CO2 Foam With Surfactants Used Below Their Critical Micelle Concentrations

Summary Using surfactants below their critical micelle concentrations, CCMC, to reduce gas mobility throughout a reservoir can be advantageous. When used in reservoir brines below their CMCMC inexpensive anionic surfactants propagate through rock with little delay owing to adsorption. Yet gas mobility is reduced below that of a watertlood in either surfactant-water-altemating-gas (SWAG) or coinjection experiments. Moreover, oil recovery is higher than in processes without surfactant. In contrast, at concentrations above the CCMC, surfactant adsorption is much higher and the injected surfactant concentration can be greatly delayed. In addition, CO2 mobility can be reduced so far below that of a watertlood that injectivity suffers. Moreover, oil recovery can be reduced because oil is emulsified and its mobility is lowered. This type of foam should be considered only for near-wellbore fluid diversions.