Thermo-mechanical properties and fracture behavior of granite at pore scale: implications for geological storage

Geological storage of energy and carbon dioxide requires a deep knowledge of the complex thermo-hydro-chemo-mechanical processes that affect the stability and performance of reservoir rocks. In this study, we investigate the thermo-mechanical properties and mesoscale fracture behaviors of four key minerals in granites: quartz, plagioclase, amphibole, and biotite. We use a combination of experimental and analytical techniques to reveal the microscale mechanisms of rock failure under high temperature and tensile loading. We perform nanoindentation tests under dynamic heating–cooling cycles to measure the reduced modulus and hardness of the minerals. We also conduct mode I fracture tests under tensile loading conditions to evaluate the fracture toughness and tortuosity of the granite. We observe the dynamic crack propagation and fracture morphology of minerals using scanning electron microscopy. We analyze the structural and physio-chemical changes at high temperatures using X-ray diffraction, thermogravimetric analysis, and Fourier’s transform infrared spectroscopy. We find that the thermo-mechanical properties and fracture behaviors of the minerals are governed by three main factors: the alterations in mineral structure, the aperture of open cracks along cleavage planes, and the degree of heterogeneity due to mineral composition complexity. We identify two different damage modes in granite: catastrophic and non-catastrophic failure modes. We explain the underlying mechanisms of each mode and show that catastrophic failure has precursory signs, while non-catastrophic failure does not. Our results provide new insights into the microscale mechanisms of rock failure under high temperature and tensile loading, which have implications for the macroscopic understanding of rock behavior in geological storage applications. By elucidating the microscale intricacies, this study enhances our understanding of the multifaceted interactions that influence the stability and performance of rocks, and supports the development of improved geological storage strategies, such as carbon sequestration and enhanced energy storage.