Page 35 - PVT Property Correlations

16 PVT Property Correlations

(in the example figure, it is approximately 355 F). Three conditions may
exist:
1. If the reservoir temperature is above the cricondentherm and the surface
conditions are outside the two-phase region, the fluid is determined to be
“dry gas.”
2. If the reservoir temperature is above the cricondentherm and the surface
conditions are inside the two-phase region, the fluid is considered “wet
gas.”
3. If the reservoir temperature is between the cricondentherm and the criti-
cal temperature, the fluid is “gas condensate” or “retrograde gas
condensate.”
The vast majority of gases will drop some condensate in the reservoir
when the reservoir pressure declines below the gas saturation pressure.
Fig. 2.2 shows maximum liquid saturation that drops in the reservoir versus
C7 1 mole % for a large number of gas samples. The presence of larger
amounts of C7 1 signals a higher degree of gas richness (capability of the
gas to drop liquid condensate in the reservoir and on surface). The data is
provided by the constant volume depletion experiment that represents the
behavior of gas condensate fluid at reservoir temperature. The plot clearly
shows that liquid saturation (the amount of condensate dropping out) in the
reservoir increases with increasing C7 1 mole %. Liquid saturation can be
insignificant for C7 1 less than 0.7% (McCain and Piper, 1994). At these
levels of low liquid saturation, the gas is considered to behave as though it
were dry gas. At C7 1 mole % above 2%, the liquid dropout in the reservoir

FIGURE 2.2 Maximum liquid saturation versus C7 1 mole % for gas samples.