Archie's law

In petrophysics, Archie's law relates the in-situ electrical conductivity of a sedimentary rock to its porosity and brine saturation:

Here, denotes the porosity, the electrical conductivity of the fluid saturated rock, represents the electrical conductivity of the brine, is the brine saturation, is the cementation exponent of the rock (usually in the range 1.8–2.0 for sandstones), is the saturation exponent (usually close to 2) and is the tortuosity factor.