ABSTRACT

Porosity and permeability of reservoir sandstones can be related to the primary rock properties of composition, texture, and packing. Permeability is assumed to be largely a function of rectilinear pore size which, in turn, is a function of mean grain size, sorting as expressed by deviation of grain size distribution, mean grain shape, and packing of grains. By means of systematic packings of uniform spherical grains, the size and shape of rectilinear pores can be determined for porosities of 30 to 40 percent. By considering laminar flow of fluids through pores of idealized cross sections, a general equation can be derived in which permeability is a function of the square of the median grain size, of the fifth power of porosity, and of phi percentile deviation. When the equation is applied to clean sands and sandstones of 30 to 40 percent porosity, permeability may be calculated with reasonable accuracy. The agreement between theoretical and measured values suggests that this approach may be applicable to other packings and porosities in subsurface reservoir sandstones.