Leverett J function

In petroleum engineering, the Leverett J-function is a dimensionless function of water saturation describing the capillary pressure,

where S w is the water saturation measured as a fraction, p c is the capillary pressure (in pascal), k is the permeability (measured in m²), ϕ is the porosity (0-1), γ is the surface tension (in N/m) and θ is the contact angle. The function is important in that it is constant for a given saturation within a reservoir, thus relating reservoir properties for neighboring beds.

The Leverett J-function is an attempt at extrapolating capillary pressure data for a given rock to rocks that are similar but with differing permeability, porosity and wetting properties. It assumes that the porous rock can be modelled as a bundle of non-connecting capillary tubes, where the factor k / ϕ is a characteristic length of the capillaries' radii.