The alumina adsorption, acidity, rheology, image analysis and other related methods are used to characterize the produced fluid in KD18 viscous oil block in Shengli Oilfield. The fluid generally contains 68–75% water cut and about 50–60% bound water. The apparent viscosities of the water-in-oil (W/O) emulsions, varying from 7000mPa.s to 12000mPa.s at 50 °C and the shear rate of 51s−1, are 4–6 times higher than those of the corresponding dehydrated oil. The fluid is transported by a 259-mm-ID, 23.8-km-length pipeline with 2 intermediate heat-pump stations because of its high viscosity, which is followed by high energy and associated gas consumptions. A viscosity reduction method of the W/O emulsion to be inverted into oil-in-water or other composite emulsions by directly adding a sort of viscosity reducer VRKD18 is given in this paper. Composed of two types of nonionic surfactants, VRKD18 is developed by a series of preparations. VRKD18 reduces the apparent viscosity of the W/O emulsion to less than 100 mPa.s at 50 °C and 51 s−1, being more than 98% of apparent viscosity reduction. The reason for this significant viscosity reduction is that VRKD18 changes the outer and inner phase structures of the W/O emulsion, the modes of inner friction, and the drop-drop interaction. A field test for the fluid treated with VRKD18 is performed through the production pipeline. VRKD18 solution is only injected into the fluid by a metering pump at the head heat and pump station, while the other fluids along the pipeline which they are pumped into is not treated. In this article, the inlet temperature of the pipeline is about 50–57°C. The inlet and outlet flow rates are approximately 1200m3/d and 2600m3/d respectively. When the concentration of VRKD18 in the fluid is 300mg/kg, the friction loss along the whole pipeline will be reduced from 1.397MPa to 0.566MPa, i.e. 59.5% of drag reduction. Based on our observation and numerical simulation, such drag reduction is due to the apparent viscosity reduction of the transporting fluid, the wettability improvement on the pipeline inner wall and partial isolation of the viscous oil by the gathered gas at the pipeline top.

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