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Collaborating Authors
Aramco Services Company: Aramco Research Center-Houston
Field Evidence and Elastic Dislocation Modeling of Stress Field Alteration in the Rock Mass Adjacent to Salt
Reeher, Lauren J. (University of Arizona) | Busetti, Seth (Aramco Services Company: Aramco Research Center-Houston) | Hughes, Amanda (University of Arizona)
ABSTRACT: We present a geomechanical analysis of stress and fracture development in the rock mass adjacent to a salt body under tectonic loading. This is accomplished with 3D elastic dislocation modeling to evaluate stress conditions adjacent to a salt wall in the Paradox Basin, southern Utah, USA. Detailed field work has documented stress indicative strain patterns adjacent to an exhumed salt wall that suggest a rotation of principal stresses and a decrease in differential stress magnitude in proximity to salt relative to regional conditions. A geomechanical model of the area was constructed to solve for 3D stress field perturbations using the elastic dislocation method to simulate rock deformation due to fault slip and salt creep under tectonic loading. The model results suggest both faulting and salt deformation may have contributed to the local stress field that produced the observed strain pattern. These findings help constrain geologic and geomechanical parameters used in elastic dislocation modeling and enhances ability to predict stress field perturbations in locations with limited data. This work aims to improve the accuracy of predicted stress conditions while drilling near salt, as well as assessing fracture development with fluid flow implications adjacent to salt bodies. 1. INTRODUCTION The formation of natural fracture systems in brittle rocks and the state of stress under which they form have long been a subject of interest as fractures are important conduits for subsurface fluids in many applications in petroleum systems, carbon capture and storage, induced seismicity, hydrology, and ore forming systems. The state of stress can locally vary where stress and strain perturbations are present. These perturbations are often associated with geologic deformation such as faults and fractures or in proximity to salt bodies or volcanic intrusions. Changes in stress state due to slip or dilation along faults and fractures have been modeled using elastic dislocation theory (Comninou and Dundurs, 1975; Maerten et al., 2005; Meade, 2007; Okada, 1992). We employ a proprietary geomechanics code (Busetti, 2021b) to solve for 3D stress and strain fields on a target surface following the triangular elastic dislocation method (Meade, 2007), which has been used to model the stress and strain effects of faulting and fracturing in previous studies (Busetti, 2019, 2021a). This project uses the capabilities of the software to model stress perturbations in the rock mass adjacent to a salt body. Due to the weakness of salt, it will internally deform under small amounts of differential stress. Because the stress field must equilibrate across welded salt-sediment boundaries, the stress field in the rock mass adjacent to a salt body is also altered from regional stress conditions. Stress anomalies in formations adjacent to salt have been extensively observed and modeled in subsurface applications (Bradley, 1978; Dusseault et al., 2004; King et al., 2012; Seymour et al., 1993), but field-based analog studies, such as this, permit laterally extensive observations that are otherwise limited in subsurface applications. Detailed field work examining stress indicative strain patterns adjacent to an exhumed salt wall in the Paradox Basin has documented altered stress patterns in a deformed homogeneous sandstone under regional tectonic loading. Utilizing this field case study to constrain geomechanical models, we predict locally perturbed stress and strain patterns in the rock mass adjacent to salt under regional tectonic stress.
- Phanerozoic > Paleozoic > Carboniferous > Pennsylvanian (1.00)
- Phanerozoic > Mesozoic (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.95)
- North America > United States > Utah > Paradox Basin (0.99)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- (28 more...)
