Comparative Evaluation of α Functions for the Soave- Redlich-Kwong Equation of State and the Peng- Robinson Equation of State to Predict Saturation Pressures for Gas(es)-Heavy Oil/Bitumen-Water Systems

To accurately predict saturation pressures for gas(es)- heavy oil/bitumen- water systems, several alpha functions have been selected and eval-uated at a reduced temperature (Tr) of 0.70 and 0.60 for the Soave-Redlich- Kwong equation of state (EOS) and Peng-Robinson (PR) EOS, respectively. More specifically, 164 data points of measured saturation pressures of gas(es)- heavy oil/bitumen- water systems are collected from the public domain, while all alpha functions developed for heavy oil-associated mixtures and water have been reviewed and selected. At Tr = 0.70, the former, including three existing alpha functions, as well as two newly developed alpha functions at Tr = 0.70 together with three new alpha functions at Tr = 0.60, and the latter, including two alpha functions, are used to evaluate saturation pressures for various gas(es)- heavy oil/bitumen- water systems under various conditions. The absolute average relative deviation (AARD) between the mea-sured saturation pressures and their predicted ones is found to decrease with either an increase in the pseudocomponent (PC) number or redefining the acentric factor (!) at Tr = 0.60 other than the conventional one at Tr = 0.70. In addition to validating our coded program, the CMG WinProp module, together with its default binary interaction parameters (BIPs) is used to, respectively, quantify saturation pressures of the aforementioned systems with an overall AARD of 27.34 and 28.39% for the PR EOS and SRK EOS. The recommended alpha function newly developed at Tr = 0.60 by Chen and Yang (2017) predicts saturation pressures more accurately with an overall AARD of 3.88 and 1.64% by, respectively, treating the heavy oil as one PC and six PCs.