448 



Subsurface Geologic Methods 



higher temperature in the bottom part. Curve 3 of figure 210 represents 

 the temperature of mud about ten hours after circulation and illustrates 

 this point. 



If a temperature record is obtained immediately after circulation, a 

 flat curve resembling curve 2 of figure 210 will result. The same type of 

 curve will be obtained after several days have passed and equilbrium has 



Figure 210. Chart showing temperature gradients. 



been reached. The most pronounced anomalies are obtained 24 to 36 

 hours after circulation has ceased. 



Although from the foregoing discussion one can see that it is possible 

 to distinguish sands from shales, the temperature log will not yet replace 

 the electric log. Factors such as chemical reaction, changes in hole size, 

 the movement of fluids between sands, and the movement of hydrocarbons 

 can alter the temperature in a well. 



Thus far only open-hole-temperature measurements have been con- 

 sidered, but the presence of a string of casing does not disturb the thermic 



