1. n. [Enhanced Oil Recovery]

An enhanced oil recovery process in which alternating slugs of a surfactant solution and gas are injected into a reservoir. The injected surfactant and gas mix and generate foam that reduces the gas mobility, especially in previously swept or high-permeability regions of the reservoir. This improves sweep efficiency by mitigating gravity override and viscous fingering during gas injection. The presence of the surfactant in the injectant can also improve recovery by reducing interfacial tension between reservoir oil and the injection phases.

Alternate Form: sag

See: gas injection,  surfactant