TABLE OF CONTENTS...subsequent seal breach by reactivation: A case study of the Zema Prospect, Otway...

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TABLE OF CONTENTS

ABSTRACT ....................................................................................................................... 2

DECLARATION............................................................................................................... 4

ACKNOWLEDGEMENTS ............................................................................................. 6

PAPER AUTHORSHIP STATEMENTS ....................................................................... 8 PAPER 1 ........................................................................................................................... 8 PAPER 2 ......................................................................................................................... 10 PAPER 3 ......................................................................................................................... 12 PAPER 4 ......................................................................................................................... 14

CONTEXTUAL STATEMENT .................................................................................... 16 INTRODUCTION .............................................................................................................. 16 LITERATURE REVIEW ..................................................................................................... 20 PAPER SUMMARY ........................................................................................................... 32 DISCUSSION ................................................................................................................... 37 CONCLUSIONS ................................................................................................................ 38

BIBLIOGRAPHY ........................................................................................................... 40

PAPERS ........................................................................................................................... 45

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ABSTRACT A new depth-based method of seismic imaging is used to provide insights into the 3D

structural geometry of faults, and to facilitate a detailed structural interpretation of the

Penola Trough, Otway Basin, South Australia. The structural interpretation is used to

assess fault kinematics through geological time and to evaluate across-fault juxtaposition,

shale gouge and fault reactivation potential for three selected traps (Zema, Pyrus and

Ladbroke Grove) thus providing a full and systematic assessment of fault seal risk for the

area.

Paper 1 demonstrates how a depth-conversion method was applied to two-way time

seismic data in order to redisplay the seismic in a form more closely representative of

true depth, here termed ‘pseudo-depth’. Some apparently listric faults in two-way time

are demonstrated to be planar and easily distinguishable from genuine listric faults on

pseudo-depth sections. The insights into fault geometry provided by pseudo-depth

sections have had a significant impact on the new structural interpretation of the area.

Paper 2 presents the new 3D structural interpretation of the area. The geometry of

faulting is complex and reflects variable stress regimes throughout structural

development and the strong influence of pre-existing basement fabrics. Some basement-

rooted faults show evidence of continual reactivation throughout their structural history

up to very recent times. Structural analysis of all the live and breached traps of the area

demonstrate that traps associated with a basement rooted bounding fault host breached or

partially breached accumulations, whereas non-basement rooted faults are associated with

live hydrocarbon columns.

Papers 3 and 4 demonstrate that for all the traps analysed (Zema, Pyrus and Ladbroke

Grove), initial in-place seal integrity was good. The initial seal integrity was provided by

a combination of both favourable across fault juxtaposition (Ladbroke Grove) and/or

sufficiently well developed shale gouge over potential leaky sand on sand juxtaposition

windows to retain significant hydrocarbon columns (Zema, Pyrus). The palaeocolumns

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observed at Zema and Pyrus indicate that there has been subsequent post-charge breach

of seal integrity of these traps while Ladbroke Grove retains a live hydrocarbon column.

Evidence of open, permeable fracture networks within the Zema Fault Zone suggest that

it is likely to have recently reactivated, thus breaching the original hydrocarbon column.

Analysis of the in-situ stress tensor and fault geometry demonstrates that most of the

bounding faults to the selected traps are at or near optimal orientations for reactivation in

the in-situ stress tensor. The main exception being the Ladbroke Grove Fault which has a

NW-SE trending segment (associated with a relatively high risk of fault reactivation and

possible leakage at the surface) and an E-W trending segment (associated with a

relatively low risk of fault reactivation and a present day live column). The free water

level of the Ladbroke Grove accumulation coincides with this change in fault orientation.

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DECLARATION

This work contains no material which has been accepted for the award of any other

degree or diploma in any other university or other tertiary institution and, to the best of

my knowledge and belief, contains no material previously published or written by

another person, except where due reference has been made in the text.

I give consent to this copy of my thesis when deposited in the University Library, being

made available for loan and photocopying, subject to the provisions of the Copyright Act

1968.

The author acknowledges that copyright of published works contained within this thesis

(as listed below) resides with the copyright holder(s) of these works.

Lyon P.J ., P.J. Boult, A. Mitchell and R.R. Hillis, 2004, Improving fault geometry

interpretation through ‘pseudo-depth’ conversion of seismic data in the Penola Trough,

Otway Basin, in P.J. Boult, D.R. Johns and S.C. Lang eds., Eastern Australian Basins

Symposium II, Petroleum Exploration Society of Australia Special Publication, p 695-

706. Copyright holder: Petroleum Exploration Society of Australia, 2004.

Lyon P.J ., P.J. Boult, R.R. Hillis and K. Bierbrauer, 2007, Basement controls on fault

development in the Penola Trough, Otway Basin, and implications for fault-bounded

hydrocarbon traps, Australian Journal of Earth Sciences, 54:5, p 675-689. Copyright

holder: Geological Society of Australia, 2007.

Lyon P.J ., P.J. Boult, R.R. Hillis, and S.D. Mildren, 2005, Sealing by shale gouge and

subsequent seal breach by reactivation: A case study of the Zema Prospect, Otway Basin,

in P. Boult and J. Kaldi eds., Evaluating Fault and Cap seals: AAPG Hedberg Series No.

2, p 179-197. Copyright holder: AAPG (American Association of Petroleum Geologists),

2005.

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Lyon P.J ., P.J. Boult, M. Watson and R.R. Hillis, 2005, A systematic fault seal

evaluation of the Ladbroke Grove and Pyrus Traps of the Penola Trough, Otway Basin.

APPEA Journal, 45 (1), p 459-476. Copyright holder: APPEA (Australian Petroleum

Production and Exploration Association), 2005.

Signed………………………………………………. Date………………………

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ACKNOWLEDGEMENTS

Peter Boult and Richard Hillis are given significant acknowledgement for their excellent

steering and supervision throughout this project. I am extremely grateful for their time

and enthusiasm.

Primary Industry Resources South Australia (PIRSA) is thanked for sponsorship of this

project. Origin Energy and its joint venture partners are thanked for the provision of 3D

seismic data and excellent collaboration. Badleys Geoscience Ltd and Schlumberger

Oilfield Services are acknowledged for their provision of software and excellent support.

Peter Bretan, Conrad Childs, Kay Bierbrauer, Quentin Fisher, Wayne Bailey, Bronwyn

Camac, Suzanne Hunt, Max Watson, Richard Suttill and Titus Murray are thanked for

insightful discussion of this work.

