18 L. J. PETERS AND J. BARDEEN 
be described. The method of survey used was the Sundberg method,‘ which 
will be briefly described. 
The primary field is the field of a long horizontal wire carrying an alternat- 
ing current with a frequency of 100 to 500 cycles. Measurements of the direc- 
tion and time phase of the magnetic intensity vector are made at a series of 
points along transverse lines. These measurements are made by means of a 
search coil connected to a compensating arrangement. 
— PROFILE LINE T 
SCALE 
ELECTRICAL INDICATION, STRONG 
--- " " » WEAK 
e OIL WELL 
Te 
© 2000 4000 6000 6000 

Fig. 10. Fault traced by electrical methods where only one well was drilled in the field. 
The induced currents are assumed to be confined to a series of beds which 
have a much higher conductivity than the surrounding beds. Each of these 
beds is characterized by a certain induction factor p which depends on its 
conductivity and thickness, and also on the frequency of the exciting current. 
From the measurements made at the surface, the induction factors and the 
“T. Zuschlag, Tech. Pub. No. 313 Inst. of Min. and Met. Eng. 
162 
