450 



Subsurface Geologic Methods 



proved technique allow for the detection of the most minute quantities 

 of oil and gas and the exact placing of these shows at the proper depth. 



The Baroid well-logging service has been developed using the fol- 

 lowing facts as a basis: In drilling a well the bit disintegrates a 

 cylindrical section of the formation. If the pore spaces of this cylinder 

 contain oil or gas, part of these fluids will be entrained by the drilling 

 mud and part will be retained on or in the cuttings. If the drilling 

 fluid and the cuttings are continuously tested on their return to the sur- 

 face and the results of these tests correlated with the depth of origin, the 

 presence or absence of oil or gas in specific formations can be determined. 



In the application of the method continuous tests are made on the 



i'lGURE 211. Baroid mud-analysis well-logging unit on location. 



mud and cuttings returning to the surface. The test for gas in the mud 

 is made by diverting a portion of the circulating mud from the flow 

 line to a separator or gas trap, where the mud is thoroughly mixed with 

 air and a portion of the gas in the mud is removed. A stream of air 

 is drawn countercurrent to the flow of mud in the gas trap, thus mate- 

 rially assisting the separation of the gas from the mud. The air-gas 

 mixture is then drawn into a "hot-wire" gas-detector instrument, where 

 the percentage of combustible gas is determined. The amount of methane 

 gas present in the total is determined by controlling the temperature of 

 the filament in the gas detector. 



Thus, the gas readings in the mud are recorded as total gas, which 