Mike Dentith, Doug Finlayson, Ric Smit, Randall Taylor, Peter Bretan, Andrew Davids,

Richard Suttill, Paul Theologou and Myra Keep are thanked for reviewing the papers that

comprise this thesis.

Members of the APCRC seals consortium, in particular Statoil, Santos and Anadarko are

thanked for giving me the opportunity to present the results of this thesis for discussion.

I would also like to thank all staff and students at the Australian School of Petroleum that

provided advice and shared technical expertise. Aaron, Pete, Max, Marie, Lotte, Dan,

Scott R, Catherine and Scott M are thanked in particular for many extended lunches and

Friday nights. Maureen Sutton is also thanked for providing absolutely top-notch

assistance.

The support and faith of my family: Mum, Dad, Christine, Nan and Granddad is

massively appreciated.

Finally a big thank you to the people at Kathleen Lumley College whom I had the

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pleasure of living with throughout my stay in Australia, in particular: Dorthe, Su Lin,

Angela, Annette, Hanne, Helen, Catherine, Simon and Thivanka who provided much

needed distraction from the PhD.

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PAPER AUTHORSHIP STATEMENTS

Paper 1 Lyon P.J., P.J. Boult, A. Mitchell and R.R. Hillis, 2004, Improving fault geometry interpretation through ‘pseudo-depth’ conversion of seismic data in the Penola Trough, Otway Basin, in P.J. Boult, D.R. Johns and S.C. Lang eds., Eastern Australian Basins Symposium II, Petroleum Exploration Society of Australia Special Publication, p 695-706. Paul Lyon (estimated % of contribution: 75%)

• Wrote Paper

• Completed all seismic interpretation

• Performed velocity analysis of well and seismic velocities

• Derived pseudo-depth conversion algorithm

• Applied and loaded ‘pseudo depth’ seismic sections

I hereby certify that the statement of contribution is accurate.

Signed………………………………………………. Date………………………

Peter Boult (estimated % of contribution: 10%)

• Suggested the investigation of converting time seismic to depth seismic

• Facilitated data gathering

• Provided supervision and suggestions

• Edited manuscript

I hereby certify that the statement of contribution is accurate and I give permission for the

inclusion of the paper in this thesis.

Signed………………………………………………. Date………………………

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Andy Mitchell (estimated % of contribution: 10%)

• Helped to derive workflow for ‘pseudo-depth’ conversion technique

• Provided programme for calculation of Dix velocities




Signed………………………………………………. Date……………………

Richard Hillis (estimated % of contribution: 5%)





Signed………………………………………………. Date………………………

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Paper 2 Lyon P.J., P.J. Boult, R.R. Hillis and K. Bierbrauer, 2007, Basement controls on fault development in the Penola Trough, Otway Basin, and implications for fault-bounded hydrocarbon traps, Australian Journal of Earth Sciences, 54:5, p 675-689.

Paul Lyon (estimated % of contribution: 80%)

• Wrote Paper

• Completed all seismic interpretation

• Integrated Gravity Data and sandbox analogue studies


Signed………………………………………………. Date………………………



• Provided magnetic intensity image and helped in interpretation




Signed………………………………………………. Date………………………






Signed………………………………………………. Date………………………

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Kay Bierbrauer (estimated % of contribution: 5%)

• Provided insight into previous interpretations made by Origin Energy.

• Discussed new interpretation and its implications.

• Provided some input to editing



Signed………………………………………………. Date………………………

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Paper 3 Lyon P.J., P.J. Boult, R.R. Hillis, and S.D. Mildren, 2005, Sealing by shale gouge and subsequent seal breach by reactivation: A case study of the Zema Prospect, Otway Basin, in P. Boult and J. Kaldi, eds., Evaluating fault and cap seals: AAPG Hedberg Series No. 2, p 179-197. Paul Lyon (estimated % of contribution: 80%)

• Wrote Paper

• Completed all seismic interpretation including 3D fault surfaces (except regional grid

of Figure 1 in introduction, see acknowledgments section)

• Performed Vshale analysis and calculation

• Integrated existing wireline log data including the calibration of Vshale curves to core

and capillary pressure measurements. Interpreted dipmeter with assistance from P.

Boult

• Performed all 3D juxtaposition, SGR and FAST analysis (some assistance from

fellow student, J. Meyer required to load fault surface and fault attributes into

MATLAB software, see Figure 10 and acknowledgments)

• Performed Triangle sensitivity analysis


Signed………………………………………………. Date………………………



• Helped in interpretation of dipmeter log

• Helped in extracting curve data

• Helped in log curve interpretation


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Signed………………………………………………. Date………………………






Signed………………………………………………. Date………………………

Scott Mildren (estimated % of contribution: 5%)

• Developed the FAST technique as published in Mildren et al. (2005), see text for

details

• Provided comments on manuscript



Signed………………………………………………. Date………………………

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Paper 4 Lyon P.J., P.J. Boult, M. Watson and R.R. Hillis, 2005, A systematic Fault Seal Evaluation of the Ladbroke Grove and Pyrus Traps of the Penola Trough, Otway Basin. APPEA Journal, 45 (1), p 459-476. Copyright holder: APPEA (Australian Petroleum Production and Exploration Association).

Paul Lyon (estimated % of contribution: 75%)

• Wrote Paper

• Completed all seismic interpretation (except for regional grid in introduction, figure

1, see acknowledgments)

• Performed all 3D modeling including 3D juxtaposition, SGR and FAST analysis and

associated sensitivity analysis

• Vshale assessment and calculation

• All lithostratigraphic correlations including the identification of ‘faulted out’ sections.

• Insitu stress calculation: Shmax direction based on image log interpretation of

borehole breakout and DITFs, vertical stress magnitude, minimum horizontal stress

magnitude, and maximum horizontal stress magnitudes


Signed………………………………………………. Date………………………






Signed………………………………………………. Date………………………

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Max Watson (estimated % of contribution: 10%)

• Acquired CO2 leakage data in the field and analysed the results

• Provided suggestions on the manuscript



Signed………………………………………………. Date………………………






Signed………………………………………………. Date………………………

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CONTEXTUAL STATEMENT

Introduction

The Penola Trough is a half-graben structure located in the onshore part of the Otway

Basin, South Australia (Figure 1). Five hydrocarbon fields have been discovered to-date

within the Pretty Hill Sandstone reservoir unit in the Penola Trough and are currently

being produced at commercial rates. However, exploration interest in this area has waned

recently due to the perceived high risk of seal breach. Recent exploration wells drilled in

the area have frequently encountered palaeo-hydrocarbon columns, i.e. hydrocarbon

columns that were once present, but have since leaked away (Figure 2). The identification

of palaeocolumns in the Penola Trough suggests that although many traps within the area

were once capable of retaining hydrocarbons, there has been a post-charge breach of their

seal integrity.

