4-1/2" DRILL PIPE 

 1-6" DRILL COLLAR 



DRILL COLLARS 



8 



DRILL COLLARS 



Figure 35-3. Relation of drill string and hole. 



pipe mechanics. Proper drill-pipe mechanics will avoid abrupt changes in hole 

 direction. If points are discovered where wall cuts are developing, reamers 

 should be occasionally spotted in the drilling string to prevent their being cut 

 so narrow that they will be wiped out on trips. Wiped-out wall cuts usually 

 produce hole enlargements that reduce the effciency of the drilling fluid to carry 

 cuttings past these points. 



Vertical Hole 



Drilling an absolutely vertical hole is practically impossible and would be 

 dynamically unstable. Most holes will be inclined a degree or more from the 

 vertical and usually will spiral in a clockwise direction towards the bottom. 

 When the drilling-string mechanics are in proper adjustment (fig. 35-3) the 

 drilling string will touch the lower side of the wall a few feet above the bit 



729 



