__ insulated Cable — __ 



:E lectrodes 



— —Steel Springs 



Rubber pad 



Electrodes 



Figure 14-13. Schematic micrologging device. 



the wall of the drill hole. The pad reduces the short-circuiting action of the 

 mud, and the electrodes measure the average resistivity of a small volume of 

 material at the face of the borehole (fig. 14-13). 



Two resistivity measurements are made by sending a current of known 

 intensity through elecrode A and recording the potential difference created, 



294 



