Miscellaneous Subsurface Methods 643 



indicates that a fault cuts the well at approximately 5,814 feet. Dipmeter 

 determinations at 3,088, 4,024 and 4,038 feet show dip values of 37° to 

 60° almost due south. A determination at 5,814 feet gives a due-north dip 

 of 50°, a sharp dip reversal. The reversal may be interpreted as an un- 

 conformity, a fold, or a fault. In view of the information available, it is 

 logical to interpret the reversal as indicating the presence of a thrust 

 fault, the reverse dip occurring in the drag of beds near the fault. Addi- 

 tional dip levels both above and below the fault would have substantiated 

 this interpretation and further localized the fault zone. The apparent 

 thickness of bed A at 7,200 feet is less than at 3,700 feet. Additional dip 

 levels might have shown a lower dip at 7,200 feet. 



Conclusion 



Dipmeter data can be used to aid the solution of many structural 

 and stratigraphic problems. Some of these have been described, others 

 only made obvious — for example the location of potential trap areas. 

 Additional applications will undoubtedly develop. 



DESIGN AND APPLICATION OF ROCK BITS 

 L. L. PAYNE 



The strength of formations encountered in drilling a hole into the 

 earth's crust varies over an extreme range. For instance, the soft, un- 

 consolidated shales and sands of the Cenozoic are relatively easy to drill 

 as compared to the high-strength lime, dolomite, and chert of the Paleo- 

 zoic. The rock bits designed for economical performance in drilling for- 

 mations of the Cenozoic must be altered to provide the types of rock bits 

 developed for the optimum performance in the older, high-strength forma- 

 tions of the Paleozoic. The manner in which the arrangement of the cut- 

 ting teeth and their action on bottom are altered to provide the types of 

 bits available for drilling the various formations encountered is discussed 

 under the basic geometry of the tricone bit and the nomenclature that 

 identifies each type of bit. 



All Hughes tricone rock bits have the same basic geometry; three-cone 

 construction with chisel-tooth arrangement and action on bottom especially 

 designed to drill the multitude of formations encountered efficiently. This 

 basic geometry has several desirable features. The cone-shaped cutters 

 enclose the antifriction bearings and bearing supports, thereby eliminating 

 any portion of the bit head near the bottom of the hole to invite balling up 

 in sticky formations. The interfitting of rows of teeth on the inner conic 

 portion of each cone into grooves on mating cones provides more space 

 which permits the use of deeper teeth and larger bearings without sacrific- 

 ing the strength of the cone body. The interfitting of teeth into grooves pro- 

 vides mechanical cleaning of the teeth and grooves, as the cutters are 



