Subsurface Logging Methods 477 



driller. His "blue" shale may upon closer examination actually be green 

 or greenish-gray; "red" shale may range from deep maroon to light 

 pink. The term "red" may be continued on the tour sheet through a gray- 

 colored section if mud contamination is excessive and samples are not 

 thoroughly cleaned, 



Interpretation of Driller's Log 



Even though a driller's interpretation of lithology may be incom- 

 plete from a geologist's or engineer's viewpoint, his log is generally a 

 result of careful and sincere observation and should under no circum- 

 stances be disregarded. Many early drillers' logs are impossible to in- 

 terpret because of inconsistencies and erroneous lithic recordings; many 

 have been found to aid materially in re-evaluation of stratigraphic sec- 

 tions, however, particularly when supplemented by more recently and 

 carefully analyzed stratal data. Interpretation of these logs involves the 

 understanding of routine procedures of the driller and the significance 

 to him of their results. 



It is now standard practice in rotary drilling to adhere to constant 

 weight on the bit and rotational speed of the drill pipe. As these opera- 



TABLE 24 

 A Typical Driller's Recording of Lithology 



Formation Top (ft.) Formation Top (ft.) 



Lime rock 24 Green shale 718 



Sand 30 Chocolate shale 719 



Blue shale 234 Gray shale 720 



Blue lime 264 Green shale 721 



Black shale 454 Hard lime 724 



Sand rock; top of Dakota 456 Chocolate shale 730 



White gumbo 458 Grav water sand; water in top 4 ft 745 



Wind rock 460 White sand 775 



White gumbo 462 Brown sand : 787 



Sand rock 468 Hard red shale; top of Morrison 844 



Water sand 470 Hard red and green shale 902 



Sand rock 485 Brown sand, oil showing 906 



Fine clay 487 Chocolate shale and green shale 944 



Sand rock 498 Brown and green sand; oil 950 



Hard sand rock 532 Green shale 956 



Lime rock 544 Green sand; oil 962 



Fine clay 554 Gumbo 963 



Sand rock 574 Green sand; oil 969 



f Jne clay 584 Green sandy shale 986 



Ij^d ro'^k 620 Green lime 1007 



TY71 •» i" ^o-7 Hard, brown lime 1010 



White lime 687 „ ' , ,.,„ 



Red clay 689 ^""^^^ ^^^^ ^^^^ 



Lime rock 692 Green, limy shale 1022 



Red clay 694 Green and blue limy shale 1050 



Chocolate shale 706 Black or bluish lime, weathers 



Gray shale 715 gray. Total depth 1065 



