Figure 17-1. Well-logging unit on location. 



Arrangement of equipment in the well-logging unit (fig. 17-1) is shown in 

 Figures 17-2 and 17-3. 



The apparatus used for determining the gas in drilling mud consists of a 

 gas detector and a gas trap through which a small stream of mud returns are 

 diverted. The mud is agitated in the presence of air to allow separation of gas 

 from the drilling mud. From this trap a small vacuum-pump compressor de- 

 livers a stream of the air-gas mixture to a hot-wire gas detector, where the gas 

 content of the mud is determined. 



The hot-wire gas detector is an adaptation of an instrument that has been 

 used to detect combustible gases in coal mines. Provisions have been made to 

 operate the filaments alternately at two temperatures. At the higher temperature, 

 all combustible gases are burned; and at a lower temperature, only the heavier 

 molecular-weight gases are burned. Thus, the difference between the two is a 

 measure of the methane. 



In determining the amount of gas in cuttings, a measured quantity of the 

 drill cuttings is placed in an agitating device with a measured quantity of 



358 



