A Wrench and Inversion Model for Structures in the Timor Sea Region, Northwest Australia

Andrew W. Nelson

A structural model is developed for part of the Timor Sea region, northwest Australia, involving multiple strike-slip episodes, and significant changes in the regional or local stress regimes. It is interpreted that both normal and reverse faults have existed since at least the Permian, and have changed their sense of movement in response to changing stress fields, with latest changes occurring as a result of Tertiary collision of the Australian and Eurasian Plates. Both 2-D and 3-D seismic data sets are used to demonstrate development of conventional simple strike-slip models into complex multi-episode models incorporating through-going and abandoned faults. After only three episodes of fault movement, one of which involves inversion, the fault linkages and structural hi tory can become very difficult to unravel.

The Jabiru Oil Field is shown to have developed at the intersection of orthogonal faults, with resultant restraining fault bend geometry. Failure to identify a large part of the field for several years after discovery may be attributed to misinterpretation of reversal of fault throw with depth (resulting from inversion), and to lack of appreciation of the significance of abandoned faults.

Factors including fault abandonment, fault dips steepening with depth (including sideways concave faults), fault inversion, and trap seal development on inverted and abandoned faults may have a significant influence on the way petroleum traps are mapped and the trapping capacity of seals.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California