Gas formation volume factor = Bg

Formation Volume Factor (FVF) for gas:

(1)	$\begin{array}{l}\displaystyle B_g(p,T) = \frac{\mathring{\rho}_g}{\rho_g} = \frac{V_g}{\mathring{V}_{Gg}} = \frac{q_g}{q_{Gg}}\end{array}$

where

$\begin{array}{l}\rho_g^{\circ}\end{array}$	fluid density at reference conditions	$\begin{array}{l}V_m^{\circ}\end{array}$	molar volume at reference conditions
$\begin{array}{l}\rho_g\end{array}$	fluid density at reservoir conditions	$\begin{array}{l}V_m\end{array}$	molar volume at reservoir conditions

The reference conditions may vary from case to case but most popular choice are: Separator, Stock Tank and SPE STP.

It can be expressed through the Z-factor as:

(2)	$\begin{array}{l}\displaystyle B_g(p,T) = \frac{Z(p, T)}{Z^{\circ}} \cdot \frac{T/T^{\circ}}{p/p^{\circ}}\end{array}$

where

$\begin{array}{l}p\end{array}$	reservoir pressure	$\begin{array}{l}p^{\circ}\end{array}$	reference pressure
$\begin{array}{l}T\end{array}$	reservoir temperature	$\begin{array}{l}T^{\circ}\end{array}$	reference temperature
		$\begin{array}{l}Z^{\circ} = Z(T^{\circ}, \, p^{\circ})\end{array}$	Z-factor at reference conditions

If reference conditions are set at SPE STP then reference Z-factor $\begin{array}{l}Z^{\circ} = 1\end{array}$ is close to 1 for all natural gases and equation (2) takes explicit form as:

(3)	$\begin{array}{l}\displaystyle B_g(p,T) = 0.3470 \cdot Z(p, T) \cdot \frac{T}{p}\end{array}$

where

$\begin{array}{l}B_g\end{array}$	Gas formation volume factor in frac = m³/m³
$\begin{array}{l}p\end{array}$	reservoir pressure in [kPa ]
$\begin{array}{l}T\end{array}$	reservoir temperature in [K]

Page tree

Gas formation volume factor = Bg