Evaluating Phase Boundaries and Physical Properties of Solvents/Water/Heavy Oil Systems Under Reservoir Conditions with the Truncated Perturbed-Chain Polar Statistical Associating Fluid Theory (tPC-PSAFT) Equation of State

Abstract In this work, the truncated perturbed-chain polar statistical associating fluid theory equation of state (tPC-PSAFT EOS) has been integrated and extended to quantify phase behaviour and physical properties of solvents/water/heavy oil systems under reservoir conditions. Experimentally, constant composition expansion (CCE) tests were conducted to measure saturation pressure (Psat), phase volumes, and phase compositions across pressures up to 20 MPa and temperatures reaching 433.2 K for the aforementioned systems with solvents including C3H8, n-C4H10, CO2, and dimethyl ether (DME) in the absence and presence of water. Theoretically, the tPC-PSAFT EOS is integrated with the characterization of heavy oil into aromatic, saturate, and polyaromatic (ASP) fractions to reproduce the experimental measurements. Such an integrated adjustment incorporates the Gross and Vrabec's dipolar term along with binary interaction parameters (BIPs) to enhance the predictive capability of the theoretical model. The addition of a polar term used to better represent the DME's dipole-dipole (DD) interactions, coupled with its modest polarity, significantly enhances the model's accuracy and robustness. The study confirms that water increases the Psat in binary solvent mixtures, yet interestingly, it reduces Psat in more complex ternary/quaternary mixtures. By minimizing deviations between the measured and calculated Psat to calibrate the BIPs, the modified tPC-PSAFT EOS outperforms the original Peng- Robinson (PR) EOS with an overall RMSRE of 2.94% for the former and 25.78% for the latter.