Enhanced Heavy Oil Recovery Due to Synergistic Interactions between Functionalized Nanoparticles and Surfactants

Herein, we aim to develop a highly efficient and stable nanofluid as a reliable working fluid for enhanced oil recovery in both cold production and post-thermal recovery of heavy oil. To address the challenges of high viscosity and poor low-temperature flowability of heavy oil, we propose a nanofluid system (NAS) based on the synergistic effect of surface-modified Al2O3 nanoparticles and surfactants. A combination of experimental investigations and molecular dynamics simulations was systematically conducted. Modified nanoparticles were first synthesized using KH550 and palmitic acid as modifiers, with optimized monomer ratios (KH550 15%, palmitic acid 20%). The structure and properties of the modified nanoparticles were characterized through a series of physical and chemical analyses. Laboratory evaluations confirmed successful surface functionalization, achieving amphiphilic modification as evidenced by a shift in surface wettability from strongly hydrophilic to neutrally wetting. Molecular dynamics simulations revealed that the introduction of the NAS system facilitates the formation of core–shell structures, with nanoparticles serving as the core and heavy oil components along with surfactants assembling as the shell. The resulting substantial steric hindrance inhibits the self-assembly of heavy components and disrupts their three-dimensional network, leading to a marked reduction in heavy oil viscosity at the macroscopic level. Physical core flooding experiments further demonstrated that the NAS system exhibits profile control and oil displacement effects under heterogeneous reservoir conditions. Enhanced sweep efficiency was achieved through nanoparticle pore-throat plugging and mobility control of oil-in-water (O/W) emulsions. Meanwhile, the O/W emulsion blended with heavy oil effectively reduced its apparent viscosity and improved fluidity, ultimately enhancing oil recovery by 16.54% to 19.51%. This study, spanning microscopic mechanisms to macroscopic performance, confirms the technical feasibility of using modified nanoparticles in synergy with surfactants for heavy oil cold production, providing practical insights for the application of nanomaterials in heavy oil reservoirs.