A Review of Molecular Simulation Techniques Applied in Microscopic Occurrence Patterns of Shale Gas

Shale gas is an unconventional hydrocarbon resource existing within the microscopic pores of shale, with a substantial fraction stored as adsorbed gas. Investigating the microscopic accumulation patterns of shale gas is critical for global shale gas exploration and development. As a new method, molecular simulation has emerged as a powerful tool to investigate the microscopic accumulation mechanisms of shale gas in nanopores. Beginning with the methodology and procedures of molecular simulation, this study first introduces the definitions of key parameters, including isosteric heat of adsorption, adsorption amount, density distribution profile, and diffusion coefficients. Subsequently, this study systematically evaluates the effects of temperature, pressure, pore morphology, pore size, gas component, and mineral composition on microscopic occurrence of shale gas. A higher temperature and lower pressure are not conducive to shale gas microscopic occurrence. Pore morphology affects shale gas microscopic occurrence at the pore scale by controlling the number and spatial distribution of adsorption layers at the microscopic scale. Shale components differ in their methane adsorption capacities. Gas competitive adsorption also influences the microscopic occurrence of shale gas. Molecular simulation elucidates the mechanism and controlling factors of adsorbed gas and free gas in shale reservoirs from the microscopic scale, and provides guidance for the optimization and efficient exploration and development of shale oil and gas “sweet spots”.