Molecular insights into gas adsorption and competitive adsorption behavior of CH4/CO2 in coal seam gas reservoir with the presence of comprehensive influencing factors

This thesis focuses on the investigation of adsorption and competitive adsorption behavior of CH4 and CO2 in coalbeds with respect to the presence of encroachment water, salinity and ethane. For that propose the thesis is split into three parts: Part I discusses the gas adsorption behavior in a simplified coalbed slit, which is represented by a three-layer graphene. The coal model is constructed by the Molecular Dynamics simulation, and the gas adsorption profiles are defined by employing the grand canonical Monte Carlo simulation. Then the effects of encroached water, salinity concentration and C2H6 on CH4 adsorption and the Preferential adsorption Selectivity are discussed. Encroached water and associated gas C2H6 usually negatively affect the CH4 adsorption process; however, an advantageous effect on the Preferential adsorption Selectivity. Part II is undertaken in a kerogen matrix, which focuses on the gas adsorption behavior within the micropores of the coalbeds. And the aforementioned terms are investigated in this kerogen model. Because H2O has superior affinity with coalbed, CH4 adsorption is dramatically reduced with the presence of encroached water and shows a further reduction with the increasing salinity of NaCl dissolution. Additionally, C2H6 has a negative on CH4 adsorption. And the above-mentioned terms promotes the Preferential adsorption Selectivity. Part III combines the two essentials of slit and micropores jointly to represent a more realistic coalbed. Comparisons of absolute, excess adsorption are made in matrix and the entire coalbed model. This shows the great essential of the embedded slit, which exhibits the significance of this combined coalbed model. The prementioned terms are probed and discussed, which have impeded influences on single phase gas adsorption but favor the Preferential adsorption Selectivity