Test on wall-adhering behavior of high water-cut waxy crude oil

Abstract

When the unheated gathering and transportation technology is adopted in oil fields at high water cut stage, the phenomenon of congealable oil adhering to the wall often occurs inside the pipeline due to the low transportation temperature, and this may lead to the reduced pipeline flow area, the back pressure rise at the wellhead and the increased energy consumption of gathering and transportation. On the basis of the traditional cold finger device, an experimental device was designed to realize the circulation of test medium. With this device, the effects of oil temperature, oil-wall temperature difference, water cut, shear strength and test time, on the wall-adhering behavior of high water-cut waxy oil-were investigated. The results show that the congealable oil wall-adhering and the multiphase wax deposition are not the same deposition behavior. Serious walladhering occurs when the temperature of oil-water mixture is lower than the initial wall-adhering temperature. The walladhering temperature of high water-cut waxy crude oil is lower than the pour point of pure oil. The higher the water cut is, the lower the initial wall-adhering temperature will be. The effects of oil-wall temperature difference and oil temperature on the wall-adhering behavior are distinguished from temperature intervals. The wall-adhering behavior below the crude pour point is mainly controlled by the oil temperature, while the wall-adhering behavior above the pour point is more affected by the temperature difference. For the unemulsified oil-water mixture, the presence of water phase weakens the wall-adhering behavior. On the contrary, the presence of water phase enhances the wall-adhering behavior. Stirring or pipeline fluid flow mainly exerts shear stripping effect on wall-adhering congealable oil. The thickness of congealable oil adhering to the wall will definitely reach the limit value with time, instead of increasing indefinitely.

Keywords

• high water cut
• waxy crude oil
• congealable oil adhering to the wall
• cold finger
• experimental study