Objective The produced fluid from the CNL joint station in Shengli Oilfield is predominantly composed of high-viscosity heavy oil. After chemical enhanced oil recovery (EOR) treatment, the liquid phase remains production enhancing treatment agents such as residual heavy oil viscosity reducers, organic retarding acid, reservoir cleaning agents. Under the production mode of gas flooding and foam flooding, highly dispersed microbubble groups are formed in the heavy oil emulsion, which makes defoaming and demulsification difficult. In view of the above technical bottlenecks, the multi-scale stability mechanism of foam heavy oil emulsion is systematically analyzed, which is a key guiding significance for the development of targeted demulsification technology.

Method Based on the mechanism of multiphase interface interaction, the characteristic components of crude oil, the interfacial activity of foaming agents and the adsorption characteristics of production enhancing treatment agents were systematically explored, and the main controlling factors affecting the stability of foam heavy oil emulsion were revealed at the molecular level. Based on interfacial dilational rheology, Zeta potential spectra and dynamic light scattering experiments, the synergistic mechanism of interfacial film strength, electrostatic repulsion effect and steric hindrance effect in emulsion stability was explained in multiple dimensions.

Result When the mass ratio of colloid to asphaltene in crude oil was 1.45∶1.00, the colloid and asphaltene were adsorbed to the oil-water interfacial film, and the stability of the interfacial film was enhanced by the steric hindrance effect. QP2 (foaming agent type Ⅱ) and CL3 (water-soluble viscosity reducer) had the strongest influence on the stability of foam heavy oil emulsion. When the two agents were compounded, the interfacial dilational viscoelastic modulus increased to 83.9 mN/m, the absolute value of Zeta potential reached 32.6 mV, and the stability parameter TSI value decreased to 23.6, which was 14.2% lower than that of the single system.

Conclusion This study first elucidates the multi-scale synergistic stabilization mechanism of chemical agent-microbubble-interface film under the combined exploitation mode of gas flooding and chemical flooding, which can guide the joint station to study the targeted demulsification system based on the reaction principle, improve the work efficiency of the joint station and reduce the production cost.