Gas saturation - Water-drive gas reservoirs

Input(s)

$G$ : Gas Initially in Place (SCF)

$G_{p}$ : Cumulative Gas Production (SCF)

$B_{g}$ : Volume Factor $(\mathrm{bbl} / \mathrm{SCF})$

$B_{g i}$ : Initial Gas Formation Factor (bbl/SCF)

$W_{e}$ : Cumulative Water Influx $(\mathrm{bbl})$

$W_{p}$ : Cumulative Water Production (STB)

$B_{w}$ : Water Formation Volume Factor (rb/STB)

$S_{w i}$ : Initial Water Saturation (fraction)

$S_{\text {grw }}$ : Residual Gas Saturation to Water Displacement (fraction)

$\mathrm{S}_{\mathrm{g}}$ : Gas Saturation (fraction)

\mathrm{S}_{\mathrm{g}}=\frac{\left(G-G_{p}\right) * B_{g}-\frac{W_{e}-W_{p} * B_{w}}{1-S_{w i}-S_{g r w}} * S_{g r w}}{\left(\frac{G * B_{g i}}{1-S_{w i}}\right)-\left(\frac{W_{e}-W_{p} * B_{w}}{1-S_{w i}-S_{g r w}}\right)}

Ahmed, T., McKinney, P.D. 2005. Advanced Reservoir Engineering, Gulf Publishing of Elsevier, Chapter: 3, Page: 208.