An interdisciplinary collaborative research project
Strategic partnership with Industry - Research and Training (SPIRT)
Support for the initiation of this project was provided by the
ARCO Research Fund
Motivation for TRAPS
Aims of TRAPS
Plate kinematics
Palaeostress analysis
Benefits to Industry
Supporting TRAPS
Goals of SPIRT
Primary investigators: R. Dietmar Müller 1, Iain Mason 1
Associate investigators: Louis Moresi 2, Hans Muehlhaus 2, Michael Gurnis 3,
Research Fellow: Richard Albert 1
PhD students: Tara Deen1
Jason Zhao 1
1 Department of Geology and Geophysics, The University of Sydney, Sydney,
NSW 2006
2 Solid mechanics group, CSIRO Exploration and Mining, Nedlands, WA 6009
3 Seismological Laboratory, California Institute of Technology, Pasadena, CA
91125
Fault traps are common, especially on the Northwest shelf
* Occurrence of fault-reactivation and breaching of traps is a function
of palaeo-stresses
* Present-day intra-plate stresses are well understoo
* In contrast, palaeo-stresses are not known
* We need a predictive tool to understand tectonic reactivation through time
1) Construct a comprehensive model for relative and absolute plate motions
between Australia, India, Eurasia, Antarctica and tectonic blocks in Southeast
Asia in the Cenozoic.
2) Model dynamic boundary topography of the Australian plate through time
3) Model plate driving forces for the Australian plate through time using the
geometry and nature of plate boundaries from (1) as well as results from (2)
4) Compute intraplate stresses based on results from (3)
5) Compare orientations of predicted stresses from (4) with structural observations
from Australia's continental shelves and onshore basins to groundtruth models
6) Establish links between modelled patterns of stresses from (4), structural
observations (5) and hydrocarbon migration/breaching of traps.
Changing intraplate stresses through time have a direct impact on regional subsidence or uplift in sedimentary basins. The present day stress field of Australia is fairly well understood, both from observations and models. However, for understanding basin evolution on the Australian Plate, it is necessary to model plate motions, plate driving forces, and resulting intraplate stresses for the geological past. Understanding trap integrity is crucial for successful petroleum exploration. Many tentative links between plate tectonic events and tectonic reactivation on the Northwest shelf have been proposed. Yet it is not well understood exactly how the two are connected. Partly due to the availability of high-speed workstations at relatively low cost, a new brand of 3-d geodynamic models is being developed that include mantle convection, the history of plate motions, changing plate geometries through time and a realistic lithosphere. These models come closer to modelling the "real Earth" than ever before, and give us an opportunity to link these models to exploration targets. At the same time, the dense gravity anomaly grid from satellite altimetry has brought about a quantum leap in our knowledge of the tectonic structure of the seafloor and past plate kinematics. Therefore, we are forming an alliance of theoretical and observational geophysicists, as well as structural geologists, to link these fields and create models of the evolution of intra-plate stresses through time integrated with observations from basins.
Basal Cretaceous TWT contour map and perspective view in the Carnarvon Terrace
area. Light blue lines are reactivated faults interpreted from seismic
data.
We propose to create an integrated plate kinematic model for Australasia. It will include recently acquired geological and paleomagnetic data from Southeast Asia and new models for the relative and absolute motions of the major plates around Australia based on marine geophysical and satellite altimetry data. The plate model will include :
* New kinematic models for the evolution of all Australian margins as well
as Southeast Asia
* An updated absolute plate motion model
Conventional models for intraplate stresses do not take into account varying dynamic surface topography through time resulting from mantle convection. Combining mantle convection and a brittle lithosphere is important for understanding changing plate stresses through time as caused by the interaction of mantle buoyancy with plate geometries. For instance, our models show that dynamic surface topography, due to Australia overriding a sinking slab in the mantle (below), contributed to a major subsidence event in the Eromanga and Cooper basins at about 100 Ma.
* Create geodynamic models integrating mantle convection with other plate driving forces
* Compute intraplate stresses through time
Cretaceous Vertical Motion of Australia
and the Australian-Antarctic Discordance
The changing geometry of plate boundaries, the forces acting on them, and mantle-lithosphere interactions are the main factors controlling lithospheric in-plane stresses and dynamic topography. Palaeostress and fault kinematic data as well as structural data from seismic data provide important boundary conditions on evolving plate tectonic processes that affect continental margins. For instance, in eastern Australia, pre-Quaternary, Cenozoic dyke patterns show distinctly different trends from those that conform to the modern E-W compressional stresses. These older sets display N-S or NE-SW trends suggesting pre-Late Tertiary changes in orientation of principal stresses.
Recent research in Australian petroleum exploration has focussed on understanding why some traps on the Northwest shelf have been reactivated, while others have not. Even though much attention has been given to using a combination of fluid inclusions, fission track analyses, vitrinite reflectance and other data to understand the thermal and fluid migration history of hydrocarbon traps, there is no predictive framework to distinguish between low- and high-integrity traps. For example, it has been speculated that some traps may maintain their integrity because faults are reactivated in a "non-dilational" way, because of their geometry and alignment. Clearly, what we need to know to address this problem is the orientation of paleo-stresses through time, and their alignment with existing faults. Palaeo-stress orientations would have to be combined with other data from fault-trap reservoirs, such as faults mapped from seismic data and pore-pressure magnitudes.
* Integration of observations with numerical models will lead to a new understanding of how the crust responds to applied stresses through time.
* In particular, we will address the integrity of fault-traps by combining
structural and physical property data from hydrocarbon reservoirs with modelled
palaeo-stresses.
It has been recognised that many basins of the Australian Northwest shelf area and the Timor Sea have been subject to a number of repeated extensional and compressional tectonic periods. In subsidence analyses of wells northwest and northeast of Australia, a number of different events of accelerated subsidence (or uplift) at ~60 and ~50 Ma (Timor Sea), 20 Ma (Carnarvon and Roebuck basins, NW shelf, see example below), and 5 Ma (Timor Sea and Queensland Plateau). The 5 Ma event is known to be related to Miocene/Early Pliocene fault reactivation intimately associated with breaching of traps and remigration/loss of oil. The earlier events (60 and 50 Ma) may have been caused by the onset of collision between Greater India and Eurasia, and appear to be associated with the charging of some traps on the northwest shelf. The 20 Ma event correlates with the breaking-up of the Indo-Australian plate into two separate plates. Considering Australia's drastically changing absolute plate motion velocities through time (see page 4), it is clear that intra-plate stress directions and magnitudes would have varied dramatically through time. How instrumental were individual changes in plate geometries and associated stress-fields for the formation of structural traps, and how is oil charge or loss related to reactivation in a particular paleo-stress regime?
*We propose to link plate tectonic events, changing intraplate stresses, tectonic subsidence, fault reactivation, and formation/breaching of traps to understand basin evolution integrated with plate evolution.
* Create a predictive framework for fault reactivation, the timing and location
of hydrocarbon migration and the breaching of seals through time and space
* Distinguish potentially low- and high-integrity traps before drilling
* Offer students an opportunity to take part in cutting edge research in close
collaboration wit industry
* Produce a pool of graduates who are capable of addressing Australian petroleum
industry research and exploration needs
Contact: Dr. R. Dietmar Müller
Phone: (02) 9351 2003
Fax: (02) 9351 0184
E-mail: dietmar@geocsi.usyd.edu.au