Extended Reach Wells Research Articles

Construction of Mechanical Earth Modeling for Mitigating Wellbore Instability in Tanuma Shaly Formation -Southern Iraqi Oil Field

Wellbore instability has become an increasing concern for horizontal and extended-reach wells, especially through shale cap rocks. This paper presents a comprehensive analysis of the factors that led to the wellbore being unstable in the Tanuma Formation, the Nasiriyah oilfield in southern Iraq. By constructing a mechanical earth model using open-hole wireline data from two drilled wells. Mohr-Coulomb, Mogi-Coulomb, and Modified Lade failure criteria are used to analyze the breakouts and determine the density of mud that is required for a safe wellbore wall. The results indicated that the Mogi-Coulomb criterion is more similar to the actual well failure than the other two criteria. The wellbore instability findings showed that the most stable wells are those that are vertical and have a low deviated angle (less than 10°), and it is advised that these wells be drilled with a mud weight of 11.3 to 14 ppg. The acceptable range for the weight of the mud for horizontal and greatly deviated wells is between 11.9 and 13.8 ppg. Consequently, the future wells development plan for the studied region is improved and leads to cost reductions.

Optimizing the Influence of Fly Ash as an Anti-Sagging Additive in Highly Deviated Geothermal Well Drilling Fluids Using Surface Response Method

Weighting materials such as barite and ilmenite are crucial for controlling fluid density during deep or ultra-deep drilling operations. However, sagging poses significant challenges, especially in highly deviated high-pressure and high-temperature (HP/HT) wells. This leads to inadequate well control, wellbore instability, and variations in hydrostatic pressure in extended-reach wells. Given the challenges of experimental research, reliable prediction models are imperative for evaluating the interaction between the ratio of anti-sagging additives, temperature, and wellbore inclination on sag factor (SF). This research presents statistical-based empirical models for predicting the SF at various wellbore inclinations (0°, 30°, 45°, 60°, 70°, 80°, and 90°) and assessing the influence of fly ash on the SF. The regression equations, developed using the Response Surface Methodology in Minitab 18 software, show high reliability, with R2 values approaching unity. Contour and surface response plots provide a clear understanding of the variable interactions. The analysis reveals that sagging is most severe at 60° to 65° inclination. At 400 °F and 60° inclination, adding 4 lb/bbl of fly ash reduces sagging in barite and ilmenite-densified fluid by 63.9% and 63.1%, respectively. Model validation shows high accuracy, with percentage errors below 3%. This study offers valuable insights for optimizing drilling fluid formulations in HP/HT well environments.

Reducing Torque and Drag in Extended-Reach Wells Using Thermoplastic Polymers for Protective Sliding Rings

Extended-reach drilling represents an advanced way of drilling and accessing reservoirs that were previously economically not feasible to drain, impossible to reach or in an environmentally sensitive area. One of the main issues that appears while drilling such wells is caused by the high values of friction factor which cause high values of torque and drag. One of the suggested solutions is to use a protective sliding ring made from materials such as POM, Teflon and PA6 in combination with lubricants added to a polymer mud system. First, measurements were conducted on a lubricity tester to choose the best material and, after finishing, a mechanical wear test was conducted on a specially designed device to measure mechanical wear. Results showed that Teflon showed lower values of friction factor in comparison to steel and the mechanical wear was minimal. The lowest value of friction force was recorded for blocks made from Teflon in tested mud systems. It is also noticeable that, in polymer mud with weighting additives and lubricant, the value of the friction force is higher than in polymer mud with lubricant only.

Numerical investigation of flow patterns in cuttings transport for extended-reach horizontal wells with rotation drillpipe

During the drilling process of extended-reach horizontal wells, the formation of the cuttings bed at the bottom of the wellbore is prone to cause drilling sticking and pump accidents. A coupled method of Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) is used here to study the flow patterns and transition of cuttings transport. Firstly, the model is validated with experimental results, which shows a good agreement. Then, the impact of the rotation speed, eccentricity, and conveying velocity on cuttings flow pattern are analyze. The total Reynolds number is introduced here to established a curve with dimensionless pressure drop, which divides the parameter interval of each flow pattern, and the change rule of cuttings flow pattern is also revealed. This study will establish a theoretical foundation for enhancing borehole cleaning efficiency and hold practical significance in guiding the drilling field construction of extended-reach wells.

