Subsurface Imaging

Joint seismic VVAz-AVAz inversion: case study Offshore Abu Dhabi

Fracture characterization is critical for optimizing reservoir production. Velocity Variation with Azimuth (VVAz) and Amplitude Variation with Azimuth (AVAz) are the primary methods used in the industry for characterizing azimuthal anisotropy, whether fracture- or stress-induced, from PP seismic data. While each method has its strengths and limitations, they are often used separately to predict fracture networks in reservoirs. This paper presents a joint azimuthal velocity and amplitude inversion workflow for characterizing fracture orientation and intensity in a Middle East offshore carbonate reservoir, utilizing a high-density WAZ ocean-bottom cable (OBC) 3D seismic survey.

Elastic time-lag full-waveform inversion using OBN data in shallow water environments

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 FWI of multi-component ocean-bottom seismic to update shear-wave velocity models

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.