Experimental Study on the Key Influencing Factors and Patterns of Emulsion Stability During ASP Flooding

The emulsion formed by alkali /surfactant /polymer (ASP) flooding not only increases the swept volume but also improves the displacement efficiency for enhancing oil recovery (EOR). However, premature demulsification hinders emulsions’ effectiveness due to their thermodynamic instability. Therefore, investigating the key influencing factors and patterns of emulsion stability during ASP flooding is of crucial significance for EOR. This study examines ASP flooding production fluids from the ASP flooding block in Daqing Oilfield. Initially, the optimized emulsion preparation method of ASP flooding system was optimized based on particle size and morphology in the target block. Subsequently, the study investigates the impact of polymer, surfactant, alkali concentrations, salinity, and temperature on emulsion stability with water precipitation rate as evaluation indices. Finally, a three-factor three-level orthogonal experiment is designed with chemical concentrations as variables to explore the key influencing factors and patterns on emulsion stability. The study's results indicate that the simulated emulsion prepared by the homogenizer at a shearing speed of 2500r/min for 10 minutes closely resembles the real emulsion in the target block. The emulsion prepared with a polymer concentration of 2000 ppm, a surfactant concentration of 0.4%, and an alkali concentration of 1.2% has good stability, particularly in the target block characterized by water salinity (4409.4mg/L) and temperature (45°C). Orthogonal experiments revealed that polymer concentration exerted the most significant influence on emulsion stability in Daqing Oilfield's ASP flooding reservoirs. Elevated polymer concentrations enhanced stability primarily by increasing aqueous-phase viscosity, which amplified emulsification intensity and impeded droplet coalescence through heightened resistance to merging. Alkali concentration demonstrated a secondary impact, wherein higher levels promoted saponification reactions between alkali ions and acidic crude oil components, generating natural surfactants that densified the interfacial film and augmented mechanical strength. In contrast, surfactant concentration exhibited a comparatively minor effect. Orthogonal experimental analysis has definitively identified the primary controlling factors of chemical agent concentrations on emulsion stability in ASP flooding systems. This finding has fundamentally challenged the conventional view that surfactant concentration dictates emulsion stability in ASP flooding systems, thereby expanding the theoretical framework of ASP technology.