酸性水-岩作用下花岗岩孔隙结构与热-力学性能劣化机理的实验研究

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

摘要:

干热岩开采过程中的水岩作用是影响储层长期稳定的关键因素。针对传统实验方法难以同时兼顾“长期效应”与“试样完整性”的难题，本研究自主研发了一套高温高压水岩作用模拟装置，以酸性溶液为加速介质，对花岗岩岩样开展了3、6、9 d的动态作用实验。结合核磁共振、热常数分析及力学测试，系统揭示了酸性环境下花岗岩孔隙结构及热-力学性能的协同劣化机理。结果表明：酸性水-岩作用导致花岗岩孔隙度非线性剧增（9 d内增幅448%），孔径由小孔主导向中、大孔调整；孔隙结构的改变引发导热系数与单轴抗压强度显著衰减，9 d内分别降低8.63%和33.19%，二者演化趋势高度一致。本研究成功构建了实验室短周期加速模拟与工程长期演化行为的定量关联，为精准预测干热岩储层服役期间的物理力学行为、评估储层稳定性，进而保障地热资源安全高效开发，提供了关键的实验依据和理论支撑。

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.