Downhole Environment Research Articles

Box-Behnken Design Approach Toward Predicting the Corrosion Response of 13Cr Stainless Steel

13Cr stainless steel, the most commonly used oil country tubular good material with good mechanical and corrosion behavior, has the drawback of sensitivity to localized corrosion, particularly in offshore downhole environments, limiting the life span of the parts. A careful assessment of the corrosion behavior of the material can be done by the perception of the most influential environmental factors combined with the material’s intrinsic microstructure. This study aims to focus on the former, the effect of environmental factors, including pH, temperature, and chloride concentration, varying in the ranges of 4 to 7, 22°C to 80°C, and 1,000 mg/L to 22,000 mg/L, respectively, on the pitting corrosion behavior of 13Cr stainless steel. Adopting a response surface methodology, using a Box-Behnken design, a carefully designed set of corrosion tests at various combinations of the environmental factors were performed. Considering the pitting potential measured from the cyclic potentiodynamic polarization testing, as the response of each experiment, a quadratic model was developed correlating the studied environmental factors and the pitting potential values. Further analysis of the developed model was conducted through analysis of variance, followed by optimizing the model according to the highest, medium, and lowest pitting potentials. The optimized results confirmed that the best corrosion behavior occurs at approximately the lowest chloride concentration and temperature, and the highest pH value. However, contrary to the expectations, the worst corrosion response was detected at the medium temperature of 52°C, instead of the highest temperature of 80°C. It was concluded that at higher temperatures, the corrosion tends to be more uniform, resulting in the formation of a layer of corrosion products that covers the sample’s surface. The corrosion product layer acts as a barrier against the diffusion of the aggressive ions, causing deceleration of the corrosion reactions.

Sensorless Control of CSC-fed PMSM Drives with Low Switching frequency for Electrical Submersible Pump Application

In this article, current source converter (CSC)-fed permanent magnet synchronous motor (PMSM) drives are investigated for electrical submersible pump (ESP) applications. The CSC features motor-friendly waveform with low dv/dt , which is very suitable for long cable application. High-speed ESP by adopting a PMSM has higher efficiency and shorter length and diameter compared with the counterpart adopting induction motor. Sensorless control instead of mechanical sensor can further reduce the system size/cost and improve reliability due to the harsh downhole environment. However, low switching frequency and an inverter-side output filter cause great challenge in controller and observer design. These kinds of influence become more serious under a higher speed region due to the limited updates per fundamental cycle. To overcome these challenges, the dynamic capacitor voltage control is employed in a field-oriented control scheme to enhance the system dynamic response. Moreover, a discrete-time sliding mode observer based rotor position estimation method is proposed to reduce estimation error and improve parameter uncertainty robustness. The effectiveness of the proposed method is verified on a CSC-fed PMSM with simulation and experimental results.

Analysis and modeling of thermoelectric power generation in oil wells: A potential power supply for downhole instruments using in-situ geothermal energy

With the increasing development of smart well technology in the oil and gas industry, there is a need for robust and reliable downhole power supply in order to provide stable power for downhole sensors and control tools. Usually, the produced fluid from the reservoir carries abundant thermal energy, which can be converted to electric power with thermoelectric technology. To realize in-situ power generation in the downhole environment, the design of downhole segmented concentric cylindrical thermoelectric generators (CCTEGs) with a cold fluid is proposed. A mathematical model for downhole thermoelectric generation is presented, which considers the heat transfer in the interior of thermoelectric element and from surrounding formation. The power performance in an oil well with 50% of water cut is investigated by using an engineering equation solver program. Numerical results show that about 800 W of power output could be obtained with 200 m length of segmented CCTEG, which is enough to provide power for typical downhole applications. The length of the segmented CCTEG and the injection rate of cold fluid dominantly affect the power output. The power consumption requirement for downhole applications in different operation periods could be met by simply adjust the injection rate of cold fluid.

