Cuttings Transport Research Articles

Next-generation drilling fluids for horizontal and multilateral wells: A conceptual approach

The development of next-generation drilling fluids is crucial for the success of horizontal and multilateral wells, which pose unique challenges such as torque and drag, hole cleaning difficulties, and wellbore instability. This review explores the evolving role of drilling fluids, focusing on the desired properties required to address these challenges, including enhanced cuttings transport, reduced torque and drag, and improved wellbore stability. Furthermore, the paper discusses innovative additives, such as nanoparticles, high-performance polymers, and biodegradable lubricants, which are key to optimizing fluid performance. Environmental considerations and the chemical and mechanical interactions between fluid components are also analyzed. Finally, the paper examines future trends in drilling technology, highlighting the expected benefits of next-generation fluids and identifying potential challenges for future research and development. These advanced fluids are positioned to revolutionize drilling efficiency while maintaining sustainability in increasingly complex drilling environments.

Experimental Analysis of Shale Cuttings Migration in Horizontal Wells

The extraction of shale gas via horizontal drilling presents considerable challenges, primarily due to the accumulation of cuttings within the annular space, resulting in increased friction, torque, and potential drilling complications. To address this issue, the study proposes an experimental setup aimed at simulating cuttings transport under various operational conditions, with a particular emphasis on gas wells. The methodology encompasses the modulation of the drilling fluid flow rate and the drill’s rotational speed to examine the transport velocity of cuttings. Furthermore, the study analyzes the impact of annular eccentricity on return volume, transport time, and cuttings bed height. Critical initiation velocities for cuttings across different motion modes were also determined, and theoretical calculations were compared with empirical data. The findings indicate that an increased flow rate of drilling fluid and higher rotation speed substantially improve the transport of cuttings, thereby minimizing bed formation, whereas increased eccentricity hinders this process. The results revealed that the theoretical model showed a greater overestimation of the start-up velocity for spherical particles, with average errors ranging from 15.50% to 17.56%. In contrast, the model exhibited better accuracy for non-spherical (flaky) particles, with errors between 8.63% and 9.61%. Under non-rotating conditions, the average error of the model was approximately 8.32%, while the introduction of drill tool rotation increased the average error to 11.94%. These results have the potential to optimize operational parameters in shale gas well drilling and may contribute to the development of specialized borehole purification tools.

Foam Properties Evaluation under Harsh Conditions: Implications for Enhanced Eco-Friendly Underbalanced Drilling Practices

Summary Foam drilling offers advantages such as reduced formation damage and faster drilling in underbalanced drilling (UBD) operations. The efficacy of foam drilling is influenced by factors including pressure, temperature, salt content, foam quality, and pH levels. However, a gap exists in the evaluation of foam properties under rigorous conditions, particularly those involving high pH and mixed salt environments common in drilling scenarios, highlighting the need for further research. In this study, a high-pressure, high-temperature (HPHT) foam analyzer and rheometer were employed to examine the stability and rheological behavior of ammonium alchohol ether sulfate (AAES) foam under simulated alkaline drilling conditions. The foaming solution, designed to replicate such conditions, consisted of synthetic seawater (SW) with a salt mixture totaling approximately 67.70 g/L and a 0.5 wt.% foaming agent adjusted to a pH of 9.5. This approach differs from the individual salt studies prevalent in existing literature and provides a unique perspective on foam stability and behavior. Driven by environmental sustainability considerations, the effects of eco-friendly surfactant AAES and various drilling fluid additives: polyanionic cellulose (PAC), carboxymethyl cellulose sodium (CMC), and xanthan gum (XG), were investigated for foam formulation. The apparent viscosity of the AAES foam was evaluated at different pressures and temperatures across varying shear rates. A consistent decrease in foam viscosity with increasing shear rates was observed, irrespective of pressure and temperature. An increase in foam viscosity was also noted with higher pressures (from 14.7 psi to 3,000 psi) at low shear rates, with values rising from 8.04 cp to 14.74 cp, and from 3.71 cp to 5.79 cp at high shear rates of 1,000 s⁻¹. Increasing foam quality from 65% to 85% resulted in significant improvements in viscosity, approximately 37% at low shear rates and about 79% at high shear rates. The introduction of additives to AAES foam at 1,000 psi and 90°C led to a substantial increase in viscosity, with PAC showing the most significant enhancement: 33.28 cp at low shear rates and 18.15 cp at high shear rates. Conversely, the viscosity of both base AAES foam and additive-enhanced foams decreased with rising temperatures, although PAC exhibited the greatest resistance to viscosity variations due to temperature changes. The addition of PAC also resulted in a notable increase in foam yield stress, potentially leading to more efficient cuttings transport and hole cleaning. Furthermore, foam stability was significantly improved by the additives, with XG and CMC doubling stability to 48 minutes, and PAC resulting in a threefold increase in half-life to 65 minutes. This study presents AAES and the tested additives as viable components for eco-friendly foam formulations, promoting enhanced properties suitable for UBD applications.

