Subsurface Logging Methods 



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to the drilling-rate curve. The drilling-rate curve and the sand-index 

 curve are used as indications of porosity and permeability values and 

 of changing formation. They are also used for correlation between wells 

 in the same general area because of characteristic variations in formation 

 hardnesses and sand or lime content. 



The well-logging service is used as wells are being drilled, and re- 

 sults on any formation are available as soon as the mud used in drilling 

 the formation reaches the surface. The system does not interfere with the 

 drilling operations in any way, and no changes in ordinary drilling equip- 



FiGURE 214. Special filter press designed to test efficiency of fibrous materials for 

 restoring lost circulation. "Core" consists of sized rock. 



ment or procedure are required to make it workable. The logging units 

 are in reality mobile field laboratories. In addition to the logging in- 

 struments, each unit is equipped with complete mud-testing equipment. 

 Tests for mud weight, viscosity, water loss, cake thickness, salinity, and 

 other characteristics can be made so that a satisfactory drilling mud may 

 be maintained. 



The principal application has been in the drilling of wildcat or 

 exploratory wells, vvhere its usefulness is apparent in many phases of the 

 well program. Coring can be reduced to a minimum by using mud-analysis 



