Simulation of electric field response of horizontal circular electric half wave dipole antenna for seabed logging

Abstract

Seabed logging (SBL) is a direct and remote application of controlled source electromagnetic (CSEM) method to detect hydrocarbon resources beneath the seafloor in offshore conditions. In this method, electromagnetic waves are used to detect the resistivity contrast between various sediment layers. The current source of electromagnetic waves is a horizontal electric dipole (HED) antenna. The antenna design represents a challenge in shallow waters (less than500 m seawater depth) due to the presence of airwaves that lead to a low signal-to-noise ratio, hence hindering the detection of a hydrocarbon reservoir. A horizontal circular electric half-wave dipole will be used in this work as the source of electromagnetic waves. The numerical solution for the electric field response will be developed based on solving the Maxwell equations in two modes: the poloidal and toroidal modes. Simulation results have shown that the new antenna is able to detect the presence of deep hydrocarbon reservoirs (up to 5000 m) in shallow-water environment. Comparison of the average percentage difference in delineation between the circular and the HED was carried out. The new antenna results in 61 % delineation compared to 15 % for the HED at 5000 m hydrocarbon depth and 200 m seawater depth, indicating the ability of the antenna to disperse the airwaves. The results also show that the airwaves are significantly reduced from nearly 15000 m (for the HED) to 10000 m offset for the proposed antenna, hence increasing the signal-to-noise ratio. These results seem to indicate the potential for the new antenna to be used as an EM source for SBL in shallow-water environment.