Generating PVT tables with correlations

You can use correlations to generate PVT regions specific to your simulator. To do this, you first describe the fluid and then how the deck section is to be created.

You can generate PVT regions from correlations for four different fluid types; gas, gas condensate, saturated oil and undersaturated oil. You select the fluid type in the first entry of the table. Depending on your fluid selection, the required parameters are slightly different and are described below. All correlations used can be found in chapter 3 of Phase Behavior (Whitson and Brulé, SPE Monograph Volume 20, 2000, Society of Petroleum Engineers, Richardson Texas).

Once the fluid is described, the PVT region can be created. The creation of a PVT region results in a table with entries at specific pressures. The second table specifies the min, max and pressure step for the table as well as whether an entry will be added for standard pressure.

Gas

The gas correlation is appropriate for gas reservoirs. The required parameters are the reservoir temperature, gas gravity and compositions of N2, CO2 and H2S.

Z factor is calculated from the Hall Yarborough equation. Critical temperature is calculated using the Sutton correlation. Gas viscosity is calculated using the Lucas correlation.

Gas condensate

Gas condensate is appropriate for reservoirs in which the fluid is gas in the reservoir but liquids drop out at the surface. In addition to parameters required for the gas correlation, the temperature and pressure of the first stage separator as well as the surface oil/gas ratio is required. The API gravity of the condensate is also required.

The molecular weight of the condensed oil is calculated from the Cragoe correlation. Z factor, critical temperature and gas viscosity calculations are identical to the gas correlation.

Saturated oil

This correlation is appropriate for oil reservoirs where both oil and gas exist at reservoir conditions.

This correlation requires the same parameters as for gas condensate except for the producing oil/gas ratio. The correlations used to model the gas phase are the same as used for the gas correlation. Undersaturated oil compressibility and bubble point pressure is calculated using the Vazquez and Beggs correlation. Dead oil viscosity is calculated using the Beggs and Robinson correlation.

Undersaturated oil

This correlation is appropriate for reservoir in which there is no gas component at reservoir conditions.

The parameters required are the same as for saturated oil, except that the surface gas/oil ratio must also be specified. Correlations used are as described for saturated oil.

In the case of dead oil, the producing gas/oil ratio can be specified as 0 and the gas properties are then ignored.