Molecular Simulation of the Occurrence States of Methane in Wedge-Shaped Quartz Pores

The adsorption state of methane is significantly influenced by the shape of pores in different matrices. To investigate the occurrence states of methane in heteromorphic quartz pores, three wedge-shaped triangular quartz pores were established, and comparison with the scanning electron microscope photographs of actual shale was conducted. The adsorption states of methane in the wedge-shaped triangular quartz pores at the temperature of 323 K and the pressure of 30 MPa were simulated using the molecular dynamic method. Simulation results show that the adsorption state of methane is distinctly influenced by the wedge angle. At the wedge vertex, the methane density increases as the wedge angle increases. Inside the pores, methane adsorption reaches 2-3 layers near the slit wall surface, and the number of adsorption layers increases as the wedge angle increases. For the first adsorption layer, the larger the wedge angle is, the higher the rate of density decreases is. From the whole model, the effect of wedge angle on the adsorption state of methane decreases with increase in distance from the wedge vertex. The total interaction between methane and quartz and the energy state of each methane molecule determine the state of methane in the pore. The distance from the wedge vertex increases, and the weight of the energy state of each methane molecule gradually increases; however, the total interaction between methane and quartz is still dominant. This study shows that the occurrence states of methane are closely related to the shape of quartz pores.

Automated summary

The shape of quartz pores significantly impacts the adsorption state of methane. In this study, wedge-shaped triangular quartz pores were created to investigate the occurrence states of methane. Molecular dynamic simulations were conducted at a temperature of 323 K and a pressure of 30 MPa. The results show that the adsorption state of methane is influenced by the wedge angle, with increased density and number of adsorption layers as the wedge angle increases. The interaction between methane and quartz, as well as the energy state of each methane molecule, determine the state of methane in the pore.