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Foams, as a conformance improvement technology for use during gas flooding (e.g., steam, CO2, and miscible gas flooding), have historically been most widely studied and applied when the foams are to be used in the form of a "viscosity-enhancing" mobility-control agent that is injected from the injection-well side. Because relatively large volumes of foam are required and because the foam must be propagated significant distances in the reservoir, applying foams for mobility control has proven technically and economically challenging. This article discusses applications and challenges associated with foams as mobility control agents. As discussed in Foam properties, the low effective density of most mobility-control foams, which are used during a gas flood such as a steam or CO2 flood, provides a driving force for the foam to flow and be desirably placed in the upper reservoir vertical interval where the offending gas override is occurring and where the foam will be most effective at countering the negative impact of the gas override. Shi and Rossen[1] describes an "improved" surfactant-alternating-gas foam injection process to control gravity override during gas flooding projects.
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