Probing on competitive adsorption-modification mechanisms and their impact on recovery efficiency during synergistic action of ternary composite flooding agents

At present, the research on the adsorption of Alkali-Surfactant-Polymer (ASP) is mostly limited to a single scale, making it difficult to establish a direct correlation between the microscopic mechanism and the macroscopic effect. In order to study the ability of a single chemical oil displacement agent and a compound system of multiple oil displacement agents to change the surface properties of rocks, their influence on the effect of enhanced oil recovery was analyzed, and the adsorption behavior of the ternary composite oil displacement system within the formation rocks was investigated in this study. The multi-scale model of ‘core scale experiment-pore scale analysis-molecular scale simulation’ was established, and the correlation between the adsorption capacity of different oil displacement agents and the effect of enhanced oil recovery was studied. The results show that under the synergistic effect of the ternary system, alkali is preferentially adsorbed on the rock surface by virtue of its strong migration ability, which changes the surface properties of the rock, and then the subsequent adsorption of macromolecular polymers and surfactants is significantly inhibited. The multilayer adsorption structure between polymer molecules is formed through hydrogen bonds and van der Waals forces, which has high adsorption stability and thus provides a guarantee for the long-term effect of the oil displacement agent. However, excessive polymer adsorption on the rock surface increase the complexity of its internal space, resulting in increased retention of adsorbed surfactants and affecting oil recovery. Low-permeability cores have a large specific surface area, poor pore-throat connectivity, and a higher adsorption capacity of chemical agents than high-permeability cores. Excessive adsorption exacerbates pore throat blockage, reduces fluid fluidity, and leads to a reduction in recovery rate by approximately 10%. The pre-polymer slug can saturate the adsorption sites on the core surface, reducing the adsorption and retention amounts of subsequent surfactants and alkali. When the concentration reaches 1500 mg/L, the adsorption regulation effect tends to be saturated. This study clarified the competitive adsorption and rock modification mechanisms among the oil displacement agents in the ASP flooding system from a microscopic perspective. The relationship between the adsorption behavior of chemical agents and the recovery rate was characterized in the macroscopic oil displacement effect, providing important theoretical support for optimizing the oil displacement scheme and enhancing the crude oil recovery rate.