Study on the Interaction Mechanism Between CO2 Injection into Jimsar Shale Oil and Rock and Formation Water

CO2 injection development has the advantages of improving reservoir properties, reducing reservoir crude oil viscosity, and expanding crude oil volume, which is an important measure to improve shale oil recovery. However, after CO2 enters the reservoir, it will disrupt the original balance of the formation system, leading to a series of gas water rock reactions with complex mechanisms. By conducting CO2 rock formation water reaction experiments and numerical simulations on the core samples of the Lucaogou Formation in Jimsar, the CO2 rock formation water reaction law of the main reservoir in Jimsar was explored, and the characteristics of mineral dissolution, precipitation, and mineral transformation caused by CO2 injection in the reservoir were determined. The influence of CO2 fluid on the pore characteristics of the reservoir was revealed. The experimental and numerical simulation results indicate that the soluble minerals in the reservoir are feldspar minerals, and the precipitated minerals are carbonate minerals such as calcite and dolomite. In the case of continuous dissolution of feldspar, a certain amount of quartz precipitation was generated in the simulation of the five rock samples used to study the reservoir, which is one of the factors affecting the overall porosity reduction of the reservoir. Injecting CO2 into the upper sweet spot of a reservoir is beneficial for oil recovery and extraction, while generating carbon fixing minerals from the lower sweet spot is beneficial for long-term CO2 sequestration.