Microscopic Investigation of Phase Behavior in Heavy Oil Emulsions Using Confocal Laser Scanning Microscopy

Due to its high viscosity and low mobility, heavy oil cannot be efficiently displaced by conventional water flooding methods. The early-formed water-in-oil (W/O) emulsions often suffer from increased flow resistance and structural instability. While previous studies have primarily focused on the macroscopic rheological behavior, traditional optical microscopy is limited in resolving the interfacial layer thickness, droplet size distribution, and localized coalescence behaviors at high resolution. To better elucidate the microstructural evolution and rheological mechanisms of heavy oil emulsions, this study introduced confocal laser scanning microscopy (CLSM) combined with rheological measurements and optical microscopy to systematically analyze the structural evolution and viscosity variation of emulsions under varying water contents (30%–70%) and oil viscosities. Results demonstrated that the emulsion viscosity increased exponentially with water content, reaching up to 23.2 times the base oil viscosity at 70% water content. The mean droplet size and distribution heterogeneity (maximum coefficient of variation 0.32) both increased significantly with water content. CLSM imaging vividly revealed interface layer thickening, droplet aggregation, and rupture dynamics, especially prominent in emulsions with higher base oil viscosity. Notably, emulsions based on medium-viscosity heavy oils exhibited more uniform droplet structures and superior rheological stability. This study highlights the advantages of using CLSM to overcome the limitations of traditional observation methods, clarifying the intrinsic relationship between microstructural evolution and macroscopic rheological performance. The findings provide theoretical insights and experimental support for improving early-stage flowability and optimizing recovery strategies in heavy oil development.