Molecular insights into recovery of shale gas by injecting CO2-rich industrial waste gas in kerogen slit nanopores

The injection of CO2-rich industrial waste gas into shale reservoirs to enhance shale gas recovery is a new option for achieving a green and low-carbon development of shale gas extraction. In this work, the performance of using CO2-rich industrial waste gas for shale gas replacement was investigated in terms of adsorption behaviors and mechanisms. Grand canonical Monte Carlo simulations were conducted to study the adsorption behaviors and mechanisms of CO2-rich industrial waste gas components in the kerogen slit nanopores. It was found that adsorption capacity in kerogen slits is ranked as SO2 > CO2 > NO > CH4 > CO at pressures less than 4 MPa and the sequencing changes as follows: SO2 > NO > CO2 > CH4 > CO with increasing pressure until 30 MPa. The higher isosteric adsorption heat and stronger interaction between gas molecules and kerogen result in better gas adsorption capacity at low pressures, which is influenced by competitive adsorption at high pressures. The competitive adsorption characteristics of CO2-rich industrial waste gas components with CH4 were also revealed. The results indicated that except for CO/CH4, the adsorption selectivity coefficients of SO2/CH4, CO2/CH4 and NO/CH4 in reservoirs below 4 km are all larger than 1, implying that CO2-rich industrial waste gas has good potential for shale gas replacement. The results are helpful to evaluate the ability of using CO2-rich industrial waste gas for shale gas replacement and provide some guidance for practical application in shale reservoir.