EGS地热能开发过程中水岩作用对热储层特征的影响

Impacts of water-rock interactions on thermal reservoir characteristics in EGS geothermal development

增强型地热系统(EGS)是一种从地下深部低孔低渗高温岩层提取大量热能的能量利用工程,通过注水孔注入的冷水在高温岩层中循环实现热量的提取。在EGS地热能开发过程中,冷水的循环扰乱了地下深部水岩系统的热平衡和化学平衡,导致部分矿物溶解或沉淀,进而改变储层的孔隙度和渗透率。文章利用不锈钢密闭反应釜进行室内高温水岩反应试验,结合数值模拟分析水岩相互作用对EGS热储层特征的影响。研究结果表明,注入冷水到花岗岩热储层中导致石英矿物沉淀,其相对质量分数增大13%,碱性长石、斜长石、黑云母矿物溶解,其相对质量分数分别减小7%,5%,1%,总体上使得溶液中Si元素浓度降低,Ca2+,Na+,K+浓度升高,储层孔隙度、渗透率均随时间逐渐增大,提高了EGS储层地热能开发的热提取效率。

Enhanced geothermal system（EGS） is an energy project that extracts a large amount of thermal energy from a low porosity and permeability rock formation with high temperature in deep of the earth. EGS uses the cycle of cold water injected into the high temperature formation to extract heat.However, the cold water circulation disrupts the thermal balance and chemical balance of the waterrock system, which leads to mineral dissolution or precipitation, thereby affects the porosity and permeability of reservoir. In this paper, the impact of water-rock interaction on reservoir characteristics is analyzed though a water-rock reaction experiment which uses a sealed stainless steel reactor and a numerical simulation. The results showed that cold water injected into the granite reservoir causes precipitation of quartz mineral whose relative mass fraction increases by 13%, and dissolution of alkali feldspar, plagioclase and biotite, and their relative mass fraction decrease by 7%,5% and 1% respectively. The concentration of Si decreases and the concentration of Ca2 ＋, Na＋, K＋increase in the solution. Consequently, reservoir porosity and permeability increase with time gradually, which improves the heat extraction efficiency of EGS geothermal exploitation.