Technologies to improve wellbore cleaning

Relevance. The main technological process when constructing oil and gas wells is effective wellbore cleaning, especially when drilling horizontal and deviated wells. The article deals with the peculiarities of wellbore drilling technology according to the traditional method in combination with water and hydrocarbon-based polymer-clay solutions, as well as improvement of drilling mud removal properties taking into account density, drilling pump productivity, rheological parameters of the fluid, geometry of the well annulus, shape and concentration of drill cuttings particles. Insufficient cleaning of the well bottom hole causes undesirable phenomena leading to various complications. The object of the research is the technology of cuttings transportation along the wellbore to the surface. The basic formulas characterizing the work of interchangeable hydromonitor nozzles are given. The quality of wellbore cleaning depends on the degree of flow turbulence. Aim. To develop technical solutions that contribute to improving the quality of wellbore cleaning. Methods. Optimal geometrical parameters of hydraulic nozzles for double-deck anti-vibration bit and design of drill pipes with helical ribs have been established by experimental works. Results and conclusions. A double-deck anti-vibration bit with interchangeable hydro-monitor nozzles and drill pipes with helical ribs were developed. Implementation of these developments in the practice of drilling operations will improve the quality of wellbore cleaning by creating a turbulent regime of drilling fluid flow.

Study on flow pattern transition of cuttings transport in extended-reach drilling

Inadequate hole cleaning is one of the major challenges in extended-reach drilling, especially prominent in large-sized hole sections, such as 121/4-in. section. As the drilling parameters including flow rate, ROP and rotational speed change, the cuttings flow pattern converts between fully suspended flow, two-layer flow, and three-layer flow. However, most existing cuttings transport models only study the problem of cuttings transport under a certain flow pattern and do not consider the dynamic conversion of different cuttings flow patterns. Pipe rotation plays a key role in cuttings transport in rotary drilling, but the existing studies have not fully revealed the effect of pipe rotation on the conversion of cuttings transport patterns. In this paper, a stirring diffusion factor is presented to quantify the effect of pipe rotation on cuttings transport, and the mathematical expression of the stirring diffusion factor is obtained through numerical simulations and the nonlinear regression method. Secondly, the critical conditions for the conversion of cuttings flow patterns are obtained by combining mechanical analysis and numerical simulation results, clarifying the applicable scope of different cuttings flow patterns. According to the comparison with experimental results, the prediction error of the new model considering the conversion of cuttings flow patterns is not higher than 11.1%, and the minimum prediction error is only 3.07%. Thirdly, the flow pattern maps for cuttings transport under different drilling parameters are drawn to provide guidance for the identification of cuttings transport pattern and optimization of drilling parameters. Finally, the flow pattern maps are applied to a case study of an extended-reach drilling. The results show that there is a delay effect in the conversion of cuttings flow patterns due to the nonlinear characteristics of annular geometry. Furthermore, the effects of flow rate, ROP and rotational speed on cuttings transport patterns are not independent, but mutually reinforcing and constraining each other. Inappropriate selection of drilling parameters will result in three-layer flow of cuttings transport, and then pipe sticking is likely to occur. The cuttings transport pattern can be converted from three-layer flow to two-layer flow by optimizing drilling parameters, which can significantly improve the hole cleaning effect.

