Effect Of Initial Cooling Temperature On Waxy Crude Oil Rheological Properties And Wax Crystals Dynamic Behaviors

It is common for waxy crude oil to appear complex rheological behaviors by shear and thermal history,which makes it prone to gelation accidents in transportation and storage.Therefore,it is of great significance to study the rheological properties of waxy crude oil under action of complex historical factors,and it is also the basis of heat treatment transportation of waxy crude oil in engineering.At present,it is generally recognized in related fields that the microscopic kinetic behavior and interactions of internal particles play a direct and decisive role in the macroscopic rheological properties of multiphase systems.However,in the aspect of rheological properties of waxy crude oil,the study on the kinetic evolution and dynamic behavior of wax crystal microstructure under shear and other external forces is still a blank.Therefore,based on the methods of rheological measurement and innovatively constructed rheo-polarized microscopy in-situ sync measurement,this paper studied the influence by initial cooling temperature on rheological properties and wax crystals microscopic dynamic behaviors of waxy crude oil under coupling effect of cooling rate and shearing.Also,adopting a new perspective of microscopic dynamic behavior analysis of wax crystals,this paper aimed to dissect micromechanism in complex rheological properties of waxy crude oil under synergistic action of multiple factors.The main research contents are as follows:Above all,based on rheo-polarized microscopy in-situ sync measurement and improved multi-angle light sources,it is first realized in in-situ sync measurement of microscopic observation and rheological properties for dynamic evolution and dynamic behaviors of wax crystals micro morphology under shearing condition.Thus,the connection between the microscopic dynamic behavior of wax crystal and the macroscopic rheological properties of waxy crude oil was constructed.On this basis,this paper established the basic control equations of wax crystals dynamic behaviors,clarified 6 different stages for wax crystal dynamics behavior and microstructures in cooling process,illustrated the dominant force at each stage,and proved that the wax crystal space distribution,the density of space and fringe spacing plays a decisive role.The shear thinning and gelation structure behavior of non-Newtonian waxy crude oil during static and dynamic cooling were systematically studied by rheological measurement technique.It is found that there are different initial cooling temperature ranges which make rheological properties of waxy crude oil deteriorate,improve and change steadily under static cooling conditions,and the essential differences of internal structures of waxy crude oil in different ranges were clarified.Furthermore,the rheological properties of waxy crude oil and response of gelation structure behavior to shear action at different initial cooling temperatures were deeply analyzed,and influence rule and reason of initial cooling temperature on rheological properties of waxy crude oil were clarified.Finally,the mechanism of effect of initial cooling temperatures on rheological properties of waxy crude oil was comprehensively analyzed from three aspects: the microscopic morphology of wax crystals during cooling and gelation process,the evolution of wax crystals' kinetic behavior and dynamic behavior under constant temperature shear.Based on the micro-morphology,spatial distribution,kinetic behavior and interaction forces,the essential differences of wax crystals formed at different initial cooling temperatures were classified into two different types,and the influence mechanism on rheological properties of waxy crude oil was further explained.In addition,based on the dynamic behavior of wax crystal under constant temperature shear,the microscopic mechanism of shear thinning of waxy crude oil was analyzed.The different shear thinning caused by different flocculation tendency and structural properties of wax crystals at different initial cooling temperatures were analyzed,and the influence mechanism of initial cooling temperature on rheological properties of waxy crude oil was further demonstrated.In general,the research of this paper not only help to deepen the understanding of rheological response and mechanism of waxy crude oil in response to the changes of complex rheological properties and thermal history,but also provide new ideas and technical means for study of complex flow and heat transfer law of waxy crude oil.