Displacement efficiency defines the fraction of the initial pore-saturating fluid displaced in a the piston sweep by invaded fluid

$\begin{array}{l}\displaystyle E_D = 1- \frac{V_{FLUID, \ INITITAL} - V_{FLUID, \ INVADED}}{V_{FLUID, \ INITITAL}}\end{array}$

Water-Oil Displacement Efficiency (E_Dow)

$\begin{array}{l}\displaystyle E_{Dow} = 1- \frac{V_{o, \ LEFT}}{V_{o, \ INITITAL}} = \frac{1-s_{wi}-s_{orw}}{1-s_{wi}}\end{array}$

where $\begin{array}{l}s_{wi}\end{array}$ – initial water in oil pay, $\begin{array}{l}s_{orw}\end{array}$ – residual oil to water sweep.

Gas-Oil Displacement Efficiency (E_Dog)

(1)	$\begin{array}{l}\displaystyle E_{Dog} = 1- \frac{V_{o, \ LEFT}}{V_{o, \ INITITAL}} = \frac{1-s_{wi}-s_{org}}{1-s_{wi}}\end{array}$

where $\begin{array}{l}s_{wi}\end{array}$ – initial water in oil pay, $\begin{array}{l}s_{org}\end{array}$ – residual oil to gas sweep.