Study On Mechanism And Countermeasures Of Casing Damage In Water Injection Wells In Weibei Oilfield

With the development of water flooding in Weibei oilfield,due to the influence of natural and artificial factors,the phenomenon of shut-down caused by shrinkage and breakage of casing in water injection wells is increasing day by day.These problems seriously affect the normal development and production of Weibei oilfield,and restrict the effect of water flooding in oilfield.Therefore,it is of great theoretical and practical significance to clarify the casing damage mechanism of water injection wells in Weibei oilfield and optimize the prevention and control scheme of water injection wells for improving the development efficiency and increasing oil and gas production in Weibei oilfield.In view of the casing necking and casing breakage in more than 20 wells after waterflooding development in Weibei Oilfield,this paper studies the influencing factors from two aspects of theoretical analysis and casing corrosion experiment according to the geological data of each shut-down wells in Weibei Oilfield,and from mudstone water absorption creep,mudstone swelling vertical deformation,perforation effect and ground.The mechanical model of casing string under the action of inhomogeneous in-situ stress and internal pressure is established from four aspects of layer slip,and the casing damage mechanism is analyzed according to the casing strength.The influence of high salinity formation water,salt substance,electrochemical corrosion and other factors on casing damage should be studied.The results show that for mudstone creep injection wells,the injection pressure can be reasonably controlled,and the injection pressure should be lower than the minimum principal stress of the water injection layer,so as to prolong the service life of the casing.For seriously corroded wells,the injection water should be optimized with non-corrosive or less corrosive formula.According to the influence of p H,temperature,bicarbonate ion,chloride ion,magnesium ion and calcium ion on Corrosion of N80 casing in single factor experiment,the ion concentration in injected water should be optimized reasonably.