Page 180 - PVT Property Correlations

154 PVT Property Correlations

FIGURE 7.7 Isothermal compressibility of oil.

plot, and it shows the sudden increase in oil compressibility between the
values above and below the bubble-point pressure.
Compressibility of oil above the bubble point is of particular importance
because it affects the material balance calculations for volumetric oil reser-
voirs. It is also the value used in pressure transient analysis for single phase
oil wells. Oil compressibility is also used in vertical lift performance calcula-
tions and others. The value of oil compressibility can range from as low as
3 3 10 26 psi 21 for low GOR undersaturated oils to approximately
150 3 10 26 psi 21 for saturated high GOR oils.

HANDLING PVT PROPERTIES FOR BLACK OILS
PVT properties for black oils can be determined in the PVT laboratory with
the reservoir fluid study. For black oils, the reservoir fluid study usually con-
sists of five experiments [composition, CCE, differential liberation (DL),
separator test(s), and viscosity measurement]. When a representative fluid
sample or PVT laboratory report is not available, we rely on correlations to
calculate the PVT properties for oils. Other texts have discussed the use of
PVT laboratory reports in calculation of PVT properties for black oils (e.g.,
McCain, 1990; Dandekar, 2006; Ahmed, 2010).
Over the years, numerous correlations to calculate PVT properties for
oils have been developed. The correlations are usually simple expressions
(equations) that allow engineers to calculate the PVT properties from readily
available inputs. The correlations inputs should not rely on measured values
that can be arrived at only in the PVT laboratory.