Performance characteristics of a 10-inch turbodrill show that maximum 

 power and maximum turbine efficiency are reached at a shaft speed of about 

 600 revolutions per minute, which is half the idling speed of 1200 revolutions 

 per minute. The torque drops to zero at the idling speed. At the other extreme, 

 if the turbine becomes stalled, the torque is twice that developed at 600 revolu- 

 tions per minute. This fixed maximum torque at stall is automatic protection 

 against overloading of the pipe in deep holes. 



TURBINE DRILLING The technique of turbine drilling is relatively 



PROCEDURES new to the American petroleum industry. 



When more experience is gained, new methods 

 and new techniques will be developed. As a greater number of drilling crews 

 become familiar with the operation of this tool, more precise methods of opera- 

 tion will be established. In general, it has been found that good rotary drilling 

 practice is also good turbodrilling practice. 



The first step in running a turbodrill, before running it in the hole, is to 

 verify that it will start easily with low pump pressure. Then, with the pumps 

 still operating at low pressure, the drill is lowered until it is a few feet off 

 bottom. Full pressure is then applied to the turbodrill to redrill the last few 

 feet of hole in order to avoid damaging the turbine by a return of cuttings 

 inside the unit while it is still being lowered to bottom. When it is on bottom, 

 the weight on the bit is gradually increased until the maximum power of the 

 turbine is developed and the maximum rate of penetration of the formation 

 is obtained. Before coming out of the hole, the turbodrill should be operated off 

 bottom for a few moments to make sure that the hole has been thoroughly cleaned. 



The following basic requirements may eventually be standard practice in 

 outfitting a rig to an 8-inch- or 10-inch-diameter turbodrill: 



1. A spare turbodrill should be provided for each rig to permit maintenance 

 and continuity of drilling. 



2. Pumping facilities are required to deliver approximately 800 to 1000 

 gallons per minute at sufficient pressure to satisfy the 600 to 1000 pounds per 

 square inch additional pressure drop across the turbine. Rigs with pumps for 

 jet bits may already have sufficiently high pumping capacity. 



3. Effective pulsation dampeners should probably be used, particularly 

 with mud pumps operating in parallel. Dampeners help to smooth the hydraulic 

 loading on the turbine's thrust bearing, as well as the operation of the bit. 



4. The drill pipe should be of a slightly larger diameter than is normally 

 used with rotary. The larger pipe will help to reduce the pumping pressure and 

 the power lost in friction. Tool joints should also be designed with a larger 

 bore to cut down flow resistance. Dual or larger diameter stand pipe, and per- 

 haps dual mud hoses may be recommended to provide a double connection into 



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