DEPARTMENT OF PRIMARY INDUSTRIES

Production Licences Retention Leases VIC/M-04(1) Current Permits 2003 Acreage Release NT Qld. 2004 Acreage Release WA. SA NSW

Victoria Tas

VIC/M-04(2)

MURRAY BASIN VIC/M-04(3)

0 50 100

Kilometres

04-1(v) GIPPSLAND BASIN OTWAY BASIN

200m

200m 1000m

1000m 2000m

2000m V04-2 3000m V04-1

3000m Victoria 4000m Tasmania

4000m VIMP REPORT 83c

HPYDROCARBON ROSPECTIVITY OF THE 2004ARAVA CREAGE ELEASE REAS, ICTORIA, USTRALIA

T. Bernecker J. Driscoll A. Powell J.H. Thomas

GSEO CIENCE V ICTORIA -P-P ETROLEUM March 2004 . VIMP Report 83c

Hydrocarbon Prospectivity of State Waters Block 04-1(v), Otway Basin, Victoria.

J.H. Thomas T. Bernecker A. Powell

March 2004 . Bibliographic reference: BERNECKER, T., DRISCOLL, J., POWELL, A. AND THOMAS, J.H., 2004. Hydrocarbon Prospectivity of the 2004 Acreage Release Areas, Victoria, Australia. Victorian Initiative for Minerals and Petroleum Report 83, Department of Primary Industries

© Crown (State of Victoria) Copyright 2004 Petroleum Development

ISSN 1323 4536 ISBN 1 7414 6915 5

This report may be purchased from: Business Centre Department of Primary Industries 8th Floor, 240 Victoria Parade East Melbourne, Victoria 3002

For further technical information contact: Director, GeoScience Victoria Minerals and Petroleum Division Department of Primary Industries PO Box 500 East Melbourne Victoria 3002

Website: www.dpi.vic.gov.au/minpet/

Authorship and Acknowledgments: This report is a Basin Studies Group publication prepared by Tom Bernecker, Hywel Thomas, Jim Driscoll and Anne Powell. The authors acknowledge the assistance of Eddie Frankel who provided technical support for the project. Mike Woollands is thanked for providing editorial comments.

Disclaimer This publication may be of assistance to you but the authors and the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaim all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. . HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA i

Table of Contents

EXECUTIVE SUMMARY...... 1

1. INTRODUCTION ...... 2

2. EXPLORATION HISTORY ...... 4

3. BASIN EVOLUTION ...... 12

3.1 Oxfordian to Barremian rifting...... 12 3.2 Early Cretaceous (Aptian to Albian) rift to sag...... 13 3.3 Mid-Cretaceous Compression - Cenomanian Unconformity ...... 13 3.4 Turonian to Maastrichtian rifting...... 13 3.5 Late Maastrichtian break-up ...... 14 3.6 Late Maastrichtian to Middle Eocene - Wangerrip Group ...... 15 3.7 Middle Eocene to Early Oligocene – Nirranda Group ...... 15 3.8 Early Oligocene to Recent –Heytesbury Group ...... 15 3.9 Tertiary Volcanics ...... 16

4. OTWAY BASIN PETROLEUM SYSTEMS ...... 16

4.1 Austral 1 (Casterton-Crayfish) petroleum system ...... 16 4.2 Austral 2 (Eumeralla-Waarre) petroleum system ...... 19 4.3 Austral 3 (Belfast-Waarre-Paaratte-Pebble Point) petroleum system ...... 21

5. EXPLORATION POTENTIAL OF 04-1(V) ...... 22

5.1 Well Control ...... 22 5.2 Seismic Data ...... 25 5.3 Structural Setting ...... 25 5.4 Play Types and fairways...... 26

6. PROSPECTS AND LEADS ...... 30

7. SUMMARY ...... 31

8. REFERENCES...... 32 HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA ii

9. APPENDIX ...... 36

NORMANBY-1 ...... 37

Structure...... 37 Target…………………………………………………………………………………………..37 Stratigraphic tops ...... 37 Palynological data...... 37 Reservoir...... 38 Seal……………………………………………………………………………………………..38 Hydrocarbon shows ...... 38 Geochemical analysis...... 38 Well analysis...... 39 Data available...... 39

VOLUTA-1 ...... 41

Structure...... 41 Target……………… ...... 41 Stratigraphic tops ...... 41 Palynological data...... 42 Reservoir...... 42 Seal……………...... 42 Hydrocarbon shows ...... 42 Geochemical analysis...... 42 Well analysis...... 43 Data available...... 43

10. VICTORIAN INITIATIVE FOR MINERALS AND PETROLEUM (VIMP) REPORT SERIES ...... 45 HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA iii

LIST OF FIGURES

Fig.1: Otway Basin permit map showing the location of the 2004 gazettal blocks and pipeline infrastructure Fig.2: Otway Basin Acreage Release VIMP Reports 1997-2004 Fig.3: Otway Basin Tectonostratigraphy Fig.4: Otway Basin Structural Elements Fig.5 Well and Borehole location map Fig.6 Seismic Surveys Fig.7 Seismic Survey with SEGY data Fig.8 Top Sherbrook Group Depth Structure Fig.9 Northeastern Bridgewater Bay Play types Fig.10 Seismic Line OP80-09a through Normanby-1

List of Tables

Table 1: Petroleum exploration and stratigraphic wells Table 2: Water bores > 1200 m deep Table 3: Onshore seismic surveys Table 4: Offshore seismic surveys HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 1

Hydrocarbon Prospectivity of the State Waters Block 04-1(v), offshore Otway Basin, Victoria, Australia

Executive Summary

The Victorian Government is inviting applications for 04-1(v), a State Coastal Waters exploration area in the Otway Basin. The block covers an area of 260 km2 and is located approximately 350 kilometres WSW of Melbourne (population 3,370,000). The port city of Portland (population 9,600) is located 20 km to the east.

Applications for this block close Thursday, 30th September 2004.

Geologically, the gazettal block is underlain by a NW-SE striking Late Jurassic - Early Cretaceous rift system overprinted by the NW-SE striking Late Cretaceous - Early Tertiary Portland Trough. No wells have so far been drilled in the block, however four offshore and numerous onshore wells have been drilled nearby. In addition many stratigraphic and water bores, many exceeding 1200 m in depth, have been drilled by the Victorian Government onshore immediately north of the block.

Although no commercial accumulations of hydrocarbons have yet been found in the area, numerous oil and gas shows have been observed, the most significant being Lindon-1, which intersected a 3 m oil column in the Early Paleocene Pebble Point Formation. Lack of exploration success in the area is partially attributed to poor seismic control, with many onshore wells located on poor quality seismic data. Offshore, until the recent Essential Petroleum VIC/P46 survey, the pre-existing Phillips OP80 survey provided a coarse 2 km x 5 km grid of seismic data on which Normanby-1, Bridgewater Bay-1 and Discovery Bay-1 were based.

Hydrocarbons sourced from basins along the southern margin of Australia have been assigned to the Austral Petroleum Supersystem. Within this supersystem, three petroleum sub-systems related to the Otway Basin have been recognised as follows:

• Austral l – Late Jurassic to earliest Cretaceous fluvio-lacustrine shales. • Austral 2 – Early Cretaceous fluvial and coaly facies. • Austral 3 – Late Cretaceous to earliest Palaeogene fluvio-deltaic facies. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 2

Play fairways in the gazettal area include:

• Sandstones of the Eumeralla Formation and Crayfish subgroups, sealed intraformationally in tilted fault-blocks. • Waarre/Flaxman Formation sandstones, sealed by Belfast mudstones in tilted fault-blocks. • Paaratte Formation sandstones, sealed by intraformational shales of the Belfast Mudstone in tilted fault-blocks. • Pebble Point Formation and Timboon sandstones, sealed by Pember mudstones in tilted fault- blocks, drape features or palaeogeomorphic traps.

