grinding action even if the optimum drilling-string mechanics are in use. The 

 more rapidly cuttings and cavings are removed from the bore hole, the less 

 they will be broken down by the grinding action of the drilling string. As long 

 as the flow properties of the drilling fluid remain unchanged, increasing the 

 annular velocity will remove the cuttings and cavings from the hole more rapidly. 

 This rapid removal will assure maximum cutting recovery and minimum drilling- 

 fluid maintenance costs. 



Wall Cutting 



Wall cuts will occur frequently in wells in removing drilling pipe and bits 

 from the hole. If these wall cuts wear deeper than the radius of the drill pipe, 

 they will be wiped out on trips (fig. 35-2). This wiping out will dump large 

 quantities of shale into the drilling mud and thereby confuse interpretation of 

 cutting samples. Wall cuts can be minimized by paying strict attention to drill- 



WALL CUT- 



■WALL CUT 



WIPED OUT 

 "WALL CUT 



BRIDGE 



WIPED OUT 

 WALL CUT " 



FILL ON 

 BOTTOM 



Figure 35-2. Wall cuts in a drill hole. 



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