Subsurface Logging Methods 



355 



TABLE 19 



Example of Sample-Description Form 



Operator No Lease County 



Block 

 Section League Survey 



Labor Twp Range Footage 



Elevation T.D Date Examined by.. 



since the logs can be plotted in several places at the same time and a 

 record is kept which is not subject to destructive wear as is the plotted 

 log which is used constantly in the field and laboratory. A type of de- 

 scription form is included (table 19) . In addition to the constituents 

 shown on this form, others may be specified according to the nature of 

 stratigraphic sections in the area worked. Pyrite and differently colored 

 shales will be the most likely additions. In areas where sand production 

 is important, separate columns for porosity and saturation in sandstone 

 may be desirable. 



Color of the rock fragments in cuttings samples is a very important 

 attribute. At present there is a wide variation in the descriptions of color 

 by subsurface geologists. The same rock may be described as tan by one 

 and brown or gray by another. It is desirable in any organization attempt- 

 ing to start sample examination work to standardize some color scheme, 

 possibly that being developed by the inter-society committee.^ 



Size of particles in dolomites and limestones is another matter on 

 which subsurface geologists vary. The following table gives the tentative 

 scale of crystal sizes which was developed by the West Texas Geological 

 Society several years ago. It would be to the advantage of anyone under- 

 taking sample description for the first time to adopt a scale with appro- 

 priate abbreviations for the sample-description sheets.^ 



^ DeFord, R. K., Rock Color Chart for Field Geologists: Am. Assoc. Petroleum Geologists Bull., 

 vol. 31, no. 10, pp. 1903-1904, 1947. 



^ A more elaborate scale is advocated by Ronald K. DeFord, Grain Size in Carbonate Rocks: Am. 

 Assoc. Petroleum Geologists Bull., vol. 30, no. 10, pp. 1921-1928, 1946. 



