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Summary In this paper, we integrated our polycrystalline diamond compact (PDC) cutter model (Chen et al. 2021) into a PDC bit model that can predict the weight on bit (WOB), torque on bit (TOB), and imbalanced side force on a bit under given drilling conditions. We first proposed a method to determine the actual cutting plane and depth of cut of each cutter on a PDC bit. Once the two parameters for each cutter are determined, the cutter model can then be applied to calculate the cutting force of each cutter. The final bit force and moment (i.e., WOB, TOB, and imbalanced side force) are calculated as the resultant force and moment of cutting forces of all cutters. The PDC bit model in this paper considers all bit design parameters, including bit matrix geometry, blade profile, cutter layout, and the inclination of each cutter. Furthermore, the bit model also considers some bottomhole assembly (BHA) parameters (e.g., bit tilt angle, location of first fulcrum point, and tool face/steering plane angle), which allows the bit model to simulate a bit under different drilling modes. The bit model is also validated by published test data and field applications. Finally, case studies are conducted, and the influence of bottomhole stresses, BHA parameters, and drilling modes on bit force and moment are discussed. A field application of the bit model is also provided. The bit model can be directly used for PDC bit design and simulation. In fact, this paper presents a general way to integrate a cutter model into a PDC bit model. Readers are also encouraged to apply this method to integrate their own cutter model into a PDC bit model.
- North America > United States (1.00)
- Asia (0.92)
Summary The effect of axial flow of power-law drilling fluids on frictional pressure loss under turbulent conditions in eccentric annuli is investigated. A numerical model is developed to simulate the flow of Newtonian and power-law fluids for eccentric annular geometries. A turbulent eddy-viscosity model based on the mixing-length approach is proposed, where a damping constant as a function of flow parameters is presented to account for the near-wall effects. Numerical results including the velocity profile, eddy viscosity, and friction factors are compared with various sets of experimental data for Newtonian and power-law fluids in concentric and eccentric annular configurations with diameter ratios of 0.2 to 0.8. The simulation results are also compared with a numerical study and two approximate models in the literature. The results of extensive simulation scenarios are used to obtain a novel correlation for estimation of the frictional pressure loss in eccentric annuli under turbulent conditions. Two new correlations are also presented to estimate the maximum axial velocity in the wide and narrow sections of eccentric geometries.
- Asia (1.00)
- North America > United States > Louisiana (0.46)
- North America > United States > Oklahoma (0.28)
- North America > United States > Texas (0.28)
- Research Report (0.48)
- Overview (0.46)
Experimental Investigation of Depletion- and Injection-Induced Changes in Poromechanical, Transport, and Strength Properties of High-Porosity Sandstone
Rafieepour, Saeed (University of Tulsa (Now with University of Tehran)) | Miska, Stefan Z. (University of Tulsa) | Ozbayoglu, Evren M. (University of Tulsa) | Takach, Nicholas E. (University of Tulsa) | Yu, Mengjiao (University of Tulsa) | Zhang, Jianguo (BP America)
Summary In this paper, an extensive series of experiments was performed to investigate the evolution of poromechanical (dry, drained, undrained, and unjacketed moduli), transport (permeability), and strength properties during reservoir depletion and injection in a high-porosity sandstone (Castlegate). An overdetermined set of eight poroelastic moduli was measured as a function of confining pressure () and pore pressure (). The results showed larger effect on pore pressure at low Terzaghi’s effective stress (nonlinear trend) during depletion and injection. Moreover, the rock sample is stiffer during injection than depletion. At the same and , Biot’s coefficient and Skempton’s coefficient are larger in depletion than injection. Under deviatoric loading, absolute permeability decreased by 35% with increasing effective confining stress up to 20.68 MPa. Given these variations in rock properties, modeling of in-situ-stress changes using constant properties could attain erroneous predictions. Moreover, constant deviatoric stress-depletion/injection failure tests showed no changes or infinitesimal variations of strength properties with depletion and injection. It was found that failure of Castlegate sandstone is controlled by simple effective stress, as postulated by Terzaghi. Effective-stress coefficients at failure (effective-stress coefficient for strength) were found to be close to unity (actual numbers, however, were 1.03 for Samples CS-5 and CS-9 and 1.04 for Sample CS-10). Microstructural analysis of Castlegate sandstone using both scanning electron microscope (SEM) and optical microscope revealed that the changes in poroelastic and transport properties as well as the significant hysteresis between depletion and injection are attributed to the existence and distribution of compliant components such as pores, microcracks, and clay minerals.
