Peeling off mechanism and influencing factors of adhesive oil film in ultra-deep tight reservoir − insights from molecular dynamics

Abstract

Molecular dynamics simulations were conducted to investigate the microscopic interactions among rock, crude oil, and surfactants, elucidating the fundamental principles governing adhered oil film detachment in ultra-deep reservoirs. The study systematically analyzed surfactant-induced oil film peeling dynamics through three perspectives: (1) interfacial adsorption behavior, (2) energy evolution during peeling off, and (3) component-dependent peeling mechanisms. Furthermore, temperature, pressure, and surfactant concentration effects were quantitatively evaluated. Surfactant intervention triggered crude oil peeling off from rock surfaces, resulting in oil droplet dispersion within the water phase. The peeling process progressed through four characteristic phases: rapid acceleration, sustained growth, stabilization, and asymptotic equilibrium. This staged behavior originated from competitive surfactant interactions at both the oil–water interface and rock surface. Structural simplicity governed peeling efficiency, with saturated hydrocarbons (94.15 % removal at 3000 ps) significantly outperforming polar resins and asphaltenes (52.9 % residual). Thermal activation played a critical role: below 393 K, suppressed molecular mobility limited peeling off effect (lower than 40 %), whereas elevated temperatures (>413 K) promoted water channel penetration and enhanced peeling off efficiency (over 80 %). Pressure variations (42–62 MPa) exhibited negligible impact (<10 % peeling off efficiency fluctuation). Increasing surfactant concentration (0.0–10.0 wt%) exponentially reduced oil-rock interaction energy from −20000 kJ/mol to −12000 kJ/mol. Enabling removal 85 %-90 % oil within at concentrations of 5.0 %-10.0 %. These findings establish a mechanistic framework for designing surfactant-enhanced waterflooding systems in ultra-deep tight reservoirs.