8. Clean hole: Lifting capacity of the drilling fluid is improved by the 

 higher annular-velocity characteristics of turbodrilling. The cuttings are smaller 

 because of the higher bit speed and can be carried out more efficiently. 



9. Multiple operation: Several turbodrills can be coupled together in series 

 to afford a reduction in flow rate and bit speed as the hole deepens, without 

 sacrificing turbine-power output. Often the power may be increased. This 

 flexibility in turbodrill operation provides a more effective relationship between 

 torque, bit speed, and drilling weight to satisfy most drilling conditions that may 

 occur, except perhaps in some soft formations. 



10. Better directional drilling: Accurately controlled directional drilling 

 is possible by the use of new turbodrill techniques, that do not require whip- 

 stocks. 



11. Less maintenance: Swivel and rotary -table maintenance can be mini- 

 mized because the pipe is turned only occasionally to free cuttings around the 

 drill string, and to obtain accurate weight indications. 



DISADVANTAGES OF As with any drilling system, turbodrilling has 



TURBODRILLING its disadvantages. 



1. Viscous-mud problem: If drilling conditions require an extremely vis- 

 cous mud, the turbodrill should not be used because of the excessive pump 

 pressures required. 



2. Bit performance: Although the turbodrill increases the penetration rate 

 of our present-day drilling bits to a remarkable extent, it should be possible 

 with better bit design to extend the bit life considerably. The development of 

 bits especially designed for turbodrilling is now being undertaken by Security 

 Engineering Division in the United States, Security Rock Bits, Ltd., in England, 

 and by other companies. 



3. Soft-formation drilling: Because the turbodrill rotates between 600 

 and 800 revolutions per minute, some formations now drilled by rotary at bit 

 speeds of 50 to 70 revolutions per minute may not respond as well to the turbo- 

 drill. Turbodrilling in soft, sticky formations in the Gulf Coast area, for example, 

 may not equal or keep pace with certain rotary techniques now used with jet 

 bits. However, the final answer cannot be obtained until there is more turbo- 

 drilling experience in America. 



ECONOMIES OF Although actual experience with the turbodrill 



TURBINE DRILLING in America is limited, authenticated reports 



from Russia indicate some evaluation of the 

 turbodrill. In the Bashkir oil field between Bugulma and Tuymazy in the Tartar 

 Republic, 170 drilling rigs were running in late 1956, all using the turbodrill. 



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