A study on the flow behavior inside fluidic oscillation tools for friction-reduction in extended reach well

The drilling distance of extended-reach wells is limited by mechanical friction between the drill string and the borehole wall. The fluidic oscillator axial vibratory tools (AVTs) can effectively reduce friction and increase the weight on bit, thereby extending the reach of horizontal wells. However, few studies have delved into the evolutionary mechanism of the internal flow field of fluidic oscillator AVTs. In this paper, two types of fluidic oscillators with different flow path are presented. One is the reverse-feedback oscillator, and the other is sweeping-chamber oscillator. Through computational fluid dynamics method, the internal flow field of these two fluidic oscillator AVTs were analyzed, and the frequency and pressure drop were verified by experiments. The results show that the LES turbulence model provides more accurate simulations, showing an error range of less than 9%. The pressure drop and vibration frequency of the two tools are linearly related to the flow rate. The pressure drop of the reverse feedback oscillation tool is in the range of 0.1–1 MPa, and the vibration frequency is between 13 and 50 Hz. The sweeping-chamber oscillator can reduce vibration frequency to below 15 Hz. The results also show that it is crucial to consider the lag in pressure signals when designing and analyzing fluid oscillator systems, as it can affect the timing and behavior of the system. This research provides profound insights for understanding and optimizing fluidic oscillator systems.

Wellbore Pressure Modeling for Pumping and Tripping Simultaneously to Avoid Severe Pressure Swab

A pumping-while-tripping method is proposed to mitigate pressure swabs during tripping out in wells with a narrow mud density window and extended reach. In the proposed tripping-out process, the fluid circulation is started by using a special pump from a customized circulation line before tripping is initiated. During the tripping out, drilling fluid is circulated in the wellbore simultaneously while the drilling string is moving. A model to simulate the dynamic pressure changes in this process is developed based on the Navier–Stokes (N-S) equations and a damped free vibration system. The model was initially developed for Herschel–Bulkley (H-B) fluid; however, it can be applied to other fluid models by eliminating the non-existing terms. An analysis was conducted to investigate the effect of tripping velocity and circulation pumping rate on the pressure changes. The results show that pumping-while-tripping is effective in mitigating the pressure swab during tripping out, which is especially useful for extended-reach wells. It can also help to increase tripping out velocity and save tripping time for drilling operations.

A real-time drilling parameters optimization method for offshore large-scale cluster extended reach drilling based on intelligent optimization algorithm and machine learning

Offshore large-scale cluster extended reach wells (ERWs) are widely used to develop offshore oil & gas resources. Due to the complex downhole environments and complicated geological conditions, drilling parameters real-time optimization is challenging in offshore large-scale cluster ERWs drilling. In this paper, a real-time drilling parameters optimization method for offshore large-scale cluster extended reach drilling based on an intelligent optimization algorithm and machine learning (IOA-ML) is proposed. The method takes ROP as the objective function, establishes a ROP model based on long short-term memory (LSTM) neurons, and obtains drilling parameters optimization results asynchronously by combining the genetic algorithm, differential evolution algorithm, and particle swarm algorithm. The results show that ROP has been improved by 33.33% on average after the optimization by this real-time intelligent optimization method with an optimization time within 60s, which meets the requirements of real-time optimization of drilling parameters.

Fly ash as an additive for controlling sagging tendency in ilmenite densified water-based mud for a highly inclined high temperature well

