Visualizing the Effect of Light Oil on CO2 Foams

This paper describes a series of high-pressure, CO{sub 2}-tertiary-foam, microvisual experiments. The results suggest how oil affects CO{sub 2} foam. Foam-stability, emulsion-stability, and spreading-coefficient calculations show how vaporization and condensation of hydrocarbons in the CO{sub 2} process change oil composition, spreading behavior of oil at the water/gas interface, and mobility control. This analysis suggests that water is the spreading phase near the injector but that oil is the spreading phase elsewhere. Spreading oil benefits CO{sub 2} foam because mass transfer of miscibility-developing components into CO{sub 2} is maintained, while condensation of light hydrocarbons into oil reduces mobility control enough for reservoir injectivity to be reasonable. A high concentration of light hydrocarbons in the oil, which causes oil to spread, and oil wetness appear to be the main reasons that oil impairs foam.