含杂质气体的CO2地质储存多相多组分反应迁移转化机理和数值模拟

Carbon dioxide geologic sequestration (CGS) is regarded as one of the most potential technology to reduce CO2 emissions from fossil fuels at a large sacle. To reduce the cost of capture, it seems to be economically favorable to co-store CO2 along with impurities from the capture process. However, impurities contained in CO2 stream would affect geophysical and geochemical properties of the systems, further affect flow and reactive transport processes, and eventually affect storage efficiency and safety of CGS. This study, firstly, based on extensive experimental data (collection and supplementary experiment) establishes the mutual solubility model for CO2-impurities-brine systems at wide temperature from 0 to 200 OC, pressure up to 600 bar and salinity up to 6 mol/kg water. Then the equation of state (EOS) is developed and is coupled into the general multiphase and multicomponent reactive transport simulator TOUGH. The new module is verified by comparison with the other standard simulator. An experiment of gas mixture-water-rock interaction, in which the rock is from the typical basin in China for potential CGS, is implemented to analyze the transformation mechanism of CO2 from the gas phase to the aqueous phase, and then to the solid phase (minerals). Finally, a site-scale simulation of multiphase and multicomponent reactive transport for injection of CO2 with impurities based on the new simulator and mechanism is employed to evaluate the effect of impurities on the CO2 storage efficiency.

CO2地质储存被认为是大规模减排CO2最有潜力的方法之一。为了降低捕获成本，CO2联合捕获阶段的杂质气体一起进行地质封存是相对经济的方案。然而，这些杂质的介入会改变地下体系的物理和化学性质，进而影响CO2的迁移转化过程，最终影响CO2地质储存效率和安全。本文首先基于大量的溶解度实验数据（收集和实验补充）建立广阔温度（0-200 OC）、压力（0-600 bar）和盐度（0-6 mol/kgw）下的CO2-杂质气体-咸水体系的相互溶解度预测模型，然后开发相关的状态方程，并耦合到通用的多相多组分反应模拟器TOUGH中。选取我国典型的潜在CO2地质储存场地储层岩心进行室内混合气-水-岩石相互作用实验，分析CO2和杂质由气相到液相，再到矿物相的转化机理。最后，利用开发的模拟器和机理认识开展场地尺度CO2混合杂质气体地质储存的多相多组分反应迁移数值模拟，分析杂质气体对CO2的迁移转化和最终储存效率。

CO2联合捕获阶段的杂质气体一起进行地质封存是降低高昂CCS技术成本的方法之一。然而杂质的介入会改变地下体系的物理和化学性质，进而影响CO2的迁移转化过程，最终影响CO2地质封存效率和安全。本项目通过文献收集和实验补充的大量溶解度数据，采用逸度-活度模型建立了温度0-200 OC，压力0-600 bar和盐度0-6 M范围下CO2-H2S-CH4-咸水体系、CO2-O2-N2-咸水体系的相互溶解度预测模型，并耦合进入到TOUGH框架中，形成了新的非纯CO2地质封存模拟评价模块EOS7Cm，并与已有程序进行了对比验证其可靠性。基于通辽盆地非纯CO2（含空气）的注入试验，评价了CO2、N2和O2的迁移转化规律。模拟结果显示：由于气体组分溶解度的差异，气相前缘出现明显的层析现象，N2在最前缘，其次为O2，最后为CO2；短期（20天）注入过程中，碳酸盐矿物在CO2注入导致的低pH下的溶解反应是主要的水-岩反应过程。基于四川盆地黄草峡枯竭气体的相关地质资料，评价了CO2驱气开发和封存的可行性，并优化相关的注入方案。结果显示：由于储层低压（2 MPa），CO2的高压注入将会引起井筒附近较大的温度降低。在多种限制条件下（比如最大储层压力和温度降等），优化的井口注入压力和温度分别为10.5 MPa和 60oC，对应的单井注入能力为6.89kg/s（21.73万吨/年）。