Sagging has a detrimental outturn on the drilling effectuation and increases the drilling risks. Drilling deviated wells and wells with high pressures and temperatures has a greater impact on the sagging occurrence. It is desirable for a drilling operator to ensure stability and maintain the suspension of weight material in the fluid throughout the drilling operation. Optimum drilling fluid design for the drilling industry aids in the effective removal of cuttings and suspension of cuttings to avoid expensive complications and maintain the stability of the well particularly for drilling highly deviated wells and wells in high-temperature harsh formations. Drilling fluid physio-chemical behavior changes because of the weighing agent separating from the liquid phase and settling down, which is referred to as sagging and is more prevalent in highly inclined wells and wells with high temperatures. Few studies are geared toward understanding and possibly mitigating the occurrence of solid sagging to improve the drilling performance, particularly in highly deviated wells and wells in high-temperature harsh formations. This study evaluates the effectiveness of fly ash buffered with an industrial standard polymer to eliminate ilmenite sag encountered with water-based drilling fluids at high-pressure high-temperature (HPHT)environments when accessing geothermal wells, extended-reach wells, and high-inclined wells. Four laboratory barrels of water-based drilling fluids were formulated for this study. Fly ash of 130 μm particle size was added to mud samples at 0, 1, 2, and 3 lb./bbl ratio. Each industrial standard polymer of 1lb./bbl was added to all four samples prepared. The influence of fly ash on drilling fluids properties was thoroughly evaluated by measuring static and dynamic sagging at vertical and inclined (300, 450, 600, 700, 800, and 900) conditions over a range of temperatures (2500F, 3000F, 3500F, and 4000F). It was observed that the inclusion of fly ash improves the sagging phenomena and the rheological behavior of the water-based mud samples to satisfy the industrial API standard value.

Prediction of the rate of penetration in offshore large-scale cluster extended reach wells drilling based on machine learning and big-data techniques

Large-scale cluster extended reach wells (ERWs) are usually drilled from one platform to target distant multiple reservoirs in offshore oil & gas development. Due to the complicated downhole environments and complex geological conditions in various azimuths, the accurate prediction of the rate of penetration (ROP) in offshore large-scale cluster ERWs drilling is a challenging task. In this work, a ROP prediction method for offshore large-scale cluster ERWs drilling based on machine learning and big-data techniques is presented. 27 input parameters affecting ROP are collected from block N of China Bohai Oilfield, with a total of 9,193,408 data points. The internal relation between various parameters and ROP at the data level is revealed, which verifies the feasibility of the collected data set training. Based on various machine learning algorithms, 12 kinds of ROP prediction models based on support vector regression (SVR), random forest regression (RFR), back propagation neural network (BPNN), and recurrent neural network (RNN) are established respectively. Meanwhile, the prediction accuracy of the ROP prediction models is evaluated based on six performance indicators. It shows that the prediction results of the RNN model with LSTM as neuron structure are the best (all of the 6 indicators are optimal) among the 12 kinds of ROP prediction models, and the mean absolute error is only 6.12 m/h. The RNN model with LSTM as neuron structure is the best machine learning model in the prediction of ROP in offshore large-scale cluster ERWs drilling. It provides a practical method for enhancing cleaner development of offshore oil & gas.

Characterization of a novel fluidic friction-reduction tool used in extended-reach well considering periodic particle-laden jet

Fluidic oscillators (FOs) can be used as an efficient fluidic vibration tool to solve high friction problems in extended-reach wells. However, the complex mechanism of FOs makes the design challenging, and the dynamic erosion behavior inside FOs is still unclear. In this paper, new FOs are proposed and the working characteristics under the influence of periodic particle-laden jets are investigated. Firstly, the results reveal the working mechanism of new FOs, showing that the generation of pressure pulses is closely connected with periodic jet switching and the development of vortices. Secondly, the important performance parameters, i.e., pressure pulse and oscillation frequency, are extensively studied through numerical simulation and experimental verification. It is found that the performance can be optimized by adjusting the tool structure according to different engineering requirements. Finally, the oscillating solid-liquid two-phase flow inside FO is studied. It is demonstrated that the accumulation of particles leads to a significant reduction in performance. The results also reveal five locations that are susceptible to erosion and the erosion behavior of these locations are studied. It has been shown that the periodic jet causes fluctuations in the amount of erosion at the outlet and splitter. This research can provide valuable references for the design and optimization of vibration friction-reduction tools.

