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Effect of evaporative drying on complex conductivity spectra of sandstones

Zhang Zeyu, Andreas Weller, Sabine Kruschwitz and Sven Nordsiek
Effect of evaporative drying on complex conductivity spectra of sandstones
Geophysics (January 2019) 84 (1): MR61-MR72

Abstract

Dehydration is a common process occurring in natural environments, rocks, and building materials. Suitable methods for monitoring the changing moisture content should be identified. We have investigated the impact of dehydration of sandstones on complex conductivity spectra. Spectral induced polarization measurements were performed on five sandstone samples during evaporative drying. The complex conductivity spectra indicate considerable changes with decreasing saturation. The relationship between conductivity and saturation can be described by a power law known as the second empirical Archie equation. Separate saturation exponents have been determined for the real and imaginary parts of conductivity. The imaginary part of conductivity indicates higher saturation exponents for the investigated sandstones compared to the real part. Obviously, the saturation exponents depend on the method used for changing water saturation. Evaporative drying, which is used in our experiments, causes an increase of pore-water salinity and results in lower saturation exponents for the real part of conductivity but higher exponents for the imaginary part in comparison with the classical imbibition/drainage technique. We evaluate a theoretical approach that considers the influence of pore water salinity on the saturation exponents of the real and imaginary parts of conductivity. The complex conductivity spectra are processed by a Debye decomposition procedure. The resulting integrating parameters such as direct current resistivity, total chargeability, normalized chargeability, and mean relaxation time indicate a power law dependence on saturation. Our experiments indicate that the imaginary part of conductivity and normalized chargeability have a high sensitivity related to the drying process of rocks and might be suitable indicators to monitor the changes of moisture content in sandstones.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 84
Serial Issue: 1
Title: Effect of evaporative drying on complex conductivity spectra of sandstones
Affiliation: Southwest Petroleum University, School of Earth Sciences, Chengdu, China
Pages: MR61-MR72
Published: 201901
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 28
Accession Number: 2019-006910
Categories: Applied geophysicsSedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendices
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Technische Universitaet Clausthal, DEU, GermanyBundesanstalt fuer Materialforschung und -pruefung, Universitaet Bayreuth, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201906
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