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Fault Growth
• Synsedimentary growth from the Late Pliocene
• Large faults extend to Sea Floor
• Small faults terminate in the Pleistocene
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Strain Localisation
• Proportion of large to small faults
increasing over time
• Smaller faults become inactive in the Late
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Displacement contours on fault surface
• Maximum displacement at 1100 m
(about Mid Miocene)
• Lateral linkage of two segments
• Displacement decreasing below 1100 m
• Unlikely to link with deeper faults
Pleistocene.
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PESA WA Branch April 10th Luncheon Meeting

Evolution of the Neogene fault population, Laminaria area, Timor Sea
by Jane Cunneen, Tectonics Special Research Centre, University of WA

Abstract
The interaction between reservoir-level Jurassic faults and Neogene faults in the Timor Sea is poorly understood. A fault population analysis of Neogene faults in the Laminaria area uses high resolution 3D seismic data as a tool for determining fault linkage properties and the likelihood of Neogene trap breach. The evolution of the Laminaria fault population is described in terms of fault initiation, fault growth and partitioning of strain.

Fault initiation occurred in two stages. Large E-W trending faults initiated in the Early Miocene, while smaller ENE-WSW trending faults initiated in the Early Pliocene. Maximum fault lengths were rapidly established during the Miocene and fault growth was mainly facilitated by increases in cumulative displacement during the Late Pliocene to Late Pleistocene.

Partitioning of strain onto the major faults occurred from the Late Pliocene and only the major faults remain active today. Although Jurassic horst structures exert a geographic control on the location of Neogene faults, displacement-length relationships indicate that Neogene faults are unlikely to penetrate the Mesozoic sequence, decreasing the likelihood of Neogene trap breach.

Biography
Jane received her BSc (Hons) in Geology from the University of Western Australia in 1997. She then spent several years working and travelling overseas before returning to UWA in mid 1999 to commence a PhD. Her thesis topic is "Neogene deformation styles and fault reactivation in the Timor Sea, Northwest Australia", supervised by Myra Keep and sponsored by Woodside Energy Ltd. and Shell Development Australia. Jane is currently finishing her PhD and working as a technical consultant for IHS Energy, preparing petroleum prospectivity assessments for major Australian basins.

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A Tethyan Influence?

Open Depositional Fabric
Mid ramp rudstones/grainstones = reservoir potential.

Secondary porosity in dolomitised rudstone/grainstone from Woodada14.

PESA WA Branch April 10th Luncheon Meeting

Depositional and Diagenetic History of the Upper Permian Beefkeeper Formation, Woodada Gas Field, Onshore Northern Perth Basin, Western Australia
by Jirka Just

Abstract
The mixed carbonate/siliciclastic Beekeeper Formation is the key reservoir interval in the gas-bearing Woodada Field in the onshore northern Perth Basin. The objective of this study was to establish a depositional model for the Beekeeper Formation and to examine post-depositional aspects, notably its diagenesis and fracture porosity and permeability, and their implications for reservoir quality.

The Beekeeper Formation is Late Permian (latest Ufimian to Kazanian) in age and is restricted to the subsurface. The Beekeeper Formation rocks are predominantly 'clean' rudstones/grainstones, wackestones/packstones and bioclastic quartz sandstones, with minor mudstones. Seven facies are recognised and three facies associations. The formation is very fossiliferous with a typical Heterozoan Association of cool-water sessile filter feeding fauna dominated by brachiopods, bryozoans, and crinoids, with minor bivalves and benthic foraminifera.

Deposition was controlled by temporal and/or lateral alternation of two phases: fair-weather, low energy conditions, during which primary carbonate production occurred; and storm-dominated conditions of erosion and redeposition by storm waves and storm ebb-currents. The storm-deposited strata make up the rock record and the fairweather phase of primary deposition is inferred from the faunal assemblage in preserved storm deposited facies. Deposition of the Beekeeper Formation occurred on a shallow, low-gradient, coolwater, storm-dominated ramp.

The first Australian recognition of the typically warm-water microgranular foraminifer Abadehella coniformis in a cool-water setting may have palaeogeographic significance for models of the breakup of Gondwana.

