Study on the mathematical model for predicting settling of water-in-oil emulsion

Abstract

Owing to the increment efficiency, the generation of water-in-oil (W/O) type emulsion in the flooding process affects the displacement efficiency. After the generation of emulsion in reservoir conditions, multiple mechanisms such as creaming, sedimentation, flocculation, phase inversion, coalescence, and Ostwald ripening cause the break of emulsion; and thus, the viscosity of the emulsion phase changes. However, owing to the lack of an appropriate model, the viscosity fluctuation caused by the emulsifying and demulsifying processes of the displaced phase has not been considered in general numerical simulations. In this study, a mathematical model that included the water cut, viscosity prediction, droplet displacement models, and droplet breakdown probability was established to predict the settling process of W/O type emulsion at different conditions. Multiple influencing factors, such as oil/water ratio, rotation speed, stirring time, and surfactant concentration were considered. The mathematical model for predicting emulsion settling provides excellent fitting results on the emulsion W/O system. The introduction of droplet breakdown probability can be used to adjust the prediction model to different emulsion systems. The size of the droplet is the key factor in the settling of the emulsion system. A larger droplet increases the coalescence probability, viscosity, droplet size, and descent rate. The oil/water ratio, stirring time, and rotation speed have a significant influence on the size of the emulsion droplet. More external and low water content can help generate smaller size droplets, which improves the emulsion stability. The emulsion with a different surfactant concentration possesses a similar initial condition. However, a low surfactant concentration system achieves a weaker stability during the settling process because of the relatively large droplet size and high descent rate. • The droplet breakdown probability can predict emulsion settling. • The size of the droplet is a key factor for emulsion settling. • The oil/water ratio, stirring time, and rotate speed influence on the emulsion droplet size. • Surfactant concentrations possessed significant influence on emulsion stability.