BHA Behavior-Prediction Model Offers Potential for Automated Analysis

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191780-18ERM-MS, “Field Validation of a New BHA Model and Practical Case Studies in Unconventional Shale Plays, With a Framework for Automated Analysis for Operations Support,” by J.K. Wilson, Scientific Drilling International, prepared for the 2018 SPE/AAPG Eastern Regional Meeting, Pittsburgh, Pennsylvania, USA, 7–11 October. The paper has not been peer reviewed. A new 3D drillstring model determines the static and dynamic behavior of bottomhole assemblies (BHAs) in realistic wellbores. The modeling approach provides a prediction of the BHA’s mechanical and dynamic behavior and can be used as a planning tool for BHA design, an investigative tool for root-cause analysis, or, potentially, as a real-time optimization tool for avoiding harmful operating conditions. Introduction When using any model, engineers cannot forget the limits of calculation. However, they can settle for “good enough” as long as they adhere to the following two rules: The results capture the general behavior of the system with respect to the parameters of interest. The engineer using the results fully understands the limits of the model used to obtain them. These rules are particularly important when considering highly nonlinear systems, such as the 3D behavior of BHAs. Nonlinearity arises in these systems from the large, coupled deflection that occurs in the downhole components as they move within the wellbore, and the frictional contact that results from the borehole wall restraining that movement. These inherent complexities have been a driving factor for continued research on the subject of BHA modeling for years. On the basis of the author’s own investigative studies and working experience, there appear to be three primary areas of focus within the study of BHA mechanics and dynamics: The mechanical loading on the downhole components The directional performance of various drilling assemblies The dynamic response of BHAs The purpose of the current project was to develop a BHA model that could analyze each of these topics in an efficient manner while maintaining a reasonable level of accuracy. Such a model could then be leveraged routinely to design more-robust tools and provide a reliable approach to engineering support for drilling operations. BHA Simulation Model As a response to the need to estimate downhole performance better, a mathematical model has been developed for estimating the mechanical and dynamic behavior of BHAs in realistic wellbores. It is based on a nonlinear finite-beam element and accounts for various intricacies of the downhole environment. Modeling a drilling assembly using this approach allows for the complexities of the BHA components to be easily represented as a series of beams with varying mechanical properties. The model was initially developed to analyze the behavior of vibration- inducing devices in unconventional horizontal wells, but has since been expanded to examine a multitude of different drilling•scenarios.

Ultra-Stable Silica Nanoparticles as Nano-Plugging Additive for Shale Exploitation in Harsh Environments.

Owing to the harsh downhole environments, poor dispersion of silica at high salinity and high temperature can severely restrict its application as the nano-plugging agent in shale gas exploitation. The objective of this study is to improve salt tolerance and thermal stability of silica. Herein, silica was successfully functionalized with an anionic polymer (p SPMA) by SI-ATRP (surface-initiated atom transfer radical polymerization), named SiO2-g-SPMA. The grafted pSPMA brushes on silica provided sufficient electrostatic repulsion and steric repulsion for stabilizing silica in a harsh environment. The modified silica (SiO2-g-SPMA) had excellent colloidal stability at salinities up to 5.43 M NaCl (saturated brine) and standard API brine (8 wt% NaCl + 2 wt% CaCl2) for 30 days at room temperature. Simultaneously, the SiO2-g-SPMA was stable at 170 °C for 24 h as well as stable in weakly alkali environment. Furthermore, the plugging performance of SiO2-g-SPMA in water-based drilling fluids for low permeate reservoir reached to 78.25% when adding a small amount of 0.5 wt% SiO2-g-SPMA, which effectively hindered the water invasion into formation and protected the reservoir.

