The Archie Equation
Sw = [ (a / Fm)*(Rw / Rt) ](1/n)
- Sw: water saturation
- F: porosity
- Rw: formation water resistivity
- Rt: observed bulk resistivity
- a: a constant (often taken to be 1)
- m: cementation factor (varies around 2)
- n: saturation exponent (generally 2)