Fundamentals of Fluid Flow in Porous Media
Anisotropy means that some properties of the porous medium do not have the same value in different directions. In an anisotropic porous medium, the permeability, formation resistivity factor, and breakthrough capillary pressure depend on the direction. In the most general case these properties are function of both location in the medium and orientation. Thus the probability density function for each property can be described with five independent variables (x, y, z) for location and (θ , φ) for orientation. If the probability density distribution is independent of the angular coordinates, the medium is isotropic, otherwise it is anisotropic. In the reservoir formation generally anisotropy can be caused by periodic layering. So generally we have different properties such as permeability at z direction compare to the x and y direction.