The Investigation Of The Polymer Separate Injection Technology In Second Class Reservoir Of Southern District Ⅱ&Ⅲ In Sanan Oil Field

At the end of polymer flooding in the main reservoir in Daqing Oilfield,the target of the displacement of the polymer flooding had changed to the second class reservoir with lower permeability and greater heterogeneity.During the polymer separate injection,due to the complex geological characteristics of the second class reservoir,although most oil layers can be injected into the polymers with higher relative molecular weight,for those thin and poor oil layers,with the improvement of the capture capacity of adsorption,the residual resistance coefficient increases continuously,greatly weaken the ability of penetration of these thin oil layers,reduce the use of these oil layers.Although,reducing the overall relative molecular weight of the polymers can improve the control of the polymer flooding,the effect of the polymer flooding in high-permeability layers will be decreased.Therefore,aiming at these characteristics of the second class reservoir,we can study the technique of polymer interstitial injection,achieve the effective adjustment on the molecular weight and injection rate of each layer,and investigate the effective method to improve the use of low-permeability oil layers and the recovery efficiency in the middle and late period of polymer flooding.In this paper,by using well logging,geology and development data,we develop the research about the characteristics of sedimentation,heterogeneity and fluid in southern district II & III of Sanan oil field,figure out the geological characteristics of the second class reservoir.In view of the actual situation that thin and poor oil layers are poorly used,we optimize 19 injection wells,and implement the research on the technology of polymer separate flooding by the separate molecular weight and pressure injection technology.The main research include the division of different oil layer types,the determination of the permeability contrast and the ratio of reservoir thickness,the relationship between the molecular weight of different polymers and different types of oil layers,the profitable time of interstitial injection,the optimization of interstitial injection parameters,the comprehensive adjustment of injection wells and the fracturing time of extraction wells.Finally,it was concluded that the oil layers of thin-thickness interaction are suitable for alternate injection of low and medium molecular weight during the water recovery periodt,the thin oil layers is suitable for low-level injection of the whole process,and the low-value period has the best effect,and the single low-molecular weightn slug injection is more effective.