34 



METHODS OF GEOPHYSICAL EXPLORATION 



[Chap. 2 



Chemical and physical processes responsible for changes of the normal 

 temperature gradient are: the transformation of anhydrite to gypsum; 

 the oxidation of sulfides; the influx of water, oil, and gas into the hole; 

 and the heat developed by the setting of cement behind the well casing. 



Grounded y \ 

 Current Terminal \ 



' to ohm m 



Petisf 



Recording 

 Potenfiomehr 



f.'J/Ks'J''\WH K\Wf\,K\i/A.VI//^ 



\ eMneaJ 

 Lofs 



Fig. 2-15. Electrical logging arrangement (schematic). 



It is clear, therefore, that temperature measurements in wells will furnish 

 valuable information in connection with the location of oil, gas, and water- 

 bearing strata, cementation problems, and so on. Correlation of tem- 

 perature curves obtained in a series of wells will give valuable clues to 

 geologic structure. 



