A multiscale framework for the simulation of the anisotropic mechanical behavior of shale

Abstract

Summary Shale, like many other sedimentary rocks, is typically heterogeneous and anisotropic and is characterized by partial alignment of anisotropic clay minerals and naturally formed bedding planes. In this study, a micromechanical framework based on the lattice discrete particle model is formulated to capture these features. Material anisotropy is introduced through an approximated geometric description of shale internal structure, which includes representation of material property variation with orientation and explicit modeling of parallel lamination. The model is calibrated by carrying out numerical simulations to match various experimental data, including the ones relevant to elastic properties, Brazilian tensile strength, and unconfined compressive strength. Furthermore, parametric study is performed to investigate the relationship between the mesoscale parameters and the macroscopic properties. It is shown that the dependence of the elastic stiffness, strength, and failure mode on loading orientation can be captured successfully. Finally, a homogenization approach based on the asymptotic expansion of field variables is applied to upscale the proposed micromechanical model, and the properties of the homogenized model are analyzed. Copyright © 2017 John Wiley & Sons, Ltd.

Fracture Properties of Nash Point Shale as a Function of Orientation to Bedding

“…Hydraulic fractures in unconventional oil and gas reservoirs are often modeled as having straight geometries with little or no correction for roughness, tortuosity, or deflection (Li et al, ; Wangen, ; Zhao et al, ). Furthermore, many models also consider reservoirs to be mechanically isotropic (Feng & Gray, ; Li et al, ; Wangen, ; Zhao et al, ). Our results demonstrate that neither assumption is likely to be valid either for shale units or reservoirs composed largely of shale.…”

“…While there have been numerous reports of tensile strength anisotropy in layered rocks (e.g., Islam & Skalle, 2013;Li et al, 2017;Rybacki et al, 2015;Tavallali & Vervoort, 2013), there have been relatively few reported measurements of fracture toughness anisotropy in such rocks. This is particularly true for shales, for which only a handful of studies to date report data on the fracture toughness in more than one orientation (Chandler et al, 2016;Kabir et al, 2017;Lee et al, 2015;Schmidt, 1977).…”

Anisotropic elastic, strength, and fracture properties of Marcellus shale

“…Their mineralogical composition exhibits a wide range, including clay, quartz, feldspar, and other minerals [1]. The heterogeneities exist at different length scales ranging from microscopic level to an entire rock mass, which leads to a large variety of macroscopic behaviors [1,2]. As a result, the experimentally determined properties are not singlevalued, well-defined parameters for a given type of shale.…”

Joint Elasticity Effect on the Failure Behaviours of Rock Masses using a Discrete Element Model

“…Based on their assessment, they recommended the discontinuous models with two identified failure modes, i.e., sliding failure along the joint and shearing failure of rock matrix. However, the mixed failure mode is widely observed when the joint orientation becomes larger than the joint friction angle in previous studies [6][7][8].…”

“…The estimation of anisotropic mechanical properties for these rock masses is critically important in rock engineering applications such as rock slope, rock tunnel, underground excavation, etc. To fully capture the mechanical properties of anisotropic rock masses, many laboratory studies have been performed on the sedimentary rocks [4,5] and jointed rock masses [6][7][8]. The results obtained from those laboratory tests indicate that the weakness orientation largely influences the failure strength of rock masses.…”