Study on the resistance coefficient of hot dry rock cuttings in Herschel-Bulkley fluid: experiments and modeling

Most hot dry rock geothermal wells are small angle directional wells, and rock cuttings easily accumulate at the bottom of the borehole to form a cuttings bed, causing accidents such as drill sticking, reducing the rate of penetration, and drilling tool breakage. Accurately calculating the resistance coefficient and settling velocity of hot dry rock cuttings can improve cuttings transportation efficiency, design and optimize drilling hydraulic parameters, and is crucial to solving borehole cleaning problems. Through visual experiments, this paper obtained experimental data on the settlement of 167 groups of spherical pellets, 153 groups of granite cuttings, and 174 groups of carbonate cuttings in the Herschel-Bulkley fluid. First, a prediction model for the resistance coefficient of spherical pellets consistent with Herschel-Bulkley fluid was established. Based on this, form factor-Roundness is introduced as the starting point, and two prediction models for the resistance coefficients of granite cuttings and carbonate cuttings in the Herschel-Bulkley fluid were established. The average relative errors between the resistance coefficient model predictions and experimental measurements are 9.61% for granite cuttings and 6.59% for carbonate cuttings. The average relative errors between the predicted and measured values of settlement velocity are 7.27% for granite cuttings and 6.21% for carbonate cuttings, respectively, which verifies the accuracy and reliability of the prediction model. The research results can provide a theoretical basis and engineering application guidance for optimizing drilling fluid rheology and circulation displacement in engineering.

The impact study of variable diameter stabilizer on drilling fluid and cuttings transport

Through numerical simulation, this study investigates the flow field characteristics of the variable diameter stabilizer in drilling tools under various conditions. It analyzes the influence of different flow rates and speeds on axial velocity and pressure distribution. The results indicate that more significant flow rates correspond to higher average axial velocities across sections, facilitating the transport of drilling fluid and cuttings. Increasing rotational speed leads to greater pressure differences between adjacent sections, consequently elevating the overall pressure drop of the tool, which, to some extent, aids in transporting drilling fluid with cuttings. During rotation, the vortex zone on the backside of the stabilizer creates a hovering and accumulation of cuttings, causing mud agglomeration, thereby affecting tool performance. During structural optimization of the tool, priority should be given to a transitional design of the outlet area in the functional core zone, aiming to alleviate the impact of abrupt structural expansions on cuttings transport.

Application of ultra-fine particles of potato as eco-friendly green additives for drilling a borehole: A filtration, rheological and morphological evaluation

Drilling fluid is crucial for oil and gas well drilling operations, serving key functions such as facilitating the removal of drill cuttings, maintaining borehole stability and controlling formation pressures. When the drilling fluid is lost into formations, it can alter the formation's integrity, contaminate groundwater and cause permeability damage. In addition, environmental concerns arise from the waste produced during drilling activities, particularly when discarded drilling fluids contain hazardous substances like heavy metals. This study explores the potential of integrating ultrafine potato powder (PP) into water-based drilling fluids (WBDFs) as environmentally friendly additives. Several analytical techniques including X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electronic microscope (SEM) and differential scanning calorimetry (DSC) were used to comprehensively characterize the prepared PPs. The study included API and HPHT filtration test, permeability plugging test and rheological evaluations of drilling fluids, assessing parameters such as filter loss, filter cake, apparent viscosity, plastic viscosity, yield point and gel strength under varied conditions of different particle sizes of PP, concentrations of PP, and temperature and pressure measurements. The obtaining results emphasize PP's potential to enhance the wellbore stability and reduce the fluid loss, the filtration of water or oil into the permeable formation, achieving 43% reduction in the filtration rate and 70% reduction in the filter cake thickness. Adding 0.5 wt% ultrafine PP improved the maximum gel strength to 32.2 lb/100 ft2, while the same concentration and particle size raised the plastic viscosity from 3 to 6.8 cP, which subsequently dropped to 6 cP in high temperature conditions. PP performed better compared with the reference fluid in improving the thinning behavior of the drilling fluids. Moreover, permeability plugging tests confirm that adding PP effectively lowered the filtration rate, with higher concentrations achieving greater reductions over time. These findings suggest that PP holds promise as an effective additive for drilling fluids, contributing to enhanced drilling efficiency, improved wellbore stability and a reduced likelihood of instability and lost circulation. The characterization and rheological analysis of PP biodegradable drilling fluids provide valuable insights for optimizing fluid formulations, tailoring them to specific operational conditions, and achieving a balance between fluidity, wellbore stability, and cuttings transport. This research highlights the potential of PP as a sustainable and efficient solution in the realm of drilling fluid additives.

