inside of the core barrel through a port in the side of the barrel. The cutter 

 head and inner core-barrel section is connected to the top of the core barrel 

 through universal joints that rotate the cutter head even though it is deflected 

 out through the window. A hose conducts the mud flow through the joints to 

 the lower section. The inner core barrel in the lower section is equipped with 

 the usual vent valve and core catcher. 



Preparatory to taking a core with this equipment, the bottom-hole assembly 

 is to run into the hole to a point below the deepest coring point. A dummy 

 barrel containing a wash nozzle is latched in place to keep trash out of the 

 assembly during the run. The dummy is retrieved after the body has been 

 washed clean. At this point, the minimum pressure for minimum circulation is 

 determined. After the bottom-hole assembly is positioned at the proper point, 

 the drill string is suspended in the slips, where it remains until coring is com- 

 pleted. A circulating head is attached to the drill stem because circulation must 

 be maintained while rotating. The core barrel is pumped down and, when 

 seated, rotation is started with minimum circulation. After a short run-in, coring 

 is carried on at a speed of 18 to 25 revolutions per minute, and enough circu- 

 lation is provided to maintain mud pressure at 200 to 250 pounds per square 

 inch above the minimum pressure. This hydraulic pressure drop through the 

 core barrel results in an axial load that supplies the force to feed the cutter head 

 into the formation. The core is cut from the wall at an angle of 20 degrees to 

 the main bore. When the barrel is fully extended, the circulation port in the 

 core barrel passes through the seal, by-passing the mud flow. The resulting 

 drop in pressure indicates the completion of coring, and circulation should be 

 stopped immediately. When the core barrel is retrieved by the overshot, the 

 core catcher breaks and holds the core. A resettable jar in the overshot permits 

 repeated jarring of the core barrel if it should be difficult to pull out of the 

 formation. 



This tool is equipped with several safety features. If the core barrel cannot 

 be pulled out of the formation, the overshot can be released and the barrel 

 extracted by raising the drill stem. The deflector plate will shear a pin and pivot 

 to make space for the core barrel. If the whipstock sticks in the hole, the 

 drillable fluted shoe can be sheared off, or a heavy tension can be applied to 

 the string to shear a pin in the swivel, allowing dogs in the rotating section to 

 mesh with the whipstock so it can be positively rotated. If it becomes neces- 

 sary to increase circulation while coring, a momentary application of high mud 

 pressure will shear a pin in the barrel and open an additional fluid port, which 

 will permit increased circulation at the same pressure. 



This tool can drill a relatively large core, I14 inches in diameter by 12 inches 

 long, in any type of formation. Cores can be taken at any selected level during 

 one round trip of the drill stem. This unit is used successfully all over the 

 world, but it is slower and more expensive than some other coring methods. 



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