Molecular simulation of CH4 and CO2 adsorption in shale organic nanopores

Using CO2 as an alternative working fluid to displace shale gas has been considered as a promising technology, which can not only enhance shale gas recovery but also geologically sequester CO2 in shale reservoirs. The adsorption behaviour of CH4 and CO2 in shale is the key to evaluate the efficiency of CH4 production and potential of CO2 sequestration. In the present work, the cylindrical and slit kerogen nanopores were constructed to represent the realistic organic nanopores existing in shale matrix. The adsorption behaviours of pure CH4 and CO2/CH4 mixture were investigated by employing the grand canonical Monte Carlo method. The results indicate that the adsorption capacities of CH4 in shale kerogen nanopores increase with the increment of pressure. However, temperature exhibits a negative impact on the gas adsorption capacity. The effects of pressure, temperature on competitive adsorption performances of CO2/CH4 mixture were discussed. It is found that the adsorption capacities of CO2 are significantly higher than that of CH4 at various pressure and temperature conditions. Both the adsorption capacity and selectivity should be taken into consideration to determine the proper conditions in the practical project.