In the laboratory, a standard analysis of a gas-condensate sample consists of:
• Recombination and analysis of separator samples
• Measuring the pressure-volume relationship, i.e., constant-composition expansion test
• Constant-volume depletion test (CVD)
Obtaining a representative sample of the reservoir fluid is considerably more difficult for a gas-condensate fluid than for a conventional black-oil reservoir. The principal reason for this difficulty is that liquid may condense from the reservoir fluid during the sampling process, and if representative proportions of both liquid and gas are not recovered then an erroneous composition will be calculated. Because of the possibility of erroneous compositions and also because of the limited volumes obtainable, subsurface sampling is seldom used in gas-condensate reservoirs. Instead, surface sampling techniques are used, and samples are obtained only after long stabilized flow periods. During this stabilized flow period, volumes of liquid and gas produced in the surface separation facilities are accurately measured, and the fluid samples are then recombined in these proportions.