical form. Vortex shedding occurring for the circular form results in significantly larger Cdy values as well as potentially larger dynamic Cdx for a non-fixed bluff body. For the helically grooved form, vortex shedding is successfully mitigated and Cdy is significantly lower. The helical grooves form channels that allow flow along different directions away from the free-field flow directions which function to disrupt the downstream regular flow order. This prevents the regular formation of vortex shedding in the wake of the riser which is a pre-cursor to VIV. The omnidirectional nature of the helical grooves also ensures this mechanism for breaking regular flow is achievable regardless of the environmental current direction acting on the riser.

VIV is an increasingly significant problem with deep-water exploration in harsh weather environments. The new buoyancy design provides passive vortex shedding mitigation to top-tensioned risers which would reduce the propensity of VIV occurrence.
Modified Casing Design and Low-Viscosity Wellbore Strengthening LVWS System Overcame San Andres H2S Water Flow Challenges in Midland Basin
Authors: Chen Z. , Snider C. , Linnerud B. , Griffin L. , Breeding D.
Published: February 2018

Spraberry and Wolfcamp horizontal wells drilled in the Midland Basin normally have three-string casing designs and utilize "slop" mud for the intermediate salt section (9.0-9.4 ppg). However, in some areas, due to water disposal in the San Andres, 9.6-10.0 ppg fluids are required to prevent hydrogen sulfide (H2S) water flows. These potential flows restrict the use of "slop" fluids, resulting in the need for a four-string casing design. This paper reviews several cases utilizing a modified casing design and a low-viscosity wellbore strengthening (LVWS) fluid to drill these H2S water flow wells with a three-string casing design.

San Andres H2S water flow challenges were encountered while drilling the first horizontal well (Howard County - Midland Basin) with a deep intermediate casing point. This casing point was intended to isolate the depleted zones below the San Andres; however, a casing modification was required to eliminate the H2S water flow challenges. This change was implemented, resulting in a new challenge to drill the depleted zones below the San Andres and the Spraberry and Wolfcamp "A" horizontal laterals in a single hole section.

This paper presents a modified casing design that overcame the San Andres H2S water flow issues. This paper will also discuss the LVWS system that was utilized to economically drill the depleted zones and producing lateral in a single hole section by providing wellbore strengthening with an extremely low viscosity. These changes resulted in an average cost reduction of $750,000 per well.

This paper also presents how overcoming a San Andres H2S water flow challenge resulted in an improved wellbore design that has substantially reduced well costs. While these improvements were key to handling the H2S water flow issues, they should not be limited to areas with San Andres H2S water flows. This paper may be beneficial to all operators searching for lower cost alternatives to drilling Spraberry and Wolfcamp "A" horizontal wells in the Midland Basin.
Lab-Scale Drilling Rig Autonomously Mitigates Downhole Dysfunctions and Geohazards Through Bit Design, Control System and Machine Learning
Authors: Zarate-Losoya E. , Cunningham T. , El-Sayed I. , Noynaert S. F. , Florence F.
Published: February 2018

Oilfield economic conditions today continue to emphasize the need to recognize and respond to drilling dysfunctions quickly to maximize performance and minimize well costs. It is important for drilling engineers planning wells to fully comprehend each dysfunction in order to develop a means to mitigate their impact. As progress is made in this effort, it has become increasingly clear that many issues facing the drilling industry cannot be solved or solutions implemented with traditional drilling technology and platforms. The automation of drilling data collection and control systems response is increasingly becoming a key aspect of advancing many aspects of drilling performance.

SPE's Drilling Systems Automation Technical Section (DSATS) now enters its third year of an international competition for universities to design and build a small drilling rig that can operate hands-free in an unknown formation. Much like engineers in the field, students from each team must develop technical skills to understand the drilling dysfunctions that affect their rig's performance and calculate their impact on drilling performance. For the first time, in the 2017 competition, students must design and build a downhole sensor integrated into their control scheme. They have applied several different sensor types and unique telemetry techniques in custom-machined bottom-hole assemblies (BHA) that follow a 1.125 in (28.5mm) bit. The collected data is being used for vibration mitigation in real-time without human intervention.

