CH4 and CO2 adsorption-induced deformation of carbon slit pores with implications for CO2 sequestration and enhanced CH4 recovery

Geological sequestration of carbon dioxide (CO2) into coal seams and shale gas reservoirs have the benefits of CO2 storage as well as enhanced gas recovery. However, the coal or shale swelling during CO2 enhanced methane (CH4) production significantly reduces the gas injection and production rate. In this work, the CH4 and CO2 adsorption-induced deformation of carbon slit pores as representative of coal and shale nanopores was studied using grand canonical Monte Carlo simulation. We focused on the strain difference by comparing the CO2 and CH4 adsorption-induced deformation of pores with various widths. The effect of each pore width on the bulk swelling was analyzed under different pressures and temperatures. The results showed that the strain difference between CO2 and CH4 at different conditions oscillates with a damped amplitude as the pore width increases, which can be positive or negative indicating pore swelling or contraction when CH4 is displaced by CO2. The maximum swelling occurs among the pores inaccessible to CH4 but accessible to CO2 molecules and the contracting pores contribute negatively to the bulk swelling. Furthermore, this study provided fundamental adsorption induced strain of each pore width for predicting the bulk deformation during CO2 enhanced CH4 production when the coal or shale pore size distribution is known.