BORE-HOLE INVESTIGATIONS 



1097 



tive to that element in whatever form or state of combination, or lack of it, 

 it may occur. Also it may be noted that in neutron well-logging use is 

 made of the release of the pent-up nuclear energy of the atoms of common 

 elements. The energy received by the detector in a neutron well-logging 

 instrument is released by the destruction of a small quantity of matter 

 when the neutrons coalesce with a nucleus of the rock substance. The 

 neutron curve is thus a practical modern use in the petroleum industry of 

 the principle set forth by Einstein, that matter may be converted into 

 energy. 



Instrumentation 



A typical radioactivity well-logging apparatus consists of the logging instrument, 

 a hoist truck carrying the well cable and hoisting mechanism, and an instrument truck 

 containing the electrical amplifying and recording equipment, as illustrated in Figure 

 666. 



-{CABLE HEAD] 



MAGNETIC 

 CASING COLLAR 

 LOCATOR 



! ELECTROMETER 

 JAND BATTERY 

 ISECTION 



lUINI^AI lUNI 



''gHAMBER_f 



Fig. 685. — (Left) Gamma-ray and (center) neutron logging instruments. (Right) gamma-ray 

 instrument emerging from well. A, cable head; B, magnetic casing collar locator; C, electrometer 

 and battery section; D, ionization chamber; E, water stream for washing mud from cable and instru- 

 ment. (Courtesy of Lane-Wells Company.) 



The subsurface instrument is illustrated in Figure 685, and contains a detector, 

 which continuously measures the radiation intensity as the instrument traverses the 

 well-bore, an electrometer, which converts the weak electrical signals supplied by the 



