Effects of gas components on acid-rock reaction during CO2-contained industrial waste gas (CO2-contained IWG) injection into deep shale reservoir on geologic time scale

The shortage of CO2 source and the challenges associated with the separation of pure CO2 have led to a growing interest in the potential utilization of CO2-contained IWG. Therefore, this study has established an acid-rock interaction kinetic model to characterize the long-term interactions between CO2-contained IWG and shale. The findings delineate the reaction process into three phases: during the initial 10 years, solubility trapping predominates, with minimal mineral dissolution. This increases shale porosity, promoting the diffusion and storage range of CO2-contained IWG. Between 10 and 300 years, mineral dissolution/precipitation assumes primacy, with mineral trapping gradually supplanting dissolution. Notably, shale porosity diminishes by a minimum of approximately 40%, effectively inhibiting gas leakage. After 300 years, equilibrium is reached, with rock porosity consistently lower than the initial porosity. Throughout the entire reaction process, as the initial CO2 concentration decreases, the initial pH drops from 4.42 to 3.61, resulting in a roughly 20% increase in porosity. Additionally, it is necessary to regulate its concentration to avoid H2S leakage during CO2-contained IWG geological sequestration. And particular attention should be directed towards the risk of gas leakage when the IWG exhibit high levels of SO2 or NO2.