Drillpipe Eccentricity Research Articles

A Multiparameter Coupled Prediction Model for Annular Cuttings Bed Height in Horizontal Wells

Cuttings accumulation in horizontal drilling is one of the main reasons for high drilling torque and drag and serious backing pressure and consequently influencing the rate of penetration (ROP), so inhibiting the generation of cuttings bed and keeping the hole clean is an important prerequisite to ensure the smooth and safe drilling of horizontal section. In order to master the formation mechanism of cuttings bed and reveal the influence law of influencing factors, based on the three-layer cuttings bed migration model and the two-phase solid-liquid flow theory, this paper establishes a numerical simulation method for cuttings migration characteristics in the annulus of horizontal wells, reveals the cuttings concentration distribution law and migration characteristics in the horizontal well section, and fits the engineering prediction model of cuttings bed height considering many factors such as geology, engineering, and fluid body according to the simulation results. The analysis of sensitive factors shows that the rate of penetrating, cuttings density, and drill pipe eccentricity is not conducive to borehole cleaning, and cuttings are easy to accumulate to form cuttings bed; increasing the drilling fluid density, displacement, and drill pipe speed is conducive to borehole cleaning and reducing the height of cuttings bed. The research shows that within the range of normal construction parameters, the error of the horizontal cuttings height prediction model is less than 10%, which can meet the needs of engineering analysis. The model provides convenience for engineering applications.

Simulation study on effect of drill pipe eccentricity on cuttings transportation in wellbores based on kinetic theory of granular flow

Effective drilling cuttings migration is an important issue in wellbore cleaning. The existing research mainly focuses on the influence of single factors, but lacks targeted research into comprehensive factors affecting on cuttings transport. In present work, the cuttings migration carried by drilling fluid in the wellbore is simulated using Eulerian-Eulerian two-fluid model with the kinetic theory of granular flow. The granular temperature of cuttings, solids pressure and solids viscosity in the annulus are obtained to determine interaction between cuttings particles, involving the fluctuation and stress of cutting particles in wellbore. Effects of drill pipe rotating speed and inlet velocity of drilling fluid in different wellbore inclinations under different eccentric conditions on the efficiency of cuttings migration are analyzed. Simulation results reveal that comprehensive consideration of drill pipe eccentricity and well inclination, increasing rotational speed of drill pipe and inlet velocity of drilling fluid can result in reduction in the cuttings bed height and rise in the efficiency of cuttings migration within limits. Increasing the inlet velocity of drilling fluid is more positive effect to cuttings migration in the inclined wellbore with eccentricity, while increasing rotational speed is more beneficial to improve efficiency of cuttings migration at the horizontal wellbore.

Comprehensive Experimental Investigation of Hole Cleaning Performance in Horizontal Wells Including the Effects of Drill String Eccentricity, Pipe Rotation, and Cuttings Size

Abstract Extended reach drilling (ERD) wells with a horizontal and highly deviated section are widely applied in the oil and gas industry because they provide higher drainage area than vertical wells and hence increase the productivity or injectivity of the well. Among many issues encountered in a complex well trajectory, poor hole cleaning is the most common problem, which occurs mainly in the deviated and horizontal section of oil and gas wells. There are significant parameters that have a serious impact on hole cleaning performance in high-angle and horizontal sections. These include flowrate, rheology, and density of the drilling fluid, drill string eccentricity, pipe rotation, and cuttings size. It has been recognized that the action of most of these parameters to transport drilled cuttings is constantly a point of controversy among oilfield engineers. In the present study, extensive experiments were conducted in an advanced purpose-built flow rig to identify the main parameters affecting on circulate the cuttings out of the test section in a horizontal position. The flow-loop simulator has been designed to allow easy variation of operational parameters in terms of flowrate, mud density, drill string eccentricity, pipe rotation, and cuttings size. In addition, the study covers the impacts of laminar, transition, and turbulent flow regimes. The goal of such variation in the operational conditions is to simulate real-field situations. The results have shown that drill string rotation and flowrate were the operational parameters with the highest positive influence on the cuttings transports process. In contrast, drill pipe eccentricity has a negative influence on cuttings removal efficiency. The cuttings transportation performance is further improved by pipe rotation at different levels of eccentricity, especially at fully eccentric annuli. It was also shown that larger cuttings appeared to be easier to remove in a horizontal annulus than smaller ones. The experimental results would provide a more in-depth understanding of the relationship between drilling operation parameters and hole cleaning efficiency in ERD operations. This will help the drilling teams to realize what action is better to take for efficient cutting transportation.

