Recent displacement tests have indicated that under certain conditions the stabilized oil bank formed during dilute surfactant flooding may be composed of as many as three distinct oil banks. These secondary oil banks are characterized by the arrival of high oil cuts, high sulfonate concentrations, and low interfacial tensions in the effluent stream. The mechanisms governing the formation of these three banks, although different for each bank, are related to the interactions between the oil, rock, surfactant solution, and mobility buffer.

To determine the mechanisms governing the formation of these banks, a series of core floods was designed to isolate and study each bank separately. The experimental results, including the production histories and effluent analysis of these tests are presented and discussed.

The results of these tests indicate that two of the banks are formed by the chromatographic separation of high and low equivalent weight sulfonates, while the third is formed by the desorption of sulfonate during the injection of low saline fluids (mobility buffers). Also discussed are the means to alter the production profiles of displacement tests by manipulation of these mechanisms.

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