# Dictionary:Compaction

Jump to navigation
Jump to search
,
.

{{#category_index:C|compaction}}
Loss of porosity with increasing differential pressure, usually in a nonelastic way, e.g., by grain deformation, repacking, recrystalization, etc. The normal porosity of shales given by the **Hubbert-Rubey law** is

where is the initial porosity (the *Atterberg limits*, q.v.), *c* is a constant, and *P* is the differential pressure, the difference between the overburden pressure and the formation fluid pressure. This leads to a pressure-with-depth curve that is roughly logarithmic:

Compaction is nearly irreversible, i.e., relieving the pressure that compacted a rock does not uncompact it, but releaving the pressure is apt to produce a small change (**unloading effect**).