Abstract
When oilfield development enters the middle and late stages, the crude oil-water mixture (COWM) produced from oil wells often has a high water cut and cannot form a stable emulsion. The traditional viscosity model of an emulsion is not suitable for this unstable mixture. Mastering the viscosity characteristics of the unstable crude oil-water mixture with high water cut (UCMH) for pipeline transportation of such mixtures is important. The apparent viscosities of UCMH (water cut of mixture ranging from 0.70 to 0.90) for 16 crude oils were determined via the stirring viscometric method. The results showed that the apparent viscosity of UCMH decreased with increasing shear rate, water cut of mixture, and temperature, demonstrating the property of shear thinning. The apparent viscosity of UCMH did not depend on the content of single surfactants such as resins, asphaltenes, waxes, and mechanical impurities but was closely related to the content of the above-mentioned combinatorial surfactants. The parameter exergy loss rate of shear that describes energy consumption was determined to characterize the external shear action on UCMH, which can fully reflect the essence of the mechanical energy consumption in the emulsifying process under different shearing conditions. A new viscosity model for UCMH was established by the quantitative characterization of the energy consumption and crude oil physical properties (i.e., saturate content, aromatic content, surfactant content, acid value, and crude oil viscosity). In light of the statistical results of 336 groups of validation experimental data from four crude oils, the average relative deviation between the apparent viscosity calculated by the new model and the measured apparent viscosity of UCMH was 5.3%, which is considerably better than the traditional emulsion viscosity models, that is, the Einstein, Vand, Taylor, and Richardson models.
NSTL
Elsevier