Constant composition expansion

A volume of undersaturated oil is expanded in a PV-cell in which all of the fluid is contained within the cell during a series of pressure decrements: usually from the initial pressure (or above) to the bubble point. (Fig. 3.2.2.). 
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Fig. 3.2.2. Constant composition expansion
After each pressure step, the oil volume is measured and reported as a relative volume (RV):
RV=VVb
In which Vb is the volume at the bubble point. From inspection it will be apparent that the RV is necessarily less than unity and decreases with increasing pressure. Oil density and compressibility are also reported. The bubble point pressure is manifest, as described above, by the sudden large change in volume for a small change in pressure, due to the evolution of high compressibility gas.

Differential vaporization experiment

The differential vaporization experiment defines the changing FVF and solution GOR below the bubble point pressure. Gas saturated oil is charged to a PV-cell and the pressure is reduced in steps below the bubble point; after each, the evolved gas is removed from the cell and its volume measured along with the volume of gas saturated oil remaining in the cell. Once the pressure has been reduced to atmospheric, the temperature is decreased from the reservoir value to 20 ^oС (60 ^oF), meaning that the final state is the stock tank condition (14.69 psi, 60 ^oF), at which the remaining oil in the cell is referred to as the "residual7' volume (stb), to which all oil volumes are related at any stage of depletion. (Fig. 3.2.3.).
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Fig. 3.2.3. Differential vaporization experiment
From the volumetric measurements of the oil and gas it is possible to calculate:
B_od – FVF of the oil at each stage of depletion:
Bodk=VokVor
R_sd – corresponding solution GOR:
Rsdk=j=1k∆VgjVor
The subscript «d» relates to the differential experiment.

Separator tests

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