Well-Log Seq-Strat

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