SP 



RESISTIVITY 



INDUCTION 

 LOG 



MICROLOG 



BIT SIZE! 9 7/8" 



R m at BHT: 0.2 

 Figure 14-16. Example of induction log. 



of 4.2 is reached. Similar observations apply to the other sands. The induction 

 log readings are systematically lower than the readings made with the long 

 normal, essentially because of the effect of bed thickness and also of invasion. 



The effect of invasion can be discriminated over a thick interval like A 

 (28 feet) where the presence of the adjacent formations has little effect on the 

 normal readings. Here the short normal attains a minimum value of 2 ohms 

 and the long normal 1 ohm; the effect of invasion is the smallest on the induction 

 log, which reads down to 0.66. As for the lateral, the readings are disturbed 

 by two resistive beds immediately above and within section A. 



Conclusions 



Induction logging seems to be the most proper method for the investigation 

 of true formation resistivities, particularly in thin beds, in wells drilled with 

 comparatively fresh muds. 



It is now used more and more extensively in those regions where the 

 reservoir formations have a high or medium porosity. Its combination with 



305 



