Analysis of Dual‐Porosity Model With Fissure Skin Effect in Confined Karst Aquifer

Abstract

In fractured media with rough fissure skins, ignoring the fissure skin effect limits the accuracy of parameter inversion. In karst aquifers, groundwater storage and movement are typically governed by dual‐porosity models, where the fissure skin plays a key role in water exchange between fissures and the rock matrix. This study develops a radial CRT model incorporating the fissure skin effect based on a quasi‐steady state approach, deriving an analytical solution in the Laplace domain and obtaining a real‐time domain solution via Stehfest method. The improved model deepens the understanding of drawdown responses in fractured aquifers. The ratio of fissure skin storage coefficient ( α ) and exchange coefficient ( β ) jointly control the shape of the drawdown curve. An increase in α enhances the storage capacity of system, significantly reducing drawdown in the later stages. When β  > 1, the fissure skin strengthens the hydraulic connection between the matrix and fissures, causing the early‐stage drawdown curve to shift downward, while β  < 1 exhibits a typical flow resistance effect. Validation through a constant‐rate pumping test (CRT) in a mining area of Inner Mongolia demonstrates that the new model provides a better fit than the classical dual‐porosity model. Automatic inversion further confirms improved transition‐stage fitting with stable parameter estimates, providing a more reliable basis for characterizing fissure–matrix transition zones in karst aquifers.