Abstract
In this paper, main and interactive effects of four important factors, temperatures, adsorption thicknesses, fracture apertures, and feed CO2 concentrations, on the thermodynamic phase behavior for CO2 storage processes in the fractured nanopores of shale/tight reservoirs with adsorptions are investigated. First, a modified analytical equation of state is developed by considering the effects of confinements and intermolecular interactions, which is applied to predict the confined pure/mixing fluid phase behavior in fractured nanopores coupled with a novel empirical correlation for the adsorption thickness and the fracture geometry equation. Second, the aforementioned four important factors are studied to evaluate their main and interactive effects on the phase behavior of pure CO2, N2, O2, Ar, alkanes of C1–10, and their mixtures. It is found that all the pure and mixing fluid pressures monotonically and linearly increase to different extents with an increasing temperature. Moreover, the pressures/critical shifts and critical properties perform downward and upward parabola curves with respect to the adsorption thicknesses, respectively. On the other hand, the pressures/critical shifts are monotonically decreased, while the critical properties increase with the fracture apertures increasing from 0.01 up to 10 nm and remain constant afterward. By increasing the feed CO2 concentrations, the critical shifts and pressures for all of pure and mixing fluids are increased, while both the critical pressures and temperatures decrease. In addition, three interactive effects on the phase behavior are analyzed that the effect of a single factor behaves differently with the variations of any other factors. Finally, the amounts of the N2, O2, Ar, and light alkanes of C1–4 are suggested to be controlled for CO2 storage in the fractured nanopores because additions of these components strongly affect the mixture phase behavior.