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Gas Material Balance Equation
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Gas Material Balance Equation
The gas material balance data is based on actual production data and is typically presented as a P/z plot. The material balance equation is a simple expression of the conservation of mass in a reservoir.
Eq. 1
P / z = ( P_{i} / z_{i} )  [ ( P_{sc} T ) / ( T_{sc} V ) ] G_{p}
Where:
( P_{i}/z_{i} ) = Ratio of Pressure to Compressibility Factor at Initial
Conditions (psi)
P_{sc} = Pressure at Standard Conditions (psi)
T_{sc} = Temperature at Standard Conditions (°R)
T = Current Temperature (°R)
V
=
Original Gas Volume (ft^{3})
G_{p} = Cumulative Gas Production (SCF)
P/z = Ratio of
Pressure to Compressibility Factor at Current Conditions for P/z vs Gp plot
(psi)
mD = Millidarcy
MSCF/d = Thousand standard cubic feet per day
Standard
conditions are normally set at 60 degF and 14.7
Source: Reference: Ahmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering.
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