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 CH 4 –CO 2 competitive adsorption is of significance for CH 4 recovery and CO 2 geological sequestration. This study first obtained the structure and size data of anthracite nanopores based on the methods of scanning electron microscopy and N 2 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 CH 4 –CO 2 mixed gas and their underlying mechanisms in nanopores with different geometry shapes were investigated. The research results indicate that the interaction strength between CH 4 and CO 2 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 CH 4 and CO 2 adsorption. At high-pressure conditions, the configurations for CH 4 and CO 2 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. CO 2 injection can effectively recover adsorbed CH 4 . The sequestration rate of adsorbed CO 2 can be significantly enhanced through water content, wedge-shaped region, and curved surface feature of pore geometry shape.