The distribution of these play fairways in the vicinity of 04-1(v) is largely controlled by the thickness of the Late Cretaceous - Tertiary section across the Tartwaup-Mussel Fault System. The main play fairway includes the Late Cretaceous Waarre Formation, base-Tertiary Pebble Point Formation and Late Cretaceous Timboon and Paaratte formations. The Waarre Formation possibly has the best reservoir potential and is already a proven reservoir in the Port Campbell area. The underlying Otway Group play fairways (i.e. the Casterton Formation, Pretty Hill Formation, Katnook Sandstone, Windermere Sandstone Member and Heathfield Sandstone), on the other hand, are probably too deep to be viable reservoirs. Charge for the Waarre and Pebble Point Formation plays would most likely be from the Eumeralla Formation, which in the Portland Trough, is overlain by 3000 - 3500 m of Late Cretaceous - Tertiary sediments; the optimum burial thickness for Tertiary hydrocarbon generation.

Leads have been proposed along the northern flank of the Normanby High where potential exists for closures in Cretaceous and Early Tertiary fault bounded structures; however, the current seismic coverage is inadequate to map these in detail. This potential is enhanced by access to the Victorian and South Australian gas markets through the close proximity of the area to the recently commissioned SEA Gas Pipeline.

1. Introduction

The objective of this report is to review the hydrocarbon potential and prospectivity of the State Coastal Waters Block 04-1(v) (Fig. 1) which was gazetted for work program bidding during the 2004 acreage release. Applications for Block 04-1(v) close on Thursday, 30th September 2004.

The report includes information extracted from previously published VIMP (Victorian Initiative for Minerals and Petroleum) reports on the Otway Basin; notably Lavin (1997); Mehin & Constantine HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 3

(1999); Reid et al. (2001); and Constantine (2000). The areas covered by these VIMP reports are shown in Figure 2.

No wells have been drilled in 04-1(v), however, a total of 25 petroleum exploration and stratigraphic wells have been drilled nearby (see Table 1), as well as 29 deep (> 1200 m) water bores drilled by the Geological Survey of Victoria (see Table 2). Only six of these wells, however, reached the Cretaceous.

The block is located in the Otway Basin, which is one of a series of Late Jurassic - Tertiary basins that developed along the southern margin of Australia during the break up of eastern Gondwana. The basin extends into South Australia and covers an area of c.150 000 km2, of which about one-third is located onshore. It is a composite basin consisting of an early, non-marine, intra-cratonic rift basin of Late Jurassic - Early Cretaceous age, overlain in part by a marginal marine rift basin of Late Cretaceous age, which is in turn succeeded by a fully-marine basin of Tertiary age. Total basin fill is about 10 000 m.

Three regional hydrocarbon play fairways have so far been recognised in the basin. These are:

• an Early Cretaceous (Neocomian) play associated with the basal Late Jurassic - Early Cretaceous non-marine rift system (Otway Group),

• a base Late Cretaceous (Turonian) play associated with a Late Cretaceous non-marine/restricted marine rift system (Sherbrook Group), and

• a base Tertiary (Late Maastrichtian - Paleocene) play associated with a Latest Cretaceous - Early Tertiary marine passive margin system (Wangerrip Group).

The Early Cretaceous play, the Crayfish Subgroup, is best developed in the Penola Trough where sandstones of the Pretty Hill Formation and Katnook Sandstone host commercial quantities of gas. Four fields are currently in production: Katnook, Ladbroke Grove, Haselgrove and Haselgrove South.

The base Late Cretaceous play, the Waarre Formation, is best developed onshore in the Port Campbell area approximately 120 km to the ESE of 04-1(v). Seven producing gas fields are located in this area, Boggy Creek, Wallaby Creek, Iona, North Paaratte, Skull Creek, Mylor and Fenton Creek. Offshore gas fields to the south of Port Campbell in the Shipwreck Trough include Casino, Minerva, La Bella, Geographe and Thylacine.

HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 4

The third regional play, the base Tertiary Pebble Point Formation, was a popular exploration target during the 80’s and early 90’s. Although no commercial quantities of hydrocarbons were ever found in this unit, sub-commercial quantities of oil have been recovered from Lindon-1 and Lindon-2 in PEP150, and strong oil shows have also been observed in Fahley-1, Wilson-1 and Pine Lodge-1 in PEP151.

04-1(v) exhibits elements of all three play fairways, however the Neocomian play is probably too deeply buried to be a viable exploration target.

2. Exploration History

The exploration history of the onshore area prior to 1999 is detailed in Mehin & Constantine, 1999.

The area immediately to the north of 04-1(v) was gazetted in 1999, and following successful negotiations with the Native Title claimants, Gunditjmara People, was awarded on 16th May 2002 to Essential Petroleum (100%) as PEP151. The Nelson 2D/3D survey was acquired in the Glenelg National Park in early 2003 just north of 04-1(v) using a Vibroseis crew to acquire 256 line-kilometres.

The area northeast of 04-1(v) was offered to Origin and Essential Petroleum as PEP 150 and is currently undergoing Native Title negotiation.

In other recent onshore exploration activity, Essential Petroleum farmed into Santos’ Permit PEP 152 for a 33.9% interest and Lakes Oil for a 15.59% interest. The farminees drilled Port Fairy-1 in January 2002, which recovered gas and light oil from within the Flaxman Formation. Banganna-1 was drilled in February 2003 in PEP 159 by Origin (50%) / Essential (50%).

Exploration of the offshore Otway Basin is described in Reid et al., 2001; Constantine, 2000, and Lavin, 1998 . The permit immediately south of 04-1(v) was awarded to Essential Petroleum (100%) as VIC/P46 on 28th May 2001. Essential subsequently farmed out equity to Mittwell Energy Resources, a subsidiary of Mitsui. A 750 km seismic survey was acquired to infill the pre-existing OP80 survey.

Further east in permit VIC/P44 (Santos 50%, AWE 25%, Mittwell Energy Resources 25% ), Casino-3 was drilled in November 2003 and tested gas from Waarre sandstones at a rate of 45 MMcfd. In VIC/P51 (Santos 80% / npex 20%) Santos acquired the OS02 2D/3D seismic and the OS03 surveys and drilled Hill-1 in December 2003, which was plugged and abandoned at 2575m. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 5

Table 1A Nearby Onshore Victoria Petroleum exploration and stratigraphic wells

Name Operator Year Permit Total Depth Basal Unit (m)

Palpara-1 Point Addis Oil 1925 356 Nirranda Grp Wells

Nelson-1 Western Petroleum 1939 PPL102 468

Portland North-1 Western Petroleum 1942 PPL125 844 Dilwyn Fm

Mirams-1 H N H Mirams Esq 1940?? PPL120 382.7 undiff. Nirranda Grp

Glenelg-1 Stt & Cmmnwlth 1941?? PPL102 2226 Paaratte Fm

Pretty Hill-1 Frome Broken Hill 1962 PEP5 2478 Palaeozoic Co P/L basement

North Eumeralla-1 Shell Dev (Aust) 1973 PEP5 2964.9 Palaeozoic basement

Green Banks-1 Beach Petroleum 1983 PEP105 1226 Palaeozoic basement

Lindon-1 Beach Petroleum 1984 PEP105 3011 Pretty Hill Fm??

