452 



Subsurface Geologic Methods 



ultraviolet or white light. The magnitude of the oil shows in fluid-logging 

 units is based on the amounts of observed flourescence of the crude oil. 



Oil in the cuttings is determined by using the same ultraviolet-light 

 arrangement. Freshly washed cuttings are placed under the light and 

 observed for fluorescence. The cuttings are then treated with various 

 leaching agents to see if they will give a "cut." Certain minerals 

 fluoresce when subjected to ultraviolet light. This fluorescence can be dis- 

 tinguished from crude-oil fluorescence by the fact that mineral fluorescence 

 will not give a "cut" when treated with a leaching agent. 



Figure 213. Control panel of Baroid mud-analysis well-logging unit. 



Further, the cuttings are subjected to a detailed examination under the 

 microscope, in which the operator records the estimated percentage of 

 limestone, sandstone, shale, and anhydrite. Note is also made of in- 

 dications of porosity and permeability. 



A depth meter, pump-stroke counter, and pump-rate meter provide 

 the necessary data for obtaining a rate-of -penetration curve and for 

 properly correlating with depth any shows of oil and gas found in the 

 mud and cutting samples at the surface. The log is prepared as a plot 

 of the magnitude of the oil and gas shows versus depth. Also given is 

 a sand- or lime-index curve showing the relative amounts of either sand 

 or lime in the cuttings. This curve is intended to be used as a supplement 



