We present micromechanical modeling of an indentation experiment on Green River Shale with simultaneous X-ray micro-computed tomography of internal sample deformation that provides new insights into the ductile-brittle micromechanical behavior of shales relevant to proppant embedment. Brittle wing cracks appear from the indenter along the shale bedding, but indentation depth is dominated by ductile plastic shear deformations governed by extreme compressive stress magnitudes below the indenter-shale contact. Simultaneous analysis of the experimental loading-unloading indentation curves and the imaged shale deformations were used to constrain elasto-plastic properties and strength anisotropy of the tested Green River shale sample.
The evolution of rock fractures and their fluid transmissivity are critical in underground energy geosciences activities, such as hydrocarbon production, carbon sequestration, geothermal energy, and nuclear waste disposal (Rutqvist and Stephansson, 2003). The fluid transmissivity of a fracture depends on factors such as the local stress across the fracture, fracture surface roughness, shear displacement offset, and host rock properties (Barton et al., 1985). In hydrocarbon production, proppants such as sand are frequently injected into fractures to keep them open for enhanced hydrocarbon production (Kadende et al., 2021a). However, even proppant-filled fractures may close significantly because of embedment of the proppant into the fracture surfaces and proppants may also be crushed under high stress (Kantende et al., 2021b). The embedment of proppants may be particularly severe in shales high in organic carbon or clay, shales that may be characterized as self-sealing (Bourg, 2015).
In this study we present micromechanical modeling of an indentation experiment on a soft Green River shale of high organic carbon content. The experiment was conducted under simultaneous synchrotron X-ray micro-computed tomography to image internal three-dimensional sample deformation. This include tomographic images of internal deformation anisotropy, fracturing, and surface pileup adjacent to the indenter. The modeling presented in this paper shows that matching the experimental loading-unloading indentation curves and the shale deformation field in three dimensions can be used to constrain elasto-plastic properties and strength anisotropy of the tested shale sample. The work also provides new insights into the ductile-brittle micro-mechanical behavior of shales relevant to proppant embedment.
