Simulation of Methane Occurrence in Rough Nanokerogen Slits

Understanding the occurrence state of methane in real kerogen nanopores is essential for the development of shale gas. This study presents a novel method for constructing rough kerogen surfaces to investigate the adsorption phenomena and the mechanism of methane occurrence in kerogen nanorough slits. Various organic matter slits with different roughness (Rms) were constructed based on the rough kerogen surface. In addition, the dynamic behavior of methane within these slits was then simulated by using Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) methods under specific environmental conditions. Finally, the simulation results were compared with the experimental isothermal adsorption results of four samples from Well Liye 1 in the Lishu Fault Depression of the Songliao Basin. The results show that the average methane density (ρave) and the occurrence state within the pores are significantly affected by the roughness, with the average methane density generally decreasing as the surface roughness increases. The methane adsorption state forms intermittent adsorption layers at the concave and convex parts of the rough kerogen surface. Additionally, the increase in surface roughness leads to a decrease in the adsorption amount per unit of specific surface area. Finally, the methane adsorption potential analysis reveals that the primary methane adsorption site is at the concave part of the kerogen surface and methane remains stable under high pressure, low temperature, and rough slit adsorption conditions.