Cuttings Transport Research Articles

Experimental investigation of hydrate formation, plugging and flow properties using a high-pressure viscometer with helical impeller

Slurry transport has become a subject of interest in several industries, including oil and gas. The importance of slurry/solid transport in the oil and gas industry is evident in areas of cuttings transport, sand transport and, lately, hydrates. Hydrate formation, if not properly monitored and controlled, may lead to pipeline blockage. To avoid pipeline blockage and other hydrate formation risks, chemical additives are added to the system. Additives such as anti-agglomerants help improve hydrate transportability by dispersing the formed hydrates into slurries and preventing them from sticking to the pipe wall. This enables transportation of highly concentrated slurries. However, the high hydrate volume fractions (HVF) slurries may exhibit complex rheology. There is therefore a great need to correlate flow properties such as friction factor and viscosity to HVF. Hydrate slurry transport is important whether hydrates are deliberately generated for energy storage purposes or hydrates formed because of the prevailing flow conditions. However, when determining the viscosity of a fluid containing solid particles, the conventional viscometer types such as concentric cylinders and cone and plate are often not suitable. This is because either the narrow gap would not accommodate the particle size or their inability to maintain the particles suspended leading to bed formation. In this work, a high-pressure mixer-type viscometer was used to generate and characterize hydrate slurries. This work aims to generate a significant amount of hydrate slurry characterization data that may be used as basis for better rheometer designs, hydrate slurry flow properties modeling or integration of hydrate transportability into general multiphase modeling. Results showed that intermediate watercuts posed the greatest pipeline plugging risk for all the oils tested. The amount of transportable hydrates increased with oil viscosity. Generally, hydrate slurries generated exhibited shear thinning behavior that increased with increasing hydrate volume fraction. However, the overall rheology of these slurries is a complex function of the oil used, watercut, gas added to the system and hydrate solid fraction. Lowering shear rates for high HVF systems resulted in separation. Results in this work further suggest that hydrate transportation may be possible with minimum risk if anti-agglomerants are used and high enough shear is applied. On the other hand, if no anti-agglomerant is used, severe aggregation may result in flow line plugging.

Interior Research of Resistance to High 220 Degrees Heat Resistance Drilling Fluid System

Focusing on high temperature rheological stability and filtration control of high temperature resistant drilling fluid system, in this context, further research has been made on mud formula and the formula of high temperature resistant drilling fluid system was optimized, Finally, a kind of organic silicon drilling system with high 220 degrees heat resistance and good performances was developed, in combination with the evaluation of the validity for the overall performance of the drilling system. In virtue of the behavior of high temperature stabilizing agent, the system provided excellent shale inhibition, lubrication and tough hole stabilization. The filtrate value is low, the mud cake is thin and tough, which are good for bit balling prevention; the capacity of cuttings transportation is efficient, as well as the easy-control rheological property. In high salinity conditions, the entire drilling fluid properties maintain stability; limit the pollution of 6% NaCl or 0.5%CaC12. The composition of fluid is non-toxicity, non-fluorescence, which is fitful for deep drilling.

