| With the progress of experiment and pilot test and field application of chemical flood, we have met many theoretical and practical problems that need prompt solution. Some of them are as follows: If polymer flood can improve displacement efficiency; how to choose the molecular weight of polymer; how to further increase the molecular weight of partially hydrolyzed polyacrylamide(HPAM); how to complete and develop the characterization of rheological behavior and seepage flow character of I-IPAM solution in order to direct the project optimization and performance prediction of polymer flood.In this paper modem molecular simulation technology and quantum chemical calculation method are adopted to determine the material for synthesizing difunctional peroxide initiator. Through the selection of catalyst, initiator 2,5-dimelhyl-hexane-2,5-dihydroperoxide(DIOOH) is synthesized. This synthetic method changes one material from the original 60-70% H202 which needs to be prepared specially to the commercial 30% H202 which is easy to access, with good repeatability and good potential of commercial production.By adopting oxidation-reduction initiating system composed of difunctional peroxide initiator DIQOH, a kind of polyacrylamide(PAM) with ultra-high molecular weight of 25-30 million and good solubility can be obtained. Comparing with single functional oxidation-reduction initiating system, this initiating system has the characteristics of lower usage, more stable and good repeatability in polymerization. Hydrolysis conditions has been optimized, under optimized condition, PAM with super-high molecular weight is hydrolyzed and NPAM is obtained at expected hydrolysis degree with good solubility and intrinsic viscosity over 30g/dl. This kind of synthetic HPAM is much better than other kind of HPAM in thickening ability and increase oil recovery. And the usage of the polymer can be 40% lower in achieving same improved recovery efficiency.The research on displacement mechanism of HPAM from microscopic to macroscopic verifies that HPAM can improve displacement efficiency through its viscoelasticity and changing the wettability of rocks, thus revises the traditional view that polymer flood can not improve recovery efficiency.In this paper the selection method of polymer molecular weight is put forward and set up for the first time by using polymers having different 7molecular weight and cores with different pore size taken from reservoirs in Daqing Oil Field. Many core floods have been performed. The behaviors of both solution and propagation in porous media, such as viscosity of polymer solution, resistance and residual resistance factor, incremental oil recovery and mechanical degradation, have been studied as a factor of molecular weight. The injectivity has been studied as a mutual factor of pore size of core and molecular weight. The results show that all those parameters in terms of viscosity of polymer solution, resistance and residual resistance factor, incremental oil recovery and mechanical degradation increase as molecular weight increases. The remaining viscosity of the polymer solution is higher though the polymer with higher molecular weight has bigger viscosity loss caused by mechanical degradation under conditions of Daqing Oil Field. The results also show that no plugging occur in a core when the mid-value of pore radius is over 5 times of the gyration-radius of molecules in the polymer solution. Field results of polymer flooding performed in similar geological and operational conditions indicate that the polymer flooding with higher molecular weight has better response and the polymer produced from producers has higher remaining viscosity and molecular weight than those with lower molecular weight.Systematic research is also conducted to analyze permeability reduction(Rk) in polymer flooding as a function of HPAM molecular weight, hydrolysis degree(HD), polymer concentration(C~) and salinity(C5), core type, permeability(K4, temperature (T) and flow rate (V). Mathematical model is s...
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