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Fault-Seal Efficiency and Siliciclastic Trap Integrity Assessment Using Geomechanical Modelling and 3-D Seismic Multi-Attributes

Langhi, Laurent 1; Zhang, Yanhua 2; Gartrell, Anthony 3; Dewhurst, David N.1; Underschultz, James 1; Strand, Julian 1
1 CSIRO Petroleum Resources, Kensington, WA, Australia.
2 CSIRO Exploration & Mining, Kensington, WA, Australia.
3 Brunei Shell Petroleum, Seria, Brunei Darussalam.

Hydrocarbon provinces located on continental margins often experience post-charge structural activity with renewal of fault movements. While critically-stressed faults are widely cited as conduits for fluid flow, reactivation of trap-bounding faults can cause fault-seal breach and therefore represents a major risk to the preservation of trapped hydrocarbons.

Coupled deformation and fluid flow numerical modelling can be used to evaluate the effects of regional deformation on local strain and fluid flow partitioning during fault reactivation and to predict risks associated with up-fault leakage of hydrocarbon.

This approach is applied to the offshore Bonaparte Basin (Laminaria High, Australian NW Shelf) to unravel the effect of Tertiary to recent tectonic reactivation on several Late Jurassic traps, and to explain the complex distribution of paleo and preserved oil columns. The 3D numerical model with the size of 50x25 km (map view) and 10 km (depth) is used simulate the response of complex trap-bounding fault networks to extensional reactivation and then to characterise the interaction between the stress/strain state and fault seal efficiency and to predict up-fault flow pattern. Leakage indicators and remigration pathways indicated from 3D seismic multi-attributes are used as a benchmark to evaluate the outcomes of the numerical model.

The results show that the distributions of shear strain and positive volumetric strain as well as fluid flux are clearly heterogeneous along and near fault planes. This suggests that specific fault segments might be prone to experience leakage when others might retain a hydrocarbon column. It emerges that fault growth processes and linkage styles, faults distribution and density, and fault tip arrangements are key elements driving the partitioning of strain and flow behaviour. These elements along with the specific geometry of individual traps are then critical in determining oil preservation during the late reactivation phase on the Laminaria High.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009