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

Ionic modificationof injected brines (Smart Water EOR)has previouslydemonstrated great potential for wettability alteration in carbonatesfrom 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 & DEG;C). Moreover, at low temperature conditions, theacid number of crude oils tends to increase in the reservoir, causinga stronger oil wetting character and less water-wet initial conditions.This paper evaluates the wettability alteration potential of surface-activeionic liquids added to Smart Water to obtain a synergistic enhancedoil recovery effect in low-temperature carbonate reservoirs. [C(12)mim]Br, [C12Py]Cl, and [C16Py]Cl wereformulated in Smart Water (SW0Na) and tested as wettability modifiersin mixed-wet carbonate chalk cores. Spontaneous imbibition oil recoverytests showed that the addition of [C(12)mim]Br and [C12Py]Cl can cause wettability changes, resulting in increasedoil recovery compared to pure SW0Na brine at 90 & DEG;C. The highestincremental oil recovery in tertiary mode of 24.6 % OOIP was obtainedusing [C(12)mim]Br in SW0Na, followed by [C12Py]Clin SW0Na with 22.4 % OOIP, and only 11.5 % OOIP was recovered by pureSW0Na brine. The potential for wettability alteration for carbonaterocks was further evaluated in viscous flooding tests using the bestformulation from the results obtained in the spontaneous imbibitionexperiments ([C(12)mim]Br in SW0Na). The core flooding resultsshowed an ultimate recovery of 79.3 % OOIP achieved in secondary modeinjection. Despite the difference in the head groups of the cationic[C(12)mim]Br and [C12Py]Cl ionic liquids, bothformulations showed abilities to desorb polar organic components ofcrude oil from the chalk mineral surfaces, thus improving the performanceof Smart Water EOR at 90 & DEG;C.