Nearly all of the traps in the area have fault dependant closure and are thus reliant on a

fault seal in addition to the overlying top seal to retain hydrocarbons. The overlying top

seal unit, the Laira Formation, is both laterally extensive and of sufficient seal capacity to

hold back hydrocarbons far beyond the structural spill point of these traps (Boult, 1997;

Jones et al., 2000). Hence fault seal integrity has long been considered the critical issue to

exploration risk in the Penola Trough (Jones et al., 2000; Willink and Lovibond, 2001).

Post-charge fault reactivation is a widely considered mechanism of fault seal breach

(Mildren et al., 2002; Jones and Hillis, 2003). Recently reactivated faults are known from

outcrop studies to be associated with permeable, open fracture networks (Barton et al.,

1995). Recent reactivation of faults had long been considered the key mechanism of seal

breach in the Penola Trough (Jones et al., 2000; Willink and Lovibond, 2001). However,

previous attempts to predict the likely occurrences of fault seal breach due to recent

reactivation, failed to satisfactorily explain the occurrence of all breached and non-

breached hydrocarbon traps in the area (Jones et al, 2000; Boult et al., 2002). Hence

Boult et al. (2002) suggested an alternative hypothesis of fracturing of intact cap rock

caused by the localised build up of high differential stress, citing evidence of stress

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perturbations around faults. However, attempts to predict seal breach by cap rock

fracturing through stress modelling also failed to yield unequivocal results. Boult et al.

(2002) suggested that these techniques may have been unsuccessful due to poor definition

of faulting and an incomplete understanding of the complexity of the fault geometry and

structural history of the area. One of the key challenges faced in resolving the issue of

fault seal integrity was thus the accurate interpretation of the full 3D geometry of faults in

an area of structural complexity and generally poor–moderate quality seismic imaging.

Furthermore, fault juxtaposition and fault damage aspects of fault seal integrity had not

been fully considered in the previous assessments of fault seal integrity.

Figure 1 The location of the Penola Trough, Otway Basin, South Australia.

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Figure 2 Close up view of Penola Trough depocentre highlighting the areal distribution of

breached, partially breached and live hydrocarbon accumulations (see Figure 1 for location).

This thesis was funded by PIRSA (Primary Industry Resources South Australia) in order

to address the issue of fault seal risk in the Penola Trough. The aims of this study were as

follows.

i) Improve the knowledge of fault geometry in the Penola Trough.

ii) Complete a new seismic interpretation of the Penola Trough and improve

understanding of the evolution of faulting throughout the structural history of the

area.

iii) Apply a systematic 3D fault seal analysis to selected prospects.

iv) Determine the critical factors affecting fault seal integrity in the area.

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These aims were met by the following research programme, the results and conclusions

of which are presented as a series of peer-reviewed and published papers in subsequent

chapters.

i) Uncertainty in the fault geometry and structural complexity of the area was

reduced by a new depth-based seismic imaging method (Paper 1).

ii) Depth-scaled and conventional two-way time seismic sections were used to

interpret 3D fault geometries and key megasequences to fully constrain fault

development (Paper 2).

iii) The structural interpretation presented in Paper 2 was used to generate 3D

prospect models over three traps (Zema, Ladbroke Grove and Pyrus) for

systematic fault seal analysis including the assessment of fault reactivation

potential using the FAST (Fault Analysis Seals Technology) method (Paper 3

and 4).

iv) Conclusions were reached on the key risks to fault seal integrity from the

combined results of all papers and are summarised in this overview.

This chapter provides the overall context for this thesis. A review of the relevant

literature is given, highlighting the specific knowledge gaps that existed prior to this

research. A summary of the key findings of each of the papers and the linkages between

each paper are stated. The significance of the findings of all the papers, in light of the

current knowledge gaps on fault seal integrity both within the Penola Trough and in the

wider global context, are then given in the conclusions section of this overview.

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Literature Review

Fault seal potential is an important exploration risk to consider in the assessment of fault-

bound hydrocarbon prospects (Smith, 1966; Allan, 1989; Bouvier et al., 1989). It has

been identified as one of the critical factors for exploration success in the Penola Trough

(Boult, 1997; Jones et al., 2000; Willink and Lovibond, 2001). Fault seal risk is difficult

to assess and is frequently associated with high uncertainty. Hence there has been much

debate within the literature regarding the controls on fault seal integrity (Lindsay et al.,

1993; Fisher et al., 2003; Bretan and Yielding, 2005). It is important that quantitative

analysis is suitably integrated with all sub-surface data using a systematic approach

(Jones and Hillis, 2003). There are three key research disciplines relevant to the

assessment of fault seal integrity in the Penola Trough.

i) Seismic imaging.

ii) Structural development.

iii) Fault seal analysis.

This section gives an overview of each discipline area, highlighting in more detail the

current status of research and the relevant knowledge gaps within each field, in order to

provide the overall context for this thesis.

i) Seismic Imaging

It is essential to accurately define the geometry of a fault plane in order to accurately map

out and predict fault seal properties on that fault plane. One of the key issues that have

hampered the reliability of previous fault seal studies in the area has been the inability to

accurately interpret the fault geometries (Boult, 1997; Boult et al. 2002). There are two

main reasons for this. Firstly the seismic data quality is only poor–moderate in quality

and secondly the structural evolution of the Penola Trough is complex with multiple

phases of faulting (Kopsen and Schofield, 1990; Finlayson et al., 1993; Lovibond et al.,

1993; Chantraprasert et al., 2001). This combination of complex fault geometries and

poor imaging has made interpretation in the area particularly difficult (Boult, 1997).

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Previous interpretations of faults, based mainly on 1990 vintage 2D regional lines and

two moderate quality 3D surveys (the Balnaves-Haselgrove and St George surveys) have

differed significantly. Faults were frequently interpreted as large listric features from near

surface to basement levels. However, Boult (1997) suggested that such fault geometries

were unrealistic and argued that multiple fault sets of different ages were likely to be

present. He suggested a need to improve the interpretation of fault geometry and

understanding of the structural evolution of the area as a basis for meaningful fault seal

evaluation.

Various reprocessing techniques were applied to the 3D Balnaves-Haselgrove survey to

locally improve the quality of the seismic data in the main hydrocarbon bearing part of

the Trough. PSDM (Pre-stack depth migration) was applied to a test line over the

Jacaranda Ridge prospect (Figure 2). Although PSDM did considerably improve the

clarity of the seismic data, it was time-consuming and was thus only applied to selected

test lines (Willink and Lovibond; 2001).

