Subsurface Logging Methods 



501 



is plotted with a dotted line, and the "low" gas reading with a dashed line. 

 The oil and methane shows are colored green and red, respectively, on 

 the final log for quick noting. The last column of the log is devoted to a 

 detailed escription of the lithology. Formation tops and results of coring 

 and drill-stem tests, as well as any other pertinent data, are suitably 

 located on the log. A modified daily log covering the previous 24-hour 

 period is sent each day to operators upon request. 



Figure 237. Plotting composite daily log, which includes drilling time, oil and gas 

 shows, and detailed lithologic descriptions. 



The cuttings-analysis-logging method is a direct means of determin- 

 ing the presence of oil- or gas-bearing formations. Oil and gas in the 

 cuttings can be detected by the instruments maintained in quantities too 

 minute to be observed in any other way. Accurate determinations can be 

 made of odorless gases as well as high-gravity oils or distillate. These 

 may be too elusive to detect with a microscope and the human senses. 

 With a geologist or technician on duty 24 hours a day, an accurate valu- 

 ation of the section may be made consistent with the drilling. Experience 

 has shown that not all productive zones are drilled at a faster rate even 

 though porosity is present, an example being the Simpson sand of south- 

 ern Kansas and Oklahoma. However, since cuttings are analyzed each 

 two feet regardless of the rate of penetration, a zone of this type would 



