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Subsurface Geologic Methods 



Cores are described individually from the top down. If the entire 

 core is of homogeneous material, it may be described as a unit. If it is 

 lithologically heterogeneous, each lithic unit requires description. 



An example for describing a core of diversified lithology is given 

 below: 



Comments: Drill-time data indicated at least four feet of sandstone between the 

 depths 5,920.5 and 5,924.5. The corrected lithologic subdivision follows: 

 mudstone, 5,919-5,920.5, sandstone, 5,920.5-5,924.5, limestone, 5,924.5- 

 5,926.5, dolomite, 5,926.5-5,928, shale, 5,928-5,929. Minor amounts of 

 gas appeared in the porous dolomite unit; formation test is recom- 

 mended. 



Core Sampling 



Core-sample intervals will vary in different wells according to the 

 rock types and subsequent evaluation methods to be applied. During 

 sampling the stratigraphic position of the sample and the interval of 

 which it is typical should be noted. Even though a composite sample of 

 several small fragments is taken, it is advisable to include sections that 

 exhibit dip, porosity, or other special features that may be of significance 

 in evaluating the cored interval. 



Samples should be dried under atmospheric conditions before being 

 submitted to the laboratory. A tag showing the well number and the type 

 and depth of the sample should be attached on the outside of the sacked 

 sample. If it is a core sample, the cored interval, the recovery, the loca- 

 tion of the sample in the core, and the interval of which it is typical 

 should be noted. 



