Geoscience Reference
In-Depth Information
For single phase oil, the derivative on the right-hand side can be
replaced using equations (3.12b) and (3.12c).
(3.12b)
(3.12c)
This results in equation (3.12d).
(3.12d)
The use of oil compressibility in the final equation did not require
integration. Thus, the derivative in the oil compressibility equation,
equation (3.12b), must be determined with the slope of a tangent line to
the isothermal density-pressure curve at the pressure of interest. This oil
compressibility will be called c o .
These three applications require very different values of oil
compressibilities. Figure 3-8 shows values of oil compressibilities
calculated using the constant composition expansion data reported
in a well-known sample reservoir fluid study. 23 A value of 5,000 psig
was used as initial pressure for the reservoir for the c oi calculations.
This figure shows that the values of oil compressibilities used in the
three applications are 20%-30% different depending on the pressure
of interest.
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