Enhancing the detectability of a high-resistivity target by using a synthetic aperture source for 3D marine CSEM modelling of a rugged seafloor

When processing marine controlled-source electromagnetic (CSEM) data from a rugged seafloor, enhancing the reservoir response and suppressing the topographic effect and other interference are significant issues, especially in shallow water. We simulated the CSEM responses specific to these issues using an efficient finite-difference (FD) code. The synthetic aperture technique was applied to steer the EM field toward a high-resistivity target on the seafloor. A weighted 2D synthetic aperture source was constructed by imposing a real weighting factor on each source point. Numerical experiments showed that using the weighted 2D synthetic aperture source significantly enhanced the effective CSEM signals. Because of the destructive interference between bathymetric distortion and the airwave effect in shallow water, the synthetic aperture technique is useful for dealing with seafloor topography. Better results can be obtained before steering the distorted response with a bathymetric correction. However, the detectability results may exhibit a huge difference in numerical values if the background resistivity of the bathymetric model is estimated incorrectly.