Viscoelastic properties of waxy crude oil

Abstract

Waxy crude oil usually represents viscoelastic property when temperature is below its wax appearance temperature (WAT). The more the waxy crystals precipitated in crude oil, the stronger the structure and the viscoelasticity formed by waxy crystals. As the structure of waxy crystals relates to viscoelasticity that can be described by the storage modulus G′ and loss modulus G″, the small amplitude oscillation (SAOS) method was introduced to determine these moduli. This shows that the temperature at which storage modulus equals loss modulus is just the pour point of waxy crude oil. The structure intensity or yield stress of waxy crude oil can be determined by τ′_y=G′/50. In this way wall slid can be avoided. It also shows that 60 min. will at least be taken for waxy crystals to build up the structure completely in oil. It means that waxy crude oil sample should be stayed still at test temperature in the sensor of rheometer more than 60 min. before the viscoelasticity or yield stress of waxy crude is tested. That is structure building time.

Keywords

waxy crude / viscoelasticity / structure strength / small amplitude oscillation(SAOS)

References

[1] CawkwellM. G., CharlesM. E.. Characteristics of Canadian Arctic thixotropic gelled crude oil utilizing an eight-parameter model[J]. J Pipelines, 1989, 7: 251-264