Evaluation of Local Viscosifiers as an Alternative to Conventional Pac-R

Hole cleaning is a key parameter in every drilling program. Efficient bottom hole cleaning is achieved through adequate transportation of cuttings from the wellbore to the surface. Modified natural polymers like Poly anionic cellulose regular (PAC-R), with bentonite clay has been used to achieve good carrying capacity of drilled cuttings in water base mud (WBM). These conventional polymers have adverse effect on the environment, especially the mud-filtrate which pollutes and contaminates the aquifer and the spent mud that requires caution for its disposal. In this work, Local viscosifers were obtained from Mucuna Flagellipe (Ukpo), Brachystegea Eurycoma (Achi), Afzelia Africana (Akpalata) and Detarium microcapum (Ofor) as a substitute for the imported viscosifiers (PAC R) used as a drilling fluid additives. Water-based muds were formulated from the aforementioned locally sourced viscosifiers and that of the conventionally used viscosifier (Pac-R). Laboratory tests were carried out on the different muds formulated and their rheological properties evaluated, such as yield stress, , shear stress plastic viscosity and shear rate. The concentrations of the locally sourced viscosifiers were varied and rheological tests performed show that Mucuna Flagellipe (Ukpo) had a better viscosity compared to Achi, Akplata and Ofor of the same concentration. It was also observed that 5g of Mucuna Flagellipe (Ukpo) and 8g of detarium microcapum (Ofor) gave an equivalent rheological properties of 27lb/100ft2and 26lb/100ft2 as yield stress when compared to2g of Pac-R which gave a yield point of 29lb/100ft2 at a temperature of 180˚F. Also, 8g of Mucuna Flagellipe (Ukpo) gave an equivalent of 5g of PAC-R. Hole cleaning parameters such as slip velocity, annular velocity and cuttings transport efficiency were also considered for evaluating the effectiveness of the proposed muds with local viscosifiers and conventional viscosifiers on hole cleaning. 5g and 8g of Mucuna Flagellipe (Ukpo) compared favourably with PAC-R in terms of hole cleaning. Finally in terms of cost, the locally sourced viscosifiers are cost effective when compared with the conventional vscosifier. Therefore, locally sourced viscosifiers (Mucuna Flagellipe, Ukpo) can be used as a substitute to the conventional Pac-R when drilling top hole at a temperature of 150˚F and below since these holes are drilled within a thermal gradient of 150˚F and below in the Niger delta region of Nigeria.

CFD modelling and simulation of drill cuttings transport efficiency in annular bends: Effect of particle sphericity

Accurate prediction of the flow behaviour of drill cuttings carried by a non-Newtonian fluid in an annular geometry is important for the successful and efficient design, operation, and optimisation of drilling operations. Although it is widely recognised that practical drilling operations hardly involve perfectly spherical cuttings, the relative ease in mathematical description coupled with speedy computation are the main reasons for the prevalence of this simplifying assumption. The possibilities offered by the modification of the interphase exchange coefficient of the Syamlal-O’Brien model as well as its scarce implementation in literature have motivated the authors to delve into this area of research as far as the transport phenomena of non-spherical drill cuttings is concerned. Another aspect of this work was influenced by the need to understand the flow dynamics around bends (horizontal to inclined and inclined to vertical sections) during deviated drilling operations using two high viscosity muds (0.5% CMC and 0.5% CMC + 4% Bentonite mud). The Eulerian-Eulerian model was adopted for this study while considering particle sphericities of 0.5, 0.75 and 1 and diameters of 0.002 m, 0.003 m, 0.004 m, 0.005 m and 0.008 m respectively. It was discovered that particle deposition intensifies at the inclined-to-vertical bend compared to other locations in the flow domain. We also observe increased dispersion effects and transport velocities of non-spherical particles compared to particles of a perfectly spherical geometry. Furthermore, an improvement in the rheological properties of the drilling mud shows a remarkable increase in cuttings transport efficiency especially with the smaller particles. However, increased deposition of larger particles still poses a challenge to the wellbore cleaning process despite this rheological enhancement. The proposed CFD modelling methodology is thus capable of providing critical insight into the dynamics of cuttings transport, and the resulting computational observations are consistent with relevant experimental investigations.

Experiments and Simulations for Horizontal Pneumatic Transport of Dry Drill Cuttings

AbstractInvestigation of the possibility of using a pneumatic conveying technique for the transportation of dry drill cuttings is the main objective of this study. Both pilot‐scale experimental and simulation approaches were carried out for sand, which was used as a model material that mimics the properties of dry drill cuttings. Simulations based on the multiphase particle‐in‐cell method, which is a Eulerian‐Lagrangian model, were used to predict the pressure drop, and the predictions are in good agreement with the experimental results. Both approaches supported the possibility of using a pneumatic conveying technique for the transportation of dry drill cuttings under the tested conditions. The study provides the foundation for further analysis of the pneumatic conveyance of wet drill cuttings.

