Page 414 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

380 Production

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GOR

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Rs i pressure\
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Figure 6-10. Schematic representation reservoir pressure (P) and GOR vs.
time and mass and composition in reservoir differential vaporization process.

Sampllng Process and Laboratory Measurements
The overall quality of the reservoir fluid study and the subsequent engineering
calculations based upon that study can be no better than the quality of the fluid
samples originally collected during the field sampling process.
Samples representative of the original reservoir can be obtained only when the
reservoir pressure is equal to or higher than the original bubble point or dew point.
The pressure drawdown associated with normal production rates will cause
two-phase flow near the wellbore if the fluid in the formation was initially
saturated or only slightly undersaturated. Relative permeability effects may then
cause the material entering the wellbore to be different from the original overall
(total) composition fluid existing at the boundary of drainage area. The problem