684 



Subsurface Geologic Methods 



(4) to determine the size of pipe in the hole, (5) to gain information for 

 setting liners, (6) to locate casing seats, and (7) to aid in calculating 

 cement volumes before setting pipe in open holes. 



Water-Locating Surveys 



The accurate location of points of water entry into a well bore is val- 

 uable in the planning of reconditioning or work-over programs and is 

 the first step in remedial operations to halt intrusion of the waters. The 

 water-locating survey is one of the several services that employ the electric- 

 pilot unit. For water-locating work the unit is used in conjunction with 

 an electrode consisting of two dissimilar metals, which, when immersed 



36Q0 



36IQ 



262SL 



364Q 



3650 



40 80 120 



METER READINGS 



160 



200 



Figure 370. Chart of a typical water-locating survey. 



in electrolyte solution, act as a primary cell, generating electrical current. 

 This current, generated at the electrode, is measured at the surface, the 

 meters being capable of detecting very slight voltage fluctuations at the 

 electrode. 



In operation it is necessary to condition water in the well with a 

 solution of electrolyte prior to conducting the survey. Then, as the survey 

 is made, any local weakening of concentration of the electrolyte caused 

 by infiltrating formation waters is immediately detected by a voltage 

 drop at the electrode as it reaches that point. After the survey the meter 

 readings plotted against depth indicate points where water is entering the 



