Recognizing Coiled Tubing Defect Characteristics Based on Weak Magnetic Detection Technology

The development of coiled tubing operation technology has continuously improved with the higher requirements of coiled tubing on-line detection technology. The current coiled tubing field weak magnetic on-line detection system calculates the gradient of the signal for improving the locating precision. Quantitative identification of defect shape, based on the weak magnetic detection and magnetic leakage flux systems, is a key issue to evaluate whether coiled tubing can continue to be used. The 2-D finite-element models with different typical defect shapes were established, and the gradient changes of the magnetic-field intensity are calculated. The influence of defect size on signal characteristics is analyzed, and a functional model can be obtained. The signal characteristics of a 2-D self-leakage magnetic field were further analyzed, and a 2-D cloud image was established used to identify the shape of defects. The level of damage as a result of coiled tubing use is evaluated according to the identified defect shape, which is significant for a quantitative description of defects and the accurate evaluation of conditions in the coiled tubing on-line inspection system. This research of identification of defect shape and size makes up the disadvantage that weak magnetic detection can only judge whether the defect of log exists or not.