Miscellaneous Subsurface Methods 

 Soft to Medium-Soft Formation Bits 



653 



Weight Applied 



In drilling top-hole shales, unconsolidated and broken formations 

 of shale, gypsum, salt, chalk, medium-soft anhydrite, and the like, the 



Figure 348. Hughes type W7R tricone bit and pattern it generates while drilling on 

 bottom. Note that circumferential gage cutting teeth prevent relatively coarse- 

 pitch rock teeth from joining waU, and that resulting rock teeth are more easily 

 removed. The fine-pitch rock teeth generated by inner rows of cutter teeth are 

 readily removed during rotation of bit. 