Research on the mechanism of the influence of flooding on the killing of empty wells

In empty well killing, in order to save the time and cost of killing the well, the dynamic replacement method is often used to kill the well. The main problem of the dynamic replacement method for killing wells is how to avoid terrible working conditions caused by flooding, such as gas carrying fluid, killing fluid being brought to the wellhead. Based on the principle of flooding formation and the basic tenets of flooding correlation experiment and dynamic replacement method, this paper incorporates the kill fluid viscosity, surface tension, droplet diameter, inclination angle, drill pipe joint outer diameter, and drill pipe eccentricity into the calculation range and establishes a new mathematical model suitable for dynamic replacement kill. Based on the calculation results, the influencing factors of flooding are analyzed, and the following conclusions are drawn: the increase of dynamic viscosity, gas density in the well, casing pressure, well angle, the outside diameter of drill pipe, the outer diameter of drill pipe joint, and eccentricity of drill pipe can promote the occurrence of flooding; The increase of surface tension, well-killing fluid density, and casing inner diameter have an obstacle to flooding.

Sealing performance and failure mechanism analysis of packing unit used in rotary blowout preventer for under-balanced drilling

The packing unit is the key part of a rotating blowout preventer (RBOP) and its sealing performance affects the operation of under-balanced drilling, but sealing failure often happens. This paper studies the influence of various parameters on its sealing performance and discusses the packing unit's failure mechanism. Firstly, the Yeoh constitutive model is chosen through a group of tensile tests of the packing unit material. Then, the finite element model of the packing unit is established, and the influence of well pressure, tripping and drilling speed, friction coefficient and five structural parameters on the contact stress between the packing unit and drill pipe are discussed. Finally, the failure mechanism of the packing unit is analyzed, and the structural parameters of the packing unit are optimized. The results show that during the tripping process, the contact stress is the largest when the drill pipe joint passes through the packing unit, and the contact stress of the packing unit increases with the increase of well pressure and friction coefficient. The tearing at the top of the packing unit is caused by shear stress. The failure mechanism of the packing unit at the inner angle is divided into two types, one is that excessive contact stress causes the tongue piece to fall off, the other is that alternating von Mises stress and shear stress cause lumpy to fall off. Alternating von Mises stress and CSHEAR 2 (Transverse friction shear stress) causes tearing at the inner lower angle. The drill pipe eccentricity causes the Y-shaped cracks at the side of the packing unit. The optimized parameters of the packing unit are as follows: The tripping and drilling speed is 0.15 m/s, the inner diameter of the primary sealing section is 107 mm, the outer angle is 154°, the inner angle is 150°, the inner lower angle is 135°, and the length of the primary sealing section is 107 mm. In this paper, the failure mechanism and various influencing factors of the packing unit were analyzed, and the reliability of the finite element model was verified, which has reference value for failure analysis and structural design of the packing unit.

