Study On Structural Destroying Experiment Of Gelled Crude Oil Based On Large Amplitude Oscillatory Shear(LAOS)

In pipeline restart process,structural destroying characteristic of gelled crude oil is of great significance to the safe operation of pipeline.At present,the study on structural destroying characteristic of gelled crude oil is limited to the rotary shearing experiment,and rarely refer to large amplitude dynamic oscillatory shear mode.Therefore,through carrying out large amplitude dynamic oscillatory shear experiment on the gelled crude oil,we can study the structural destroying characteristic of gelled crude oil more comprehensively.In this article,through carrying out rotary shearing and large amplitude dynamic oscillatory shearing experiment on gelled crude oil using the rheometer,we study the measurement criterion of structural destroying degree of gelled crude oil and structural destroying characteristic of gelled crude oil in large amplitude dynamic oscillatory shearing experiment.The test results showed that,in large amplitude dynamic oscillatory shearing experiment,“Shear stress” or “Energy dissipation rate” is not one-to-one correspondence to dynamic state of equilibrium,so “Shear stress” or “Energy dissipation rate” can not be the measurement criterion of structural destroying degree of gelled crude oil;The size of “Shear rate” decides the structural strength of gelled crude oil in a state of equilibrium,and the“Shear rate” is one-to-one correspondence to dynamic state of equilibrium,therefore the“Shear rate” can be used as a measurement criterion of structural destroying degree of gelled crude oil,providing a basis for selecting or establishing the structural failure rate equation.Firstly,we study the changing characteristic of the Lissajous curve of gelled crude oil along with the shearing time in large amplitude oscillatory shearing experiment,the test results showed that,the Lissajous curve of gelled crude oil change from irregular oval to similar parallelogram even thin rod,and continually deflect to strain axis along with the increasing of the shearing time.Secondly,quantitatively analyze the changing of dissipatedenergy of gelled crude oil along with shearing time in large amplitude oscillatory shearing experiment,proposing a formula that can describe the changing of dissipated energy along with shearing time greatful.Then,evaluating two nonlinear elastic modulus-minimum strain modulus’ MG and maximum strain modulus’LG in large amplitude oscillatory shearing experiment,the test results showed that,the minimum strain modulus’ MG is not suitable for quantitatively analysis to the visco-elastic properties of gelled crude oil,but the maximum strain modulus’ LG describing the visco-elastic properties of the gelled crude oil is relatively reasonable to a certain extent,but there are some limitations.Finally,choosing reasonable structural failure rate equation,we propose an equation that can quantitatively describe the destroying process of gelled crude oil in large amplitude oscillatory shear,all the parameters in the equation having clear physical meaning,and the model is verified through the experiment,having higher fitting precision.