Difference between revisions of "P/Z plot"

Revision as of 09:19, 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.

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:

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

The previous equation in the well known form:

Discussion

Griffith correlation adds a hook to the originally straight Hagedorn and Brown VLP curve.

Nomenclature

= gas initially in place, ft³

= 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

= reservoir volume (constant), ft³

= volume of gas in reservoir converted to standard conditions (changing), ft³

= gas compressibility factor (changing), dimensionless

References

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