DNAPL-water two-phase flow in rock fractures.

摘要

Determination of dense non-aqueous phase liquid (DNAPL) migration and distribution in rough-walled rock fractures is essential to remediate DNAPL contaminated fractured aquifers. This study investigated the DNAPL-water two-phase flow processes in rock fractures, experimentally and theoretically, under capillary forces dominated and viscous forces dominated conditions. Four rock fractures created in rock specimens obtained from Alberta Paskapoo formation were utilized in the laboratory program.;Single-phase DNAPL and water flow tests were conducted to estimate the average aperture of the fractures. The estimated average apertures were more close to the geometric mean of the measured aperture distributions than the arithmetic mean. The classical local cubic law could not predict the single-phase flow accurately. High fracture aperture variations and undulations lead to high deviation in simulation results from experimental results and vice versa. Single-phase flow simulations in geostatistically generated aperture distributions revealed that high spatial continuity in flow direction improves the permeability of the fracture.;The experimental results of two-phase, DNAPL-water flow tests indicated that the conventional relative permeability concept cannot analyze the viscous forces dominated two-phase flow in fractures accurately. Instead, the Lockhart-Martinelli model that is used to analyze two-phase flow in pipes demonstrated a better match. The governing equations for viscous forces dominated two-phase flow in fractures were formulated using parameters introduced by Lockhart-Martinelli model. The parameters necessary to solve the above governing equation were measured from laboratory experiments. The DNAPL and water distribution in rock fractures were non-destructively measured from X-ray CT scanning technique.;Capillary pressure-saturation relationship was identified as the most important parameter to be determined from the laboratory experiments to solve the governing equations of capillary forces dominated DNAPL-water two phase flow in rock fractures. The experimentally determined capillary pressure-saturation relationship for the rock fracture illustrated a behavior similar to the capillary pressure-saturation relationships of the porous media. The invasion-percolation method was used to determine the capillary pressure-saturation relationship, theoretically. A reasonable comparison was observed between the experimentally and theoretically determined curves. Further, the capillary pressure--saturation relationships of geostatistically generated aperture distributions demonstrated that the amount of spatial continuity in aperture distributions in flow direction affects the properties of the capillary pressure-saturation relationship.