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Pore‐scale mechanisms for the enhancement of mixing in unsaturated porous media and implications for chemical reactions
Author(s) -
JiménezMartínez Joaquín,
Anna Pietro de,
Tabuteau Hervé,
Turuban Régis,
Borgne Tanguy Le,
Méheust Yves
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl064513
Subject(s) - porous medium , vadose zone , wetting , mixing (physics) , saturation (graph theory) , porosity , multiphase flow , materials science , viscous fingering , geology , permeability (electromagnetism) , mechanics , geotechnical engineering , chemistry , groundwater , physics , composite material , quantum mechanics , biochemistry , mathematics , combinatorics , membrane
Porous media in which different fluid phases coexist are common in nature (e.g., vadose zone and gas‐oil reservoirs). In partially saturated porous media, the intricate spatial distributions of the wetting and nonwetting phases causes their flow to be focused onto preferential paths. Using a novel 2‐D experimental setup allowing pore‐scale measurement of concentration fields in a controlled unsaturated flow, we highlight mechanisms by which mixing of an invading fluid with the resident fluid is significantly enhanced when decreasing saturation. The mean scalar dissipation rate is observed to decrease slowly in time, while under saturated conditions it decays rapidly. This slow decrease is due to sustained longitudinal solute fingering, which causes concentration gradients to remain predominantly transverse to the average flow. Consequently, the effective reactivity is found to be much larger than under saturated conditions. These results provide new insights into the role that multiphase flows play on mixing/reaction in porous media.