--> Abstract: Mechanism of Up-Fault Seepage and Seismic Expression of Discharge Sites from the Timor Sea, by Laurent Langhi, Yanhua Zhang, Anthony Gartrell, Dave Dewhurst, Jim Underschultz, and Bozkurt N. Ciftci; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Mechanism of Up-Fault Seepage and Seismic Expression of Discharge Sites from the Timor Sea

Laurent Langhi1; Yanhua Zhang1; Anthony Gartrell2; Dave Dewhurst1; Jim Underschultz1; Bozkurt N. Ciftci1

(1) CSIRO, Kennsington, WA, Australia.

(2) Brunei Shell Petroleum, Seria, Brunei Darussalam.

3D coupled deformation (FEM) and fluid flow numerical modeling, charge history analysis and seismic imaging of leakage geobodies have been integrated to investigate the response of a complex set of Jurassic trap-bounding faults to extensional reactivation and assess hydrocarbon up-fault seepage on the Laminaria High (Timor Sea, Australian NW Shelf).

Fluid inclusion data are consistent with the presence of palaeo-oil columns below the current accumulations in the Laminaria and Corallina Fields. Additional data shows evidences for underfilled (current and palaeo-oil column) and breached (dry with palaeo-oil column) closures in the area implying active and widespread seepage took place after the time of charge.

The deformation model results show the heterogeneous distributions of strains along fault planes and the high correlation with current and palaeo-accumulations. It suggests that, with sufficient reactivation shear strain accumulated by reservoir faults, ductile deformation gives way to brittle failure in the top seal allowing active pathway to develop and up-fault seepage to take place from the reservoir to thief zones or the free-surface.

The distribution of leakage indicators, defined on 3D seismic data, correlates with the numerical prediction of fault seal effectiveness and emphasizes that strain and up-fault fluid flow partitioning is constrained by pre-reactivation fault size, lateral fault tips distribution and the presence of fault jogs inherited from growth processes.

Theses elements explain the complex distribution of paleo and preserved oil columns in the study area and support the Cenozoic tectonics being the driving mechanism behind trap breaching and hydrocarbon seepage.