CHAPTER IV 



CORE ORIENTATION 



Introductory Note. — This branch of instrumental survey 

 in boreholes being the older of the two main divisions 

 previously noted, we will deal with it first. It has not been 

 so extensively employed as the other department of bore- 

 hole surveying dealing with the course of the borehole 

 proper. Among the chief factors not already discussed 

 which either influence the relative positions of boring tool 

 and strata pierced or provide useful evidence of the same, 

 we may mention the following, of which a running record 

 should be kept.^ 



1. The type, size, and dimensions of bit used. 



2. The size of drill stem. 



3. The size and depth of the hole. 



4. Weight of mud used. 



5. Pressure employed on the bit. 



6. Speed of rotation or number of strokes per minute. 



7. The stroke or fall in percussive boring. 



8. The weight on the tool in percussive boring. 



9. Rate of water circulation. 



10. Ease of running in and coming out with drill stem. 



11. Ease of setting the casing. 



The various orientation methods can be nearly all 

 grouped into the four following classes: 



a. Orientating the core barrel by measuring or aligning 

 the drill pipe out of the hole. 



b. Attaching an instrument to the core or core box in 

 the hole during operation previous to extraction. 



^ See also a useful questionnaire by F. H. Lahee for the Research Com- 

 mittee of the American Association of Petroleum Geologists, Bull. Amer. 

 Assoc. Petroleum Geol., July, 1929, for notes on checking observations, etc. 



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