Chap. 11] 



GEOPHYSICAL WELL TESTING 



857 



water and drilling fluid will produce quite different geothermal effects, 

 depending on relative temperatures, hydrostatic head, and agitation. As 

 shown in Fig. 11-27, the trend of temperatures in static condition may be 

 as in curve a. Drilling will result in cooling the lower portion of the well 

 by the drilling fluid, and in heating the upper portion in comparison. 



ohm-m 200 



Temp. 

 lOO-f ffO' 



6400' 



5800' 



Fig. 11-26. Anomaly in depth-temperature curve due to escaping gas (after 



Leonardon). 



When the well is left idle, the 

 lower portion will again tend to 

 take the temperature of the sur- 

 rounding formations and cool 

 the upper portions further. A 

 gradual approach to static con- 

 ditions takes place. In practice, 

 the order of events is reversed 

 when several runs are taken for 

 locating water flows. If the well 

 has been idle for a time and a 

 first run is taken, curve c is ob- 

 tained. If, then, the mud is 

 circulated for a few hours, a 

 second run will give curve hP"^ 

 Following this, the hydrostatic 

 head of the mud is generally re- 

 duced by bailing to allow (warm) 

 water to flow into the hole. 

 This will give rise to a definite 



peak in the curve. Fig. 11-28 shows a series of water sands with their 

 corresponding temperature peaks recorded through the casing. Note the 



100' 150' F 



Fig. 11-27. Depth-temperature curves in idle, 

 drilling, and flowing wells (after French) . 



"a R. W. French, Oil and Gas J., April 27, 1939. 



