Airwaves effect in Sea Bed Logging for shallow water environment

Controlled Source Electromagnetic (CSEM), method used in Sea Bed Logging (SBL), has shown very promising results in detecting subsurface hydrocarbons. A powerful electric dipole antenna which is used as transmitter of electromagnetic (EM) wave is towed above the seabed to detect resistivity contrasts in the subsurface. The signal will propagate through the layers and then recorded by receivers, which consist of both electric and magnetic antennas, placed on the sea bed. One of the major problems in implementing this method is the airwaves effect that occurs at shallow water environment. It should be noted that the air waves could dominate the measured EM data such that the presence of the thin resistive body may not be readily detected. This paper is going to discuss the effect of airwaves in SBL for shallow water environment. EM data for with and without hydrocarbon were collected via simulation using CST EM Studio for various water depths from deepwater 1000 m to shallow water 100 m. Magnitudes versus Offset (MVO) values were plotted. Results showed that airwaves started to dominate at water depth of 600 m and became more significant at water depths of 300 m and below.