Study on equilibrium and non-equilibrium PVT behavior of foamy oil using experiments and PVT correlations

Abstract

The traditional understanding of PVT behavior of conventional oil is rather different under foamy oil condition. This paper focuses on the PVT tests with Venezuela heavy oil, and development of a new methodology for equilibrium and non-equilibrium PVT properties of foamy oil. Firstly, the study involved PVT tests to reveal the equilibrium and non-equilibrium PVT properties of foamy oil. Then, in order to give the best equilibrium PVT correlations for field applications, some classic equilibrium PVT correlations were tested against the experimental data with strong foamy oil tendencies. Finally, several functional relationships were developed to describe the time effects on non-conventional PVT properties of foamy oil by fitting the experimental results. Then, a set of models for non-equilibrium PVT properties were proposed and validated with experimental data in literature. The results show that, for the measured crude oil, a higher depletion rate leads to a lower pseudo bubble point pressure and higher oil compressibility, indicating a stronger tendency for foamy oil occurrence. The foamy oil exhibits stable solution GOR, high formation volume factor, low oil density and slightly low oil viscosity below bubble point pressure. The selected and developed equilibrium PVT correlations have a wide scope of application and high precision. A comparison of the estimated and experimental PVT data show differences of 6.55% for solution GOR, 9.05% for oil compressibility, 0.84% for oil FVF, 4.5% for oil viscosity and 0.46% for oil density. The proposed non-equilibrium PVT models for the foamy oils provide average error of 7.07% for solution GOR, 16.07% for oil compressibility, 0.73 for oil FVF and 10.68% for oil viscosity and 0.63% for oil density. Application of this developed methodology can avoid the accomplishment of conventional and non-conventional PVT tests.