The teams realize that the measurement and control aspects of drilling are as important as the equipment design, so they must model the drilling-states to determine appropriate response algorithms. Issues must be identified, and drilling parameters adjusted before dysfunctions severely limit performance. Teams often conduct a series of structured tests in various rock types to pre-tune their drilling algorithms. With improved state-detection algorithms and new optimization techniques, the drilling parameters that maximize performance are immediately calculated and implemented. DSATS intentionally challenges each team by choosing a thin-walled pipe which limits the ability to apply weight on the bit (WOB), ultimately generating an environment that promotes bit whirl. DSATS also provides an unknown rock sample of varying material, formation dips and other "surprises."

This paper presents the results of on-site testing of the winning team, Texas A&M University, who drilled a high-quality wellbore in the shortest amount of time. It also details the decision-process for the rig's design, based on background lab tests and engineering calculations.
How to Test for Compatibility Between Fluids and Shales
Authors: Oort Eric van
Published: February 2018

Fluid-shale compatibility testing is as old as the drilling fluid industry itself, and remains a highly relevant topic as drilling applications explore new, more complex territory. Incompatibilities of fluids with clay-rich shale formations can lead to a plethora of operational problems, ranging from minor dispersion and accretion issues to major stuck pipe and production impairment events. The nature of fluid-shale interactions has confounded scientists since the birth of the drilling fluid industry, and has led to a variety of different test methods and protocols, many now decades old. The question remains: what are the best, most representative fluid-shale compatibility tests to characterize fluid-shale interactions and avoid making costly mistakes based on misleading test results?

Historical fluid-shale compatibility tests are often severely limited by over-emphasizing the role of clay swelling behavior, by not paying attention to shale sample condition, and by not being specific with regard to the intended purpose. Test selection is often based on a superficial assessment of the "reactivity" of the shale, and results are indiscriminately applied whether the intended purpose is maintaining cuttings integrity, promoting borehole stability or avoiding reservoir incompatibility to name a few. This paper points out the various pitfalls and problems associated with conventional tests such as atmospheric swelling tests and capillary suction time tests, which still find wide-scale application in the oil and gas industry. A case is made to abandon such tests in future. New sets of tests are proposed that may overcome the drawbacks of the conventional tests. These tests are also conducted with a clear purpose in mind. For instance, to evaluate borehole stability, it is argued to forego traditional swelling tests and instead focus on triaxial failure testing, mud pressure transmission testing and borehole collapse testing. The latter can be accomplished with a novel, low-cost alternative to the downhole simulation cell test in the form of a modified thick walled cylinder test. This new test exposes cylindrical shale samples, confined under downhole temperature and pressure, to mud formulations at overbalance for a specified period of time and assesses the failure strength of the sample thereafter.

Recommendations for shale characterization and to investigate fluid shale interactions relevant to shale cuttings integrity, borehole stability and reservoir compatibility for conventional and unconventional reservoirs are given here. The tests are illustrated with representative results obtained for novel mud systems such as high-salinity fluids and muds containing nano-particles. Recommendations with respect to applying laboratory results to field operations are provided.
On the Importance of Boundary Conditions for Real-Time Transient Drill-String Mechanical Estimations
Authors: Cayeux Eric
Published: February 2018

The extraction of mechanical friction, during drilling operations, is an important source of information to estimate whether the downhole conditions are sub-optimal, for instance because of poor cuttings transport or additional tortuosity induced by the directional work. Traditionally, the friction factors are extracted using steady state torque and drag models. But, there are contexts, like when drilling from a floater, where it is difficult to find any periods where stable conditions can be observed.

A possible solution to this problem consists in running, in real-time, a transient torque and drag model connected to a high refresh-rate feed of measurements taken by the drilling machines sensors, and to utilize continuous calibration methods to extract information about the unknown or ill-defined parameters that influence the drill-string mechanical system. For those parameters that should stay constant throughout a bottom hole assembly (BHA) run, the estimation method shall account for the totality of the observations and therefore utilizes calibration methods based on statistical global optimization principles, while time-dependent parameters are estimated using a filtering technique.

This approach is only valid when utilizing a trustworthy transient drill-string mechanical model. Comparisons between estimated values from transient torque and drag models and actual measurements have highlighted the importance of robust modelling at the boundaries of the mechanical system. For instance, when modelling precisely the top-drive and the hoisting system mechanical behavior with its associated heave compensation system, it is then possible to obtain a good match between estimated and observed top-drive torques and top-of-string forces, while the bit is off bottom. Furthermore, it requires a precise modelling of the bit/formation interaction to get a truthful dynamic response of the model when the bit is on bottom and only passive heave compensation is used. Associated with its continuously updated calibration of the ill-defined parameters of the system, such a transient torque and drag model enables the visualization, in real-time, of the internal displacements of the drill-string even in the most complex drilling conditions.