- Europe (1.00)
- North America > United States > Oklahoma (0.28)
- North America > United States > California (0.28)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Summary The main purpose of this paper is to present our polycrystalline diamond compact (PDC) cutter model and its verification. The PDC cutter model we developed is focused on a PDC cutter cutting a rock in 3D space. The model studies the forces between a cutter and a rock and applies the theory of poroelasticity to calculate the stress state of the rock during the cutting process. Once the stress state of the rock is obtained, the model can then predict rock failure by the modified Lade criterion (Ewy 1999). This work also developed a trial-and-error procedure to predict cutting forces, and the stress state of a rock before cutting process is also considered. A complete verification of the cutter model is conducted. The model results (i.e., predicted cutting forces) are compared with measured cutting forces from cutter tests in multiple published articles. The major influencing factors on cutting forces—backrake angle, side-rake angle, depths of cut, worn depth (or wear flat area), and hydrostatic pressure—are all studied and verified. A good agreement between the model results and cutter test data is found, and the overall mean relative error is approximately 15%. The influence of inhomogeneous precut stress state of a rock is also studied. Overall, the cutter model in this paper is complete and accurate. It is ready to be integrated into a PDC bit model.
- Europe (0.67)
- North America > United States > Texas (0.28)
- North America > United States > Massachusetts (0.28)
- Research Report > Experimental Study (0.46)
- Research Report > New Finding (0.46)
- North America > United States > New Mexico > San Juan Basin > San Juan Basin Field > Mancos Formation (0.99)
- North America > United States > Colorado > San Juan Basin > San Juan Basin Field > Mancos Formation (0.99)
Combined Experimental and Well Log Evaluation of Anisotropic Mechanical Properties of Shales: An Application to Wellbore Stability in Bakken Formation
Rafieepour, Saeed (The University of Tulsa) | Zheng, Danzhu (The University of Tulsa) | Miska, Stefan (The University of Tulsa) | Ozbayoglu, Evren (The University of Tulsa) | Takach, Nicholas (The University of Tulsa) | Yu, Mengjiao (The University of Tulsa) | Zhang, Jianguo (BP America Inc.)
Abstract Frequently, shales are treated as isotropic formations. However, organic rich shales are anisotropic due to their laminated structure and chemical properties. In this study, shale mechanical properties with respect to different bedding plane orientations was studied. The goal of this study is to evaluate anisotropic mechanical properties of shale by triaxial tests and to predict these properties by well logging data along with a 3-D transversely-isotropic wellbore stability analysis (WBS) in Bakken formation. Shale samples were prepared with bedding plane angles equal to 0, 45, and 90 degrees. Young's modulus, shear modulus, and Poisson's ratio in different directions were measured. Parameters of stiffness tensor were calculated by mechanical properties. The compressive strength of shale samples was measured under different confining pressures: 0, 500, 1000, and 1500 psi. Simple Plane of Weakness was applied to describe shear failure mechanism. Well logging data was used to connect experimental and field data. Next, a three-dimensional numerical wellbore stability model based on finite difference method was used to evaluate stress and deformation alterations due to drilling of vertical to extended reach wellbores in Bakken formation, Williston Basin, North Dakota. Both anisotropic and isotropic conditions were considered and the Mohr- constitutive relations were implemented in the numerical model. Vertical Young's modulus (perpendicular to the bedding plane) found to be smaller than horizontal Young's modulus (parallel to the bedding plane). Shale is a transversely isotropic rock; which isotropy plane is generally the bedding plane. The result of tests for stiffness tensor showed that the shale can be characterized by only five independent stiffness constants. The Simple Plane of Weakness model is suitable to estimate shale anisotropic compressive strength. The P-wave velocity calculated from the stiffness tensor is a used to connect the experimental data and field data. P-wave velocity is increasing as the bedding inclination angle increases. The predicted compressional wave velocity for a 45-degree inclination angle showed a perfect fit with the field logging data. Steps of inverse sonic log data to stiffness parameters were shown by a flow chart. From the WBS model, the effects of anisptropy on stress distribution and wellbore convergence was investigated for two different constitutive models: isotropic model (IM) and transversely isotropic model (TIM). It was found that neglecting shale anisotropy will lead to erroneous prediction of wellbore deformation.
- North America > United States > North Dakota (1.00)
- North America > Canada > Saskatchewan (1.00)
- North America > Canada > Manitoba (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Summary During the drilling process, many operations will cause cyclic loading of the wellbore, including surge/swab pressure generated by tripping operations and pressure fluctuations induced by shutdowns/startups of the mud pumps. With cyclic loading, the wellbore rock may fail even if the stress level is lower than the predetermined static rock strength because of fatigue. In this paper, comprehensive triaxial cyclic compression tests have been conducted under different maximum cyclic loading levels, confining pressure, amplitude, and frequency. New methods have been proposed and successfully applied to predict the monotonic strength of the rock samples. These approaches overcome the uncertainty caused by the standard average method. Using these experimental results, some empirical models (amplitude and fatigue life, frequency, and fatigue life) are proposed. Also, the evolutional laws of rock parameters (strain, residual strain, energy dissipation, etc.) during the cyclic loading stage are generated. A clear three‐stage behavior is observed: early stage, steady stage, and late stage. Finally, the experiments are combined with two field‐drilling cases. Results show to avoid rock fatigue because of tripping operations and shutdowns/startups of the mud pump, the maximum loading level should be less than 95% of the static strength for Berea Sandstone used in this study. Therefore, the maximum equivalent loading stress should avoid being close to the failure boundary. A safe buffer zone should be designed between the wellbore collapse boundary and actual bottomhole pressure.
