Subsurface Logging Methods 



407 



almost entirely controls the microresistivities. Too much importance 

 should, therefore, not be attributed to the absolute values determined for 

 the microresistivities, nor to the amount and type of departure between 

 the two curves. 



The diagnostic is based in this category on the fact that all micro- 

 resistivities are superior to a certain limit Rum which, as said before, can 

 be taken equal to about 20 or 30 times the resistivity of the mud in the 

 average cases. Such high microresistivities on both micrologs could not 

 normally be recorded for a permeable formation. Both the invaded zone 

 of the permeable formation and the mud cake would contribute to lower 



Rni'0.9 of 85* 



Resistivity 



16' NORMAL 



Microlog Permeability In md 



r NORMAL 



Figure 184. Example of microlog. 



