@&afrten, 17 



MUD AND 

 CUTTINGS 

 LOGGING 



W. H. Russell 



As the drilling of a well progresses, the bit dislodges and disintegrates 

 a cylindrical section of the formation. As the cuttings travel upward and as 

 the hydrostatic pressure in the mud column decreases, any gas in the pore 

 space of the cuttings will expand. A portion will escape to, and be entrained 

 in, the drilling mud and a portion will usually remain in the cutting. In an 

 oil-bearing formation, the associated gas will expand and force a portion of 

 both oil and gas into the mud stream, while a portion of each remains in the 

 cuttings. These hydrocarbons can be detected with sensitive equipment when 

 the mud and cuttings reach the surface. By continuous analysis of the mud and 

 cuttings and by making suitable allowance for time necessary to reach the 

 surface, the oil- and gas-bearing formations can be detected and their depth 

 determined. 



EQUIPMENT The equipment used in mud-analysis and cut- 



tings-analysis logging involves three groups: 



1. Equipment used directly in making determinations of oil and gas. 



2. Equipment used to relate shows to depth of origin. 



3. Auxiliary equipment. 



357 



