CH ₄ –CO ₂ Competitive Adsorption on Water-Bearing Anthracite Nanopores with Various Geometry Shapes

Investigating the control mechanism of the geometry shape of water-bearing nanopores on CH4–CO2 competitive adsorption is of significance for CH4 recovery and CO2 geological sequestration. This study first obtained the structure and size data of anthracite nanopores based on the methods of scanning electron microscopy and N2 adsorption and combined molecular simulation technology to construct four types of nanopore models: triangular pore, square pore, circular pore, and slit-shaped pore. Then, the differences in the adsorption of CH4–CO2 mixed gas and their underlying mechanisms in nanopores with different geometry shapes were investigated. The research results indicate that the interaction strength between CH4 and CO2 with nanopores of different geometric shapes is as follows: circular pore > triangular pore > square pore > slit-shaped pore. The geometric shape of nanopores is closely related to the configurations for CH4 and CO2 adsorption. At high-pressure conditions, the configurations for CH4 and CO2 adsorption in the triangular pore and square pore gradually tend toward a circular shape. The wedge-shaped region of the nanopores exhibits stronger adsorption capacity, and an acute angle possesses the stronger interaction with adsorbates than a right angle. As the water content increases, the peak density of adsorbed phase transitions from a symmetric distribution to an asymmetric distribution. CO2 injection can effectively recover adsorbed CH4. The sequestration rate of adsorbed CO2 can be significantly enhanced through water content, wedge-shaped region, and curved surface feature of pore geometry shape.