Drawing Oil Well Vitta Failure Mechanism And Accident Prevention Study

In recent years, the tubing broken accidents of pumping wells in Daqing Oilfields have been taken place with increasing frequency, which has caused enormous economic loss to the oil fields. And the essence of the tubing failure accidents is the failure of the tubing thread. So far, the study on the tubing broken has not been carried out in depth at home and abroad. Therefore, in this paper, experimental study and theoretical analysis are made systematically on the tubing failure in Daqing Oilfields.A set of sensor used for tubing load testing was designed. The sensor can be used to measure not only tensile load, but also torsion load and bend load. Loading status of tubing in oilfields was mastered by doing lots of tubing load tests and analyses. And then the theoretical model about the limit load and the vibration of tubing has been constructed. This paper also analyzes the reasons why tubing bears bent load. As well as the geometric dimension, the shape change and the working capability of the tubing threads have been studied.The mechanical characteristics what the tubing connections subjected to the cycle tension load exhibit are gained in the third section, so are the cycle laws and the amplitude of stress and stain. The uninstall laws of the tubing connections which are also described in this section are that the tubing connections are uninstalled in linear elastic manner, in other words, the fatigue type of tubing connections belongs to the high-cycle fatigue. A set of dynamic testing signal system was designed so as to find out the strain-changing rule under different loads on inner wall of the tubing thread by simulating tubing on-site working load. The real-time and dynamic strain signal can be caught. The signals caught are stable and credible. The correctness of Finite Element calculating method and the reliability of experimental testing results were verified by contrasting the results of experimental testing with Finite Element Calculation.By means of the chemical composition analysis, the mechanical test of the tubing produced by specialized factory and fractured in oil field, we conclude that the material quality of the tubing used in Daqing has some defects, but itaccords with the API standard basically, in other words, the improper fatigue break of tubing is not mainly caused by the material quality defects.Through observing and analyzing on tubing's fractured surface, combining with stress analyzing for tubing thread root, the mechanism of the origin and extension of tubing fatigue crack is discussed. The actual fatigue strength at the root of thread dangerous section is estimated by applying description and analyzing methods on fatigue strength and life-span. The view that normal used tubing should possess 'undated life' is realized. The observation and energy spectrum analysis to the corrosion on the origin and extension area of tubing crack is made. It is concluded that corrosion cannot cause fatigue crack directly.The main reasons for improper fatigue fracture of tubing are found, that is, screwing and unscrewing with heavy torque for many times makes thread root of dangerous section be with high stress level, which results in the rapid decreasing of anti-fatigue strength, so as to produce congenital source of fatigue crack, and bring on abnormal fracture of the tubing. So the key measure for preventing tubing failure is to control the tightening torque. The developed 'Torque-Pump Pressure' monitor system in this dissertation is very effective for controlling the magnitude of tightening torque.