Improving the stability of multi-walled carbon nano-tubes in extremely environments: Applications as nano-plugging additives in drilling fluids

Owing to the harsh downhole environments, poor dispersion of multi-walled carbon nanotubes (MWCNTs) at high salinity and high temperature can severely limit their application in oil & gas exploitation industry. Herein, the objective of this study is to improve salt tolerance and thermal stability of MWCNTs by modification. In this study, MWCNTs was successfully functionalized with an anionic polymer by a SI-ATRP (Surface-initiated atom transfer radical polymerization) method. By varying the ratio of monomer and initiator, two composites were obtained, named MWCNTs-g-SPMA-1 and MWCNTs-g-SPMA-2, respectively. Both were well dispersed in saturated brine and standard API brine (8 wt% NaCl + 2 wt% CaCl2) for 60 days at room temperature. Moreover, the modified MWCNTs were stable at 170 °C for 24 h, as well as stable in weakly alkali environment. Afterwards, MWCNTs-g-SPMA-2 as the nano-plugging additive in water-based drilling fluids exhibited excellent plugging performance. The plugging efficiency reached 50.96% with adding a small amount of 0.3 wt% MWCNTs-g-SPMA-2.

Use of Far-Field Diverters To Mitigate Parent- and Infill-Well-Fracture Interactions in Shale Formations

Summary Hydraulic-fracturing treatments in shale infill wells are often impacted by existing parent-well depletion and asymmetrical fracture growth. These phenomena can result in excessive load-water production, deposition of proppant and deformation of casing in the parent well, and unbalanced stimulation of infill wells. This study determines the effectiveness of particulate materials (i.e., far-field diverting agents) for mitigating the above negative outcomes by bridging near the extremities of dominant fracture wings. Fracture propagation was modeled to characterize the width profile at fracture extremities in a depleted-stress environment. A slotted-disk device was used to evaluate and optimize particulate blends for bridging slots representative of width near the fracture tip. Rheological tests replicating the downhole environment were used to formulate a system for transporting the diverting materials. Statistical analysis of 511 fracture hits at 30 parent wells was performed on key treatment indicators by the category of diverter type and post-hit parent-well condition. Production trends of the influenced wells were compared to area-specific type curves and offset wells without diverter trials. On the basis of the simulation and testing results, two types of high-graded far-field diverter systems were field-tested in a shale play: dissolvable, extremely fine particulate mixed with a 100-mesh sand, and mixtures of a nominal 325-mesh silica flour and a 100-mesh sand. Proppant dust collected at the fracturing site was also evaluated for replacing commercial silica flour. High-graded blends of the above diverting systems demonstrated superior fracture-hit and productivity metrics as compared to the base case of not applying far-field diverters. The silica flour and 100-mesh-sand mixture performed on a par with the significantly more expensive blend of dissolvable fine particulate and 100-mesh sand. Borate-crosslinked-guar gel was an effective carrying fluid for transporting diverting materials to the fracture extremities. Statistical analysis of fracture-hit events shows that the application of far-field diverters did not reduce the magnitude of pressure buildups during fracture hits; however, it significantly increases the post-hit pressure-falloff rate at the parent wells. On the basis of the area-specific type curves, pumping far-field diverters increased the P50 estimated ultimate recovery (EUR) by approximately 6% compared with the base cases of not applying diverters. For all the wells impacted by far-field diverters, the infill wells saw larger benefits with an increment of P50 EUR by approximately 7% compared with the parent wells.

