Source directivity is a key mechanism of imaging illumination loss under rugged seabeds

ABSTRACT In offshore explorations, the amplitudes and frequencies of seismic data under rugged seabeds are often distorted, and the imaging amplitudes are partially attenuated with obvious energy banding distributions. The attenuation critically affects the quality of seismic profiles, reducing the effectiveness of seismic data interpretation and undermining the reliability of assessments for oil and gas resource development. Furthermore, the mechanism behind the attenuation beneath rugged seabeds remains unclear, as extensive research has yet to explain this phenomenon, presenting a significant challenge in the field. In practice, the observed amplitude reductions may result from a combination of intrinsic attenuation and illumination effects. To investigate the influence of rugged seabeds on seismic wave propagation and imaging, 2D and 3D rugged seabed models were constructed, and acoustic and elastic simulations, illumination analysis, and prestack depth migration (PSDM) imaging were conducted. In this study, a specific illumination-related mechanism was identified: the coupling between source directivity and rugged seabed topography, which leads to the banded amplitude variations beneath the bulges and depressions of the seafloor that can be observed in real seismic profiles. Exploring the interaction between the source directivity and rugged seabed can serve as guidance for effective amplitude compensation of seismic profiles for offshore explorations and provide high-quality seismic data for interpretations.