Failure Analysis Of Drilling String In Oil And Gas Wells

Working conditions of oil and gas wells drill string is very poor, and stress state is complex. Drill string bears the dynamic load,and alternate load like pull, pressure, bending force, torsional force and so on.It is affected by corrosion, abrasion, temperature, pressure and so on. So oil/gas well drill string is prone to failure and failure forms are varied. Drill string becomes the weak segment of drill fixtures because of the poor conditions. Especially while drilling deep, ultradeep and complex geology wells, drill string failures often emerge and economic losses are huge. The fault failure of high-intensity drill string is becoming increasingly prominent. Therefore, the safety and reliability of drill string is a very prominent issue.Wherefore, based on having done many failure case analysis of drill string and combing with failure analysis equipment in the application of the oil industry, this thesis summed up a more comprehensive failure analysis and evaluation methods for drill string. This article expounded the application and development of failure analysis in metal component parts, and focused the necessity and importance of application on oil and gad drill string,and described detailedly the methods, procedures and techniques. This article analyzed focally several typical failure forms in oil and gad drill string, such as drill string cracking failure being caused by stress corrosion, drill string corrosion failure being caused by electrochemical corrosion,the drill string fault failure being caused by corrosion fatigue, operators’s crude operation to drill string and fault failure being caused by overloading, etc. The third chapter introduced detailedly these types in the case of the failure. This article also established finite element model from the point of fracture mechanics to evaluate and analyse the drill string. And simulated test of the affection of oil field environment to drill string was made to evaluate its failure.Based on the failure analysis method to metal component parts and combinated the unique environmental conditions of oil field,this article explored some new failure analysis being fit for the drill string analysis and evaluation.Summarizing the failure situation of oil and gas drill string,it can conclude the failure types of drill string,such as the stress corrosion cracking failure of drill pipe, electrochemical corrosion failure of drill string because of mud cake on the drill string, corrosion fatigue fault of drill string, wornout failure of drill pipe sub thread, the facing layer welding procedure of drill pipe wearproof site is unreasonable, the failure of drill crew operators’s crude operation to drill fixture and so on.Many failure of drill string were caused by fatigue and corrosion.To each failure type, this article proposed feasible and scientific methods and measures for preventing drill string failure. And propositions were recognized by producers and oil field consumers. It was of very important sense to promoting the oil industry development.