On the Correspondence between Brooks‐Corey and van Genuchten Models

A procedure is described for converting van Genuchten (VG) saturation (S) - capillary pressure (P) - permeability (k) model parameters to equivalent Brooks-Corey (BC) parameters or vice-versa. Differential fluid saturation capacities of the VG and BC S-P relations are equated at an effective wetting fluid saturation of 0.5 to relate the BC pore size distribution parameter Ι to the VG parameter n. To obtain the BC nonwetting fluid entry capillary head, h_d, from the VG parameters α and m, the VG and BC retention functions are matched at an effective wetting fluid saturation which is estimated from an empirical function that was developed by minimizing differences between VG and BC Sln(P) relations. Van Genuchten S-P and k-S relations are compared to Brooks-Corey S-P and k-S relations when the BC parameters are estimated by the described procedure. Close correspondence is found in S-P relations between the VG and BC models for parameters indicative of both clayey and sandy porous media. Poorer agreement is found in k-S relations, which is more likely a result of inherent differences between the VG and BC models.