Archie's Law


In petrophysics, Archie’s law relates the in-situ electrical conductivity of a sedimentary rock to its porosity and brine saturation as shown here.


Archie’s law is named after Gus Archie (1907–1978) who developed this empirical quantitative relationship between porosity, electrical conductivity, and brine saturation of rocks. Archie’s law laid the foundation for modern well log interpretation as it relates borehole electrical conductivity measurements to hydrocarbon saturations (which, for fluid saturated rock, equals 1-S_w).

Related formulas


Ctelectrical conductivity of the fluid saturated rock (S/m)
atortuosity factor (dimensionless)
Cwelectrical conductivity of the brine (S/m)
ϕporosity (dimensionless)
mcementation exponent of the rock (usually in the range 1.8–2.0 for sandstones) (dimensionless)
Swbrine saturation (dimensionless)
nsaturation exponent (usually close to 2) (dimensionless)