High-concentration polymer flooding (HCPF) is an enhanced-oil-recovery (EOR) method that has been used since conventional polymer flooding was applied in the main reservoirs of the Daqing oil field because its higher viscoelasticity can improve the oil-displacement efficiency. However, as a result of more produced hydrolyzed polyacrylamide, the oil/water mixture is emulsified easily and separated with more difficulty. In this work, a case history of dehydration technology for HCPF production in the Daqing oil field is reviewed, and a laboratory investigation to assess the emulsification behaviors of HCPF-produced emulsions is conducted. Besides the dehydration-mechanism description of a high-voltage pulsed electrical field, electrostatic demulsification performance for produced liquid from HCPF production is improved, and the operation parameters are optimized. Recent actual acceptance of the optimization recommendations is presented, and the field-application results are also discussed. The results indicate that dehydration technology for the Daqing oil field has been innovated with the industrialization of the EOR process. Traditional methods of gravity or centrifugal settling are replaced; this upgraded freewater knockout has the functions of adsorption, wetting, collision, and coalescence, and oil pretreating for HCPF production. Because it is dominated by periodic vibration as its main mechanism, the pulsed-direct-current (DC) electrostatic demulsification technique has some advantages in overcoming the obstacles encountered by regular types of electrical-field dehydration processes at strong emulsification stability. Compared with previous dehydration processes having complex alternating-current (AC)/DC electrical fields, the process with a pulsed-DC electrical field shows a unique advantage in terms of emulsified water-separation efficiency, energy conservation, environmental protection, lower labor intensity, and more-stable operation, and the dehydration performance meets the oil-treating standards. As the surface-matching technology of EOR, this improvement in dehydration technology is significant for promoting the construction of an HCPF demonstration project and accelerating petroleum development and production efficiently.
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Zhihua Wang and Xinyu Lin, Northeast Petroleum University; Tianyu Yu, University of Western Australia; Zhiwei Hu, Daqing Oilfield Company Limited; and Mengmeng Xu and Hongtao Yu, Northeast Petroleum University