Thixotropy and its estimation of water-in-waxy crude emulsion gels

• We find that the extent of shear stress decay increases with increasing water cut.
• The models describing the thixotropy of waxy crude can also be used for emulsions.
• A relative shear stress of an emulsion gel is defined.
• A method is developed to estimate the shear stress decays of emulsion gels.

The thixotropic behavior of water-in-waxy crude emulsion gels is important to flow assurance of deep water production systems. In this research, the shear stress decay with time under constant shear rate was studied for three waxy crudes and their W/O emulsion gels. The results show that the emulsion gels become more thixotropic than the crude. A relative shear stress was defined by referring to the definition of the relative viscosity of disperse systems. It is found that the relative shear stress is almost independent of time after sheared for 20 s, and the average relative shear stress increases exponentially with increasing water cut. Accordingly, an empirical method was developed to estimate the shear stress decays of waxy crude emulsion gels with time at constant shear rates. By using this method and with the help of measured thixotropic data of crude oil and emulsions at three different water cuts, the shear stress decays of emulsion gels at arbitrary water cuts can be estimated with encouraging accuracy from the viewpoint of engineering application.