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

The cuttings transport is a critical factor influencing the success of horizontal well operations. Most existing studies focus on cuttings transport using Newtonian or non-Newtonian single-phase fluids. In present study, a numerical model based on the kinetic theory of granular flow is employed to simulate the flow of non-Newtonian fluid with cuttings, using an Euler-Eulerian two-phase model. The fluid properties are described based on the power-law rheology model. The effects of cutting size, drill pipe eccentricity, diameter ratio, and fluid rheology under varying fluid velocity conditions and drill pipe rotation are analyzed with respect to the cuttings transport rate and pressure drop. The results show that drill pipe rotation increases the cuttings transport rate, though the effect is limited. The pressure drop increases with higher drill pipe rotation. However, the increase in fluid velocity and the presence of non-Newtonian fluids significantly improve the cuttings transport performance. A decrease in fluid flow velocity in an eccentric annulus results in a reduction in the cuttings transport rate. Moreover, an increase in the cuttings diameter ratio at lower flow velocities has a more pronounced impact on the transport rate. The findings of this study are essential for optimizing drilling parameters to enhance the cuttings transport rate.

SummaryHorizontal wells are designed to have smooth (straight), curved, and lateral sections. However, the actual drilled path usually suffers from unwanted undulations from the planned well trajectory known as wellbore tortuosity. Wellbore tortuosity can slow the drilling penetration rate, aggravate drillstring vibration and buckling, complicate the casing and cement job, and lead to inaccurate wellbore position. This paper presents a validated computational fluid dynamics (CFD) model to investigate the impact of wellbore tortuosity on hole cleaning. The Eulerian-Eulerian approach is used to simulate solid-liquid laminar flow in annular geometry using polyhedral mesh. Then, the impact of wellbore tortuosity on cuttings accumulation, annular pressure loss, and fluid velocity was investigated and compared with the flow behavior in a straight horizontal well. A parametric analysis of spiral period length, spiral amplitude, drillstring rotation, flow rate, annular eccentricity, drilling rate of penetration (ROP), and cuttings size was conducted to assess their influence on cuttings transport in spiral tortuous holes and their relative magnitude to other design or operating factors.Simulation results show that polyhedral mesh is an optimum meshing technique for spiral profile geometry. Wellbore tortuosity aggravates hole cleaning in lateral sections based on the length of the spiral period and/or the spiral amplitude. Reduction in cuttings velocity was observed in the top part of the spiral geometry (crest), causing large deposition of cuttings in this area compared to the spiral lower part (trough). Drillstring rotation from 0 to 200 rev/min is the critical range for efficient hole cleaning in spiral geometry. Cuttings size can improve cuttings accumulation if the particle size is larger than the viscous layer located near the bed velocity profile. The drilling ROP and annular eccentricity aggravate cuttings accumulation and bed deposition in a spiral hole, similar to what is normally observed in straight horizontal wells.

In the production and pipeline transport of various fluids, such as oil and natural gas, solid particles may be entrained in the fluid. These particles, commonly consisting of numerous types and sizes of sand, can travel apart from the streamlines of the fluid and impact the surface of the pipe. With time, enough particles may impinge a pipe wall at a sensitive location, such as an elbow or tee, to result in a measurable wall thickness loss. This may ultimately lead to severe erosion damage causing a leak in a pipeline, a dangerous and costly problem. As a result, a pipeline’s service life may often depend on the rate at which a pipe wall is eroded. The erosion rate, or amount of material loss over a certain time period, depends on a large number of factors. The target material, or material experiencing a thickness loss, such as a pipe wall, influences the rate at which damage occurs. Its density, hardness, yield strength, and microstructure combine to present a certain resistance toward erosion occurring from solid particle impact. Furthermore, the solid particle’s diameter, sharpness, and shape will influence its trajectory, speed, and momentum transfer into the target, thereby requiring the analysis of various particle types in predicting erosion. Finally, the carrier fluid being transported through a pipeline will further affect the solid particle’s movement as it approaches the target. As a result, the fluid’s density and viscosity must be carefully considered in particle tracking and erosion analysis. By considering the aforementioned properties of the target, solid particles, and carrier fluid, it is desirable to be able to predict the erosion rate from a single erosion equation. Other factors depending on these properties may be found in this expression, such as particle impact speed and impingement angle at the target. Velocity measurements by way of Laser Doppler Velocimetry (LDV) were made for particles entrained in a viscous liquid traveling in a submerged, direct impingement jet. In an attempt to obtain representative particle impact characteristics during material erosion, data was collected from the nozzle exit to the target surface in order to track fluid and particle velocities prior to impact with a wall. Average particle sizes of 120 and 550 μm were used to represent typical sand sizes, while much smaller particles with an average diameter of 3 μm were utilized in fluid velocity measurements. The carrier fluid viscosity was varied from 1 to 100 centiPoise, while the nozzle flow rate and fluid density were maintained constant. Changes in approach and estimated impingement velocity occurring due to fluid viscosity and particle size are then presented. For the same impingement geometry and flow situations, metal loss erosion measurements have been made by way of an Electrical-Resistance (ER) probe. Oklahoma #1 sand particles with an average diameter of 150 μm were suspended in a viscous carrier fluid at a measured sand concentration. The measured erosion rate and particle velocities at near target wall locations are then compared to observe the effect of viscosity on material erosion and impact speed. Particle tracking and erosion predictions made by Computational Fluid Dynamics (CFD) can then be experimentally validated.

