Complete Wavefield Imaging: High Fidelity Velocity Model Building and Imaging from Dual-Sensor Streamer Data

Abstract

We demonstrate the success of combining wavelet shift tomography, full waveform inversion (FWI) and separated wavefield imaging (SWIM) for pre-stack depth migration (PSDM) velocity model building and imaging. The workflow is referred to as Complete Wavefield Imaging (CWI) as it utilizes reflection, multiple, and refraction arrivals in the dual-sensor seismic data. Wavelet shift tomography, operating on reflection arrivals, was used to update the shallow overburden in a legacy PSDM velocity model. FWI updates based on matching modelled versus observed refraction arrivals were subsequently able to resolve high resolution velocity variations associated with channels, pockmarks and gas pockets in the shallow overburden. Additionally, gathers from SWIM were generated using up- and down-going separated wavefields uniquely provided by the dual-sensor data. The SWIM approach exploits the greater illumination of the near surface inherent in the multiple arrivals. SWIM image gathers were used to validate the longer wavelength features not seen by FWI. The study illustrates how reflection, refraction, and multiple arrivals from dual-sensor data can contribute towards high-fidelity model building and imaging. Resolution of the complex shallow overburden leads to more accurate positioning and depth predictions for the reservoir, directly impacting estimation of reserves.