Until recently, drill-string dynamic modelling has mostly focused on the lower part of the drill-string, i.e. just above the BHA, and has been reserved to post-analysis evaluations, as existing solutions have been very computer intensive. This paper describes a solution that runs in real-time and that considers the whole drill-string, allowing for the extension of drilling automation functions to very dynamic conditions like those encountered on a floater.
Mud-Cement Displacement in Eccentric Annuli: Analytical Solution, Instability Analysis, and Computational Fluid Dynamics Simulations
Authors: Foroushan Hanieh K. , Ozbayoglu Evren , Gomes Paulo J. , Miska Stefan , Yu Mengjiao
Published: February 2018

A successful cement placement can provide zonal isolation and environmental safety. Effective design of cement placement and mud removal impact all the stages of the wellbore life from drilling ahead to production. Accurate predictions of fluid displacement in the wellbore are vital to design fluid properties and plan the cementing job. In this work, an analytical model is developed to simulate the displacement of fluids in eccentric annuli.

This paper presents a novel method for the solution of cement/mud displacement and evaluation of inter-fluid contamination during displacement for eccentric annuli. This new approach starts by addressing the problem of single fluid flow in eccentric annuli by solving analytically the governing transport equations for a flow inside an unwrapped annulus. The solution is, then, extended to a system of two fluids in a vertical annulus by adjusting the boundary conditions for displacement. The model is completed by adding the time-dependent calculation of interface between the two fluids, enabling the accurate determination of the amount of mixing and displacement efficiency.

The analytical method proposed is used to simulate single and multi-fluid flows and study the effect of fluid properties of cement, spacer, and drilling mud at different flow rates on displacement efficiency, for both concentric and eccentric, vertical annuli. 3-dimensional Computational Fluid Dynamics (CFD) simulations were also performed and the results were compared to the analytical solution. Moreover, instability of the interface in all the cases was studied and the analysis offers an understanding of the role of fluid properties and proposes applicable optimized design to enhance the displacements. The amount of mixing and contamination that occurs during the displacement was calculated for both methods. The analytical solution and CFD produce results within a 13% difference, which validates the analytical model. Evidence was gathered to support that the improper design of fluid properties and flow rate along with a highly eccentric annulus can lead to substantial cement contamination. This may lead to under-designing the amount of fluids to be pumped to provide a complete mud removal and an efficient cement placement. On the other hand, learnings and models developed allow optimizing fluid properties that may lead to best outcomes even for highly eccentric annulus.

The undeniable importance of a complete cement displacement is addressed by means of an analytical solution of the displacement, which provides a realistic prediction of the amount of inter-fluid mixing and cement contamination. This approach coupled with the interface instability analysis, which offers improvement techniques for the displacement, provide beneficial enhancements for practical industrial applications.
In-Situ Fluid Rheological Behavior Characterization Using Data Analytics Techniques
Authors: Ettehadi Reza , May Roland , Dahl Thomas , Clapper Dennis , Swartwout Rosa
Published: February 2018

The accurate characterization of drilling fluid rheological properties at the in-situ downhole temperature and pressure is essential for designing the hydraulic program as well as for managing potential challenges during the drilling operation. A rheometer capable of operating at high temperature and high pressure (HTHP) is the common experimental method used to measure drilling fluid rheological properties at in-situ conditions. This method is costly and time consuming and requires skilled fluids laboratory personnel to carry out the tests. At the rigsite these devices are usually not available.

This paper/study presents an analytics based method to estimate drilling fluid rheological properties at in-situ downhole temperature and pressure and provide the required inputs for hydraulic modeling during well planning, for real-time monitoring and automation. The performance of the developed method is evaluated by utilizing data obtained from both, Mud Check tests and HTHP Viscosity measurements of synthetic and oil based drilling fluid samples.

Drilling fluid samples were collected from the rigs in operations around the world. An algorithm is developed to retrieve data out of unstructured field service laboratory databases and to uncover hidden patterns by utilizing the text pattern matching, text analytics, table-based approach, data visualization and classification techniques. Several computational intelligence techniques and statistical methods are applied to interpret the data by correlation of variables measured in the Mud Check tests and HTHP rheometer data. Of the available data 70 percent have been randomly extracted to train the data driven-model to predict drilling fluids rheological behavior at the in-situ downhole temperature and pressure.

