Viscoelasticity of gelled waxy crude oil

Abstract

When the temperature of waxy crude oil is below the wax precipitation temperature, wax will precipitate out from oil solution. On further cooling, more and more wax crystals separate out and interlock to form a network that entraps liquid oil into its structure, resulting in gelation of the crude oil. The gelation extent and strength can be expressed with viscoelastic parameters. A controlled-stress rheometer RS150H was used to measure the viscoelastic parameters of Daqing crude under different history conditions by oscillatory shear experiment. The results indicate that the storage modulus and loss modulus increase in an exponential relation as the measuremental temperature is decreased. There exists a worst heating temperature for the rheological behavior. The strength of wax crystal structure and gelation temperature increase with decreasing cooling rate. Under the same shear temperature, the strength of wax crystal structure decreases rapidly and finally tends to a steady state as the energy dissipation due to viscous flow is decreased. Under the same energy dissipation due to viscous flow, the closer the shear temperature is to the measuring temperature, the lower the storage modulus, loss modulus and gelation temperature will emerge. When the shear temperature is close to or higher than abnormal point, the viscoelastic parameters vary little. The recovery of wax crystal structure after shear action exhibits an irreversible property.

Keywords

waxy crude / viscoelastic property / oscillatory shear

References

[1] ZhangJ.-jun.. Technologies for pipeling high-pour-point and viscous crudes and their development[J]. Engineering Science, 2002, 4(6): 71-76

[2] WuQ.-m., RuanJ.-m., HuangB.-y., et al.. Rheological behavior of fumed silica suspension in polyethylene glycol[J]. Journal of Central South University of Technology, 2006, 13(1): 1-5

[3] YuanX.-g., SongS.-gen.. Wave equation for wave-field reconstruction in viscoelastic media[J]. Journal of Central South University of Technology(Natural Science), 2003, 34(5): 559-561

[4] ChangC., BogerD. V.. The yielding of waxy crude oils[J]. Ind Eng Chem Res, 1998, 37(4): 1551-1559

[5] CAZAUX Q, BARRE L, BRUCY F. Waxy crude cold start: assessment through gel structural properties[R]. SPE49213. 1998: 729–739.

[6] HENAUT, VINCKE O, BRUCY F. Waxy crude oil restart: mechanical properties of gelled oils[R]. SPE56771. 1999: 349–355.

[7] SinghP., FoglerH. S.. Prediction of the wax content of the incipient wax-oil gel in a pipeline: An application of the controlled-stress rheometer[J]. Journal of Rheology, 1999, 43(6): 1437-1459

[8] LuoT.-hu.Rheological Characteristics and Pipeline Transportation of Waxy Crude Oil[M], 1991, Beijing, Petroleum Industry Press

[9] ZhangJ.-jun.Shear effect in pipelining waxy crudes treated with the Pour-Point-Depressant and its simulation[D], 1998, Beijing, China University of Petroleum