Real-Time Control Algorithm of Well Trajectory for Push-the-Bit Rotary Steering Drilling System

Summary A “push-the-bit” rotary steering system (RSS) is one kind of advanced steering technology widely used in the drilling of extended-reach wells and horizontal wells. However, some problems, including instability of buildup rate and large deviation of well trajectory, still occur frequently in directional drilling with push-the-bit RSS due to the drillability anisotropy of formation rock, external disturbance, and so on, especially under complex operating conditions. In this paper, we build a compound control algorithm for well trajectory of push-the-bit RSS to solve this problem. The compound control algorithm includes two novel control modules—slight hole deviation control and severe hole deviation control. The slight hole deviation control can improve the smoothness of well trajectory, and the severe hole deviation control can ensure high control accuracy. The comprehensive performances of the compound control algorithm are compared with other control algorithms, including severe hole deviation control, slight hole deviation control, and intelligent switch control, in terms of trajectory smoothness, trajectory control accuracy, control smoothness of pushing force, and computational efficiency. The results indicate that the compound control algorithm is the best. This algorithm is also applicable for trajectory correction in cases of severe hole deviation and azimuth drift on different well sections.

Technology Focus: Extended-Reach and Complex Wells (May 2023)

A clear change in the last 2–3 years is that the energy transition is becoming the undisputable trend for almost all major oil and gas companies and oilfield services providers, as evident from the news of rebranding, the roll-out of companies’ new strategies, and announcements of commitments to net zero. Geothermal energy, especially within deep, hot, dry rock, is abundant around the globe. It can be a great opportunity for the majors to boost their energy-transition process and open new business opportunities. Previously, however, deep geothermal development activities were rather limited and participation from the majors was sporadic. One reason was that drilling into such extra-hot and extra-deep impermeable rock could render excessively high cost and risk, making the development of deep geothermal energy far from economical and scalable and discouraging many companies from entering this hot spot. The domain expertise and technologies in the oil and gas industry such as integrated project planning and operating, extended-reach drilling (ERD), high-pressure/high-temperature drilling tools, multilateral drilling and completions, geomechanics, flow and thermal dynamics modeling, and artificial intelligence have been fueling the ongoing march for new records on ERD, multilateral, and other complex wells. They have made it possible to drill faster, further, and with more production, which will be the keys to accelerating the learning curve, filling the technology gap, and breaking the economic barrier on deep geothermal drilling, which in turn will attract more players to this new arena. A bold move of the majors into deep geothermal drilling could accelerate the removal of the economic and technical hurdles in harnessing the enormous baseload renewable energy and meanwhile backfeed new drilling technologies developed in deep geothermal applications to the oil and gas industry for a more sustainable future. Recommended additional reading at OnePetro: www.onepetro.org. SPE 206616 Deep Geothermal Well-Construction Problems and Possible Solutions by Mikhail Yakovlevich Gelfgat, Gubkin University, et al. SPE 200792 Lessons Learned and Case Studies of Overcoming Sustained Casing Pressure in Extended-Reach Wells by Svetlana Nafikova, SLB, et al. IPTC 21439 Application of Multilateral Wells for Production and Enhanced Oil Recovery: Case Studies From Canada by Eric Delamaide, IFP-Technologies

Numerical Simulation of the Effect of Reservoir Properties on Oil Production from the Low-Permeability Formation by Extended Reach Wells

At present, extended reach wells (ERWs) are widely applied on oil and gas exploitation in numerous reservoirs around the globe, and this is attributed to their superiority in the development of marginal oil and gas fields and cost-effectiveness. Identifying the effects of reservoir properties on production is significant to the operation of ERWs for oil and gas extraction. This work utilizes numerical modeling techniques to simulate the application of ERWs in low-permeability formations. The impacts of low permeability on the oil production and the pressure distribution of the reservoirs with different formation properties are analyzed, and the simulation results of the oil exploitation by ERWs are compared with the oil production and pressure distribution of that by horizontal wells (HWs). A test scheme is designed to analyze the effect of reservoir properties on oil extraction through ERWs and quantify the sensitivity of oil production to reservoir properties. The reservoir properties of formation rock compressibility, formation fluid compressibility, initial reservoir pressure, reservoir saturation pressure, formation porosity, and absolute permeability are studied through 66 ERW cases. The results illustrate that low permeability leads to a fast decrease of oil production rates and significantly uneven pressure distribution. The pressure is lower at the center of the ERW but is higher at both ends of the ERW, while the pressure is evenly distributed along the horizontal well in the HW cases. In addition, the oil production is in direct proportion with the initial reservoir pressure, formation rock compressibility, formation porosity, and formation fluid compressibility but is in an inverse ratio with the reservoir saturation pressure. Furthermore, the initial reservoir pressure has the largest impact on both the total cumulative oil production driven out by natural energy and the cumulative oil production after the development of ten years by natural energy; on the contrary, the absolute permeability has no effect on the total cumulative oil production driven out by natural energy.

