1. fracture reason
1.
In order to save investment, the directional drilling equipment used by the construction contractor does not match the actual requirements of the project 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 directional drilling force uneven. At the same time, the stop-and-go construction results in poor hole quality, irregular holes, and easy locking of drilling tools, resulting in drill pipe fracture;
2.
The reamer model selection is unreasonable, and the matching type selection is not carried out according to the actual geological conditions, which makes the drilling torque increase, the drill pipe wear increases and breaks;
3.
Drill pipe selection is unreasonable, due to the lack of tracking and management of drill pipes and the lack of statistics of drill pipe detection data, resulting in uneven service life of a set of drill pipes used, in which the drill pipe with large wear is broken due to stress concentration;
4.
The pilot hole deviation control is unreasonable and the deviation is too large. In the later correction process, due to the unreasonable actual curve and the excessive bending moment borne by the drill pipe, it is easy to increase the stress of the drill pipe or directly cause the surface of the drill pipe to be fractured due to friction. Especially, the drill pipe joint bears high lateral friction. When it periodically contacts and frictions with the hole wall, a large amount of heat is generated, which makes the joint surface material undergo periodic heating and cooling to produce brittle martensite, under the influence of the excessive bending moment, the longitudinal crack of the internal thread of the drill pipe joint is caused;
5.
The reaming classification is unreasonable, and the construction unit reduces the reaming classification in order to catch up with the construction period, which greatly increases the drilling torque and easily leads to the increase of drill pipe wear and fracture;
6.
Due to the unsatisfactory geological conditions, the hole is broken and collapsed, and the drilling cuttings are too much, which increases the risk of drilling tool locking and causes the drill pipe to break.
2. solutions
1.
In view of the unreasonable selection of directional drilling rig and reamer, the directional drilling start management is strengthened. Relevant design documents (especially relevant geological survey data) shall be carefully studied before directional drilling commencement, and the construction scheme submitted for approval by the construction contractor and directional drilling equipment to be used shall be reviewed to ensure that the configured directional drilling equipment and drilling tools match the actual requirements of the project construction.
2.
For the problem of unreasonable drill pipe selection, strict drill pipe selection and management.
① Drill pipe selection should be matched with the parameters of the drilling rig. According to the previous construction experience, the maximum torque of the drill pipe should be selected according to 2 times of the maximum estimated torque (the calculation formula of the maximum estimated torque can refer to the relevant technical documents);
② The drill pipe entering the site shall be tested and classified according to the Test Method for Drill Pipe Classification (SY/T5824), and the first-class drill pipe shall be used for the project with high progress risk;
③ A drill pipe management file shall be established, and the usage of each drill pipe shall be recorded in the whole process, and the use shall be reversed during the use to make the life of each drill pipe uniform;
④ The stress analysis and life evaluation of the drill pipe shall be carried out by finite element simulation analysis for the directional drilling project with large progress risk;
⑤ Two to three thickened drill pipes shall be arranged before and after the reamer for transition between drill pipe and drill collar.
3.
For the problem of excessive guide hole deviation, strengthen the guide hole deviation control. The deviation between the actual curve and the design curve of the pilot hole shall not be greater than 1% of the crossing length, and the deviation shall comply with relevant regulations. After the construction of the pilot hole is completed, the acceptance must be carried out by the supervisor or the owner, and the reaming can only be carried out after the acceptance is qualified.
4.
For the problem of unreasonable reaming classification, scientific reaming classification. The construction supervisor and the owner shall urge the construction unit to classify reasonably. For pipelines with a diameter of more than 400mm, the reaming shall be classified and reamed for many times. The reaming grade shall be determined according to the drilling rig, mud system, drill pipe specifications and geological conditions. In general, the first stage of reaming has a diameter of 20 "to 24", followed by 4 "to 10" graded reaming.
5.
With regard to the unsatisfactory geological conditions and other issues, it is required to closely monitor the reaming process. During the reaming process, the changes of various parameters shall be closely tracked and analyzed. If the torque and tension are found to be too large, the hole washing operation shall be carried out in time. After the hole washing is completed, the reaming shall be continued. For directional drilling with rock geological fracture, the hole shall be washed at least once after each reaming.
