A study of the oil recovery potential and mechanisms of an alternative Alkaline-Surfactant-Polymer formulation for carbonate reservoir

Abstract

Despite the promising nature of alkali-surfactant-polymer (ASP) flooding, its application is associated with various limitations that yield economic uncertainties about ASP projects. These limitations are aggravated in carbonate reservoirs where prevailing reservoir conditions attenuate the performance of various chemical agents in enhancing oil recovery. The goal of mitigating the impact of these limitations has led to research into the oil recovery potential of alternative chemical agents. Nevertheless, the literature has not reported a ternary combination of these alternative chemical agents. Therefore, this study focuses on investigating the potential of alternative ASP formulations composed of monoethanolamine (ETA), hexadecyl-3-methyl imidazolium bromide (C16mimBr), and Schizophyllan (SPG) for their enhanced oil recovery in carbonate reservoirs at high temperature (80 °C) and high salinity (4100 ppm) conditions. A conventional ASP formulation is deployed for comparative purposes. The current study is a sequel to our study on the oil recovery potential of an alkali-surfactant (AS) formulation made of ETA and C16mimBr. A comprehensive approach has been deployed to study the EOR potential of the proposed formulation. The approach included rheological measurements, core flood experiments, and micromodel experiments. The combination of ETA and SPG alleviates the detrimental effect of inorganic alkalis on HPAM. Therefore, the alternative ASP formulations showed better rheological properties than their conventional counterparts in bulk phase and porous media. The ETA–C16mimBr–SPG formulation also exhibited excellent EOR potential by recovering ∼27.05% additional oil, while the conventional counterpart achieved an additional oil recovery of ∼19.24%. Based on the results of the micromodel experiments, direct pore-to-pore displacement and emulsification are the main oil recovery mechanisms, and their occurrence depends on prevailing reservoir conditions. The study also confirms that wettability alteration as an oil recovery mechanism is more effective when the headgroup charge of the surfactant is the same as the surface charge of the rock. This study, therefore, reveals that a combination of organic alkali, surface-active ionic liquid, and biopolymer has excellent potential in enhancing oil recovery in carbonate reservoirs at high salinity–high-temperature conditions.