A solids-free brine drilling fluid system for coiled tubing drilling

Abstract There are many problems associated with coiled tubing drilling operations, such as great circulation pressure loss inside pipe, difficulties in weight on bit (WOB) transferring, and high probability of differential sticking. Aiming at these problems, solids-free brine drilling fluid system was developed on the basis of formulation optimization with brine base fluid experiment, which was evaluated and applied to field drilling. Based on the optimization of flow pattern regulator, salt-resisting filtrate reducer, high performance lubricant and bit cleaner, the basic formula of the solids-free brine drilling fluid system was formed: brine + (0.1%−0.2%) NaOH + (0.2%−0.4%) HT-XC + (2.0%−3.0%) YLJ-1 + (0.5%−2.0%) SDNR + (1.0%−2.5%) FT-1A + (1.0%−5.0%) SD-505 + compound salt density regulator. Lab evaluation showed that the fluid had satisfactory temperature resistance (up to 150 °C), excellent cuttings tolerance (up to 25%), and strong inhibition (92.7% cuttings recovery); Moreover, its lubrication performance was similar to that of all oil-based drilling fluid. The wellbore could be fairly cleaned at annular up-flow velocity of more than 0.8 m/s if the ratio of yield point to plastic viscosity was kept above 0.5. This fluid system has been applied in the drilling of three coiled tubing sidetracking wells in the Liaohe Oilfield, during which the system was stable and easy to adjust, resulting in excellent cuttings transportation, high ROP, regular hole size, and no down hole accidents. In summary, the solids-free brine drilling fluid system can meet the technical requirements of coiled tubing drilling.

Numerical Simulation and Modeling of Critical Sand-Deposition Velocity for Solid/Liquid Flow

SummaryEfficient transport of sand or cuttings is very important in the oil and gas industry, and the fluid velocity in these processes should be sufficiently high to keep particles continuously moving along the pipe. This minimum fluid velocity below which particles deposit—defined as the critical velocity—depends on various factors, including flow regime, particle size, particle concentration, phase velocities, and fluid viscosity. The objective of this study is to investigate the effect of parameters such as particle size and liquid viscosity on solid/particle transport in horizontal pipelines by use of computational-fluid-dynamics (CFD) simulations and to validate the numerical-model predictions with experimental data. Also, a mechanistic model that is based on force balance is proposed to predict the critical velocity under various experimental conditions.CFD simulations have been conducted with a commercially available software (ANSYS-FLUENT). An Eulerian model with a k-ω shear-stress transport (SST) turbulence-closure model is used to simulate the fluid flow while particles are tracked as the Lagrangian phase. In these simulations, an eddy-interaction model is included to consider the effect of flow turbulence on particle tracking. The simulations are created for a 0.05-m pipe diameter with a 4-m length. The simulations are initialized at relatively high fluid velocity, which is gradually reduced until the particle velocity drops below the acceptable critical velocity.The CFD simulation and proposed mechanistic model results are validated with experimental data from literature (Najmi 2015; Najmi et al. 2016) for two particle sizes and multiple liquid viscosities. The simulation and model results show that, depending on the flow regimes (laminar or turbulent) and particle size, the critical velocity demonstrates a similar trend with carrier liquid viscosity as that of the experimental data. However, both the CFD and developed models show poor performance for higher particle size (600 µm). Also, the CFD simulations, experimental data, and proposed-model results are compared with three models currently used in the industry, namely, the Oroskar and Turian (1980) model, the Salama (2000) model, and the Danielson (2007) model.