Well-Abandonment Solutions Use Bismuth and Thermite Effectively and Safely

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193118, “Well-Abandonment Solutions Using Bismuth and Thermite,” by Paul Carragher, SPE, and Jeff Fulks, BiSN Oil Tools, prepared for the 2018 SPE Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 12–15 November. The paper has not been peer reviewed. Traditional methods of abandoning a well by use of cement and bridge plugs are still common practice among most operators globally. Although resins have been used as an alternative, no major developments have been made in well-abandonment materials for nearly a century. This paper demonstrates a new way to create gas-tight seals during well abandonment, overcoming the limitations of traditional methods and reducing the operator’s liability and potential environmental impact after decommissioning has been completed. Statement of Theory and Qualification Testing Bismuth has multiple commercial uses outside of the oil and gas industry. The idea of using bismuth for sealing in downhole environments is not new; the earliest patents were filed in the 1930s. Bismuth possesses many unique qualities, including Relatively low melting point (273°C) compared with other metals Viscosity very similar to water when in liquid form High density, with a specific gravity of 10 Noncorrosive and unaffected by hydrogen sulfide or carbon dioxide Expands approximately 3% upon solidification Nontoxic (used in place of lead in some commercial applications for this reason) Eutectic metal, converting from liquid to solid state almost instantaneously when it cools below its melting point, bypassing the gel phase The challenge in creating a seal with bismuth has always been how to deploy it downhole—melting it and then causing it to solidify and expand where the seal is required. Previous attempts were made with electrical heaters. These heaters required large amounts of power (480 V and 11 A to generate 540 kJ of energy) for hours to melt a relatively small amount of bismuth alloy. Voltage drops in the electric line limited the depth at which the tool could be run in the well. After melting, the electrical heaters could not keep the bismuth in the liquid phase long enough for it to reach the sealing area and fill the void it was intended to seal. To obtain the energy necessary for this application, thermite was considered as a heating element. Thermite is a combination of iron oxide and aluminum powder. When these are combined in the correct chemical composition and activated, a reaction occurs that results in byproducts of aluminum oxide, iron, and large amounts of heat. To activate the chemical reaction, thermite must be heated to a temperature greater than 2000°C; the resulting output is in excess of 10 000 kJ. The temperature at which the thermite burns can reach as high as 2000°C. For the thermite heating element to be used with the bismuth, the burning temperature would have to be controlled and consistent. To accomplish this goal, binding and damping agents were added to the thermite. The binding agents ensure that the chemical composition of iron oxide and aluminum powder remains consistent without separating, resulting in a repeatable reaction. The damping agents control the amount of heat generated and the speed at which the reaction takes place.

Development of a subsurface LIBS sensor for in situ groundwater quality monitoring with applications in CO2 leak sensing in carbon sequestration

Sub-surface activity such as geologic carbon sequestration (GCS) has the potential to contaminate groundwater sources with dissolved metals originating from sub-surface brines or leaching of formation rock. Therefore, a Laser Induced Breakdown Spectroscopy (LIBS) based sensor is developed for sub-surface water quality monitoring. The sensor head is built using a low cost passively Q-switched (PQSW) laser and is fiber coupled to a pump laser and a gated spectrometer. The prototype sensor head was constructed using off the shelf components and a custom monolithic, PQSW laser and testing has verified that the fiber coupled design performs as desired. The system shows good calibration linearity for tested elements (Ca, Sr, and K), quick data collection times, and Limits of Detection (LODs) that are comparable to or better than those of table top, actively Q-switched systems. The fiber coupled design gives the ability to separate the PQSW LIBS excitation laser from the pump source and spectrometer, allowing these expensive and fragile components to remain at the surface while only the low-cost, all optical sensor head needs to be exposed to the hostile downhole environment.

Wirelessly Powered Microchips for Mapping Hydraulic Fractures

Summary The onset of the era of internet of things and artificial intelligence comes with the ever-growing demand for self-sustaining and efficient sensors. Sensors based on complementary metal oxide semiconductors (CMOSs) have attracted significant attention in the implementation of distributed sensor systems for a vast number of applications because of their economical and complex integration benefits. In this work, we report CMOS-based energy-harvesting chips as wireless nodes for mapping hydraulic fractures during the shale gas extraction process. The CMOS chips are tested in a custom benchtop core-holder chamber that emulates a downhole environment. An induction coil, sized at 5 × 5 mm, connected to a custom CMOS chip, is used as a receiver inside the core holder to harvest electromagnetic (EM) energy transmitted by an external antenna. On the basis of the custom core-holder experiment, it is shown that encapsulated CMOS chips are able to harvest EM energy and thereby operate wirelessly. The receiver has a resonance frequency of 198 MHz. The CMOS chip is equipped with an integrated power management unit (PMU), energy-harvesting unit, and a signal-generation block. The CMOS chip inside the chamber produces an output signal with a frequency proportional to the harvested power. By measuring the frequency of the output signal produced by the chip, we are able to localize the chips within the rock inside the custom core holder.

