612 



Subsurface Geologic Methods 



essity of pulling the drill pipe from the hole after each core has been 

 cut, to recover the core. 



Diamond Coring 



Diamond-coring equipment has been used in the mining industry for 

 many years to core small-diameter holes. In the past few years experi- 



FiGURE 316. Four designs of diamond-core heads. 



mental work with full-size diamond bits and core bits in the oil industry 

 has led to the adoption of diamond coring for oil-field use in some cases. 

 Experience indicated in general that the largest-diameter core that could 

 be cut in a given-size hole gave a maximum penetration rate at a minimum 

 cost. Usually no additional surface drilling equipment is necessary to do 

 diamond coring. The core barrel, shown in figure 315, is a two-tube as- 

 sembly similar to the conventional barrels used in the conventional-coring 



