Modeling of droplet diameter of water-in-oil crude oil emulsion by characterization of crude oil physical properties

During the mixed transportation of crude oil and water, the mixture is susceptible to forming an emulsion that comprises a substantial quantity of droplets with differing diameters. The diameter and distribution of emulsion droplets exert a crucial role in determining the viscosity characteristics of the crude oil emulsion (COE). Sixteen different crude oils were utilized to prepare stable water-in-oil (W/O) emulsions, and the droplets diameters were statistically analyzed using microscopic observation. The results indicated that the Sauter average droplet diameter (SADD) of different COEs showed two trends of increasing and decreasing with the change of temperature. The SADD of COE did not increase or decrease monotonically with the change of water cut, and there is no significant regularity between them. The droplet diameter distribution of COEs could be described by probability statistical distribution functions of Gauss distribution, Extreme distribution, LogNormal distribution, and Lorentz distribution. The concept of droplet density was defined, and based on this concept, a characterization method of Sauter average droplet diameter weighted by droplet density (SAWDD) was proposed, which enabled a single parameter to reflect the comprehensive influence of average droplet diameter and droplet density on the apparent viscosity of COE. Five parameters, namely saturates content, aromatics content, surfactants content, acid value, and crude oil viscosity, were identified to characterize the crude oil physical properties (COPPs). A prediction model of SAWDD was established by quantitative characterization of COPPs. The verification results indicated an average relative deviation of 9.2% between the model-calculated and experimental values of SAWDD.