Molecular Simulation Study On Desorption Of Methane In Deep Coal Seam Affected By Multiphase Fluid

As for the exploitation of coal bed methane (CBM) buried deeper than1000m, the technologies of CO2injection for enhanced coal bed methane (ECBM) recovery and CO2storage for replacing methane in coal are still at the exploration stage. Methane adsorption in coal is an important factor in studying these two techniques. Methane, CO2and N2adsorb competitively and an understanding of each gas’s adsorption behavior is significant for determining the feasibility and effect of real treatment. Coal is very heterogeneous with wide distribution in pore size; however, above90%of methane in coal mainly exist in state of adsorption in the micro pores of coal. As the diameter of micro pores has the same magnitude order as that of molecular, so the adsorption and diffusion behaviors of gas and liquid in micro pores has some particularity for difficult to achieve an effective study result through conventional experiment. In order to understand the influence of water and various gas components in micro pores on methane adsorption on coal, a grand canonical monte carlo molecular simulation is applied in this paper, which forces on the research of the following aspects.(1) Based on the period research on the characteristic of deep coal bed methane (CBM) reservoir and the methane occurrence, the limitations of present studies and the solution are outlined. A micro pore model for different pore sizes and water contents is established and the water distribution rule in micro pores is investigated as well.(2) The isothermal adsorption curve of pure gas is simulated base on the model and results are compared and analyzed carefully, including the changing rules of total adsorption capacity and excess adsorption capacity under the influences of temperature, pore size, water content and so on.(3) The competitive adsorption simulations for CH4/CO2(1:1), CH4/N2(1:1)and CH4/CO2/N2(10:3:7)are completed, with considering the changing rules of total excess adsorption capacity under water contents and pore sizes affecting.In general, this paper is innovative in performing the molecular simulation method to study the methane adsorption behavior in deep coal bed methane reservoir under the influence of external fluids. Based on the period researches, the methane adsorption regulation under multi factors, such as temperature, pore size, water content, component, is analyzed, which plays an important role for developing CO2injection for enhanced coal bed methane (ECBM) recovery and scaling up CO2storage for replacing methane in coal.