The potential for using mixed surfactants at low concentration to improve mobility control in CO flooding was evaluated in laboratory experiments. We examined various mixed surfactant systems, such as alpha olefin sulfonate and ethoxylated alcohol sulfate, through foam durability and flowing tests.

In foam durability tests, we used a high pressure device to assess the stability of CO-foam bubbles and other pertinent properties. In flowing tests, we used a composite core to measure the flowing properties of foam in two differing sections of permeability.

Our foam durability test results showed that some mixed surfactants exhibit either comparable or better foam stability than the foam generated using the individual surfactants. During the foam flowing tests, we observed substantial mobility reduction of CO with mixed surfactants at very low concentration. Depending on types of surfactant mixed, some mixed nonionic and anionic surfactants demonstrate a better mobility reduction than that produced by an anionic surfactant alone. Additionally, improved mobility dependence on rock permeability is observed for most of the mixed surfactants.

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