A known volume of reservoir fluid is charged to a high-pressure PVT cell and heated
to the reservoir temperature. A partial constant composition expansion (CCE) is
performed on the sample down to an operating pressure selected by the client. A
known volume of the gas phase is then pumped from the cell, to return the sample
to a constant volume equal to the measured volume at dew point pressure. The composition
of the displaced gas phase is measured.
A known volume of injection gas is then added to the cell and mixed, by inverting
the cell, to create a new fluid equilibrium at test conditions. The sample is continually
agitated and stabilised at operating pressure until no pressure change is observed.
Once this has been achieved the total sample volume as well as the change in relative
liquid and gas phase volume is determined. The excess gas phase is then removed
from the cell and analysed.
The test can be repeated at several gas increments to determine change in fluid
properties, composition and liquid volume as a function of the gas revaporization
process. The client normally supplies the injection volumes but a typical series
of tests would be 0.2, 0.5, 1.0, 3.0 and 5.0 moles of injection gas, per molar volume
of original sample volume at test conditions. Following the series of injections
a constant volume depletion may also be performed.
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