Chap. 11] ^ GB^OPHYSICAL WELL TESTING 843 



thermometers must therefore be chilled before and after the run. Other- 

 wise they may be left in the well over night and be hauled up in the early 

 morning hours. The time required for the thermometers to acquire forma- 

 tion temperature is about Ij hours in air and f hour in water. Since the 

 reading at 100 feet is from 1" to 4° F. higher than annual mean tempera- 

 ture, the latter provides a convenient check on the upper portion of the 

 depth-temperature curve and may be obtained from the volume on Climato- 

 logical Data for the U. S. by Sections, published by the U. S. Weather 

 Bureau. With maximum thermometers, readings are taken at intervals 

 of 250-500 feet. Such thermometer assemblies are lowered at the rate of 

 200 feet per minute maximum and removed at the rate of 100 feet per 

 minute maximum. Readings are taken with a telescope and corrections 

 for constant and stem deviation are applied. 



Fig. 11-17. Device for well-temperature measurements (after Van Orstrand). 



For detailed temperature investigations required in connection with pro- 

 duction tests, continuously recording thermometers are more suitable than 

 maximum thermometers, since they do not require hoisting after every 

 reading. The following thermometers are suitable: (1) bimetallic ther- 

 mometers, (2) thermocouples, and (3) resistance thermometers. The 

 former require a recording mechanism inside a water-tight case and do not 

 require wires for remote surface indication. Thermocouples and resistance 

 thermometers are widely used, since cables are usually available in con- 

 nection with electrical logging. 



Fig. 11-18 shows three arrangements of resistance thermometers. Fig. 

 II-I80 represents a Wheatstone bridge circuit with Siemens lead-resistance 

 compensation. Fig. 11-186 shows a customarj'^ method of measuring 

 resistance variations by galvanometer deflection. For recording, the 

 switch S is in position 2; for calibration (by adjusting 72 to a predetermined 



