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

Abstract

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.