CO2-Foam Mobility Tests at Reservoir Conditions in San Andres Cores

ABSTRACT The development of a foam technology for CO2 flooding has been an active research area with a large emphasis in finding effective surfactants. A number of surfactants have been suggested in the literature as effective CO2 foaming agents. Reported here are foam mobility reduction tests which were conducted at reservoir conditions in restored field cores from the San Andres formation of west Texas. Tests were also conducted in San Andres outcrop rock material. In contrast to most previous studies, an attempt was made to establish both a representative wettability and a CO2 flood residual oil saturation prior to conducting the foam tests. Many surfactants were tested, and most of them, including those previously identified as especially good foaming agents, did not generate effective foam in representative west Texas rock. The limited number of surfactants which did reduce CO2 mobility substantially are identified. Foam behavior in the restored field cores is also discussed. The best surfactants reduced gas mobility by less than a factor of ten. Some surfactants were found to change core conditions so that subsequent tests with previously ineffective surfactants showed mobility reduction. Successful results with cationic surfactants are also reported. An extremely important limitation of a surfactant's usefulness is its level of adsorption on rock surfaces; consequently, adsorption tests were conducted for some of the surfactants. Successful results using sacrificial agents to reduce adsorption are also reported.