The model is further tested with the remaining 30 percent of the available data to confirm that the model can not only fit the data used for training but also characterize the drilling fluid rheology at the in-situ downhole temperature and pressure with the required accuracy. This study indicates that in addition to temperature and pressure, several parameters including density, salt concentration, low and high gravity solid volume percentage, oil-water ratio, and oil phase volume percentage should be considered to accurately predict the rheological properties of drilling fluids at downhole conditions. Since the method presented here depends on several variables measured in the Mud Check tests, it can effectively be employed independent of location or formation.

The developed method can be utilized at the rigsite by field personnel to estimate downhole rheological properties of drilling fluids with a small error margin, without using expensive test equipment and time consuming procedures.
Using Aluminum Drill Pipe with Axial Oscillation Tools to Significantly Improve Drilling Performance
Authors: Mills K.. , Menand S.. , Grissom R.. , Kaufmann P.. , Schulte C.. , Evans N..
Published: February 2018

Aluminum drill pipe has already been proven as a viable alternative to steel drill pipe when drilling long horizontal wells thanks to its lighter weight that does not compromise resistance to yield and buckling. At the same time, the development of unconventional wells has seen the deployment of numerous technologies to further improve the performance and increase the lateral section to reduce costs. An operator has recently and successfully tested a new aluminum drill pipe with an axial oscillation tool to push further the limits of the drilling system.

This paper presents the key findings of the case study using a mixed aluminum-steel string combined with an axial oscillation tool. First, the innovative drill pipe design is presented, followed by lessons learned during rig operations regarding pipe handling practices, rig compatibility and pipe inspection. Then, results of the drilling simulations performed during the well planning phase are presented. This modeling led to an optimum drill string design associating the steerable mud motor assembly, aluminum drill pipe, axial oscillation tool and steel drill pipe. The number and placement of aluminum drill pipe along the string was key to reducing friction and improving weight transfer between the bit and the axial oscillation tool.

Through extensive modeling and field data interpretation, this paper presents the comparison of the overall drilling performance between steel only and aluminum-steel drill pipe strings, and provides metrics in terms of weight transfer and rate of penetration improvement. This innovative and promising drill string design opens the doors to set new limits in terms of horizontal departure.
Dynamic Kill Method Using Staged Fluid Densities can Improve the Killability of Relief Wells for Challenging Blowouts
Authors: Chantose Prasongsit , Oskarsen Ray , Emilsen Morten , Negrao Alvaro
Published: February 2018

In the event of a blowout, the kill method that usually has the highest probability of success is a relief-well intervention. After the relief well gains hydraulic communication with the blowing well, a dynamic kill is often used to bring the well under control. In some cases, the pumping operation may call for more than one fluid density, which is referred to as a staged kill. Although the staged-kill technique has been around for a long time and has been successfully used on many blowouts, little information is available on applications, benefits, technical challenges, and operational requirements. In this paper, two case studies demonstrate how a staged kill can successfully kill challenging blowouts under various conditions. One example, for a staged-kill application, is an actual gas-condensate blowout that could not be brought under control with a standard dynamic-kill operation. Staging a heavy kill mud ahead of a lighter mud that would not fracture the exposed formations successfully killed the well. The second example summarizes the results from a relief-well contingency study for a planned high-pressure, ultradeepwater well with a weak formation that would be fractured by the required kill mud. Dynamic simulations demonstrate that a lighter mud circulated ahead of the static kill fluid could bring the well under control without fracturing the weak zones.
How to Manage Geomagnetic Field Disturbances in the Northern Auroral Zone to Improve Accuracy of Magnetic MWD Directional Surveys
Authors: Edvardsen I. , Nyrnes E. , Johnsen M. G. , Hansen T. L. , Aarnes I.
Published: February 2018

The auroral zone is the region surrounding the geomagnetic north and south poles and is where the largest and most frequent disturbances in the Earth's magnetic field are experienced. Since the accuracy of magnetic MWD directional surveys are affected by geomagnetic disturbances, surveying wells in the auroral zone is challenging. Development of industry practices to enable accurate surveying and safe operations in these areas is therefore important.

