Experimental study on the degradation mechanism of granite pore structure and thermo-mechanical properties under acidic water-rock interaction

Abstract:

Water-rock interaction（WRI） during Hot Dry Rock （HDR） exploitation is a critical factor affecting the long-term stability of geothermal reservoirs. To address the challenge that conventional experimental methods struggle to simultaneously simulate long-term effects while preserving sample integrity， this study introduces a self-developed high-temperature and high-pressure WRI simulation device. Using an acidic solution as an accelerating medium， dynamic interaction experiments on granite samples were conducted for 3， 6， and 9 days. Through a combination of nuclear magnetic resonance， thermal conductivity analysis， and mechanical testing， this research systematically reveals the synergistic degradation mechanism of the granite''s pore structure and thermo-mechanical properties under acidic conditions. The results demonstrate that acidic WRI leads to a non-linear and dramatic increase in granite porosity （by 448% within 9 days）， with a shift in pore size distribution from predominantly micropores to a higher proportion of meso-and macropores. The deterioration of the pore structure induces a significant decline in thermal conductivity and uniaxial compressive strength， which decrease by 8.63% and 33.19%， respectively， over the same 9-day period， showing highly consistent evolutionary trends. This study successfully establishes a quantitative link between short-term accelerated laboratory simulations and long-term in-situ evolutionary behavior， providing crucial experimental data and theoretical support for accurately predicting the physical-mechanical behavior of HDR reservoirs during their service life， assessing their long-term stability， and ultimately ensuring the safe and efficient development of geothermal resources.