Research On The Influence Degree Of Polymer-Bearing Sewage For Oil Layer

With the popularization of chemical flooding in the oil field,the polymer concentration in produced wastewater is one of the most important factors causing reservoir damage.The influence of poly sewage on reservoir permeability has always been oilfield waterflood development priorities,which is of great significance to improve water injection.Aiming at the produced sewage of Xingnan oilfield in Daqing,this paper firstly analyzes the microstructure of injected water and the matching relationship between the size of polymer molecular cluster and the microstructure of different reservoirs,and obtains the plugging mechanism of polymer containing sewage.Then the core flow experiment in the laboratory was carried out to figure out the plugging types and limits of injected polymer concentration in the sewage.Finally,through the oil displacement experiment,the feasibility of improving the oil recovery of the reservoir by using the polymer-containing sewage reinjection was proved,and the optimal polymer concentration suitable for different reservoirs was figured out through the combination of different flow experiments.Core flow tests show that the reservoirs with permeability of 20×10^-3μm² and 50×10^-3μm² are suitable for an injected polymer which contains 5mg/L suspended oil and the limited value of polymer concentration is 100mg/L;The reservoir with 110×10^-3μm² permeability is suitable tothe polymer containing 5mg/L suspended particle and the limited value of polymer concentration is 100mg/L;The reservoir with 180×10^-3μm² is suitable for a polymer whose limited concentration is 200mg/L and this polymer cannot contain neither 5mg/L suspended oil nor5mg/L suspended matter.The oil displacement experiment shows that the polymer limited concentration which is suitable for the reservoir with 20×10^-3μm²,110×10^-3μm² and50×10^-3μm² permeability is 100mg/L,and that of 180×10^-3μm² is 200mg/L.Combined with the experimental results of the influence of the reinjection wastewater on the reservoir permeability and recovery rate,it is suggested that the limited value of polymer concentration for the reservoirs whose permeability are 20×10^-3μm²,50×10^-3μm² and 110×10^-3μm² should be 100mg/L,and the limited polymer concentration for 180×10^-3μm² reservoir should be200mg/L.The polymer concentration in the injected water should be reduced as much as possible after reach the minimum value.In this paper,the research on the index of water quality has a certain guiding significance.