Performance Evaluation and Optimization of a Compound Microemulsion System for Enhanced Oil Recovery in Low-Permeability Reservoirs

In low-permeability reservoirs (≤30 mD), conventional surfactants often fail due to strong capillary forces, limiting oil recovery. To address this challenge, a microemulsion system (M3ME) was developed using a blend of sodium methyl ester sulfonate (MES) and fatty alcohol polyoxyethylene ether-3 (AEO-3). The formulation was optimized through orthogonal experiments by adjusting the ratios of cosurfactant (TGME), kerosene, and 1% KCl to achieve a transparent, stable microemulsion. With a particle size of 86.1 nm, M3ME achieved a 25.61% increase in oil recovery compared to water flooding, enabling deep penetration into nanoscale pore throats. Low interfacial tension enhanced oil displacement efficiency by mitigating capillary forces and promoting oil-water interface interaction. Core flooding and spontaneous imbibition tests on Changqing low-permeability cores showed that 0.2% M3ME outperformed the M3 surfactant system by 7.49%, demonstrating its superior potential for enhanced oil recovery in tight reservoirs. Low-field NMR and microetched model analysis confirmed that M3ME mobilizes residual oil by penetrating nanoscale pore throats, highlighting its effectiveness for EOR applications.