SCHEMATIC CROSS SECTION 



OF A PERMEABLE BED 



80UN0ED BY 



IMPERVIOUS FORMATIONS 



® 



RADIAL 



DISTRIBUTION 



OF RESISTIVITIES 



Water Bearing 



Formation R *o : F Rr " f - 



Distance from the a<is 



d = hole diameter 

 Di = E lectr icolly equivalent dio- 

 meter of invaded zone 

 e ; bed t hickness 



R m ■ mud resistivity 

 Rmc = mud cake resistivity 

 R«o : 'lushed zone resistivity 



R| = uncontaminated zone 

 ( true resistivity ) 



"s = resistivity of odiacent 

 impervious formation 



Figure 14-5. Schematic diagrams involving mud filtration. 



mud (/?,„)• The difference may be appreciably greater in some oil-emulsion 

 muds. 



Flushed Zone: Resistivity R^, o 



Behind and close to the wall of the hole, it is believed that the interstitial 

 water which originally existed in the pores has been flushed entirely by the mud 



274 



