Critical factors controlling shale gas adsorption mechanisms on Different Minerals Investigated Using GCMC simulations. (February 2019) - Chen, Guohui
Abstract: Understanding the adsorption mechanisms of different gas molecules on various minerals is crucial for accurately modelling shale gas adsorption behaviors and for objectively evaluating adsorbed gas contents under geological conditions. We simulated the adsorption behaviors of CH4, CO2 and N2 on both organic matter and inorganic minerals at 60 °C and 90 °C over a range of pressures up to 50 MPa by using the Grand Canonical Monte Carlo (GCMC) method. It has been found that both the comprehensive effect of the adsorption sites with differential adsorption capacity and the distribution density of the adsorption sites on the organic matter and inorganic mineral surfaces control the adsorption capacity in terms of per unit surface area of minerals. For individual minerals with a certain adsorption capacity in terms of per unit surface area, the specific surface area of individual minerals is the critical factor that determines the adsorption capacity in terms of per unit mass of the minerals. The interaction among gas molecules also affects the adsorption behavior slightly. We further compared the adsorption capacity among various gas molecules on both organic matter and inorganic minerals by inspecting the strength and distribution density of the adsorption sites on mineral surfaces, the specific surface area of the minerals and the interaction strength among gas molecules. These investigations allowed us to identify the key factors controlling shale gas adsorption mechanisms on different minerals, which provide some helpful insights for both of the exploration and the development of shale gas. Highlights: Both strength and density of adsorption sites control adsorption capacity of mineral surface. Strengths of adsorption sites on clay surface are different, but similar on kerogen surface. Specific surface area is one of the main factors controls adsorption behaviors. Density of adsorption sites and specific surface area of kerogen are larger than that of clay. Interactions among gas molecules also affect the adsorption behaviors.