Journal Article

PreJuSER-6379

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Characterization of seawater intrusion using 2D electrical imaging

Nguyen, F.FZJ* ; Kemna, A. ; Antonsson, A. ; Engesgaard, P. ; Kuras, O. ; Ogilvy, R. ; Gisbert, J. ; Jorreto, S. ; Pulido-Bosch, A.

2009
EAGE Houten

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Please use a persistent id in citations: doi:10.3997/1873-0604.2009025

Abstract: We have investigated the potential of 2D electrical imaging for the characterization of seawater intrusion using field data from a site in Almeria, SE Spain. Numerical simulations have been run for several scenarios, with a hydrogeological model reflecting the local site conditions. The simulations showed that only the lower salt concentrations of the seawater-freshwater transition zone could be recovered, due to the loss of resolution with depth. We quantified this capability in terms of the cumulative sensitivity associated with the measurement setup and showed that the mismatch between the targeted and imaged parameter values occurs from a certain sensitivity threshold. Similarly, heterogeneity may only be determined accurately if located in an adequately sensitive area. At the field site, we identified seawater intrusion at the scale of a few kilometres down to a hundred metres. Borehole logs show a remarkable correlation with the image obtained from surface data but indicate that the electrically derived mass fraction of pure seawater could not be recovered due to the discrepancy between the in-situ and laboratory-derived petrophysical relationships. Surface-to-hole inversion results suggest that the laterally varying resolution pattern associated with such a setup dominates the image characteristics compared to the laterally more homogeneous resolution pattern of surface only inversion results and hence, surface-to-hole images are not easily interpretable in terms of larger-scale features. Our results indicate that electrical imaging can be used to constrain seawater intrusion models if image appraisal tools are appropriately used to quantify the spatial variation of sensitivity and resolution. The most crucial limitation is probably the apparent non-stationarity of the petrophysical relationship during the imaging process.

Keyword(s): J

Note: We would like to thank the associate editor Lee Slater and the two reviewers Kamini Singha and Mark Goldman for their pertinent comments and suggestions, which have greatly improved this manuscript. We also thank Frederic Day-Lewis for fruitful email exchanges. We would like also to thank all the people who contributed to this work on the field, in Almeria and in the laboratory of the Forschungszentrum Juelich. This work is part of the EU project ALERT (GOCE-CT-2004-505329). We thank also the Fonds de la Recherche Scientifique - FNRS (Belgium) and the University of Copenhagen for providing logistical support to this research.

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Research Program(s):

1. Terrestrische Umwelt (P24)

Appears in the scientific report 2009

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