Characteristics of the Gidgealpa Group Composite Resource Play in the Cooper Basin, South Australia

The Patchawarra Formation is characterised by Permian aged fluvial sediments. The conventional hydrocarbon play lies within fluvial sandstones, attributed to point bar deposits and splays, that are typically overlain by floodbank deposits of shales, mudstones and coals. The nature of the deposition of these sands has resulted in the discovery of stratigraphic traps across the Western Flank of the Cooper Basin, South Australia. Various seismic techniques are being used to search for and identify these traps. High seismic reflectivity of the coals with the low reflectivity of the relatively thin sands, often below seismic resolution, masks a reservoir response. These factors, combined with complex geometry of these reservoirs, prove a difficult play to image and interpret. Standard seismic interpretation has proven challenging when attempting to map fluvial sands. Active project examples within a 196 km2 3D seismic survey detail an evolving seismic interpretation methodology, which is being used to improve the delineation of potential stratigraphic traps. This involves an integration of seismic processing, package mapping, seismic attributes and imaging techniques. The integrated seismic interpretation methodology has proven to be a successful approach in the discovery of stratigraphic and structural-stratigraphic combination traps in parts of the Cooper Basin and is being used to extend the play northwards into the 3D seismic area discussed.

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HIGH RESOLUTION PALAEOGEOGRAPHIC MAPPING OF THE FLUVIAL-LACUSTRINE PATCHAWARRA FORMATION IN THE COOPER BASIN, SOUTH AUSTRALIA

The APPEA Journal ◽

10.1071/aj01005 ◽

2002 ◽

Vol 42 (1) ◽

pp. 65 ◽

Cited By ~ 4

Author(s):

P.C. Strong ◽

G.R. Wood ◽

S.C. Lang ◽

A. Jollands ◽

E. Karalaus ◽

...

Keyword(s):

High Resolution ◽

South Australia ◽

River System ◽

Structural Features ◽

Gas Reservoirs ◽

Predictive Tool ◽

Sequence Stratigraphic ◽

Channel Belt ◽

Reservoir Connectivity ◽

Cooper Basin

Fluvial-lacustrine reservoirs in coal-bearing strata provide a particular challenge for reservoir characterisation because of the dominance of coal on the seismic signature and the highly variable reservoir geometry, quality and stratigraphic connectivity. Geological models for the fluvial gas reservoirs in the Permian Patchawarra Formation of the Cooper Basin are critical to minimise the perceived reservoir risks of these relatively deep targets. This can be achieved by applying high-resolution sequence stratigraphic concepts and finescaled seismic mapping. The workflow begins with building a robust regional chronostratigraphic framework, focussing on widespread lacustrine flooding surfaces and unconformities, tied to seismic scale reflectors. This framework is refined by identification of local surfaces that divide the Patchawarra Formation into high-resolution genetic units. A log facies scheme is established based on wireline log character, and calibrated to cores and cuttings, supported by analogue studies, such as the modern Ob River system in Western Siberia. Stacking patterns within each genetic unit are used to determine depositional systems tracts, which can have important reservoir connectivity implications. This leads to the generation of log signature maps for each interval, from which palaeogeographic reconstructions are generated. These maps are drawn with the guiding control of syn-depositional structural features and net/ gross trends. Estimates of fluvial channel belt widths are based on modern and ancient analogues. The resultant palaeogeography maps are used with structural and production data to refine play concepts, as a predictive tool to locate exploration and development drilling opportunities, to assess volumetrics, and to improve drainage efficiency and recovery during production of hydrocarbons.

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EXPLORATION IN THE COOPER BASIN

The APPEA Journal ◽

10.1071/aj88031 ◽

1989 ◽

Vol 29 (1) ◽

pp. 366 ◽

Cited By ~ 3

Author(s):

R. Heath

Keyword(s):

