Enhanced gas recovery by CO 2 sequestration in marine shale: a molecular view based on realistic kerogen model

摘要

Injection of CO~(2)into shale reservoir is regarded as one potential scenario for CO~(2)sequestration and enhanced gas recovery (CS-EGR). In this work, a realistic molecular model of kerogen in Chinese Silurian marine black shale was generated using molecular dynamics (MD) simulations. The competitive adsorption of CH~(4)and CO~(2)was simulated by the grand canonical Monte Carlo (GCMC) method under different reservoir pressures, temperatures, geological depths, CO~(2)mole ratios, and moisture contents of kerogen model. Results show that CO~(2)/CH~(4)adsorption selectivity decreases with increasing reservoir pressure, indicating that CS-EGR can be more efficient if CO~(2)injection is conducted at the late development stage. The temperature has a negative effect on the selectivity, which indicates that thermal stimulation has an adverse effect on the efficiency of CS-EGR. Also, the selectivity decreases with increasing geological depth, suggesting that shallow shale formations are more suitable for CS-EGR. At low pressures, the selectivity increases with increasing CO~(2)mole ratio, while at high pressures, the selectivity decreases with the increase of CO~(2)mole ratio. This result suggests that CO~(2)mole ratio should be dynamically adjusted with the production so as to adapt to the changing reservoir pressure. At higher pressure condition, both the amounts of CO~(2)sequestration and CH~(4)desorption increase with the increase of CO~(2)mole fraction. However, the adsorption stability of CO~(2)weakens with increasing injection amounts of CO~(2). Moreover, the adsorption selectivity decreases initially, and then increases with the moisture content of kerogen. Thus, the performance of CS-EGR may be improved by increasing the kerogen moisture content for Silurian shale gas reservoirs. This study gains enhanced insights on the effect of reservoir pressure, temperature, geological depth, CO~(2)mole ratio, and kerogen moisture content on CO~(2)/CH~(4)competitive adsorption