Polypropylene beads in water-based mud for cuttings transportation improvement

Good wellbore cleaning is highly essential to cut off unnecessary spending due to related problems in drilling operations. Many new technologies have been introduced to address the poor wellbore cleaning issues. In this study, the experimental investigation focuses on the use of polypropylene-based polymer beads as a mechanism to enhance cuttings transportation in water-based mud. The primary objective of the experimental investigation is to observe the performance of the polymer beads in lifting the different sizes of drilled cuttings in water-based mud. Six different sizes of drilled cuttings, ranging from 0.50 to 3.34 mm, were used and the lifting performances were done at five different angles, i.e., 0° (vertical), 30°, 60°, 75°, and 90° (horizontal). From 250 conducted tests, the experimental results showed that the cuttings transport efficiency with the presence of polypropylene beads for small cuttings in basic water-based mud improved by 6-8 % for hole angles less than 30° and 4 % between angles of 60°-90°. Drilling mud with polymer beads transported smaller cuttings more efficiently compared to larger cuttings. Despite a relatively low recovery at highly deviated angles, the use of polymer beads has shown improvements in cuttings transportation. This approach might be suitable to transport smaller cuttings to the surface in directional wells.

CUTTINGS TRANSPORTATION MODELING IN INCLINED AND HORIZONTAL DRILLING

Efficient cuttings transport is very important for obtaining an effective drilling operation. In inclined and horizontal drilling, if we could ensure a good hole cleaning of the wellbore from the cuttings, we can avoid other drilling problems and successfully drill it to the designed depth with minimal time. Despite the long history of drilling inclined and horizontal wells there is a very small number of works devoted to this subject. The article explores the impact of various drilling parameters, and how they affect the required flow rate by modeling. The article analyzes two models developed empirically, namely Larsen model and Rubiandini model. Two simulation scenаrios of a well drilled in offshore Vietnam have been considered. The calculations based on two empirical models showed the same trend for required cuttings transport flow velocity and flow rate when drilling parameters, such as mud weight, rate of penetration, mud rhelogy varied. For vertical and inclined cases, we observe that both Larsen model and Rubiandini model predict flow rates that are close to flow rates typical in operation. For the horizontal case, the predicted flow rates don’t seem to coincide with flow rates in operation. In the conclusion, several recommendations on achieving better cuttings transport and hole cleaning are listed.

Transient modeling of one-dimensional solid-liquid flow in conduits

We consider the transient modeling of liquid-solid flow in conduits. Current models available in the literature are typically based on a three layer – two phase representation which, for the general transient case, results in a six-field model, entailing significant complexity in analysis and implementation. In this paper, we propose a transient three layer model represented by three equations (a third order PDE) by assuming a static momentum balance and then exploiting certain properties of the continuity relations. We illustrate how the transient model can be completed by introducing deposition–erosion closure relations from the literature, and describe its implementation by an upwind numerical scheme. Finally, some of the transient properties of the model are illustrated in six simulations comparing the simulated trends with six cuttings transport experiments found in the literature, motivated by application to horizontal drilling.

Cuttings-Transport Modeling–Part 1: Specification of Benchmark Parameters With a Norwegian-Continental-Shelf Perspective

SummaryIn oil and gas drilling, cuttings-transport-related problems are a major contributor to well downtime and costs. As a result, solutions to these problems have been extensively researched over the years, both experimentally and through simulation. Numerous review articles exist, summarizing not only the research history but also the qualitative effect of individual case parameters such as pump-flow rate, pipe rotation, and rate of penetration (ROP) on cuttings transport. However, comparing different studies is challenging because there is no common reference defined in the form of a typical and representative set of case parameters.To develop relevant and accurate cutting-transport models, it is critical that both experiments and models are targeting flow cases relevant for respective drilling operations. Development of a clear understanding of the industrial-parameter space, as well as establishing benchmarks, will help achieve a more-concerted effort in development of models and corresponding laboratory experiments.Other industries have established research benchmarks, such as the “NREL offshore 5-MW baseline wind turbine” (Jonkman et al. 2009) in wind-power research, providing a standardized set of case parameters and profiles, readily available for use to researchers worldwide, and resulting in straightforward benchmarking and validation as well as faster establishment of projects.For application to the modeling of cuttings-transport phenomena, we propose a methodology for deriving a well-defined and standardized set of geometrical, operational, and environmental case parameters describing various operating points of drilling operations and procedures as well as simplified problems. The methodology is exemplified with an 8.5-in.-section drilling-ahead use case with aggregated wellbore data from the Norwegian Petroleum Directorate (NPD). The relevance and application of the derived parameters are briefly discussed in light of modeling, both experimentally and through simulations. Applying this methodology before any cuttings-transport study may enable a better definition of industry-relevant case parameters.In Part 2, we will apply and discuss the derived parameter sets in the context of nondimensional numbers for assessment of scalability.

