AGSO Marine Survey 176 Direct Hydrocarbon Detection North-West Australia: Yampi Shelf; Southern Vulcan Sub-Basin; Sahul Platform (July/September 1996) -Operational Report and Data Compendium-

The Australian Geological Survey Organisation (AGSO) carried out a regional water column geochemical `sniffer' program on the north-west Australian continental margin, from 28 July to 02 September 1996. The survey acquired data on bottom water hydrocarbon concentration and composition on the Yampi Shelf, southern Vulcan Sub-basin and Sahul Platform. A primary goal was to detect natural hydrocarbon seepage. A total of 3535 line km (150 survey lines) of sniffer data were acquired during the program, using the RV Rig Seismic. In addition to the sniffer program, the survey tested a new high-resolution seismic cable. Also, a total of eight gravity cores were taken. The principal areas of seepage detected were on the Yampi Shelf where very high, dry, thermogenic gas concentrations (~1%wet) were detected where the regional seal thins onto the Kimberley Block basement (O'Brien et al.,1998a). Principal areas of seepage were located inboard from the Cornea trend. In addition, significantly lower concentrations of relatively wet gas were detected around the Skua field, in the southern Vulcan Sub-basin. Drier, low-level methane seepage was detected around the breached East Swan and Eclipse fields.

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