1074 



EXPLORATION GEOPHYSICS 



lating a suitable mud. For example, Ennisf has developed methods 

 wherein the desired electrolytic concentration of the mud is produced 

 by lowering a soluble electrolyte into the hole. The bailing process is 

 then used to cause a flow into the well. Measurements of the electro- 

 chemical potentials are made throughout the length of the hole, before 

 and after bailing. 



Thermometric Method. — The thermometric method does not re- 

 quire special- conditioning of the mud. The only preparation necessary 

 is circulation. Measurements of this type are particularly adapted to 

 dynamic wells and to wells in which there is an interchange of fluid be- 

 tween two formations. 



In one actual case, a well was drilled to 6441 feet, with casing set 

 at 6373 feet. When tested, the well produced no water and only a small 

 amount of oil, A small nitroglycerine shot was then made, after which 

 water appeared. It was believed that the shot had caused bottom water 

 to break into the well. After standing for several days, the fluid level rose 

 to about 2400 feet. 





Fig. 669. — Comparison of temperature data and photoelectric 

 data for the same well. (Courtesy of Schlumberger Oil Well Sur- 

 veying Corp.) 



A thermometric survey was then made. (Figure 669.) The temperature- 

 depth curve showed an abrupt temperature change between 3913 and 3945 

 feet. The temperatures above the anomaly followed the normal curve, 

 and the temperatures below the anomaly were less than the normal values. 

 The data suggested that the temperature increase between 3913 and 

 3945 feet was due to entrance of water which had a slightly higher 

 temperature than the normal temperature of the bore hole at that depth. 



This water had a temperature of approximately 106° and flowed 

 doivn the hole. Hence, it exerted a cooling efifect on all formations below, 



t Geo. H. Ennis, U.S. Patents 1,725,979; 1,786,196; 1,865,847; 1,8 

 1,994,762. 



>; 1,994,761; and 



