Research On Identification Method Of Thief-zone Between Injection And Production Wells Based On Numerical Simulation

After a long period of water flooding,the eastern NS block of Daqing has entered an extremely high water cut stage.Its reservoir is water-out,and the thief-zone develops rapidly.Injected water circulates low and non-effective circulation in the reservoir,which reduces the development effect and economic benefits of the oilfield and hinders the enhanced oil recovery.In this regard,this paper carries out research work on identification of thief-zone in the eastern NS block of Daqing.Providing an effective identification system of thief-zone for the NS block of Daqing,and it provides theoretical support for the next step of plugging the thief-zone in the block.Based on the analysis of oilfield geological data and oilfield development dynamic data,sedimentary micro-facies,reservoir heterogeneity and the material composition of reservoir will affect the formation of the thief-zone,which in turn will affect the shale content and water saturation of reservoir,as well as the production parameters of injection wells and production wells.The changes of static and dynamic parameters are analyzed,and the thief-zone identification system is established by using the fuzzy comprehensive evaluation method.Firstly,the evaluation set and factor set are established,and the weight of each factor is determined by analytic hierarchy process.Secondly,the membership degree of each parameter is determined by normal distribution function.Finally,the product of weight and membership degree is taken as the evaluation set of the thief-zone,which is used to judge whether there is the thief-zone between oil wells and water wells.Result,the direction of the thief-zone between oil wells and water wells is determined.Using numerical simulation technology and reservoir engineering method,the limit of the water saturation,oil displacement efficiency,water injection multiple and recovery percent of the thief-zone is determined.Firstly,the geological model and fluid model are integrated by reservoir numerical simulation technology to lay a foundation for quantitative description of injection-production relationship.Secondly,tracer is added to the model to track the flow direction of liquid and mark the fluid in real time,determine the injection-production relationship between oil wells and water wells.Finally,the water saturation of channel sand body,main sand body,non-main sand body and inter-channel sand body is counted.The water saturation,oil displacement efficiency,water injection multiple and recovery degree of the four sand bodies when forming the thief-zone are determined under the condition of 98% water cut,so as to determine the region of the thief-zone.Through the fuzzy comprehensive evaluation system and the tracing function of numerical simulation tracer,the quantitative identification of the thief-zone and the determination of injection-production relationship between oil wells and water wells are realized.The region of the thief-zone is determined by numerical simulation and reservoir engineering methods.This study is significant for identifying the thief-zone in high water cut oilfields.