Improvement of a Surfactant Blend for Enhanced Oil Recovery in Carbonate Reservoirs by Means of an Ionic Liquid

The promising experimental performance of surfactant blends encourages their use in recovering the large quantity of crude oil still remaining in carbonate reservoirs. Phase behavior studies were carried out in this work to propose a blend for practical application. To that aim, the surfactants dioctyl sulfosuccinate sodium (AOT) and polyoxyethylene(8) octyl ether carboxylic acid (Akypo LF2) were mixed. A formulation consisting of 1 wt% of AOT(50wt%)/LF2(50wt%) blend in synthetic sea water (SSW) led to a low value of interfacial tension with crude oil of 1.50·10(−2) mN/m, and 0.42 mg/g(rock) of dynamic adsorption. A moderate additional oil recovery (7.3% of the original oil in place) was achieved in a core flooding test. To improve this performance, the surface-active ionic liquid 1-dodecyl-3-methylimidazolium bromide ([C(12)mim]Br) was added to the system. The electrostatic interactions between the oppositely charged surfactants (AOT and [C(12)mim]Br) led to a higher surface activity. Thus, a formulation consisting of 0.8 wt% of AOT(20.7wt%)/[C(12)mim]Br(25.3wt%)/LF2(54wt%) in SSW reduced the interfacial tension and surfactant adsorption achieved with the binary blend to 1.14 × 10(−2) mN/m and 0.21 mg/g(rock), respectively. The additional oil recovery achieved with the blend containing the ionic liquid was 11.5% of the original oil in place, significantly improving the efficiency of the binary blend.