Seismic Data

Shallow water environments pose challenges for seismic inversion due to hard water-bottoms and near-surface complexities causing guided waves and elastic effects. Conventional acoustic-based full-waveform inversion (FWI) struggles in such conditions. This study demonstrates a time-lag FWI workflow using ocean-bottom node data from the North Sea. The approach models shallow heterogeneities accurately, producing clearer subsurface images. Elastic FWI further enhances deeper structures, particularly in complex chalk formations, offering superior event continuity and signal-to-noise ratios compared to traditional methods.

Elastic full-waveform inversion (FWI) is increasingly recognized as a powerful tool for building compressional velocity (Vp) models, primarily utilizing diving and reflected P-waves. However, updating shear velocity (Vs) models through S-wave inversion in elastic FWI has traditionally been more challenging due to data acquisition limitations and the reduced sensitivity of surface seismic to Vs. This paper introduces a practical methodology for low-wavenumber Vs updates using elastic FWI, driven by converted waves in multi-component ocean-bottom seismic data. The approach involves two key steps: first, building a high-quality Vp model using hydrophone and vertical geophone data, and second, using horizontal geophones to reconstruct the low-wavenumber components of the Vs model from converted wave kinematics. We demonstrate the effectiveness of this methodology in a field application, showcasing improved PS reverse time migration (RTM) imaging and better alignment with PP RTM. Additionally, we compare the elastic FWI approach to a Born-based PS-reflection FWI method, with the elastic FWI model yielding superior PS RTM imaging.

The Santos Basin’s pre-salt oil fields in Brazil have moved from exploration to development, requiring deeper reservoir insight. This study showcases how five years of ocean-bottom node (OBN) processing advancements enhance understanding of the Tupi field’s complex pre-salt reservoirs. Techniques like elastic Time-Lag FWI, RTM angle gathers with spherical binning, and internal multiple attenuation improve velocity models, fault definition, and AVA response. These advancements reduce uncertainty in Vp/Vs-based reservoir inversion, enabling more precise subsurface characterization.