Investigation of the technique of gas/polymer alternate injection at the middle-late stage of polymer flooding

In order to improve the polymer flooding and thus enhance oil recovery from intermediate and low permeability oil layers,we conducted a study on gas/polymer alternate injection.By laboratory experiments,parameters for gas/polymer alternate injection were optimized,including gas-liquid ratio,combination of slugs,relative molecular weight of polymer,mass concentration of polymer solution and injection rate.Experimental result shows that gas/polymer alternate injection can increase oil recovery by more than 10% over pure polymer flooding.Field pilot test was implemented,which shows that by applying gas/polymer alternate injection at the middle stage of polymer flooding,water cut of oil wells can be decreased significantly and secondary effect is obvious.This study proves that gas/polymer alternate injection is an effective method to improve polymer flooding.Because gas is used to replace certain amount of polymer,this technique can save polymer and achieve much better economical benefit.