apparent that the failure to indicate improved performance was a result of in- 

 adequate jet-nozzle velocities. In 1948, the Humble Oil Company began an 

 extensive experimental program in an effort to determine the hydraulic require- 

 ments of the jet bit. From these investigations it was concluded that jet velocities 

 in the order of four times those of conventional bits were desirable. Other factors 

 had to be considered, however, because the premium price of jet bits and in- 

 creased operating and maintenance costs had to be offset by the increase of 

 apparent that the failure to indicate improved performance was a result of in- 

 adequate jet-nozzle velocities. In 1948, the Humble Oil Company began an 

 extensive experimental program in an effort to determine the hydraulic require- 



Figure 30-3. Cross-section jet rock bit 

 (courtesy Reed Roller Bit Com- 

 pany) . 



Figure 30-4. Jet drag bit (courtesy 

 Reed Roller Bit Company) . 



penetration rates obtained with jet rock bits. The tests were difficult to evaluate 

 because very few rigs then operating were equipped with sufficient power and 

 pump capacity to meet the hydraulic requirements. Those rigs that were proper- 

 ly equipped were concentrated in the West Texas and Gulf Coast areas. 



Gradually more emphasis was placed on drilling-rig requirements: rotary 

 speed, drill collars, horsepower, and pump size. At the present stage of develop- 

 ment, it is diffcult to determine how much improvement was gained from the 

 use of jet bits and how much was gained by improved engineering application 

 of the known principles. Penetration rates by conventional rock bits have im- 



655 