One of the main problems with previous interpretations was that they were undertaken

using conventional two-way time seismic data. It is common practice in seismic

interpretation to interpret horizons and faults in two-way time and then convert the

completed horizon interpretation to depth using time-depth data obtained from wells or

seismic velocities (Veeken et al., 2005). Although this is often appropriate for horizon

interpretation, it is often unsuitable for accurate interpretation of fault geometry. The

main reason for this is that faults imaged in two-way time are frequently not

representative of their true depth geometry. Planar faults for example often appear as

listric features in two-way time due to increases in velocity with depth. Ideally the

interpretation of faults should be performed using seismic scaled by depth rather than

two-way time particularly in areas such as the Penola Trough were imaging of fault

geometries is ambiguous and fault geometries are complex.

For the above reasons, it was decided that scaling the seismic sections by depth rather

than time would facilitate a more robust and structurally valid interpretation. Paper 1

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summarises how the two-way time seismic sections were rescaled to depth using a

'pseudo-depth' conversion technique. It also demonstrates how this ‘pseudo-depth’

conversion technique had significant impact on the interpretation of seismic data in the

area.

ii) Structural development

Accurate interpretation of 3D fault geometry requires a thorough understanding of the

regional structural history. An extensive amount of research has been conducted on the

regional structure of the Otway Basin (O' Brien et al., 1994; Cockshell et al., 1995;

Norvick and Smith, 2001; Palmowski et al., 2004). However, the link between the

regional structure and prospect-scale structure has been less widely described

(Chantraprasert et al., 2001). This section attempts to place the structural understanding

of the Penola Trough in the context of regional scale structural analysis and discusses the

knowledge gaps within the literature and how these were addressed with Paper 2.

The Penola Trough is one of several Early Cretaceous Troughs found along the presently

onshore part of the Otway Basin (Figure 1). These rift structures were established during

the initial rifting event between Antarctica and Australia in Late Jurassic times (Norvick

and Smith, 2001). The Penola Trough is a NW–SE trending half-graben, bound to the

south by a large landward dipping listric fault zone known as the Hungerford/Kalangadoo

(H/K) Fault system. The underlying Palaeozoic basement consists of highly deformed

metasediments of the Kanmantoo Group that were deformed during the Cambro-

Ordovician Delamarian Orogeny. The structural history of the Penola Trough can be

subdivided into five distinct phases as follows.

Early Cretaceous initial rifting

Initial rifting of the Palaeozoic basement to form the Penola Trough commenced in the

Late Jurassic (Tithonian) and was accompanied by the syn-deposition of the lacustrine

Casterton Formation (Figure 3). Extensional faulting continued throughout the Early

Cretaceous (Berriasian–Hauterivian), accommodating further syn-rift deposition of the

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extensive fluvio-lacustrine Crayfish Group which comprises three units; the Pretty Hill

Formation (main reservoir interval) at the base of the sequence, the Laira Formation and

Katnook Sandstone unit at the top of the sequence. The Crayfish Group exhibits

thicknesses of up to 6 km in the deepest parts of the trough.

Figure 3 Summary of stratigraphy and key tectonic events

Faults formed during the initial rifting event show a broadly E–W trending orientation in

the deep, central part of the Penola Trough and exhibit relatively large displacements of

syn-rift units. In contrast, those in the western part of the trough show a more NW–SE

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trend and exhibit smaller displacements (Figure 2). The prevailing regional extension

direction has been variably interpreted. A NNE–SSW regional extension is advocated by

Etheridge et al. (1985), while other workers propose a NW–SE extensional regime

(Williamson et al., 1990; O’Brien et al., 1994).

Initial rift related faulting ceased by the end of the Hauterivian in the Penola Trough and

minor erosion ensued across footwall fault scarps marked by the Crayfish unconformity.

Mid-Cretaceous subdued rifting

Major faulting activity had by Mid-Cretaceous times shifted south of the onshore rift

system that included the Penola Trough to the presently offshore parts of the Otway

Basin, south of the Tartwaup Fault Zone (Figure 1). Hence the onshore rift system

became a failed rift (Finlayson et al., 1993; Lovibond et al., 1995; Palmowski et al.,

2004).

Subdued fault activity occurred throughout Mid-Cretaceous times in the Penola Trough,

associated with the deposition of the fluvio-lacustrine Eumeralla Formation which

comprises interbedded volcanogenic lithic sandstones, siltstones coals and claystones

(Cockshell et al., 1995; Morton et al., 1995). The thickness of this unit within the study

area is fairly uniform (~1 km).

Late Cretaceous post-rift faulting

Intense fault activity recommenced during the Late Cretaceous deposition of the

Sherbrook Group. New faults formed in the Penola Trough with a more consistent NW–

SE trend. Several prominent Early Cretaceous initial rift faults were also reactivated

during this time. A NE–SW extension direction within the Penola Trough is advocated

for this event (O’Brien et al., 1994; Chantraprasert et al., 2001).

Continued rifting south of the Tartwaup Fault zone eventually led to the on set of sea-

floor spreading between Antarctica and Australia at the end of the Late Cretaceous

(Finlayson et al., 1998).

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Miocene compression

A major change to a NW–SE orientated compressional regime occurred in the Otway

Basin during Miocene times, due to changes in plate boundary configurations along the

northern and eastern margins of the Australian plate (Perincek et al., 1994) possibly

combined with ridge push effects from the developing Southern Ocean between Australia

and Antarctica (Hill et al., 1995). This compressional event resulted in localised inversion

along several major faults of the Otway Basin (Perincek et al., 1994). Evidence of

compression in the Penola Trough during this time is recorded by subtle hanging wall

doming across several major faults (Rowe, 1996). However, large-scale fault inversion

and reverse faulting is absent from the central Penola Trough area.

Early Pliocene–Recent strike slip faulting

Increased convergence and possibly coupling between the Pacific and Australian plates in

the Early Pliocene, coincident with the formation of the Southern Alps of New Zealand,

is likely to have caused further changes in the stress regime throughout SE Australia

(Sandiford et al. 2004). Sandiford (2003) and Sandiford et al. (2004) suggest formation of

the Southern Alps provides a key control on the present day stress regime within the

region which, in the case of the Penola Trough, is strike slip with a NW–SE maximum

horizontal stress orientation (Jones et al., 2000; Nelson et al., 2006).