The objective of this study is to investigate how the geomagnetic field parameters declination, dip angle and total magnetic field intensity are influenced by magnetic disturbances in the auroral zone. This is done by analysing the statistical properties of data from 20 land-based magnetic observatories and variometer stations in Alaska, Greenland, and Scandinavia, all located in the auroral zone. The results are used to estimate models for magnetic field disturbance variations as function of distance and direction. Additionally, methods and correction procedures to reduce azimuth uncertainty using data from distant monitoring stations are presented.

Uncritical use of data from monitoring stations can result in uncertain azimuth measurements. In cases where data from more than one nearby monitoring stations are available, the challenge is often related to identifying which stations that provide the most accurate corrections. As will be shown, important criteria for the selection of monitoring stations are not only limited to directions and distances, but also the position of the ionospheric current relative to the rig-location. Procedures and methods for how to predict the positions of ionospheric currents are presented.

The datasets analysed in this study contain measured deviations from the quiet mean for periods with low, moderate and high geomagnetic activity. Station-pairs with mutual distances ranging from 150km to 850km are considered. The general trends are that magnetic data from station-pairs located along the east-west direction are more correlated than data from stations located along north-south, and that differences in magnetic fluctuations between station-pairs are lower east-west than north-south. This accounts for all distances, directions, and disturbance levels.
Unlocking Reserves in a BP Operated High-Pressure Gas Field through Reliability Based Casing Design
Authors: Miller Richard A. , Ramtahal Rishi , Owoeye Oladele O.
Published: February 2018

The BP project team has considered increased reserves recovery by lowering the reservoir abandonment pressure below the initial design value. Through a multi-disciplinary approach, design assumptions and equipment ratings were systematically reviewed to determine which aspects factored into the decision to change reservoir management. Collapse loading of the 10 in. production liner was identified as a key variable.

The conventional design factor, a ratio of the design load to the API collapse rating, was deemed to be an insufficient way of characterizing design margin, primarily due to the perception of conservatism in the rating. While design factors are convenient for screening a casing string against an agreed-upon set of inputs and assumptions, there is little insight gained from comparing a 1.03 design factor to a 1.02 other than one value is higher than the other. The team embarked on a scope of work to characterize the probability of collapse as a function of reservoir abandonment pressure using reliability based design (RBD).

Physical testing was conducted to characterize the distribution of collapse resistance and the distribution of dimensional and strength parameters which govern collapse. The quality data sets are combined using the Klever-Tamano limit state equation to indirectly derive a distribution of collapse resistance. The destructive collapse tests provide both a direct measure of the distribution of collapse and a way to calibrate the limit state equation model uncertainty. Both the direct and indirect methods are useful in determining the probability of collapse for a design load.

Load uncertainty was characterized by considering variability of conditions across the wellstock, including depth, temperature and completion configuration. Casing wear was also considered in the assessment.

This paper outlines the RBD methodology used to support the decision to lower reservoir abandonment pressures. Details on how to construct the statistical collapse model are provided along with a discussion on interpretation and continuous improvement activities.
New Design Limits Plot for Overview of Load-Resistance Relationship in Wellbore Tubular Design
Authors: Liu Zhengchun , Samuel Robello , Gonzales Adolfo , Kang Yongfeng
Published: February 2018

In the tubular design of oil and gas wells, visualization of the loads and design limits (resistance over design factor) in a single 2D plot can help provide well designers a safety-factor overview of a particular string section. This plot is called a design limits plot (DLP). This paper illustrates the theoretical foundation and construction procedure of a new DLP, which is believed to more accurately represent safety factors.

The new DLP was built by plotting differential pressure, ΔP, vs. equivalent axial load Feq (= Fa + min(pi, po)×AS, where Fa is the axial force, AS is the cross-sectional area, and pi and po are the internal and external pressures, respectively), for both envelopes (design limits) and load points. Temperature-deration effects were applied to load points instead of envelopes so that the safety factor could be neatly represented by the relative load-point location with respect to the room-temperature envelopes. For comparison, the triaxial yield envelope was plotted together with API envelopes (axial, burst, and collapse).

A field example is presented that demonstrates the application of the new DLP for wellbore tubular design. It is shown that, for load cases in which counter-load pressures (which are defined as pi for collapse loads and po for burst loads) are high, the new DLP represents the safety factors more accurately and comprehensively.

