Optimization Of Separate Zone Water Injection In The High Water-cut Oilfield

Separate zone water injection is an effective measure to improve injection-production structure and enhance recovery factor in the high water-cut oilfield.In order to maximize the effect of separate zone water injection,this article studied the interval number,interval combination and injection allocation systematically and fully.Based on reservoir engineering method,considering the effect of starting pressure gradient,we established a method to predict multi-layer heterogeneous reservoir development index.This method was used to research the effect of permeability difference,viscosity difference,main big thick layer and injection pressure on commingling injection from seepage resistance,effective injection-production pressure difference,injection ratio and recovery extent.We cleared the law and characteristics of commingling injection for multi-layer heterogeneous reservoir.On this basis,considering the influence of reservoir property and development situations of each layer,we established the evalution index system of separate zone water injection interval division combination,and screened the best interval combination by optimal segmentation method.Combined with the well pressure constraints on layer injection,we take the cumulative oil production as objective function,and established the optimization mathematical model for describing the allocation of separate zone water injection.By comparing all kinds of optimization algorithm,we proposed a reservoir engineering+patternsearch optimization algorithm,which takes the layered allocation scheme of reservoir engineering as the initial solution of PS optimization iteration.Compared with genetic algorithm,it improved the efficiency of solving calculation.The analysis on the application of above theory in shengli oilfield showed that within a reasonable range of interval number,through interval division and allocation optimization,we got the separate zone water injection scheme under every interval number respectively.By comparing these schemes,the optimal separate zone water injection scheme was selected.On the basis of the optimal separate zone water injection scheme,we studied two ways to improve the effect of separate zone water injection,which were combine separate zone water injection with injection-production optimization and combine separate zone water injection with layered production.The results showed that separate zone water injection can effectively improve waterflood effect,and different ways of separate zone water injection to improve the degree of development effect is different.What's more,combined separate zone water injection with injection-production optimization and layered production,it can further improve the structure of injection-production and the effect of development.