CSEM component analysis: Analysing the contribution of different components to the HED response in a typical 1D VTI medium

A MATLAB program was built around 1D closed form representations of the radial electrical field in a vertical transverse isotropic (VTI) medium driven by an horizontal electric dipole (HED) in the transverse magnetic (TM) and transverse electric (TE) mode published in Andréis and MacGregor (2008). It is able to compute the contribution of the different pathways and coupling events, by mathematically decompressing the global reflection coefficients and coupling terms, while not exceeding a 1% error with Web Hosted Active-Source Modelling (WHAM) code. The program is limited to a 5 layer 1D VTI model, where source and receiver are present in the second layer seen top down. This program was used to analyse different 'airwaves' as described in various controlled-source electromagnetic (CSEM) publications. The airwaves observed include two different types of ’coupled’ airwaves; one first encountering the subsurface and subsequently the air-sea interface, the other vice versa. 3 models were analysed; deep sea – deep source-receiver setup; shallow sea–deep source-receiver setup and shallow sea– shallow source-receiver setup. Differences in the two types of airwave signals in both modes for each model are observed. The most notable difference between the two types of airwaves is increased amplitude and reduced phase shift plateauing in the shortest-pathway signal. For the shallow sea – shallow setup model, the airwaves have the same magnitude as the earth-reflected signal.
Civil Engineering and Geosciences
Applied Geophysics and Petrophysics
Applied Earth Sciences