Integration of geophysical and field data for seepage detection and characterisation in Northwest and North Australia

Abstract

Seepage detection and shallow gas distribution are used as a tool for hydrocarbon exploration around Australia. The integration of remote sensing (SAR, Landsat), seismic data (3D and 2D lines), sub-bottom profile, multi-beam, side-scan sonar, echo-sounder, sea surface fluorescence data and geochemical analyses of seabed and the water column samples was used to test a combination of tools and techniques in an area of inferred seepage on the Yampi Shelf prior deployment of tools for seepage detection and characterisation in more poorly understood regions and frontier basins, in the Arafura Sea and Rowley Sub-basin. Active present-day hydrocarbon seepage has been imaged on the tropical carbonate Yampi Shelf, in 50 and 90 m water depth. Seepage is evidenced by gas plumes in the water column that are associated with seabed features, such as clusters of reflective blocks, hard-grounds, pockmark fields, and mounds. Seepage activity and intensity seems to vary with changes in pressure related to macro-tidal cycles. The seabed features coincide with sub-surface features such as areas of seismic signal attenuation under high amplitude reflectors, seismic discontinuities and bright spots. Hydrocarbon migration-seepage pathways appear to be controlled by the reactivation of pre-existing fractures and dykes within the basement. The experience gained during the Yampi Shelf survey was used to identify and sample locations of potential active hydrocarbon seepage in the Arafura Sea and Rowley Sub-basin. These integrated seepage surveys represent the initial work to identify new exploration opportunities and reduce risks for future petroleum exploration in these frontier regions.