Study On The Structural Destructing Charateristic And Constitutive Model Of Gelled Crude Oil

Waxy crude oil with a gelled structure under low temperature, whose study on responsecharacteristics under different loading modes are important components of crude oil rheologymeasurement, and this article study on response characteristics regularity and correlation oflow temperature gelled crude oil under various load systematically. Main content andconclusions of the study are as follows:Based on constant cutting speed starting experiments of Sudan gelled crude oil at lowtemperature, combining application of statistics and continuum damage theory, establishdamage rheological mode of describing Sudan gelled crude oil initial destroying process, andanalyse the physical meaning and variation regularity of the parameters in the model;Combining experimental results showing the definition of damage variable, studying on theevolution process of damage variable, and comparing with the damage variable calculatedvalues resulting from damage rheological models, analysing the causes of the deviation,caming to the conclusions that the given definition applies to low cutting speed, and regardthe damage variable as a characteristic parameter measuring gelled crude oil starts yielding.Chad and DaQing gelled crude oil were scanned in steady and dynamic frequency at lowtemperature，it turned out that absolute complex modulus grow with increasing scanningfrequency at double logarithmic coordinate system, and a function was presented.Reversely,absolute complex viscosity reduces with increasing scanning frequency the same assteady-state apparent viscosity; the viscosity difference between the two experiment typesreduces with increasing scanning frequency and temperature, and the curves at differenttemperature show to be parallel lines at double logarithmic coordinate system.According tothe result, an equation related to absolute complex viscosity and apparent viscosity wasestablished, in addition, steady-state nonlinear measures were integrated with dynamicviscoelastic measures to establish an formula related to dynamic absolute complex modulusand steady shear stress.Experimental study on cyclic strain loading of Daqing gelled crude oil under differentconditions show that stress response cycle is shorter than the applied strain cycle and stressovershoot phenomenon appears along with the action of high strain amplitude. After data processing, stress response stress-strain curve changes—rod–spindle-oval-parallelogram–rectangle—with the strain amplitude increases. With strain amplitude growth, temperatureincrease and action cycle extension, the curve is deflected to the strain axis and additionalpeak point appears when the stain amplitude is large. Dissipated energy denstiy of gelledcrude oil is defined according to the experimental data. The results show that dissipatedenergy denstiy has empirical relationship with strain amplitude and experimental temperature.Dissipated energy denstiy increases with strain amplitude growth, decreases linearly withtemperature increase and changes small in different cycles. Dimensionless to the stress-straincurve shows that the curve is symmetrical about the origin and doesn’t deflect withtemperature change and has a characteristic line. When strain amplitude is applied, thedimensionless dissipation energy in different temperatures slightly decreases with temperatureincrease.The strain response strain-stress curves obtained by the experiment showed theseconclusions.First, with the increase of cycle-index，the curve expanded continuously. Second,as the stress amplitude ingcreased, the shape experienced spindle,oval and football-shapedcycle in turn.Third, with the increease of the temperature and the action circle,the strain axisshowed deflection.According to the experimental data, with the increase of cycle times,stressamplitude, temperature and action circle,the dissipated energy denstiy calculated by integralincreased and had the functional relationship between the stress amplitude.By analyzing thestrain response of the dimensionless strain-stress curve,the conclusions were as follow:First,under the small stress amplitude,the curve appeared to be the oval that the ratio betweenthe macroaxis and brachyaxis was relatively large, and was symmetrical about a straightline.Second,as the stress amplitude increase,the curve appeared to be clockwise deflection,theshape tended to be football-shaped,and the tangent point with dimensionless strain axismoved along the positive direction of strain axis.Third,when the temperature was relativelylow,nondimensionalized strain-stress curves almost coincided in different temperature,but inhigh temperature,the curve appeared to be an obvious inflexion,which corresponded to thecritical temperature of the strength of waxy crude oil gelled structure.