Wavenumber of the guided wave supported by a thin resistive layer in marine controlled-source electromagnetics

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.