Application of foam as drilling fluid for cuttings transport in horizontal and inclined wells: A numerical study using computational fluid dynamics

Gas turbines are of great importance in industry. In the turbine section within a jet engine, thermal barrier coatings (TBCs) are utilized to protect the metal turbine blades, thus improve the efficiency of engine. However, this coating is extremely vulnerable to attack by injected particulates. This ingested particulate is often referred to as "CMAS" (Calcia-Magnesia-Alumina-Silica). Among all the CMAS materials, Volcanic Ash (VA) is the most common type which aeroengines may encounter during the flight. This type of CMAS material would melt in the combustion section by ultra high temperature and then impact the turbine blades with relatively high speed. Some of the particles would then stick on and bond with the TBC, thus cause degradation of the protecting coating. In this way, the jet engine would be permanently damaged. In the recent years, experiments have been done by different researchers to elaborate the effect of CMAS materials on TBCs. However, there is still a lack of knowledge in the bonding mechanism and physical adhesion between the CMAS particles (especially VA particles) and the substrate. A study of VA particle impingement is required in order to understand particle impingement, phase transition and heat transfer, bonding mechanism and splat morphology in detail. In this research, experiments were carried at Cambridge University, by Prof. Trevor William Clyne, Dr. James Dean and Dr. Catalina Taltavull to reproduce the VA-substrate impingement in jet engine. A Vacuum Plasma Spray (VPS) system was utilized to create a high-temperature, high-velocity flow field. Different types of Volcanic Ashes (VAs) were introduced into the experimental set-up. Sticking rate, Scanning Electron microscope (SEM) micrographs of deposition morphology were examined and collected. Chapter 3 elaborates the details of this experiment set-up and data collected from the experiment. This experiment set-up is utilized by the author for building numerical models and the result of this experiment is used to validate the numerical models. Three numerical models were built to perform a systematic study. Firstly, in Chapter 4, a Computational Fluid Dynamic (CFD) model was created to simulate the steady-state of the VPS flow field. The Discrete Particle Method (DPM) model was then utilized to simulate the injection of volcanic ash particles. After calculating the BI number, non-isothermal effects within the ceramic particles were simulated by introducing the heat transfer function by a user-defined function (UDF). This model gives the temperature gradient within and velocity of the in-flight VA particles at any time during the spray. It is shown that small particles (diameter < $10____ ____mu m$) would easily be melted and reach the iso-thermal state. However, these particles would be largely influenced by the flow field thus bypass the turbine blades. The large particles (diameter > $50____ ____mu m$) would easily impact the turbine blades, but would remain unmelted due to the large grain size. It is concluded that VA particles with diameter of $15____ ____mu m$ to $40____ ____mu m$ are the most "dangerous" particles, because these particles have both relatively high possibility to be melted, and high possibility to impact thus adhere on the substrate. Second of all in Chapter 5, systematic study of Yttria-stabilized Zirconia (YSZ) particle impingement and deposition on stainless steel in thermal spray process has been performed. A Coupled Eulerian and Lagrangian model was developed. This model contributes to simulate the process of semi-molten particle impact. By utilizing this model, both the large deformation of liquid part and the plastic deformation of the solid part could be extracted. One fully molten and two semi-molten(solid core with liquid shell and solid shell with liquid core) cases were studied. The results of the numerical model matches well with the experiment and analytical data. Interest parameters such as velocity, temperature, fraction of liquid part were varied. The contact area, splat morphology and local contact temperature were collected and studied. It is shown that, the larger the liquid fraction is, the larger the contact area would be. Moreover, effect of roughness of substrate is also studied. It is suggested that substrate roughness whose average asperity size is higher than the 1/10 of particle size is beneficial for adhesion. Third of all in Chapter 6, in order to simulate the impact for high-viscosity glass-state ceramic particles, Smoothed Particle Hydrodynamic (SPH) model was built. For high/ultra viscosity cases, traditional CFD method and Finite Element Method (FEM) would be extremely slow. SPH model transfers the Eulerian equations into Lagrangian equations. By utilizing this method, computational resources could be saved, and high viscosity impact could be simulated. The SPH algorithm was coded and equations for heat transfer was introduced to simulate the solidification of liquid. Systematic study were performed by utilizing this model. Viscosity, contact angle, velocity of particles were varied. Contact area, splat morphology and solidification at the contact area were examined. It is shown that, large contact angle would result in large contact area. However, particles impingement with low viscosity and high contact angle could result in the break up of the particles. The similar phenomena could be seen in experiment - small particles have lower viscosity and are approaching the substrate with a large contact angle. Therefore, the deposition of these types of particles show an obvious evidence of break up and oblique impact.

