--> Abstract: A Multi-Disciplinary Evaluation of the Key Controls on Trap Integrity in Australia's Timor Sea Using Integrated Remote Sensing Technologies, by G. W. O'Brien, P. Quaife, and B. Messent; #90937 (1998).

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Abstract: A Multi-Disciplinary Evaluation of the Key Controls on Trap Integrity in Australia's Timor Sea Using Integrated Remote Sensing Technologies

O'BRIEN, GEOFFREY W., Australian Geological Survey Organisation; PAUL QUAIFE, World Geoscience Corporation; BARRY MESSENT, BHP Petroleum

Summary

Poor trap integrity, which relates to Mio-Pliocene continental convergence and fault reactivation, is the principal exploration risk within Australia's Timor Sea region. In this area, the style of the Neogene structural reactivation is a direct function of the first-order, margin-scale architecture. Flexural extension, associated with localised proto-foreland formation on the Timor Trough, has resulted in significant extensional reactivation of pre-existing Jurassic rift faults. At a sub-basin scale, the nature (throw and orientation) of the Neogene faulting is due to a complex interplay between the orientation and displacement of the underlying Jurassic fault segments, the total amount of Neogene flexuring (particularly the proximity to Timor Trough), the manner in which fault displacement is transferred along strike, and the nature and orientation of the under-pinning Proterozoic structures.

In spite of this complexity, empirical data show that the faults which define the moderate integrity traps (ie. the traps that host the majority of the oil in the Timor Sea) have only leaked along very limited parts of their length. Typically, the ‘leaky' fault segments in these traps extend for no more than 1,500 m, with 500-1,000 m being more typical. These leaky segments are effectively ‘point sources' which produce very areally restricted sniffer and ALF responses.

In contrast, breached traps have ‘leaky' fault segments which extend for 3,000 to 6,000 m along strike. Since most or all of the hydrocarbons were lost from these traps several million (3-5 Ma) years ago, they usually do not have associated sniffer anomalies (ie. insufficient volumes of hydrocarbons are present within the trap to substantially affect the concentration within the water column). However, areally extensive ALF anomalies are commonly present, possibly because these traps are still receiving low level charge from the source depocentres, which continually produces very low level seepage to the sea surface.

Such observations suggest that the acquisition of sniffer and/or ALF data, when used in conjunction with regional geological information and detailed seismic mapping, could significantly decrease exploration risk, whilst increasing exploration efficiency, in this prospective, but complex, geological province.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah