Gas reservoir volumetrics are on 13 RES 1 and 2. The basic equation is:
G(Bg - Bgi) = WpBw + GpBg - We
Looks simple enough. But the devil is in the units. I like to stick with MCF.
For example, assume a gas reservoir with IGIP and all production known.
Reservoir water influx is easily calculated (I'll use round numbers):
G = 10E6 MCF; Gp = 6E6 MCF
Bg = 5 rcf/MCF; Bgi = 4.5 rcf/MCF
Wp = 2 MSTB = 11 MCF; Bw = 1 rcf/CF
G(Bg - Bgi) = GpBg + WpBw - We
10E6 MCF (5 - 4.5 cf/MCF) = 6E6 MCF (5 cf/MCF) + 11 MCF (1 Mcf/MCF) - We
5E6 cf = 30E6 cf + 0.1E6 cf - We
We = 25 MMcf = 4.5 MM Bbl water.
With gas it's all about the units.
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