Using well logs to infer permeability: Will there ever be a permeability log?

Absolute permeability is a property of the rock only, while effective perm is a property of the rock and the fluids present in the rock. In the most general sense, permeability used in the petroleum industry is a constant in Darcy's flow equation that equates flow rate, pressure gradient, and fluid properties. Even though a formation has a permeability regardless if it is flowing or not, by this definition a direct measurement of permeability requires a dynamic process not a static process. Historically, well logs have been used to estimate permeability via correlations related to a commonly logged property: porosity. Perm-porosity correlations are generated from core and transformed to well log porosity. These correlations are generally semilog in nature in the general form of y = ax^b. Other correlations attempt to estimate effective perm by incorporating irreducible water saturation estimated from resistivity logs and Archie's equation. Most well logging environments are static conditions, where invasion of mud filtrate into the permeable formations has ceased at the time the well is logged. This paper reviews traditional and new methods of quantitatively inferring permeability from well logs and addresses the feasibility of a true permeability log.