Hole-Cleaning Fibers Improve Cuttings-Carrying Capacity

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 203147, “Investigating Hole-Cleaning Fibers’ Mechanism To Improve Cutting Carrying Capacity and Comparing Their Effectiveness With Common Polymeric Pills,” by Mohammad Saeed Karimi Rad, Mojtaba Kalhor Mohammadi, SPE, and Kourosh Tahmasbi Nowtarki, International Drilling Fluids, prepared for the 2020 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, held virtually 9–12 November. The paper has not been peer reviewed. Hole cleaning in deviated wells is more challenging than in vertical wells because of the boycott effect or the eccentricity of the drillpipe. Poor hole cleaning can result in problems such as borehole packoff or excessive equivalent circulating density. The complete paper investigates a specialized fibrous material (Fiber 1) for hole-cleaning characteristics. The primary goal is to identify significant mechanisms of hole-cleaning fibers and their merits compared with polymeric high-viscosity pills. Hole-Cleaning Indices Based on a review of the literature, most effective parameters regarding hole cleaning in different well types were investigated. These parameters can be classified into the following five categories: - Well design (e.g., hole angle, drillpipe eccentricity, well trajectory) - Drilling-fluid properties (e.g., gel strength, mud weight) - Formation properties (e.g., lithology, cutting specific gravity, cuttings size and shape) - Hydraulic optimizations (e.g., flow regime, nozzle size, number of nozzles) - Drilling practices (e.g., drillpipe rotation speed, wellbore tortuosity, bit type, rate of penetration, pump rate) In this research, rheological parameters and parameters of the Herschel-Bulkley rheological model are considered to be optimization inputs to increase hole-cleaning efficiency of commonly used pills in drilling operations. The complete paper offers a detailed discussion of both the importance of flow regime and the role of the Herschel-Bulkley rheological model in reaching a better prognosis of drilling-fluid behavior at low shear rates. The properties of the fibrous hole-cleaning agent used in the complete paper are provided in Table 1. Test Method Two series of tests were performed. The medium of the first series is drilling water, with the goal of evaluating the efficiency of Fiber 1 in fresh pills. The second series of tests was per-formed with a simple polymeric mud as a medium common in drilling operations. Formulations and rheological properties of both test series are provided in Tables 4 and 5 of the complete paper, respectively.

Improving hole cleaning in horizontal wells by using nanocomposite water-based mud

Efficient cuttings transport is important for achieving safe and successful drilling operations. However, poor hole cleaning is considered to be one of the main issues that happens frequently in horizontal and highly deviated wells. The selection of the drilling fluids with enhanced rheological properties is one of the effective methods to increase cuttings transportation efficiency. The major purpose of the present research is to investigate the application of silica (SiO2) nanoparticles in improving hole cleaning in extended reach drilling (ERD) operations. Nanocomposite drilling fluids were prepared by adding silica nanoparticles into water-based mud (WBM) at different weight percent concentrations (0.1–1.5 wt%). The flow loop experiments were performed on a sophisticated purpose-built flow rig by circulating the tested fluid samples into the test section in a horizontal position, considering the influence of drill pipe rotation, flow rates, cuttings sizes, mud density, and drill pipe eccentricity. In addition, the study covers the impacts of laminar, transition, and turbulent flow regimes. The goal of such variation in the operational parameters is to simulate real field conditions. The results indicated that the addition of the silica nanoparticles to WBM increases the colloidal interactions with cuttings, therefore leading to a substantial enhancement in cuttings removal efficiency especially with the higher concentration of silica nanoparticles. It was shown that nanoparticles in drilling fluid increase cuttings transport by 20.32%–32.75% for different nanocomposite water-based drilling fluids used in this study. The proposed investigation demonstrates the feasibility of using silica nanoparticles in WBM to enhance the capability of drilling fluids in transporting and circulating drilled cuttings out of the wellbore. Furthermore, the results of this project would provide a more reliable understanding of the relationship between drilling operation parameters and hole cleaning performance in ERD operations.

Experimental investigation of cuttings transport with nanocomposite water-based drilling fluids modified by cellulose nanoparticles

Extended reach (ERD) wells with a horizontal and highly deviated section are commonly utilized in deep oil and natural gas exploration operations. Among many difficulties faced in this complex wellbore trajectory, good hole cleaning is one of the biggest challenges. The main objective of the present study is to investigate the application of cellulose nanoparticles (CNPs) in improving hole cleaning in horizontal drilling operations. Nanocomposite drilling fluids were prepared by adding CNPs, including cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs), into water-based mud (WBM) at different weight percent concentrations (0.15–0.60 wt%). The flow loop experiments were implemented on a sophisticated purpose-built flow rig by circulating the tested fluid samples into the test section in a horizontal position, considering the influence of drill pipe rotation, flow rates, cuttings sizes, and drill pipe eccentricity. The goal of such variation in the operational parameters is to simulate real field conditions. The cuttings transport ratio (CTR) which is defined as the ratio of the weight of recovered cuttings to the weight of injected cuttings is chosen as the measurement to evaluate hole cleaning. The results revealed that the nanocomposite drilling fluids displayed a considerable enhancement in cuttings removal efficiency, especially with the higher concentration of CNPs. The morphology of CNPs played a vital role in improving the rheological properties of the water-based drilling fluids. In comparison, the drilling fluid samples with CNCs had comparatively lower cuttings transports ratio (CTR) than these of the fluids with CNFs. These differences were connected to their distinguished morphologies and different interactions with bentonite in the fluid system. This work is the first attempt to evaluate the applications of renewable, biodegradable, environmentally friendly, and more cost-effective nanoparticle additives to enhance the capability of drilling fluids in transporting and circulating drilled cuttings out of the wellbore.

