Fatigue failure analysis of drilling tools for ultra-deep wells in shunbei Block

The ultra-deep wells in the north of the Shunbei block have a vertical depth of about 7500m. During the drilling process, the upper drilling tools often fail. The failure modes are based on the fatigue damage of the drill joint surfaces and threads. The causes of failure are analyzed from the axial and bending stresses and the high temperature and corrosion environment of ultra-deep wells. The major axial stress is the main feature of ultra-deep well drilling. The step surfaces and threads are the stress concentration sites, and the maximum load is close to the material yield limit. The bending stress is the main factor that causes the fatigue load, its size increases with the increase of the rotational speed. The high temperature and the corrosive environment will cause the drilling material to reduce the fatigue limit. The NCODE software was used to perform fatigue finite element simulation on the drilling tool, and the fatigue life of the drilling tool under different stress conditions was analyzed. The main influencing factors of drilling tool failure during ultra-deep well drilling in the north of the area were pointed out, providing a reference for drilling tool design in this area. (paper)