Computer algorithm for airwave prediction in marine controlled source electromagnetics data

This paper presents a methodology for quantifying airwaves as a noise component in Sea Bed Logging environment. Sea bed logging is an application of marine controlled source electromagnetic sounding applied for mainly offshore hydrocarbon detection in the subsurface. The basis of the approach is the difference in resistivity values of matter which comprise the subsurface and the overlying layers. A mobile electric dipole emits a low frequency electromagnetic signal both into the overlying water column and downwards into the seabed. An array of sea floor receivers measures both the amplitude and the phase of the received signal that depend on the resistivity structure beneath the seabed. A survey consisting of many transmitter and receiver locations can be used to determine a multidimensional model of subsea floor resistivity. The received signal is a composition of many signal which are multiplexed to form a complex signal. This signal consists of wanted and unwanted data of which the technique described in here separates the unwanted air waves from the wanted. A mathematical model to quantify the amount of airwave at any given sea water depth from a defined offset is proposed. The method described here has managed to eliminate more than 99.5 percent of the airwave noise from shallow water deep target environment data. Data used was collected from a simulated model of offset 50Km, and cross sectional depth of 10km of which 6km makes the subsurface.