ПРОЦЕССЫ ТРАНСПОРТА ШЛАМА ПРИ ОЧИСТКЕ СКВАЖИН С ПРОИЗВОЛЬНОЙ ОРИЕНТАЦИЕЙ БУРОВЫХ ТРУБ, СОДЕРЖАЩИХ ЭКСЦЕНТРИЧНО РАСПОЛОЖЕННОЕ КРУГЛОЕ ЯДРО С ПОДВИЖНОЙ СТЕНКОЙ: ПРОБЛЕМЫ, РЕЗУЛЬТАТЫ, ПЕРСПЕКТИВЫ (ОБЗОР)

Актуальность работы вызвана необходимостью современной оценки решения проблем: моделирования течений смеси вязкой жидкости с твердыми частицами и взаимодействия ее со стенками устройств, предназначенных для бурения; очистки скважин с произвольной ориентацией буровых труб с эксцентрично расположенным вращающимся ядром. Цель: уяснение методов управления процессами транспорта шлама из скважин с участками вертикально-горизонтального сочленения в рамках комплексных численных и экспериментальных исследований; выдача рекомендаций в практику процессов очистки. Методы. Теоретические и практические методы исследований из смежных областей гидродинамики и тепломассопереноса реологически сложных вязких сред при решении задач о влиянии режимов течения, вращения стенок эксцентричного ядра на расположение и поведение частиц дисперсного потока, а также правомерность идеализаций явлений в смесях; методы исследований процессов, характеризующих перемещение частиц сквозь жидкость совместно, в общей массе, как это происходит при осаждении, а также в режимах: неподвижности частиц, соответствующих плотно упакованному слою; относительного движения частиц и жидкости, осложненного турбулентностью; движения частиц относительно друг друга при сложном сдвиговом течении несущей среды. Результаты. Представлен обзор результатов исследований процессов в скважинах и бурильных колоннах. Проанализированы достоинства отдельных критериальных связей поведения шлама. Уясняется правомерность допущений, возможностей ряда моделей турбулентности и их замыкающих связей в определении структуры, теплогидродинамических и диффузионных свойств смеси, условий и механизмов образования, накопления, осаждения, транспорта и отделения частиц шлама от жидкости, в которой они взвешены. Отмечается, что в приложениях очень популярны исследования транспорта шлама в полях действия центробежных, массовых сил (гравитации, вращения), вызывающих изменение плотности частиц в режимах сальтации, включающих серии отрывов/присоединений частиц, чередующихся с ударами о стенку трубного ядра. Наблюдения процесса взаимодействия твердых и жидких частиц бесконтактными средствами регистрации могут служить информацией для валидации и верификации современных RSS-моделей турбулентности (Reynolds Shear Stresses) с опорной базой из kL/kɛ-уравнений для кинетической энергии турбулентности (k) и ее интегрального масштаба (L)/скорости диссипации (ɛ). Они корректно предсказывают изменения в анизотропной неоднородной структуре сложного турбулентного течения смеси частиц шлама и жидкости. Отмечены достоинства разработок универсального алгоритма очистки скважин с выдачей сведений о: формировании шлама в произвольной точке затрубного пространства; получении минимальной скорости, обеспечивающей его образование и удаление. Сформулированы направления перспективных исследований; даны рекомендации по эффективной очистке отверстий.

