An empirical correction applied to [[porosity]] derived from the [[sonic log]] in uncompacted [[formation|formations]] such as sands at shallow depths or formations under abnormally high pressures.

In applying the empirical correction to the [[time average relationship|time-average relationship]] for obtaining apparent porosities from [[interval transit time|interval transit times]], the relationship becomes:

{{ :terms:p20f1.gif }}

where C<sub>p</sub> is the compaction-correction coefficient; other symbols as described in time-average relationship. In [[consolidated]] formations C<sub>p</sub> = 1 (corresponding to no correction). In [[unconsolidated]] formations (which generally occur at shallow depths) C<sub>p</sub> has values greater than 1.