A capillary number for physical displacement of TCE-DNAPL trapped in a rough-walled fracture

Abstract

A heterogeneous nature of rough-walled rock fractures complicates a recovery of DNAPL trapped in fractured rock aquifers, which forms a persistent plume within the fractured rocks and present a long-term source of contamination. Experimental studies were conducted to suggest a criterion for the physical displacement of DNAPL from rough-walled fractures in the context of capillary number (N ca ), a dimensionless number representing the ratio of the viscous to capillary forces. A series of experiments using water, surfactant solution and dense fluid were conducted in the range of capillary number from 2.29 × 10 -4 to 3.41 × 10 -2 . The experimental results suggested that a higher capillary number than 1 × 10 -2 be required for a near complete DNAPL removal (more than 95% of initial saturation) from rough-walled fractures. For capillary number on the order of 10 -3 , DNAPL can be mobilized or recovered to some degree. For the capillary number below 1 × 10 -3 , any kind of remedial fluids would have no effect on physical displacement. It is suggested that remedial fluid utilizing physical displacement be formulated to comply with N ca > 1 × 10 -2 to maximize a complete physical removal and the fluid utilizing chemical solubilization or reaction do with N ca < 1 × 10 -3 to minimize unwanted migration.

The behaviors of LNAPL migration and entrapment in a rough-walled vertical fracture

“…The relationship between capillary number and recovery rate has been shown by Lee et al (2011). For the entrapped blobs from upward migration here, the distribution and location were more The behaviors of LNAPL migration and entrapment in a rough-walled vertical fracture 9 http://www.springer.com/journal/12303 http://dx.doi.org/10.1007/s12303-016-0057-2 complex than those presented by Lee et al (2011). The recovery of entrapped LNAPL in vertical fracture is ongoing and future work.…”

“…Several studies on NAPLs behavior in rough-walled fractures have been conducted, which involve details on migration, residual, dissolution, removal and bioremediation of NAPLs (Yeo et al, 2003;Lee et al, 2011Lee et al, , 2013Yang et al, 2012bYang et al, , 2013aEssaid et al, 2015). The mobilization and entrapment of NAPL are controlled by many factors, including medium properties (e.g., aperture distribution and roughness of fracture walls); fluid properties (e.g., density, viscosity and interfacial tension); fluid-solid interactions (e.g., wettability); and force conditions (e.g., capillary, gravitational, buoyancy and viscous forces) White et al, 2004;Singh, 2009;Yang et al, 2012aYang et al, , 2013b.…”