Formation of residual NAPL in three-phase systems: Experiments and numerical simulations

Abstract

The formation of residual, discontinuous nonaqueous phase liquids (NAPLs) in the vadose zone is a process that is not well understood. The simulators have conveniently implemented the Leverett concept (Leverett and Lewis, 1941) which states that in a water-wet porous media, when fluid wettabilities follow the order water-NAPL-air, the water content is a function of the NAPL-aqueous phase capillary pressure and the total liquid content is a function of the gas-NAPL capillary pressure. This concept assumes that when liquid NAPL is present in three-phase systems, the NAPL is spreading and completely covers the water phase. Nonspreading behavior, leading to residual saturations, is not addressed by the Leverett concept. To obtain data that can be used to study the development of a residual NAPL saturation in the vadose zone and to test current numerical models, detailed transient experiments were conducted. Simulations with an established multifluid flow simulator show the shortcomings of a constitutive model based on the Leverett concept. © 2002 Elsevier B.V. All rights reserved.