Flow-Simulation Model Improves Analysis of Perforated-Rock Cleanup and Productivity

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 190113, “Advanced Analysis of Cleanup and Productivity From Perforated Rocks Using Computational Fluid Dynamics,” by Rajani Satti, SPE, Stephen N. Zuklic, and Derek Bale, SPE, Baker Hughes, a GE company, and Nils Koliha, Andrew Fager, SPE, Gana Balasubramanian, Bernd Crouse, SPE, and David Freed, SPE, EXA, prepared for the 2018 SPE Western Regional Meeting, Garden Grove, California, USA, 22–27 April. The paper has not been peer reviewed. Because of inherent complexities, understanding the characteristics of perforations in downhole environments is a significant challenge. Perforation-flow laboratories have been used to provide insight into cleanup and productivity mechanisms around perforation tunnels. In contrast to previous studies, the model presented in this work uses the perforation-flow laboratory, micro-computed-tomography (CT) and conventional CT imaging, and, most importantly, an advanced simulation approach to provide an accurate assessment of cleanup techniques and productivity. This full-scale 3D flow model accounts for realistic aspects of tunnel geometry, perforation damage, and blockages that impede flow. Introduction In recent years, numerical tools increasingly have been used in conjunction with experiments to provide better insight into the flow characteristics of perforated cores and perforated well-scale formations. Several numerical studies on perforation fluid flow have been conducted for core scale. However, comprehensive details relating to the modeling of perforation-zone damage and thickness, flow directionality, debris mechanisms, and implications for cleanup have not been studied in detail. In addition, most computational fluid dynamics (CFD) studies have used traditional Navier-Stokes-based solvers. In this study, the authors have used a commercially available flow-simulation software based on the lattice Boltzmann method (LBM) to calculate the complex flow and cleanup mechanisms around the perforation tunnel. Lattice-based methods, an alternative to traditional CFD methods, track the advection and collisions of fluid particles on a computational grid. Because the average number of particles per grid cell far exceeds the computing power required to track them individually, the particles are grouped into an integer number of discrete velocities. LBM has been well validated and is in common use for many flow applications. The flow solver used here includes a turbulence model that is similar conceptually to the large-eddy simulation approach. The flow solver also includes a porous-media model that is used, in this study, to model the rock. The porous-media model invokes a Darcy-type pressure loss by applying a flow resistance determined from the known permeability of the rock. The resistance can include a viscous (linear) and an inertial (quadratic) term with respect to local velocity and can be made to vary spatially to model rock heterogeneity.

A novel approach in high performance deep hole drilling of Inconel 718

Application of deep holes is extensively found in the oil and gas industry to manufacture downhole equipment. These deep holes are fabricated in drill collars to deploy delicate sensors downhole for obtaining vital information like temperature, pressure and other geo-physical data from the bottom of the hole. High temperature and corrosion resistant materials like Inconel 718 is often used for drill collars to shield these sensitive communication equipment from the hostile downhole environment. Gundrilling is an established hole making method known for drilling precise and high aspect-ratio (AR>10) holes in conventional materials such as steels, cast iron and aluminium alloys etc. However, gundrilling of Inconel 718 offers unprecedented challenges like excessive tool wear, hole straightness deviation due to poor thermal conductivity and work-hardening tendency of the alloy. Moreover, as the drilling depth increases the deviation is further exacerbated due to the low rigidity of long gundrill shafts. The present study in the Phase 1 introduces a dynamic model using multispan Euler-Bernoulli beam theory to evaluate the effectiveness of coolant pressure and rotation speed during deep hole fabrication in Inconel 718. In addition, experimental investigations have been conducted to validate the model by studying the effects of coolant pressure and rotation speed on straightness of the fabricated holes. It was found that the straightness deviation was 0.37 mm corresponding to 137.89 bar and 1600 rpm coolant pressure and rotation speed respectively. In Phase 2, a non-contacting EDM process was used to fabricate a straight guide hole followed by conventional gundrilling (CG) with optimum pressure (137.89 bar) and speed (1600 rpm) obtained from the Phase 1 trials. The experimental results revealed that the thrust force reduced drastically from 800 N (CG) to 250 N (EDMG). Moreover, a significant improvement in both rake wear and flank wear was also observed. Finally, a straightness deviation of 0.19 mm was recorded for a maximum drilling depth of 350 mm which is 48.65% lesser than CG. From the study, it was found that this novel EDMG process improved the drilling capability of Inconel 718 by reducing the thrust force generated, enhancing tool life and minimizing the straightness deviation.

