Molecular simulation of displacement of shale gas by carbon dioxide at different geological depths

• We investigate the displacement of shale gas by carbon dioxide at different conditions.
• The increase of pore size is beneficial for the displacement of shale gas.
• The optimum operating conditions of carbon dioxide displacing shale gas are recommended.

The rising worldwide energy demand has greatly stimulated the exploitation of shale gas. Meantime, global warming mainly caused by CO2 emission is a significant concern. As a new scenario, injecting CO2 to displace shale gas is proposed to improve the exploitation efficiency of shale gas and reduce the amount of CO2 emission. In this work, we use a grand canonical Monte Carlo simulation to investigate the displacement of shale gas by CO2 and the sequestration of CO2 simultaneously in a modeled shale matrix at different geological depths from 1 to 4 km, where the shale is modeled by inorganic clay mineral and organic matter. We find that both the displacement amount of CH4 and the sequestration amount of CO2 increase with the pore size of the shale at a fixed CO2 injection pressure, which suggests that the hydro-fracturing technology would be very beneficial for displacement exploitation of shale gas. Moreover, we also find that the optimum operating condition for CO2 displacing shale gas is at the depth of 1 km, which provides a guidance and reference for displacement exploitation of shale gas by CO2.

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