Causes and solutions of drill pipe fracture in directional drilling

1、 Fracture cause

1. In order to save investment, the directional drilling equipment used by the construction contractor does not match the actual demand of the engineering construction, the tonnage of the directional drilling equipment is too small, the maintenance is not timely, and the failure rate is high, which makes the drilling force of the directional drilling uneven. At the same time, the stop and go of the construction makes the hole quality poor, the hole is irregular, and the drilling tool is easy to lock, leading to the drill pipe fracture.

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、 Solutions

1. In view of the unreasonable selection of directional drilling rig and reamer, strengthen the start-up management of directional drilling. Relevant design documents (especially relevant geological exploration data) shall be carefully studied before the commencement of directional drilling, and the construction scheme submitted by the construction contractor and the directional drilling equipment to be used shall be reviewed, so as to ensure that the configured directional drilling equipment and drilling tools match the actual needs of engineering construction, and the commencement is prohibited if they do not meet the requirements, and the tracking and adjustment shall be carried out in time according to the actual drilling situation after the commencement.

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);

② The drill pipe entering the site should be tested and used according to the grading inspection method for drill pipe (SY / t5824), and the first grade drill pipe should be used for the project with high schedule risk;

③ The management file of drill pipe shall be established, and the use of each drill pipe shall be recorded in the whole process. The service life of each drill pipe shall be uniform during the use;

④ Finite element simulation analysis should be used for stress analysis and life evaluation of drill pipe in directional drilling project;

⑤ Two or three thickened drill pipes should be set before and after the reamer for the transition between drill pipe and drill collar.

3. For the problem of excessive deviation of guide hole, strengthen the control of guide hole deviation. The deviation between the actual curve and the design curve of the guide hole shall not be greater than 1% of the crossing length, and the deviation shall comply with relevant regulations; After the completion of the construction of the guide hole, it must be accepted by the supervisor or the owner, and only after the acceptance is qualified can the hole be expanded.

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.