Bending Deformation and Ultimate Moment Calculation of Screen Pipes in Offshore Sand Control Completion

Horizontal wells, extended-reach wells, and multi-branch wells were often used to exploit subsea oil and gas efficiently. However, during the sand control screen completion of those wells, the sand control screen pipe was easily deformed. Failure occurred when passing through the bending section due to the large bending section in the wellbore trajectory. A parametric analysis model of the screen pipe was established based on ABAQUS and Python software under pure bending load first. Then, deformation patterns and mechanisms were identified and discussed. The effects of parameters on the screen pipe bending deformation patterns and the ultimate moment were analyzed. Finally, an empirical formula for calculating the ultimate moment of the screen pipe was established. The results showed that the deformation of the screen pipe was complex, and three deformation patterns were related to the hole parameters. Due to an increase in the diameter and number of circumferential and axial holes, the ultimate moment of the screen pipe gradually decreased, and the circumferential holes had a more significant effect on the ultimate moment than the axial holes. The established empirical formula could accurately calculate the ultimate moment of the screen pipe, and the average difference between the formula and numerical simulation results was 3.25%.

Prediction of Cuttings-Induced Annular-Pressure Loss in Extended-Reach Wells

Prediction of Cuttings-Induced Annular-Pressure Loss in Extended-Reach Wells

E&P Notes (December 2022)

E&P Notes (December 2022)

Risk Analysis and Scheme Optimization of Sand Control String Running in Extended Reach Horizontal Well

Due to the structure of the wells and other factors, the sand control string in offshore extended-reach wells is subjected to great friction resistance and even buckling phenomenon when being lowered, which ultimately leads to the failure of the string to be lowered in place. Based on elastoplastic and other relevant theories, this paper took an extended reach horizontal well in an oilfield in the South China Sea as an example and analyzed the friction and wellhead suspension weight of different well structures and completion string combinations in the process of running and finally carried out the risk analysis of the running string and the optimization of completion scheme. The results show that the friction resistance of the four-hole structure (8 1/2″) is lower than that of the five-hole structure (6″). Among them, an 8-1/2″ open hole 5-1/2″ high-quality screen is preferred, and a 6″ open hole 4″ high-quality screen is preferred. The friction coefficient in the open hole section is less helpful in improving the running safety of the sand control string, while reducing the friction coefficient in the casing is more obvious to reduce the friction. The results can provide guidance for the running of the screen and control string in the extended reach horizontal well.

Case Study: Hitting the Bullseye: The Evolution of RSS and LWD Technology in Horizontal Wells

