Study On The Initial Structural Destruction Properties Of The Gelled Crude Oil Pipeline Under Constant Pressure Startup

By virtue of laboratory experimental loop, some research has been done on thestart-up destructive properties of gelled crude oil under the restart method ofconstant pressure.The basic physical properties of Chad and Sultan crude oil have been measuredon the coaxial cylinder rheometer. The dynamic viscosity-temperature curves of thetwo crude oils have been obtained through the Model Loop-line Test Apparatus(MLTA).Studies on the transmission, distribution and attenuation law of start-uppressure along pipeline are carried out on the MLTA. During the constant pressurerestart process, the transmit speed of the pressure is lower than the speed of thepressure wave and the transmit speed of the pressure becomes smaller when thedistance of the pressure transmission extends. We analyze the influence of differentfactors on the transmit speed of the pressure, such as start-up temperature, start-uppressure, shut-down time and static temperature drops. The changing laws of thestart-up wave speed are also analyzed under the restart method of constant pressure,the start-up wave speed is lower than the pressure transmission speed at the samecondition. The influence of different factors on the start-up wave speed is similar tothe pressure transmission speed. We also analyze the attenuation properties ofstart-up pressure, and we conclude that the attenuation coefficient of gelled crude oilis not influenced by the start-up pressure but have a linear increase relation with thedistance of the pressure transmission.Studies on the yield stress and start-up energy which were the parameters to weigh the strength of the gelled structure have been carried on the MLTA. The yieldstress is a conditional parameter; it is influenced by the start-up pressure. The yieldstress used to weigh the strength of the gelled structure has limitations. For thegelled crude oil which has a specific strength, the start-up energy is a constant value,and the value is not changed at different start-up pressures. Compared with the yieldstress, the start-up energy can evaluate the strength of gelled crude oil more exactly.Special experiments have been done to research the subatmospheric pressure ofthe pipeline during the shut-down process. The phenomenon of the subatmosphericpressure has been elaborated, and the changes of subatmospheric pressure underdifferent shut-down temperatures have been researched. When the shut-downtemperature is55℃,45℃or40℃, there is only a slight pressure drop, and no thesubatmospheric pressure phenomenon. When the shut-down temperature is34℃,30℃, or26℃(the temperature around the pour point), the pressure of the wholepipeline drops to the subatmospheric degree quickly. And we conclude that thetemperature is lower, the drop speed is bigger. We analyze the influences of thesubatmospheric pressure on the calculative yield stress. Because of the nonuniformsubatmospheric pressure, the calculative yield stress will be relatively small. So thepressure data should be zero cleared, when we deal with the experimental data.