Using the equivalent axial load instead of the axial force in the new DLP allows for better consistency with both the von Mises triaxial yield criterion and the API 5C3 2015 addendum. The new DLP not only represents a more accurate overview of safety factors, but also facilitates direct reading of pipe burst/collapse ratings.
Novel Drill Bit Technology Combined with System Matcher Increases Torque Efficiency and Reduces Stick-Slip and Vibrations
Authors: Rahmani Reza , Omidvar Navid , Hanley Chris
Published: February 2018

Major performance challenges for deepwater applications from a drill bit standpoint were identified as (1) High surface torque in salt is one of the major ROP limiters. (2) Inability to control depth of cut in soft rocks including shale and salt and when drilling in interbedded formations results in torsional oscillations and stick-slip. (3) Improper combination of bit and reamer induces drillstring vibrations. This paper presents the development of new drill bit technologies combined with a new system matching analysis package to address those problems.

Salt mechanical behavior was evaluated using triaxial testing under confining pressures up to 5,000 psi. Full scale pressurized testing was then conducted to evaluate salt drilling behavior versus rock characteristics. The following specific challenges were addressed: Non-planar PDC geometries were tested in salt, among other rocks, to identify a geometry which results in maximum increase in ROP at any given torque.New insert shapes were developed and tested for more effective and accurate depth of control.A full drillstring analysis model was developed with the ability to predict downhole and surface torque and WOB as well as drillstring dynamics, torque, and drag.

The new shaped cutter full scale pressurized test resulted in an increase in ROP/torque ratio throughout the different rock and a 28% increase in salt. The cutter also increased ROP/WOB ratio by 42%. Furthermore, the new insert shapes proved to be more effective in controlling depth of cut, resulting in an extra 35% reduction in torque/WOB ratio compared to standard insert shapes.

The project is now in field evaluation and the new drill string analysis tool has been applied to several field applications including some in the Middle East, North Sea, Gulf of Mexico, and the Caribbean for different purposes. Some of those purposes include buttonhole assempbly (BHA) selection for given bit and reamer, bit selection for a given BHA design and reamer, and drilling parameter optimization for a given BHA design, bit, and reamer. New insert shapes were run in multiple applications in North America, including in North Dakota and Oklahoma, with promising results proving that although the project was focused on deepwater drilling challenges, the novel solutions are applicable to a wide range of applications.
A 300 Degree Celsius Directional Drilling System
Authors: Stefánsson Ari , Duerholt Ralf , Schroder Jon , Macpherson John , Hohl Carsten , Kruspe Thomas , Eriksen Tor-Jan
Published: February 2018

The typical rating for downhole measurement-while-drilling equipment for oil and gas drilling is between 150°C and 175°C. There are currently few available drilling systems rated for operation at temperatures above 200°C. This paper describes the development, testing and field deployment of a drilling system comprised of drill bits, positive displacement motors and drilling fluids capable of drilling at operating temperatures up to 300°C. It also describes the development and testing of a 300°C capable measurement-while-drilling platform.

The development of 300°C technologies for geothermal drilling also extends tool capabilities, longevity and reliability at lower oilfield temperatures. New technologies developed in this project include 300°C drill bits, metal-to-metal motors, and drilling fluid, and an advanced hybrid electronics and downhole cooling system for a measurement-while-drilling platform. The overall approach was to remove elastomers from the drilling system and to provide a robust "drilling-ready" downhole cooling system for electronics. The project included laboratory testing, field testing and full field deployment of the drilling system. The US Department of Energy Geothermal Technologies Office partially funded the project.

The use of a sub-optimal drilling system due to the limited availability of very high temperature technology can result in unnecessarily high overall wellbore construction costs. It can lead to short runs, downhole tool failures and poor drilling rates. The paper presents results from the testing and deployment of the 300°C drilling system. It describes successful laboratory testing of individual bottom-hole-assembly components, and full-scale integration tests on an in-house research rig. The paper also describes the successful deployment of the 300°C drilling system in the exploratory geothermal well IDDP-2 as part of the Iceland Deep Drilling Project. The well reached a measured depth of 4659m, by far the deepest in Iceland. The paper includes drilling performance data and the results of post-run analysis of bits and motors used in this well, which confirm the encouraging results obtained during laboratory tests. The paper also discusses testing and performance of the 300°C rated measurement-while-drilling components – hybrid electronics, power and telemetry - and the performance of the drilling tolerant cooling system.