Oil And Gas ◽

South Australia ◽

Mature Stage ◽

Small Contribution ◽

Terrestrial Source ◽

Seismic Acquisition ◽

Proterozoic Basement ◽

Gas Fields ◽

Coal Measures ◽

Cooper Basin

The Cooper Basin is located in the northeastern corner of South Australia and in the southwestern part of Queensland. The basin constitutes an intracratonic depocentre of Permo- Triassic age. The Cooper Basin succession unconformably overlies Proterozoic basement as well as sediments and metasediments of the Cambro- Ordovician age. An unconformity separates in turn the Cooper succession from the overlying Jurassic- Cretaceous Eromanga Basin sediments.The Permo- Triassic succession comprises several cycles of fluvial sandstones, fluvio- deltaic coal measures and lacustrine shales. The coal measures contain abundant humic kerogen, comprising mainly inertinite and vitrinite with a small contribution of exinite. All hydrocarbon accumulations within the Cooper Basin are believed to have originated from these terrestrial source rocks.Exploration of the basin commenced in 1959 and, after several dry holes, the first commercial discovery of gas was made at Gidgealpa in 1963. To date, some 97 gas fields and 10 oil fields, containing recoverable reserves of 5 trillion cubic feet of gas and 300 million barrels recoverable natural gas liquids and oil, have been discovered in the Cooper Basin. Production is obtained from all sand- bearing units within the Cooper stratigraphic succession.The emphasis of exploration in the Cooper Basin is largely directed towards the assessment of four- way dip closures and three- way dip closures with fault control, but several stratigraphic prospects have been drilled. Furthermore, in the development phase of some gas fields a stratigraphic component of the hydrocarbon trapping mechanism has been recognised.Improvements in seismic acquisition and processing, combined with innovative thinking by the explorers, have facilitated the development of untested structural/stratigraphic plays with large reserves potential. Exploration for the four- and three- way dip closure plays in the Cooper Basin is now at a mature stage. However, reserves objectives are expected to continue to be met, with the expectation of a continuing high success rate.Selected new plays are expected to be tested within a continuing active exploration program as exploration for oil and gas in the Cooper Basin refines the search for the subtle trap.

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A SEISMIC MODEL OF FAULTS IN THE COOPER BASIN

The APPEA Journal ◽

10.1071/aj83033 ◽

1984 ◽

Vol 24 (1) ◽

pp. 421

Author(s):

R. J. Gray ◽

D. C. Roberts

Keyword(s):

Hanging Wall ◽

South Australia ◽

Shadow Zone ◽

Seismic Line ◽

Seismic Section ◽

Seismic Modelling ◽

Geological Cross Section ◽

Major Fault ◽

Seismic Lines ◽

Cooper Basin

A synthetic seismic section was modelled to help in the interpretation of Cooper Basin seismic lines which cross major faults and exhibit shadow zones.A major fault bounding the northwest flank of the Packsaddle Structure in the Merrimelia-Innamincka Farmout Block in South Australia was selected for modelling. A geological cross-section postulated on the basis of wells on either side of the fault was fed into the seismic modelling package AIMS (Advanced Interpretive Modelling System — licensed by Geoquest International Inc.) to produce a synthetic seismic line. This synthetic line provided a realistic match with an actual seismic line across the fault. Pre-stack migration of the actual seismic data is suggested to provide additional evidence for the reliability of the model.The shadow zone in the synthetic section is caused by dipping events in the fault shadow zone created by compaction of the Toolachee and Patchawarra Formations along the hanging wall of the fault plane. The dipping events cause reflected energy to be detected outside the fault zone. The large component of compaction within the Permian section is largely ascribed to thick coal horizons. The possibility of petroleum traps in the hanging wall of the fault is inferred and drilling is recommended.

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PETROPHYSICS OF THE COOPER BASIN, SOUTH AUSTRALIA

The APPEA Journal ◽

10.1071/aj71004 ◽

1972 ◽

Vol 12 (1) ◽

pp. 23

Author(s):

Chris R. Porter ◽

Hugh Crocker

Keyword(s):

Water Saturation ◽

South Australia ◽

Clay Content ◽

Computer Applications ◽

Test Results ◽

Upper Limits ◽

Porosity And Permeability ◽

Log Interpretation ◽

Logging Tool ◽

Cooper Basin

In the Cooper Basin lithologic types can be recognised and related to logging tool response. Empirical relationships between log readings and porosity and permeability can be developed locally by comparing log readings with core data. Water saturation/porosity relationships are found to be convergently hyperbolic. The effects of clay minerals upon water saturation determination show that only in the low porosity range is correction for clay necessary.A plot of Sw versus Sxo allows prediction of probable test results and has been confirmed by actual Cooper Basin well tests.An attempt to relate clay content to permeability has been successful in estimating tentative upper limits of permeability. Computer applications to log interpretation are utilized in achieving petrophysical parameters.

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