Effect of pulsating flow induced by a percussive drilling tool on cuttings transport in horizontal directional drilling—A CFD study

Cuttings deposition and removal has always been a key issue in horizontal directional drilling due to its correlation with numerous problems such as rate of penetration, reduction and stuck pipe.In this paper, the relationship between the impulse flow generated by a fluidic jet hammer and cuttings removal was discussed. A Eulerian-Eulerian two-fluid model was used to simulate the cuttings transport in horizontal wells on a sliding grid basis. Results show that the flow pulsation induced by a fluidic hammer contributes to easier cuttings transport. Compared to constant flow, impulse flow showed a 22.03% improvement in more optimal borehole cleaning with the same system inlet flow rate. In addition, the asymmetric flow pulsation was more sensitive to amplitude than the sinusoidal waveform pulsation flow, and as amplitude increased, the average exit flow rate of cuttings increased by 30.95%. Cuttings transport in annular is sensitive to rate of penetration, average velocity of pulsation, pulsation amplitude and cuttings size. The effect of pulsation frequency seems to be not much significant, probably because the frequency or other parameters used in this work did in the range of optimal particle-carrying frequency. These findings can provide references for the utilization of downhole pulsating fluids by drilling tools.

Fully Coupled CFD–DEM Simulation of Oil Well Hole Cleaning: Effect of Mud Hydrodynamics on Cuttings Transport

This paper presents a coupled computational fluid dynamics–discrete element method (CFD–DEM) simulation to predict cuttings transport by the drilling fluid (mud) in different oil well drilling conditions. The mud rheology is expressed by the Herschel–Bulkley behaviour and modelled in a Eulerian framework (CFD), while the cuttings are modelled using the Lagrangian approach (DEM). In this work, the effects of drill string rotation, inclination angle, cutting size, mud rheology, and annular velocity on cleaning efficiency are investigated. It is found that increasing the well deviation from vertical to horizontal leads to a higher cuttings concentration. However, at low annular velocity, the cuttings concentration for the inclined (45-degree) annulus is found to be higher than the horizontal one due to the sliding motion of cuttings on the lower section of the annulus. Overall, the drill pipe rotation has little effect on decreasing the cuttings concentration, but the effect is more pronounced at low annular velocity.

Numerical simulation and experimental study of hole cleaning

Insufficient hole cleaning causes tool wear and reduces drilling efficiency. Existing evaluation methods and models are limited. In this study, a universal method is proposed to assess hole cleaning efficiency (HCE). A coupled computational fluid dynamics and discrete element method (CFD-DEM) numerical model for non-Newtonian fluid simulation of cuttings transport is developed. The influence of various factors on HCE was analyzed from an energy and particle collision perspective, with a particular focus on the mechanisms of fluid viscosity and rate of penetration (ROP) on cuttings settling. Results show that increased fluid viscosity improves HCE, while excessive viscosity negatively affects it. Higher ROP results in increased solid particle concentration and collision probability, leading to energy loss and reduced efficiency. Lower HCE was observed when the inclination deviated from the vertical. The HCE can be significantly improved by increasing the fluid velocity and reducing the eccentricity. A comprehensive prediction model for HCE is established using Design of Experiment (DOE), dimensional analysis, and nonlinear regression. This model incorporates a generalized fluid apparent viscosity, taking into account the impact of each rheological parameter. Additionally, it can be applied to predict hole cleanliness in both Newtonian and non-Newtonian fluids. By comparing the experimental results of hole cleanliness in three distinct fluids, the regression model yielded reliable predictive results. The findings enhance understanding regarding how fluid properties and the ROP affect cuttings transport and enable precise and convenient prediction and optimization of hole cleaning efficiency.

