866 



GEOPHYSICAL WELL TESTING 



[Chap. 11 



r^ 



5 oft Iron 

 5hield 



deviation from vertical and the azimuth of deviation. For this purpose, 

 an earth inductor with vertical axis of rotation has been applied. As in 

 the earth inductor compass, the e.m.f. induced in the coil depends on the 

 orientation of the brushes, and, therefore, on the orientation of the appa- 

 ratus with respect to the magnetic meridian. By suspending a pendulum 

 (which can be magnetized at will from the surface) in a universal joint 



vertically above the coil, an e.m.f. 

 is produced when the apparatus 

 (and the hole) is not vertical. An 

 accuracy of 0.5° is claimed.^ This 

 apparatus can naturally be used 

 only in an open hole. 



It appears possible that earth- 

 inductor measurements can be used 

 to determine the magnetization of 

 subsurface formations in open hole. 



C. Acoustic Measurements 



Water flows in deey wells and gases 

 escaping from formations, or from 

 behind the casing, may be detected 

 by acoustic measurements. Geo- 

 phones of high frequency (about 

 1000 cycles) are lowered into the 

 well in the same manner as are 

 seismic detectors. 



In shallow holes (maximum of 

 several feet) acoustic measurements 

 are applied in the location of leaks in 

 water pipes under pavement, side- 

 walks, and the like. A rod provided 

 with a directional vibration pickup 

 may be lowered into the hole so that 

 (since the approximate course of a 

 buried pipe is generally known) the longitudinal component in the direction 

 of the pipe, as well as the transverse component of vibration produced by a 

 leak, may be measured.^ Since the transverse component is much more 



■Micrometer 



Astatic 

 -l^k-^ dystem 

 I 

 I ^^ dumper 



Specimen 



Fig. 11-35. Magnetic core orientation 

 apparatus (after Roberts and Webb). 



" See Chapter 8, section iii c, p. 363. 



" C. and M. Schlumberger and E. G. Leonardon, A.I.M.E. Geophys. Pros., 269, 

 (1934). 



" Known as vibration differentiation method, Western Instrument Company (see 

 also p. 962). 



