-w 



Figure 29-5. A dull bit showing excessive tooth breakage. 



bit has been run too long. The solution to this problem is to reduce the rotating 

 hours, or to change to a bit type having more hardfacing at the gage. When 

 such wear occurs on a soft or medium-soft-formation bit, one should not im- 

 mediately decide to use a hard-formation bit with maximum gage protection 

 because such a decision may result in uneconomical drilling costs. The extent 

 of the gage wear, condition of inner-row teeth, and length of rotating hours may 

 indicate that only slightly more gage protection is needed, and it might be found 

 advantageous to select a medium-hard-formation bit. 



Figure 29-4 shows the results of extreme gage wear. Note that wear has 

 progressed to a point where the roller bearings have been lost. This bit was run 

 much too long in a hard, abrasive formation. A bit in this condition indicates 

 that a portion of the hole drilled was not economical since some of the hole 



645 



