Simulating the Dissolution of a Complex Dense Nonaqueous Phase Liquid Source Zone: 1. Model to Predict Interfacial Area
Water Resources Research
A thermodynamically based model for predicting two-fluid interfacial area (IFA) within a porous medium as a function of wetting phase saturation (S W ) and saturation history is presented. The model considers consistency with multiphase flow constitutive relationships, the conversion of total to effective specific interfacial area, energy losses, and the change of interfacial area as residual nonwetting phase dissolves. The model requires as input only the capillary pressure–saturation relationships and porosity. Published, high-resolution interfacial area-saturation data sets were adequately reproduced when independent measures of these parameters were employed by the model. In particular, the model is found to reproduce key IFA(S W ) features including the IFA magnitude and S W value corresponding to the function's maximum, negligible IFA at residual S W and the observed hysteresis of IFA(S W ). Varying key model parameters reveals that the magnitude of the IFA(S W ) relationship is predicted to be linearly related to the porosity and entry pressure of the porous medium and is unaffected by interfacial tension. Interfacial area is a parameter in the single boundary layer expression of mass transfer between two immiscible liquids in porous media. The model's ability to predict local-scale IFA for a wide variety of fluid-fluid-porous media systems while accounting for saturation and saturation history thus provides an avenue for simulating the dissolution of complex source zones containing both pooled and residual dense nonaqueous phase liquids.