BORE-HOLE INVESTIGATIONS 



1067 



than the temperatures in the upper portion. In Figure 660, the curve 

 B-B represents the true temperatures of the formations, and C-C the 

 temperatures of the mud immediately after circulation. It will be noted 

 that the curves cross at point A where mud temperature and formation 

 temperature are the same. 



As the mud temperature and formation temperature seek equilibrium, 

 curve C-C rotates about point A, tending to approximate curve B-B. 

 However, certain formations, due to differences in heat capacity, tend to 

 give up or acquire heat from the well mud faster than other formations. 

 Thus, after a given time, a curve D-D is produced which shows deviations 

 from the normal trend at the locations of the sand formations. After a 

 longer time, the temperature curve for the mud approximates curve E-E 

 and finally B-B wherein the anomalies due to the formations have 

 disappeared. 



The operation of this tem- 

 perature method of logging for- 

 mations may be summarized as 

 follows. Use is made of a suit- 

 able mud circulation, following 

 which a number of temperature 

 curves are recorded in order to 

 obtain curves C-C, D-D, and 

 E-E. (Curve B-B is seldom ob- 

 tained, due to the length of 

 time involved in allowing the 

 formations and mud to reach 

 their original value.) 



In the interpretation of the 

 results, use is made of the fact 

 that most gases absorb heat dur- 

 ing expansion. Therefore, be- 

 cause a certain amount of gas 

 escapes from a sand during drill- 

 ing and circulation, a gas sand 

 will be relatively cool, and will 

 produce a temperature drop on 

 the temperature curves. (Fig- 

 ure 661.) 



Under certain conditions 

 temperature data are indicative 



of structure and hence constitute an important parameter in drill-hole log- 

 ging. Such a condition is illustrated in Figure 662, which shows a graph 

 of thermometric data obtained after casing was set, and graphs of original 

 porosity and resistivity data obtained prior to setting of casing. 



Temperature measurements may also be used to locate lost circulation. 



Fig. 602. — Comparison of original resistivity and 

 porosity logs of the uncased well and a thermo- 

 metric log obtained after setting of casing. (^Thc 

 Fetroleiim Engineer, Feb. 1937, p. 155.) 



