Unveiling the Reservoir Beneath Complex Channels in Australia’s Otway Basin

The La Bella narrow azimuth towed-streamer data was acquired in 2013 within the Otway Basin in southern Australia. The data is challenging due to the presence of shallow Tertiary channel complexes overlying the target reservoir. This leads to weak reflection energy and image distortion resulting from unresolved velocity anomalies. The lack of diving wave due to insufficient streamer length limits conventional FWI utility. Furthermore, the Tertiary channel complex casts strong diffracted multiples onto the underlying reservoir, complicating both demultiple and velocity model building derived from ray-based tomography.

To address the challenge, we propose a two-pronged approach utilising dynamic resolution time-lag FWI (DR-TLFWI) and an advanced demultiple flow. DR-TLFWI is a newly-developed algorithm that can better utilise the weak tomographic term in the FWI gradient beyond the diving wave penetration. This results in a more reliable low-wavenumber and consequently high-wavenumber velocity update. The advanced demultiple flow combines various multiple models to mitigate the limitations of each technique and better capture the amplitude of recorded multiples.

The workflow improves signal-to-noise ratio on images and greatly reduces imaging distortions in the legacy volume. The higher fidelity and resolution images allow for significantly improved mapping of the reservoirs beneath the complex channel system.