1、 Fracture cause
2. The selection of reamer model is unreasonable, and the matching selection is not carried out according to the actual geological conditions, resulting in the increase of drilling torque and the increase of drill pipe wear and fracture.
3. Unreasonable selection of drill pipe, lack of tracking management of drill pipe and statistics of drill pipe testing data, lead to uneven service life of a set of drill pipe, in which the drill pipe with larger wear is fractured due to stress concentration.
4. The deviation control of the pilot hole is unreasonable and the deviation is too large. In the later correction process, the actual curve is unreasonable and the bending moment of the drill pipe is too large, which is easy to increase the stress of the drill pipe or directly cause the friction and hot cracking of the drill pipe surface, especially when the drill pipe joint bears high lateral friction, which produces a lot of heat when it contacts with the hole wall periodically, the material on the joint surface is heated and cooled periodically to produce brittle martensite. Under the influence of excessive bending moment, the longitudinal crack of internal thread of drill pipe joint is caused.
5. the grading of reaming is unreasonable. The construction unit reduces the hole expansion classification in order to rush the work period, which makes the drilling torque greatly increase, which is easy to cause the increase of drill pipe wear and fracture.
6. Because the geological condition is not ideal, the hole is broken and collapsed, and there are too many drilling cuttings, which increase the risk of tool locking and lead to drill pipe fracture.
2. For the unreasonable selection of drill pipe, the selection and management of drill pipe should be strictly enforced.
① The selection of drill pipe should match the parameters of drilling rig. According to the previous construction experience, the maximum torque of drill pipe should be twice of the maximum estimated torque (the calculation formula of maximum estimated torque can refer to relevant technical documents);
4. For the unreasonable grading of reaming, scientific grading of reaming should be carried out. The construction supervisor and the owner shall supervise and urge the construction unit to reasonably grade. For the pipeline with diameter over 400mm, the reaming shall be graded and repeated. The reaming grade difference shall be determined according to the drilling rig, mud system, drill pipe specifications, geological conditions, etc. In general, the diameter of the first stage reaming is 20 ″～ 24 ″, and then the grading reaming is 4 ″～ 10 ″.
5. For the problems of unsatisfactory geological conditions, it is required to closely monitor the reaming process. In the process of reaming, the changes of various parameters should be closely tracked and analyzed. If the torque and tension are too large, the hole washing operation should be taken in time. After the hole washing, the reaming should be continued; For the directional drilling of rock geological fracture, the hole should be washed at least once after each reaming.