A comprehensive micro scale study of poly-ionic liquid for application in enhanced oil recovery: Synthesis, characterization and evaluation of physicochemical properties

Abstract

Ionic liquids (ILs) have found their application as novel green surfactants in different chemical industries. These ILs are emerging as a substitute for the surfactants employed in petroleum industries. The quest for a reliable surface-active agent for enhanced oil recovery application has led to the investigation of polymeric ionic liquid as chemical agents. Poly-ionic liquids (PILs) are unique compounds that possess distinctive properties of ILs such as, thermal stability and salt tolerance, along with the specific property of polymers such as flexibility and durability of the polymeric backbone. In present work, poly [1-hexadecyl-3-vinyl-imidazolium bromide] (poly [C16VIm+][Br−]) was synthesized and investigated as a chemical agent for enhanced oil recovery. The interaction of PIL with aqueous injection fluids and crude oil has been analyzed by different properties such as interfacial tension, wettability alteration, dynamic light scattering (DLS), and rheological parameters, which help in understanding the performance of PIL flooding. Surface tensiometry studies revealed the critical micellar concentration (CMC) of PIL to be much lower (200 ppm) in comparison to analogous ILs. The synthesized poly-ionic liquid showed good salt tolerance behavior (>10%) and long-term thermal stability (90 °C) in the presence of monovalent and divalent ions, thus confirming its applicability in the high saline reservoir. Highly beneficial low interfacial tension (IFT) values were obtained at crude oil-aqueous interfaces, which further decreased with an increase in salinity and temperature. DLS studies revealed that hydrodynamic particle size of PIL at CMC to be ~180 nm and it increased with concentration due to aggregation of molecules. PIL showed pseudoplastic or shear-thinning behavior, and viscosity increased with concentration due to the formation of transient network and entanglement of molecules. Contact angle studies showed that poly [C16VIm+][Br−] aqueous solution alters the wetting characteristics of rock from intermediate-wet to water-wet condition (below 20°). Analyzing the above properties, core-flooding experiments were conducted, and additional oil recovery of 31.25% of the original oil in place was obtained after the conventional water flooding.