Fahley-1 Beach Petroleum 1985 PEP105 3211 Waarre Fm

Fahley-2 Beach Petroleum 1987 PEP105 1300 Paaratte Fm

Windermere-1 Minora Resources 1987 PEP111 1852 Eumeralla Fm

Henke-1 Beach Petroleum 1987 PEP105 1435 Timboon Sst

Wilson-1 Beach Petroleum 1987 PEP105 1317 Eumeralla Fm?? HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 6

Table 1A (cont) Nearby Onshore Victoria Petroleum exploration and stratigraphic wells

Windermere-2 Minora Resources 1989 PEP111 3595 Eumeralla Fm

Pine Lodge-1 Gas And Fuel 1990 PEP105 2150 Eumeralla Exploration Fm

Lindon-2 Taipan Petroleum Pty 1991 PEP105 970 Paaratte Fm Ltd

Shaw-1 Minora Resources 1992 PEP111 960 Eumeralla Fm

Table 1B Nearby South Australia Petroleum Onshore exploration and stratigraphic wells

Name Operator Year Permit Total Depth Basal Unit (m)

SAOW Caroline-1 255 Nirranda Grp

Picks-1 320 Dilwyn Fm

Picks-2 566

Caroline-1 Alliance Oil 1966 OEL22 3371 HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 7

Table 1C Nearby Petroleum Offshore exploration and stratigraphic wells

Name Operator Year Permit Total Basal Unit Depth (m)

Normanby-1 BP Petroleum Dev 1986 VIC/P14 3308 Waarre Fm Aust

Discovery Bay-1 Phillips Aust Oil Co 1982 VIC/P14 2776 Belfast Mdst

Voluta-1 Shell Dev (Aust) 1967 PEP22 3974 Waarre Fm

Bridgewater Bay-1 Phillips Aust Oil Co 1983 VIC/P14 4200 Waarre Fm

Table 2 Water bores > 1200 m deep

Name Year Total Depth (m) Bottom Fm

Portland-2 1958 1438 Dilwyn Fm

Portland-3 1958 1718 Pember Mudstone

Homerton-3 1968 1579 Eumeralla Fm

Gorae-2 1969 1844 Pember Mudstone

Gorae-4 1969 1855 Pember Mudstone

Portland-8 1970 1343 Dilwyn Fm

Portland-10 1970 1595 Dilwyn Fm

Portland-11 1970 1243 Dilwyn Fm

Cobboboonee-2 1971 1836 Pebble Point Fm

Cobboboonee-4 1971 1916 Eumeralla Fm

Heywood-10 1972 1643 Belfast Mudstone

Mumbannar-4 1972 1227 Paaratte Fm

Narrawong-15 1972 1905 Paaratte Fm

Trewalla-5 1973 1659 Dilwyn Fm HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 8

Table 2 (cont) Water bores > 1200 m deep

Ardno-2 1974 1463 Paaratte Fm

Malanganee-4 1974 1719 Dilwyn Fm

Mumbannar-6 1974 1653 Eumeralla Fm

Palpara-4 1975 1461 Timboon Sandstone

Tarragal-3 1975 1737 Pember Mudstone

Wanwin-1 1975 1785 Paaratte Fm

Warrain-7 1975 1786 Paaratte Fm

Drik Drik-1 1976 1222 Eumeralla Fm

Heywood-13 1842

Narrawong-13 1713

Narrawong-15 1904

Narrawong-16 1670

Tyrendarra-13 1406

Codrington-1 1265

Yambuk-2 1537

Belfast-11 1483

Portland-13 1976 1241 Dilwyn Fm

Kentbruck-3 1977 1733 Dilwyn Fm

Cobboboonee-5 1984 1769 Paaratte Fm

Gorae-5 1984 1799 Pember Mudstone

Homerton-4 1984 1669 Eumeralla Fm

Mouzie-1 1984 1925 Pember Mudstone

Portland-14 1984 1420 Dilwyn Fm

Wanwin-3 1984 1852 Paaratte Fm HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 9

Table 3 Onshore Seismic Surveys

Year Survey Name MPV Operator number

G007 1958 Portland And Port Campbell-Timboon OFB85A Frome – Broken Hill Company Pty. Ltd. G017 1961 Yambuk-Portland Seismic Survey OFBH61B Frome – Broken Hill Company Pty. Ltd. G018 1961 Dartmoor-Nelson Seismic Survey OFBH61C Frome – Broken Hill Company Pty. Ltd. G035 1963 Branxholme-Koroit Seismic Survey OFBH63B Frome – Broken Hill Company Pty. Ltd. G045 1964 Reflection Seismograph Survey, Glenelg Area, OFBH64B Frome – Broken Hill Company Pty. Victoria Ltd. G056 1966 Port Fairy – Nelson Onshore Seismic Survey OS66B Shell Development (Australia) Pty. Ltd. G080 1969 Hawkesdale Seismic Survey OFBS68 Shell Development (Australia) Pty. Ltd. G092 1969 Portland Macarthur River Seismic Survey OFBS69 Shell Development (Australia) Pty. Ltd. G104 1970 Nelson-Koroit Seismic Survey OFBS71B Shell Development (Australia) Pty. Ltd. G112 1972 Dartmoor Seismic Survey OFBS72B Shell Development (Australia) Pty. Ltd. G117 1973 Coastal Strip Survey OFBS73A Shell Development (Australia) Pty. Ltd. G124 1973 Ross Creek Onshore Seismic Survey OFBS73B Shell Development (Australia) Pty. Ltd. G143 1981 Portland Trough Seismic Survey OB81C Beach Petroleum N.L. G163 1982 Ardonachie Seismic Survey OB82A Beach Petroleum N.L. G166 1982 Tarragul Seismic Survey OB82B Beach Petroleum N.L. G178 1983 Denhelm Seismic Survey OB83A Beach Petroleum N.L. G185 1984 Terang Seismic Survey OPX84A Phoenix Oil & Gas N.L. G187 1984 Wanwin Gorae Seismic Survey OB84A Beach Petroleum N.L. G198 1984 Greenslopes Seismic Survey OPX84B Phoenix Oil & Gas N.L. G202 1985 Wanwin-Gorae Detail Seismic Survey OB85B Beach Petroleum N.L. G203 1985 Glenelg Seismic Survey OB85A Beach Petroleum N.L. G205 1985 Toolong Seismic Survey OPP85A Pan Pacific Petroleum Victoria N.L. G211 1985 Najaba-Maten Seismic Survey OB85D Beach Petroleum N.L. G214 1985 Windermere To Port Fairy Seismic Survey OPP85B Pan Pacific Petroleum Victoria N.L. G223 1986 North Portland Seismic Survey OB86C Beach Petroleum N.L. G225 1987 Henke Seismic Survey OB86E Beach Petroleum N.L. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 10

Table 3 (cont) Onshore Seismic Surveys

G246 1988 St. Helens Seismic Survey OM88A Minora Resources N.L. G250 1988 Crawford River OB88A Beach Petroleum N.L. G268 1989 Shamrock Seismic Survey OPX89A Phoenix Oil & Gas N.L. G277 1990 Orford Seismic Survey OM90A Minora Resources N.L. G284 1991 Moyne Seismic Survey OM91A Minora Resources N.L. G300 1992 Ardno S.S. OAGL92A AGL Petroleum Operations Pty Ltd G305 1993 Heywood OGF92B Gas & Fuel Exploration N.L. G310 1993 Myaring S.S. OMN93A Santos G311 1993 OC93a OC93A Cultus G317 1994 Annya S.S. OGF94B Gas & Fuel Exploration N.L. G319 1994 Merrylands OC94A Cultus G323 1995 Tower Hill OC95A Cultus G333 1996 Trewalla OC96C Cultus G340 1997 Malseed OC97D Cultus HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 11

Table 4 Offshore Seismic Surveys

Year Survey Name MPV Operator number

G034 1963 Permit 22 S.W. Victoria OFBH63D Frome Broken Hill Pty. Ltd. G049 1964 Cape Grim-Cape Jaffa Seismic Survey OH65 Hematite Petroleum Pty. Ltd. G054 1966 Offshore 0tway OS66A Shell Development (Australia) Pty. Ltd. G060 1966 Offshore Otway Seismic Survey OS66C Shell Development (Australia) Pty. Ltd. G062 1966 Esso EO-67 Survey OE67A Esso Exploration Australia Inc. G070 1967 EP-67 OE67B Esso Exploration Australia Inc. G078 1968 Offshore Otway Er-68 Seismic And Magnetic OE68A Esso Exploration And Production Survey G088 1969 Australia Marine Seismic Survey O69B OE69B Esso Standard Oil (Australia) Ltd. G094 1970 Portland Experimental OS70A Shell Development (Australia) Pty. Ltd. G116 1972 Portland King Island Seismic Survey OH72 Hematite Petroleum Pty. Ltd. G116A 1972 Scientific Investigation 'Petrel' Survey PETREL Shell G120 1973 Cape Nelson To Cape Otway Seismic Survey OH73 Hematite Petroleum Pty. Ltd. G126 1974 HO4 Offshore Seismic Survey OH74 Hematite Petroleum Pty. Ltd. G139 1980 OE-80a Marine Seismic Survey OE80A Esso Australia Limited G140 1980 OP80 Seismic Survey OP80 Phillips Australian Oil Company G167 1982 OP82a OP82A Phillips Australian Oil Company G167A BMR-1982 040 BMR G173 1982 OP-82b Marine Seismic Survey OP82B Phillips Australian Oil Company G288 1991 OH91a OH91A BHP Petroleum Pty Ltd G291 1991 OH91b OH91B BHP Petroleum Pty Ltd G307 1992 OHGS93a OHGS93A H.G.S. Special Division G322 1995 AGSO 1995 137 AGSO G334 1996 Howick OC96D Cultus G381 2002 VIC/P46 infill OEP02A Essential G384 2002 Nelson OEP03A Essential HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 12