The formation and broken of cuttings bed during reaming process in horizontal directional drilling

Horizontal Directional Drilling (HDD) is an environment-friendly and high efficient method for underground utilities and pipelines crossing. The formation of cuttings bed, due to low Cuttings Transport Performance (CTP) in large-size HDD, has resulted in the overwear of reamer and been required additional borehole cleanups which will result in high construction risk and extending the work period. In order to investigate the formation and broken mechanism of cuttings bed, two tests were designed to determine the potential effect of mud rheological properties, flow rate, borehole inclination and rotation of drill rod on the cuttings bed state. The drill rod laid down at the invert of the borehole, broke the stability state of cuttings bed and take some cuttings away from the cuttings bed, which causes an incremental trend of CTP, even for the cuttings bed consisting of 8–12 mm diameter cuttings. The observations and results of the tests indicated that drill rod rotation had a positive impact on the instability of cuttings bed, whereas, YP of mud, average velocity of mud and borehole inclined shown a limited effect on it for the large-scale HDD reaming. Further study is needed to determine the details about drill rod behavior and extend the tests results by the finite element method.

A unified transient solid-liquid two-phase flow model for cuttings transport- modelling part

A unified transient model is presented for predictions of flow pattern transitions, pressure gradient, solid particle concentration in solid-liquid two-phase flow. The transient mechanistic model is based on the conservation of mass and momentum and coupled with flow pattern prediction methods. Changes of flow patterns are reflected by assigning certain terms to zeros in the general equations and changing the number of equations. Thus, the model can be automatically adjusted for flow patterns in transient simulation.A semi-implicit approach is used to solve the model. The velocities and pressures are solved implicitly based on the momentum conservation equations and the solids concentrations are updated explicitly based on the mass conservation equations.The model is validated by conducting a series of experimental tests on a full scale flow loop (0.2 × 0.11 × 25 m). The validation of the transient simulation includes the validation of the transient build-up stage and the validation of the cuttings volumetric concentration at fully developed stage. Results found that increase of the flow rate significantly reduces the build-up time, and effects of pipe rotation vary at different inclined angles. The effect of inclination angle on solids profile build-up is similar to the effects of well inclination angle on steady state cuttings concentration. Below 60°, the build-up time increases significantly as the well inclination angle increases. When the well inclination angle goes to over 60°, the effects of well inclination angle become insignificant.

Functionalization of fly ash for the substitution of bentonite in drilling fluid

Oil exploration activities have increased the demand for American Petroleum Institute (API-) grade drilling bentonite leading to a significant increase in the cost of naturally occurring bentonite and overall cost of the drilling operations. In this work, fly ash (FA) was functionalized to replace API-grade drilling bentonite for drilling of wells. Epichlorohydrin and aminopropyl triethoxysilane were used to functionalize the ultrafine-structured planetary ball-milled FA. The morphology, mineralogy, structure and specific surface area of the functionalized FA were determined by the field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry and Brunauer-Emmett-Teller analysis, respectively, to determine the efficacy of functionalized FA as a colloidal base in aqueous suspension. Fourier-transform infrared spectrometer and X-ray photoelectron spectroscopy analysis was used to confirm the grafting of alpha-glycol and amine functional group on FA surface and quantified by iodometric and acid-base titration method, respectively. The zeta potential and cation-exchange capacity of functionalized FA were found to be −47.1 to −68.1 mV in pH range 8–12 and ∼68.0 meq/100 g of functionalized FA, respectively, and were found comparable to API-grade drilling bentonite. Rheological behavior and filtration loss properties of the functionalized FA in aqueous suspension were determined and compared with the API-grade drilling bentonite yielding similar results. The performance of the functionalized FA-based drilling mud system involving tamarind gum and polyanionic cellulose was evaluated by determining the thermal stability, cuttings transportation ability, friction and shelf-life properties under the downhole condition at 75 °C and 100 psig and the results were compared against the existing drilling mud system, yielding the comparable performance. Finally, the functionalized FA was found to be cost-effective over API-grade bentonite.

