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Gas Material Balance (P/Z) Calculator
Plot P/Z vs cumulative gas production (Gp). Perform linear regression to estimate Original Gas in Place (OGIP) and remaining reserves.
Pressure-Production Data
Pressure (psi)Z-factorP/Z (psi)Gp (Bcf)
Results
OGIP (Bcf)
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Remaining Reserves (Bcf)
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Recovery Factor
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R-squared
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Initial P/Z (psi)
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Slope (psi/Bcf)
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P/Z vs Gp Plot
How this works
Material Balance: P/Z = (Pi/Zi) * (1 - Gp/OGIP). A plot of P/Z vs Gp gives a straight line for volumetric gas reservoirs.
OGIP: X-intercept of the P/Z vs Gp line (where P/Z = 0).
Linear Regression: Least-squares fit of P/Z = a + b*Gp. OGIP = -a/b.
Z-factor: You can enter Z-factor directly or approximate with 1.0 for shallow reservoirs.
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