Enhanced oil recovery in high temperature carbonates using microemulsions formulated with a new hydrophobic component

• Application of biodiesel as renewable hydrocarbon component of microemulsion at 75 °C.
• Crucial role of surfactant concentration and co-solvent ratio on the phase behavior.
• Reduction of IFT to ultra-low value (2 × 10−3 mN/m) using optimum formulation.
• Wettability alteration from intermediate-wet (107°) to water-wet (57°) status.
• EOR in spontaneous imbibition (20.0%) and core-flood (6.4%) tests of carbonate rocks.

The positive feedback from previous studies has confirmed the high performance of microemulsion flooding. However, there are few researches assessing this efficient method in carbonates reservoirs, particularly at high temperature. This paper attempts to fill the gap. Furthermore, biodiesel is introduced and evaluated as a new hydrocarbon source of mixture. For this purpose, phase behavior of surfactant/brine/biodiesel/co-solvent was systematically studied using response surface methodology to find the optimum formulation. Thereafter, optimized microemulsion was characterized in terms of particle size distribution, zeta potential, electrical conductivity, polarized light microscopy, surface tension, interfacial tension, and viscosity. Finally, oil recovery tests comprising spontaneous imbibition, contact angle, core-flood and microvisual experiments were conducted to examine the potential of optimum formulation for chemical enhanced oil recovery (CEOR) purpose in carbonates. Experiments of different stages were carried out at elevated temperature (75 °C). Employing optimal microemulsion, 20.0% original oil in place (OOIP) in spontaneous imbibition and 6.4% OOIP in core-flood tests were tertiary added to oil recovery. The results of this study illustrate the efficacy of proposed formulation to increase oil recovery factor of carbonate formations.

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