针对我国砂岩热储地热尾水回灌率低、地下水位持续下降的现实问题，特别是水热资源开发利用规模化的天津地区新近系馆陶组和咸阳地区新近系蓝田灞河组砂岩热储，本课题拟从地球化学角度探讨人工注入CO2及其混合气（CO2+H2S/SO2）改造砂岩热储的机理及其对改善储层孔隙度和渗透率的意义。通过开展水-岩-气反应实验、驱替实验以及相应的数值模拟，基于CO2及其混合气（CO2+H2S/SO2）注入前后热储层水样的水化学组分、氢氧同位素和碳同位素值和岩样的矿物组分、化学组分、表面形态以及孔隙度和渗透率变化，研究(1)天然条件下热储水化学形成机制；（2）砂岩热储对CO2及其混合气（CO2+H2S/SO2）注入的地球化学响应、可能的反应过程及其对储层孔隙度和渗透率的影响；（3）利用CO2或其混合气（CO2+H2S/SO2）改造砂岩热储的机理。这对提高砂岩热储尾水回灌率和实现地热资源可持续利用意义重大。

The low waste water reinjectivity into sandstone reservoirs has lead to problems of groundwater level keeping decreasing and environmental concerns, especially for Neogene Guantao formation in Tianjin and Lantianbahe formation in Xianyang area, where hydrothermal resources were commercially developed and exploited. This study tries to discuss the mechanisms of transforming sandstone reservoirs by injecting CO2 or its mixture with H2S (CO2+H2S/SO2) and its significances on improving porosity and permeability. Water-rock-gas interaction and migration experiments and corresponding numerical simulations for these two typical sandstone reservoirs will be carried out. Changes of hydrogeochemistry, hydrogen-2, oxygen-18 and carbon-13 of formation water, mineral & chemical compositions and surface morphology of cores and porosity & permeability before and after CO2 or CO2+H2S/SO2 injection were analyzed to study (1) water chemistry formation mechanism within natural conditions; (2) geochemical responses of sandstone reservoirs to artificial CO2 or CO2+H2S/SO2 injection and its influences on porosity and permeability; (3) the mechanisms of transforming sandstone reservoirs by injecting CO2 or CO2+H2S/SO2. This study will help solving problem of low reinjectivity of waste water for sandstone reservoirs and realizing both sustainable exploitation and utilization of geothermal energy and energy conservation.