Duties and Reports of the Subsurface Geologist 813 



be exercised to refine or confirm important stratigraphic data by selective 

 coring. 



Side-wall cores should be taken in uncored sands that appear prom- 

 ising on the electric log and also at points where samples may be required 

 for special geologic information. All sand samples from sidewall cores 

 should be tested in ultraviolet light and by other methods immediately 

 after their extraction. 



Preparation of Core Samples for Analysis and Shipment 



A short description of the procedure in wrapping cores for shipment 

 follows. It is not necessary to ship excessively large cores for testing, the 

 ideal length being about eight inches. A different technique is employed 

 in shipping cores, when fluid saturations are to be determined, from that 

 when permeabilities and porosities are desired. 



When only the permeability, porosity, or grain size is required, pre- 

 cautions against fluid loss need not \)e considered. Generally, it is better 

 to leave the mud cake intact rather than to remove it, as the cake offers 

 some support to the core. The core sample should be labeled with the 

 name or number of the well, the depth of the core, and, where applicable, 

 the zone name. The core can then be packed in waste, sawdust, excelsior, 

 or shredded newspaper in an individual container. The most satisfactory 

 containers are, in order of preference, sealed metal cans, cylindrical card- 

 board ice-cream containers, and glass fruit jars. The containers should be 

 packed in suitable wooden boxes and packing material added to minimize 

 breakage. 



When the fluid saturations are desired, that is, the oil and water 

 content of the core, rapidity in preparing the core for shipment is essen- 

 tial in order to prevent evaporation losses. As soon as possible after the 

 core is removed from the core container, it is tightly wrapped in at least 

 two layers of lead foil. After the core is wrapped, the label is applied, 

 and the core is dipped in melted parafin wax for proper sealing. The 

 core can then be packed in the individual container. Care should be taken 

 to avoid breaking the wax coating during packing and shipping. 



Core Descriptions 



The geologist should examine the core immediately upon its extrac- 

 tion and prior to cleaning it in order to observe any oil or gas indications 

 that may appear on or within the mud cake. However, the core should be 

 thoroughly cleaned before a description of the lithology or sampling is 

 attempted. Certain types of cores are best cleaned immediately after they 

 are removed from the core barrel; others may be cleaned after the mud 

 cake has almost dried. 



The first data recorded when describing cores are the cored interval 

 and the footage recovered. Core dips, fracturing, and striae direction 

 should be noted and carefully rated. 



