Archie's law

In petrophysics, Archie's law relates the in-situ electrical conductivity of a sedimentary rock to its porosity and brine saturation: In petrophysics, Archie's law relates the in-situ electrical conductivity of a sedimentary rock to its porosity and brine saturation: Here, ϕ {displaystyle phi ,!} denotes the porosity, C t {displaystyle C_{t}} the electrical conductivity of the fluid saturated rock, C w {displaystyle C_{w}} represents the electrical conductivity of the brine, S w {displaystyle S_{w}} is the brine saturation, m {displaystyle m} is the cementation exponent of the rock (usually in the range 1.8–2.0 for sandstones), n {displaystyle n} is the saturation exponent (usually close to 2) and a {displaystyle a} is the tortuosity factor. Reformulated for electrical resistivity, the equation reads with R t {displaystyle R_{t}} for the fluid saturated rock resistivity, and R w {displaystyle R_{w}} for the brine resistivity.