Rheology Research Of Crude Oil Around The Freezing Point

Rheological property of the waxy crude oil around its freezing point is needed to be comprehensively measured for waxy crude oil safe transportation. In this thesis, I have researched the gelled property of Qinghai crude oil and its emulsion, using RS75 Rheometer at the mode of oscillatory measurement at small amplitude(f=1Hz,γ=0.0015). Furthermore, I studied its yielding property by increasing the shearing stress continuously at constant temperatures. The exterior factors such as thermal history and shearing history can greatly affect the waxy crude oil's interior structures, especially its wax crystal network. Therefore, after undergoing different histories, the crude oil showed different gelled property and yielding property. Because of the existence of small droplets, the emulsion's gelled property is different from the waxy crude oil.The waxy crude oil's gel can be divided into two parts, which are cooling gel and isothermal thixotropy gel. The latter can differentiate the gel by exerting pre-shear or not. Cooling gel is a kind of gel structure which is flocculated by irregular wax crystals, which is caused by the lower crude oil temperature, the wax crystal concentration increase, the enhanced attraction and size increase. The regularity of cooling gel structure is almost identical after the crude oil undergoing different histories. Isothermal thixotropy gel is a kind of flocculated structure that is the result of Non-Newton's wax crystal moving and rearranging, which are forced by the limited Van Der Waals'attraction under the condition of static isothermal and stated concentration of wax crystal precipitate. Different history can affect this gel structure greatly.This thesis researched the effects of thermal history, shearing history and high-speed shearing on the two kinds of isothermal gel property about Qinghai wax crude oil. Based on this, two kinds of isothemal gel properties of emulsion are also studied under the corresponding condition(A condition which can make the emulsion more stable and well-distributed is chosen), and the experimental results are also analyzed. The results show that these exterior factors can make different effects on these two kinds of isothermal gel structures, and their effects on the emulsion are different from the crude oil. Some of which are absolutely opposite. Especially for the high-speed shearing, it is very complicated, so one criterion does not fit for both the crude oil and emulsion.