Influence of smectite and salinity on the imaginary and surface conductivity of volcanic rocks
(2019) In Near Surface Geophysics 17(6). p.653-673- Abstract
We investigate the complex conductivity behaviour of natural volcanic rocks containing variable amounts of smectite in multi-salinity experiments. We compare the results with relationships established for sandstones. Considering only samples with little volume of metallic particles, we observe similar and small phase-angles at low frequency for all samples at all salinities (less than 25 mrad at 1 Hz). Yet, a wide range of cation exchange capacity, porosity and formation factor is covered by the sample set: 0.5–50 meq/100 g, 4–40% and 18–780, respectively. Our results show that, in the absence of metallic particles, the ratio between imaginary conductivity and surface conductivity is significantly lower for altered volcanic rocks than... (More)
We investigate the complex conductivity behaviour of natural volcanic rocks containing variable amounts of smectite in multi-salinity experiments. We compare the results with relationships established for sandstones. Considering only samples with little volume of metallic particles, we observe similar and small phase-angles at low frequency for all samples at all salinities (less than 25 mrad at 1 Hz). Yet, a wide range of cation exchange capacity, porosity and formation factor is covered by the sample set: 0.5–50 meq/100 g, 4–40% and 18–780, respectively. Our results show that, in the absence of metallic particles, the ratio between imaginary conductivity and surface conductivity is significantly lower for altered volcanic rocks than for sandstones and decreases with the smectite content. These observations indicate that an increased smectite content causes more conduction and less polarization, which could be explained by the onset of a continuous conduction pathway throughout connected interfoliar spaces of smectite. Due to this pathway, cations from the pore fluid may penetrate the solid lattice, for example through connected smectite aggregates clogging the fracture network, thus preventing polarization. We also observe that the relationship between imaginary conductivity and surface conductivity, at one salinity or over the whole salinity range, is not more significant than the relationship between the imaginary conductivity and the total real conductivity. Therefore, we suggest that the imaginary conductivity cannot be used to discriminate the contributions from smectite and pore water to the total conductivity of altered volcanic rocks.
(Less)
- author
- Lévy, Léa LU ; Weller, Andreas and Gibert, Benoit
- publishing date
- 2019-12-01
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Complex conductivity, Geothermics, Induced polarization, Resistivity
- in
- Near Surface Geophysics
- volume
- 17
- issue
- 6
- pages
- 21 pages
- publisher
- EAGE
- external identifiers
-
- scopus:85075970157
- ISSN
- 1569-4445
- DOI
- 10.1002/nsg.12069
- language
- English
- LU publication?
- no
- additional info
- Funding Information: We sincerely thank the editor, as well as Andreas Hördt, Philippe Leroy and a third anonymous reviewer for their recommendations that helped improve the quality of the manuscript. L.L. thanks Jacinthe Caillaud for EPMA analyses on clay minerals and Nicolas Marino for his valuable assistance in electrical conductivity measurements and uncertainty quantifications. This work was supported by a PhD grant from Paris Sciences et Lettres to Léa Lévy and the IMAGE FP7 EC and GEMex H2020 projects (grant agreements 608553 and 727550). Funding Information: We sincerely thank the editor, as well as Andreas H?rdt, Philippe Leroy and a third anonymous reviewer for their recommendations that helped improve the quality of the manuscript. L.L. thanks Jacinthe Caillaud for EPMA analyses on clay minerals and Nicolas Marino for his valuable assistance in electrical conductivity measurements and uncertainty quantifications. This work was supported by a PhD grant from Paris Sciences et Lettres to L?a L?vy and the IMAGE FP7 EC and GEMex H2020 projects (grant agreements 608553 and 727550). Publisher Copyright: © 2019 European Association of Geoscientists & Engineers
- id
- e68acb21-f66b-4486-9189-6c1497cf99b4
- date added to LUP
- 2021-12-14 12:59:10
- date last changed
- 2022-04-27 06:38:44
@article{e68acb21-f66b-4486-9189-6c1497cf99b4,
abstract = {{<p>We investigate the complex conductivity behaviour of natural volcanic rocks containing variable amounts of smectite in multi-salinity experiments. We compare the results with relationships established for sandstones. Considering only samples with little volume of metallic particles, we observe similar and small phase-angles at low frequency for all samples at all salinities (less than 25 mrad at 1 Hz). Yet, a wide range of cation exchange capacity, porosity and formation factor is covered by the sample set: 0.5–50 meq/100 g, 4–40% and 18–780, respectively. Our results show that, in the absence of metallic particles, the ratio between imaginary conductivity and surface conductivity is significantly lower for altered volcanic rocks than for sandstones and decreases with the smectite content. These observations indicate that an increased smectite content causes more conduction and less polarization, which could be explained by the onset of a continuous conduction pathway throughout connected interfoliar spaces of smectite. Due to this pathway, cations from the pore fluid may penetrate the solid lattice, for example through connected smectite aggregates clogging the fracture network, thus preventing polarization. We also observe that the relationship between imaginary conductivity and surface conductivity, at one salinity or over the whole salinity range, is not more significant than the relationship between the imaginary conductivity and the total real conductivity. Therefore, we suggest that the imaginary conductivity cannot be used to discriminate the contributions from smectite and pore water to the total conductivity of altered volcanic rocks.</p>}},
author = {{Lévy, Léa and Weller, Andreas and Gibert, Benoit}},
issn = {{1569-4445}},
keywords = {{Complex conductivity; Geothermics; Induced polarization; Resistivity}},
language = {{eng}},
month = {{12}},
number = {{6}},
pages = {{653--673}},
publisher = {{EAGE}},
series = {{Near Surface Geophysics}},
title = {{Influence of smectite and salinity on the imaginary and surface conductivity of volcanic rocks}},
url = {{http://dx.doi.org/10.1002/nsg.12069}},
doi = {{10.1002/nsg.12069}},
volume = {{17}},
year = {{2019}},
}