Permeability is a property of the porous medium that measures the capacity and ability of the formation to transmit fluids. The rock permeabil- ity, k, is a very important rock property because it controls the directional movement and the flow rate of the reservoir fluids in the formation. This rock characterization was first defined mathematically by Henry Darcy in 1856. In fact, the equation that defines permeability in terms of measur- able quantities is called Darcy’s Law.