Investigation on the properties of water-in-heavy oil emulsion of heavy oils with different viscosity

Water-in-heavy-oil (W/O) emulsions are widely formed during heavy oil production and transportation, significantly affecting flow behavior and viscosity characteristics. This work systematically investigates the effects of water content and base oil viscosity on the rheological behavior and microstructural evolution of W/O emulsions prepared from three heavy oils with viscosities ranging from 533 to 3913 mPa s at 50 °C. Rheological measurements and microscopic characterization were conducted to reveal the relationship between microstructural evolution and viscosity amplification behavior. Experimental results show that emulsion viscosity increases nonlinearly with water content and reaches up to 21.1 times that of the corresponding base oil. Increasing water content promotes droplet crowding, broader droplet size distribution, and stronger interfacial interactions, which progressively restrict droplet mobility and intensify internal flow resistance. As a result, the viscosity amplification behavior gradually becomes dominated by microstructural interactions within the emulsion system. Therefore, the viscosity enhancement coefficient (K) exhibits strong structure dependence rather than behaving as a constant empirical parameter. By incorporating microstructural parameters into the Richardson model under dimensional constraints, a modified predictive model for K was established with a high prediction accuracy (R2 = 0.991) and prediction errors below 4%. These results provide improved physical insight into the viscosity amplification mechanism of W/O emulsions and offer a more reliable approach for predicting the rheological behavior of heavy-oil emulsions.