Hole cleaning evaluation and installation spacing optimization of cuttings bed remover in extended-reach drilling

In extended-reach or long-horizontal drilling, cuttings usually deposit at the bottom of the annulus. Once cuttings accumulate to a certain thickness, complex problems such as excessive torque and drag, tubing buckling, and pipe stuck probably occur, which results in a lot of non-productive time and remedial operations. Cuttings bed remover can efficiently destroy deposited cuttings in time through hydraulic and mechanical stirring effects. This paper aims to build a method for hole cleaning evaluation and installation spacing optimization of cuttings bed remover to improve the wellbore cleaning effect. Firstly, a Computational Fluid Dynamics approach with Eulerian–Eulerian multiphase model was utilized to investigate the mechanism of cuttings transportation, and a new type of cuttings bed remover was designed. Next, an evaluation method of hole cleaning effect of remover was established. After that, the effects of several drilling parameters on hole cleaning including flow rate of drilling fluid, rotational speed of drillpipe, rate of penetration, wellbore size, rheological property of drilling fluid, and remover eccentricity on the performance of cuttings bed remover were investigated. The results demonstrate that the new type of remover with streamline blade performs better than conventional removers. The efficiency of hole cleaning is greatly improved by increasing the rotational speed of drillpipe, flow rate of drilling fluid, remover eccentricity, and 6 rpm Fann dial reading for drilling fluid. While higher rate of penetration and large wellbore size result in worse hole cleaning. These findings can serve as an important guide for the structure optimization design of cuttings bed remover and installation spacing of removers.

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.

Interaction between Pipe Rotation and Cuttings Transport in Extended-Reach Drilling: Mechanism, Model, and Applications

Summary High drag and torque on drillstring and difficulty in hole cleaning are two major challenges in extended-reach drilling, and these two challenges are usually coupled with each other. However, previous studies considered the drillstring mechanics and hole cleaning as two relatively independent issues and studied them separately, which cannot fully reveal the complex mechanisms of pipe sticking and obtain proper drilling parameters to ensure hole cleaning and reduce drag and torque. To solve this problem, in this paper we present the concept of pipe-cuttings interaction and elaborate on the two interaction mechanisms, which are the effect of pipe rotation on cuttings transport and the effect of cuttings distribution on pipe load. Second, we introduce the stirring diffusion factor and pipe-cuttings contact stress to quantify the pipe-cuttings interaction, and we obtain their mathematical expressions through nonlinear regression of numerical simulation results. Third, we establish the mechanical pipe-cuttings interaction model by modifying and combining the tubular mechanical model and the cuttings transport model. Finally, we validate the interaction model and apply it to a case study of extended-reach drilling in the South China Sea. The results show that the interaction model is of high prediction accuracy and is superior to the conventional tubular mechanical and cuttings transport models because the interaction between pipe rotation and cuttings transport is sufficiently considered. The problem of poor hole cleaning for a 12¼-in. section is serious, and pipe sticking occurs frequently for the extended-reach well in the case study because the stationary bed height is more than 10% in actual drilling. It is usually difficult to ensure hole cleaning of a 12¼-in. section by only optimizing a single parameter of rate of penetration (ROP), flow rate, or rotational speed, but optimizing two of the parameters at the same time can achieve better results. Lastly, we establish a recommended chart of drilling parameters, which can aid engineers in making comprehensive recommendations on drilling parameters.

Performance Analysis of the Vortex Cuttings Cleaner: Turbine Hydraulic Drive and Cuttings Transport in Wellbore Annulus

Summary In the process of directional and horizontal well drilling, cuttings tend to settle and form a bed at the low side of the annulus due to gravity, which decreases the drilling rate and even causes accidents in severe cases. This paper analyzes the performance of a new tool, the vortex cuttings cleaner, which can be effective without rotation of the drillpipe. Based on the computational fluid dynamics (CFD) approach, together with the discrete phase, Euler, and dynamic mesh models, the vortex cuttings cleaner is investigated with respect to the turbine torque, turbine velocity, pressure drop, and cuttings transport in the annulus. The working mechanism of the vortex cuttings cleaner is clarified. Finally, field tests are conducted on the tool to evaluate its application in terms of service life, wellbore friction, and rate of penetration (ROP). The results show that the turbine can rotate continuously under hydraulic drive. The turbine torque/velocity and the tool’s pressure drop increase with increasing displacement. The cuttings transport in the annulus is jointly affected by factors such as turbine velocity, fluid velocity, and particle size. A too low or high turbine velocity is unfavorable for cuttings transport. Through the analysis of the number of particles and particle concentration, the optimal velocity is determined to be 125 rev/min. The swirling flow intensity in the annulus flow field increases with the increase in turbine velocity. Field applications suggest a service life longer than 200 hours, a notable decrease in wellbore friction, and an average increase in ROP by more than 20%. This study provides a theoretical basis for the research on wellbore cleaning tools.

