Subsurface Logging Methods 475 



is at the present time. Many companies publish catalogs of logs avail- 

 able for distribution. If drilling-time logs were added to these lists, they 

 would benefit geologists whose responsibility it is to interpret properly 

 the records made in the drilling of a test for oil or gas. 



DRILLER'S LOGGING 

 L. W. LeROY 



The driller and his assistants assume major responsibility for the 

 successful operation and completion of their assigned well. Frequently 

 these men fail to receive full credit for their role in exploration and 

 exploitation programs. Too often have their opinions and suggestions 

 been neglected or considered unworthy by "technical" personnel. 



One of the many duties of the driller during drilling operations is 

 to record and tabulate to the best of his ability the character of the 

 penetrated strata. Frequently his lithologic "calls" are unreliable; many 

 of them, however, are exceptionally accurate, particularly if he is familiar 

 with the drilled section. There are numerous examples where a driller's 

 recordings of formational "tops" are as exact as those determined by 

 the geologist. 



Drillers' logs would be greatly improved if geologists would take 

 the time and effort to create a lithologic interest among drillers. Since 

 oil companies are constantly demanding more accuracy in well logging, 

 the driller can be of great assistance in this phase, if he has an under- 

 standing of the rock types through which he is drilling. It would not 

 be out of line if these men were given, prior to drilling, an introduction 

 to the various rock varieties to be expected in their wells. 



Drillers' Terminology 



Examination of drillers' logs (See table 24) often reveals such terms 

 as "lime," "sand," "shell," "gumbo," "broken sand," "broken lime," 

 "dry sand," "quicksand," "hard rock," "pebble shale," "muck," "sand 

 rock," "loam," "caving shale," and "niggerheads." Possible interpreta- 

 tions of these terms are as follows: caving shale, muck, gumbo, loam, 

 the equivalent of soft shale; sand, broken lime, hard rock, shell, the 

 equivalent of limestone or sandstone; lime, broken sand, hard rock, shell, 

 the equivalent of limestone. 



"Shale with niggerheads" may represent a shale containing thin, 

 calcareous streaks or concretionary structures. "Quicksand" could be 

 interpreted as soft, easily penetrated sand. "Caving shale" may suggest 

 to the geologist the presence of bentonite. "Lime" recordings often in- 

 corporate such rock types as anhydrite, highly calcareous sandstone, 

 light-colored tuff, or dolomite. 



The color of rock types many times is inadequately recorded by the 



