834 



GEOPHYSICAL WELL TESTING 



[Chap. 11 



C. Determination of Resistivity of Drilling Mud 



The resistivity of the drilling fluid is determined with closely spaced 

 electrodes. Its practical importance lies in the location of water flows. 

 To this end, the hole is first conditioned by washing with fresh-water mud, 

 and the first run indicated in Fig. 11-8 is taken immediately afterward. 

 The level of the mud is then lowered, allowing formation water to pene- 

 trate the hole. Another run (second curve in Fig. 11-8) is taken, which 

 indicates the portion of the hole filled with (low-resistivity) formation 

 water. 



Ohm - m 



0,5 I 



1.5 



1080 

 IIOOH 



1160 



Fig. 11-8. Location of water 

 flow by measuring resistivities of 

 drilling mud (after Schlum- 

 berger) . 



Fig. 11-9. Electrode arrangement for 

 measuring dip and strike in wells (after 

 (Schlumberger) . 



D. Measurement of Dip anu Strike 



Since in stratified formations the conductivity in the beddmg planes is 

 greater than at right angles thereto, the equipotential surfaces about a 

 source are not spheres but elUpsoids of revolution. These ellipsoids are 

 tilted when the strata dip. If an electrode configuration, as illustrated in 

 Fig. 11-9, is lowered into the hole with a rigid rotatable connection between 



