研究CO2在不同地质环境下的封存情况，是实现CO2节能减排的重要手段。当前全球主要研究集中在深部咸水层封存技术，但咸水层埋深较深，封存难度大且耗时久。考虑到煤矿采空区开采结束后地下空间资源丰富并且伴随着大量离子浓度较高的矿井水，本文以煤矿采空区为切入点，深入探究能否将CO2以深部咸水层封存CO2类似机理封存在煤矿采空区，研究封存状况下煤岩力学参数变化特征。本文通过CO2-盐水互溶试验，得到CO2-盐水溶解度与温度成负相关；与压力呈正相关的溶解规律；试验中随着盐水浓度增大，CO2-盐水溶解度呈现波动上升趋势，因为矿井水中复杂离子的影响，总体促进了CO2在水中的溶解过程。利用COMSOL Multiphysic软件，建立CO2-盐水-煤岩的固液耦合模型，综合考虑孔隙压力、吸附膨胀以及化学反应后模拟得到煤岩在CO2-盐水体系中孔隙率以及渗透率的变化，得出在CO2-盐水共同作用下煤岩孔隙率与渗透率会有一定程度增大，但吸附带来的膨胀效果更为显著，煤岩孔隙率与渗透率小幅下降的结论。利用FLAC 3D软件进行实际工程三维开挖模型建模，探究开挖后的采空区稳定性。利用COMSOL Multiphysics软件构建采空区-CO2-盐水流固耦合模型，拟合流场以及温度场，探究此时采空区的稳定性；通过摩尔浓度扩散模拟封存效果得到长时间封存下CO2扩散情况，模拟结果表明长期封存情况下扩散集中在煤矿采空区，对周围岩层影响较小，有利于CO2封存。
Studying the storage of carbon dioxide in different geological environments is an important means to achieve energy saving and emission reduction of carbon dioxide. At present, the main research in the world focuses on the storage technology of deep saline formations storage, but the storage is difficult and time-consuming. There are a lot of underground space and mine water in the goaf, so this paper takes the goaf of coal mine as the entry point to deeply explore whether CO2 can be stored in the goaf of coal mine by a mechanism similar to the storage of CO2 in deep salt water layer, and study the characteristics of mechanical parameters of coal and rock under the storage condition.In this paper, the CO2-brine miscibility experiment shows that the solubility of CO2-brine is negatively correlated with temperature. The dissolution law is positively correlated with pressure; In the experiment, with the increase of salt water concentration, the solubility of CO2-salt water fluctuates and rises, because the influence of complex ions in mine water generally promotes the dissolution process of CO2 in water.Through COMSOL Multiphysic software, a CO2-saline coupled model of coal and rock was established. After considering pore pressure, adsorption expansion and chemical reaction, the changes of porosity and permeability of coal and rock in CO2-saline system were simulated. It is concluded that the porosity and permeability of coal and rock will increase to a certain extent under the co-action of CO2-salt water, but the expansion effect caused by adsorption is more significant, and the porosity and permeability of coal and rock will decrease slightly.FLAC 3D software is used to build 3D excavation model of actual engineering, and explore the stability of goaf after excavation. COMSOL Multiphysics software was used to construct the goaf -CO2-brine fluid-solid coupling model, which fitted the flow field and temperature field, and explored the stability of the goaf at this time. The CO2 diffusion under long-term storage was obtained by simulating the effect of molar concentration diffusion. The simulation results show that the diffusion is concentrated in the goaf of coal mine under long-term storage, which has little influence on the surrounding rock strata and is conducive to CO2 storage.