Time-dependent cuttings transport modeling considering the effects of eccentricity, rotation and partial blockage in wellbore annuli

This paper presents a new cuttings transport model that captures the time-dependent effects of pipe rotation, drillpipe eccentricity and annulus blockage on hole cleaning. By integrating the time-dependent model with well construction data, the level of cuttings deposition along the trajectory of the wellbore can be simulated in real-time. The model recalculates its hole cleaning assessment at every time-step, and can use real-time drilling data at pre-determined time/depth intervals for calibration purposes.The integrated, real-time hole cleaning model was applied to a field case. Field data from an actual stuck pipe event was used to calculate the behavior of the cuttings profile in time along the wellbore. The data show that a high rate of penetration whilst sliding with a directional motor in the near-horizontal section of the well resulted in a significant amount of cuttings buildup around the bottom hole assembly (BHA). Unsurprisingly, the drillstring packed off and became stuck on the final trip out of the hole. Moreover, the casing-hole annulus packed off and caused induced losses while cementing because of the cuttings bed left in the hole. If the proposed time-dependent cuttings transport model had been utilized, these well problems and associated non-productive time (NPT) could have been better predicted and possibly avoided.

Analysis of Cuttings Transport and Flow Pattern in Nearly Horizontal Extended Reach Well

During the drilling activity, in an extended reach well, the deposition of cuttings (solids) in the annulus can lead to issues such as differential sticking and inefficient hole cleaning. This makes it essential to identify different multi-phase flow patterns and study the effect of drill pipe eccentricity and rotational speed on cutting transport in the annulus. Therefore, in this study, the experiments were conducted in a near-horizontal flow loop system, where the length of an annulus section was 6.16 m (20.2 ft) long and the outer and inner diameters were 4.5 in. (11.4 cm/0.37 ft) and 2.5 in. (6.4 cm/0.21 ft), respectively. A high-speed CCD camera was used to perform the in-situ visualization of the multiphase-flow through the annulus. Then the recorded videos were used to investigate the cuttings transport for both 2 and 5 wt% solid concentrations. Glass beads having a diameter of 0.5-2 mm were used as cuttings for the experiments. The video recordings were used to scrutinize the flow behavior pattern which depicts the possible flow patterns for the gas-liquid-solid multiphase-flow through horizontal annuli. The effects of varying pipe eccentricity (0 to 75 %), drill pipe rotational speed (0- 120 RPM), air pressure (0.4-0.8 bar) and solid concentration on the cuttings transport through the annulus were investigated. It was observed that high rotational speed and eccentricity of the drill pipe lead to better hole cleaning. At 30% eccentricity, the solid bed height was found to vary from 8 to 20 times at different rotational speeds for changing the solid concentration form 2 wt% to 5 wt%. Moreover, while different drilling conditions were tested for cutting transport, six distinguishable flow patterns were observed. The findings also show that 75% of eccentricity may not be optimum drilling conditions because of the contact between cutting and the drill pipe. The novelty aspect of this work was the use of three phases (solid, liquid and gas) to investigate the flow pattern behavior and cutting transport phenomena in the annular flow loop system by varying drill pipe rotational speed and drill pipe eccentricity. The flow map of this work can be used to develop 3-phase models to figure out optimum conditions for cutting transport in horizontal wells for enhanced oil recovery.

The effect of orbital motion and eccentricity of drill pipe on pressure gradient in eccentric annulus flow with Newtonian and non-Newtonian fluids

The correct prediction of the pressure gradient is the fundamental parameter to establish an effective hydraulics program, which enables an optimised drilling process. In the present work, the effect of the orbital motion of the drill pipe on the pressure drop in an eccentric annulus flow with Newtonian and non-Newtonian fluids is studied numerically for both laminar and turbulent regimes using finite volume method (FVM). Furthermore, the effect of eccentricity when the inner pipe makes an orbital motion is evaluated. Different behaviours are observed in laminar and turbulent regimes. In the laminar regime, the simulation results showed that an increase of the orbital motion speed causes a considerable increment of the pressure gradient for the Newtonian fluid. For the power-law, non-Newtonian fluid in the laminar regime, on the contrary, a decrease of the pressure gradient is observed due to the shear-thinning effect. In the turbulent regime the mentioned trends are predicted to be much weaker. As eccentricity increases, the pressure drop of the non-Newtonian fluid decreases with a more pronounced diminish in pressure drop when the drill pipe is in orbital motion for both laminar and turbulent flow regimes.