A one dimensional transient mechanistic model of cuttings transport with conventional (incompressible) drilling fluids in horizontal wells has been developed. The model is solved numerically to predict cuttings bet height as a function of drilling fluid flow rate and rheological characteristics (n, K), drilling rates, wellbore geometry and drillpipe eccentricity. The results of the sensitivity analysis showing the effects of various drilling operational parameters on the efficiency of solids transport are presented. The model developed in this study can be used to develop computer programs for practical design purposes to determine optimum drilling fluid rheology (n,K) and flow rates required for drilling horizontal wells. Introduction Poor hole cleaning can lead to pipe sticking, higher drag and torque, slower rate of penetration, formation fractures and wellbore steering problem1. It has been estimated that one third of stuck pipe problems are due to inadequate hole cleaning2. Azar and Sanchez3 presented a comprehensive review of the factors that affect cuttings transport and listed drilling fluid rheology, flow rate, annular eccentricity, drillstring rotation and drilling rate as the most important ones. Iyoho4 presented some extensive experimental results on the cuttings transport performances in directional wells. He found that the major factors affecting cuttings transport are drilling fluid velocity, inclination angle, drilling fluid viscosity and drilling rate. Specifically, it was observed that the increase of hole angle or drilling rate had negative effect on cuttings transport, while higher drilling fluid viscosity was more favorable than the lower drilling fluid viscosity for cuttings transport within the same flow regime, and annular eccentricity had moderate effect although the concentric annulus provided the best transport performance. Larsen5 confirmed Iyoho's results by concluding that the angle of inclination and drilling fluid flow rate had the most significant effect on hole cleaning. Tomren et al. 6 extended the Iyoho's work and found that concentric annulus yields maximum efficiency of cuttings transport for inclined holes. They also determined that, in inclined annulus, cuttings bed formation in high viscosity drilling fluid was slower than that of in low viscosity drilling fluid in laminar flow. Okrajni and Azar7 particularly investigated the effects of drilling fluid rheology on hole cleaning in directional wells. The drilling fluids with yield values in the range of 0 to 9.6 Pa (0 to 20 lbf/100 ft2) and with three values of YP/PV ratio (0.5, 1.0 and 2) were used in the tests. Investigations revealed that drilling fluid rheological properties (yield value and YP/PV ratio) generally did not affect the cuttings transport under turbulent regime although the drilling fluid with higher yield value resulted in better cuttings transport under laminar flow regime. The trends observed were identical for both the bederosion (annulus-cleaning) and cuttings transport experiments. An experimental study of drilled cuttings transport in inclined boreholes by Ford et al. 8 found that cuttings were removed by two distinct mechanisms including rolling/sliding and transport in suspension. Seven slurry flow patterns were observed including homogeneous suspension, heterogeneous suspension, suspension/saltation, sand cluster, separated moving bed (dunes), continuous moving bed and stationary bed.