This is the industry's first 300°C capable drilling system, comprising metal-to-metal motors, drill bits, drilling fluid and accompanying measurement-while-drilling system. These new technologies provide opportunities for drilling oil and gas wells in previously undrillable ultra-high temperature environments.
Real-Time Eye-Tracking System to Evaluate and Enhance Situation Awareness and Process Safety in Drilling Operations
Authors: Kiran Raj , Salehi Saeed , Jeon Jiwon , Kang Ziho
Published: February 2018

Lack of situational awareness in drilling operations has become an important factor in causing safety accidents or cause of non-productive time. Process safety is another critical aspect for such high risk operations and cannot be ignored. A review of testimony from offshore rigs worker suggests long working shifts and fatigue as one of the crucial issues impacting performance.

The study here presents results from experiments conducted in a Virtual Reality Drilling Simulator (VRDS) equipped with eye tracking technology. The eye tracking technology can be used to distinguish between less and more aware/alert participants which is most of the times related to fatigue or onsite distraction. The ocular activity can be used to obtain visual cues that can quantify the state of drilling operator while operating. These cues can help in generating some warning alarms to alert the driller. Therefore, the system can reduce not only accidents but can also save a tremendous amount of non-productive time by improving their efficiency. Since human eyes express the most direct reaction during less alert or distracted mental state, ocular activity data has been used as the basis for quantification of situation awareness by researchers. In recent years, eye tracking system has been developed in the form of static and dynamic devices. The camera installed in these devices capture different characteristics of the participants' ocular movement in real-time. These oculomotor data such as eye fixation count and duration and pupil size, has been implemented in several industries such as aviation and medical to assess the performance of participants in recent years.

In this paper, we use eye tracking techniques for investigation of alertness and awareness of participants while conducting different drilling operations on the simulator. Results obtained from this study indicate that the system can detect the distraction and alertness exhibited by humans. The results show the very promising application of this technology on the drilling rigs. The novelty in this work is the development of framework for implementation of real-time eye tracking technology in various drilling operations such as drilling rigs and Real Time Operation Centers (RTOCs).
The Barlow Equation for Tubular Burst: A Muddled History
Authors: Adams A. J. , Grundy K. C. , Kelly C. M. , Lin B. , Moore P. W.
Published: February 2018

The Barlow equation for tubular internal yield pressure is widely used in American Petroleum Institute (API) and International Organisation for Standardisation (ISO) standards, but its provenance and accuracy have never been established: indeed, until very recently, the original reference had been lost to the industry. This has led to doubt and confusion about its use. This paper presents the work done by ISO TC67 SC5 workgroup 2 to remedy this, and explains the background and technical basis for the upcoming revisions to ISO TR 10400.

It is shown that Barlow's 1836 derivation violates the 3D constitutive law, and the result is therefore incorrect as originally purposed (a thick wall hoop stress). Moreover, hoop stress is a uniaxial (1D) check: the modern approach is 2D or 3D checking, based on a material failure condition such as the Von Mises yield criterion.

However, the result also happens to represent the thin wall approximation to the VME failure pressure for plane stress (i.e., zero axial load), which gives an accurate measure of the yield pressure. Remarkably, this does not seem to have been recognised in previous work. The derivation is given, and the assumptions and limitations explained.

Present design practice is over-conservative for thick wall pipe, and potentially unconservative for thin wall. This is not the fault of the Barlow equation per se: it is caused by the difference in physics between the design equation (VME yield) and the ultimate limit state (ULS) behaviour (ductile rupture).

The industry should therefore consider revising OCTG burst ratings and accompanying design practice to achieve a more uniform safety level over the full D/t range of casing and tubing.
Annular Casing Seal Test Method
Authors: Fleckenstein W. W. , Baker R. , Eustes A. W.
Published: February 2018