The effect of orbital motion and eccentricity of drill pipe on pressure gradient in eccentric annulus flow with Newtonian and non-Newtonian fluids

The correct prediction of the pressure gradient is the fundamental parameter to establish an effective hydraulics program, which enables an optimised drilling process. In the present work, the effect of the orbital motion of the drill pipe on the pressure drop in an eccentric annulus flow with Newtonian and non-Newtonian fluids is studied numerically for both laminar and turbulent regimes using finite volume method (FVM). Furthermore, the effect of eccentricity when the inner pipe makes an orbital motion is evaluated. Different behaviours are observed in laminar and turbulent regimes. In the laminar regime, the simulation results showed that an increase of the orbital motion speed causes a considerable increment of the pressure gradient for the Newtonian fluid. For the power-law, non-Newtonian fluid in the laminar regime, on the contrary, a decrease of the pressure gradient is observed due to the shear-thinning effect. In the turbulent regime the mentioned trends are predicted to be much weaker. As eccentricity increases, the pressure drop of the non-Newtonian fluid decreases with a more pronounced diminish in pressure drop when the drill pipe is in orbital motion for both laminar and turbulent flow regimes.

Effects of drill string eccentricity on frictional pressure losses in annuli

It has been shown that drill pipe eccentricity can significantly reduce the annular pressure losses and must be taken in to account for accurate prediction of equivalent circulating density (ECD). This study investigates effects of axial flow of Yield-Power-Law (YPL) drilling fluid on frictional pressure losses in eccentric annuli. A numerical model is developed to simulate the laminar flow of yield-power-law fluids in eccentric annular geometries. The governing equations are solved numerically using an implicit finite difference method and employing a non-uniform grid distribution system. The numerical solution yields velocity profile in the annular space, which is integrated to obtain the volumetric flow rate. The frictional pressure losses are calculated using an iterative scheme that is based on convergence of the calculated volumetric flow rate to the given flow rate. Comparing the frictional pressure loss predictions of the model with three previous numerical studies indicates an excellent agreement for the case of non-Newtonian fluids. The numerical model is validated through extensive comparisons between the predicted frictional pressure losses and experimental data derived from the literature. Our analysis indicates excellent agreement between the model prediction and the experimental data. The numerical results conclude that the reduction in frictional pressure losses due to eccentricity is more prominent at high radii ratios. Results of extensive simulation scenarios for yield-power-law fluids are fitted using non-linear regression analysis, which provides a new correlation for prediction of frictional pressure losses of yield-power-law fluids in eccentric annuli. Comparing the predictions of the developed correlation with the published correlation in the literature reveals more accurate estimation of frictional pressure losses for the proposed correlation and hence safer controlled drilling operations.

Numerical method and analysis of ultrasonic detection of gas kick in deepwater risers during Offshore drilling

Ultrasonic monitoring of gas kick in risers is an effective method for early gas kick detection in deepwater drilling operations. At present, the research on the ultrasonic propagation in gas-liquid two-phase flow within the risers and the response rules of ultrasonic signals under actual working conditions is not deep enough. In this paper, the numerical simulation method that can accurately control parameters such as the distribution and size of bubbles was introduced, and its effectiveness and accuracy were verified by experimental means. Through the analysis of the effective sensitivity fields under different gas-fraction conditions, the key monitoring parameters (emission frequency and receiving probe position) were optimized first. On this basis, the characteristic parameters of ultrasonic signals were optimized and their applicable conditions were also analyzed: The response law of coda wave velocity to the gas fraction was gained by using the coda wave interference method and it is suitable for the condition of small gas fraction (less than 0.42%); The response rule of main frequency on gas fraction was obtained through frequency domain analysis; The arrival time of head wave was relatively sensitive to the gas fraction of 2–8%. Finally, the conditions of the eccentricity of drill pipe and the non-uniform distribution of bubbles were discussed. The influence of drill pipe eccentricity on ultrasonic propagation under different frequencies was noted, and the monitoring solution under the condition of non-uniform distribution of bubbles was proposed based on the effective sensitivity of different receiving positions. This study not only optimized the key parameters of ultrasonic monitoring method, but also explored its applicable conditions and the influence rules of actual working conditions on the ultrasonic propagation.