Temperature Estimation and Vibration Monitoring for Induction Motors and the Potential Application in Electrical Submersible Motors

Condition monitoring is essential for the reliable operation of induction motors. Temperature estimation serves as a basis for motor protection. Developing accurate and real-time temperature calculation algorithms is critical for thermal and overload protection for induction motors. Vibration monitoring is a widely used approach for induction motors' fault diagnosis. Vibration signals are usually analyzed by time-, frequency-, or time-frequency-domain signal processing methods. Recent advancement of fault diagnosis by machine learning makes intelligent approaches feasible. Although decades of efforts have been put on condition monitoring of regular induction motors, electrical submersible motors operating in a very unique downhole environment in the oil industry have not received much attention. Currently, electrical submersible motors rely on downhole monitoring tools to transmit temperature and vibration data measured by sensors from downhole to the surface; however, such data are transmitted at a slow rate, and there are no fault diagnosis algorithms in place. An advanced condition monitoring and fault diagnosis method for electrical submersible motors is needed in the near future. In this paper, a literature review is conducted on temperature estimation and vibration monitoring techniques for induction motors, the state-of-the-art methods are summarized, and their potential application in electrical submersible motors are recommended.

The Application of Downhole Vibration Factor in Drilling Tool Reliability Big Data Analytics—A Review

In the challenging downhole environment, drilling tools are normally subject to high temperature, severe vibration, and other harsh operation conditions. The drilling activities generate massive field data, namely field reliability big data (FRBD), which includes downhole operation, environment, failure, degradation, and dynamic data. Field reliability big data has large size, high variety, and extreme complexity. FRBD presents abundant opportunities and great challenges for drilling tool reliability analytics. Consequently, as one of the key factors to affect drilling tool reliability, the downhole vibration factor plays an essential role in the reliability analytics based on FRBD. This paper reviews the important parameters of downhole drilling operations, examines the mode, physical and reliability impact of downhole vibration, and presents the features of reliability big data analytics. Specifically, this paper explores the application of vibration factor in reliability big data analytics covering tool lifetime/failure prediction, prognostics/diagnostics, condition monitoring (CM), and maintenance planning and optimization. Furthermore, the authors highlight the future research about how to better apply the downhole vibration factor in reliability big data analytics to further improve tool reliability and optimize maintenance planning.

Comparison of Salinity Dependent Mechanical Behaviours of Geopolymer and OPC: An Application to CCS and Oil / Gas Wells

