Seismic reprocessing and PreSDM in the Gippsland Basin

Abstract

Woodside holds significant equity in the VIC/RL2 and VIC/RL6 permits, which are located in the Gippsland Basin, Australia. These permits contain several fields that are spread over an area of 300 km2. This area is covered by two overlapping 3D seismic surveys within which 11 wells have been drilled. Our recent reprocessing, merging and PreSDM of these surveys produced a single seismic data volume of high quality over the study area. During the reprocessing we were afforded the chance to remove striping effects and suppress coherent noise more strongly than before. Full-waveform synthetics were computed from wells in the survey and used to optimise the design of a Radon filter with more `p traces' than used in the initial processing only a few years before. When compared to the field gathers, the synthetics revealed persistent multiples in the deep section and often these had been inadvertently picked during previous velocity analyses. Careful QC of the velocity picking also resolved a major problem in the overlap zone between the two surveys. PreSDM clearly improved fault definition over both the PreSTM and PosTM applied to the respective surveys during the initial processing. Time-variant spectral whitening helped to restore the bandwidth after migration and deliver a large improvement in temporal resolution. Interval velocities from the PreSDM depth model were used to shape the depth conversion away from well control. Subsequent re-interpretation, amplitude studies and seismic inversion have identified new prospects and have narrowed the large range of uncertainty in developing this area.