Performance of polyethylene and polypropylene beads towards drill cuttings transportation in horizontal wellbore

Drilled cuttings removal is critical in drilling operations, especially in horizontal wells. These cuttings are postulated to be among the possible causes of many costly complications, such as mechanical pipe sticking, bore hole instability, drag and torque. This study proposes a new approach that uses polymer beads as a mud additive to improve cutting transportation. In this study, the effect of the concentration of polyethylene (PE) and polypropylene (PP) polymer beads on cuttings transport efficiency (CTE) in water-based mud in a horizontal wellbore was investigated. Experiments were conducted in a lab-scale flow loop equipped with a 13-ft (3.96 m) test section consisting of a concentric annulus acrylic outer casing (2 in. ID) and a static inner PVC drill string (0.79 in. OD). A total of 150 tests were conducted using 10 ppg water based mud (WBM) with 1%–5% by vol. Concentrations of polymer beads (PE and PP) were added at a range of 8–9.5 cp. Six different sizes of drilled cuttings ranging from 0.5 to 4.0 mm were used as samples to determine the CTE at a constant 0.69 m/s average annular fluid velocity. The results revealed that CTE increased with the increase of polymer bead concentrations and that PP is better compared to PE overall due to its low density. The highest CTE was recorded at a 5% concentration of water-based mud polypropylene (WBMPP), which is approximately 96% for cutting sizes of 0.50mm–0.99 mm.

Numerical prediction of flow behavior of cuttings carried by Herschel-Bulkley fluids in horizontal well using kinetic theory of granular flow

The cuttings transport was numerically simulated based on kinetic theory of granular flow in combination with sliding mesh for drill pipe rotation in the horizontal well. The Herschel-Bulkley (H-B) model was implemented to describe the rheological behavior of drilling mud. Three distinguishable flow regions of cuttings and swaying phenomenon of cuttings distribution along the direction of drill pipe rotation were observed. The granular temperature of cuttings is high near the wall of drill pipes, which indicates that the energy from the rotating drill pipe is transferred to cuttings. Effects of three rheological parameters (τ0, KHB and n) on the flow behavior of cuttings and HB fluid were analyzed. With the increase of Herschel-Bulkley fluid rheological parameters, the height of cuttings bed decreases, and the axial flow of cuttings at the lower side is significantly enhanced, but the pressure drop through the annulus is increased. When the value of consistency coefficient and flow behavior index of H-B fluid is low, the cuttings transportation in the wellbore is unstable with the pulsation of cuttings volume fraction in the annulus. Among the three rheological parameters, the flow behavior index plays the most significant role in pressure drop through the annulus.

Study of the cuttings transport in stable foam drilling

Based on the special rheological model of foam fluid, the mathematical models of cuttings transport for stable foam drilling in vertical/near vertical sections, the transitional section, and inclined/horizontal sections are established in this paper. The effects of various flow parameters on the cuttings bed thickness in the annulus are analyzed. The results show that inclination, annulus velocity, foam flow rate, and eccentricity are key factors affecting cuttings transport. The thickness of a cuttings bed gradually decreases with the inclination decrease of the highly deviated/horizontal sections. When the inclination is reduced to approximately 60°, the dynamic and static cuttings bed disappears and is substituted by the glide lamella, which consists of cuttings grains. Cuttings grains have various forms of movement on the lower borehole wall. When the inclination is reduced to below 30°, the cuttings are brought out of the well by the stable foam if the returning velocity of the annulus foam is larger than the depositing velocity of the cuttings. The thickness of the cuttings bed gradually decreases with the increase of annulus velocity. The increased foam quality reduces the concentration of annulus cuttings when the annulus velocity is constant and when it reaches a stable status earlier than the foam drilling fluid of lower foam quality. However, the concentration of the annulus cuttings at the final stage is constant. The thickness of the cuttings bed increases with increased eccentricity of the drill stem. When the eccentricity is large, the change of eccentricity has a high effect on the cuttings bed thickness.