Solid particle erosion is a micromechanical process that is influenced by flow geometry, material of the impacting surface, impact angle, particle size and shape, particle velocity, flow condition and fluid properties. Among the various factors, particle size and velocity have been considered to be the most important parameters that cause erosion. Particle size and velocity are influenced by surrounding flow velocities and carrying fluid properties. Higher erosion rates have been observed in gas-solid flow in geometries where the flow direction changes rapidly, such as elbows, tees, valves, etc, due to local turbulence and unsteady flow behaviors. This paper presents the results of a Computational fluid dynamic (CFD) simulation of dilute gas-solid flow through a U-Bend and the dynamics behavior of entrained solid particles in the flow. The effect of liquid and gas velocities on location of erosion were investigated for 50, 100, 150, 200, 250 and 300 microns sand particles. Three different fluid velocities of 15, 30.48 and 45 m/s were used in the CFD analysis. The magnitude and location of erosion presented in the paper can be used to determine the areas susceptible to maximum erosive wear in elbows and U-bends, along with corresponding rate of metal loss in these areas.

Cuttings transportation from the bit up the annulus to the surface is one the essentialfunctions that are performed by drilling fluid. Predication of drilling fluid efficiency totransport cuttings in the annulus is very complicated due to numerous parameters that haveaffected drilling operations. Computational Fluid Dynamics (CFD) is widely used as anumerical technique in handling complex multiphase flow problems in differentoperational conditions.The present work has taken the advancement of CFD to computationally analyse theinfluence of the effects of various parameters like drilling fluid rheology, flow rate, piperotation, cuttings density, shape, concentration and drilling fluid- cuttings particle couplingregimes on the cuttings transport in a vertical wellbore. The CFD simulation was carriedout by using transient solver of ANSYS-FLUENT CFD commercial code.The dense discrete phase model (DDPM) is suggested in this work to overcome themain shortcomings of Eulerian–Eulerian and CFD-DEM approaches in simulating drillingfluid-cuttings flow. Also, some of the experimental investigations were involved indetermining the fluid physical properties and essential input data to perform the CFDsimulations. Regarding the results validation and verification, well agreement has beenachieved between results obtained in this study with those reported in other studies

Supercritical water fluidized bed is a promising reactor which can realize the efficient and clean gasification of coal to produce hydrogen. As the high pressure and temperature inside supercritical water fluidized bed, the study of the detail flow behaviors needs the help of numerical method. Considering the limitation of the two-fluid method and discrete element method, the computational particle fluid dynamics method was applied to this work. When particle size distribution was taken into consideration, the simulated results showed that the transformation from fixed bed regime to fluidized bed regime is a gradual process. With the increase in superficial fluid velocity, particles in small diameter migrate to the top of the bed and there exits layering phenomenon in the bed. Besides, though the particles are categorized as Geldart B group, the minimum fluidization velocity is not equal to the minimum bubbling fluidization velocity and there is a complicated bed expansion process after incipient fluidization. The bed expansion process is also influenced by the particle size distribution.

The impact of particle size and concentration on the characteristics of solid–fluid two-phase flow in vertical pipe under pulsating flow

Accurate pressure drop estimation is vital in wellbore hydraulic design. The present study investigates the effects of diameter ratio, fluid velocity, fluid type, fluid rheology and drillpipe rotation speed on pressure drop in eccentric horizontal wellbore with the presence of cuttings using computational fluid dynamics (CFD). The drillpipe is positioned at eccentricity of 0.623 and rotates about its own axis at 80 rpm and 120 rpm. The diameter ratio varies from 0.64−0.90. Results show significant increase in pressure drop with increasing fluid velocity and diameter ratio. Increase in drillpipe rotation speed from 80 rpm to 120 rpm shows insignificant effect on pressure drop for both Newtonian and non-Newtonian fluids. Non-Newtonian fluid exhibited large pressure drop compared to Newtonian fluid especially at low fluid velocities. Fluid rheology effects are also discussed. Experimental data confirmed the validity of the current model setup with a mean percentage error of 0.84%.

