Coupled thermo-hydro-mechanical (THM) behaviour of rock relevant to the geothermal industry

Australian contains one of the hottest granite on earth at reasonable drilling depth and Hot Dry Rock (HDR) geothermal energy is considered as a practical prospect in the future. This thesis aims to study the mechanical behaviours geothermal reservoir rock at the deeply buried earth. Temperature, pressure and fluid flow forms a complex mechanism that can be extremely differs from the surface rocks. A large amount of experimental works have carried out and the results will contribute information for the development of guidelines for engineering design at depth, including the rock physical property (mineralogy, grain size and porosity) dependence, temperature dependence and pressure dependence. Besides, a new multiphase high pressure and temperature controlled triaxial testing apparatus for geomaterials is designed and constructed in purpose of simulating the actual underground condition. This apparatus allows confining pressure up to 130 MPa, temperature up to 400 °C and fluid injection of 160 MPa, with axial loading capacity of 100 tonnes. Numerical study was generated using the finite element method and ABAQUS software. Acoustic emission (AE) technology was used to study the stress thresholds of rock failure process; nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) were used to observe the micro-structure and chemical composition changes of rock subjected to high temperatures. This research has developed an empirical and numerical understanding of the mechanical behaviour expected of rock in deep engineering scenarios, especially for enhanced geothermal energy.