In exploratory geologic work the geologist may use coring and core-analysis 

 data to ( 1 ) obtain a detailed formation description of the beds that are penetrat- 

 ed, (2) determine the dip and direction of dip of formation beds, and (3) deter- 

 mine the probable fluid content of prospective pay sections. After a core has been 

 obtained and removed from the well, it is usually laid out in the same linear 

 position it held in the core barrel so that the recovery amount and the formation 

 depth can be recorded. By visual examination and measurement, a detailed 

 description of the core is made, the formation composition, the texture, the 

 probable geologic age, the dip of formation beds, and the probable fluid content 

 being observed. If indications are that the core may contain oil or gas, further 

 field and laboratory tests are usually made. Should a core contain oil or gas, 

 the visual examination can usually determine only what section may be a potential 

 producing zone. A special coring method must be used to determine the direction 

 of the dip of formation beds, and obviously such a determination may be very 

 valuable in locating the probable direction in which a structure may be located. 



Field or proved-area geologic problems usually resemble those encountered 

 in exploratory work to some extent. The principal difference is that proved-area 

 geologic work generally is directed toward obtaining data that may be used to 

 evaluate a known pay zone or to locate a formation marker. When an exploratory 

 well encounters an oil- or gas-bearing zone, the geologic problems then resemble 

 proved-area problems. In proved areas, the geologist may use coring and core 

 data to aid in (1) determining the amount of pay section present, and (2) esti- 

 mating the amount of oil and gas in place. 



CORING IN RELATION TO Frequently coring and core data can be used 

 PRODUCTION WORK to an appreciable advantage in production 



operations and petroleum-engineering work, 

 in addition to helping the geologist with his various problems. Probably the 

 greatest use of coring in production work is for determining zones that should 

 be formation- or production-tested and for determining, if possible, the gas-oil 

 and water-oil contacts in those zones. Also, at times in production operations, 

 it may be desirable to make an open-hole completion; that is, one in which the 

 oil-string casing is set above the pay section to be tested and produced. Coring 

 can be used to aid in determining the presence of undesirable upper sloughing 

 shales and water-bearing zones immediately above the pay zone. The casing 

 seat may then be picked at a point that would shut off the undesirable formations 

 and yet allow the entire desired section to be tested. Information about the 

 texture of the formation in a prospective pay zone usually aids in picking the 

 most desirable type of completion method and helps determine the possibility of 

 sand-production problems. At times diamond coring can aid in operations in 



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