Rheological behavior and viscosity reduction of heavy crude oil and its blends from the Sui-zhong oilfield in China

This paper presents an experimental study on the rheological behavior and viscosity reduction of heavy crude oil and its blends to improve the pipeline transportation by using a Haake RS6000 rheometer and a lab scale flow loop. The apparent viscosity, thixotropic behavior, yield stress and viscoelastic properties were investigated. The results of rheological measurements indicated that with the increase in the diesel volumetric concentration, the viscous modulus and thixotropic behavior of the mixture decreased remarkably; on the contrary, the elastic modulus of heavy crude oil was found to increase slightly. When the start-up rates during the pipe flow were constant, the yield stress decreased exponentially with the increase in temperature. A comparison between rheological measurements and pipe flow data showed that the yield stress measured by the rheometer could be used to predict the start-up yield stress during pipe flow through linear interpolation. In pipeline flow, the pressure drop was reduced greatly by both heating and dilution with lighter crudes because the viscosity of the heavy crude oil decreased significantly. Drag reduction due to gas injection only occurred at low temperatures or large superficial oil velocities. Moreover, a new viscosity model of heavy crude oil was developed based on the viscosity at 50 degrees C to predict the viscosity of heavy crude oil from several oil fields in China. The results reveal that the developed model provided good predictions. Considering that the data contained a wide range of viscosity values, the model suggested in this work is acceptable for practical applications in industry.