Conventional reservoirs with high residual oil saturation are often targets for chemical flooding during enhanced oil recovery processes designed to mobilize and solubilize oil. Chemical additives (such as surfactants) are usually added to brine to decrease the interfacial tension (IFT) and contact angle, thereby reducing the capillary drawdown inside the pores. The decrease in oil/brine IFT allows the spontaneous emulsification and mobilization of bulk oil whereas solubilization of adsorbed oil results in wettability reversal. Recent studies suggested that putting surfactants into a micro-emulsified state prior to injection might improve their performance. Most of these studies proved that microemulsion (ME) efficiency depends on test conditions and the proper selection of their chemical formulations and brine chemistry.<sup> </sup>However, the impact of rock characteristics (such as mineralogy, roughness, and wettability state) on the complex fluid-rock interactions is still unclear, especially in heterogeneous rocks. The goal of this study was to examine the effect of MEs on oil recovery from three different aged rocks (Berea, Edwards, and Tensleep) and identify the test conditions in which MEs outperform surfactants alone. The effectiveness of an environmentally friendly ME formulation was evaluated from different sets of spontaneous imbibition tests and petrographic analyses. Two ME solutions containing low and high concentrations of a nonionic surfactant were used and compared to surfactant solutions at the same concentrations. Several mechanisms such as IFT reduction, oil emulsification, and wettability alteration were responsible for the improved recovery. Both surfactant and ME lowered the IFT from 12 mN/m to less than 1 mN/m. However, high ME concentration was able to decrease the size of oil droplets by one order of magnitude, significantly enhancing oil mobilization in all three rocks. The solubilization capability of MEs was superior in Tensleep rock due to the unique ability of ME components to penetrate certain types of minerals and alter their wettability.

Impact of microemulsions on mobilization, emulsification, and solubilization of oil in heterogeneous rocks

253rd National Meeting (2017)

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