Difference between revisions of "P/Z plot"

Revision as of 11:46, 21 November 2017

Brief

The P/Z plot is a plot of P/z versus cumulative gas production, G_p.

The interpretation technique is fitting the data points with the straight line to estimate GIIP.

The P/Z plot is based on the Gas Material Balance equation.

P/Z plot at ep.pengtools.com

Math & Physics

Applying Real Gas EOS at reservoir conditions:

(1)

Applying Real Gas EOS at standard conditions:

(2)

Dividing eq. 2 by eq. 1 and rearranging:

(3)

Applying eq. 3 for initial conditions and for any point in time:

Applying eq. 3 for any point in time:

Therefore at any time:

Or:

Thus a plot of P/z vs cumulative produced gas is a straight line intersecting X axis at GIIP.

Discussion

P/Z plot is a part of the Reservoir Management workflow in the E&P Portal used to estimate Reservoirs GIIP.

Gas Flowing Material Balance is the more advanced tool to determine the Reservoirs GIIP as well as Well's EUR and JD.

Nomenclature

= gas initially in place, scf

= cumulative gas produced, scf

= reservoir pressure (changing), psia

= initial reservoir pressure (constant), psia

= pressure at standard conditions, psia

= initial reservoir pressure (constant), °R

= reservoir pressure (constant), °R

= temperature at standard conditions (constant), °R

= volume of gas in reservoir converted to standard conditions (changing), scf

= reservoir volume (constant), ft³

= gas compressibility factor (changing), dimensionless

= initial gas compressibility factor (constant), dimensionless