3. Basin Evolution

The Otway Basin is a NW-SE striking passive margin rift basin that extends from Cape Jaffa in South Australia to the northwestern coast of Tasmania. It belongs to a series of basins that were generated in the context of Gondwana break-up and the separation of Antarctica from Australia. The sedimentary section in the basin ranges from the Late Jurassic to Recent and covers an area of 150 000 km2, 80% of which is located offshore.

The structural evolution and stratigraphy of the basin is described in various VIMP reports with the following description taken from Constantine, 2000. The tectonic history and stratigraphy are summarised in Figure 3 and the structural elements of the basin shown in Figure 4.

3.1 Oxfordian to Barremian rifting

The Otway Basin rift system was initiated in the Late Jurassic when N - S extension created a series of E-W to NW-SE symmetric half-grabens across the proto-rift (Williamson et al., 1990; Cooper & Hill, 1997). The major controlling extensional faults were moderate to relatively steeply dipping generally in a northward or landward direction (Hill & Durrand, 1993). Cooper & Hill (1997) equated the structural style of this region with oblique-rift analogue models and suggested that the extensional history of the region was strongly controlled by the prevailing basement fabric. This was addressed in a recent study by Moore (2002) which outlined basement and basin relationships in the Otway Basin.

The incipient Jurassic half-grabens were of limited lateral extent, but as extension progressed into the Early Cretaceous and subsidence continued, the rift basins expanded substantially. In excess of 5000 m of non-marine fluvio-lacustrine Otway Group sediments infilled the growing half-grabens.

Initial lacustrine sedimentation (interbedded with flow basalts) of the Casterton Formation gave way to dominantly fluviatile sedimentation of the Pretty Hill Formation. Lower energy fluvial and lacustrine deposits characterise the Laira Formation while the Katnook Sandstone represents the return to higher energy fluvial deposition. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 13

3.2 Early Cretaceous (Aptian to Albian) rift to sag

Major extensional faults active during Late Jurassic to Early Cretaceous rifting, became significantly less active in the early Aptian across most of the Otway Basin. Formerly high footwall blocks foundered as widespread thermal subsidence took hold across the basin. In excess of 4000 m of Aptian to Albian sediments belonging to the Eumeralla Formation were deposited in a progressively widening, regional sag basin. Deposition occurred in a variety of non-marine depositional environments including fluvial, flood plain, coal swamp and lacustrine. A feature of these sediments is the large amount of volcaniclastic detritus they contain, derived from intra-rift volcanic complexes located to the east of the Gippsland Basin (Bryan et al., 1997).

3.3 Mid-Cretaceous Compression - Cenomanian Unconformity

Rifting ceased in the late Albian as the Otway Basin was subjected to significant compression giving rise to a major angular unconformity, the Cenomanian Unconformity. Several areas including the Otway Ranges, King Island High and Stawell Basement Block underwent several kilometres of inversion. However, structuring was not uniform across the basin, with many areas experiencing only mild uplift. Studies of apatite fission track (AFTA) data and vitrinite reflectance (Rv) data from borehole samples in the Otway Basin, suggest that the Otway Basin experienced regionally elevated palaeotemperatures (50-60oC/km) in the Early Cretaceous (Foster & Gleadow, 1992; Duddy et al. 1991; Duddy, 1994; O'Brien et al., 1994; Cooper & Hill; 1997; Mitchell, 1997). Palaeotemperatures fell sharply in the early Late Cretaceous with cooling facilitated by uplift and erosion together with a declining geothermal gradient.

3.4 Turonian to Maastrichtian rifting

After a hiatus lasting 6.5 Ma (Partridge, 1997), the basin was again subjected to extension and rift- related subsidence beginning in the Turonian. Rifting continued to control basin development and deposition of the syn-rift Sherbrook Group through much of the Late Cretaceous until the latest Maastrichtian when final continental break-up took place (Lavin & Naim, 1995; Lavin, 1997). This second rifting stage involved a change in crustal extension direction to NE-SW, oblique to the earlier N–S extension. The resulting structures are different in style to those developed by the earlier rifting. In the offshore part of the basin, where the Late Cretaceous rifting was most focussed, the resulting structures overprinted those of the early rift stage. Most of the major structural features (Fig. 4) HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 14

including the Voluta Trough (the major rift-induced depocentre), Mussel Platform, Prawn Platform, Tartwaup-Mussel Fault System, Shipwreck Trough and Sorell Fault System, were formed by the Late Cretaceous rifting processes. In some areas such as the Shipwreck Trough and Mussel Platform in the eastern part of the basin, sinistral strike-slip motion resulted in the development of transpressional structures with both extensional and compressional components. These structures take the form of folded, north-trending anticlinal structures, which are particularly well developed in the Shipwreck Trough.

In the Late Cretaceous, most of the space created by the extensional rifting was accommodated by large displacement, NW-striking and SW-dipping normal listric faults such as those that comprise the Tartwaup-Mussel Fault Zone that forms the northern margin of the Voluta Trough (Fig. 4). This rift- controlled faulting resulted in the development of large and deep depocentres, including the Voluta Trough, along the outboard part of the Otway Basin. Late Cretaceous syn-rift deposition of the Sherbrook Group was initiated by a major sea level rise that occurred close to the Cenomanian/Turonian boundary. It is the first indication of major marine incursion into the Otway Basin.

Deposition throughout the Late Cretaceous was dominated by deltaic sedimentation. Large deltas prograded southwards across the marginal platforms into the Voluta Trough, where the Sherbrook section attains a thickness in excess of 5000 m. While sedimentation was influenced by eustacy, overall development of the Sherbrook Group was controlled by active rift-related tectonism. A three- fold stratigraphic subdivision is recognised in the Sherbrook Group: the basal Waarre Formation; the Flaxman Formation; and an overlying sequence comprising the Belfast Mudstone, Skull Creek Mudstone, Nullawarre Greensand, Paaratte Formation and Timboon Sandstone that represent facies equivalents of major, prograding delta complexes.

3.5 Late Maastrichtian break-up

Moderate structuring and regional uplift that accompanied late Maastrichtian continental break-up of Antarctica from Australia, resulted in development of the Late Maastrichtian Unconformity that separates pre-rift from post-rift strata. Post-rift (Tertiary and Recent) sediments were deposited along the continental shelf in a divergent, passive margin setting as Antarctica separated and drifted further away from Australia with concurrent opening of the Southern Ocean. The post-rift succession is made up of three distinct mega-sequences separated by major unconformities that represent different stages of passive margin development and subdivided into three groups: the Wangerrip, Nirranda and Heytesbury groups. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 15

3.6 Late Maastrichtian to Middle Eocene - Wangerrip Group

The structured and peneplained Late Maastrichtian Unconformity surface was flooded during major transgression of the incipient Southern Ocean in the latest Maastrichtian resulting in deposition of the Pebble Point Formation. This shallow marine to coastal sequence is succeeded by strongly progradational Paleocene to Early Eocene sediments belonging to the Pember Mudstone. This sequence was deposited in shelfal to shallow marine environments on a southwesterly building marine shelf that trended approximately parallel to the present day coastline (Arditto, 1995). The Pember Mudstone is equivalent in part and succeeded by the Dilwyn Formation (represented by topset beds) deposited in coastal plain and deltaic environments. All three formations are time equivalent to terrestrial sediments of the lower Eastern View Formation that are restricted to the Torquay Sub-basin and the Colac Trough.

