Hydro-mechanical-chemical Coupling Mechanisms and Synergistic Optimization of CO2 Geological Storage and Enhanced Oil Recovery in Low-Permeability Carbonate Reservoirs

Carbon geological storage is critical for mitigating greenhouse gas emissions. This study is aimed at lowpermeability carbonate reservoirs during CO2 injection and investigates the Hydro-Mechanical-Chemical (HMC) coupling mechanisms by using an integrated approach combining theory, experiments, and simulation. In this work, a coupled mathematical model considering nonlinear flow, effective stress and mineral reaction kinetics was established. The core experiments provided variation curves of permeability with effective stress and mechanical parameters to establish a coupled HMC relationship, and the process of CO2 injection into carbonate rock reservoirs was numerically simulated. The results of the rock stress sensitivity test indicate that the reservoir permeability decreases by up to 33.3% with the effective stress increases. The injection of carbon dioxide increased the pore pressure of the reservoir and reduced the effective stress, and resulted in 1.67% and 15% increase in porosity and permeability of the reservoir within two years. The mineralization reaction of the reservoir rock led to a decrease in the contents of calcite and dolomite from 78.3% and 13.6% to 57% and 1.6%, respectively, while the content of chlorite increased from trace amounts to 34.9%. which are mainly attributed to the processes of mineral dissolution and precipitation. By adopting a five-point well pattern with a daily injection volume of 10,000 m3/day, and a 60-day cyclic cycle, higher oil recovery efficiency and CO2 sequestration effect can be achieved. This work provides systematic theoretical and engineering foundations for the safe CO2 geological storage and enhance oil recovery efficiency in low-permeability carbonate reservoirs.