Study On Treatment Of Polymer Flooding Produced Water With High Concentration Of Calcium And Magnesium

With large-scale application in conglomerate reservoir of the?and?type domestically,polymer flooding technology is drawing more and more attentions of researchers for its prospects in conglomerate reservoir of the III type.This,however,did not crystalize until RIPED developed suspension microcrystalline polymer flooding technology since polymer flooding has a stringent requirement for salinity(especially calcium and magnesium).As a technical storage of the flooding technology which has been proved feasible by experimental evaluation and will be put into mine tests in 2019,this paper studied treatment methods and processes of the produced water in such oil extraction method.Based on the actual formation temperature,salinity and ionic composition of Bamianhe Oilfield,this paper investigates the rheological properties of crude oil and HPAM,the effect of HPAM on petroleum in solution,and the water quality of artificial wastewater.The results show:Separation of oil from produced water is a ticklish question since oil droplets of such heavy oil are difficult to coalesce,and solution of the HPAM with high molecular weight and high concentration are extremely viscous,which also leads to high dispersion of oil droplets in the produced water.Although the viscosity of HPAM solution is seriously jeopardized in high salinity,high temperature and acidic condition,the previous addition of suspended microcrystalline agent helps keep its 90%viscosity under high salinity.Also,the artificial wastewater formed by compounding treated water-flooding produced water,an appropriate amount of HPAM(M_n:15 million)and excessive crude oil through 120s-stirring(16000rpm)at 60°C.The process of gravity sedimentation-chemical flocculation-composite filter filtration has been proved valid experimentally in the treatment of polymer flooding produced water when it contains 0?300mg/L HPAM,the water quality of treated water could meet the requirement of reinjection in conglomerate reservoir with 0.05?0.15?m~2average air permeability.This paper evaluates the feasibility of the process in treating the produced water with higher concentration of HPAM.The results show:Gravity sedimentation and chemical flocculation are inefficient in degreasing the produced water with 400mg/L and 500mg/L HPAM(Oil removal efficiency decreases 26%and43%compared to that with 300mg/L HPAM),and the filter unit is thoroughly clogged after running for10h and 4h respectively.Therefore,the process is inapplicable to treat the produced water when its HPAM concentration is higher than 300 mg/L.Having prepared simulated polymer flooding produced water with 500mg/L HPAM,ozonation and ceramic membrane filtration are introduced to improve the previous treatment process.The combined process of gravity sedimentation,ozonation,chemical flocculation and ceramic membrane filtration was proposed to cope with such artificial wastewater.The water quality of treated water meets reinjection requirement:Turbidity<0.2NTU,oil content<10mg/L,COD<2000mg/L,mean particle size<0.8?m.Moreover,membrane fouling process is analyzed by mathematical models,and the results show:Membrane fouling caused by surface entrapment can be obviously alleviated when artificial wastewater is pretreated by ozonation and chemical flocculation,and such treatment process could keep normal operation for 28.3h.