Full Waveform Inversion for Shallow Hazard Identification on a Narrow Azimuth Dataset

Summary Site survey seismic is usually acquired as 2D seismic lines with specific acquisition configurations for imaging close to the seabed at high frequencies. The resulting images have excellent detail and they are then interpreted and potential drilling hazards identified largely from the stack amplitudes. However we lack other methods by which to constrain the interpretation of high amplitudes, such as being able to map their extent in 3D or use other seismic attributes derived from pre-stack data. In many prospects around the world, shallow gas is a known issue for drilling and as an experiment we ran a full waveform inversion study to test if we could detect velocity anomalies caused by these accumulations. To isolate anomalous velocities, the FWI velocity model was smoothed in a horizon-consistent manner and the smoothed model subtracted to give an “anomaly volume”. This was then compared with conventional site survey seismic data. We also verified the FWI velocity model by remigrating the 3D seismic data using the original tomographic model, the smoothed FWI model and the full FWI model.