Difference between revisions of "P/Z plot"
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:<math> T_r </math> = reservoir pressure (constant), °R | :<math> T_r </math> = reservoir pressure (constant), °R | ||
:<math> T_{SC} </math> = temperature at standard conditions (constant), °R | :<math> T_{SC} </math> = temperature at standard conditions (constant), °R | ||
| + | :<math> V_g </math> = volume of gas in reservoir converted to standard conditions (changing), ft<sup>3</sup> | ||
:<math> V_r </math> = reservoir volume (constant), ft<sup>3</sup> | :<math> V_r </math> = reservoir volume (constant), ft<sup>3</sup> | ||
| − | |||
:<math> z </math> = gas compressibility factor (changing), dimensionless | :<math> z </math> = gas compressibility factor (changing), dimensionless | ||
Revision as of 10:41, 21 November 2017
Brief
The P/Z plot is a plot of P/z versus cumulative gas production, Gp.
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:
Or:
Thus a plot of P/z vs cumulative produced gas is a straight line intersecting X axis at GIIP.
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
= volume of gas in reservoir converted to standard conditions (changing), ft3
= reservoir volume (constant), ft3
= gas compressibility factor (changing), dimensionless
References
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