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TitleCapacitive conductivity logging and electrical stratigraphy in a high-resistivity aquifer, Boise Hydrogeophysical Research Site
AuthorMwenifumbo, C J; Barrash, W; Knoll, M D
SourceGeophysics vol. 74, no. 3, 2009 p. E125-E133, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20080254
PublisherSociety of Exploration Geophysicists
Mediapaper; on-line; digital
File formatpdf
AreaBoise River; Idaho; United States
Subjectsgeophysics; hydrogeology; stratigraphy; conductivity; electrical properties; electrical resistivity; aquifers; porosity
Illustrationslocation maps; cross-sections; logs
AbstractWe tested a prototype capacitive-conductivity borehole tool in a shallow, unconfined aquifer with coarse, unconsolidated sediments and very-low-conductivity water at the Boise Hydrogeophysical Research Site BHRS. Examining such a high-resistivity system provides a good test for the capacitive-conductivity tool because the conventional induction-conductivity tool known to have limited effectiveness in high-resistivity systems did not generate expressive well logs at the BHRS. The capacitive-conductivity tool demonstrated highly repeatable, low-noise behavior but poor correlation with the induction tool in the lower-conductivity portions of the stratigraphy where the induction tool was relatively unresponsive. Singular spectrum analysis of capacitive-conductivity logs reveals similar vertical-length scales of structures to porosity logs at the BHRS.Also, major stratigraphic units identified with porosity logs are evident in the capacitive-conductivity logs. However, a previously unrecognized subdivision in the upper portion of one of the major stratigraphic units can be identified consistently as a relatively low-conductivity body i.e., an electrostratigraphic unit between the overlying stratigraphic unit and the relatively high-conductivity lower portion - despite similar porosity and lithology in adjacent units. The high repeatability and resolution and the wide dynamic range of the capacitive-conductivity tool are demonstrated here to extend to high-resistivity, unconsolidated sedimentary aquifer environments.