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Accident and treatment of pilot hole drilling in frozen stratum during reverse well drilling rig construction

Source: xe1x.com Author: admin Date: 2018-07-24 14:46 heat:
Inverter drilling rig construction in frozen formation pilot hole drilling accidents and handling pilot hole drilling in accordance with the construction organization design and reverse well drilling technology requirements, and mud performance control is better, the drilling work is smooth. But after reaching a depth of 160m through the freezing section, an abnormality suddenly occurred:
① The pressure of the mud pump suddenly increased, so that the safety valve was ejected many times, and the mud pump belt slipped or even broken;
② The mud in the hole becomes thinner and the viscosity decreases. After the drilling is stopped and a stream of water returns to the hole, the pump is circulated to make the mud in the hole return unevenly. Difficulty in decentralization;
④ In the end, a lot of rock particles blocked the hole and had to lift the drill.
After the drilling tool was raised, it was found that the inner holes of the three drill pipes were blocked by slag. At first it was thought that the belt was damaged due to the mud pump and the slag was not discharged in time. Therefore, the belt was replaced and the drill was re-drilled. The above phenomenon occurred again at 55 ~ 60m. After repeated punching, the drilling tool was lowered to 160m. After drilling 10m, the hole blocked again, and it was more serious than the first time. The amount of slag discharged from the hole far exceeded the amount that should be discharged. Therefore, the drill was lowered again. Tools, but can only be lowered to 55-60m.
The borehole data is compared with the geological histogram of the wellbore and the geological data of the main and wind wells that have been dug. After repeated analysis and discussion, it is determined that the source of the collapsed hole is a muddy cemented gravel layer in the section of 55-60m. The return of confined water in the lower non-frozen section caused the temperature of the circulating mud to rise, which caused the local thawing of the formation. The physical and mechanical properties of the gravel layer after thawing changed greatly, and the block structure became scattered. The confined water also caused The mud becomes thinner, and the solid wall performance is reduced, resulting in hole collapse.
Due to the lack of experience in drilling in frozen formations for the first time, the hole collapse treatment adopted the ordinary hole drilling and hole collapse treatment methods: such as the use of cement slurry to fill holes, ordinary scraper bit sweeping and other measures, have not achieved results; also adopted We have not strengthened the freezing method. Finally, a thick slurry was used for forcibly drilling, and finally the pilot hole was opened.
Keywords: Reverse rig construction
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