Investigation of Thermal Induced Damage of Deep Shale Considering In-Situ Thermal Shock Effects

Thermal shock caused by injecting cold fluids into hot underground formations, like deep shale hydraulic fracturing and geothermal extraction, is believed to cause deterioration of rock mechanical properties. Conse-quently, investigating thermally induced damage in deep shale under in-situ conditions is necessary to under-stand its mechanical behaviors. In this study, the structure and permeability characteristics of shale rock before and after different cooling modes are measured with the gas permeability measurement and CT-Scanning, the compression mechanical response of thermal shock specimens under in-situ conditions and its application prospects are discussed, and a statistical damage model is established eventually to predict deep shale me-chanical constitutive. Results show that cooling rate was critical in the deterioration of rock properties, since micro-cracks were induced in water-cooling specimens, the physical properties of these samples were signifi-cantly enhanced. Moreover, rock mechanical properties were also deteriorated by thermal shock immensely and the deterioration was aggravated as the contact temperature difference increased. The understanding suggested that thermal shock was beneficial to increase fracture complexity and enhance shale seepage capacity, cryogenic fracturing techniques were applicable in enhancing stimulation response. Finally, the overall experimental and modeling methods introduced in this paper could well reflect the mechanical behaviors of deep shale considering thermal shock effects.