Study On Thixotropic Properties Of Gelled Crude Oil Influenced By Methane Basede On Magneticlly Coupled Rheometer

The production and transportation of crude oil will inevitably face the precipitation and dissolution of light components.Therefore,the influence of light components on the rheological properties of waxy crude oil cannot be ignored.Rheology testing is the main means to obtain the thixotropic characteristics of saturated dissolved gas crude oil.Based on the theory of thixotropy of waxy crude oil and the thixotropic test of gelled crude oil,the shear mechanical response characteristics of saturated dissolved gas crude oil are systematically studied.The main research contents and results are as follows:Considering the motor inertia,internal and external magnetic loop inertia,rotor inertia and jewel bearing friction loss of the magnetic coupling type rotational rheometer test system,a physical model of the transmission process of the magnetic coupling rotary rheometer test system is established,which consists of the external magnetic ring torque balance formula,the internal magnetic ring torque balance formula and the internal magnetic ring magnetic force coupling formula.Taking the HAAKE-MARS60 high-pressure rheometer as an example,the parameters of the inner magnetic ring are calculated by the chasing method based on the physical parameters of the outer magnetic ring measured by the rheometer,and the true wall stress of the test fluid in the initial unsteady flow phase is obtained,which solves the problem of"distortion"of rheological test results under high-pressure rheometer test system.The measurement parameters of Newtonian fluid under constant shear rate loading are modified.The corrected viscosity value is closer to the true value,which proves the correctness of the model established in this paper.It also provides a basis for the further study of the thixotropic characteristics of Shengli crude oil.The thixotropic test of gelled crude oil under different experimental conditions was carried out by high pressure rheometer.The shear mechanical response characteristics of saturated dissolved gas gelled crude oil were studied,and the influence of light components on the shear mechanical response characteristics of gelled crude oil was explored.In this paper,the saturated dissolved gas pressure is converted into the result of static pressure and gas dissolution.The shear mechanical response characteristics of Shengli crude oil under static pressure and saturated dissolved gas pressure are compared,it is found that the influence of CH₄ dissolution on the structure under the same test conditions is More than the influence of static pressure,although the static pressure will make the internal structure of crude oil more dense,the molecular spacing of wax crystals will decrease,the interaction force will increase,the internal microstructure of crude oil will be promoted,and the proportion of complex structure will increase,making structural strength of the crude oil increasing.However,the dissolution of CH₄ causes the crude oil to swell,and the distance between the wax crystals increases.CH₄ is continuously adsorbed on the surface of the wax crystal,which makes the wax crystals aggregate less,inhibits the precipitation of wax molecules,and hinders the formation of the wax crystal network structure,the gelation structure of crude oil was weakened.With the increase of saturated pressure,the effect of CH₄ solubility on the structure is greater than that of static pressure.Based on the above theoretical and experimental data analysis,the formulas for predicting shear mechanical response parameters such as yield stress,apparent viscosity,equilibrium time and critical strain of gelled crude oil under different static pressure,CH₄ solubility,temperature and shear rate test conditions and prediction formula of viscoelastic-thixotropic curve of structures were established.