This log measures of the speed of sound in the formation, and is related to both the porosity and lithology of the rock being measured. Thus, if the lithology of a formation is know, this log can be used to determine its porosity. Shales have lower velocity (higher transit time) than sandstone of same porosity, making this log a good indicator of grain size.
Sonic log values (in ms/ft) for some rock types are: sandstone 51-56, limestone 47.5, dolomite 43.5, anhydrite 50, halite 67.
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