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New Guinea – A Structural Kibosh With >40 Tcf gas; What Have We Learned?
By Dr Kevin Hill, 2001 PESA Australian Lecturer (PAL)
Summary
This talk illustrates, in technicolour and superanimation, the great variety
of structural interpretations applied to the Fold Belt in New Guinea,
and their success, fortuitous or otherwise, in discovering hydrocarbons.
It is interesting to observe that the present paradigm is similar to the
models proposed in the 1960s. The talk then reviews the key elements of
modern structural and tectonic analysis and the potential to add to the
40 Tcf of gas already discovered in New Guinea.
Detailed
Abstract
Both structural and tectonic models for the evolution of New Guinea have
evolved through time, using the popular model of the day. This is largely
because of the lack of data in the karstic jungle-covered terrain, requiring
the use of external models. 60s inter-pretations involved geosynclines
(remember them?) gravity sliding and asymmetric folds. 70s interpretations
used the new plate tectonics, ie. arc-continent collision, to build a
thrust belt with little folding. The 80s 'rigorous' thin-skinned geometrical
analyses ruled out prospectivity just as the first discovery was drilled.
Adoption of the inversion bandwagon in the 90s overcom-pensated, generating
enormous (farmout?) prospects.
Drilling
of the Kutubu and Gobe oil field development wells, acquisition of modern
seismic data, and analysis of the mechanical stratigraphy demonstrate
complex structures with considerable asymmetric folding and break-through
thrust-faults (as inferred in the 60s) underlain by inverted basement
exten-sional faults and asymmetric detach-ment folds that break through
the overturned forelimb.
Modern
structural and tectonic analysis indicates major changes in structural
style along strike, probably due to the strength and nature of the underlying
crust, just as along the NW Shelf. In the oil province of Papua New Guinea,
the relatively low fold belt has not yet impinged on strong Australian
crust. The adjacent gas-condensate province in the western Papuan Fold
Belt has just impinged on the strong crust, developing basement-cored
anticlines, such as the 5+ Tcf Hides gas field. In the Irian Jaya Fold
Belt, a 15 km thick Palaeozoic and Mesozoic sequence has been thrust over
strong Australian crust building 5 km high mountains and an adjacent foreland
basin. Structures in the mountains are breached but the adjacent foreland
basin has hydrocarbon potential. Further west, in the 'Bird's Neck' area,
the poorly known Lengguru Fold Belt resembles the Papuan oil province
but has been subject to deep burial and Pleistocene extensional faulting.
The exception is in the northern Lengguru Fold Belt where further discoveries
like the 30 Tcf Tangguh gas province are possible, as well as large oil-bearing
anticlines.
One-Day
Workshop
Practical Interpretation of Extension, Inversion and Compression Structures;
a Workflow.
Workshop
Most hydrocarbon prospects are critically dependent upon structural interpretation
yet routine validation of the interpretation is rare. This one day structural
workshop will focus on practical methods to interpret extensional, inversion
and compressional structures on seismic data and from outcrop. It will
focus on the relationships between faults, folds, sedimentary packages
and regional elevation and how they can be used predictively to validate
an interpretation and hence a prospect. Emphasis is placed on the 'Structural
Family' present in an area, which depends strongly on the basement architec-ture
and tectonic history.
Seismic
interpretation examples are drawn from the Timor Sea, Bass Strait, the
Taranaki Basin and New Guinea, amongst others. Field examples of 2D and
3D structures include Watchet, the Otway Basin, Cape Lip-trap, the Rockies
and PNG.
To
further validate an interpretation, balancing and restoration of structural
interpretations will be demonstrated by hand and using GeosecTM and 2D/3DMove.
Introduction
• The nature of faults and folds, the relationship between them and
to adjacent sedimentary packages. (Exercise – seismic packages)
• Changes in extensional and compres- sional interpretation through
time.
• Structural families
• Examples of restoration.
• A workflow for structural interpretation
Extension
• Planar, domino, listric faults and rollover anticlines (Figs 1
& 2)
• The Chevron construction and growth packages (Exercise)
• Seismic restoration - Geomorpher
• 3D fault geometries (Fig. 3)
• Fault plane displacement maps (Exercise)
• 3D restoration
Inversion
• Definition and examples
• Seismic interpretation (Exercise) and restoration (Fig. 4)
• 3D geometries
• Inversion to mountain belts - Pyrenees
Compression
• Ramps, flats and detachments (Fig. 5)
• Detachment folds (Fig. 6)
• Fault bend folds - ramp anticlines (exercise)
• Fault propagation folds (exercise)
• 3D geometries
• Restored sections from New Guinea
Biography
Kevin Hill is a principal partner in 3D-GEO, the structural interpretation
and restoration consultancy, and an Associate Professor in Earth Sciences
at the University of Melbourne. After graduating from Oxford, Kevin obtained
an MSc on foothills structure in the Canadian Rockies and then worked
for BP in Canada and in their Structural Specialist's Group in London.
Structural analysis covered extensional, inversion and compressional terranes,
ranging from the Apennines to Tunisia and British Columbia to Kalimantan.
Returning to academia, Kevin undertook a PhD on the structure and thermochronology
of the Fold Belt in New Guinea and has since undertaken projects on Australia's
Bass Strait and Timor Sea margins, as well as consulting in SE Asia. Kevin
has recently moved from La Trobe University to the University of Melbourne
and is setting up 3D-GEO for a mid-year launch.
Dr
Kevin C. Hill
3D-GEO, Earth Sciences University of Melbourne,
VIC 3052
Email: kevin@3d-geo.com
Mobile: 0411 161 608
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