Migration mechanism of light non-aqueous phase liquids in stratified heterogeneous media with low-permeability lenses

The migration and distribution of non-aqueous phase liquids in porous media are governed by the complex properties of unsaturated soil. A systematic analysis of light non-aqueous phase liquid (LNAPL) transport in layered heterogeneous soils is essential for developing effective remediation strategies at contaminated sites. However, existing models have insufficient consideration for the Klinkenberg effect and the dynamic capillary effect in low-permeability lens bodies. To this end, this study innovatively established a low-permeability layer permeability model considering the Klinkenberg effect, and for the first time, combined two-dimensional visualization experiments with multiphysics field coupled numerical simulation (COMSOL), systematically studied the migration and distribution laws of LNAPL in heterogeneous porous media containing low-permeability lens bodies. Results indicate that the low-permeability layer plays a key controlling role in the migration of LNAPL, which can be clearly divided into three stages: gravity-driven vertical seepage, accumulation and lateral expansion on the layer, and accelerated migration after penetration. This study, for the first time, accurately fitted the migration distance using a high-order polynomial model (longitudinal fourth order/transverse ninth order) and quantified the significant impact of porosity on peak pressure and saturation. This research provides an effective methodology for monitoring and mechanistically analyzing soil contamination from long-distance oil pipeline leaks.