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Case Histories from Europe and Australasia

January 01, 2002


An integrated seismic, water-column geochemical sniffer, and Airborne Laser Fluorosensor (ALF) study of the Vulcan Subbasin, Timor Sea, Australia, has been undertaken to develop a simple and predictive exploration methodology to reduce exploration risk associated with hydrocarbon migration and trap integrity in this region.

Close and consistent agreement has been obtained between the distributions of hydrocarbon seepage, as defined by the three independent technologies: seismic data, ALF, and geochemical sniffer. In particular, the methane concentrations in the bottom waters mimic the distribution of the ALF anomalies at the sea surface. This suggests that the ALF anomalies are produced via the transportation of aromatic hydrocarbons to the surface by the methane, either as a dissolved phase or as a thin “skin” on the surface of the methane gas bubbles.

Mapping of leakage-related velocity effects using seismic data has shown that the faults that define the commercial oil fields in the Timor Sea (all of which have leaked to some extent) have leaked only along limited parts of their length. These leaky fault segments extend for no more than 1500 m, with 500–1000 m being typical. These segments are effectively “point sources” for hydrocarbon leakage and seepage, and they produce intense, but areally restricted, ALF and geochemical sniffer responses.

In contrast, breached traps and breached migration fairways have leaky fault segments extending for 3000 to 6000 m. Areally extensive (but low-intensity) ALF anomalies are present over these traps and fairways, probably because they are still receiving a low level of hydrocarbons migrating from the thermally mature source depocenters. The geochemical sniffer anomalies associated with these traps typically are weak, because insufficient volumes of hydrocarbons are presently migrating through the trap to substantially affect the hydrocarbon concentration within the water column.

A simple “relative response matrix,” based on these multiple approaches and technologies, has been constructed, allowing the ranking of exploration prospects in the Timor Sea (in relation to probable charge history and trap integrity) prior to drilling. This matrix may be sufficiently generic to be applicable to numerous other structurally reactivated basins around the world.

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AAPG Studies in Geology

Surface Exploration Case Histories: Applications of Geoschemistry, Magnetics, and Remote Sensing

Dietmar Schumacher
Dietmar Schumacher
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Leonard A. LeSchack
Leonard A. LeSchack
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American Association of Petroleum Geologists
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Publication date:
January 01, 2002




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