3.7 Middle Eocene to Early Oligocene – Nirranda Group

The Middle Eocene Unconformity separates the Wangerrip Group from the overlying Nirranda Group. It is recognised in all basins along the southern Australian margin and is correlated with minor tectonism produced by a significant increase in the rate of seafloor spreading in the Southern Ocean south of Australia (Yu, 1988; Lowry & Longley, 1991). The erosional surface, which in some parts of the Otway Basin is channellised and exhibits considerable relief, is infilled and draped by sediments of the Middle Eocene to Early Oligocene Nirranda Group. The Nirranda Group comprises prograding nearshore to offshore marine clastics of the basal Mepunga Formation that pass to increasingly open marine carbonates of the Narrawaturk Marl. Both formations are time equivalent to the proximal Demons Bluff and Eastern View formations recognised onshore in the northeastern part of the Otway Basin and Torquay Sub-basin (Abele et al., 1976; Blake, 1980; Tickell, 1991).

3.8 Early Oligocene to Recent –Heytesbury Group

The boundary between the Nirranda Group and overlying Heytesbury Group is represented by an Early Oligocene regional unconformity that displays marked angularity and relief in some areas, including and most spectacularly, along the flanks of the Otway Ranges. This unconformity coincides with a major worldwide lowstand event and also the start of NW-SE directed compression that continues to the present day as shown by seafloor relief. Although this compression affects the entire HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 16

southeastern margin of Australia, it is most pronounced in the Otway and Strzelecki Ranges that underwent significant folding and uplift. Despite the ongoing compressional regime throughout the late Tertiary to Recent, much of the Otway Basin continued to undergo significant subsidence and continuation of open marine conditions along the basin margin. The Heytesbury Group is dominated by carbonates, including marl and bioclastic limestone. Widening of the Southern Ocean in the Oligocene, caused by a rapid increase in the spreading rate across the Southern Ocean, resulted in the establishment of the Circum-Antarctic Current. This current provided enhanced conditions for the production of shelfal carbonates.

3.9 Tertiary Volcanics

Volcanic eruptions culminated during the Paleocene, the rocks being known as the 'Older Volcanics' (Megallaa, 1986). Volcanic eruptions during the Neogene formed a series of basaltic sheets covering much of central and western Victoria, known as the 'Newer Volcanics'.

4. Otway Basin Petroleum Systems

Hydrocarbons sourced from basins along the southern margin of Australia have been assigned to the Austral Petroleum Supersystem (Bradshaw, 1993 and Summons et al., 1998). Within this supersystem, three petroleum sub-systems related to the Otway Basin have been recognised (Edwards et al., 1999). Each sub-system correlates geochemically to distinct oil families and related source rock facies with differences primarily related to the type of depositional environment. The three sub-systems are:

• Austral l – Late Jurassic to earliest Cretaceous fluvio-lacustrine shales. • Austral 2 – Early Cretaceous fluvial and coaly facies. • Austral 3 – Late Cretaceous to earliest Palaeogene fluvio-deltaic facies.

4.1 Austral 1 (Casterton-Crayfish) petroleum system

4.1.1 Source In the Otway Basin, source rocks of the Austral 1 petroleum system comprises non-marine, Upper Jurassic to Lower Cretaceous fluvio-lacustrine and lacustrine shales deposited in rifted half-grabens (Casterton Formation and Crayfish Subgroup). Edwards et al., (1999) grouped liquid hydrocarbons sourced by Austral 1 source rocks into four oil families based on isotopic and biomarker signatures HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 17

and interpreted source rock depositional environments. The Austral 1 petroleum system is recognised as the source for oil recovered from an RFT in Troas-1 and a DST in Nunga Mia-1 in South Australia.

The Casterton Formation is widely recognised as an excellent source rock (Lovibond et al., 1995; Lavin & Muscatello, 1997). In Victoria, the Casterton Formation has an average TOC content of 2.6% (range 0.4-8.9%) and consists largely of Type II-III kerogens which suggests it is both oil- and gas- generative (Mehin & Constantine, 1999). Geochemical studies (Padley et al., 1995; Edwards et al., 1999) have also identified the Casterton Formation and/or Crayfish Subgroup as the most likely source for oil and gas in the Pretty Hill Formation in South Australia. The source rocks have been geochemically linked to four depositional environments: saline lacustrine, freshwater lacustrine, fluvio-lacustrine/peat swamp, and marginal marine (Edwards et al., 1999). The interpretation of a marginal marine source at that time, however, is difficult to support based on palaeogeographic and tectonic reconstructions (Norvick & Smith, 2001). The Katnook-Ladbroke Grove hydrocarbons are thought to be derived from a fluvio-lacustrine/peat swamp source.

The Crayfish Subgroup in Victoria consists of two units: the Pretty Hill Formation and Laira Formation, the latter restricted in its distribution to the west near the South Australian border where it conformably overlies the Pretty Hill Formation. Geochemical analysis suggests that the Pretty Hill Formation has fair source rock potential, with an average TOC content of 1.7% (range 0.4-13.8%) (Mehin & Constantine, 1999). Type III kerogens predominate, with some Type II and IV also present, which suggests the unit is both oil- and gas-generative (Mehin & Constantine, 1999). Maturation studies (Hill, 1995a; Hill, 1995b) show the Crayfish Group is approaching peak maturity for oil generation within the Robe Trough in South Australia.

As yet, however, there have been no commercial petroleum discoveries sourced by the Austral 1 petroleum system in the Victorian part of the basin. However, oil shows have been observed in several wells including Garvoc-1, Woolsthorpe-1 and Hawkesdale-1 (Kopsen & Scholefield, 1990). It is possible that source rocks in the Victorian Otway Basin may no longer be oil-generative as maturation and hydrocarbon expulsion from these units may have occurred before Late Cretaceous to Neogene trap formation, particularly in the offshore area where deep burial of the potential source rocks is expected.

4.1.2 Reservoir The Pretty Hill Formation (Crayfish Subgroup) is the major play fairway in the South Australian part of the Otway Basin and is the producing unit in the Katnook, Ladbroke Grove, Haselgrove and

Haselgrove South gas fields. The Katnook field contains 40.5 Bcf GIIP (< 0.05% CO2), with the discovery well, Katnook-2, flowing 16.3 MMcfd on production testing plus 119 bbl of 52o API HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 18

condensate (Morton & Sansome, 1995). The Ladbroke Grove field, in comparison, contains 17.4 Bcf

GIIP (54% CO2), with the discovery well, Ladbroke Grove-1, flowing 4.6 MMcfd on production testing plus a small amount of 37.8o API condensate (Morton & Sansome, 1995). The Pretty Hill Formation in Victoria has good reservoir potential at shallow to moderate depths (1000-2300 m), with measured porosities ranging from 13.2-32.0% (average 20.7%), and average permeabilities of 390 mD (Mehin & Constantine, 1999). The reservoir potential below 2300 m is uncertain as very few wells in the state penetrate the unit below this depth. Reservoir data from the Penola Trough gas fields, however, suggest its porosity/permeability potential could still be quite high because the gas zones, between 2500 2800 m, have effective average core porosities of 10-18% and permeabilities of 0.6-549 mD (Parker, 1992).

4.1.3 Seal Vertical and cross-fault sealing for the Penola Trough gas fields is provided by the Laira Formation (Parker, 1992; Lovibond et al., 1995). In Victoria, the sealing unit would most likely be the Eumeralla Formation as the Laira Formation is absent except for several wells located near the Victorian - South Australian border (Mehin & Constantine, 1999).

4.1.4 Traps Trap types in the Penola Trough gas fields area are represented by either E-W striking faulted anticlines with closure at the producing Pretty Hill Formation level (e.g. Katnook Field), or by tilted fault-blocks with footwall closure (e.g. Ladbroke Grove Field) (Parker, 1992).

4.1.5 Maturity The thermal maturity of the Casterton Formation in Victoria is poorly constrained because only wells drilled along the northern basin margin intersected the unit at relatively shallow levels (< 2100 m). In these wells, the Casterton Formation is presently mature for oil (Rv 0.7-1.0%), and probably increases in maturity towards the basin centre towards the southwest (Mehin & Constantine, 1999).

Most of the wells that intersect the Pretty Hill Formation in Victoria are also located along the northern margin of the basin. In these wells, the top of the unit is presently early mature for oil (Rv 0.5-

0.7%), reaching mid-level maturity (Rv 0.7-1.0%) towards the coast (Mehin & Constantine, 1999).

4.1.6 Migration Burial history modelling (Lovibond et al., 1995; Duddy, 1997) indicates that hydrocarbons were generated towards the end of the Early Cretaceous in the Penola Trough gas fields area. The hydrocarbons presumably migrated into the traps via vertical migration (Lovibond et al., 1995) as HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 19

condensate and were presumably derived from source rocks at the Rv 0.7-1.0% maturity level as indicated by geochemical data analysis (Tupper et al., 1993).

4.2 Austral 2 (Eumeralla-Waarre) petroleum system

4.2.1 Source With the exception of the Penola Trough, the Early Cretaceous, Austral 2 petroleum system is widely recognised as the source for the majority of gas and minor oil discoveries made in the Otway Basin to date (Edwards et al., 1999).

Geochemical studies have identified the Eumeralla Formation as the source interval for the gas in the Port Campbell/Shipwreck Trough area (Mehin & Link, 1994; Foster & Hodgson, 1995; Luxton et al., 1995). Gas shows reported at Triton-1 in the Victorian offshore (Luxton et al., 1995) and gas accumulations at Troas-1 and Breaksea Reef-1 in South Australia are also ascribed to the Austral 2 petroleum system. The gas is derived from two coaly horizons in the Eumeralla Formation; one of Aptian age (P. notensis biozone) near the base of the unit, the other of Lower Albian age (C. striatus biozone). The coal-bearing sequences are about 200 m thick and consist of multiple 2-3 m thick seams with intercalated mudstones that are rich in disseminated organic matter. Well control and seismic indicate that these sequences extend across the basin (Tupper et al., 1993) and have excellent source rock potential for gas and light oil (Preston, 1992a-e; Geary & Reid, 1998).

Although there is significant potential for liquids generation, exploration results in the offshore areas suggest the source rocks are predominantly gas-prone with only minor quantities of condensate. Oil potential within this petroleum system cannot, however, be entirely ruled out, as the medium-gravity, waxy oils recovered from onshore Victorian wells (Flaxmans-l, Windermere-1, -2 and Port Campbell- 4) demonstrate. Whole-oil gas chromatograms indicate that the oils are derived from terrestrial, land- plant material (Kopsen and Scholefield, 1990; McKirdy et al., 1994). The Lindon-1 and -2 oils also belong to this petroleum system but have been extensively altered by microbial activity and water washing (McKirdy 1986; Tabassi and Davey, 1986).

4.2.2 Reservoir Buffin (1989) divided the Waarre Formation in the Port Campbell area into three units called (in ascending stratigraphic order) A, B and C. The basal section, Unit A, is a fining-upward package of fine-grained volcanolithic sandstones and carbonaceous mudstones. Unit B is a predominantly carbonaceous mudstone package with subordinate thin interbeds of fine-grained dolomitic and calcareous sandstones. The third horizon, Unit C, is a well-developed medium- to coarse-grained quartz sandstone, and is the reservoir unit for the Port Campbell gas fields and the offshore Minerva HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 20

and La Bella gas fields (Geary & Reid, 1998). Unit C has the best reservoir potential, with an average porosity of 17% and permeability of 2700 mD (Mehin & Constantine, 1999).

The Waarre Formation is the major regional reservoir interval in the Victorian part of the Otway Basin. Producible gas has been encountered in sixteen onshore fields in the Port Campbell area ranging in size from Skull Creek (2.2 Bcf GIIP) to Iona (40.3 Bcf GIIP) (K. Mehin pers. comm). In the offshore Shipwreck Trough, the Waarre Formation hosts the gas accumulations at Minerva, La Bella, Geographe, Thylacine and Casino, all of which, except La Bella, are currently being considered for development. Gas in Thylacine and Geographe are estimated to have combined reserves of 800Bcf (Woodside 2003 Reserves Statement). Minerva is estimated to contain reserves of 300Bcf (BHP

Billiton News Release 30/02, May 2002), primarily methane with some CO2, whereas the La Bella Field has about 210 Bcf of GIIP (Luxton et al., 1995).

4.2.3 Seal The sealing units for the Port Campbell and Shipwreck Trough gas fields are marine claystones of the overlying Flaxman Formation and Belfast Mudstone. Both units are regionally developed and thickest in the offshore part of the basin. In the Shipwreck Trough area, marine sandstones in the basal part of the Flaxman Formation contain gas and constitute part of the total gas reservoir section for the Minerva and La Bella gas fields (Geary & Reid, 1998).

4.2.4 Traps The gas accumulations in the Port Campbell-Shipwreck Trough area are trapped in faulted anticlines and tilted fault-blocks of Late Cretaceous age which were slightly modified by Late Tertiary compression (Foster & Hodgson, 1995; Geary & Reid, 1998).

4.2.5 Maturity Vitrinite reflectance data indicates that the Eumeralla Formation west of the Moyston Fault Zone increases in maturity in a southwesterly direction (Mehin & Constantine, 1999). Onshore, the top of the unit is presently immature for oil (Ro < 0.50%) along the northern margin of the basin (Mehin &

Link, 1996), but becomes increasingly mature (Ro 1.0-1.3%) offshore (Geary & Reid, 1998). The base of the unit, in comparison, is early mature for oil (Ro 0.5-0.7%) onshore along the northern margin of the basin and increases to gas mature (Ro 1.3-2.6%) near the coast.

Burial history modelling indicates the Eumeralla Formation in this area has a two-stage hydrocarbon generation history consisting of an initial Early Cretaceous phase of hydrocarbon expulsion followed by a smaller Tertiary expulsion phase (Duddy, 1994, 1997; Mehin & Link, 1997b). Early Cretaceous expulsion was associated with the initial rift event when the geothermal gradient was about 50- HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 21

70oC/km (Mehin & Link, 1997a; Mitchell, 1997). This event would have resulted in significant hydrocarbon generation from the Casterton Formation, Crayfish Subgroup and basal part of the Eumeralla Formation, peaking at the end of the Early Cretaceous. During the Late Cretaceous, hydrocarbon expulsion from the Casterton Formation (Crayfish Subgroup) and base Eumeralla Formation ceased after the regional geothermal gradient dropped from 50-70oC/km to 30-40oC/km (Duddy, 1997; Mitchell, 1997). Further hydrocarbon generation did not recommence until the Eumeralla Formation experienced burial temperatures greater than those attained at the end of the Early Cretaceous. Duddy (1997) and Mehin & Link (1997b) believe this occurred in the Tertiary with peak generation occurring in areas where the Eumeralla Formation is overlain by about 2000 m of Late Cretaceous sediments and 1000-2000 m of Early Tertiary sediments.

4.2.6 Migration Hydrocarbons from the Eumeralla Formation are thought to have reached the Waarre Formation via vertical migration along faults. Sandstones in the unit are unlikely conduits because pervasive chlorite cementation has occluded most pore spaces (Geary & Reid, 1998).

