First-principles calculation of adsorption for tight gas on α-SiO₂ (010) surface

The occurrence of tight gas in sandstone reservoirs has been a hot topic. To demonstrate the adsorption strength of tight gas on the quartz sandstone surface, the adsorptions of CH₄, C₂H₆, CO₂ and N₂ molecules on α-SiO₂ (010) surface have been studied, respectively, by using first principles method based on the density functional theory (DFT). The results show that the adsorption capacity of CH₄, C₂H₆, CO₂ and N₂ molecules on α -SiO₂ (010) surface from small to large is in turn: CO₂, N₂, CH₄ and C₂H₆. The lowest adsorption energy -0.5379 eV and minimal geometric change of CH₄ molecule is at B12 site, where the adsorption is the most stable and it belongs to physical adsorption. The adsorption of hydrocarbon gases is stronger than that of non hydrocarbons. The adsorption energy changes small at different adsorption sites, which indicates that gases are easy to move on α -SiO₂ (010) surface; After adsorption at B12 site, the partial density of states (PDOS) curves of CH₄ molecule are shifted to the lower energy region about 3.2 eV, while the curves of silicon atoms in α-SiO₂ (010) surface are basically coincident. (authors)