Difficulties and Technical Countermeasures for Automatic Vertical Drilling in Ultra-Deep Wells in the Bozi Block of the Tarim Basin

The Bozi Block of the Tarim Basin belongs to a typical piedmont high steep structure that has a large dip angle and strong natural deviation capacity, which is difficult for deviation-prevention straight drilling. It is hard to ensure the hole deviation control effect by using conventional deviation-prevention straight drilling technology. This paper analyzes difficulties in the application of automatic vertical drilling technology in ultra deep wells of the Bozi Block. In view of the strong downhole vibration and the difficulty in deviation prevention during straight drilling in the upper conglomerate formation of Bozi Block, research on deviation-prevention technology was carried out on a number of different aspects. They included damping optimization, ultra deep well signal transmission, the optimization of deviation-prevention straight drilling process, etc. The automatic vertical drilling system was applied in the spud in sections of 198–417 m and 565–1 000 m in Well BZ1501. The cumulative working time of two trips was 281 h, the average ROP was 2.43 m/h, and the hole deviation was 0.2°. Compared with the conventional pendulum drilling string used in this well and the automatic vertical drilling system in Well BZ18, the system had the advantages of long service life, high ROP and good deviation control effect. The field application demonstrated that the deviation-prevention straight drilling technology could be successfully implemented for ROP enhancement in the ultra deep wells of the Bozi Block in the Tarim Basin, and its application could be popularized in the block.