554 



Subsurface Geologic Methods 



barrel lands on the bridger. The different barrel tops are interchangeable 

 so that the instrument may be run by removing the kelly and lowering 

 the instrument into the drill pipe. The barrel is withdrawn after the 

 reading has been taken, the kelly is screwed on, and drilling is resumed. 

 If it is necessary to come out of the hole to change bits, the featherhead 

 may be screwed onto the barrel, and the instrument dropped into the 

 drill pipe. When the bit and bridger are removed, the barrel is slid out 

 of the drill collar. Standard barrels are If inches- in diameter but a 

 smaller If-inch barrel may be used. When the larger barrel is used, the 

 seven-eighths-inch-diameter instrument is screwed into an inner barrel to 



Figure 276. Type "W" drift indicator and supplies. 



compensate for the larger bore of the If-inch barrel. The smallest sizes 

 of drill pipe in which each barrel is used are shown below. 



Barrel 



diameter 



1%' 



1%' 



Internal flush 



2%" or larger 

 2%" or larger 



Drill pipe size 

 full hole 



31/2" or 



larger 

 2%" or 

 larger 



Except Hughes External Flush Acme and Reed External Flush Slim Hole Type. 



Regular 



4" 



31/2" 



External flush 



4" 

 31/2" 



The instrument and all accessories are rented on a daily, monthly, 

 or term-lease basis to drilling companies. They are operated by the well 

 crews. Kit, instrument, and supplies are furnished (fig. 276). Frequent 

 inspection and service calls by trained personnel insure the satisfactory 

 operation of the equipment. 



