Wavenumber of the guided wave supported by a thin resistive layer in marine controlled‐source electromagnetics |
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| Authors: | FN Kong SE Johnstad J Park |
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| Institution: | 1. Norwegian Geotechnical Institute (NGI), PO Box 3930 Ulleval Hageby, 0806 Oslo, Norway;2. Multifield Geophysics ASA, Damsgaardsvein 125, 5162 Lakesvaag, Norway |
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| Abstract: | This paper discusses the asymptotic behaviour of the electromagnetic fields received on the sea‐bed (target response), as well as the fields distributed inside a thin resistive target, generated by a horizontal electric dipole above the sea‐bed in marine controlled‐source electromagnetics for hydrocarbon exploration. It is found that the guided wave supported by a thin resistive target can be expressed as a single‐mode exponential function. A simple closed‐form expression is derived to relate the single‐mode wavenumber of the guided wave to the model parameters: the resistivity and thickness of the target layer, the sea‐bed resistivity and the frequency. When the air‐wave is removed, the guided wave is dominant among the fields received on the sea‐bed at far offset. Hence the wavenumber of the guided wave can be calculated from the fields measured on the sea‐bed. The closed‐form expression can then be used to invert the target property from the calculated wavenumber and hence, can be considered as a hydrocarbon indicator. |
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| Keywords: | Electromagnetics Modelling Reservoir geophysics |
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