A multiparametric CFD analysis of multiphase annular flows for oil and gas drilling applications

The increasing global energy demand has pushed the oil industry towards developing more innovative and advanced methods of enhancing oil recovery even under unfavourable technical and environmental conditions. The severity of many operational problems affecting the drilling and production of oil and gas wells is worsened by inaccessibility; hence, remedial efforts must be implemented from afar. One of these problems is ensuring efficient removal of formation rock cuttings with a suitable fluid whose rheology is often complicated. Furthermore, pressure losses along the annular geometry involved, and decreased rates of penetration (ROP) due to accumulated drill cuttings downhole, constitute significant portions of the total energy to be supplied. Thus, the application of sophisticated modelling techniques with credible elucidation of the phase distributions (solids, liquids and gas) and prevalent flow regimes becomes essential, if adequate and economic design of a drilling program is desired. The advent of computational fluid dynamics (CFD) and the growth in the available computational power to support it have provided an unprecedented opportunity to simulate and understand complex real flows, especially when experimental methods become extremely demanding. The present study employs the tool of computational fluid dynamics to simulate a two-phase solid–liquid flow in an annulus based on the analysis of cuttings concentration, pressure drop profiles, axial fluid, and solid velocities as a function of several drilling parameters: drill pipe eccentricity, inclination, drill pipe rotation, ROP and fluid rheology. Special emphasis is however placed on the impact of changing hole eccentricity on cuttings transport efficiency. The suitability of the Eulerian–Eulerian (EE) multiphase tracking scheme in modelling systems of high volume fractions is fully utilised in this work. A non-Newtonian (power law) fluid model with well-described flow parameters is implemented, considering a uniform cuttings size distribution (3mm). A commercial CFD software (ANSYS FLUENT™ 17.1) has been used; the descriptive and predictive potential of the CFD software has been confirmed on account of the reasonable agreement with previously published experimental data (a relative error of less than 11% is achieved), as illustrated by the corresponding sensitivity plots. This multi-parametric CFD analysis study of multiphase cutting transport during drilling applications has confirmed that fluid velocity, hole inclination and annular eccentricity are the most influential factors governing the cuttings transport efficiency.

Investigating the impact of drillpipe's rotation and eccentricity on cuttings transport phenomenon in various horizontal annuluses using computational fluid dynamics (CFD)

Drillpipe eccentricity is a common issue in horizontal drilling operations. The eccentricity is a non-manipulative parameter by itself but its impact is a function of various parameters such as rate of penetration (ROP), fluid flow rate (Q), cuttings bed height, wellbore path and drillpipe rotation. The goal of this study is to observe the cutting's accumulation in different eccentric annuluses by employing a multiphase Eulerian flow model including a Herschel-Bulkley drilling fluid. Turbulence was implemented using Reynolds Stress Model which reveals proper results, especially on asymmetric and complex cases. All of these are developed and calculated through a comprehensive Computational Fluid Dynamics (CFD) simulations to solve the governing equations in the multiphase medium. A sensitivity analyzes were implemented from concentric to 75% eccentric cases accompanying different variations of fluid flow rate, ROP, and drillpipe rotation. The results demonstrated that further eccentricity from a certain amount will abruptly increase the cutting's accumulation which is a function of bed height, ROP/Q, and drillpipe rotation. However, rotation's impact is negligible above a certain speed of rotation after which the sudden increase of cutting's accumulation caused by eccentricity is not observable.