Global warming is a severe issue in which the emission of greenhouse gases, especially carbon dioxide (CO2), plays a vital role. Methods that are proposed to mitigate CO2 emissions include improving the energy conversion efficiency of fossil fuels, shifting energy production to low carbon sources, enhancing CO2 uptake by terrestrial and marine biomass and capturing CO2 and storing it deep underground. Of all the methods, carbon capture and storage (CCS) deep underground is the best way to reduce atmospheric greenhouse gases which is often responsible for global warming. One of the major issues faced when storing CO2 in depleted oil or gas reservoirs is its leakage through the injection wells. Ordinary Portland Cement (OPC) based well-cement has been used in these oil and gas wells. OPC, however, has issues such as cement degradation, leakage, strength reduction, and durability reduction when used in down-hole environments. Geopolymer can be a good alternative to OPC because of its excellent acid resistance characteristics, high strength and low shrinkage. In a typical wellbore, wellcement will be exposed to saline water that can have different salinity levels. Hence, the main aim of this study was to compare the mechanical behaviours of OPC and geopolymer cement cured in saline water for 7, 28 and 45 days at different salinity levels (0 %, 10 %, 20 %, 30 % and 40 % of NaCl). A series of experiments were conducted to compare the compressive strength and Young’s modulus of OPC and geopolymer. It was observed that the compressive strength of OPC based well-cement increases as the salinity level of the brine water is increased up to 10 % NaCl and that it thereafter decreases as the NaCl percentage is further increased. On the other hand, the compressive strength of geopolymer well-cement generally increases as the brine concentration is increased. Based on the findings of this research, it can be concluded that geopolymer as a well-cement can perform better in saline water than OPC based well-cement, and that therefore geopolymer is suitable as a primary well-cement material.

Hard rock cutting with high pressure jets in various ambient pressure regimes

An alternative drilling technology has been developed, in which ultra-high pressure jetting with in excess of 2500 bar jet pressure is combined with mechanical drilling techniques. In order to investigate the cutting performance of the fluid jets in hard rock formations, experiments under various ambient conditions were performed. Core samples from several drilling sites were tested under atmospheric conditions and enabled a solid basis for the comparison of the jettability of different hard rock formations. To simulate deep downhole conditions as realistically as possible, a pressure vessel capable of up to 450 bar internal pressure was designed and built. The experiments, performed under different ambient pressure regimes, show a completely different cutting performance than under atmospheric conditions. The main influencing parameters were determined and adapted to enable a sufficient performance for all tested conditions. Furthermore the usage of drilling fluids in place of water was investigated. The study shows that high pressure jetting is feasible in the challenging simulated downhole environment, including high ambient pressure, several jets with different pressures acting simultaneously, drilling mud as jetting resp. surrounding fluid and high traverse velocities.

Design and testing of a heat transfer sensor for well exploration tools

The exploration of oil, gas, and geothermal wells is moving towards increasingly harsher downhole environments, requiring more and more advanced drilling and intervention tools. The high downhole temperatures threaten the correct functionality of intervention equipment and of standard downhole electronics, which cannot withstand temperatures above 150 °C for an extended period of time. Thermal management of downhole electronics therefore requires critical and accurate knowledge of the thermal interaction between the downhole tools and the wellbore environment for correct tool design, intervention planning and operation. In this work, we present the design, modelling and testing of a sensor for downhole tools that can determine the heat transfer rate between the tool and the harsh downhole environment. An experimental flow loop was used to simulate the interaction between the sensor and the well fluid, and to calibrate the sensor in the range of heat transfer coefficients 0–1000 W/m2 K. Good agreement between model predictions and experimental results was obtained with average and maximum errors of ∼3% and ∼10%, respectively. A sensitivity of up to 8.7 mV/(W/m2 K) was measured and a response time of about 11 s was obtained over a 25% change in the fluid velocity.

