Oil Preservation Controlled by Strain Partitioning: New Insights into Trap Integrity Prediction in a Reactivated Setting, Laminaria High, Australian Northwest Shelf

Wayne R. Bailey, Anthony Gartrell, and Mark Brincat
CSIRO Petroleum, Perth, Australia

Exploration success in the Timor Sea region has been compromised by pervasive Late Tertiary fault reactivation and associated loss of trap integrity. The Laminaria High region, central Timor Sea, constitutes an anomalous area of relatively high exploration success with the discovery of several live, fault-bound oil columns. However, here too the traps are heavily reactivated, under filled or even dry, and they often show evidence of larger oil columns in the past, suggesting at least partial leakage. Thus, the Laminaria High represents a unique opportunity to investigate the controls on trap integrity, the results of which may help to improve future exploration success in the region.

Integration of charge history and structural analyses has identified a strong spatial relationship between the distribution of Late Tertiary strain, trap geometry and the preserved oil columns on the High. Progressive localisation of strain onto the larger faults within the population appears to have protected traps with favourable geometries from breaching during fault reactivation, but promoted breaching of others. Where faults with high Late Tertiary strain are located at the crest of a trap, oil columns are not preserved. In contrast, where faults with no or minor Late Tertiary strain are located at the crest of a trap, oil columns are preserved. These observations suggests that a relatively simple assessment of a trap's basic structural geometry may provide a first order approximation of trap integrity risks and could also be predictive of preserved hydrocarbon column heights.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005