Isothermal structure development of Qinghai waxy crude oil after static and dynamic cooling

The isothermal structure development of Qinghai waxy crude oil after static and dynamic cooling has been investigated in detail by using a combination of rheological methods and microscopic observation. Particular attention is paid to the influence of test temperature, cooling rate and shear rate during cooling process. It is observed that for both static and dynamic cooled oils, the structure under isothermal condition always becomes stronger with decreasing test temperature or increasing holding time, while the variation of loss angle are different. For static cooled oil, with a decreasing of cooling rate, the structure increases during the whole holding time, while for the dynamic one, the structure increases first and then decreases. Experiments with a range of shear rates has revealed that, at a fixed cooling rate, the isothermal structure development of waxy crude oil is also strongly influenced by the test temperature. At the test temperature higher than the pour point, higher shear rate can result in stronger structure; while at the temperature approaching pour point, the structure decreases first and then increases with increasing shear rate; at relative lower test temperature, the strength of structure decreases with the increase of shear rate.