Numerical Simulation of CO2 Migration and Geochemical Reactions in Shihezi Formation Caprock, China

CO2 geological storage, which is an effective way to reduce CO2 emissions, is of great significance to mitigate the current greenhouse effect. In long-term CO2 storage, although the chemical reaction rate of CO2–brine–rock is slow, it can significantly change the mineral composition of rock and the structure and properties of pores and joints, and then change the transport process and distribution state of CO2 in porous media. Therefore, a simplified 2D geological model is established based on the geological data of the Shihezi Formation in the Ordos Basin, China. The mechanism of the CO2–brine–rock reaction and its effect on mineral transformation and pore permeability are studied. In the early stage of CO2 geological sequestration, the rate of CO2 intrusion into the caprock is fast, the CO2–brine–rock reaction in the early stage is mainly a dissolution reaction, and the porosity and permeability of the caprock show an increasing trend. During the period from 100 to 1000 years of CO2 sequestration, the vertical distance of CO2 intrusion into the caprock does not change much. During this period, the type of CO2–brine–rock reaction is mainly a precipitation reaction, which reduces the porosity and permeability of the caprock and increases the sealing ability of the caprock to a certain extent. Our results can not only provide theoretical support for the site selection and risk assessment of CO2 geological sequestration, but also provide a theoretical basis and practical guidance for large-scale commercial storage in the future.