Charge

Thermal maturity modelling suggests that hydrocarbon generation in the Penola Trough

peaked around Mid-Cretaceous times (Lovibond et al., 1995; Duddy, 1997),

contemporaneous with the deposition of the Eumeralla Formation. This early oil charge

was followed by a later gas charge (Boult et al., 2004). The presence of many structural

traps that are presently full-to-spill with gas indicates that the later gas charge must have

occurred relatively recently (i.e. within at least the last 10-20 Ma) given the rates of gas

loss by diffusion (Nelson and Simmons, 1995, 1997; Krooss and Leythaeuser, 1997).

Hence post charge seal breach can be considered likely to have occurred within last

26

~20M years.

Key Issues related to structural development of Penola Trough

The complex structural history of the area has resulted in complex fault geometries.

However, several key elements of structural analysis essential to the assessment of fault

seal integrity had not been undertaken prior to this thesis. These were as follows.

1). A detailed interpretation of the geometry of faulting of the underlying basement had

not been undertaken. Previous workers had focused on the geometry of faulting at or near

the reservoir level and in the overlying sedimentary section where fault offsets are clearly

resolvable. Previous structural interpretation in a wide range of structural settings

consistently shows that basement-rooted faults have a strong and long-lived control on

fault geometry throughout the structural evolution of a basin (Lee and Hwang, 1993;

Dore et al., 1997; Keep et al., 2000; Hinsch et al., 2002). Understanding the interaction of

basement-rooted faults and the prevailing stress regime during each deformation phase

was an essential requirement to improve structural understanding of the area and

ultimately facilitate the interpretation of more reliable fault geometries.

2). Interpretation of 3D fault surfaces had not been undertaken across all of Penola

Trough. Interpretation of 3D fault surfaces greatly improves understanding of how

different fault surfaces evolved through time (Childs et al., 1996; Walsh et al., 2003;

Morley et al., 2006). The mapping of fault attributes such as throw magnitude onto 3D

fault surfaces greatly increases understanding of fault kinematics and in some settings

allows the history of fault reactivation through time to be constrained (Walsh et al., 2003;

Morley et al., 2006).

Paper 2 presents the results of the structural interpretation of the Penola Trough which

utilised depth-scaled or 'pseudo' depth seismic sections in addition to the conventional

two-way time seismic data as described in Paper 1. The significance of the role of

basement-associated faulting in controlling fault evolution is described. New insights into

the structural evolution of the Penola Trough are described and their implications for

27

fault seal integrity are discussed.

Both Papers 1 and 2 focus on the accurate definition of fault geometry and the structural

framework of the Penola Trough from the regional to the prospect scale. The resulting

seismic interpretations were then used to generate a series of selected 3D trap

interpretations for fault seal analysis (Papers 3 and 4).

iii) Fault Seal Analysis

The juxtaposition of an impermeable seal unit against a reservoir unit as a consequence of

displacement along a fault, is a widely documented mechanism of fault sealing. Such

faults are referred to as juxtaposition seals (Downey, 1984; Watts, 1987; Jev et al., 1993).

In some circumstances, faults may still act as a barrier to fluid flow and thus seal

hydrocarbons in the absence of a juxtaposition seal. In these cases it is the fault itself

rather than the juxtaposed rocks that provides the effective seal (Lindsay et al., 1993;

Knipe 1997; Yielding et al., 1997; Yielding, 2002). Abrasion or smearing associated with

the displacement of rock along a fault causes damage/gouge material from the

surrounding host rock to be incorporated into the fault plane (Fisher and Knipe, 1998;

Doughty, 2003). These damage/gouge zones can often demonstrate considerably reduced

permeability when compared to the host rock and can hence serve as excellent seals

(Fisher and Knipe, 1998; Fisher and Knipe, 2001).

Previous studies have demonstrated that with faulting within mixed sand shale

siliciclastic sequences, there is often a relationship between seal capacity (i.e. the

maximum column height can be sustained by a seal) and the amount of shale

incorporated into a fault zone (Yielding et al., 1997; Bretan et al., 2003). Predictive

algorithms, such as shale gouge ratio (Yielding et al., 1997) and shale smear factor

(Lindsay et al., 1993; Gibson, 1994) are used to determine the seal potential of a fault by

estimating the amount of clay material entrained into the fault zone by mechanical

processes as a function of fault displacement and shale content of the displaced rock.

28

Such predictive algorithms are often compared with and calibrated against pressure data

based on known column heights (Jev et al., 1993; Yielding, 2002; Bretan et al., 2003) or

laboratory-based measurements (Sperrevik et al., 2002). Bretan et al. (2003) have

calibrated shale gouge ratio (SGR) values to across-fault pressure data for a global data

set of fault traps. These relationships have been used to define the fault zone capillary

entry pressure (FZP) for a given shale gouge ratio (SGR) by the equation:

FZP (bar) = 10(SGR/27 –C),

where C = 0.5 for burial depths less than 3km, C = 0.25 for burial depths between 3 and

3.5km and C = 0 when burial depth is greater than 3.5km.

Fault leakage occurs when the minimum FZP is exceeded by the buoyancy pressure of

the hydrocarbon column, resulting in capillary leakage across the fault (Bretan et al.,

2003; Bretan and Yielding, 2005). This allows the determination of the maximum

buoyancy pressure that can be sustained by a fault before capillary leakage would result.

The maximum column height can thus be calculated for a given hydrocarbon column if

the fluid densities are known (Bretan et al., 2003).

High SGR values do not always correlate to high fault seal potential and sand-on-sand

juxtaposition windows with low SGR may seal due to other fault zone processes. In the

case of relatively deeply buried clean sandstones subjected to high temperatures eg

Rotliegend Sandstones of the North Sea, the dominant fault damage processes consists of

cataclasis and associated in-situ quartz cementation which have excellent seal potential

despite the absence of shale within the fault zone (Fisher et al., 2003). Hence the seal

potential of fault damage zones is dependent on the type of damage zone developed

which is often controlled by factors in addition to displacement and lithology type,

principally temperature and stress history (Fisher and Knipe, 2001; Fisher et al., 2003;

Bretan and Yielding, 2005).

