Critical evaluation of empirical gas condensate correlations

Abstract

Compositionally sensitive retrograde fluids or gas condensates are particularly challenging from the standpoint of phase behavior and fluid property measurement as well as modeling. The problem is even more pronounced when dealing with the two extreme types of fluids, i.e., lean (insignificant amount of retrograde liquid) and rich (significant amount of liquid drop out, few psi below the saturation pressure). Given these complications, many researchers have proposed empirical correlations that make use of either the field data such as gas to condensate ratio (GCR) or laboratory data such as compositions, plus fraction characteristics to obtain PVT properties. In this work, using the reported experimental data of 81 gas condensate fluids in the open literature, we have critically evaluated four such empirical correlations. The evaluation focuses on the relationship between C7+ (heptanes plus) mole% and initial producing GCR; dew point prediction; molecular weight prediction; and maximum retrograde condensate (MRC). The C7+ mole% predicted from GCR showed deviations as high as 45% or the differences between the predicted GCR's from the two evaluated correlations were as high as 5000 scf/STB; dew point predictions were over and under estimated by as much as 2000 psia; overall fluid molecular weight differences were as high as 7 units; and MRC overestimated by as much as 115%. Based on this critical evaluation we demonstrate that such type of simplistic empirical approach lacks the accuracy and reliability of obtaining PVT properties that is crucial in the efficient management of gas condensate reservoirs.