Current API RP13D guidelines outline 3 methods for determining hole-cleaning efficiency based on wellbore angle. Method 1, used in low-angle wellbores (<30°) compares cuttings slip velocity with annular velocity to determine a transport ratio and cuttings concentration. Method 2, also used for low-angle wellbores (<30°) derives a carrying capacity index (CCI) based on bulk annular velocity, fluid density and power-law rheology. Method 3, used in high-angle wellbores (<30°) derives a transport index (TI) based on fluid rheology, density, and flow rate. TI is then plotted on an empirically derived chart (Luo et al., 1992, 1994) to determine maximum allowable rate of penetration (ROP) that should ensure efficient hole cleaning. Although these methods are considered recommended practices by API, Method 3 (TI) is based on an outdated study (Luo et al., 1992) with limited scope (one flow loop, one field test). Additionally, this method neglects the importance of drill pipe rotation and pipe eccentricity in cuttings transport efficiency, which has been proven to be a factor in other studies (Akhshik et al., 2015; Sanchez et al., 1997b). This paper highlights the shortcomings of current API standards and identifies what effects contributing factors such as pipe eccentricity and drill pipe rotation rates may have on cuttings transport efficiency. Further, this paper discusses the impact pipe-to-hole area ratio and wellbore flow area have on the effects of drill pipe rotation and flow channeling. Five horizontal wellbores were modeled using Siemens Star CCM+ Computational Fluid Dynamics (CFD) software, with bottom-eccentric 4 ½″ drill pipe placement, in annular diameters of 6¾″, 7 ⅞″, 8 ⅜″ 8 ½″ and 8 ⅝″. Additionally, one bottom-eccentric 5″ drill pipe in an 8 ¾" wellbore was modeled to compare identical pipe-to-hole area ratios with different flow areas. Simulations were run with drill pipe rotation speeds increasing from 0 to 180 RPM, in 30 RPM increments. In order to determine the impact fluid rheology has on flow channel development, both medium density oil-based muds and light density water-based muds were modeled and compared. Bulk annular flow velocity was set to 100 ft/min, to maximize the observable effects of drill pipe rotation. Bulk average velocity was calculated from cross sectional area, determining both annular velocity (velocity parallel to wellbore) and absolute velocity (fluid velocity magnitude regardless of direction). The resultant velocity profiles were used as the annular velocity component in API CCI and TI calculations and compared to bulk annular velocity. In addition to observing fluid velocity for CCI and TI calculations, changes in effective viscosity from the onset of pipe rotation was also analyzed to determine changes in wellbore parameters that may affect cuttings transport.

The ball valve is an essential piece of equipment in an oil and gas pipeline. The sand particles transported through the pipeline can cause erosion and wear to the ball valve, thus causing it to fail, leading to serious safety hazards. In this paper, the self-designed erosion experiment method was combined with computational fluid dynamics (CFD), while the Euler-Lagrange method was also introduced to optimize the Oka erosion model and Ford particle-wall rebound model. The erosion mechanism and characteristics of the ball valve sealing surface in gas-solid two-phase flow were simulated, while the erosion condition of the specimen was analyzed and compared when exposed to different factors, such as different particle velocities, impact angle, particle size, and specimen materials. The experimental data conformed well to the CFD erosion simulation data, verifying the accuracy of the CFD simulation analysis. The results indicated that the worn surface was caused by various wear mechanisms, while a “stagnation zone” was identified at the center of the specimen. The maximum erosion area, which was U-shaped, was also located at the center. The erosion rate increased in conjunction with an increase in the particle velocity and size, both of which failed to affect the erosion pattern. The erosion rate initially increased, after which it decreased with the impact angle, reaching the maximum value at an impact angle of 30°. This paper summarizes the erosion failure mechanism and characteristics in gas–solid two-phase flow and provides both technical support and a theoretical basis for the on-site maintenance of essential vulnerable parts in the pipeline, such as ball valves.

This study was conducted to gain a more in-depth understanding of solids transport for coiled tubing workovers, cleanouts and drilling applications. Cuttings or particle transport in Coiled Tubing operations is a complex problem that is affected by numerous parameters. Predicting effective cuttings transport requires all of these parameters to be considered simultaneously. Tests were conducted to determine the effects of the following parameters: I) Different particle size, II) Fluid rheology, including water, gel, and multi-phase fluids, III) Pipe eccentricity, coiled tubing positioned on the low and high side of the wellbore. The effects of the different parameters were investigated in two different modes: the circulation mode, that involves the development of a cuttings bed or build-up of cuttings in the wellbore, and hole cleaning mode, which is cleaning out an existing cuttings bed. It will be shown that the results indicate: 1) for the tested particle size range (0.150 – 7 mm), cleaning efficiency is partly dependant upon the particle’s size, 2) with suitable agitation, a gelled fluid is more effective for cuttings transport than water in a highly deviated wellbore, 3) Pipe eccentricity has an effect on cuttings transport for different fluids and 4) for complete wellbore clean-up it requires many more hole volumes than previous ‘rules of thumb’ would indicate.

An Eulerian-Lagrangian CFD study of a particle settling in an orthogonal shear flow of a shear-thinning, mildly viscoelastic fluid