Simulation of Pressure- and Temperature-Dependent Fracturing Fluid Loss in Multi-Porosity Multi-Permeability Formations
Liu, Chao (Aramco Services Company: Aramco Research Center-Houston) | Phan, Dung (Aramco Services Company: Aramco Research Center-Houston) | Abousleiman, Younane (The University of Oklahoma)
Abstract In this paper, the multi-porosity multi-permeability porothermoelastic theory is used to derive the analytical solution to calculate the pressure- and temperature-dependent fracturing fluid loss. A triple-porosity triple-permeability source rock formation is selected as an example to illustrate the model. The effects of fracturing fluid temperature and natural fractures on the fluid loss rate are systematically illustrated. The model successfully accounts for the varying leak-off rates in the multi-permeability channels through the hydraulic fracture faces. Furthermore, thermal diffusion near the hydraulic fracture faces contributes to a variation of pore pressure whose gradient at hydraulic fracture faces directly controls the fracturing fluid leak-off rate. The model shows that thermal effects bring almost 27% variation in the leak-off rate. Comparison study indicates that the single porosity model without considering multi-permeability systems or thermal effects significantly underestimates the rate of fracturing fluid loss and predicts nearly 84% and 87% lower leak-off rate, compared to the dual-porosity dual-permeability and triple-porosity triple-permeability models, respectively. Two case studies using published laboratory measurements on naturally fractured Blue Ohio sandstone samples are conducted to show the performances of the model. It is shown that the model presented in this paper well captures the total leak-off volume during the pressure-dependent fluid loss measured from laboratory tests. Matching the analytical solution to the laboratory data also allows rocks’ double permeabilities to be estimated.
- Asia > Middle East (0.47)
- North America > United States > Ohio (0.25)
- Europe > Norway > Norwegian Sea (0.24)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.51)
- Well Drilling > Pressure Management > Well control (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Completion > Hydraulic Fracturing > Fracturing materials (fluids, proppant) (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
A Streamlined Approach to Fault Stress Analysis and Natural Fracture Prediction
Busetti, Seth (Aramco Services Company: Aramco Research Center-Houston)
Abstract Understanding the geomechanical response of reservoir discontinuities is important for predicting permeability enhancement and is a primary factor in sweet-spot identification, containment assurance, and fault reactivation. Most reservoirs are naturally faulted and fractured to some extent, but the orientation and patterns of natural discontinuities are not consistent across reservoirs or even within a reservoir due to heterogeneous structural deformation. Based on experience working numerous case studies spanning unconventional and conventional fractured reservoirs, a specialized toolkit was created to streamline analysis of the interdependence of structural position, stress state, and natural fracture orientation. This paper summarizes an analytical modeling approach that combines fault stress analysis and natural fracture prediction and addresses three fundamental aspects of the geomechanical behavior of discontinuities. These techniques are implemented as modules in a specialized Matlab code that allows for complete customization and flexibility for ongoing geomechanics research. Geologic horizons and fault surfaces from outcrop or subsurface (e.g., seismic) field data and knowledge of the background state of stress are assumed as inputs. The first technique is to calculate the 3D displacement and strain fields due to tectonic deformation (forward kinematic modeling), as well as tectonic or in situ stress perturbations caused by faulting, folding, or hydraulic fracturing. The software uses triangular elastic dislocation methods to solve for the stress and strain fields. The second technique calculates resolved stresses on multiple input geologic surfaces based on the far field or locally perturbed stress states. Understanding the orientation of geologic discontinuities with respect to structural position and if they are likely to slip in shear, dilate, or close is useful for predicting reservoir permeability enhancement, fault leakage, microseismic susceptibility, and bedding stability. The third technique uses the 3D stress perturbation solutions to predict the orientation of natural fractures and faults throughout the field as a function of heterogeneous structural deformation. Three modes of fracturing are incorporated which are predicted at every observation grid node: tensile joints, conjugate shear fractures, and polymodal shear fractures. Combining the above techniques into a streamlined tool is helpful for addressing a range of structural geology and geomechanics reservoir problems. A few examples are highlighted to demonstrate the toolkit and applicable geologic problems.
