Evaluation of Surface-Active Ionic Liquids in Smart Water for Enhanced Oil Recovery in Carbonate Rocks

Abstract

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 temperature-dependent, 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. [C12mim]Br, [C12Py]Cl, and [C16Py]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 [C12mim]Br and [C12Py]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 [C12mim]Br in SW0Na, followed by [C12Py]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 ([C12mim]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 [C12mim]Br and [C12Py]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.