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RADIOACTIVITY 

 WELL LOGGING 



Gilbert Swift 



and 



Arthur Youmans 



Radioactivity well logging makes use of naturally occurring and induced 

 nuclear radiations to obtain useful information regarding the formations 

 penetrated by the borehole. Various types of radioactivity curves are now 

 available commercially, and additional new curves are being offered experi- 

 mentally. Those which have received most wide-spread acceptance and appear 

 to be of the greatest utility include primarily the gamma-ray and neutron 

 curves, the Densilog, and the input-profile tracer log. 



GAMMA-RAY AND The gamma-ray curve is obtained by passing 



NEUTRON LOGGING a gamma-ray detector along the well, while 



continuously recording its indications in cor- 

 relation with depth. The resulting graph shows the relative concentration of 

 natural gamma ray emitting radioactive elements in the strata traversed. With 

 few exceptions all rocks contain small but measurable amounts of these elements, 

 and in most cases a detectable increase or decrease of radioactive intensity 



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