catcher to which several types may be fitted. The barrel extends up through the 

 slush ring in the bit, and on the upper side it has an enlarged diameter. The 

 slush ring prevents the barrel from protruding too far through the bit. At the 

 upper end of the barrel is a spring-valve body or check valve to vent the interior 

 of the core barrel of trapped fluid. This spring-valve body is keyed to the upper 

 part of the slip joint, and the barrel spring is between these parts. The keys 

 transmit the rotary driving power to the lower core barrel but permit the core 

 barrel to move up and down, compressing the spring. This feature which allows 

 the main core barrel to drill ahead of the main bit, cuts the core and encloses 

 it in the barrel before it becomes contaminated or washed away by the drilling 

 fluid. This arrangement is necessary because a smaller core must be cut so that 

 the barrel will pass through the collars and tool joints of the drill pipe. The 

 smaller core is more susceptible to damage than a larger core; therefore its 

 recovery factor becomes even more important than usual. Above the spring- 

 valve body is the carrier body and an assembly containing the latching device. 

 In this device, a retractable latching dog protrudes when the barrel is in position 

 and engages the core-barrel driver, which is mounted in the end of the upper 

 sub. A finger holds the barrel down and forces it to rotate. The retractable 

 latch dog is connected to the spear head. When the barrel is to be removed from 

 the bit, the overshot is run down the pipe to the barrel spear head. Two over- 

 shot dogs latch over the spear head, and when the overshot is raised, the spear 

 head moves up and retracts the dog, thus freeing the barrel and allowing it to 

 be drawn to the surface. 



A variety of core catchers may be fitted to wire-line barrels. The basic type 

 is a spring-ring core catcher with one- or two-length springs that are fairly stiff. 

 For soft sand formations, a multi-leaved, very flexible spring-core catcher is 

 used. This type closes off completely. Either of these types of core catchers 

 may be installed in tandem. For very hard cores a slip-type core catcher is 

 installed. It has long flexible fingers that engage the core. When the barrel is 

 raised, it will slide down the taper on the inside of the cutter head, nip off the 

 core, and hold it firmly for raising to the surface. Various types of the wire- 

 line core bits will cut cores ranging from 1 to 2 3/16 inches in diameter. The 

 size of core is governed by the size of the drill pipe through which the core bar- 

 rel must be dropped. For regular 414 full-hole tool joints, a l^g-inch core is 

 possible. The core barrel will cut cores from 6 to 10 feet in length. If longer 

 cores are desired, the barrel may simply be replaced and coring continued. 



Several points must be watched when this type of equipment is used. The 

 recommended routine for preparing the tool should be followed closely. At 

 least two inner barrels should be adjusted to fit the outer barrel and bit so that 

 time will not be lost in the coring operation. The inner barrels are checked 

 for latching and protrusion after they are dropped into the outer barrel. The 

 protruding end of the barrel is rotated until it latches; then the pro- 



703 