Hole Cleaning, Torque Management Lead to Longest Extended-Reach Well in Brazil

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 28091, “The Longest Horizontal Section Ever Drilled in an Extended-Reach Well in Brazil,” by Rafael Kenupp, Affonso Lourenço, Stian Soltvedt, and Ian Thomson, Baker Hughes, a GE company, and Grazielli Simoes, Daniela L. Morosov, and Raquel Andrade, Statoil, prepared for the 2017 Offshore Technology Conference Brasil, Rio de Janeiro, 24–26 October. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. The Peregrino project, located in the post-salt zone of the Campos Basin, presents immense challenges for drilling extended-reach wells. This paper shares challenges imposed by the well profile and downhole environment on the design and execution phases. Information is included about the solutions used that led to reaching the target depth as planned, including the well-planning methodology, bottomhole-assembly (BHA) design, drill-bit selection, data monitoring, and procedures for maximizing the transfer of power downhole and minimizing rock-cutting energy. Introduction The Peregrino oil field is in the BM-C-7 area of the Campos Basin. Of 47 wells drilled from two fixed platforms in the field (Peregrino A and B), 20 were from Peregrino A, where the longest horizontal sections have been drilled. The average horizontal length was 1419 m, and the operator is pushing the technical limits to extend the overall lateral stepout, increase reservoir lengths, and maximize hydrocarbon exposure. Drilling horizontal sections beyond the field average length has several additional challenges including mud quality along the sections, high friction factors, and surface-equipment operational limits. For extended-reach wells, hole-cleaning efficiency and proper torque management have been shown to be key factors for flawless execution. Proposed Approach Considering the typical well setup in off-shore Brazil, Well A-27 had a considerable total length. The planned length of the well was 8400-m measured depth (MD), with a possible extension to 8740-m MD. The landing of a 9⅝-in.-casing shoe was planned to be at 6520-m MD with approximately 82° of inclination, and the 8½-in.-section lateral displacement was to start at 5673 m from the wellhead (Fig. 1). With a possible horizontal section of 2220 m, a rotary-steerable system was to be used, with the addition of a drilling dynamics sub and a modular motor, to reduce the demanded weight on bit (WOB) and surface rate of revolution while maintaining sufficient energy at the bit. Management of torque and equivalent circulating density (ECD) would be helped by the use of 4-in. drill-pipe, which would also provide lower torque values with less cross-sectional area. The final measure required to reduce overall friction along the horizontal well path was to add lubricant to the drilling fluid to reduce metal-to-metal friction at the drillpipe/casing interaction. Lubricant was also to be added while drilling, with the idea that drops of lubricant deposited into the mudcake would help reduce friction when drill-pipe tool joints pass through.

Design of experimental system for supercritical CO2 fracturing under confining pressure conditions

Supercritical CO2 has the characteristics of low viscosity, high diffusion and zero surface tension, and it is considered as a new fluid for non-polluting and non-aqueous fracturing which can be used for shale gas development. Fracturing refers to a method of utilizing the high-pressure fluid to generate fractures in the rock formation so as to improve the oil and gas flow conditions and increase the oil and gas production. In this article, a new type of experimental system for supercritical CO2 fracturing under confining pressure conditions is designed, which is based on characteristics of supercritical CO2, shale reservoir and down-hole environment. The experimental system consists of three sub-systems, including supercritical CO2 generation system, supercritical CO2 fracturing system and data analysis system. It can be used to simulate supercritical CO2 fracturing under geo-stress conditions, thus to study the rock initiation pressure, the formation of the rock fractures, fractured surface morphology and so on. The experimental system has successfully carried out a series of supercritical CO2 fracturing experiments. The experimental results confirm the feasibility of the experimental system and the high efficiency of supercritical CO2 in fracturing tight rocks.

Investigation and Comparison of $\varphi $ -OTDR and OTDR-Interferometry via Phase Demodulation

We investigate and compare the φ-optical time domain reflectometry (OTDR) and OTDR-interferometry methods, both using phase demodulation, for distributed acoustic sensing. By theoretical analysis and experiments we show that, while both φ-OTDR and OTDR-interferometry give proper instantaneous amplitude, frequency, and phase properties of the acoustic signal, OTDR-interferometry produces larger signals and offers higher sensitivity, better signal-to-noise-ratio, and larger demodulated signal width than φ-OTDR due to the introduction of the interferometer. This work enables the selection of the better method for distributed acoustic sensing for different situations of surface, seabed, and downhole environments.