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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 AOT50wt%/LF250wt% 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/grock 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 ([C12mim]Br) was added to the system. The electrostatic interactions between the oppositely charged surfactants (AOT and [C12mim]Br) led to a higher surface activity. Thus, a formulation consisting of 0.8 wt% of AOT20.7wt%/[C12mim]Br25.3wt%/LF254wt% 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/grock, 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.

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Ionic modification of injected brines (Smart Water EOR) has previously demonstrated great potential for wettability alteration in carbonates from initially mixed-wet toward more water-wet conditions. However, the efficiency of Smart Water application is temperaturedependent, which reduces its ability as a rock wettability modifier at low temperatures (below 100 °C). Moreover, at low temperature conditions, the acid number of crude oils tends to increase in the reservoir, causing a stronger oil wetting character and less water-wet initial conditions. This paper evaluates the wettability alteration potential of surface-active ionic liquids added to Smart Water to obtain a synergistic enhanced oil recovery effect in low-temperature carbonate reservoirs. [C 12 mim]Br, [C 12 Py]Cl, and [C 16 Py]Cl were formulated in Smart Water (SW0Na) and tested as wettability modifiers in mixed-wet carbonate chalk cores. Spontaneous imbibition oil recovery tests showed that the addition of [C 12 mim]Br and [C 12 Py]Cl can cause wettability changes, resulting in increased oil recovery compared to pure SW0Na brine at 90 °C. The highest incremental oil recovery in tertiary mode of 24.6 % OOIP was obtained using [C 12 mim]Br in SW0Na, followed by [C 12 Py]Cl in SW0Na with 22.4 % OOIP, and only 11.5 % OOIP was recovered by pure SW0Na brine. The potential for wettability alteration for carbonate rocks was further evaluated in viscous flooding tests using the best formulation from the results obtained in the spontaneous imbibition experiments ([C 12 mim]Br in SW0Na). The core flooding results showed an ultimate recovery of 79.3 % OOIP achieved in secondary mode injection. Despite the difference in the head groups of the cationic [C 12 mim]Br and [C 12 Py]Cl ionic liquids, both formulations showed abilities to desorb polar organic components of crude oil from the chalk mineral surfaces, thus improving the performance of Smart Water EOR at 90 °C.

Displacement of a viscous fluid by a less viscous one is a challenging problem that usually involves the formation of interfacial digitations propagating into each one of the fluids, mixing them and preventing their normal displacement. We propose in this manuscript a protocol that is implemented via numerical simulation of the corresponding equations to improve the efficiency of the displacement. We consider a chemically active interface between the two chemically active fluids that produce a large viscosity interface that facilitates the process. All the relevant parameters of the mechanism are numerically analyzed aiming to optimize the efficiency of the method.