Meana Petro

Reservoir

Gas material balance — P/z

Paste reservoir pressure against cumulative production and read gas in place off the intercept, with z computed at every point rather than assumed constant.

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Inputs

Pressure and cumulative production

Cumulative gas produced and the average reservoir pressure at that point.

RowCumulative producedReservoir pressure
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2
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7

Results

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How it is calculated

  • For a volumetric gas reservoir, P/z falls linearly with cumulative production: P/z = (P/z)ᵢ · (1 − Gp/G).
  • z is computed at each measured pressure from Dranchuk–Abou-Kassem with Wichert–Aziz sour-gas correction, so the plot is not distorted by a single assumed z.
  • OGIP is the intercept of the fitted line on the production axis, where P/z reaches zero.
  • Recoverable gas is read where the line crosses your abandonment pressure, which is what the recovery factor is actually built from.

Standards it speaks

Where this stops being true

The straight line is the whole model, and it only exists for a volumetric, single-tank, gas-expansion reservoir. Water influx bends it upward and makes the extrapolated OGIP too large — in strong aquifer cases, twice too large — while a geopressured reservoir bends it the same way for a completely different reason, and the plot cannot tell you which. Average reservoir pressure is also hard-won: build-ups from different wells at different times are not the same tank pressure unless the field is well connected and given time to stabilise.

The capability that automates this

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