4.3 Austral 3 (Belfast-Waarre-Paaratte-Pebble Point) petroleum system

4.3.1 Source While Late Cretaceous coastal plain sediments are regarded as the major source interval in the Gippsland Basin, the stratigraphic equivalent in the Otway Basin, the Sherbrook Group, has to date not yielded any commercial quantities of hydrocarbons. The only oil recovered from this unit was derived from the Pebble Point Formation in Wilson-1 (Lavin, 1998). This apparent lack of success does not necessarily mean that mature, generative and oil-prone Austral 3 source rocks are not developed in the Otway Basin. Most of the wells drilled in the basin to date have been located on platform areas or onshore, where the Sherbrook Group has not reached sufficient thermal maturity for hydrocarbon generation. Where wells have been drilled in basinal areas, hydrocarbons that may have been sourced from Late Cretaceous source rocks were not geochemically analysed (eg. Breaksea Reef-1, Hill, 1995a; Normanby-1, Lavin, 1998).

The hydrocarbon potential of the Sherbrook Group may be distinctly greater in areas basinward of the continental slope, the majority of which lies beyond the slope break southward of the Tartwaup- Mussel Fault Zone. The most likely source rock interval is represented by the Belfast Mudstone, which was geochemically assessed as a moderately good source in Breaksea Reef-1 (Hill, 1995a). The underlying Waarre Formation contains both marginal marine and coastal plain sediments that can be regarded as viable source rocks provided they were sufficiently buried. Until further exploration is HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 22

undertaken, the ability of the Austral 3 system to generate substantial volumes of hydrocarbons in the Otway Basin remains speculative.

4.3.2 Reservoir & Seals The delineation of reservoir and seal lithologies appears less problematic. The Paaratte Formation and Timboon Sandstones are characterised by intraformational mudstones with sealing capacity, while the Paleocene Pebble Point Formation is sealed by the seaward thickening Pember Mudstone. Although the Sherbrook Group remains untested in terms of mature source rocks, all other petroleum systems elements are developed. Only ongoing exploration, especially in the deeper parts of the basin, can shed light on the extent of this petroleum system.

5. Exploration Potential of 04-1(v)

5.1 Well Control

Well control, shown in Figure 5, includes petroleum exploration wells, stratigraphic wells and water bores. Those bores and wells drilled to a depth greater than 1200 m are listed in Tables 1 & 2. More details on the onshore bores and wells can be found in Mehin and Constantine (1999) and the offshore wells in Lavin (1998) and Constantine (2000). In the vicinity of 04-1(v) only four offshore wells and one onshore well (Glenelg-1) reached the Cretaceous.

A brief summary of the petroleum wells is given below. More details on Voluta-1 and Normanby- 1 are given in the Appendix.

5.1.1 Glenelg-1 Glenelg-1 was drilled by the Victorian State Government in 1945 and is one of the few onshore wells to have reached the Cretaceous. The well TD’d in the Paaratte Formation at 2226 m. According to the summary sheet for this well, bubbles of gas carrying globules of oil were observed at a depth of 1232.9 m in the Timboon Sandstone. No other data is available and no other shows were reported.

5.1.2 North Portland-1 North Portland-1 was drilled by the Victorian State Government in 1942. The well TD’d in Dilwyn Formation at 844.0 mGL. No electric logs were run and no shows were reported. No other data is available.

HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 23

5.1.3 Mirams-1 Mirams-1 was drilled by H.N.H. Mirams in 1940. The well is located in the southern part of PEP 150 and bottomed in undifferentiated Nirranda Group sediments at 382.7 mGL. According to the summary sheet for this well, minute gas bubbles with a faint iridescent film were observed in the drain after the cuttings from 324.9 to 335.3 mKB were cleaned. No other data is available and no other shows were reported.

5.1.4 North Eumeralla-1 North Eumeralla-1 was drilled by Shell in 1974 and TD’d in Palaeozoic metasedimentary basement at 2698.0 mKB. The well targeted a Pretty Hill Formation tilted fault-block on the upthrown side of a large down-to-the-north fault. No hydrocarbons were encountered.

5.1.5 Eumeralla-1 Drilled after Pretty Hill-1 in 1962 by Frome-Broken Hill to test the Pretty Hill sandstones of the basal Crayfish Subgroup in the hanging wall of the Windermere Fault. The well TD’d without shows at 3139 mKB in the Laira Formation without reaching its objective.

5.1.6 Windermere-1 Windermere-1 was drilled in 1987 by Minora Resources to test Pebble Point and Upper Eumeralla closures in the hanging wall of the Windermere fault. Small amounts of oil were recovered on test from the Heathfield Member of the Eumeralla Formation and the well reached TD at 1852 m.

5.1.7 Windermere-2 Windermere-2 was drilled in 1989 by Minora Resources to test the Heathfield Member of the Eumeralla Formation up-dip of the Windermere-1 oil discovery. The well reached TD at 3595 mKB in the Laira Formation of the Crayfish Subgroup having penetrated almost 2200 m of Eumeralla Formation. Minor oil shows were recorded in the Laira Formation at 3188 mKB, however at this level the well was down-dip from the structural crest.

5.1.8 Pretty Hill-1 Pretty Hill-1 was drilled in 1962 by Frome-Broken Hill to test Early Cretaceous sandstones of the Crayfish Subgroup in a tilted fault-block on the upthrown side of a large down-to-the-south fault. The well TD’d at 2478 m in ultrabasic volcanics of the Late Jurassic Casterton Formation. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 24

5.1.9 Normanby-1 Normanby-1 was drilled by BP Australia in 1986 to test the Waarre Formation in a large tilted fault- block approximately ten kilometres from the coast. The well recovered minor amounts of gas in an RFT from tight Waarre Formation sandstones.

It is notable that visual porosity in several of the sidewall cores across the Waarre Formation sandstones was noted to be fair to good, but borehole conditions were poor, and the RFT tool failed on a majority of attempts.

Post drill mapping suggests that Normanby-1 was drilled down-dip from the crest of the structure.

5.1.10 Voluta-1 Voluta-1 was located on a large Tertiary anticlinal feature subsequently named the Cape Bridgewater High. The well was drilled in 1967 and located on seismic data acquired in 1996. Despite the extensive coverage of this grid, data quality below the upper Sherbrook Group is poor, and in the vicinity of the Voluta-1 well site, the data quality at the Tertiary level is also poor. The well was deepened to provide stratigraphic control of the pre-Tertiary section.

Minor hydrocarbon shows were recorded during the drilling of the well, and it was plugged and abandoned in the Flaxman Formation.

Mapping in VIMP 57 (Lavin, 1998) suggested that Voluta-1 was substantially off structure at the Base Tertiary level. There was also no obvious structural closure within the lower Sherbrook Group at Voluta-1.

5.1.11 Bridgewater Bay-1 Bridgewater Bay-1 was drilled by Phillips in 1983 to test the Waarre Formation on a broad tilted horst block on the Bridgewater High. The stratigraphically younger Paaratte Formation was a secondary objective. The well spudded in 131 m of water and reached a total depth of 4200 mKB before being plugged and abandoned. The Waarre Formation (or Flaxman Formation as an alternative interpretation) was encountered some 1000 m deeper than prognosed and proved water-wet. Later remapping suggests that the well is located significantly off-structure, on the downthrown side of the fault-block. . 5.1.12 Discovery Bay-1 Discovery Bay-1 was drilled by Phillips in 1982. The well was designed to test the Timboon Sandstone and underlying Paaratte Formation associated with a tilted fault-block. The well TD’d in the Paaratte Formation at a depth of 2776 mKB. Only minor hydrocarbon shows were encountered. Well failure is thought to be due to poor top sealing or lateral fault seal for both target intervals. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 25

5.2 Seismic Data

Seismic surveys in the vicinity of 04-1(v) are shown in Figures 6 and 7, and listed in Tables 3 and 4. Few lines have been acquired within the gazettal blocks themselves and the coverage is dependent primarily on the tails of offshore surveys.

The main offshore survey is the Phillips OP80 survey recently infilled in VIC/P46 by Essential Petroleum’s OEP02 survey. The OP80 survey was reprocessed in part by BP in 1985, Cultus in 1989 and again by Geco-Prakla in 1993.

5.3 Structural Setting

The main structural features in the gazettal area are illustrated in Figure 4 as follows:

5.3.1 Mumbannar and Mussel Platforms

The Mumbannar Platform and its offshore extension, the Mussel Platform, is bounded to the southeast by the Tartwaup-Mussel Fault Zone. The platforms strike broadly NW-SE in a region of thin Late Cretaceous sedimentation. The Sherbrook Group is approximately 700 m thick along the southern edge and thins towards the northeast (Lavin & Naim, 1995).