Conventional fault seal analysis typically involves firstly an assessment of the

29

juxtaposition relationships across a fault often referred to as a first order fault seal

analysis, followed by an assessment of the seal potential of the fault damage zone often

termed a second order analysis (Yielding et al., 1997). First and second order analysis

allow predictions to be made on the potential of a fault to seal hydrocarbons. Shale

volume estimates derived from well log data are tied to seismic horizon data and

projected onto fault plane surfaces in the modelling of across-fault juxtaposition

(Downey, 1984; Watts, 1987; Jev et al., 1993). Shale gouge ratio (Yielding et al., 1997)

and shale smear factor (Lindsay et al., 1993; Gibson, 1994), use projected shale volumes

and throw magnitude to predict the amount of shale incorporated into the fault zone via

mechanical processes. These predictive algorithms are then used a basis for determining

the relevant fault damage process (eg clay smearing, abrasion, cataclasis) and the

resultant seal potential of the damage zone (Bretan and Yielding, 2005).

Reactivation of faults post-charge is arguably the most significant cause of fault seal

breach (Wiprut and Zoback, 2002; Mildren et al., 2005). Recently reactivated faults are

known from outcrop studies to be associated with permeable fracture networks (Barton et

al., 1995). There are many examples of studies where recent fault reactivation is

associated with breached fault dependant hydrocarbon traps (Mildren et al., 2002; Jones

and Hillis, 2003; Gartrell et al., 2006).

Jones et al. (2000) assessed the probability of recent fault reactivation in the Penola

Trough using FAST (Fault Analysis Seals Technology). FAST is a technique that

quantifies the relative risk of fault reactivation as a function of in-situ stress, fault

geometry and rock properties (Mildren et al., 2002; Mildren et al., 2005). Although FAST

predictions of fault reactivation have been successfully calibrated to the present day

distribution of live and breached hydrocarbon columns in the Timor Sea (Mildren et al.,

2002), FAST predictions of fault reactivation did not fully explain the distribution of

palaeo-columns in the Penola Trough (Boult et al., 2002). This suggested either problems

with the methodology as applied, or mechanisms other than recent fault reactivation may

be significant to hydrocarbon leakage. Boult et al. (2002) proposed a mechanism of

breach by fracturing of intact top seal due to stress perturbations that occur locally around

30

faults. Areas of high differential stress within the overlying seal, and thus high risk of cap

seal fracturing, can be predicted through stress modelling (Hunt and Boult, 2005).

However, stress modelling studies also could not entirely satisfactorily account for the

entire distribution of live and breached columns in the Penola Tough (Hunt and Boult,

2005).

Prior to this thesis, analysis of seal breach mechanisms had clear limitations and

demonstrated the need to systematically assess fault seal risk, in light of the improved

structural interpretation presented in Papers 1 and 2. These limitations / knowledge gaps

prior to this thesis were as follows.

1). 3D interpretations of fault geometry had not been undertaken, thus juxtaposition and

fault damage analysis had not been performed in 3D. At the commencement of this thesis

there were surprising few publications on the application of juxtaposition and fault gouge

potential in 3D. Publications are now emerging, which are demonstrating the importance

of performing fault seal prediction in 3D (Clarke et al., 2005).

2). Analysis of the risk of seal breach due to fault reactivation in the in-situ stress field

was required using the new 3D fault interpretations as input rather than fault geometry

approximations based on 2D horizon data, as used previously (Jones et al., 2000; Boult et

al. 2002).

3). Structural history and fault kinematics through time had not been previously

considered in addressing which faults were likely to have been recently reactivated.

Recent research on fault development has demonstrated that, for example, strain on a

fault population becomes progressively more localised onto larger faults throughout fault

development i.e. throughout the structural evolution of a fault system, larger faults

accommodate a greater amount of displacement while displacement on smaller faults

progressively terminates (Walsh et al., 2002; Meyer et al., 2002). Furthermore, recent

work by Morley et al. (2007) has demonstrated that in areas of strong pre-existing

basement fabrics and complex stress variations in the Phitsanulok Basin, Thailand,

31

basement-rooted faults show markedly different displacement profiles to smaller intra-rift

faults of the same age. Hence it was important that this thesis considered fault kinematics

through time in assessing fault reactivation risk for the Penola Trough.

Paper 3 and 4 use the new depth-based interpretation of 3D fault geometry and

associated horizons published in Paper 1 and 2 to undertake 3D modelling of

juxtaposition and fault damage seal for three traps. The choice of traps was based on the

quality of available data over the trap to allow a well constrained and conclusive analysis

to be undertaken. Paper 3 analyses the Zema trap, which is host to a 69 m

palaeohydrocarbon column. A full, systematic assessment of juxtaposition, shale gouge

ratio (SGR) and fault reactivation potential was undertaken. The results were integrated

with dipmeter, core and petrophysical analysis to conclude on the most likely cause of

fault seal breach in the trap. Paper 4 builds on the analysis and conclusions of Paper 3

and details a similar systematic analysis of juxtaposition, fault damage and fault

reactivation using FAST for the Pyrus trap (host to a similar palaeocolumn) and the

Ladbroke Grove trap (host to a live column).

The next section gives a more detailed description of the key findings of each paper.

32

Paper Summary

Paper 1 - Improving faulty geometry interpretation through 'pseudo-depth'

conversion of seismic data in the Penola Trough, Otway Basin.

This paper demonstrates how depth conversion of seismic data provides a better domain

in which to view, analyse and interpret fault geometry than the conventional time

domain. PSDM was considered cost-prohibitive by the operators in the area. A dense

sample of t-d data points extracted from checkshot surveys and seismic processing

velocities (Vstack) demonstrate that there is not a significant lateral variation in the

velocity field of the Penola Trough area. For these reasons a lateral invariant velocity

function was applied to all the seismic data to rescale the seismic by 'pseudo-depth.'

The function used to make the pseudo-depth sections in this project was Z = 1171.047*T - 471.0516*T2 + 639.5787*T3 - 218.3469*T4 + 33.68451*T5 -1.986016*T6 where T is two-way time in seconds, and Z is depth in metres.

The term 'pseudo depth' was adopted in recognition of the crude, albeit fit-for-purpose,

method of depth conversion. A series of example sections are used to highlight that

apparently listric faults as imaged on two-way time sections are in fact imaged as planar

faults on pseudo depth sections. Hence a clearer distinction could be made between

planar faults and genuinely listric faults. The paper also highlights through example

sections how a series of additional new insights into the depth geometry of faults had a

significant impact on the new interpretation of area.

33

Paper 2 - Basement controls on fault development in the Penola Trough, Otway

Basin, and implications for fault-bounded hydrocarbon traps.

This paper presents a new interpretation of the St. George and Balnaves-Haselgrove 3D

surveys and adjacent 2D seismic lines over the Penola Trough study area using the

method of depth conversion and interpretation described in Paper 1.

