Pore-scale dissolution by CO₂ saturated brine in a multimineral carbonate at reservoir conditions: impact of physical and chemical heterogeneity

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Title: Pore-scale dissolution by CO₂ saturated brine in a multimineral carbonate at reservoir conditions: impact of physical and chemical heterogeneity
Authors: Al-Khulaifi, Y
Lin, Q
Blunt, MJ
Bijeljic, B
Item Type: Journal Article
Abstract: We study the impact of physical and chemical heterogeneity on reaction rates in multimineral porous media. We selected two pairs of carbonate samples of different physical heterogeneity in accordance with their initial computed velocity distributions and then injected CO 2 saturated brine at reservoir conditions at two flow rates. We periodically imaged the samples using X-ray microtomography. The mineralogical composition was similar (a ratio of dolomite to calcite of 8:1), but the intrinsic reaction rates and mineral spatial distribution were profoundly different. Visualizations of velocity fields and reacted mineral distributions revealed that a dominant flow channel formed in all cases. The more physically homogeneous samples had a narrower velocity distribution and more preexisting fast channels, which promoted dominant channel formation in their proximity. In contrast, the heterogeneous samples exhibit a broader distribution of velocities and fewer fast channels, which accentuated nonuniform calcite distribution and favored calcite dissolution away from the initially fast pathways. We quantify the impact of physical and chemical heterogeneity by computing the proximity of reacted minerals to the fast flow pathways. The average reaction rates were an order of magnitude lower than the intrinsic ones due to mass transfer limitations. The effective reaction rate of calcite decreased by an order of magnitude, in both fast channels and slow regions. After channel formation calcite was shielded by dolomite whose effective rate in slow regions could even increase. Overall, the preferential channeling effect, as opposed to uniform dissolution, was promoted by a higher degree of physical and/or chemical heterogeneity.
Issue Date: 1-Apr-2019
Date of Acceptance: 10-Feb-2019
URI: http://hdl.handle.net/10044/1/70021
DOI: https://dx.doi.org/10.1029/2018WR024137
ISSN: 0043-1397
Publisher: American Geophysical Union
Start Page: 3171
End Page: 3193
Journal / Book Title: Water Resources Research
Volume: 55
Issue: 4
Copyright Statement: ©2019. The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.
Keywords: 0905 Civil Engineering
0907 Environmental Engineering
1402 Applied Economics
Environmental Engineering
Publication Status: Published
Open Access location: https://doi.org/10.1029/2018WR024137
Online Publication Date: 2019-02-19
Appears in Collections:Earth Science and Engineering

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