CHAPTER 5 



SUBSURFACE LOGGING METHODS 



SAMPLING AND EXAMINATION OF WELL CUTTINGS 

 JOHN M. HILLS 



Although the techniques described in this paper have been learned 

 during 14 years of subsurface work, the writer does not wish to give the 

 impression that they are original with him. They are rather the results of 

 many years' experience of hundreds of geologists engaged in cuttings sam- 

 ple work, which are summarized especially for the benefit of those enter- 

 ing the profession or setting up subsurface departments in other areas. 



Well cuttings are the source of most subsurface data obtained in the 

 Mid-Continent and Permian Basin areas of the United States. The collection 

 and examination of samples of these well cuttings are highly organized 

 and important techniques. In fact, in most holes in this province, well 

 cuttings are the only reliable source of data concerning the formations 

 penetrated. Logs made by experienced cable-tool drillers are very useful, 

 but under present conditions these are rare. It is usual to find the driller's 

 log made by an inexperienced or uninterested rotary driller. Such a log 

 gives only a general idea of the formations drilled, especially in areas 

 where there is a distinct formation change between wells. 



Of all the methods of obtaining information concerning rocks cut by 

 the drill, cores are probably the most reliable. In soft unconsolidated 

 formations these cores can be taken rapidly and with comparatively little 

 expense, by means of a wire-line core barrel. However, in the Mid-Con- 

 tinent and Permian Basin areas most of the rocks are well lithified, and 

 many are extremely hard. For this reason wire-line core bits wear out 

 rapidly, and cores are usually obtained by use of conventional core barrels 

 which are capable of cutting a maximum of 20 feet at one time. Naturally 

 this makes complete coring extremely expensive, especially in deep holes. 

 Recently a new technique of coring with diamond-studded core heads has 

 been developed which may lead to much more extensive coring. It is 

 possible that in the future as much as 100 feet of core may be taken at 

 one time by means of a diamond bit without coming out of the hole. This 

 may render practicable coring of complete sections of deep holes. 



The writer is especially indebted to W. D. Anderson, who taught 

 him the fundamentals of sample examination; to William Y. Penn for the 

 pictures of porosity; to E. Russell Lloyd, who suggested the writing of 

 this paper and has been generous with help and suggestions; and to John 

 Emery Adams and W. W. West, who kindly read and criticized the manu- 

 script. 



