Page 36 - PVT Property Correlations

Reservoir-Fluid Classification Chapter | 2 17

can become significant. At this level, liquid saturation can range from 2% to
7%. At this level, the fluid should be considered gas condensate. Treatment
of it, as dry or wet gas, may produce considerable error. The Wet Gases
(Chapter 4) and Gas Condensates (Chapter 5) discuss the economic aspects
of producing such fluids. The wet gas model can be assumed for fluids with
C7 1 between 0.7% and 2%.
Fig. 2.3 shows the reservoir pressure at which the maximum liquid drop-
out occurs. This pressure increases with the increase in C7 1 mole %. For
the range selected for wet gases (C7 1 of 0.7% 2%), the pressure at which
maximum liquid dropout occurs is usually low (less than 1500 psia). This
level of pressure will usually be reached in the reservoir at a later stage of
depletion. At higher pressures, liquid dropout in the reservoir is minimal,
thus consistent with the theoretical assumption of wet gas (no liquid conden-
sation in the reservoir).
Fig. 2.4 shows the surface GOR versus C7 1 mole %. Producing GOR
shows a clear decreasing trend with increasing C7 1 mole %. The dry gas
concept can be used for C7 1 less than 0.7%. This range of C7 1 mole % is
equivalent to GOR higher than 100,000 scf/STB (or CGR of less than 10
STB/MMscf). The wet gas model can be assumed for C7 1 range of 0.7%
2%. Fig. 2.4 shows that this range is equivalent to GOR range of 100,000 to
33,000 scf/STB (CGR of 10 30 STB/MMscf). For higher levels of C7 1 ,
gas condensate must be assumed to avoid excessive errors in phase behavior
prediction. In practice, gas richness of 30 STB/MMscf and above requires
that appropriate models be used to forecast the reservoir behavior. At this

FIGURE 2.3 Pressure at maximum liquid saturation versus C7 1 mole %.