Identification Method And Treatment Of Polymer Breakthrough In West Area Of Jinzhou 9-3 Oilfield

Jinzhou 9-3 oilfield has the characteristics of strong horizontal heterogeneity,large reservoir thickness and large well spacing.Vertically,it is divided into five reservoir groups,in which the target layer of chemical flooding is divided into three layers.The strong heterogeneity in the layers results in polymer flooding and binary composite flooding.During the process of polymer flooding and binary composite flooding,there exists the phenomenon of polymer breakthrough along the dominant percolation channel,and oil wells gather early,water cut rises fast,and sweep coefficient is low,and so on.Therefore,it is urgent to study the identification method of polymer breakthrough,and give reasonable treatment measures for polymer breakthrough,so as to improve the development effect of chemical flooding.In this paper,the effects of permeability gradient,permeability variation coefficient,horizontal heterogeneity and effective thickness gradient on polymer breakthrough are studied by numerical simulation and dynamic analysis.The results show that permeability gradient,permeability variation coefficient and horizontal heterogeneity are the main factors causing polymer breakthrough.Combined with the characteristics of production dynamic indexes such as concentration of polymer production,liquid production,water content,polymer storage rate,and the characteristics of injection dynamics such as injection pressure,apparent water absorption index and polymer injection volume,an index system for judging polymer breakthrough is proposed,which includes dimensionless instantaneous oil production consumption per ton of polymer,water saturation,dimensionless time to see polymer,dimensionless peak concentration to see polymer and dimensionless peak time to see polymer and dimensionless average polymer concentration,the influence degree and weight of six indexes on polymer breakthrough were studied by gray correlation method and analytic hierarchy process,and the PCFI which comprehensive discriminant index of polymer breakthrough was introduced to characterize six indexes.Polymer breakthrough wells and layers in Jinzhou 9-3 oilfield were identified by comprehensive discriminant index PCFI.The results show that polymer breakthrough in reservoir I is more serious.The proportion of geological reserves and pore volume in breakthrough area is 31.09%and 47.54%respectively.On the basis of identification of polymer breakthrough,the study of polymer breakthrough control measures was carried out,and the numerical simulation scheme of polymer injection area optimization and injection mode optimization was formulated.Scheme 5 was the best injection area.Alternating injection of low concentration polymer and high concentration polymer is superior to alternating injection of high concentration polymer and binary system and alternating injection of water-polymer.The optimum scheme is"2000 mg/L polymer 86.83 mg/L?PV+1500 mg/L polymer 173.66 mg/L?PV",which is 1.96 percentage points higher than the current scheme.The cumulative oil increment is 28.97╳10~4m~3,and the oil increment per ton is 28.97╳10~4m~3.The oil recovery can be further increased by 0.04 percentage points and the oil increment is 0.65╳10~4m~3when profile control measures are adopted in the serious strata of polymer breakthrough.