_ For nearly a century, conventional directional drilling served as the benchmark for drilling nonvertical wellbores. It enabled operators to access multiple parts of a reservoir from a single surface location, reducing the overall environmental impacts. Traditional directional drilling used some type of nonrotating bent sub to tilt the drill bit in a different direction from the central axis. But with the demands of the modern energy industry driven by the unconventional horizonal well market, the industry needed a step change. Operators required a system that could precisely steer through extended-reach wells, often traversing complex trajectories, with precision control and greater reliability. The evolution of rotary steerable systems (RSS) and logging-while-drilling (LWD) technology in the early 2000s addressed this demand by deploying fit-for-purpose tools and services to improve the economic viability of oil and gas fields around the world. High-Performance Drilling With Full Directional Control With more operators needing an RSS system that could drill through longer horizontals and deliver quality wellbores in as few runs as possible, Weatherford recognized the demand and responded with the Magnus RSS. Using a push-the-bit design, the system combines reliable, high-performance drilling with precise directional control to enable operators to extend the performance of each drilling run, providing faster drilling, better wellbore quality, and high-quality measurements. Directional drilling requires tools to stay in the wellbore for extended periods of time. To keep costs as low as possible, the optimal solution is to perform all drilling operations in one run. To account for the downhole stresses, a rugged design was developed for the RSS. A streamlined design, featuring a ¼-in. undergauge stabilizer and 20% junk-slot area, a fully rotating bias unit, minimal bottomhole assembly (BHA) stabilization, and an optimized junk-slot area combine to reduce the risk of expensive stuck-pipe events. The system also incorporates metal-on-metal piston seals in the mud-actuated pad, enhancing mechanical integrity in harsh and high-pressure drilling environments and greater overall system reliability. Operators also need the ability to precisely steer the bit to stay on the well plan no matter if the plan requires verticals, curves, or laterals. Three independent pads and valves provide proportional control and allow the pads to fully retract for reaming, cement/shoe drilling, or tight-hole applications. This independence also provides redundancy in the system in the event of pad or valve failure. The three pads actively manage the direction through the entire wellbore and achieve a true-inclination hold in the lateral. In many conventional directional drilling operations, even a successful run can leave the wellbore in need of underreaming to prepare it for the installation of contingency liners and casing or completions equipment. Ideally, to optimize drilling efficiency, the directional drilling and underreaming should be performed in the same run. To meet operators’ desire for hole enlargement while drilling, our engineers developed the RipTide drilling reamer, which is often coupled with the Magnus RSS, to drill a smooth, concentric underreamed hole to total depth in one trip.

Research on dynamic prediction of tubular extension limit and operation risk in extended-reach drilling

Extended-reach wells have been widely applied to efficient development of oil and gas resources in complex areas such as oceans, beaches, lakes and mountains. Extended-reach drilling has the characteristics of many constraints, high implementation difficulty and high operation risk, and the accurate prediction of tubular extension limits and operation risks is very significant for safe drilling. Firstly, local tubular deflection curves and additional contact forces due to discontinuity effects are firstly deduced, and an amended torque & drag model of tubular strings is built. Secondly, a dynamic inversion method of friction factors was presented by introducing the weight function related to well depth and considering the difference of friction factors on cased and open-hole sections. Next, a dynamic prediction of tubular extension limit and operation risk is built by combining the amended tubular mechanical model, inversion model of friction factors. At last, the above theoretical models are applied to a case study. The results indicate that curvature discontinuity and stiffness discontinuity increase contact forces obviously in build-up and azimuth turning sections, which further increase friction force and torque a lot. The long-term, short-term and real-time tubular extension limits and operation risks can be obtained by setting different values of p.

Analysis of drilling difficulty of extended-reach wells based on drilling limit theory

With the continuous increase in vertical depths and horizontal displacements of directional wells, the difficulties of drilling operations continue to increase, and more accurate methods of drilling difficulty evaluation are needed. In this paper, a drilling difficulty evaluation method is built by combining drilling limit model and expert evaluation. Firstly, the concept of drilling difficulty index is introduced, and the method to calculate drilling difficulty index is established. Next, the meanings of five drilling difficulty levels are explained and the optimization design method with drilling difficulty as the target is built. At last, the theoretical model is applied to the extended-reach drilling of the Liuhua oilfield in the South China Sea, in which drilling difficulties are evaluated and the relationship between drilling difficulty and development control radius is revealed. The results indicate that extended-reach drilling in the Liuhua oilfield is on the “normal” difficulty level on average, rotary drilling in 8 1 / 2 -in. section is the most difficult, and the main constraint conditions are excessive torque and high friction. Through technology upgradation, the drilling difficulties are decreased, the development control radius increases from 6.6 to 11.4 km, and the maximum horizontal-to-vertical ratio increases from 5.3 to 8.7. Then, the development wells in marginal oilfields and adjustment wells in old oilfields can be drilled on “normal” difficulty level. Therefore, technology upgradation, especially drilling rig upgradation, is the most important development direction for extended-reach drilling in the South China Sea.