- Asia > Middle East > Israel > Mediterranean Sea (0.34)
- North America > United States > Texas (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.46)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Faults and fracture characterization (1.00)
Numerical Modeling of Pressuremeter Test (PMT) in Rock Formations
Han, Yanhui (Aramco Services Company: Aramco Research Center-Houston) | Alruwaili, Khalid M. (Saudi Aramco) | AlTammar, Murtadha J. (Saudi Aramco)
ABSTRACT: This paper reviews literatures on pressuremeter test (PMT) with emphasis on the equations of calculating deformation modulus of rock mass from pressure-volume curve recorded in the field test. The consistence of existing equations of calculating PMT deformation modulus is assessed. Theoretical analysis of a circular borehole deformation in elastic media indicates that the deformation modulus is equivalent to the Young's modulus in plane strain condition. A numerical simulator is constructed to simulate loading-unloading process during PMT test. The simulator is applied to simulate PMT test in both elastic and elasto-plastic media. The simulation result in elastic medium shows that the deformation modulus can be accurately measured from loading or unloading curve. In the elastoplastic medium, the deformation modulus can be calculated using unloading curve or reloading curve. The simulator is then applied to analyze the field data from a PMT test program reported in the literature. 1. Introduction Determination of stiffness and strength properties of soils and rocks is essential in most geo-engineering practices. In geotechnical engineering, stiffness of soil is a key parameter in the prediction of ground deformation and impact of construction activities, such as deep excavation and tunneling, on the adjacent structures. The strength properties of soil are needed for evaluating foundation bearing capacity and slope stability. In oil and gas exploration and production, stiffness of rock is required for the evaluation of reservoir compaction and subsidence and hydraulic fracture prediction. Strength properties of formation rocks are input parameters for wellbore stability analysis, wellbore integrity assessment and sanding evaluation (Goh et al, 2012; Han et al. 2017). Both elastic stiffness and plastic strength properties can be measured by performing laboratory experiments on soil and rock samples. However, for weak and fractured rock masses, it is technically very challenging to retrieve cores and/or prepare test samples. In addition, the stiffness and strength properties measured from intact rock samples are not representative of the in-situ fractured rock mass where the samples are retrieved. In other words, in order to reproduce the in-situ mechanical response of fractured rock mass, the tested rock samples need to contain a representative number of discontinuities. Due to this technical difficulty, various in-situ test methods, such as Goodman jack, plate loading test, hydraulic jack, pressuremeter test (PMT), standard penetration test (SPT), dilatometer, seismic surface wave method, etc., have been developed for determining stiffness and strength parameters of soil and rock mass under in-situ conditions (Isik et al. 2008; Agan 2014; Birid 2015).
- Europe (0.68)
- Asia > Middle East > Saudi Arabia (0.47)
- North America > United States > Texas (0.28)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Integration of geomechanics in models (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.89)
Comparison of Finite Element and Elastic Dislocation Methods for Modeling Discrete Fault Stress Perturbations
Busetti, S. (Aramco Services Company: Aramco Research Center-Houston)
ABSTRACT: Geomechanical modeling of three-dimensional geologic structures is helpful for understanding fault related stress perturbations. The choice of which modeling technique to use depends on the available input data and physics that are to be solved, as well as a range of computational considerations such as run time and solution accuracy. For scenarios where fault and fold geometry and offsets are well defined from field or subsurface seismic data, elastic dislocation (ED) and finite element method (FEM) techniques are popular. Both approaches start from a common three-dimensional structural framework model and both produce meaningful stress perturbation results. However, geomechanical modelers must decide when to use a simpler and faster surface-based elastic dislocation model versus when a more robust volumetric finite element model is required. To explore this question, this study compares the ED and FEM approaches for solving a seismic scale (~10km) fault perturbation problem under a static linear elastic assumption. An airtight structural framework for normal faults in a relay ramp setting is built, then in one scenario the faults and horizons are exported for direct use in an ED solution. In a second scenario, a volumetrically reconciled tetrahedral mesh is created and solved using FEM with a surface contact algorithm. Solution accuracy and resolution, run time, and modeling constraints are compared to determine practical guidance for when ED or FEM models are more effective. 1. Introduction Fault related stress perturbations are common in many reservoirs and affect natural fracture orientation and intensity, fault linkage, fluid flow, and rock properties. In order to geomechanically model perturbations (e.g., Pollard and Fletcher, 2005) a structural model must first be created using available geologic information (e.g., Ferrill et al, 2004; Maerten et al., 2006; Hennings et al., 2012; Horne et al., 2020). Field, seismic, and well data are used to interpret faults and horizons, which form the basis to create the three-dimensional structural framework (Figure 1). The fault and horizon intersections are reconciled to constrain the fault geometry and offsets as defined by hanging wall and footwall cutoffs and fault polygons which define the gaps in a faulted horizon (Figure 2). With the fault offsets constrained the surfaces may be re-meshed with triangles or converted to a rectangular grid at a resolution sufficient to capture the geometry of the geologic structures throughout the extent of the model. In some cases, the individual surfaces in the structural framework model can be directly exported for geomechanical simulation. For example, one common geomechanical modeling approach uses the boundary element method to solve for the elastic dislocation (ED) of faults embedded in a half space (Comninou and Dunders, 1975; Okada, 1992; Thomas, 1993; Jonsson, 2002; Maerton et al., 2005; Meade, 2007; Nikkhoo and Walter, 2015). This approach assumes uniform elastic properties and solves for quasi-static stress perturbations surrounding displaced faults computed on an observation grid, typically a stratigraphic horizon or cross section line. The ED method requires low geometric modeling overhead, does not need perfectly reconciled fault and horizon meshes, and the computations run relatively quickly.
