&utftte*22 



MAGNETIC WELL 

 LOGGING 



R. A. Broding 



Magnetic well-logging methods were first devised as an aid to the explora- 

 tion geophysicist for control in interpretation of surface and airborne magne- 

 tometer surveys. Because of the limited magnetic surveying now being done, this 

 logging method has not been widely used. However, during this development 

 other uses for the log have been suggested. The following review of the present 

 state of magnetic well logging is presented to show some of the applications in 

 which magnetic logs have been used, with the anticipation that their application 

 to the solution of unique logging problems will stimulate their use. Much of 

 the data used in preparing this chapter were furnished the author through the 

 courtesy of the Magnolia Petroleum Company. 



The magnetic properties of rock can best be measured and evaluated from 

 magnetic susceptibility and total field measurements. Magnetic susceptibility 

 is a measure of the ability of rock to be magnetized and is considered to be the 

 most significant magnetic property. It is measured by applying an external 

 magnetizing field, H, to the rock and then detecting the field resulting from the 



induced pole strength or intensity of magnetization, I. The expression k = ^ 



relates k, the magnetic susceptibility to I and H. Because the detector measures 

 the magnetic field, it is desirable in instrumentation to make use of an alternating 



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