832 



GEOPHYSICAL WELL TESTING 



[Chap. 11 



that the factor in eq. (10-2) is about 17 instead of 11.6 for the contact of 

 clay and sihceous sand. Hence, in an experiment where p2 was 24 ohm-m 

 and pi varied from 17 to 0.04 ohm-m, the potentials varied from 2.5 to 46 



POROSITY 

 30 *10 o .10 .20 



Fig. 11-5. Variation of self-potential effects in drill holes (electrofiltration phe- 

 nomenon) with pressure of mud column, in Grozny field (after Schlumberger). 



millivolts.^ Fig. 11-7 shows results of some trials made with drilling muds 

 of three different resistivities. 



s C. and M. Schlumberger and E. G. Leonardon, A.I.M.E. Geophys. Pros., 278 

 (1934). 



