鄂尔多斯盆地深部咸水层二氧化碳地质储存热-水动力-力学(THM)耦合过程数值模拟

注入CO2到深部咸水层(CO2地质储存)被认为是一种直接有效地减少CO2向大气排放的途径。CO2地质储存涉及到热、水动力和力学耦合过程,该耦合过程是预测CO2在储层中的迁移转化、评价储层储存能力和分析潜在风险的关键。基于Terzaghi固结理论,在热-水动力(TH)耦合软件TOUGH2框架中加入了力学模块,形成了新的热-水动力-力学(THM)模拟器。结合鄂尔多斯盆地CO2捕获和储存(CCS)示范工程场地的地质、水文地质条件,采用新的THM模拟器数值分析了CO2注入后地层中的温度、压力、CO2饱和度、位移和有效应力的时空变化特征。结果显示:在井口保持8 MPa和35℃情况下,能够实现10万t/a的CO2注入量;压力上升的范围远远大于CO2运移和温度降低的范围,注入20a后,其最大距离分别达到接近边界10km、620m和100m;位移和应力变化主要与压力变化相关,注入引起最大抬升为0.14m,在注入井附近位置储层中有效应力变化水平方向要大于垂直方向,而在远井位置相反;注入引起井附近有效应力明显减小,从而导致了孔隙度和渗透率的增大,增强了CO2注入能力。

Numerical Simulation of Coupled Thermal Hydrodynamic Mechanical (THM)Processes for CO2 Geological Sequestration in Deep Saline Aquifers at Ordos Basin,China

Injecting CO2 into deep saline aquifers, referred to as CO2 geological sequestration (CGS),is considered to be a promising method to reduce the emission of anthropogenic CO2 to atmosphere.CGS involves coupled thermal-hydrodynamic-mechanical (THM) processes,which are important for predicting migration and transformation of injected CO2 , evaluating the reservoir performance,and assessing the risk associated.Based on the Terzaghi consolidation theory,a coupled mechanical module is developed that is incorporated into the existing simulator TOUGH2,which is a well-established code for TH processes in subsurface flow systems. Based on the geological and hydrogeological conditions of the Ordos CCS Demonstration Project,the new THM simulator is used to numerically analyze the spatial and temporal distribution of the temperature,pressure,CO2 saturation, vertical displacement,and effective stress.The results show that 10 5 metric tons of CO2 per year can be finished under the injection condition of wellhead pressure 8 MPa and 35 ℃.The lateral distance with pressure buildup is more than that of CO2 plume and that of temperature decrease .They are 10 km,620 m and 100 m,respectively after 20 years ’injection.The vertical displacement and change of the effective stress are mainly related to the change of the pressure.The maximum surface uplift is about 0.14 m.The effective stress change is more significant in the horizontal direction than that in the vertical direction near the injection well,while it’s in the opposite away from the injection well. Injection induces an obvious decrease in the effective stress but enhances the porosity and permeability, this,in turn increases the CO2 injectivity ultimately.