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ABSTRACT: A Neogene-Recent tectonic model for the Timor Sea Area, Offshore Australia: geomechanical implications for charge, trap and retention

Shuster, Mark W.1, David A. Castillo2, Eaton Simon1 (1) Shell Development (Australia), Perth, Australia (2) GeoMechanics International Inc. (Australasia), Magill, Australia

A tectonic model invoking wrench-related deformation and strike-slip reactivation of structures in the Greater Timor Sea from the Neogene to the present day associated with convergence between the Australian and SE Asian plates is consistent with observed kinematic and present-day stress indicators, subsidence trends, and recent earthquakes. Strike-slip faulting in the Australian sector is associated with oblique convergence and extension related to flexure of the loaded and partially subducted Australian plate, where present-day deformation is accommodated along pre-existing faults. Assessment of structural maps, isopachous maps and tectonic subsidence curves indicate that areas such as the Cartier Trough and Malita Graben formed as pull-apart basins associated with rapid infill during the Neogene wrench-related deformation. Understanding the structural history in these basins is extremely important given they are associated with late (Neogene) hydrocarbon charge.

Analysis of borehole images data, drilling pressure records, and laboratory rock strength data have been used to construct a well-constrained stress tensor for the Timor Sea area in several blocks within ZOCA and AC/P. The regional maximum horizontal stress direction (SHmax) in the Timor Sea area is approximately N-S and sub-parallel to the convergence direction between Australia and Indonesia. East of ZOCA, the convergence direction is consistent with an observed NE-SW SHmax stress direction. In situ measurements of stress magnitudes indicate a strike-slip stress regime (SHmax>Sv>Shmin) consistent with recent earthquakes. The tectonic model has direct implications for hydrocarbon exploration in that prospect risks associated with Neogene fault trap reactivation and charge can be regionally assessed before drilling.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia