Time-transgressive fault evolution and its impact on trap integrity: Timor Sea examples*
Bozkurt Ciftci A and Laurent Langhi BA CSIRO Petroleum Resources CSIRO Earth Science and Resource Engineering PO Box 1130, Bentley, WA 6102, Australia. Email: bozkurt.ciftci@csiro.au
B CSIRO Petroleum Resources CSIRO Earth Science and Resource Engineering PO Box 1130, Bentley, WA 6102, Australia. Email: laurent.langhi@csiro.au
The APPEA Journal 50(2) 701-701 https://doi.org/10.1071/AJ09065
Published: 2010
Abstract
Top and fault seal failure represents an exploration risk in the Timor Sea where hydrocarbons are typically associated with hourglass structures. These structures comprise two distinct systems of conjugate normal faults that formed by 1st-phase (late Jurassic) and 2nd-phase (Neogene) extensions. Horst blocks bounded by 1st-phase faults potentially trap hydrocarbons and are overlain by grabens bounded by 2nd-phase faults. The two fault systems generally merge and intersect in dip direction to form the composite and time-transgressive faults of the hourglass structures. The 2nd-phase of extension is seen as the dominant cause of the seal breach.
Revaluation of a series of hourglass structures on the Laminaria High confirmed two distinct sections of syn-kinematic strata. Bases of these sections correspond to maximum throws on the fault planes where the faults were probably nucleated. The presence of negative throw gradients upward and downward from the throw maximums indicate syn-kinematic deposition and fault growth, respectively. Assessment of these trends suggests that the 1st and 2nd-phase faults were detached at the onset of the 2nd-phase of extension. Connection was predominantly established by down-dip growth of the 2nd-phase faults while the reactivation of the 1st-phase faults may have remained minor.
Seismic evidence of leakage from attribute mapping is used to constrain the timing of fault linkage and to validate prediction of leaking fault planes. It was noted that downward propagation of the 2nd-phase faults towards the hydrocarbon traps stresses the top seal integrity due to fault tip deformation front and development of sub-seismic fractures.
Keywords: North West Shelf, Timor Sea, Laminaria, Corallina, Vidalia, normal fault, fault linkage, hourglass structures, crossing conjugate faults, fault tip deformation, trap integrity
Bozkurt received his BSc (1996), MSc (2001) and PhD (2007) degrees in geology. He started as an exploration geologist working for base metal projects in Eastern Black Sea region. Bozkurt then joined the national oil company of Turkey (TPAO) in 1999 and was involved in various hydrocarbon exploration projects across the Aegean and Eastern Mediterranean regions. Since 2008, he has worked for CSIRO with a focus on structural analysis, fault seal analysis and clay smear evolution. |
Laurent received an MSc (2000) and a PhD (2006) in geology from the University of Lausanne, Switzerland. After a year as a researcher at the University of Western Australia, he worked as an exploration geologist on West African basins. In 2006, he joined the Structural Geology and Reservoir Modelling Team of CSIRO Petroleum. His research integrates structural geology, geomechanical and fluid flow modelling and seismic data analysis for better trap integrity prediction and assessment of migration pathways. |
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