Reviews on Simulation Studies of Coalbed Gas Recovery and Transport Processes

Coal and shale contain enormous natural gas resources. The reservoir structures are complex, with an extensive distribution of micropores and nanopores, leading to intricate gas transport mechanisms. Simulation methods play a crucial role in unraveling the complex transport phenomena associated with coal-bed methane and shale gas. This Review examines the recent advances in simulating gas transport in porous media for predicting gas migration. It discusses the fundamental theories of gas transport in nanoscale pores, encompassing the gas transport mechanisms in porous media and the fundamental equations involved in the simulation methods. Furthermore, a review is provided on the molecular dynamics (MD) and lattice Boltzmann methods. Emphasis is placed on the methods of pore reconstruction, including pore volume, pore size, and pore shape, and their application in diffusion and transport. The advantages and limitations of these two simulation modeling methods are also discussed. The application of various coupled methods in the study of gas transport in porous media is explored, with a key focus on appropriately handling scale translations in flow modeling. This work enhances the understanding of coalbed gas transport and dispersion behavior by summarizing simulation methods for coalbed gas and shale gas transport. Coal reservoirs, compared to shale, exhibit different gas pressures and organic compositions. Hence, the gas transport mechanisms in coal nanopores are still not fully understood. Further research and analysis are needed to investigate how shale gas models can be applied to coalbed gas.