Optimization of Wellbore Annulus Cleaning Tool Based on CFD-DEM and Box-Behnken Design

During the oil and gas drilling process, inefficient cuttings transport may elevate cuttings concentration, leading to higher Equivalent Circulating Density (ECD) and easily triggering a series of wellbore stability issues. In this paper, a new type of annulus cleaning tool is developed, incorporating the H- B non-Newtonian fluid model and a coupled CFD-DEM to construct a numerical model for analyzing the cuttings transport behavior within the multi-layer wellbore annulus using the cleaning tool. The model, validated against experiments, reveals factors affecting Cuttings Transport Ratio (CTR). Through Box- Behnken Design (BBD), Response Surface Methodology (RSM), and Analysis of Variance (ANOVA), a correlation function for CTR is derived to optimize the cleaning tool parameters. Findings show an initial increase then decrease in CTR with nozzle quantity, diameter, and angle. Decreasing hydraulic diameter enhances CTR, whereas nozzle diameter variation has minimal impact at smaller diameters. After optimization, CTR reaches 95.76% with 4 nozzles of 10mm diameter, 32° angle, and 57mm hydraulic diameter. These results guide cleaning tool optimization design , improving cuttings transport efficiency, and ensuring safe oil and gas production.

CFD SIMULATION OF CUTTINGS TRANSPORT IN ECCENTRIC HORIZONTAL AND INCLINED ANNULUS

This work deals with the cuttings transport in eccentric directional wellbore based on computational fluid dynamics (CFD) simulation using Ansys Fluent. Oil and gas industries have shifted to directional drilling for excessive oil exploration. Improper borehole cleaning leads to severe drilling problems that lead to permanent loss of the drilling site. The effect of wellbore inclination and eccentricity on cuttings transport is investigated for the slurry inlet velocity, rotation of drillpipe and cuttings size. The considered flow is two-phase flow primary phase is carboxymethylcellulose-bentonite solution and secondary phase is cuttings of different sizes. The Eulerian-Eulerian multiphase model has been implemented for flow through annulus along with renormalization group <i>k-ε</i> mixture turbulence model. The important findings related to the effect of eccentricity and borehole inclination on cuttings transport has been explored for various drilling parameters. The required drilling fluid velocity increases for cuttings transport as the eccentricity increases. The drillpipe rotation is more effective in cuttings transport for borehole inclination of 0 and 60 deg for <i>e</i> = 0.5 as compared to <i>e</i> = 0.75. The eccentricity enhances the cuttings transport in a horizontal annulus as compared to an inclined annulus. The rate in increase of axial pressure drop is more for <i>e</i> = 0.5 as compared to <i>e</i> = 0.75 considering drillpipe rotation.

Cuttings Transport With Oil- and Water-Based Drilling Fluids

Abstract Deviated well sections are common in most modern offshore well construction designs. In the North Sea region, which is a good example of mature areas, practically all producer or injector wells have highly deviated well sections. These wells must be constructed in an optimal manner with respect to functionality, drill time, risk, and all affiliated costs. Throughout the years, most hole-cleaning and hydraulic models have been developed based on experimental results from relatively small-scale laboratory tests with model fluids. Hole-cleaning properties and hydraulic behavior of practical drilling fluids intended for field application differ from those of most model fluids. Furthermore, results from small diameter tests may not always be relevant for or scalable to field applications because of the presence of a huge number of dimensional quantities like velocity, fluid properties, time, length, and other scale differences. Hence, studies using sufficient large-scale experimental facilities in controlled laboratory environments with the application of various field-designed drilling fluids are necessary to improve engineering models and operational practices. The current paper presents results from such laboratory tests where field-applied drilling fluids have been used. In comparison tests, the different drilling fluids have similar density and viscosity functions within the relevant field-applied shear rate range. This shear rate range is also assessed in the tests. One of the drilling fluids is oil-based, and the other one is an inhibitive water-based drilling fluid of the KCl/polymer type.

