Investigation of Surfactant Huff-n-Puff Injection for Enhanced Oil Recovery in Unconventional Reservoirs: An Integrated Experimental and Numerical Simulation Approach Coupled with the HLD-NAC Methodology

Surfactant huff-n-puff (HnP) injection processes have become one of the most attractive enhanced oil recovery (EOR) protocols to effectively produce unconventional oil reservoirs. In this paper, the mechanism of surfactant-enhanced tight oil recovery is comprehensively investigated by experimental and numerical simulation. Imbibition experiments are employed to elucidate the impact of surfactants on enhancing the tight core recovery. Core-scale numerical simulation models are applied to match experimental data to characterize the effects of surfactants on oil and water flow capabilities. We model the microemulsion phase behavior of an optimized surfactant formulation using hydrophilic-lipophilic difference and the net-average curvature (HLD-NAC) equation, which are used to quantitatively characterize the interfacial tension (IFT) reduction, wettability alteration, and oil solubilization effects. A numerical simulation model is structured to assess the production increments of the surfactant huff-n-puff injection for a multistage fractured horizontal well in the Jimusar J305 block as a case study. An extensive parametric study is conducted employing it as a base case model. Results show that the adsorption capacity of the surfactant on the reservoir rock has a strong impact on the wettability alteration and oil production increment. For the huff-n-puff surfactant injection design considerations, the top three factors impacting oil recovery improvement are the injection volume, concentration, and number of cycles, while injection time, production time/stage, and soaking time show a less significant impact. The recovery rate of the surfactant huff-n-puff EOR ranged from 2.55 to 17.12%. The use of the HLD-NAC equation enables the characterization of microemulsion phase behavior, which makes the simulation results reliable for field practices.