Topic: Impact of Full Waveform Inversion (FWI) on Fault Shadow Imaging: A Niger Delta Case Study
The Lagos August Technical/Business Meeting was held on August 16, 2017 at the Grand Ballroom of Eko Hotel and Suites, Victoria Island, Lagos. The technical presentation was made by Auwal Ya'u, a Chief Geophysicist with IDSL and the Acting Deputy Manager, Marine, IDSL Data Processing, Port Harcourt. The topic presented was "Impact of full waveform inversion (FWI) on fault shadow imaging: A Niger Delta case study - Yoho field". The project was executed by IDSL in conjunction with Western Geco. The major challenges in the Yoho field seismic was poor fault imaging, loss of frequencies, shallow gas, high velocities and very low velocity areas. In this environment, conventional tomography model building methods alone proved inadequate to resolve the highlighted challenges. However, FWI was used to derive high-resolution velocity models that define strong lateral subsurface heterogeneities associated with fault shadows mostly present within vicinity of shallow gas anomalies. The data was migrated using kirchoff prestack migration algorithm. FWI utilizes frequency, amplitude and phase information in recorded seismic data to estimate high-resolution models of subsurface properties. FWI models produces synthetic seismograms (modeled data) that is used to improve imaging of the recorded data. Input data used in this work was narrow azimuth towed streamer dataset. A multi-scale strategy was followed via first inverting lowest frequencies, progressively increasing input data bandwidth and accordingly updating the velocity profiles. The derived highly-resolved FWI velocity models was then followed by two high resolution tomography updates to better image deeper events. The final velocity model was used by KAPSDM algorithm to provide better quality images. The result of the FWI was crispier, sharper, clearer and generally improved the imagery of the faults and the entire seismic vintage. Alternatively, it was suggested from the audience that for improved seismic resolution, it is best to acquire wide azimuth/ broadband azimuth seismic data. The meeting was sponsored by Nigerian National Petroleum Corporation (NNPC)/Integrated Data Services Ltd.
For the Presentation, Click Here.
For the meeting pictures, Click Here.