Total formation volume factor below bubblepoint

January 17, 2024
by Restec

Total formation volume factor below bubblepoint pressure

Total formation volume factor below bubblepoint pressure is the volume at reservoir conditions occupied by one stock tank barrel of oil, its remaining solution gas, and the free gas (Rsb – Rs) that has evolved from the oil. In equation form,

B_{t} = B_{o} + 0 .1801175 B_{g} (R_{s b} - R_{s})

The gas FVF can be calculated using the Z-factor.

B_{g} = \frac{P_{s} (T_{r e s} + 460) Z_{r e s}}{(T_{s} + 460) P_{r e s}}

Three methods for estimating total formation volume factor below bubblepoint pressure are presented.

Standing (1947)

\log B_{t} = a_{1} + \frac{a_{2}}{a_{3} + F}

where

F = \log (R_{s} T^{a_{4}} γ_{g}^{a_{5}} γ_{o}^{C}) + \frac{a_{6}}{a_{7} + \log P}

C = 2.9 x 10^{- 0.00027 R_{s}}

\begin{matrix} Coefficient & Original \\ a_{1} & -5.262 \\ a_{2} & -47.4 \\ a_{3} & -22.32 \\ a_{4} & 0.5 \\ a_{5} & -0.3 \\ a_{6} & 96.8 \\ a_{7} & 6.604 \end{matrix}

Glaso (1980)

\ln B_{t} = a_{1} + a_{2} \ln F + a_{3} {(\ln F)}^{2}

where

F = R_{s} T^{a_{4}} γ_{g}^{a_{5}} p^{a_{6}} γ_{o}^{C}

C = 2.9 x 10^{- 0.00027 R_{s}}

\begin{matrix} Coefficient & Original \\ a_{1} & 0.184518 \\ a_{2} & 0.47257 \\ a_{3} & 75.354436 x 10^{- 3} \\ a_{4} & 0.5 \\ a_{5} & -0.3 \\ a_{6} & -1.1089 \end{matrix}

Al-Marhoun (1992)

B_{t} = B_{o b} {(p / p_{b})}^{d}

where

d = a_{1} (T + 460) + a_{2} \ln γ_{g} + a_{3} γ_{o} + a_{4} \ln γ_{o} + a_{5} (p / p_{b}) + a_{6} \ln (p / p_{b})

\begin{matrix} Coefficient & Original \\ a_{1} & -0.352796 x 10^{- 3} \\ a_{2} & -0.35328914 \\ a_{3} & -0.24964270 \\ a_{4} & 1.64925964 \\ a_{5} & 0.36432305 \\ a_{6} & 0.08685097 \end{matrix}