Fault geometries were defined as 3D planes and the depth horizons of several key marker

units were interpreted: Top Basement, Top Pretty Hill Formation, Top Crayfish Group

and Top Sherbrook Group (Figure 3). This paper describes in detail the main faults

identified in the interpretation and discusses their interactions and development through

time. The key conclusion of this work is that basement-rooted faults in the Penola Trough

exerted significant control on fault geometry throughout the structural history of the area.

Despite clear evidence of variable extensional directions throughout the area, basement

faults were consistently active and had strong controls on associated intra-rift faulting.

Variance data is used to demonstrate how a previously unrecognised deep, basement

rooted fault is well expressed at near surface levels while other faults are not, thus

suggesting that basement rooted faults are likely to have continued to be the focus of fault

displacement up to very recent times. Given that recent fault reactivation is proposed as a

seal breach mechanism for the area, a comparison is made between each of the traps and

their relationship to basement-rooted faulting. It was found that traps bound by basement-

rooted faults were breached or partially breached. Only faults that did not offset basement

at depth were associated with unbreached hydrocarbon columns.

Paper 3 - Sealing by shale gouge and subsequent seal breach by reactivation: A case

study of the Zema Prospect, Otway Basin.

The structural interpretation of Paper 2 provided the regional context for detailed

prospect-scale evaluation of fault juxtaposition, fault gouge (using SGR algorithm) and

fault reactivation in the in-situ stress field (using FAST).

34

Paper 3 analyses the Zema Prospect which is host to a palaeocolumn of 69 m within the

Pretty Hill Sandstone reservoir unit, the palaeo-free water level of which occurs over 200

m above the structural spill point. The paper presents in detail how the analysis was

performed (including Vshale calculation), the results and conclusions on both the original

seal mechanism in place required to seal the once present column and how it

subsequently leaked away.

The juxtaposition analysis clearly shows that the Pretty Hill Sandstone reservoir is

juxtaposed against a series of sands and silty-sands within the overlying regional seal –

the Laira Formation. These sands and silty-sands are considered to be 'leaky windows'

and are positioned well above the interpreted palaeo-free water level (PFWL) of the trap.

For these reasons it is suggested that the Zema trap could not have been sealed by

juxtaposition alone and therefore the palaeocolumn must have depended on the

development of a shale gouge across the fault zone.

SGR calculated on the position of the fault where the top Pretty Hill reservoir was

displaced, show values of 15–34%. When these SGR ratios are converted to fault zone

capillary entry pressures (Bretan et al., 2003) the maximum column height predicted is 72

m. The close agreement between the PFWL and the calculated column heights based on

the SGR values support the notion that the trap depended on shale gouge to seal the

original 69 m column.

The FAST analysis performed on the Zema Fault demonstrates that the Zema Fault is

optimally orientated within the in-situ stress field for reactivation. A spontaneous

potential (SP) anomaly that coincides with the position of part of the Zema Fault zone

demonstrates the presence of permeability within the fault zone within the otherwise

impermeable Laira Formation seal, thus confirming the presence of an open fracture

network. Hence it is inferred that the trap was originally sealed by shale gauge and was

subsequently breached by fault reactivation.

35

Paper 4 - A systematic fault seal evaluation of the Ladbroke Grove and Pyrus Traps

of the Penola Trough, Otway Basin.

Paper 4 applies a similar prospect-scale fault seal analysis to the Ladbroke Grove and

Pyrus traps as presented in Paper 3 for the Zema Trap.

The Ladbroke Grove and Pyrus traps host a live column and palaeocolumn respectively.

The live column at Ladbroke Grove shows high concentrations of CO2, probably due to

present-day charge of CO2 in the area (Boult et al., 2004).

Broadly the same systematic approach of juxtaposition analysis, fault damage assessment

(using the SGR algorithm) and reactivation risk were undertaken at Ladbroke Grove and

Pyrus as applied in Paper 3 to the Zema Trap. However, in the case of the Ladbroke

Grove and Pyrus traps, more offset well data were available, allowing a more critical

assessment of lateral variations of Vshale (shale volume) away from well control. Further

refinement of the in-situ stress field was also undertaken to define a stress tensor specific

for the Penola Trough, as opposed to the regional Otway Basin stress tensor as applied to

Zema. This new stress tensor was found to be consistent with that of Jones et al. (2000).

Furthermore, measurements of CO2 at surface were available for both of these prospects

and these data provide possible indications of leakage from the CO2 rich reservoirs of the

area.

The sealing of the Ladbroke Grove live column can be attributed to favourable

juxtaposition of Pretty Hill Sandstone Reservoir against massive shale units of the Laira

Formation across the main prospect-bounding fault. Conversely, the Pyrus Fault is not

presently sealing by juxtaposition. The throw is sufficient to completely displace the

entire Laira Formation seal past the Pretty Hill reservoir in the footwall section in order

to juxtapose the Katnook sandstone against the Pretty Hill Sandstone reservoir at the top

of the trap. However, SGR ratios in excess of 40% across this sand-on-sand window

suggest that it is very likely to be sealed by shale gouge in the fault zone (as also

demonstrated by the Zema trap in Paper 3).

36

The Ladbroke Grove Fault consists of a NW–SE trending segment and an E–W trending

segment. The E–W segment of the fault seals the present day hydrocarbon column. The

free-water level of this trap is found to coincide with the change in orientation of the fault

from E–W to NW–SE. FAST predictions of the likelihood of fault reactivation in the in-

situ stress field suggest that the NW–SE trending part of the fault is more prone to

reactivation than the E–W trending segment. Hence recent slip may have occurred along

the NW–SE segment of the Ladbroke Grove Fault creating permeable fracture networks

and therefore limiting the extent of the live column to the E–W trending segment of the

fault. This hypothesis is supported by CO2 soil gas leakage profiles across the fault,

which show high concentrations across the NW–SE segment and low concentrations

(within the background range) across the E-W segment.

FAST predictions of fault reactivation for the Pyrus Fault show a relatively high risk of

fault reactivation of the fault plane. CO2 soil gas measurements across the fault are

relatively high suggesting the fault maybe leaking to surface. It is thus proposed that

recent fault reactivation breached the seal of the Pyrus Fault.

37

Discussion

The Zema, Pyrus and Ladbroke Grove traps all show excellent sealing potential due to

either favourable juxtaposition or shale gouge development (Paper 3 and 4).

Furthermore, evidence of paleocolumns and of surface flux of CO2 (Pyrus, Ladbroke

Grove; Paper 4), and of permeability within fault zones (Zema, Paper 3) suggests that

despite the initial development of excellent fault seal integrity, there was subsequent seal

breach associated with post charge fault reactivation.

