Molecular simulation of the displacement of shale gas in quartz slit by flue gas

To study the efficiency of flue gas sequestration with enhanced shale gas recovery in quartz slit, Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations were adopted to investigate the influence of burial depth, formation water content and the injection ratio of flue gas on the recovery efficiency of shale gas (CH4) in quartz slit by flue gas (CO2/N2). The density distribution, loading, adsorption heat and interaction energy of each component were systematically analyzed to reveal their adsorption mechanisms and the recovery efficiency of CH4. It indicates that the loadings of mixed CH4 and N2 (ΓCH4 and ΓN2) exhibit negative correlation with formation water content. With the increasing burial depth, both ΓCH4 and ΓN2 increase at first and then tend to be constant when the burial depth is over 2 400 m. The maximum loading of CO2 (ΓCO2) occurs at the burial depth of 2 400 m. There is a positive correlation of ΓCO2 with formation water content when the burial depth is below 2 400 m, and a negative correlation when the burial depth is over 2 400 m. The recovery efficiency of CH4 (η) reaches the maximum point at the burial depth of 400-600 m, which increases with the increasing mole fraction of CO2 in flue gas, showing that CO2 in flue gas can promote the displacement of CH4 significantly.