- North America > United States > Texas (0.48)
- Asia > Middle East > Israel > Mediterranean Sea (0.24)
- Geology > Structural Geology > Fault (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Europe > Netherlands > German Basin (0.99)
- Europe > Germany > German Basin (0.99)
- Europe > Denmark > German Basin (0.99)
- (7 more...)
Incorporation of Physics into Machine Learning for Production Prediction from Unconventional Reservoirs: A Brief Review of the Gray-Box Approach
Liu, Hui-Hai (Aramco Services Company: Aramco Research Center-Houston) | Zhang, Jilin (Aramco Services Company: Aramco Research Center-Houston) | Liang, Feng (Aramco Services Company: Aramco Research Center-Houston) | Temizel, Cenk (Saudi Aramco) | Basri, Mustafa A. (Saudi Aramco) | Mesdour, Rabah (Saudi Aramco)
Summary Prediction of well production from unconventional reservoirs is often a complex problem with an incomplete understanding of physics and a considerable amount of data. The most effective way for dealing with it is to use the gray-box approach that combines the strengths of physics-based models and machine learning (ML) used for dealing with certain components of the prediction where physical understanding is poor or difficult. However, the development of methodologies for the incorporation of physics into ML is still in its infancy, not only in the oil and gas industry, but also in other scientific and engineering communities, including the physics community. To set the stage for further advancing the use of combining physics-based models with ML for predicting well production, in this paper we present a brief review of the current developments in this area in the industry, including ML representation of numerical simulation results, determination of parameters for decline curve analysis (DCA) models with ML, physics-informed ML (PIML) that provides an efficient and gridless method for solving differential equations and for discovering governing equations from observations, and physics-constrained ML (PCML) that directly embeds a physics-based model into a neural network. The advantages and potential limitations of the methods are discussed. The future research directions in this area include, but are not limited to, further developing and refining methodologies, including algorithm development, to directly embed physics-based models into ML; exploring the usefulness of PIML for reservoir simulations; and adapting the new developments of how the physics and ML are incorporated in other communities to the well-production prediction. Finally, the methodologies we discuss in the paper can be generally applied to conventional reservoirs as well, although the focus here is on unconventional reservoirs.
- North America > United States > Texas (1.00)
- Asia > Middle East (0.93)
- Europe (0.67)
- Geology > Geological Subdiscipline (0.68)
- Geology > Petroleum Play Type > Unconventional Play (0.46)
- North America > United States > Texas > West Gulf Coast Tertiary Basin > Eagle Ford Shale Formation (0.99)
- North America > United States > Texas > Sabinas - Rio Grande Basin > Eagle Ford Shale Formation (0.99)
- North America > United States > Texas > Maverick Basin > Eagle Ford Shale Formation (0.99)
- (4 more...)
