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ABSTRACT: Fault geometry and seal attribute mapping in the Bass and Otway Basins, Australia

Boult, Peter1, and Richard M Jones2
(1) BORAL Energy Resources Ltd, Adelaide, Australia 
(2) Thebarton Campus, Adelaide, Australia

Gridding of geometrical fault attributes dip, strike and horizon displacement aids in constraining interpretation of deep horizon based data and structural history. In tectonically complex regions such as the Otway Basin the seismic image is often poor at depth and fault traces are easier to interpret than horizons. By modelling fault geometrical attributes, faults can be regarded as extra data loci linking interpretation across seismic dip lines in areas of 2D seismic. In the Bass Basin fault geometry attributes aid in the timing interpretation of cross-cutting faults.

For fault seal analysis both the tendency for fault reactivated structural permeability and across fault leakage (AFL) are assessed. The former is more important in the Otway Basin and the latter in the Bass Basin. Relative probability of seal failure through effective structural permeability is mapped directly along centreline fault locations for individual horizons. This technique provides a rapid assessment tool for risking fault bound prospects. For AFL and juxtaposition analysis, stratigraphy between mapped horizons is assigned to hangingwall and footwall locations using sedimentology principles. In the Bass Basin volcanic sills and dykes are incorporated into 3D fault models. For fault rock analysis, the tendency for fault rock / shale gouge to be entrained is calculated directly from wireline log data and attributes such as shale gouge ratio (SGR) are plotted directly onto the fault surface. For fault seal risk analysis SGR values are then cross-plotted with across fault pressure data and compared with known accumulations within the basin and world-wide analogues.

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