3D fluid-solid coupled full-waveform inversion for ocean-bottom seismic data

Abstract

Ocean-bottom seismic acquisition is attractive for the exploration of challenging marine environments. Compared with conventional streamer acquisitions, its separation of sources and receivers makes a significant improvement in terms of illumination, especially at depth. Furthermore, such acquisition system makes it possible to record four component data through a combination of hydrophones and three component (3C) geophones. The information on elastic properties of the subsurface is better captured by those 3C geophones on the seabed. This information is mostly overlooked up to now, while reconstructing jointly P-wave and S-wave velocity models would significantly improve the subsurface characterization. To achieve such a higher solution multi-parameter reconstruction, we design an efficient 3D fluid-solid coupled full waveform inversion (FWI) engine. It is based on the acoustic-elastic coupled wave-equation system, in which fluid and solid domains are divided explicitly and handled with acoustic and elastic-wave equations, respectively. A hybrid approach for the misfit gradient building is proposed in such fluid-solid coupled FWI, in which multi-parameter gradient kernels, including the one related to S-wave velocity, are constructed by using a similar modeling solver in both forward and adjoint simulations. This FWI engine is illustrated on a bilayered 2D model and a 3D extended Marmousi model. We show how P-wave and S-wave velocity models can be inferred from the data, and that the resolution improvement can be obtained from the reconstruction of the S-wave velocity model, which highlights the important contribution of 3C geophone dataset.