Study on the prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings

An open-hole extended-reach limit model was established and published by the authors to determine how far a horizontal extended-reach well (ERW) can extend. The published model shows that the open-hole extended-reach limit (the maximum measured depth of the horizontal ERW) is mainly dependent on the annular pressure drop and the fracture pressure of drilled formation. Moreover, some optimal control methods, such as lowering drilling fluid density, reducing drilling fluid flow rate and optimizing drill pipe eccentricity, were also presented to obtain greater open-hole extended-reach limit. However, the published model was established based on the assumption that the annular fluid is ideal single-phase flow. Failing to consider the effects of cuttings may lead to an inaccurate prediction of the open-hole extended-reach limit and even drilling safety hazards. In this paper, in order to overcome the shortcomings of the published model, a prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings is established and analyzed. The study shows that due to an increase of annular pressure drop, the horizontal-section limit (the maximum measured depth of horizontal-section for the horizontal ERW) is relatively smaller when considering the effects of cuttings. Meanwhile, a case study is carried out, and the results show that the horizontal-section limit is 1610 m when the cuttings are considered. In contrast, when the cuttings are ignored, the limit is 1941 m based on the published model. Furthermore, since several main parameters of the established model may greatly affect the annular pressure drop and the horizontal-section limit, parameters sensitivity analysis are also performed and some conclusions are drawn. First, the horizontal-section limit first increases and subsequently decreases with the increase in drilling fluid density. Second, there is an increase in horizontal-section limit when the drilling fluid flow rate increases. Third, the horizontal-section limit gradually increases with the increase in the drill string rotation speed. Finally, there is also a decrease in the horizontal-section limit when the rate of penetration (ROP) and the consistency coefficient increase. In sum, the simulated condition in this paper is more consistent with the situation of field drilling practice than that of the published model. This study will also provide a more accurate result of the open-hole extended-reach limit, which is of great significance to the drilling design and drilling safety.

Frictional pressure loss of drilling fluids in a fully eccentric annulus

It is common practice when drilling oil and gas wells to assume that the drillstring is placed concentrically in the annular space with either the open hole or previous casing strings in order to predict annular frictional pressure losses. The assumption of such a concentric annulus is, however, a considerable simplification that may not properly reflect the majority of drilling applications in the field. In fact, with an increasing number of deviated/horizontal and extended reach wells being drilled, a fully eccentric annulus is actually present in a large section of the wellbore.In this study, we apply experimental, analytical, and numerical approaches to investigate the impact of drillpipe eccentricity on the annular pressure loss while circulating non-Newtonian drilling fluids. The length of the experimental section of a flow loop was 27.74 m (91′) and it consisted of 0.0245 m (1″) steel drillpipe and 0.0571 m (2.25″) acrylic casing with the inner diameter of 0.0508 m (2″). Drillpipe was placed at the bottom of the casing, thereby simulating a fully eccentric annulus. Four Yield Power Law (YPL) drilling fluids were tested in this flow loop. Annular pressure loss for a wide range of laminar flow rates was recorded for each fluid. A numerical model based on a finite difference approach was developed to estimate the annular pressure loss. Subsequently, the experimental data was compared with the proposed model and also with several other widely used analytical and numerical approaches previously reported in the literature. The obtained results show that in the laminar flow regime, the annular frictional pressure loss in a fully eccentric annulus is considerably less than a concentric annulus, on occasions by less than 50%. In general, all the applied models under-estimated the effect of eccentricity on pressure loss. However, the novel proposed model showed the least discrepancy with the experimental data. Furthermore, it was found that the difference between the estimated and experimental results increases with increasing fluid yield stress. This suggests that models and/or correlations that are developed to correct for the eccentricity effect for fluids with negligible yield stress (for instance Power Law fluids) are not suitable to estimate the pressure loss for YPL fluids with elevated yield stress.

A Comprehensive Model for Circulating Pressure Loss of Deep-water Drilling and Its Application in Liwan Gas Field of China

Considering the special wellbore configuration and operating environment of deep-water drilling, a comprehensive model for circulating pressure loss of deep-water drilling is established. Based on fluid mechanics theory and heat transfer theory, wellbore temperature and pressure of riser section are calculated and a coupling approach is proposed. Comprehensive factors that affect circulating pressure loss of deep-water drilling are considered in this study. These factors are mud properties, flow regime, drill pipe rotation, drill pipe eccentricity, cuttings bed, tool joints, BHA (Bottom Hole Assembly), drill bit and surface pipeline. The model is applied to Liwan gas field of China. The results show that the data calculated by this model match the field data very well and the model can provide references for designing deep-water drilling hydraulic parameters.