Abstract
Thixotropic properties are one of the low temperature rheology behaviors of gelled waxy crudes. In order to study the thixotropic behavior of gelled waxy crudes oil under cyclic loading of linear increasing and decreasing of shear rate, three different types of waxy crude oil were studied ex-perimentally by using MARSIII rheometer. It is found that hysteresis loop area could represent strength of thixotropic properties under that loading. With increasing of the rate of share rate sweep, the area of second hysteresis loop is much smaller than first one and began a slow decline from the third hysteresis loop. Areas of each hysteresis loops were decreased with increasing temperature, but it was different in decline rate—the lower the temperature, the greater the rate of decline. The maximum rate of decrease is the first hysteresis loop with exponential decline, and remaining hysteresis hoops approximately decrease linearly. In addition, based on the experi-mental results an empirical correlation is developed to describe the relationship of hysteresis loop area and rate of share rate sweep.
Highlights
Thixotropy of waxy crude is an important but complex issue in crude oil rheology study
1) For gelled waxy crudes oil, the thixotropic behavior of hysteresis loop which is formed under cyclic loading of linear increasing and decreasing shear rate is studied
Hysteresis loop area could represent the strength of thixotropic properties
Summary
Thixotropy of waxy crude is an important but complex issue in crude oil rheology study. Most of the existing mathematical models proposed are under studying shearing stress relaxation of thixotropic process in a constant shear rate [6] [7] in which Huang put forward mathematical model for blood thixotropy at loading conditions that shear rate changes continuously [8]. It has a lot of studies in waxy crude thixotropy, there have not been reports describing change properties of thixotropic hysteresis loop in the loading conditions whose shear rate is continuously variable. Experiments study the waxy crude oil change properties of thixotropic hysteresis loop area, and result in an empirical correlation to describe the relationship of hysteresis loop area and rate of share rate sweep on basis
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