USING INTEGRATED REMOTE SENSING TECHNOLOGIES TO EVALUATE AND CHARACTERISE HYDROCARBON MIGRATION AND CHARGE CHARACTERISTICS ON THE YAMPI SHELF, NORTHWESTERN AUSTRALIA: A METHODOLOGICAL STUDY

Abstract

As part of a major interpretative study of the Yampi Shelf, northeastern Browse Basin, the Australian Geological Survey Organisation (AGSO) acquired regional seismic, water column geochemical sniffer (WaSi), RadarSat Synthetic Aperture Radar (SAR), and high resolution bathymetric data over the area between 1995 and 1998. These data have been integrated in order to better understand both the hydrocarbon charge and top seal capacity characteristics of the area, and the relative responses of assorted remote sensing technologies to hydrocarbon migration, leakage and seepage. The area investigated comprises part of a Palaeozoic to Mesozoic flexural ramp margin, which dips northwest away from the flanking cratonic Kimberley Block. The basement has a rugose topography, with some horst blocks elevated 500 m above the surrounding basement. Progressive onlap of Cretaceous post-rift seals onto the ramp causes the regional seal to become thinner and sandier margin- ward. In some of these more margin-ward locations, some prominent basement highs are 'bald' of seal, whereas in others, the seal thins dramatically onto topographically prominent, landward-dipping tilt blocks. Natural hydrocarbon seepage was confirmed independently by SAR and WaSi, though the relative response and sensitivity of each technology to seepage of varying rates and compositions are quite different. Overall, the principal seeping hydrocarbon is dry (<1% wet) thermogenic gas (δ13C = −42.45). The first-order control on both the distribution, and perhaps the composition, of the detected seepage is the thickness of the regional Cretaceous sealing units.