Fracture Causes And Solutions of Drill Pipe in Directional Drilling

Cause of fracture

1. In order to save investment, the directional drilling equipment used by the construction contractor does not match the actual needs 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 drilling force of the directional drilling uneven. At the same time, the construction stop-start makes the hole quality poor, the holes are irregular, the drill tool is easy to hold, resulting in the drill pipe breaking;

2. The type selection of the reamer is unreasonable, and the selection is not carried out according to the actual geological conditions, which makes the drilling torque increase, the drill pipe wear increase and the fracture;

3. Unreasonable selection of drill pipe, due to the lack of tracking and management of drill pipe, the lack of drill pipe testing data statistics, resulting in the uneven life of a set of drill pipe used, in which the drill pipe with greater wear is broken due to stress concentration;

4. The guide hole deviation control is unreasonable and the deviation is too large. In the later correction process, due to the unreasonable actual curve, the bending moment borne by the drill pipe is too large, which is easy to lead to increased stress of the drill pipe or direct friction and thermal cracking of the drill pipe surface, especially the drill pipe joint bears high lateral friction, which produces a lot of heat when it contacts with the hole wall periodically. The surface material of the joint is subjected to periodic heating and cooling, which produces brittle martensite, and causes longitudinal cracking of the internal thread of the drill pipe joint under the influence of excessive bending moment.

5. The reaming classification is not reasonable, 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 unsatisfactory geological conditions, hole breakage and collapse and excessive drilling cuttings increase the risk of drilling tool locking and lead to drill pipe fracture.

solution

1. In view of the unreasonable selection of directional drilling rig and reamer, strengthen the management of directional drilling start-up. Before the start of directional drilling, the relevant design documents (especially relevant geological prospecting data) should be carefully studied, the construction plan submitted by the construction contractor and the directional drilling equipment to be used should be reviewed, to ensure that the configured directional drilling equipment and drilling tools match the actual needs of the construction, and if they do not meet the requirements, the construction should be prohibited, and timely tracking and adjustment should be made according to the actual drilling situation after the start of the construction.

2. For the unreasonable selection of drill pipe, strict selection and management of drill pipe.

① The selection of drill pipe should match the parameters of the rig. According to the experience in previous construction, the maximum torque received by the drill pipe should be selected by twice the maximum estimated torque (the calculation formula of the maximum estimated torque can be referred to the relevant technical documents);

② The drill pipe entering the site should be tested and used according to the "Drill Pipe Classification Inspection Method" (SY/T5824), and the first-grade drill pipe should be used for projects with greater schedule risk;

③ A drill pipe management file should be established to record the use of each drill pipe throughout the process, and the use process should be changed to make the life of each drill pipe uniform;

(4) The stress analysis and life evaluation of drill pipe should be carried out by finite element simulation analysis in directional drilling projects with high schedule risk;

⑤ Two to three thickened drill rods should be set before and after the reamer for the transition between the drill rod and the drill collar.

3. For the problem of excessive deviation of the guide hole, strengthen the deviation control of the guide hole. The deviation between the actual curve of the guide hole and the design curve should not be greater than 1% of the crossing length, and the deviation should comply with relevant regulations; After the construction of the guide hole is completed, the supervisor or the owner must carry out the acceptance, and the reaming can only be carried out after the acceptance is qualified.

4. For the problem of unreasonable reaming classification, scientific reaming classification is carried out. The construction supervisor and the owner shall urge the construction unit to reasonably grade, for the diameter of more than 400mm pipe, reaming should be graded, multiple reaming, according to the drill rig, mud system, drill pipe specifications, geological conditions, etc., to determine the reaming stage difference. Under normal circumstances, the first stage of reaming diameter 20 "~ 24", and then according to 4 "~ 10" for hierarchical reaming.

5. Regarding the unsatisfactory geological conditions and other issues, close monitoring of the reaming process is required. During the reaming process, the changes of various parameters should be closely tracked and analyzed. If the torque and tension are found to be too large, it is advisable to carry out hole washing in time, and then continue reaming after the hole washing is finished. Holes should be washed at least once after each reaming of directional drilling for rock geological breakage.

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