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Detection and Characterization of Fracture Zones in Bedrock: Possibilities and LimitationsNormal access

Authors: G.A. Tassis, P.I. Tsourlos, J.S. Rønning and T. Dahlin
Event name: Near Surface Geoscience 2014 - First Applied Shallow Marine Geophysics Conference
Session: Potential Field Methods
Publication date: 08 September 2014
DOI: 10.3997/2214-4609.20142126
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 1.89Mb )
Price: € 20

In Norway, resistivity measurements have already been tested in marine environments in order to detect subsea fracture zones. However, most of these data have been processed without taking into account the special conditions the presence of seawater creates. More recent studies worldwide have also applied ERT in marine conditions, but under more favorable conditions nevertheless since they dealt with brackish water of considerably higher resistivity than pure seawater. This study summarizes our efforts to establish basic rules when considering whether or not pure sea water ERT can satisfactorily detect weak zones inside resistive bedrock, a problem engineers in Norway usually come up against in tunnel construction sites. The scope for this study is related to the construction of a sub-sea tunnels and the potential application of ERT to detect fractured zones as part of the geotechnical study. Our results indicate that ERT surveys for fracture zone detection in Norwegian marine environments can be promising under certain conditions but at the same time ambiguous since they suffer from reduced resolution and major artificial effects. Based on the modeling results, we were able to improve interpretations of ERT measurements made across the straits at Kvitsøy and plan further investigations in southern Norway.

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