Study On Emulsification, Viscosity Reduction And Demulsification Of Tahe Heavy Oil

With the decrease of conventional crude oil reservoir, heavy crude oil plays a more and more important role in energy sources. The characters of heavy crude oil are high pour point, high viscosity and density, so effective methods are usually adopted to reduce the viscosity of heavy oil for improving the mobility, increasing the transmission efficiency and reducing the energy consumption and cost of transportation, then achieving the goal of safe and economic transportation.The viscosity reduction of a typical Tahe heavy crude oil through O/W emulsification for improving the flow ability was studied in this article. By measuring the viscosity and diversion ratio, the single emulsifier was selected initially, then the different kinds of emulsifiers were compounded, and the selected compounding emulsifier was improved by alcohol and alkali, and then the optimized formulated emulsifier was obtained. The influence of these factors such as oil-water ratio, water content of the heavy oil, emulsifying temperature, emulsifying strength and inorganic salt content on the properties of heavy oil-in-water emulsions stabilized by the formulated surfactant were studied. At the same time, the dynamic stabilities of emulsions under different oil-water ratios and emulsifier concentrations were also studied. Based on the rheological properties of the heavy O/W emulsion, the oil-water ratio, emulsifier concentration and transport temperature which can influence rheology of the O/W emulsion and pressure loss in pipeline were studied by orthogonal experiment, and then several viscosity reduction methods, namely heating, dilution and emulsification, were comparative analyzed. At last, the demulsifier formula was gotten by single demulsifier selecting and compounding, and the effect of these demulsifiers on the water separation was also studied.The experimental results were shown as follows:the formulated surfactant of TX-100and SDBS whose optimal mass ratio was4:1had a good compatibility with the Tahe heavy crude oil. The emulsifying effect could be dramatically improved by adding NaOH. When the emulsion was prepared by the compounded emulsifier(0.75%) and NaOH(0.1%), the average droplet diameter was6.5μm, the diversion ratio was6.3%after standing for6hours, and the viscosity reduction rate was more than99%. So the compounded emulsifier mass concentration at0.75%and alkali (NaOH) mass concentrations in the range of0.08%to0.4%was identified as the emulsifier formula. In each single factor, the oil-water ratio should be controlled from6:4to8:2; the water content of the heavy crude oil should be lower than30%; the emulsifying temperature should be higher than20℃; the emulsifying strength should be lower than1500rpm. For univalent inorganic salts, the magnitude of the effect of cationic ions was K+>Na+>Li+with the increase of hydrated radius; and the magnitude of the influence of anionic ions on the water separation rates was Cl->Br->I-because of the Hofmeister order. For divalent cationic ions, the influence of MgCl2on the stability of emulsions was greater than that of CaCl2, and the total amount of monovalent cation salt and that of divalent cationic salt should be less than0.6mol/L and0.05mol/L respectively. For univalent anions, SO42- did’t have obvious effect on this O/W emulsion, but the amount of PO43" should be less than0.033mol/L, or the O/W emulsion would be unstable. After the dynamic stability of O/W emulsion was appraised, furthermore, the oil-water ratio was controlled in the range of6:4-7:3, and the concentration of NaOH in emulsifier was controlled in the range of0.08%～0.1%. The consistency coefficient (K) was determined by oil-water ratio, the power law index (n) was determined by oil-water ratio and emulsifier concentration, and the temperature of pipeline transportation had no influence on the rheology of the emulsion, the pressure drop was effected dramatically by transportation speed of O/W emulsion, the speed should be controlled less than1.5m/s for a pipeline whose inner diameter was700mm, and at the same transportation speed, the experiments group with high pressure drop had a character of high oil-water ratio and high emulsifier concentration. Comparative analysis between heating, dilution and emulsification were indicated that emulsification had an apparent advantage in energy saving and consumption reducing. In13species of demulsifiers, HCl, FeCl3, AICl3and CTAC were afforded good results, mixing HCl with high-molecular polymers for improving the clarity of separated water. At last, when the pH of the solution was equal to7, the cationic polyacrylamide (CPAM) mass concentration was0.03%, the water separation rate was92.77%after1hour at30℃, and the separated water was almost clear.