A complex diagenetic history of burial cementation and compaction is recognised. The main cement phases are sparry calcite, sparry ferroan calcite and dolomite with minor silica. Cementation and compaction have wholly destroyed primary depositional porosity with secondary porosity created by subsequent dolomitisation and fracturing. Integration of depositional and diagenetic features has shown a link between depositional facies and the creation of effective porosity and permeability. Only 'clean' rudstones/grainstones appear to be susceptible to the extensive dolomitisation required for reservoir development.

A key problem in the Woodada Field is that although a well can be confidently sited to encounter specific lithological objectives, the type and degree of porosity to be encountered has proven to be unpredictable. This study provides the first steps towards a solution. The depositional model defines the lateral and vertical relationships between the different facies. Rudstones/grainstones with reservoir potential are found only in a mid-ramp setting and may or may not be dolomitised. Matching the drill-core position of the dolomitised rocks in relation to other facies with their wireline log signature may facilitate similar recognition in wireline logs from other wells. Thus it may be possible to map facies and dolomitisation distribution over the Woodada Field.

This study has demonstrated how useful core-based analysis can be in enhancing understanding of reservoir units but has been limited by few cored intervals from the Woodada field. Routine coring of reservoir intervals is recommended during future drilling. A large amount of cuttings are available from most wells and geochemical analysis of selected reservoir interval samples will further define reservoir petrology. Reinterpretation of wireline logs based on quantitative geochemical data and depositional relationships may be the most important step in determining the distribution of reservoir rocks.

Determining the depositional relationship between the Wagina Formation, Dongara Sandstone and the Beekeeper Formation may be significant in locating potential siliciclastic shoreface sandstone reservoirs. Determining the provenance of the siliciclastic sand grains of each formation could establish a potential link. A comprehensive regional study that fully integrates all available geophysical and lithological data would be an important step toward the development a regional model for Late Permian deposition in the Woodada Field.

The interest generated by recent hydrocarbon discoveries at Cliff Head and Hovea may make it worthwhile to acquire new seismic data to better define reservoir boundaries and the role of faulting and fracturing in reservoir development at Woodada and throughout the Northern Perth Basin.

Biography
Jirka completed a B.Com (Curtin) in 1985 and then spent five years with the public service as a cost accountant (budgeting, financial forecasting and business analysis). Leaving in 1991 and getting married and travelling the world. He has since worked as a plumber's offsider, childcare centre manager and a kitchenhand on the Stag platform (Apache Energy). This motivated him to change direction and in 1999 he enrolled in the B.Sc at UWA. He completed his B.Sc Hons (Geology) last year. Currently an exploration geologist with Newcrest Mining, based in Kalgoorlie, married with two kids and looking to establish a career in the petroleum industry.

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PESA WA Branch April 10th Luncheon Meeting

Automatic Event Picking Using a Probabilistic Neural Network
by Troy Thompson

Abstract
Automatic picking of events on common image gathers has the potential to reduce the cycle time of prestack depth migration and improve inversion robustness. An algorithm incorporating supervised learning, statistical classification and image processing will be further developed as an autopicking tool. The use of wavelet-transform methods for feature creation and statistically derived constraints will be discussed.

Feature images are created from the raw data. Optimal images, which capture the important behavior of measured signals, are used for voxel classification by a probabilistic neural network. Classification produces a posterior probability image depicting the location of signal events in the raw data. Further processing converts these probabilities into final event picks. Emphasis will be placed on a new method using flow features and probability for calculating and constraining these final picks. The method gives improved results with good agreement to human interpreted picks.

Biography
Troy Thompson received a B.Sc Hons (1st class) in Exploration Geophysics from Curtin University in 1998. In 1997, he was awarded the Dean's Prize for the most outstanding third year student in the Faculty of Science at Curtin, as well as the Australian Institute of Physics Prize as the top geophysics graduate of that year. He is currently in the final year of a PhD in geophysics during which he was awarded the John Curtin Postgraduate Scholarship, a MERIWA Supplementary Scholarship and the 2001 PESA Post-Graduate Scholarship for Research in Geosciences. He is a student member of the SEG, ASEG, EAGE, and PESA. His claim to fame in 1999 was to hike the full length of the Appalachian Trail over a 7-month period.

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