- North America > United States > West Virginia (0.60)
- North America > United States > Pennsylvania (0.60)
- North America > United States > Ohio (0.60)
- North America > United States > Kentucky (0.60)
Prediction of Monotonic Strength of Sandstone for Accurate Control of Cyclic Compression Tests
Meng, Meng (Los Alamos National Laboratory) | Miska, Stefan (University of Tulsa) | Yu, Mengjiao (University of Tulsa) | Frash, Luke P. (Los Alamos National Laboratory) | Evren, Ozbayoglu (University of Tulsa)
ABSTRACT Cyclic pressure fluctuations usually happen during drilling operations. Unlike early researchers' cyclic loading tests with a large amplitude, cyclic loading on wellbore caused by drilling operations is featured with a relatively small amplitude, specific loading period in minutes, and high loading level. Under these circumstances, the accurate prediction of monotonic loading strength becomes very important because the precise control of the loading level is needed. In the beginning, the classical method of using the average strength of several parallel compression tests has been applied. Five triaxial cyclic compression tests were designed and conducted based on this value. Results show one unexpected result, which is against the common rule that more loading cycles lead to more damage. This unexpected result is found to be caused by the inappropriate prediction of the monotonic strength. To have a more accurate prediction, we innovatively applied Taheri's method and a self-proposed modified method. These innovative methods are proven to be valid for our tests, and they successfully explain the paradox we encountered by using the classical approach. They pave the way for us to have further in-depth design and analysis of wellbore fatigue during drilling operations. 1. INTRODUCTION During the drilling process, there are many operations that can cause cyclic loading of the wellbore (Meng, 2019a, 2019b), such as surge and swab pressure caused by tripping operations, pressure fluctuations caused by shut-down/start-up of the mud pumps, seismic waves caused by the earthquakes, etc. Under these loading conditions, rock fatigue can happen, which can further cause the wellbore failure within the designed safe range of mud density. Rock fatigue tests have been conducted by many early researchers, including constant amplitude uniaxial/triaxial cyclic compression test (Badge and Petros, 2005; Xiao et al, 2010; Liu et al, 2011; Ma et al, 2013), multilevel amplitude cyclic test (Sun et al, 2017), discontinuous cyclic loading test (Fan et al, 2016), etc. Badge and Petros (2005) studied the waveform effect on fatigue properties of sandstone in uniaxial cyclic loading, and found square waveform causes the most damaging effect. Xiao et al (2010) proposed the basic requirements for a reasonable damage variable under the uniaxial compression test. Liu et al (2011) performed triaxial cyclic compression tests with different confining pressure and frequency. They found the axial strain at failure increases with confining pressure and frequency. Ma et al. (2013) run the triaxial cyclic test on rock salt, and pointed out the salt exhibits strain-hardening behavior. Fan et al (2016) tested the influence of interval cyclic pressure on rock salt, and concluded that the fatigue lives of samples from interval fatigue tests dramatically reduce compared with regular cyclic tests.
- Geology > Geological Subdiscipline > Geomechanics (0.99)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.64)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.54)
- Geology > Mineral > Halide > Halite (0.45)
ABSTRACT To solve lost circulation problems and design optimal lost circulation materials, it is imperative to understand the lost circulation mechanism and infer geological or fracture characterization. In this paper, a real-time inversion method is developed to estimate fracture width and infer the geology characterization. A fluid flow model is introduced to simulate the lost circulation into the fracture, and it considers leak-off effect through fracture planes and deformable fracture width. Then, after dimensionless analysis and numerical integration, a theoretical type-curve model is obtained. Based on Hough transformation, the traditional type-curve line is transferred into digitalized type-curve map with scattered dots. Through an automatic search algorithm, field drilling data can be matched with the digitalized type-curve map, and the fracture width can be approximately calculated, then classify and infer the geology characterization for the lost circulation zone. As a result, the lost circulation materials selection and particle size distribution design can be achieved with the input of fracture width parameters and lost circulation zone geology characterization. 1. INTRODUCTION Lost circulation may result from geological causes or drilling-induced fractures, like fractured or depleted formations (Zhang, 2016 and 2019), narrow mud weight window (Li, 2017), surge pressure (Meng, 2019), etc. The prevailing problem for curing a well is to quantify fracture width for lost circulation materials selection. Studies in this area have continued for many years, but there are still some uncertainties. Additionally, lost circulation in geological fault can be a detrimental instance for drilling operations, however, some faults can be drilled through smoothly. Caine J. S (1996) proposed a geological fault as a combination of core and damage zone areas, and the ratio of fault core and damage zone is used to classify the fault as a conduit, barrier, or combined conduit-barrier system. The fault core is the result of highly localized strain and intense shear that accommodates most of the displacement within the fault zone (Wibberley, 2008). Damage zones are characterized by relatively low strain and less intense deformation compared to the fault core, and those zones generally exhibit several second-order structures such as subsidiary faults, fractures, and veins (Faulkner et al. 2010). As such, the mechanism of lost circulation into geological fault zone is very complicated.
