Tackling rugose seabed, strike-shooting, short offset NAZ data in the Otway Basin with advanced processing technologies

The Aragorn and Bellerive seismic surveys were acquired in 2006 and 2011, respectively, within the offshore area of the Otway Basin, southern Australia. Steeply dipping canyons at the seafloor, along with complex overburden geology, resulted in diffracted multiple tails that obscured the Cretaceous layer, which was the primary interval of interest. Ray tracing analysis confirmed that, due to the strike-shooting acquisition geometry, ray paths at the rugose seabed mostly fell outside the streamer spread. The resulting inadequate illumination presented significant challenges for multiple prediction and velocity model building (VMB). Heavy multiple contamination, present in the legacy volume, prevented effective application of reflection tomography, structural interpretation, and quantitative interpretation (QI) work. Furthermore, due to the narrow-azimuth (NAZ) acquisition with short streamers (up to 5 km length), diving wave penetration was limited to the Miocene interval, thereby preventing reliable low-wavelength model update with fullwaveform inversion (FWI) at depth. To mitigate these challenges, advanced demultiple techniques including wave-equation deconvolution (WEDecon), 3D model-based water-layer demultiple (3D MWD), 3D iterative SRME, and 3D simultaneous curvelet domain subtraction were applied. For VMB, 20 Hz visco-acoustic Dynamic Resolution Time-lag FWI (DR-TLFWI) was employed. DRTLFWI was recently developed to derive better low-wavelength model updates, especially from short-offset NAZ streamer data. Least-squares Kirchhoff Q migration (LSQPSDM) was utilized to reduce migration artefacts and improve illumination. The combination of advanced demultiple, DR-TLFWI, and LSQPSDM delivered a step change improvement in imaging quality compared to the legacy volume. Sedimentary sections and fault blocks that were completely masked in the legacy volume were revealed. Undulating structures were mostly corrected, particularly beneath the shallow canyons.