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DRILLING TIME 

 LOGGING 



G. Frederick Shepherd 



Rate of penetration is considered here as the time required to rotary-drill 

 a linear unit of depth of a geologic formation. It is believed that drilling-time 

 characteristics constitute a diagnostic property of a rock resulting from its com- 

 position, mode of deposition, degree of compaction, and other physical features 

 by which the rock is described. At present, drilling-time properties, measureable 

 in terms of rate of penetration, are qualitative in scope and relative in their 

 interpretation. That they may become quantitative and definable in fixed values 

 which may be significant in the determination of lithologic types is anticipated. 



Rate of penetration may be measured in terms of drilling time and drilling 

 rate, each of which has its own specific uses and limitations. The relationship 

 between the two and their differences are discussed. Drilling-time data may be 

 applied to many engineering and drilling problems and have proved of consider- 

 able value to contractors, drilling crews, and operators. The multiple uses to the 

 geologist involve general correlation problems and lithologic studies. The 

 geologic application of drilling-time data is an additional technique of particular 

 value in the determination of potentially productive sections of a well bore 

 and in the calculation of recoverable reserves. 



Many methods have been used to measure and record drilling time. A 

 technique used by the author is described and illustrated in which mechanical 

 recording of depth in reference to elapsed time is translated into graphs or logs, 



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