Synthesis, characterization, and mechanistic study of a new highly-stable comb-like polymeric surfactant in enhanced oil recovery

Numerous investigations suggest that the primary impediment to chemical flooding, particularly in cases involving surfactant-polymer (SP) and alkaline-surfactant-polymer (ASP) injection, is the resilience of the injected fluid front in severe reservoir conditions. To surmount this obstacle, one could amalgamate the characteristics of individual polymer and surfactant molecules into a singular molecule capable of achieving the desired interfacial tension reduction and viscosity enhancement. In the literature, these compounds are referred to as "polymeric surfactants" and are extensively expounded upon in terms of synthesis techniques and their practical applications. Nevertheless, the diverse facets of polymeric surfactant implementation in the enhanced oil recovery sector are scarcely explored and necessitate a systematic reassessment. The present study describes a complete procedure of polymeric surfactant analysis for an enhanced oil recovery purpose in three parts. First, we utilized the free-radical copolymerization method to build novel comblike polymeric surfactant molecules, and the accuracy of the synthesis was confirmed by multiple characterization tests. The polymeric surfactant had a CMC of 432.7 ppm and was stable up to 220degree celsius, which is accepted for most subsurface applications. In the second part, the stability of polymeric surfactant solutions was tested in various conditions and compared with some commercial SP solutions, and improved stability of polymeric surfactant solution was observed. Furthermore, interfacial tension (IFT) was measured with different oil compositions, and the relationship between oil acid/base number and IFT was figured out. In addition, a comprehensive study on surface adsorption of the polymeric surfactant was applied to find its consequent effects on rock wettability and correlations with rock composition and it was pointed out that the polymeric surfactants are adsorbed in multilayer configuration rather than monolayer over the rock surface. In the end, four core flooding experiments and capillary number analysis showed that the primary recovery mechanism in polymeric surfactant flooding is increased water viscosity, which leads to the discovery of a new unswept area of the core plugs. Nonetheless, interfacial tension reduction was the second recovery mechanism in polymeric surfactant flooding.