404 



Subsurface Geologic Methods 



have been introduced, however, to compensate for the high resistance to 

 ground of the small electrodes. 



Interpretation of Micrologs 



A discussion of the interpretation of the micrologs will be aided by 

 placing the different cases usually encountered in practice into categories; 



R^ (off scale) 



Apparent 

 Resistivities 



MicroLog 



75 R, 



I Rj^ Specific resistivity" of the 

 ground at distance "x" 



ii 



Rj( Very high (off scale) 

 except in mud film 



50 Rr 



25R, 



Rfii 



I, R^ Mud film 



2 f 1x1 



Figure 180. Impervious formation of high resistivity with a mud film of 1/64-inch 



thickness. 



Apparent 

 Resistivities 



MicroLog 



2° I" l"xl" 



6" 



12" 



Distances from pod 

 Figure 181. Impervious bed of low-resistivity shale (category I3), 



