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Geoffrey O'Brian1
(1) Australian Geological Survey Organization, N/A, Australia

Abstract: Multiple remote sensing technologies to evaluate hydrocarbon migration, Yampi Shelf, North-Western Australia

The Yampi Shelf is highly prospective, with two discrete hydrocarbon sources producing dry gas and oil. To reduce exploration uncertainty relating to gas flushing and poor top seal capacity, a study was undertaken to characterise hydrocarbon migration in the area. It used seismic amplitude and structural data (~2,000 km) integrated with shipboard water column geochemical sniffer (WaSi) data (~4,000 km), satellite Synthetic Aperture Radar or SAR data (five-fold coverage) and 3,500 km of aircraft-acquired Airborne Laser Fluorosensor (ALF) data. Data were acquired synchronously and in staged programs, to allow both direct comparison and time-series analysis of results.

Massive, natural dry gas and oil seepage was detected, though the relative abilities of WaSi, SAR and ALF to detect and characterise this seepage were markedly different. The spatial distribution, concentration and relative composition of the detected seepage was controlled principally by the regional seal's thickness and capacity, rather than by the inherent composition and flux of the migrating hydrocarbons.

WaSi preferentially identified gas seepage, often in basin-ward locations, since the high relative permeability of gas favored its early leakage, even through thick seals. SAR preferentially identified oil seepage, which was episodic and largely restricted to the basin-margin at the regional 'zero-edge-of-seal', reflecting the low relative permeability of oil, even through thin seals (it leaked 'late'). ALF detected low-level oil seepage from charged traps, but did not identify the 'basin-edge' seepage detected by SAR.

Understanding these interactions between geology and hydrocarbon charge are critical for the reliable interpretation of such remote sensing data.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana