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Abstract This paper discusses a new computational strategy for the analysis of inelastic processes in granular rocks subjected to varying levels of confinement. The purpose is to provide a flexible and efficient tool for the analysis of failure processes in geomechanical settings. The proposed model is formulated in the framework of Lattice Discrete Particle Models (LDPM), which is here calibrated to capture the behavior of a high-porosity rock widely tested in the literature: Bleurswiller sandstone. The procedure required to generate a realistic granular microstructure is described. Then, the micromechanical parameters controlling the fracture response at low confinements, as well as the plastic behavior at high pressures have been calibrated. It is shown that the LDPM model allows one to explore the effect of fine-scale heterogeneity on the inelastic response of rock cores, achieving a satisfactory quantitative performance across a wide range of stress conditions. The results suggest that LDPM analyses represent a versatile tool for the characterization and simulation of the mechanical response of granular rocks, which can assist the interpretation of complex deformation/failure patterns, as well as the development of continuum models capturing the effect of micro-scale heterogeneity. 1. INTRODUCTION An accurate knowledge of the engineering properties of rocks is crucial for a variety of geomechanical problems, ranging from wellbore stability, to failure in rock slopes, underground excavations, and crustal faults [1]. While strength and deformation properties are usually obtained from a limited number of in situ and/or laboratory tests, their determination is invariably affected by considerable heterogeneities [2]. Such lack of homogeneity impacts engineering conclusions at all length scales and requires appropriate theoretical and computational tools. Advanced numerical modeling represents a useful tool to explore how mechanical processes interact across length scales. Considerable advances in this area have based on Finite Element computations, where heterogeneities can be incorporated at both sample and site scales [3-5]. Nevertheless, to capture realistically the path-dependent response of geomaterials, continuum formulations tend to be characterized by a large number of parameters. If such constants lack clear connections with measurable attributes (e.g., grain size and sorting), their calibration becomes poorly constrained. Furthermore, the tendency of rock samples to undergo strain localization [6, 7] further prevents the validation and/or implementation of continuum models, requiring a direct link between strain localization and microstructural attributes [8].
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.64)
- Well Drilling (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.48)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (0.40)
Abstract Shale, like many other sedimentary rocks, is typically heterogeneous and anisotropic with partial alignment of anisotropic clay minerals and naturally formed bedding planes. A numerical method based on the lattice discrete particle model was formulated. Material anisotropy is introduced through an approximated geometric description of shale internal structure and a representation of material properties variation. Calibration was performed by comparing the numerical simulation results with experimental data. A series of simulated experiments, including elastic analysis, Brazilian tensile test and unconfined compression test, were demonstrated. Simulation results shows that the dependence of tested strength and failure modes on sample orientation can be captured successfully. This work will pave the way for the development of reliable hydraulic fracturing models that appropriately account for the mechanical behaviors of heterogeneous and anisotropic shale. 1. INTRODUCTION With the rapid growth of the shale gas/oil industry, especially the development of hydraulic fracturing technique, the study to promote deep understanding of the mechanical properties of shale-like rocks is becoming more important. Gas/Oil shale, described as organic rich and fine grained [1], exhibit significant mechanical anisotropy and heterogeneity due to the organized distribution of platy clay minerals and compliant organic materials [2]. Developing adequate numerical models to capture the heterogeneity and anisotropy of shale leads to a better understanding of the influence of material properties on induced fracture initiation, propagation and fracturing treatment, and therefore provides a powerful tool to predict and optimize the fracturing process. In a broader sense, the available numerical methods can be classified into continuum- and discontinuum- based methods [3,4]. The continuum approaches, such as finite element method (FEM), finite difference method (FDM) and boundary element method (BEM), treats the computational domain as a single continuous body and captures material failure behaviors through common techniques such as plastic softening and damage models. As the lack of an internal length scale, the standard continuum approaches cannot capture localization of failure, and manifests itself in mesh sensitivity [3,5]. These shortcomings can be overcame by introducing micro-structural effects with second gradient damage models, non-local models [5] etc. On the contrary, the discontinuum approaches, represented by discrete element method (DEM), treat the materials as an assembly of separate blocks or particles, and is capable of incorporating the length scale automatically. The methods of modeling material anisotropy are often classified into smeared approach and discrete approach [6]. The smeared approach utilizes a smeared representation in which the anisotropy is introduced at the level of constitutive laws by varying material parameters as a function of the relative orientation between elements and the bedding plane orientation [7]. The discrete approach utilizes a discrete representation in which the anisotropy is introduced by a geometric description of layers or joints with varying material parameters [6,8,9]. The discrete approach offers unique advantages when the extended loss of continuity inside the material makes continuum constitutive models inappropriate [6].
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.34)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline (1.00)