Well No. 



Thin Sections 



2358 

 Core Description 



Description Notes 



T.S 5723 (X40) 



T.S. 5724 1X40) 



T.S 5725 (X40) 



Figure 4-4. Example of photographic record of core and thin sections. 



geologic problem. Very useful records of cores can be made by photographing 

 both core and thin sections and mounting the photos in their proper relationship 

 as illustrated in Figure 4-4. Routine petrographic descriptions of thin sections 

 are especially valuable in gleaning all possible information from slim-hole ex- 

 ploration drilling. 



Correlation 



Thin-section studies have proved to be very helpful in correlating forma- 

 tions. Formations that may be indistinguishable in cuttings may often be dis- 

 tinguished petrographically. For example, the quartz of one sand may include 

 a high proportion of strained grains, or one sand may be predominantly felds- 

 pathic and another lithic. Even shales may be distinguished by their sand or silt 

 content. Chemical rocks can often be recognized by characteristic impurities. In 

 any correlation problem, it must be kept in mind that sudden and extreme lateral 



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