A Review and Extension of Existing Consistency Tests for PVT Data From a Laboratory

Any calculation of the phase behavior of a reservoir fluid from the reservoir to the refinery requires prior knowledge of the fluid's physical properties. Because the necessary pressure-volume-temperature (PVT) experiments are not free of systematic and random errors, the engineer involved in using fluid models is advised to check the fluid properties determined by the laboratory before application in their simulation models. This paper is designed to provide a guideline for how to obtain reliable and consistent PVT data from a laboratory. In addition, it reviews and extends existing consistency checks with a critical focus on the Y-function. Its applicability is limited to the two-phase region of a reservoir fluid. As it turns out, the Y-function can be applied not only to the constant-composition experiment (CCE) of black oil (BO), but also for the same experiment with a gas-condensate (GC). Furthermore, we show that the Y-function is a useful tool for the evaluation of the differential-liberation experiment (DLE, BO) and the constant-volume depletion (CVD, GC). In all these cases, the shape of this function is close to a straight line. After the Y-function is properly set up, it is possible to estimate the quality of the CCE and the DLE for the BO case and CCE and CVD for the GC. The second part of the review is devoted to explaining the role of the solution gas in BO, because both the formation volume factor (FVF) B-o and the oil viscosity mu(o) are affected by the amount of solution gas. Helpful functions for estimates and consistency checks are given. In addition, estimates for the isothermal compressibility and the isobaric expansion of oil are presented.