Prediction of Minimum Miscibility Pressure Using the UNIFAC Group Contribution Activity Coefficient Model and the LCVM Mixing Rule

Abstract

Minimum miscibility pressure (MMP) is a key design parameter of any gas flooding project that can be measured in the laboratory or estimated by computational methods based on the equation of state (EOS). Application of the EOS for mixtures is attainable by employing simple mixing rules, such as the van der Waals (VDW) fluid mixing rule, which has been applied widely in petroleum industry so far. The objective of this study is to estimate MMP using multiple mixing cells (MMC), developed by Ahmadi and Johns (K. Ahmadi and R. T. Johns, SPE J. 2011, 16, 733–742), with the EOS/GE mixing rule. The linear combination of the Vidal and Michelsen (LCVM) is used as a mixing rule for the modified Peng–Robinson EOS by applying the UNIFAC activity coefficient equation. Moreover, in the MMP calculations, a group contribution method is used to characterize undefined petroleum fractions. The MMP results are compared with those estimated using the VDW (classic) mixing rule and experimental data of the slim tube apparatus. ...