A generalized equation of state for associating fluids in nanopores: Application to CO2-H2O, CH4-H2O, CO2-CH4, and CO2-CH4-H2O systems and implication for extracting dissolved CH4 by CO2 injection

Abstract

A modified cubic-plus-association (CPA) equation of state is presented by considering the influences of pore sizes and intermolecular interactions. Additionally, the van der Waals (vdW) mixing rule is modified to make it applicable to predicting the phase behavior of mixtures. The predictions of the CPA–vdW model are consistent with the experimental interfacial tensions of the CH4-nC10, CO2-nC10, and N2-nC10 systems in nanopores. The predictions of the CPA–vdW model for vapor–liquid equilibria of the CO2-H2O, CH4-H2O, CO2-CH4, and H2O-CH4-CO2 systems are accurate in bulk at 273.15–513.15 K and 0.1–200 MPa. The forward and backward multiple-contact processes are used to model CO2 injection to extract the dissolved CH4. The CH4 recovery factor obtained by CO2 injection is approximately 20%–60% at 273.15–523.15 K and 20–140 MPa only under the equilibrium condition, while flow is not considered.