Percussion Side- Wall Coring Tool 



Another important method of securing side-wall samples is the percussion 

 or explosive-charge side-wall coring tool. A close-section view of this type of 

 side-wall sample-taker is shown in Figure 33-7. Hollow bullets fit into short gun 

 barrels in the body of the tool and are driven into the formation by powder 

 charges. The cutting edge on the front of the bullet is designed to permit pene- 

 tration of hard formations without shattering the core. When a bullet has been 

 fired, cables anchored to the body pull the bullet and its core from the forma- 

 tion when the tool is raised. The projectile then hangs at the end of its cable 

 out of the way of the other charges. The tool contains up to 30 shots that can 

 be fired in sequence from the surface. The electric circuit that fires the charges 

 is equipped with devices that determine whether a misfire has occurred. The 



BULLET 



RETRIEVING 

 CABLE 



GUN BARREL 



BODY OF TOOL 



Figure 33-7. Sidewall sample-taker (Courtesy Schlumberger Well Surveying Company). 



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