| As an important method of EOR technology to enhance oil recovery, polymer flooding has widely been applied in our country’s oilfield. When increases oil production, it also bring some serious problems that large amount of wastewater from polymer flooding is much more difficult to treat. Firstly,we research the stability mechanism of the wastewater that lays the theoretical foundation for the development of wastewater treatment chemicals. Then the value of residual polymer is discussed, and method of wastewater treatment is proposed. Finally, wastewater treatment chemicals are developed.In this thesis, the stability mechanism of produced wastewater from polymer flooding was studied systematically through the measurement of oil concentration in water phase, oil-water interfacial force, conductivity, viscosity, median particle size of oil droplets, Zeta potential and so on. Experimental results show that HPAM increases the viscosity of wastewater and decreases the Zeta potential values of oil droplets. As a result, it increases oil droplets floating resistance and collision resistance. Meanwhile, the electrostatic repulsion of oil droplets also increases. The stability of produced wastewater from polymer flooding becomes stronger.Besides, taking influence of some factors company with HPAM to the stability of wastewater into account, it also been researched for oil concentration and transmittance that the salinity, the initial oil content in produced liquid, suspended solids, p H, the concentration of surfactant, temperature and settling time. It shows that Increased salinity makes the polymer to precipitate from wastewater, and decreases the viscosity of wastewater; the initial oil content in produced liquid and suspended solids content have little effect on oil concentration and transmittance of wastewater; the carboxyl on the fatty acid、naphthenic acid can ionize with the p H value elevating, and Zeta potential values of oil droplets decreases. As a result, the electrostatic repulsion of oil droplets increases. The surfactant makes the wastewater having the features of serious oil-water emulsion and lesser oil droplet diameter. The wastewater will have the strongest stability when it is at 70℃; the oil content of wastewater will reduce while increases the settling time.To take full advantage of residual polymer of produced water from polymer flooding, we have researched it through the interior core flooding experiment and reservoir simulation tool, determined the relationship between improved recovery ratio and residual polymer content and molar mass, 1799.2)3592.010271.310028.2(6079.034+-′+′′=D--Mc ER, and proposed two different methods of wastewater treatment from polymer flooding. For the wastewater from polymer flooding whose residual polymer molecular weight more than 500 million, because of its value, we take the measure of that trying our best to reserve residual polymer. Otherwise, we will take the measure of degradating the residual polymer.We develop polymer degradation agents system to degrade residual polymer of produced water from polymer flooding and separate oil-water mixture through selecting oxidants and inorganic flocculants. The polymer degradation agents system formula is PAFC: modified PAC: HQ: K2S2O8: Fe SO3= 50: 50: 3: 4: 3. Field experiments indicate that wastewater transmittance rate can reaches 92.2%, oil removal rate reaches 94.5%, and its viscosity is 0.9953 m Pa·s near to water viscosity after dealing with polymer degradation agents system. we optimize formula of organic flocculants, surfactants and coagulants, and develop polymer reservation agents system. The formula is MT-5: TSG203A: SR-1= 2: 1: 1. Field experiments indicate that wastewater transmittance rate can reaches 92.6%, oil removal rate reaches 94.0%, and it’s viscosity retention rate reach 91.5% after dealing with polymer reservation agents system. Tow kinds of agents both have efficient function in dealing with produced water from polymer flooding. |
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