Investigation on phase behavior of shale condensate gas under multi-interface effect

Abstract

Shale condensate reservoirs, as a significant unconventional resource, have been gaining increasing interest in recent times. Researchers have developed a variety of models to analyze interfacial effects in nanopores, including capillary condensation, capillarity, and adsorption effects. However, there are few studies on these interface effects. Therefore, we developed a phase equilibrium model considering the multi-interface effects in nanopores. The model is first built by modifying the Peng Robinson-equation of state (PR-EOS). The gas adsorption in vacant solution (FHVSM) model is utilized to describe adsorption. The calculated results show good agreements with experimental data of this model are more consistent with the adsorption characteristics of mixed gases in the porous media. After that, the phase behavior of a typical shale condensate gas is analyzed. Results indicate that the multi-interface effects will result in incremental dew-point pressure and retrograde condensate saturation. Moreover, the injection of CO₂ and N₂ was also studied, illustrating that CO₂ reduces the dew-point pressure, while N₂ increases the dew-point pressure. Both CO₂ and N₂ reduce the retrograde condensate saturation. Finally, the change in the adsorption of mixed gases was also evaluated, which shows a decreasing trend as the reservoir pressure depleted. This work provides deeper understandings in the phase behavior of hydrocarbons in the shale condensate gas reservoirs.