| Reinjection of wastewater is the most important technique for keeping the balance between continuable exploitation of oil in Bohai oilfield and environment protection. Howerver, there are several problems for the reinjection of wastewater produced polymer flooding (WPPF) after the performance of polymer flooding in several offshore oilfield, as follows:(1) the bad water quality, low ratio between injection and recovery, and the amount of inject water is far from the demand.(2) the period of validity of water injection is not long enough and the conflict between the different horizons is obvious;(3) the degree of the emulsification of water and oil is high and is difficult to be treated, and there is no effective treating compound for now. Theses problems seriously limit the effective rejection of WPPF and the exploitation of oil in Bohai oilfield.In this paper, the common problems of rejection of wastewater produced from polymer flooding in Bohai SZ36-1oilfield, LD10-1oilfield and JZ9-3oilfield were studied. For the effective, economic and continuable reinjection of WPPF, the monitoring of the water quality in time in these oilfields was developed firstly. At the same time the degree of adaptability of between WPPF and reservoir was studied and the indexes of the reinjection of WPPF was made. Then, the characteristic compose of WPPF was analyzed and the mechanism of the stability of the WPPF was discussed. On the basis of the mechanism of the stability of the WPPF,a new effective treating compound for WPPF was prepared. At last, after the optimization and adjustment of the system of wastewater treatment, the effective rejection of WPPF was realized and the demand of reinjection was met at the same time.The results the monitoring of the water quality in time showed that the water quality was above the standard seriously and the treatment of the WPPF and the water quality were affected the polymer obviously. The reinjection the WPPF would destroyed the reservoir and the reasons were as follows:(1) there were precipitation caused by the incompatibility between the treating compounds;(2) there were production of corrosion and crustation and FeS;(3) the permanent blockage of caused by the residual polymer and emulsion reservoir. The effects of the concentration of suspended solid, size of the suspended solid, concentrations of oil and residual polymer on the destroy of reservoir were studied and a new standard of rejection of WPPF was established.After the analysis of characteristic composes in WPPF and study of the effect of residual polymer on the stability of the WPPF,the reasons for the stability of WPPF were found. There were two main reasons:(1) the amount of polar composes in water increased with the oil concentration in water;(2) the adsorption of the residual polymer on the interface between oil increased the strength of the interfacial film and the affect the floating of the oil.On the basis of the two reasons, a new polymer emulsion containing the AM, DAC and MOA was prepared. After the optimization experiment of several conditions, the best treating compound for the WPPF was get. After the treatment of WPPF by this treating compound, the oil concentration in water was30mg/L, concentration and size of suspended solid were4.2mg/L and1.627μm, respectively.In addition, on the basis of systemic study of the effect of WPPF on the treatment the system of wastewater treatment, the performance parameters of shew slab oil remover and flotator were optimized and their performance and efficiency were improved. At the same time, the technique of the remove of iron ion was successfully used in the offshore oilfield and corresponding antiscale and corrosion inhibitor were prepared.At last, the step control of water quality was proposed and the effective rejection of WPPF was realized. Theses results supplied the guarantee of the rejection of the wastewater produced from the chemical flooding. |
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