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APPLICATIONS 

 OF CORING 



H. L. Lundua 



In the past it has been found that coring is an aid in the solution of some 

 of the problems in the geology and development of oil fields that may arise when 

 subsurface formations are prospected. These problems are usually general, or 

 they may be related directly to either exploratory drilling or field or proved-area 

 drilling. The geologist must evaluate the formations pentrated by the drilling, 

 and to do this adequately he usually utilizes the best tools and methods available. 



General geologic problems usually result from a well condition in which 

 a desired tool or method cannot be used. For example, frequently it may be de- 

 sired to obtain an electric log of a well, but the circulating fluid in the well may 

 be such that the logging instrument cannot function properly; or, because of 

 sloughing formations or other hindrances, the condition of the hole may be such 

 that the instrument cannot be lowered to the desired depth. Also, in many areas, 

 the geologist prepares a formation-sample log from data obtained by examination 

 of formation cuttings. At times, however, these cuttings may not be satisfactory 

 because (1) mud-circulation rates may be too low to get them to the surface 

 without their being reground; (2) the presence of caving or sloughing forma- 

 tions may mask the drilled cuttings; or (3) the formation cuttings may be so 

 soft that disintegration occurs before they reach the surface. In such circum- 

 stances coring, even though possibly less desirable, would provide a means of 

 obtaining substitute data for geologic use. 



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