A method for modeling multiscale geomechanical effects in the stimulated rock volume
Busetti, Seth (Aramco Services Company: Aramco Research Center-Houston)
Abstract I have developed a workflow to efficiently simulate geomechanical effects in the stimulated rock volume (SRV) by including regional geologic structures such as faults and folds as well as high-resolution-oriented mechanical stratigraphy. The motivation is that the local model used for hydraulic fracture analysis should include macroscale 3D geomechanical effects derived from regional tectonic and seismic data. A practical computational strategy is developed to link multiple 3D geomechanical models derived at different scales and their associated stress effects. I apply the workflow to a synthetic reservoir problem composed of a tectonic-scale structural framework model with three embedded mechanical stratigraphic models representing three stimulated vertical wells. I first combine regional stresses solved with 3D finite-element analysis with perturbation stresses from elastic dislocation modeling using elastic superposition concepts. I then apply the macroscale stress effects as unique boundary conditions to an embedded finite-element submodel, a mesoscale stratigraphic model representing the SRV allowing for resolution of variable stress amplification, and stress rotation in geologic sublayers. Finally, I conduct hydraulic-fracture simulations within the SRV models. The simulated hydraulic fractures are controled by the structural position and mechanical stratigraphy. Closest to the back limb of the main structural anticline, hydraulic fractures tend to be height-restricted, and in some realizations, fractures propagate horizontally. Adjacent to the fold and a fault, where differential stresses are elevated, fracture growth is the most unconstrained in height and length. Results suggest that this multiscale approach can be applied to better predict and understand behaviors related to unconventional reservoir stimulation. The workflow could easily be modified for other operational problems and geologic settings.
- Asia > Middle East (1.00)
- North America > United States > Texas (0.68)
- North America > Canada > British Columbia (0.46)
- Research Report > New Finding (0.88)
- Research Report > Experimental Study (0.66)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.68)
- Geology > Geological Subdiscipline > Economic Geology > Petroleum Geology (0.46)
- (2 more...)
- Oceania > Australia > Queensland > Surat Basin (0.99)
- Oceania > Australia > New South Wales > Surat Basin (0.99)
- North America > United States > Texas > West Gulf Coast Tertiary Basin > Eagle Ford Shale Formation (0.99)
- (32 more...)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Investigation of the Effect of Pore Size Distribution on the Produced Oil from Surfactant-Assisted Spontaneous Imbibition in ULRs
Alhashim, Hassan W. (Texas A&M University) | Zhang, Fan (Texas A&M University) | Schechter, David S. (Texas A&M University) | Chen, Jin-Hong (Aramco Services Company: Aramco Research Center-Houston)
Abstract Observations from field applications along with laboratory experiments have revealed the significant potential of the surfactant-assisted spontaneous imbibition (SASI) as an encouraging EOR method in unconventional liquid reservoirs (ULR). This study focuses on unveiling the target pore size range for SASI EOR through a combination of experimental results, computed tomography (CT), Scanning Electron Microscope (SEM) and Nuclear magnetic resonance (NMR) technologies. In addition, laboratory results were upscaled to the field-scale to evaluate the effectiveness of the SASI EOR in production enhancement in the Wolfcamp formation. Eight SASI experiments were performed at reservoir temperature using different surfactants on quartz- and carbonate-rich side-wall core samples obtained from the Wolfcamp formation. Contact angle (CA), interfacial tension (IFT), and zeta potential were measured for the saturated core samples. CT-Scan technology is used to visualize the process of oil expulsion from the core plugs and generate core-scale simulation model to history-match laboratory results. SEM is used to match the NMR Pore Size Distribution (PSD) and obtain the Surface Relaxivity for each core sample. The target pore size range for SASI EOR in ULR is determined from NMR results. In addition, the laboratory results were upscaled to estimate the production enhancement through SASI EOR using the field scale model. The primary production mechanism of SASI EOR is highly influenced by wettability alteration and IFT reduction. SASI experiments showed optimistic oil recovery results in both quartz-rich and carbonate-rich core samples with up to 36% and 17.5% of the Original Oil in Place (OOIP), respectively. The NMR technique is used to determine the pore size range from which the oil is produced during the SASI experiment. NMR results revealed that the pore size distribution plays a significant role in SASI EOR with the majority of the imbibed fluid is observed in smaller pores. The consideration of the pore size distribution has a significant impact on successful surfactant selection and a proper EOR process design in ULR. CT-scan technology is utilized to demonstrate the movement of the fluids inside the cores throughout the experiments. CT-scan technology is also used to validate the NMR results, which revealed a direct relation between CT imaging and NMR results. A CT-generated core-scale model was utilized to history-match laboratory results. The capillary pressure and relative permeability curves for the field-scale model were estimated from scaling group analysis and core-scale simulation. The simulation results indicate that SASI EOR has significant potential of enhancing oil production in ULR. The novelty comes from the insight of the essential role of the pore size distribution in SASI EOR through CT and NMR technologies. Besides, a new workflow for surfactant selection is proposed to unveil the real potential of SASI in ULR.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (1.00)
