Geostatistical estimation of structural vulnerability

Anders V. Christiansen, Esben Auken, Kurt Sørensen, F. Jørgensen, Rolf Johnsen

Research output: Contribution to conferencePaper at conferencepeer-review

Abstract

In this abstract we present a newly developed concept using geostatistical estimation and nonlinear inversion to optimize a function translating geophysical resistivity models to geophysical clay thickness. The algorithm uses information on reported clay thicknesses in drill holes. We call it geoStatistical estimation of Structural Vulnerability (SSV). The clay thickness in the upper part of the subsurface is an important factor for the water infiltration speed and thereby the vulnerability of underlying aquifers to pesticides, nitrate etc. Drill hole information contains the most detailed information on clay thicknesses, but most often drill hole information is too sparse for the detail level required in actual mapping situations. Geophysical data, on the other hand, has the desired spatial coverage (Christensen and Sørensen, 1998, Thomsen et al., 2004) but the measured quantity is resistivity and not clay thickness. The SSV concept act as a hands off interpolator between the drill holes translating the geophysical models to geophysical clay thickness. The SSV concept introduced here incorporates several aspects 1. Layered models obtained from inversion of geophysical data. This includes layer resistivities and layer thicknesses and their uncertainty. 2. The spatial distribution of the geophysical data in connection with the spatial distribution of the drill hole information. 3. Clay thicknesses described in drill holes and accompanying uncertainties. The presentation summarizes the central aspects of the SSV concept and discusses the various uncertainties. Finally we show an example in which SSV was used to estimate the geophysical clay thickness in a survey in Denmark. The results have been confirmed by a follow-up drill campaign.

Original languageEnglish
Publication statusPublished - 2005
Externally publishedYes
Event11th European Meeting of Environmental and Engineering Geophysics of the Near Surface Geoscience Division of the EAGE, Near Surface 2005 - Palermo, Italy
Duration: 4 Sep 20057 Sep 2005

Conference

Conference11th European Meeting of Environmental and Engineering Geophysics of the Near Surface Geoscience Division of the EAGE, Near Surface 2005
Country/TerritoryItaly
CityPalermo
Period4/09/057/09/05

Programme Area

  • Programme Area 2: Water Resources

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