Study On Injectivity Profile Variations And Profile Reverse Identification Methods In Polymer Flooding Reservoirs

For heterogeneous reservoir,in the early and middle stage of polymer injection process,its injectivity profile can be improved.However,as polymer flooding in oil reservoirs enters mid-and-late stages,‘injectivity profile reverse phenomenon' appears in some blocks with strong anisotropy where more fluids transport through the formation with higher permeability than that in water flooding reservoirs,while the formation with lower permeability absorb fewer fluids.This phenomenon dramatically affects the performance of polymer flooding,resulting in unsatisfied EOR.Through the study on injectivity profile reverse in polymer flooding,oilfield can take appropriate measures in time to reduce injectivity profile reverse phenomenon,thus improving polymer flooding effect of increasing oil recovery to the largest degree.Firstly,based on the profile reverse achievements of Daqing polymer injection well,well test data of PetroChina's Surfactant Demonstration Area and experimental results,regularity of injectivity profile reverse phenomenon is analyzed,underlying causes of profile reverse is explored,and dynamic responding characteristics are concluded.Secondly,by establishing the numerical model of injection well group,critical parameters of injectivity profile reverse including injection pressure and production rate are extracted.If the injection pressure of injection well and production rate of communicated production well present the trend that increases first and then decreases,profile reverse occurs.Then,effects of injection velocity,interlayer permeability ratio and polymer concentration are investigated.Higher injection velocity,bigger permeability ratio and higher polymer concentration result in earlier appearance of injectivity profile reverse phenomenon.Third,the well shut-in test is designed and implemented.Thus well test identification method through wellhead pressure monitoring profile reverse is proposed in this paper.The results show that when the distribution rate of low permeability layer presents the trend that increases first and then decreases,profile reverse occurs.Finally,according to the dynamic data of polymer injection well group,the dynamic characteristics of wells are analyzed,the connection coefficient is calculated,and dynamic responding characteristics identification method is proposed.The results show that when the injection pressure increases first and then decreases,the production rate first increases and then decreases in the same well group,and the connected coefficient presents the same trend simultaneously,profile reverse phenomenon happens in this period of time.