A method and apparatus to test the annular seal of a casing string placed in a wellbore is presented. This method and apparatus, called the Annular Casing Seal Test (ACST), successfully measures the annular casing seal in the wellbore using a positive pressure test. Results presented document the experimental studies using prototypes under a variety of cemented casing conditions to determine the ability to detect effective and poorly cemented casing annular seals. When the interior of the tool is drilled out, an array of encapsulated bores is exposed, allowing pressure and flow communication between the interior and the annulus of the casing. Prototypes tested in experimental wellbores confirm the ability of the technology to detect casing annular conditions. A well-cemented casing annulus is easily detected, since the test pressure only encounters the annular cemented across the full circumference of casing. A poorly cemented annulus is similarly detected because pressure escapes the ports into the void in the cemented annulus. An important application of this method allows the annular seal at the surface casing shoe to be inexpensively and quickly tested, providing positive confirmation of the protection of the aquifer. This test is an improvement over the casing shoe test, which is in reality, a measure of formation strength and has demonstrated short comings in detecting poor cement jobs near the casing shoe in a variety of applications. This method is also an improvement over cement bond logs (CBLs), which are more expensive, time consuming, and do not provide a positive test of hydraulic isolation.
Real-Time Quantitative Composition of Formation Fluids While Drilling
Authors: Colombel Emilie , Guerriero Nicolas , Ringer Maurice
Published: February 2018

Mud-gas technologies for continuous PVT-like analysis of reservoir fluids in the drilling mud require a calibration procedure to determine the efficiency of the gas extraction process. This procedure is required because the efficiency of the hydrocarbons extraction process is strongly affected by the drilling mud type and properties, and so it must be performed any time the mud significantly changes.

The calibration procedure requires a sample of drilling mud that contains significant amounts of alkanes. Currently, this sample is collected while drilling during a gas peak and stored until the end of the phase, when the calibration can be performed. Thus, the gas extraction efficiency can only be determined at the end of each drilled section, and the quantitative analysis of the reservoir fluid in the mud is made available only at the end of each section.

This paper presents a new procedure, in which a Calibration Mud sample is built by injecting and emulsifying several alkanes into the mud. The calibration can then be performed at any time before drilling commences.

It is extremely difficult to inject and dissolve gaseous light hydrocarbons into a mud sample at the rigsite. For this reason, we inject a sample of six liquid alkanes into the mud and emulsify it to build a mud sample suitable for the calibration procedure. The extraction efficiencies for the lighter gas alkanes are then extrapolated from those of the injected alkanes using a model of the extraction process.

The new calibration process has been tested in several wells around the world. In each test, the new calibration process and standard calibration (performed at the end of the phase using mud collected while drilling) were performed. Validation of the new technique comes from ensuring the extraction efficiency coefficients using our new calibration mud match those coming from the standard calibration. The results were conclusive with similar coefficients obtained in each test. The uncertainty intervals overlap, and the calibration coefficients are statistically equivalent.

The new calibration procedure represents an innovative methodology enabling real-time, continuous quantification of the light hydrocarbons content (C1-C6) of the reservoir fluid, comparable to the PVT monophasic composition, while drilling, at surface. This is the first time that such data can be delivered in real-time while drilling. The resulting measurements have multiple applications such as enhanced geosteering and well placement, real-time identification of gas-oil contacts, and real-time selection of sampling points and can be integrated with downhole tool measurements to provide a true real-time understanding of the subsurface fluids.
Premature Failures of Rotary-Shouldered Connections RSC Due to Improper Re-Cut and Repair Procedures
Authors: Koneti Srinivasa , Gokhale Samit
Published: February 2018

Premature failures of rotary-shouldered connections (RSC) resulting from improper re-cut and repair operations performed on used connections can cause immense financial loss to oil and gas operators. One of the reasons for improper re-cut and repair procedures is the desire to limit the loss of tool length during thread repair operations. However, this leads to residual damage which can compromise the connection performance and lead to premature connection failures.

To study the issue, finite element analysis (FEA) modeling was utilized to determine the distribution of the stresses in RSCs and to map the stress profile at critical locations which could be affected by improper repair operations. In addition, two case studies where the connections of the components failed prematurely in their first run after the connections were freshly re-cut were investigated. The thread repair protocols and post-threading nondestructive inspections were reviewed. Visual examination and optical metallography were utilized to characterize the failure mechanism along with the location of the failures. The failures were not located at the last engaged threads of the connection, which is not typical. Both case studies indicated that the residual damage left from improper thread recut operations had led to the thread failures at non-standard locations.

The paper presents the case studies, the details of the metallurgical analysis along with the FEA simulation data. The paper lists the various options available for thread repair along with the commercial benefits associated with these repair options in terms of tool length savings. The paper also presents the failure risks associated with the thread repair techniques. Additionally, the paper discusses the correct re-cut and repair procedures for RSCs along with required NDE inspections that need to be performed after the repair of the connection. By applying and following the recommended repair and inspection protocols, premature connection failures resulting from improper thread repair may be eliminated.