地下热-水动力-力学耦合过程数值模拟:以CO_2地质储存为例

在地下流动系统问题的研究中,热-水动力-力学(THM)耦合过程是研究的热点问题。在地下多相非等温数值模拟软件TOUGH2的框架内,基于Biot固结理论和摩尔-库仑破坏判定准则,建立了THM耦合模型;采用积分有限差和有限元联合的空间离散方法,开发了THM模拟器TOUGH2Biot。该模拟器中热和水动力过程是全耦合,力学过程是部分耦合。通过与解析解的对比,验证了其正确性。基于鄂尔多斯盆地CCS示范工程,采用TOUGH2Biot研究了CO2注入地层后的THM响应。结果显示CO2的注入引起流体压力急剧增加,地层有效应力减小,地表隆起,隆起大小在几十个厘米,同时孔渗增加,利于CO2注入引起的压力上升向外消散。CO2注入最有可能导致剪切破坏的位置位于最大速率注入点上部盖层,其次为靠近地表的位置。

Numerical simulation of subsurface coupled thermo-hydro-mechanical (THM) processes: Application to CO2 geological sequestration

Coupled thermo-hydro-mechanical (THM) process is an important and hot-spot issue. Based on Biot consolidation theory and Morh-Coulomb failure criteria, coupled THM model is built in the framework of TOUGH2 which is a multiphase fluid flow, nonisothermal simulation software. At the same time, a new simulator-TOUGH2Biot is developed with fully coupling between thermal and hydrodynamic processes and partly coupling for mechanics, using mixed integral finite difference and finite element method. Analytical solution is employed to verify the simulator. Finally, TOUGH2Biot is used to numerically analyze the THM response of formations after CO2 injection. The results show that the CO2 injection induces to a quick increase in fluid pressure and corresponding decrease in effective stress. Consequently, there is an uplift of tens of centimeters at the surface. Also, the porosity and permeability are enhanced, which are favorable for dissipation of pressure buildup. The most possibility of shear slip failure is at the caprock above the maximum injection rate location. The second potential failure location is near the surface.