Qatari tight Gas Reservoirs: Molecular Simulation insights toward Estimation of Ultimate Recovery (EUR) from Carbonated Reservoirs

The geometrical properties of the reservoir rocks are usually affected by natural thermodynamics or environmental changes that may affect the amount of gas in place in the reservoir. To address these properties, we conduct density functional theory calculations to study the effect of gas composition on the adsorption (Eads), considering surface strain and curvature effects. Additional analyses, like geometrical analysis, and surface energy, were conducted to explain the results. The results of the strain effect showed that regardless of the strain values or curvature levels, all considered gases are physisorbed, with CO2 having the largest Eads. In addition to their weak interaction with the surface, CH4 shows no particular changing trend of the Eads with strain. The effect of strain becomes more pronounced in the case of CO2 and C2H6. A new model of the nanopore, which is the cylindrical-shaped nanopore, is introduced. Cylindrical nanopores have greater adsorption affinity compared to the flat surface, which demonstrates their higher gas capacity. Additionally, a mathematical model of the Eads vs. the diameter is developed. The capacity test of CH4 and CO2 showed adsorption of >24 molecules. These findings can be useful for determining the estimated ultimate recovery in carbonaceous tight gas reservoirs.