Roughness of a layered geological medium and implications for interpretation of the transient electromagnetic response of a loop source
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A new theoretical model has been developed for transient controlled-source electromagnetic (CSEM) exploration of multi-layer aquifers. The method is applicable to fractured rock and other types of lithology which exhibit length-scale dependent heterogenity. A roughness parameter β is used, in the present paper, as a proxy for fracture density. The Maxwell equations governing CSEM responses are generalized to incorporate a spatial derivative of fractional order 1-β. An analytical solution is derived for inductive loop excitation of a mulitple plane-layered formation which includes one or more spatially rough layers. The resulting synthetic CSEM step-off response curves indicate that it is possible to detect the fracture density of a buried fractured-rock layer if it is conductive relative to its surroundings. The CSEM method is also able to resolve the depth to such a fractured layer. These new theoretical results have important implications for fractured-rock hydrogeophysics.
author list (cited authors)
Decker, K. T., & Everett, M. E.