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Polymer flooding is drawing lots of attention because of the technical maturity in some reservoirs. The first commercial polymer flooding in China was performed in the Daqing oilfield and is one of the largest applications in the world. Some laboratory tests from Daqing researchers in China showed that the viscoelasticity of high molecular weight polymers plays a significant role in increasing displacement efficiency. Hence, encouraged by the conventional field applications and new findings on the viscoelasticity effect of polymers on residual oil saturation (ROS), some high-concentration high-molecular-weight (HCHMW) polymer-flooding field tests have been conducted. Although some field tests were well-documented, subsequent progress was seldom reported. It was recently reported that HCHMW has a limited application in Daqing, which does not agree with observations from laboratory core flooding and early field tests. However, the cause of this discrepancy is unclear. Thus, a systematic summary of polymer-flooding mechanisms and field tests in China is necessary. This paper explained why HCHMW is not widely used when considering new understandings of polymer-flooding mechanisms. Different opinions on the viscoelasticity effect of polymers on ROS reduction were critically reviewed. Other mechanisms of polymer flooding, such as wettability change and gravity stability effect, were discussed with regard to widely reported laboratory tests, which were explained in terms of the viscoelasticity effects of polymers on ROS. Recent findings from Chinese field tests were also summarized. Salt-resistance polymers (SRPs) with good economic performance using produced water to prepare polymer solutions were very economically and environmentally promising. Notable progress in SRP flooding and new amphiphilic polymer field tests in China were summarized, and lessons learned were given. Formation blockage, represented by high injection pressure and produced productivity ability, was reported in several oil fields due to misunderstanding of polymers' injectivity. Although the influence of viscoelastic polymers on reservoir conditions is unknown, the injection of very viscous polymers to displace medium-to-high viscosity oils is not recommended. This is especially important for old wells that could cause damage. This paper clarified misleading notions on polymer-flooding implementations based on theory and practices in China. [ABSTRACT FROM AUTHOR]

Abstract: To solve the severe PCP scaling during the ASP flooding in the Daqing Oilfield, PCP anti-scaling and lifting techniques are studied. This paper comprehensively analyzed the reasons and principles of PCP scaling during the ASP flooding, and the common failure modes in PCP wells by scaling. The fit accuracy between PCP''s rotor and stator dropping, frictional behavior irregular changing and severe abrading by scaling are the main reasons for the increase of the PCP''s failures. Based on these, a comprehensive anti-scaling lift technique for PCP wells was proposed including PCP rotor/stator wring optimization, instrument material surface modification, and chemical clear/anti-scaling technique. By the end of 2010, the comprehensive methodology has been applied in 216 PCP producers 425 times, the average running lives of PCP producers in the ASP flooding were improved from less than 100 days to 298 days after applying the above PCP anti-scaling methodology, the longest one is 1 370 days. [Copyright &y& Elsevier]

Daqing oil field is one of the earliest to develop displacement technology by polyacrylamide (HPAM). One tonne of polymer can increase 1(30 to 120 tonnes of oil: the recovery increases from 40% (OOIP) to 50% (OOIP). In view of the geological and physicochemical characteristics, a series of technologies have been developed, such as polymer-flooding mechanism, productivity forecasting, proposal optimization, domestic excellent-quality polymer production, surface injection, downhole separate-layer injection, and separate-layer testing during injection. The oil field is characterized as a heterogeneous multilayer sandstone reservoir. During polymer flooding, separate-layer injection technology is also needed to mitigate the interlayer differences, enhance oil recovery, and improve the whole development effect. After polymer flooding in main oil layers, polymer flooding in Daqing oil field turned to lower-permeability layers. To obtain a better displacement effect, the injected-polymer molecular weight is usually determined according to the injectivity of high-permeability layers. However, if polymer solution with the same molecular weight is injected in each layer, it will cause blockage in low-permeability layers. In order to solve this problem, a new technology is developed that can control both separate-layer polymer molecular weight and injection rate; the injection profile was improved greatly in later field applications. This paper introduces the development and practice of separate-layer polymer-injection technologies, and presents the principle, string structure, and parameters of eccentric different-molecular-weight polymer-injection technology and its field applications in Daqing oil field. [ABSTRACT FROM AUTHOR]