Optimization of Enhanced Oil Recovery via Hybrid Alkali-Surfactant-Polymer (ASP) Polymer Flooding in Heterogeneous Carbonate Reservoirs

Project Abstract

Optimization of enhanced oil recovery (EOR) in heterogeneous carbonate reservoirs remains a pivotal challenge due to contrasting rock properties, complex wettability, and salinity sensitivity that hamper conventional techniques. This study presents a comprehensive evaluation of a hybrid alkali-surfactant-polymer (ASP) polymer flooding strategy designed to maximize oil displacement efficiency, mitigate incremental costs, and reduce water production while maintaining reservoir integrity. A multi-scale approach combines core-flood experiments, surface chemistry analyses, and numerical simulation to quantify the synergistic effects of alkali-generated in-situ soaps, interfacial tension (IFT) reduction, charge reversal of rock minerals, and polymer-viscosity enhancement on sweep efficiency and recovery factors. Core samples representative of heterogeneous carbonate formations are subjected to sequential flooding sequences under reservoir-relevant temperatures, pressures, salinities, and mineral compositions to capture the influence of heterogeneity on ASP performance. The alkali component targets reactive mineral surfaces to alter wettability toward more water-wet conditions, while surfactants decrease IFT between oil and brine, promoting displacing efficiency in high-tortuosity pore networks. The polymer component increases the displacing viscosity ratio, suppresses 'viscous fingering,' and supports gravity-stable displacement in vertical sections prone to early breakthrough. Experimental results indicate substantial improvements in relative permeability endpoints and residual oil saturation reduction when ASP is combined with optimized polymer concentration, surfactant formulation, and alkali dose tailored to carbonate rock chemistry. advanced characterization techniques, including contact-angle measurements, pendant-drop tensiometry, zeta potential analysis, and nanoparticle-enabled imaging, elucidate the mechanistic pathways of wettability alteration, IFT thinning, and interfacial film stabilization that govern mobilization of trapped oil. A validated compositional reservoir simulator integrates the measured laboratory data to perform sensitivity analyses across heterogeneity profiles, oil viscosity, temperature, salinity, and injection strategies. Key findings reveal that the hybrid ASP system achieves a favorable balance between chemical costs and incremental oil production by enabling re-wettability shifts, sustained low IFT, and viscosity-enhanced displacement without excessive adsorption losses. The study demonstrates that an adaptive optimization framework—incorporating sequential injection schemes, slug sizing, and stage-wise chemical dosing—can maximize recovery while minimizing chemical consumption and adverse environmental impact. Economic evaluation highlights reduced water cut, lower surface facility loads, and improved project economics in mature fields encountering diminished driving forces. The integrated approach offers a scalable methodology for field deployment, including diagnostic screening for carbonate-specific chemistries, field-appropriate ASP formulations, and best-practice operational guidelines for surface blending, injection timing, and surveillance. Overall, the research provides a rigorous, data-driven roadmap for deploying ASP polymer flooding as a viable, efficient, and economically sound EOR method in heterogeneous carbonate reservoirs, with potential applicability to similar rock systems and evolving chemical families.

Project Overview

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