A practical methodology for incorporating volume-translated equation of states in isochoric-isothermal phase equilibrium calculations for liquid phase pressure prediction.

Accurately predicting the phase behavior and properties of reservoir fluid plays an essential role in the simulation of petroleum recovery processes. Similar to the inaccurate liquid-density prediction issue in the isobaric-isothermal (PT) phase equilibrium calculations, an inaccurate pressure prediction issue can also be observed in isothermal-isochoric (VT) phase equilibrium calculations which involves a liquid phase. In this work, a practical methodology is proposed to incorporate a volume-translated equation of state in VT phase equilibrium calculations for more accurate pressure predictions. For this purpose, we adopt the state-of-art volume translation model recently proposed by Abudour et al. (Fluid Phase Equilib 349:37-55 2012, Fluid Phase Equilib 349:37-55, 2013). Single liquid phase calculations for 18 compounds and two hydrocarbon mixtures are conducted to demonstrate the soundness of the proposed methodology and evaluate the accuracy of pressure predictions. The calculated pressures by VT calculations with volume translated PR-EOS are compared to the actual pressures. The calculation results demonstrate that, by incorporating Abudour et al. (2012, 2013) volume translated PR-EOS models into the VT-based phase equilibrium calculation algorithm, the accuracy of pressure prediction in the single liquid phase region for both pure substances and mixtures can be significantly improved. Lastly, we apply the proposed algorithm to the two-phase VT phase equilibrium calculations for a ten-component oil sample MY10 which contains only normal alkanes. We numerically correct the pressure by applying the Abudour et al. VTPR-EOS to both the liquid phase and vapor phase. The pressures calculated by different phases become different. The pressures predicted based on the liquid phase are shifted downwards significantly, which leads to more accurate pressure predictions. To our knowledge, this issue is rarely investigated to incorporate the volume translation concept in VT phase equilibrium calculations.