Page 44 - PVT Property Correlations

24 PVT Property Correlations

oils, the range is wider. API gravity can range from slightly less than 20 to

more than 60 API. For volatile-oil fluids, API gravity can range from 35 to

60 API.

SUMMARY OF RESERVOIR-FLUID CLASSIFICATION CRITERIA
The most important criteria in classifying reservoir fluids are initial produc-
ing GOR and C7 1 mole %. The initial producing GOR is readily available
from production data records in the field. C7 1 mole % requires the mea-
surement of reservoir-fluid composition. The compositional measurement is
usually found in PVT laboratory reports. Other criteria (API gravity, color of
stock-tank liquid, and oil-formation volume factor at bubblepoint pressure)
can be used only as confirmation, as reported previously. Table 2.1 sum-
marizes the essential criteria for reservoir-fluid classification.
For the vast majority of the fluids, both the GOR and the C7 1 criteria
are honored. However, Table 2.1 shows some overlap between gas conden-
sate and volatile-oil fluids. Some fluids can be identified as gas condensates
in the PVT laboratory even though their C7 1 mole % is close to 12.75%,
while other fluids may be identified in the laboratory to be volatile oils with
C7 1 around 12%. On rare occasions, due to the extremely volatile nature
of the fluid, the liquid volumes may not be visually confirmed to approach
an all-gas or all-liquid system. Presence of high concentrations of H 2 S in the
fluid sample (above 15%) usually complicates the fluid identification
problem.

NOMENCLATURE
CGR condensate gas ratio
CVD constant volume depletion
EOS equation of state
FVF formation volume factor
GOR gas oil ratio

REFERENCES
Ahmed, T., 2016. Equations of State and PVT Analysis, second ed. Gulf Professional
Publishing, ISBN: 9780128017524.
Craft, B.C., Hawkins, M.F., 1959. Applied Petroleum Reservoir Engineering. Prentice-Hall,
Englewood Cliffs, NJ.
McCain Jr., W.D., 1993a. Chemical composition determines behavior of reservoir fluids. Pet.
Eng. Intl. 18 25 (Oct.).
McCain Jr., W.D., 1993b. Black oils and volatile oils what’s the difference? Pet. Eng. Intl.
24 27 (Nov.).
McCain Jr., W.D., 1994a. Revised gas oil ratio criteria key indicators of reservoir fluid type.
Pet. Eng. Int. 57 60 (April).