a drilling method that uses a turbodrill. An efficient solution to the problem of turbodrilling was obtained with the use of the multistage turbodrill at a drilling speed of 600–800 rpm. Within this range of drilling speeds, the conical toothed choppers of the bit, under axial loads of up to 1–1.5 tons percentimeter of the bit diameter, effectively fragment the rock while rolling over the bottom of the borehole; as a result, the bottom hole is deepened. Since the early 1950’s, turbodrilling has been the principal method of drilling in the USSR; as of 1975, it accounted for 70–80 percent of the oil-and gas-well drilling in terms of total depth.
The development of the method of directional turbodrilling made it possible to drill inclined wells at the same rates as vertical wells. Directional turbodrilling became of great economic importance in multiple drilling in Western Siberia and from offshore platforms in the Caspian Sea. In order to increase the wear resistance of the chopper bits, turbodrilling is performed at 300–400 rpm; in particularly deep wells the drilling speed is 150–250 rpm. High-speed turbodrills are used mainly in drilling with diamond bits.
The use of turbodrills with an inclined pressure line makes it possible to control the drilling speed at the bottom of the borehole and to optimize the drilling conditions. The maximum drilling rates for turbodrilling in soft rocks are 40–50 m/hour.
Turbodrilling is used in rocks of any toughness (hardness) both in production drilling and in exploratory drilling. The maximum well depth reached in turbodrilling is 7,500 m.
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R. A. IOANNESIAN