Motivation = maintain formation pressure at sweep interface with alternating inejction of water and gas in case of high residual oil to water sweep is high s_{orw} and gas sweep is less than to water sweep s_{org} < s_{orw}.
| (1) | E_D = \frac{1-s_{wi}-s_{org}}{1-s_{wi}} |
See also
Petroleum Industry / Upstream / Production / Field Development Plan / Recovery Methods