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Constant Volume Depletion

The constant volume depletion (CVD) experiment is one of the standard depletion experiments. The main output of the CVD experiment are the liquid drop-out curve and consequently the approximate saturation pressure. A series of experiments is typically conducted on the produced fluid as well (e.g. gas Z-factor). The CVD experiment emulates the depletion of gas condensate to a certain extent, and has been used in the methodology by Whitson and Torp1 to develop black-oil properties.

Procedure

The procedure for CVD experiment is shown as an animation and as a schematic below. A PVT-cell is fill with a fluid sample and pressurized to the saturation pressure. The PVT-cell volume is then expanded at a constant temperature, reducig the pressure. Once the pressure is below the saturation pressure, the incipient phase is either condensed or vaporized out of solution. When the PVT-cell volume has reasched a certain value, gas (and potentially oil) is removed until the PVT-cell volume is the same as the initial volume (keeping the pressure contstant). This procedure is repeated a number of times and the produced fluids are analyzed. If the PVT-cell is a visual cell, then the liquid and vapor volumes can also be reported.

Animation of CVD PVT experiment

Animation 1: Animation of a CVD procedure for a saturated gas reservoir.

Figure of CVD PVT experiment

Figure 1: Schematic of a CVD experiment for a saturated gas reservoir.

Results

The main results of the CVD experiment is the relative volume, and a range of properties of the removed gas; the gas Z-factor and gas specific gravity.

  1. C. H. Whitson and S. B. Torp. Evaluating constant volume depletion data. In SPE Annual Technical Conference and Exhibition, paper SPE–10067–MS. Society of Petroleum Engineers, 1981. doi:https://doi.org/10.2118/10067-MS. ↩