Generator 



Meter 



Generator 



Meter 



(a) AMN Lateral (b) MAB Lateral 



Figure 14-10. Schematic lateral device. 



ent on the spacing of the device. When a very short electrode spacing is used, 

 the mud in the hole may have a dominant effect on the value of resistivity ob- 

 tained. If the spacing is increased, the volume of the media appreciably in- 

 fluencing the measurement increases; and the effect of the formations sur- 

 rounding the mud column begins to become important. For large spacings, the 

 resistivity of the surrounding formations becomes dominant. 



For the determination of true formation resistivities, it is useful to record 

 curves having large radii of investigation. This is particularly true in permeable 

 formations which have been deeply invaded by the mud filtrate and which, 

 therefore, have encircling the hole a zone whose resistivity differs from the true 

 resistivity of the formation. 



Electrode Combinations for Well Logging 



The relative positions of the electrodes making up the sonde or exploring 

 device lowered into the hole for the measurement of resistivity have a bearing 

 on its general properties. Depending on the distribution of electrodes, a 



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