Summary A successful cement placement can provide zonal isolation and environmental safety. Effective design of cement placement and mud removal affects all the stages of the wellbore life, from drilling ahead to production. Accurate predictions of fluid displacement in the wellbore are vital to design fluid properties and plan the cementing job. In this work, an analytical model is developed to simulate the displacement of fluids in eccentric annuli. This paper presents an analytical method for the solution of cement/mud displacement and evaluation of interfluid contamination during displacement in vertical eccentric annuli. This new approach starts by addressing the problem of single‐fluid flow in eccentric annuli by analytically solving the governing transport equations for a flow inside an unwrapped annulus. The solution is then extended to a system of two fluids in a vertical annulus by adjusting the boundary conditions for displacement. The model is completed by adding the time‐dependent calculation of interface between the two fluids, enabling the accurate determination of the amount of interfluid mixing and displacement efficiency. The analytical method proposed is used to simulate single‐ and multifluid flows and study the effect of fluid properties of cement, spacer, and drilling mud at different flow rates on displacement efficiency for both concentric and eccentric vertical annuli. Noting that the drilling fluids are non‐Newtonian, the concept of apparent viscosity is used, accounting for variable apparent viscosity at different annular gaps. 3D computational‐fluid‐dynamics (CFD) simulations were performed and the results were compared with the analytical solution. Moreover, instability of the interface in all cases was studied, and the analysis offers an understanding of the role of fluid properties and proposes applicable optimized design to enhance the displacements. The amount of interfluid mixing and contamination that occurs during the displacement was calculated for both methods. The analytical solution and CFD produce results within a 13% difference, which sufficiently validates the analytical model. Evidence was gathered to support that the improper design of fluid properties and flow rate along with a highly eccentric annulus can lead to substantial cement contamination. This can lead to underdesigning the amount of fluids to be pumped to provide a complete mud removal and an efficient cement placement. On the other hand, learnings and models developed allow the optimization of fluid properties that can lead to the best outcomes, even for a highly eccentric annulus. The present work aims to take part in addressing the undeniable importance of a complete cement displacement by means of a semianalytical solution for the fluid displacement coupled with the interface‐instability analysis, attempting to provide a realistic prediction of the amount of interfluid mixing and cement contamination, along with qualitative judgements on the quality of the cementing job. This methodology is intended to offer improvement techniques for the displacement and provide enhancements for practical industrial applications.
- Europe (0.67)
- North America > United States > Texas (0.46)
Modeling of Dynamic Cuttings Transportation during Drilling of Oil and Gas Wells by Combining 2D CFD and 1D Discretization Approach
Zhang, Feifei (Yangtze University) | Wang, Yidi (Yangtze University) | Wang, Yuezhi (Yangtze University) | Miska, Stefan (The University of Tulsa) | Yu, Mengjiao (The University of Tulsa)
Summary This paper presents an approach that combines a two‐dimensional (2D) computational fluid dynamics (CFD) and one‐dimensional (1D) continuous model for cuttings transport simulation during drilling of oil and gas wells. The 2D CFD simulates the flow profile and the suspended cuttings concentration profile in the cross section of the wellbore and the 1D continuous model simulates the cuttings transportation in the axial direction of the wellbore. Different cuttings sizes are considered in the model by using a new proposed superposition method. Experimental tests conducted on a 203 × 114 × 25 mm flow loop are used to validate the model from three different perspectives: the single-phase flow pressure drop, the steady‐state cuttings bed height, and the transient pressure changes. Compared to layer models, the new approach is able to catch accurate flow details in the narrow flow region and overcome the shortcoming of traditional models that underpredict bed height under high flow rate conditions. The computational time increases by the order of 10∼10 from the level of millisecond to seconds but is still within the acceptable range for engineering applications, and the model provides close to three‐dimensional (3D) accuracy at a much shorter central processing unit (CPU) time compared to 3D CFD models.
- Asia (1.00)
- Europe (0.93)
- North America > United States > Oklahoma (0.46)
- Personal (0.46)
- Overview > Innovation (0.34)