Modification of Esmaeilzadeh–Roshanfekr equation of state to improve volumetric predictions of gas condensate reservoir

Abstract

The Peneloux–Rauzy–Freze (PRF) method of improving volumetric predictions by introducing the volume shift into the equation of state, is applied to the Esmaeilzadeh–Roshanfekr equation of state (ER-EOS). The ER-EOS is a new three parameter equation of state that was developed in 2006 aiming to be applied to reservoir fluids. First, this equation of state was developed for pure hydrocarbons and then was extended to mixtures by using mixing rules [M. Bonyadi, F. Esmaeilzadeh, Fluid Phase Equilib. 260 (2007) 326–334]. The modified ER-EOS (mER-EOS) is expected to improve volumetric predictions of gas condensate by applying volume shift for heavy end(s). In this study, three gas condensate fluid samples taken from three wells in a real field in Iran, referred here as SA1, SA4 and SA8, as well as two samples from literature have been used to check the validity of the modified ER-EOS in calculating the PVT properties of gas condensate mixtures. Some experiments such as constant composition expansion (CCE), constant volume depletion (CVD) and dew point pressures are carried out on these samples. Relative volume and condensate drop-out in CCE and CVD tests were predicted by ER-EOS, mER-EOS, PR-EOS and SRK-EOS [D.Y. Peng, D.B. Robinson, Ind. Eng. Chem. Fundam. 15 (1), (1976) 59–64; G. Soave, Chem. Eng. Sci. 27 (1972) 1197–1203]. Comparison results between experimental and calculated data indicate that the mER-EOS has smaller error than the ER-EOS, PR-EOS and SRK-EOS. By this modification, the total average absolute deviations of the predicted liquid saturation from CVD experiments and relative volume from CCE experiments are 13.17% and 0.99%, respectively.