Figure ll-'A. Instrument panel tor well-logging unit. 



water. In this device the cuttings are violently agitated and broken up. 

 After the agitation period, readings are taken from one or, in more advanced 

 equipment, two sets of filaments in the container. On one set of filaments 

 all combustible gases and then heavier hydrocarbons are indicated in the same 

 manner as the mud-gas analysis. The second set of filaments indicates hexane 

 and heavier hydrocarbon gases in the cuttings and are indicative of oil. Lighter 

 hydrocarbons — methane through pentane — are normally not detected by these 

 filaments but may affect the readings if the amount of C 6 + is considerable. 



The ultraviolet-light method is used to detect oil in both the drilling mud 

 and the cuttings. A sample of drilling mud, representative of that which flushed 

 the bit while a certain interval of the hole was being drilled, is collected at the 

 mud-flow line and is treated to reduce viscosity and to allow the oil to break 

 out and rise to the surface of a shallow dish that is placed in the ultraviolet-light 

 viewing box, where it is alternately subjected to ultraviolet and white light. 



It is usually possible to distinguish between crude oil and the rig oils and 

 greases by close examination of the particles which fluoresce on the surface of 



359 



