Drill pipe joints fatigue analysis and optimization under special working conditions

Abstract

Recently, the number of ultra-deep and extended reach wells has continuously increased. The failure of the drill pipe is prominent when drilling. The thickened area of the drill pipe body and the position of the drill pipe joint often appear fatigued, especially the internal thickening zone for the nonlinear structure of the cast component. Fatigue failure occurred at the drill pipe joint due to non-linear contact between the male and female snaps. The fatigue life S-N curves show that the overall life of drilling with high-resistance torsion drill pipe is increased by 136% compared with API drill pipe, though the maximum stress value was reduced by 8.4%. The high-bend drill pipe has an overall life improvement of 174% over the API drill pipe. High flexural drill pipe reduces stress by 10% compared to the maximum value. At the same time, the drill pipe’s fatigue period and safety factor can be improved by adjusting the drilling speed and annulus pressure properly.