Wellbore Safety Evaluation Of Eater Injection Well Conversion To CO₂ Injection Well In Jiyuan Oilfield

At present,the development of reservoirs in many oil fields in China has entered the middle and late stages.Conventional water injection techniques are difficult to tap.As a creative new EOR technology,CO₂ injection safety is directly related to the promotion and application in oil fields.It needs to form a systematic safety assessment system through laboratory experiments,wellbore integrity analysis,wellbore risk analysis and safety assessment and control measures,which promotes the development and improvement of related safety supporting technologies.It is of great significance to the application and promotion of CO₂ flooding technology in other blocks of Changqing Oilfield.This paper mainly studies four parts.The effect of CO₂ injection on the explosion limit of flammable gas（associated gas）has been studied through experiments;Material risks and safety hazards in the CO₂ flooding process is studied and analyzed;Combining the characteristics of CO₂ flooding process and actual conditions,a method for integrity evaluating injection-production wellbore of water injection well conversion to CO₂ injection well is established,and the integrity of wellbore in the test block was analyzed using this method.The PHA and FTA are used to evaluate the risk of CO₂ flooding wellbore,analyzing their main risks and harmful factors,and formulating corresponding protection and control measures;Through the study,the following conclusions are drawn:the risk of associated gas burning and explosion after CO₂ injection is reduced compared with water injection;The main safety hazards of the CO₂ injection and production wellbore include the wellbore explosion of the production well,the low-temperature brittle fracture and frostbite at the wellhead of the gas injection well,the high-pressure harm at the wellhead of the gas injection well,the leakage at the wellhead of the gas injection well,and the corrosion of the injection-production wellbore;A method to evaluate the integrity of CO₂ injection-production wellbore is developed,which is suitable for Jiyuan Oilfield;The main reason for the leakage of the wellbore of the gas injection well is high pressure and corrosion,and the cause of the fire and explosion of the production well is corrosion.