Application of Digital Volume Correlation and X-ray Computed Tomography Reveal Shale Geomechanical Properties at Elevated Temperature

Experiments were conducted using 1-inch diameter vertical and horizontal core samples of Green River Formation shale. We investigated the Young's modulus and Poisson's ratio of the samples at 200 and 350 °C under triaxial stresses of roughly 1 - 16 MPa employing an unique apparatus that permits time-lapse visualization of the sample. X-ray Computed Tomography (CT) images were collected at a resolution of 195 by 195 by 625 μm while the samples were heated and stressed. In situ CT observations show the conversion of organic matter to mobile hydrocarbon. The FIDVC (Fast Iterative Digital Volume Correlation) method was applied during image processing to obtain and visualize the distribution of axial and radial strains from the CT images. FIDVC also reveals important details about hydrocarbon conversion under maturation conditions at 350 °C. Significantly, the strain using CT imaging and FIDVC agrees with conventional geomechanical measurements including linear variable differential transformer transducers. The strain profiles from FIDVC show the location of greater strain within the sample associated with subcore scale heterogeneity such as differences in density of layer materials. Young's modulus decreased due to rock softening and production of hydrocarbon after maturation processes at 350 ^oC, but Young's modulus did not change post-pyrolysis at a temperature of 200 ^oC. These observations agree with trends found in the literature using conventional geomechanical characterization [White et al., 2017, Burnham, 2018]. Additionally, Poisson's ratio increased post maturation and pyrolysis.