Correlation of capillary pressure data and the development of the widely used J(S) correlating function are reviewed. The pore structures of core samples, which give the same (in practice closely similar) J(S) curves, are described as operationally similar. Similarity of J(S) curves can be recognized by parallelism of semi-log plots of capillary pressure vs. saturation. Curves so identified were grouped to obtain a pore structure factor based on J(S) curve shapes rather than determining Purcell lithology factors for individual formations. The modified Purcell method gave improved correlation between measured and predicted permeabilities.

A general solution of the Thomeer model in terms of the tangent angle for the Pc(S) curve is presented which facilitates tests of correlations between permeability and selected features of capillary pressure curves. Single point correlation methods based upon the tangent α as introduced by Swan son for α=45°, are shown to hold for a wide range of saturation. Curve methods which consider all of the curve such as suggested by Purcell or any selected parts can be tested at will. The method is designed for semi-empirical investigation of a very large database of core analysis results which include porosity, permeability, and capillary pressure by mercury injection.

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