INVESTIGATION OF OIL RECOVERY IMPROVEMENT BY COUPLING AN INTERFACIAL TENSION AGENT AND A MOBILITY CONTROL AGENT IN LIGHT OIL RESERVOIRS

Investigation of Oil Recovery Improvement by Coupling an Interfacial Tension Agent and a Mobility Control Agent in Light Oil Reservoirs will study two major areas concerning co-injecting an interfacial tension reduction agent(s) and a mobility control agent. The first area defines the interactions of alkaline agent, surfactants, and polymers on a fluid-fluid and a fluid-rock basis. The second area concerns the economic improvement of the combined technology. This report examines the interactions of different alkaline agents, surfactants, and polymer combinations on a fluid-fluid basis. Alkali and surfactant combine to reduce the interfacial tension between a low acid number, 42 API gravity crude oil and the aqueous solution to values lower than either agent alone. Surfactant structure can vary from linear chain sulfonates to alkyl aryl sulfonates to produce low interfacial tension values when combined with alkali. However as a class, the alkyl aryl sulfonates were the most effective surfactants. Surfactant olefInic character appears to be critical in developing low interfacial tensions. For the 42 API gravity crude oil, surfactants with molecular weights ranging from 370 to 450 amu are more effective in lowering interfacial tension. Ultra low interfacial tensions were achieved with all of the alkaline agents evaluated when combined with appropriate surfactants. Different interfacial tension reduction characteristics with the various alkali types indicates alkali interacts synergistically with the surfactants to develop interfacial tension reduction. The solution pH is not a determining factor in lowering interfacial tension. Surfactant is the dominate agent for interfacial tension reduction. Increasing the temperature up to 170?F did not significantly alter the interfacial tension reducing capability of an alkaline-branched alkyl aryl sulfonate solution but changed interfacial tension for linear alkyl aryl sulfonates. Shifts in the alkali concentration and/or the range of alkali concentrations which produce the ultra low interfacial tension values were observed consistent with the change in surfactant solubility. The alkyl surfactants which did not produce low interfacial tension at 72?F were still not effective as the temperature increased. Increasing the salinity of the surfactant and alkaline plus surfactant solutions demonstrates that the interfacial tension reduction synergism is not the result of changing salinity for the range tested. Ultra low interfacial tension values for surfactant plus alkali solutions could not be achieved with surfactant plus sodium chloride before alkyl-aryl surfactants precipitated from solution. The alkali plus surfactant solutions with the more water soluble surfactants gave lower interfacial tension values than surfactant plus sodium chloride at the tested salt concentrations. For alkaline plus surfactant solutions which produce ultra low interfacial tensions, an increase of the solution salinity shifted the surfactant which was most effective to a slightly more water soluble type. Also, an increase in temperature increased the salinity at which the minimum interfacial tension occurred for alkyl aryl surfactants. For non-optimum surfactants, increasing the temperature did not change the salinity effects with any consistent trend.

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