A significant issue arising from the results of this thesis is the controls on fault

reactivation within the area. Prior to this thesis, previous studies had only considered the

orientation of the fault with respect to the in-situ stress field in risking likelihood of fault

reactivation (Jones et al. 2000). It was advocated that fault segments optimally orientated

in the in-situ stress field for reactivation would be more likely to reactivate than non-

optimally orientated faults. However, the results from Paper 2 demonstrate that

basement-involved faults have, throughout the structural history of the area, been the

main focus of fault displacement / fault development, despite varying stress fields.

Furthermore, Paper 2 shows that basement-involved faults have a clear association with

breached traps, whereas non-basement faults are associated with non-breached traps. It is

therefore likely that recent fault reactivation was strongly controlled by pre-existing

weakness within the basement and hence basement faults have preferentially reactivated

over non-basement intra-rift faults. This explains an association of basement-rooted faults

with breached and partially breached paleocolumns and an association of intra-rift faults,

which are not linked to basement, with live columns in the present day.

The above does not preclude that fault reactivation is also controlled by the orientation of

the fault relative to the in-situ stress field. The orientation of faults relative to the in-situ

stress field will exert a dominant control on reactivation of intra-rift fault segments of

similar size, where deep linkages to basement faulting is absent (eg Ladbroke Grove

Fault, Paper 4).

38

Conclusions

Depth-based seismic imaging; careful interpretation of fault geometry, and; systematic

3D assessment of juxtaposition, fault damage and fault reactivation potential have

significantly improved understanding and considerably de-risked the issue of fault seal

integrity within the Penola Trough.

Depth-scaled seismic interpretation has allowed much clearer definition of faults in a new

structural interpretation of the area. Structural analysis of these faults demonstrates that,

despite variable stress orientations throughout structural development of the Penola

Trough, basement-rooted faults have continually been reactivated. They have also exerted

a dominant influence on the geometry and intensity of associated intra-rift faulting.

Fault-dependant traps within the Penola Trough were initially sealed by either favourable

across fault juxtaposition of reservoir against seal (Ladbroke Grove trap), or by the

development of sufficient shale gouge with the fault zone (Zema and Pyrus traps). This

allowed the initial retention of significant hydrocarbon columns in the area.

Subsequent post-charge, reactivation of faults caused some of the hydrocarbon columns

to leak away. This is supported by evidence of paleocolumns associated with open

permeable fracture networks at Zema, for example.

Recent fault reactivation in the Penola Trough is primarily associated with faults that

show offset of basement at depth (basement-rooted faults) Hence basement rooted faults

are associated with breached or partially breached columns whereas intra-rift faults are

associated with live hydrocarbon columns in the present day.

Recent reactivation of intra-rift faults is likely to have occurred in addition to recent

basement-rooted fault reactivation. For intra-rift faults the orientation of the fault relative

to the in-situ stress is particularly significant and hence predictions of fault reactivation

using the geometry of the fault with respect to the in-situ stress are more applicable. This

39

can be demonstrated in the case of the Ladbroke Grove Field, which clearly shows that

the Free Water Level of a live column bounded by an E–W trending part of an intra-rift

fault, coincides with a change in orientation of the fault from E–W (associated with low

risk of reactivation in the in-situ stress field) to NW–SE (associated with a high risk of

reactivation in the in-situ stress field). This is supported by CO2 concentration data,

which shows that the NW–SE part of the fault is associated with a high CO2 flux at

surface, suggesting possible leakage, whereas the E–W trending part is not.

Fault dependant traps that are bound by faults that are basement rooted and/or are

optimally orientated in the in-situ stress field should be considered high risk due to a high

likelihood of recent fault reactivation.

40

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PAPERS Paper 1

Lyon P.J ., P.J. Boult, A. Mitchell and R.R. Hillis, 2004, Improving fault geometry interpretation through ‘pseudo-depth’ conversion of seismic data in the Penola Trough, Otway Basin, in P.J. Boult, D.R. Johns and S.C. Lang eds., Eastern Australian Basins Symposium II, Petroleum Exploration Society of Australia Special Publication, p 695-706.

Paper 2

Lyon P.J ., P.J. Boult, R.R. Hillis and K. Bierbrauer, 2007, Basement controls on fault development in the Penola Trough, Otway Basin, and implications for fault-bounded hydrocarbon traps, Australian Journal of Earth Sciences, 54:5, p 675-689.

Paper 3

Lyon P.J ., P.J. Boult, R.R. Hillis, and S.D. Mildren, 2005, Sealing by shale gouge and subsequent seal breach by reactivation: A case study of the Zema Prospect, Otway Basin, in P. Boult and J. Kaldi eds., Evaluating Fault and Cap seals: AAPG Hedberg Series No. 2, p 179-197.

Paper 4

Lyon P.J ., P.J. Boult, M. Watson and R.R. Hillis, 2005, A systematic fault seal evaluation of the Ladbroke Grove and Pyrus Traps of the Penola Trough, Otway Basin. APPEA Journal, 45 (1), p 459-476.

Lyon, P.J., Boult, P.J., Mitchell, A. & Hillis, R.R. (2004) Improving fault geometry interpretation through ‘pseudo-depth’ conversion of seismic data in the Penola Trough, Otway Basin, in Boult, P.J., Johns, D.R. & Lang, S.C. eds., Eastern Australian Basins Symposium II, Petroleum Exploration Society of Australia Special Publication, pp. 695-706.

NOTE: This publication is included in the print copy of the thesis

held in the University of Adelaide Library.

Lyon, P.J., Boult, P.J., Hillis, R.R. & Bierbrauer, K. (2007) Basement controls on fault development in the Penola Trough, Otway Basin, and implications for fault-bounded hydrocarbon traps. Australian Journal of Earth Sciences, v. 54 (5), pp. 675-689



It is also available online to authorised users at:

http://dx.doi.org/10.1080/08120090701305228

http://dx.doi.org/10.1080/08120090701305228�

Lyon, P.J., Boult, P.J., Hillis, R.R. & Mildren, S.D. (2005) Sealing by shale gouge and subsequent seal breach by reactivation: A case study of the Zema Prospect, Otway Basin, in Boult, P. & Kaldi, J. eds., Evaluating Fault and Cap seals: AAPG Hedberg Series No. 2, pp. 179-197.



Lyon, P.J., Boult, P.J., Watson, M. & Hillis, R.R. (2005) A systematic fault seal evaluation of the Ladbroke Grove and Pyrus Traps of the Penola Trough, Otway Basin. APPEA Journal, 45 (1), p 459-476.



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