Fuzzy logic modelling of liquid-solid two-phase flow in horizontal and inclined wellbores

In this study, liquid-solid two-phase flow in horizontal and inclined wellbores is modelled using fuzzy logic approach. Cuttings transport experiments were conducted at flow loop using water as a drilling fluid. Cuttings bed thickness inside annulus was recorded during experiments for various flow rate, hole inclination, inner pipe rotation speed and the rate of penetrations (ROP). Cuttings bed thickness is estimated using a fuzzy logic (FL) model. Experimental data was collected from cuttings transport experiments in order to train proposed models. Results showed that the cuttings bed thickness could be estimated using the developed model with a reasonable accuracy when compared with the experimental results. Also, the thickness of the stationary bed can be detected within an error range of ±6.8, more accurately than the widely used models available in the literature. The method in the present study may handle the challenges on the field within a reasonable time and budget due to its ease to describe the variables and gather the necessary information for solving the problems on the field sufficiently. [Received: August 22, 2015; Accepted: January 28, 2017]

Quemada model approach to oil or synthetic oil based drilling fluids rheological modelling

Understanding and modelling the deviations from Newtonian behavior of synthetic-based drilling fluids (SBFs) is essential to design optimal flow systems and efficient cuttings transport. This research develops a better insight into synthetic fluid rheology based on the theory of internal structural units (SUs) suspensions. Although different studies have been proposed to characterize SBF rheology, yield stress and time dependency proved difficult to determine. This study explains how most difficulties disappear when taking thixotropy into account. The behavior of structural units and effective volume fractions as a function of shear rate, has been analyzed by Qemada (1998) to develop a rheological model for particles suspension. This rheological model has been modified to describe the behavior of SBFs. For validation purposes, an industrial SBF used for drilling in a shale reservoir is analyzed. A novel experimental procedure is proposed that makes extensive use of rotational rheometers to estimate the parameters of the model. Various combinations of temperatures and resting times have been tested to develop semi-empirical correlations for the model parameters. In addition, a practical use of the model is demonstrated by accurately estimating the settling of retrieved shale cuttings through the analyzed synthetic fluid. The experimental protocol represents a design tool for onshore and offshore drilling operations that involve SBFs, with potential improvements on optimization of flow systems and cuttings transport efficiency.

Numerical prediction of cuttings transport behavior in well drilling using kinetic theory of granular flow

The cuttings transport during well drilling was numerically simulated based on kinetic theory of granular flow in combination with sliding mesh for drill pipe rotation. The power-law model was implemented to describe the rheological behavior of drilling fluid. Numerical results were compared with available experimental data in the literature to validate the algorithm, and good agreement was found. Three distinguishable regions of cuttings flow pattern and swaying phenomenon of cuttings distribution were observed along the direction of drill pipe rotation. Increasing the fluid velocity results in a reduction in the height of cuttings bed and weakening of the swaying phenomenon. Higher apparent viscosity of drilling fluid contributes to a good performance of cuttings transport at a low annular velocity, but rising in pressure loss. There is critical inclination angle of the well θctr for cuttings transport ratio and θdp for pressure drop through the annulus. The most difficult of cuttings transport occurs in the well inclinations around 35°–65°. There is no additional contribution of drill pipe rotation to cuttings transport after reaching a critical rotation speed. Increasing the cutting size leads to a reduction in the cuttings transport ratio and an increase in pressure drop.