Subsurface Logging Methods 



451 



includes all the combustible gases and methane gas. This "breakdown" 

 of gas readings is made because recent studies have indicated that, with 

 few exceptions, all productive horizons logged by the mud-analysis 

 method have shown a definite increase of methane gas. Therefore, in- 

 clusion of the methane curve on the new log is important to operators, 

 since, normally, those zones that do not show that an increase of methane 

 may be condemned. 



The test for gas in the cuttings is made by placing a small sample of 



Figure 212. Operating equipment in Baroid mud-analysis well-logging unit. 



the cuttings with a measured amount of water in a closed-container-type, 

 high-speed grinder. After cuttings are ground, the air-gas mixture in the 

 container is examined for gas in the same manner as described in the 

 preceding paragraph. Here, too, the gas is reported as total gas and 

 methane gas. 



The presence of oil in the drilling fluid is detected by a physical 

 examination of the drilling mud under ultraviolet light. A sample of the 

 mud is treated to reduce the surface tension and gel strength, after which 

 it is placed in a viewing box. This box is so constructed that all external 

 light is excluded; thus the sample may be subjected selectively to either 



