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1 International Journal of Applied Mechanics and Engineering

1 2003

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Time-dependent rheology of crude oils and effect of wax and asphaltene constituents

El-Gamal I. M., Schnabel R., Anton W.

International Journal of Applied Mechanics and Engineering

2003

Vol. 8, no spec.

25-32

Time-dependent rheological behavior of four Egyptian crude oils was studied below, at and above pour point via rheometric measurements. The obtained hysteresis loops showed thixotropic pseudoplastic character for all crude oils at and below pour point. However, at 10°C above pour point, waxy and intermediate-base crude oils exhibited anti-thixotropic behavior. The thixotropic degree increases with the decrease of temperature. Time-effect at constant shearing showed a slight continuous decrease of viscosity for asphaltic crude oil, while displayed an increase for intermediate-base one. Further increase of wax content led to steep fall decrease of viscosity followed by gradual increase for the other crude oils according to the degradation-reformation competition of paraffin interparticles during shearing. Recovery of structure after shearing revealed a progressive viscosity increase with the increase of holding time periods and that viscosity after recovery exceeded the initial values in many cases. At the corresponding temperatures, high asphaltene constituent induces high viscosity of asphaltic crudes that equals orders of magnitude higher than that of waxy crude oil. Pseudoplasticity of crude oils increases with the decrease of temperature except for asphaltic crude oil and that this increase is correlated with the increase of wax/asphaltene ratio contained in the crude oils.