Single-Phase Pseudo-Pressure Calculation Steps

To calculate single-phase pseudo-pressure (gas condensate):

1. Tabulate gas viscosity (mg) and compressibility factor (z) at various pressures.

2. Calculate pseudo-pressure using numerical integration (trapezoidal rule):

3. Obtain the slope (m) of the semi-log plot of y  versus log (time function), or from the derivative or regression analysis.

4. Calculate permeability, kg = k krg from:

5. Calculate total skin (s'):

Drawdown:

Buildup:

6. If rock relative permeability data and condensate PVT data are available, krg is calculated as a function of pressure, as outlined below:

First, kro/ krg is calculated from one of the following equations shown below:

If rg and ro are molar densities:

If rg and ro are mass densities and Mo and Mg are the molecular weights (g / mol):

If relative permeability data (kro, krg, So) are available, a tabulation of kro/ krg as a function of oil (condensate) saturation (So) is generated:

From these two tabulations, a relationship of krg as a function of pressure is generated.

7. The two-phase skin (s2p) is calculated by numerical integration from:

Drawdown:

Buildup:

8. The skin due to damage (sd) is calculated as shown below: