Gas Formation Volume Factor

Definition - What does Gas Formation Volume Factor mean?

Gas Formation Volume Factor is the formation volume factor (FVF) that relates the volume of gas in a reservoir with the volume of gas which actually got produced during the standard operating conditions. It is one of the important parameters which have to be calculated during the production of natural gas from a gas well. It enables to calculate the density of the gas.

Petropedia explains Gas Formation Volume Factor

Gas Formation Volume Factor is a dimensionless factor and is represented as “Bg”. It is represented in the form of ratio of volume of natural gas present in the reservoir to the volume of same quality of natural gas actually produced when operating an oil or a gas well at standard pressure and temperature conditions.

Bg = (Vr)/(Vac)


Vr = Volume of natural gas in the reservoir

Vac = Actual volume of natural gas produced

Vr and Vac is given by the formula:

Vr = znRT/P and Vac = zac x n x R x Tac / Pac

Where, z = compressibility factor of gas

T = reservoir temperature

P = reservoir pressure

n = number of moles of gas

zac = gas compressibility factor at standard conditions = 1

Pac = 14.7 psi (101 kPa)

Tac = 289 K

R = gas universal constant = 8.3143

Adjusting these values in the formula, we get gas formation volume factor (Bg) = 0.3495 x (zT/P)

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