- Geology > Mineral > Silicate > Tectosilicate > Quartz (0.48)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (26 more...)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Core analysis (1.00)
Regularization of surface consistent processing: Decomposition of source and receiver functions
Baek, Hyoungsu (Aramco Services Company: Aramco Research Center-Houston) | Mubarak, Mohammed S. (EXPEC Advanced Research Center, Saudi Aramco) | Zhang, Dongliang (EXPEC Advanced Research Center, Saudi Aramco)
ABSTRACT Surface consistent processing, such as amplitude balancing and deconvolution, suffers from non-uniqueness and the solution depends on the starting point for an iterative solver. Data volumes have increased rapidly as more shots and more receivers are used in modern surveys; however, more data points do not help mitigate the non-uniqueness. The commonly used L2 norm and its siblings show limited success. When the source/receiver solutions have discontinuities, it is more challenging to impose reasonable constraints and to obtain accurate results. To address these issues in underdetermined surface consistent problems, we propose a new model that explains the data, utilizing available information about surface conditions. The effectiveness of the method is demonstrated with both synthetic data and ocean bottom node data examples. Presentation Date: Wednesday, September 18, 2019 Session Start Time: 1:50 PM Presentation Start Time: 3:05 PM Location: Poster Station 7 Presentation Type: Poster
Numerical Simulation of Slot-Shaped Breakout in High-Porosity Sandstone
Wang, Tuo (Key Laboratory of Geotechnical & Underground Engineering of Ministry of Education, Tongji University, College of Civil Engineering, Tongji University) | Zhang, Fengshou (Key Laboratory of Geotechnical & Underground Engineering of Ministry of Education, Tongji University, College of Civil Engineering, Tongji University) | Han, Yanhui (Aramco Services Company: Aramco Research Center-Houston)
Abstract Mechanism of slot-shaped borehole breakouts observed in experiments of drilling through high-porosity sandstone is investigated using DEM-continuum mechanics coupled modeling approach. The rock in DEM is modeled as an assembly of particles with flat joints at contacts. The failure mechanism in the slot-shaped breakout is mainly caused by particle crushing, which is different from the dilatant V-shaped breakout where shear failure plays the primary role. The damage evolution of slot-shaped breakout can be divided into three stages, i.e., breakout initiation induced by the stress concentration near the excavated borehole, formation and propagation of slot-shaped borehole breakout as a result of particle crushing and removal, and formation of compaction band at the tip of the breakout with the ceasing growth of breakout length. The dynamic change of stress with breakout slot extending is modeled. The continuous particle breakage at the tip of the breakout maintains the same level of stress concentration as the breakout is propagating. The majority of the particle loss is caused by the particle crushing and subsequent removal. 1 Introduction In 2003, Haimson and Kovacich reported the unique type of breakouts observed for the first time in high-porosity Berea sandstone (Haimson & Kovacich, 2003). Drilling experiments in rock blocks subjected to critical far-field true triaxial stress regimes, simulating in situ conditions, induced breakouts that were unlike the ‘dog-ear’ ones previously observed in granites, limestones, and lowporosity sandstones. The newly observed breakouts were thin, tabular, and very long, resembling fractures that counterintuitively extended perpendicular to the maximum principal stress (Figure 1). The formation of the slot-shaped breakout is related to compaction band and has a significant effect on borehole instability in porous sandstone (Haimson, 2007). In this paper, we simulate the experiments and replicate the forming process of slot-shaped breakout by employing the coupled PFC3D/FLAC3D modeling. The flat-jointed bonded-particle model embedded in PFC3D software was conducted to create a sandstone material by particles while FLAC3D was used to enclose the PFC3D domain and enlarge the model. In this way, the stress boundary could be well controlled and computation efficiency was much improved compared with the model with PFC3D only.
- North America > United States > West Virginia (0.25)
- North America > United States > Pennsylvania (0.25)
- North America > United States > Ohio (0.25)
- North America > United States > Kentucky (0.25)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)