Oil formation volume factor at bubblepoint pressure

Oil formation volume factor at bubblepoint pressure is the volume at reservoir conditions occupied by one stock tank barrel of oil plus its solution gas. Three methods for estimating bubblepoint oil FVF are presented.

1. Standing (1947)
$${{\displaystyle B}}_{ob}={{\displaystyle a}}_1+{{\displaystyle a}}_2{[{{\displaystyle R}}_s{({{\displaystyle \gamma }}_g/{{\displaystyle \gamma }}_o)}^{a_3}+{{\displaystyle a}}_4{{\displaystyle T}}_{}]}^{a_5}$$ $$\overline{)\begin{array}{cc}\text{Coefficient}& \text{Original}\\ a_1& 0.9759\\ a_2& 0.00012\\ a_3& 0.5\\ a_4& 1.25\\ a_5& 1.2\end{array}}$$




2. Vasquez & Beggs (1980)
$$B_{ob}=1+a_1{R}_s+a_2\left(T-60\right)\left({\gamma }_{\text{API}}/{\gamma }_g\right)+a_3{R}_s\left(T-60\right)\left({\gamma }_{\text{API}}/{\gamma }_g\right)$$ $$\overline{)\begin{array}{cc}\text{Coefficient}& \text{Original}\\ \multicolumn{2}{c}{\text{For}{\gamma }_{\text{API}}\le \mathrm{30\; :}}\\ a_1& 0.4677x{10}^{-3}\\ a_2& 17.51x{10}^{-6}\\ a_3& -18.11x{10}^{-9}\\ \multicolumn{2}{c}{\text{For}{\gamma }_{\text{API}}>\mathrm{30\; :}}\\ a_1& 0.467x{10}^{-3}\\ a_2& 11.00x{10}^{-6}\\ a_3& 1.337x{10}^{-9}\end{array}}$$




3. Al-Marhoun (1992)
$$B_{ob}=1+a_1{R}_s+a_2{R}_s\left({\gamma }_g/{\gamma }_o\right)+a_3{R}_s\left(T-60\right)\left(1-{\gamma }_o\right)+a_4\left(T-60\right)$$ $$\overline{)\begin{array}{cc}\text{Coefficient}& \text{Original}\\ a_1& 0.177342x{10}^{-3}\\ a_2& 0.220163x{10}^{-3}\\ a_3& 4.292580x{10}^{-6}\hfill \\ a_4& 0.528707x{10}^{-3}\end{array}}$$





Above bubblepoint pressure, increased pressure will compress the liquid and reduce its volume.

For the case of P > Pb, the oil FVF is calculated from

$${\text{B}}_{\text{o}}={\text{B}}_{\text{ob}}{\text{e}}^{{\overline{\text{c}}}_{\text{o}}{\text{(P}}_{\text{b}}-\text{P)}}$$

Correlation for calculating average oil compressibility Co at various conditions is presented later.