Reservoir Voidage

Reservoir voidage (F) is an important parameter to most material-balance plots. Reservoir voidage has unit of res bbl. The equations of F for different types of reservoir are as follows:

• Dry gas reservoirs: No hydrocarbon-liquid phase, therefore Nfoi=0, and no volatile liquid in the gas phase, therefore Rvi = Rv = 0. General equation (9.8) is F = (Gfgi * Eg) + delta_W + (Gfgi * Bgi * Efw). The term (Gfgi * Bgi * Efw) can be neglected. In dry gas reservoirs without waterdrive, delta_W is neglected, so the equation is now reduced to: F = Gp * Bg (Eq 9.9)

• Saturated oil reservoirs: Reservoirs with pressure above bubblepoint. General equation (5.32) is F = Np * ((Bo * (1 - Rv * Rp) + ((Rp - Rs) * Bg)) / (1 - Rv * Rs)). For non-volatile reservoirs, Rv = 0. For volatile reservoirs, Rv != 0

• Undersaturated oil reservoirs: Reservoirs with pressure below bubblepoint. General equation (5.32) is reduced to F = Np * Bo, because Rv = 0 and Rp = Rs = Rsi.