BORE-HOLE INVESTIGATIONS 



1065 



and of the drill hole opposite the cement, is at a maximum between twelve 

 and forty-eight hours after cementation, depending on the conditions and 

 the nature of the cement. Consequently, it is only necessary to make one 

 or more continuous temperature surveys 

 during this period. The portions of the 

 hole showing abnormally high tempera- 

 tures, as compared to the normal curve, 

 indicate the position of the cement behind 

 the casing. (It is desirable to avoid any 

 circulation immediately prior to the survey 

 in order that the thermal conditions pro- 

 duced by the setting of the cement will not 

 be disturbed.) 



The temperature log is recorded photo- 

 graphically on film, usually at the same 

 scale value employed for the electrical log. 

 The log extends from a point well above 

 the expected cement top. Above the cement 

 the temperature will generally increase 

 gently, with small anomalies due to the 

 heat characteristics of different forma- 

 tions. When the cement top is reached 

 there is ordinarily a very marked increase 



in the temperature, and the temperature anomalies due to the formations 

 behind the cement are greatly exaggerated (Figure 659). 



no izo 

 TEMP.— "I 



MO /so 



Fig. 658. ■ — • Temperature curve after 

 thermal equilibrium has been reached. 

 (Note change in slope at about 2300 

 feet.) 



Fig. 659. — ^Temperature log, showing top of cemented zone. 



Cement top indications are usually quite definite and can generally be 

 pointed out as soon as the photographic record of the survey has been 

 developed. 



