1088 



EXPLORATION GEOPHYSICS 



lUCTtlCAL SUIVfT 



SICTION SAUCt SUIVtT 



is such that the voltage induced in the pick-up coil varies proportionally with the 

 effective cross-sectional area of the hole. The voltage induced in the pick-up coil is 

 transmitted through the cable to the surface, 

 then rectified into direct current, and re- 

 corded as a log showing diameter versus 

 depth. 



In another type of caliper, a variable 

 resistor is actuated by each finger, and this 

 change is recorded at the surface as a log 

 showing depth versus resistance, i.e., hole- 

 diameter.f 



tuMtnt or Mou 



:^^^ 



i''iG. 679. — Operating principle of the bore-hole 

 section gauge. 



Fig. 680. — Comparison of electrical survey 

 and section gauge survey. 



The Section Gauge Log. — An example of a section gauge log is shown in Figure 

 680, along with the S.P. and the resistivity logs. 



Section logs are generally run on a standard scale, the width of a single film 



t C. P. Parsons, "Caliper Logging," A.I.M.E. Pet. Tech., Vol. 151, 1943. 