Transportation of cuttings by drilling mud in horizontal wells. Part 2. Numerical results of drilling at optimal rheological properties of mud

The relevance. Ensuring technological equipment operation efficiency when drilling wells with an arbitrary orientation of their wellbores. In particular, the search for productive hydrocarbon reservoirs requires drilling deeper wells with extended horizontal sections, for which the removal of the cuttings bed is the key problem of modern drilling. The aim. Study the features and establish the patterns of cuttings movement through the annulus eccentric space formed by a drill string and well walls under various modes (in-situ) and drilling conditions within the framework of modern mathematical models of hydrodynamics, numerical algorithms and approaches implemented in ANSYS CFD. Optimize the parameters that determine drilling, such as an inclination angle, mass-average velocity and morphology of the inlet rheologically complex viscous flow to form the maximum allowable drilling velocity for various combinations of mud effective viscosity and mixture flow rate. Give practical recommendations for engineers to reduce time, costs and material resources for maintenance and optimization of well cleaning. The object. A well with an eccentric core and an extended horizontal section operating in modes and conditions close to real drilling. The methods. Complex of physical and mathematical analysis and numerical modeling of hydrodynamics and mass transfer in homogeneous and heterogeneous continuous media. The media were widely tested on the class of internal rheological complex flows, the verification of which was carried out under appropriate conditions, performed by other authors when solving problems of drilling and cleaning wells. The results. The paper presents the results of a numerical study of hydrodynamics of a dispersed flow of a rheological complex viscous mixture of a drilling fluid with the properties of a Herschel–Bulkley type fluid and sand particles in wells with an arbitrary generatrix of its wellbore in an eccentric space. The results are required to clarify the features that accompany direct-flow and swirling flow (the moving wall method), identify the patterns in such modes, accounting for which allows for effective cleaning of the annulus. The calculations were performed within the framework of modern mathematical models of the RANS-method and the Euler–Lagrangian approach to describing the motion of heterogeneous media, implemented in the ANSYS CFD software and efficient numerical algorithms for determining intra- and interfacial processes of mass and momentum transfer in mixtures. The authors have determined that when drilling a vertical section, the most effective parameter in terms of cleaning control is the effective viscosity of the mud; the most problematic configurations for cleaning are wells with sloping sections at angles close to the vertical. When drilling a horizontal section, the eccentricity of the drill string creates “the dead” zone of flow and complicates cleaning. This zone should be removed by creating swirling flow conditions through relatively weak rotation of a drill string (30–60 rpm). When drilling inclined sections, it is necessary to reduce a solution viscosity (preferably to the level of fresh water) and increase the flow rate (in this case, to 2 m/s or higher). When drilling a horizontal section, a mud with a viscosity close to fresh water is recommended at flow rates of about 2 m/s (or 640 gpm) at the well inlet and a maximum drilling velocity of 9 m/h.

Study on cuttings transport behavior in annulus and bottom-hole using CFD-DEM

The increased demand for energy has led to the development of innovative drilling methods and technologies in the oil and gas industry. Inefficient transportation of cuttings causes downhole cleanliness issues, which have drawn widespread attention. One way to overcome cuttings transport inefficiency is to use suitable modeling methods to determine capable drilling parameters that will ensure the effective removal of cuttings particles. In this paper, Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) are combined to deeply investigate the impact of various drill parameters on cutting transport. The effects of cuttings particle size, eccentricity, fluid velocity, drill pipe/bit rotation speed, and bit offset angle are analyzed by studying the velocity of cuttings particles and the spatial distribution of particles in the annulus and bottom-hole. The results show that an increase in eccentricity and particle size reduces the velocity of cuttings particles, with the velocity decreasing more significantly when the eccentricity is greater than 0.5 and the particle size exceeds 2 mm. An increase in fluid velocity and speed of drill pipe/bit significantly increases the velocity of cuttings particles, which has a positive feedback effect on the migration of cuttings particles in the downhole. Bit offset angle leads to changes in the bottom-hole spatial structure and reduces the cuttings transport efficiency. These findings provide a useful strategy for improving cuttings migration and downhole cleaning.