Page 218 - PVT Property Correlations

Low Gas Oil Ratio Oils Chapter | 8 191

Applicability, lists the ranges of applicability of each correlation. In general,
the variation of most PVT properties with pressure (at reservoir temperature)
is not significant for low GOR oils. This fact is true for oil formation volume
factor, oil density, and oil compressibility. Many correlations can predict the
PVT properties (except for oil viscosity, as discussed earlier) with sufficient
accuracy. Oil formation volume factor can also pose a challenge in predic-
tion for some correlations, as will be illustrated in Problem 1.
The inputs to PVT correlations for low GOR oils include initial produc-
ing GOR, API gravity of stock-tank oil, specific gravity of separator gas, and
reservoir temperature. The initial producing GOR is a low value in the case
of low GOR oils and is sometimes unavailable in field production data. In
this case, it can be assumed at a low value. The same applies to specific
gravity of separator gas. API gravity of stock-tank oil and reservoir tempera-
ture are usually readily available.

Sequence of Calculations

The sequence of calculations for PVT properties of low GOR oils is the
same as that of black-oils. The only difference is that the saturated part of
the curve is not usually calculated. After data input, bubble point pressure is
either input (e.g., estimated from offset wells), or calculated using any of
bubble-point pressure correlations. The oil formation volume factor is then
calculated with the selected correlation(s). Following that calculation, oil
compressibility, formation volume factor of oil, and oil density are calculated
for the undersaturated portion of the curve. Dead oil viscosity is then
calculated, followed by live oil viscosity using the undersaturated viscosity cor-
relations. The sequence of calculations is provided in the flow chart of Fig. 8.7.

ENGINEERING LOW GAS OIL RATIO OILS
Problem 1—Calculating PVT Properties for Low Gas Oil Ratio
Oil Reservoirs
You are given the following basic field information for three different low
GOR fluids. Use Standing (1947) and De Ghetto et al. (1995) correlations to
calculate the bubble point pressure for the three fluids and compare with
laboratory-measured values of bubble point pressure. Use Standing (1947)
correlations family to compute solution GOR, oil formation volume factor,
oil density, oil compressibility, and oil viscosity for Fluid 1. Then, use the
two correlations to calculate oil formation volume factor, oil compressibility,
oil density, and oil viscosity for Fluid 3. Compare the calculated properties
with laboratory-measured values. The basic fluid parameters and laboratory-
measured values at the bubble point pressure for the three fluids are given in
Tables 8.4 and 8.5.