Study On The Sticking Wall Mechanism Of High Water-cut Heavy Oil

With oil fields’ exploration and development entering middle and later stages,water flooding for enhancing oil recovery has become an easy effective and environmentally friendly method.The water-cut of crude oil –water system can be as high as 70%.During this stage,flowing characteristics of crude oil-water mixtures are significantly different with that of single oil phase.Compared with the initial stage,the viscosity of oil-water mixture is reduced substantially.And when the temperature of the fluid is low,oil particles can stick on the pipe’s inner wall.Hence,a series of engineering problems occur,for instance,the decrease of effective flowing area of the pipeline,aggravation of oil’s wastage,wellhead back pressure is too high and so on.In order to study the mechanism of crude oil’s sticking wall in crude oil-water two-phase system during high water-cut period,taking two basically non-waxy heavy oils as experimental examples,firstly the emulsifying property of two-phase system was determined by microscopic observation,and rheological properties were studied by the stirring method.Then the cold finger device with stirring and temperature-controlling was adopted to stimulate oil sticking wall process.Inspired by the wax deposition experimental method,five external factors including water-cut,hot water bath temperature,temperature difference,stirring speed and duration had been explored to investigate the sticking wall law.It turned out that bulk temperature in the cold finger device was the main factor that obviously changed the heavy oil’s viscosity in two-phase,the lower this temperature,the larger the viscosity of the oil phase in the two phases was,the more likely it was that the oil phase sticked on the cold finger wall.Taking Venezuela oil as an example,the sticking wall thickness of high water-cut two-phase system was between 0.19-0.59 mm while the single heavy oil’s sticking wall thickness is between 0.18-0.52 mm at the same experimental settings.So the difference was pretty minor.Accordingly,when simulating the temperature profile in the cold finger device with ANSYS software,we could use the result of single oil phase to replace the two-phase system.When the temperature of the hot water bath,the cold finger wall temperature and the stirring speed of the mixing propeller were prescribed respectively,the bulk temperature inside the cold finger device could be simulated to predict the viscosity of the oil phase.Further analysis showed that the change of heavy oil’s viscosity was the internal factor that affected the sticking wall thickness.According to the theory of adhesive wetting,using the contact angle as the characterization parameter,the adhesion characteristics of the heavy oils under different temperature and different base materials were investigated microscopically.The experiment found that,at the low temperature of 20℃,glass was preferentially wetted by oil phase while at higher temperature,other materials such as 304 stainless steel and copper were preferentially wetted by water phase.And the wetting of the aqueous phase by the glass changes from moderate wetting to strong wetting with increasing temperature.