5.3.2 Tartwaup-Mussel Fault Zone

The Tartwaup-Mussel Fault Zone separates the Mussel and Mumbannar platforms from the Voluta Trough. The zone comprises a series of laterally extensive NW-SE trending faults that throw to the southwest. The faults propagate upwards to the Late Maastrichtian Unconformity where they are either truncated or show only relatively minor Tertiary reactivation. Structural growth occurred on the faults throughout the Late Cretaceous with the Sherbrook Group showing variable amounts of offset along the fault zones. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 26

5.3.3 Voluta Trough

The Voluta Trough is a NW-SE trending Late Cretaceous depocentre located entirely offshore. The Early Cretaceous Waarre Formation and Otway Group are generally buried to depths well in excess of 3500 m and as such are not considered viable exploration targets.

5.3.4 Portland Trough

The Portland Trough is a large NW-SE striking syncline of Late Paleocene - Early Eocene age. The trough is located above the hanging wall of the Tartwaup-Mussel Fault Zone and is separated from the Voluta trough by the Bridgewater High. The trough is a major Tertiary depocentre with around 1000 m of Wangerrip Group sediments along its axis which lap out along the Bridgewater High to the south.

5.3.5 Bridgewater High

The Bridgewater High is located south of the Portland Peninsula and appears to have been a significant structural feature during the Early Tertiary. The high forms a southeast plunging anticline at the Late Maastrichtian Unconformity level where Early Maastrichtian sediments of the Sherbrook Group are truncated on the northern limb at high angle by the overlying Late Maastrichtian - Early Eocene sediments of the Wangerrip Group. The Otway Group was encountered at 4079 mSS in Bridgewater Bay-1 but as shallow as 3057 mSS at Normanby-1.

5.4 Play Types and fairways

Gazettal Area 04-1(v) lies at the juncture of the Portland Trough, the Bridgewater High and the Voluta Trough. A structure map on Top Sherbrook Group is shown in Figure 8. Play types are shown schematically in Figure 9.

5.4.1 Waarre Formation Play

The Waarre Formation is the major regional play in the Victorian part of the Otway Basin. The Waarre sandstone is the reservoir unit for seven producing onshore gas fields in the Port Campbell Embayment (Boggy Creek, Wallaby Creek, Skull Creek, Iona, North Paaratte, Mylor, Fenton Creek) HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 27

as well as the offshore gas fields in the Shipwreck Trough (Minerva, La Bella, Geographe, Thylacine and Casino).

In the South Australian part of the Portland Trough, Caroline-1 has flowed gas from the Waarre Formation for the past three decades (Hill, 1995a).

These traps are associated with tilted fault-blocks developed within the Sherbrook Group and require cross-fault seal to be effective. The Belfast Mudstone provides an excellent regional top seal while the Flaxman Formation has also demonstrated intra-formational sealing potential.

Reservoir potential To the south of the Tartwaup-Mussel Fault Zone, the Waarre Formation is likely to be deeply buried and while the Waarre and Flaxman sandstones often exhibit excellent reservoir properties, reservoir development is strongly facies-dependant. Where buried deeply (> 3000 m), deleterious diagenetic effects significantly reduce their potential as viable reservoir targets, particularly for oil (Geary & Reid, 1998). This suggests that south of the Tartwaup-Mussel Fault Zone only small areas of the Bridgewater High and Portland Trough may be shallow enough to preserve suitable reservoir qualities.

Sealing units The sealing unit for this play fairway is the Belfast Mudstone. This is a proven seal in the eastern part of the basin. In the Portland Trough, the Belfast Mudstone is about 200 m thick and should provide good vertical and cross-fault seal on tilted fault-blocks in this area. However, on the Mumbannar Platform, the Belfast Mudstone is only about 30 m thick and is unlikely to provide a good lateral seal for tilted fault-block plays in these areas.

Trap types Potential trap types for the Waarre Formation play fairway include: • tilted fault-blocks, and • fault-bounded horst blocks.

Risks The principal risks associated with this play fairway are reservoir quality and seal thickness.

5.4.2 Intra-Paaratte Play

Although a hydrocarbon accumulation is yet to be discovered associated with this play, it has only been the primary target of one offshore well (Discovery Bay-1). The occurrence of massive sandstones HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 28

within thick shale units in the Paaratte Formation along trend from Bridgewater Bay-1, suggests significant prospectivity exists in the gazettal block for this play. Much of the area has access to present day oil and gas charge from Waarre Formation source rocks, whilst to the north Eumeralla Formation source rocks provide secondary source potential.

Reservoir potential The often coarsening-upwards quartz sandstones display excellent reservoir development.

Sealing units The net to gross of the Paaratte Formation is expected to diminish as it interfingers with the laterally equivalent Belfast Mudstone. The potential for fault seal will increase in a basinward direction.

Trap types Rollovers associated with anticlinal structures developed on the hanging-wall of listric faults may provide independent four-way dip-closure with no reliance on fault seal. Downthrown fault closures with fault juxtaposition of Paaratte Formation reservoirs against lower net to gross sequences or Belfast Formation mudstones would pose a lesser fault seal risk.

Risks Intra-Paaratte fault traps rely on both intraformational and cross-fault seal. The adequacy of these seals is recognised as the main exploration risk.

5.4.3 Top Paaratte/Timboon Play

Paaratte and Timboon sandstone traps at the top of the Sherbrook Group depend upon the development of seal above the Maastrichtian Unconformity within the overlying Tertiary passive margin sequence.

Seal potential Potential sealing units within the Wangerrip Group include the basal K/T Shale (Massacre Shale), Pember Mudstone, basal mudstone units of the Dilwyn Formation, and mudstones in the Mepunga Formation associated with Eocene channelling. Throughout most of the gazettal area a thick Tertiary sequence is predicted. Thick Pember Mudstone seals are predicted through the Portland Trough. Where transgressive marine sandstones of the Pebble Point Formation overlie the Late Maastrichtian Unconformity a significant top seal risk exists for the Paaratte and Timboon formation play. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 29

Trap Potential A variety of different traps have been identified including: • large Tertiary-related anticlinal features such as Bridgewater High, • low-relief tilted fault-blocks, • stratigraphic traps, and • palaeogeomorphic relief (erosional knolls) developed at the unconformity surface.

Risks The main play risks relate to the presence of an adequate top seal and leakage of hydrocarbons into an overlying thief zone such as the Pebble Point Formation.

5.4.4 Pebble Point Formation Play

Interest in the Pebble Point Formation as an exploration target began in 1982 when a strong oil show was encountered in Curdies-1 in the Port Campbell Embayment (Tabassi & Davey, 1986). Since then, oil shows have been reported in four other Victorian wells which have targeted the Pebble Point Formation, namely Lindon-1, -2, Fahley-1 and Wilson-1. Lindon-1 intersected a three-metre column of 28.8o API oil (Tabassi & Davey, 1986). Lindon-2 and Wilson-1, in contrast both had strong oil shows, while Fahley-1 encountered weak gas.

Reservoir potential Poor reservoir development (high porosity up to 25% but low permeability) in these wells due to the presence of chamositic clay in the matrix prevented significant oil flows on test. Little data is available on the porosity and permeability of the Pebble Point Formation. The only well with any measured data is Lindon-1, which has an average porosity of 20.8% (range 5.5-28.2%) and permeability of 45.3 mD (range 0.02-1135 mD).

Play validity depends on the presence of better reservoir development elsewhere in the basin. Yang (1997) interpreted the direction of Pebble Point Formation onlap from seismic data from the axis of the Portland Trough onto its flanks. Low net to gross ratios and poorer reservoir quality are inferred for the axis of the Portland Trough. However, along the flanks of the trough and on the Bridgewater High, higher net to gross and better reservoir development are envisaged due to winnowing of transgressive marine sandstones. The excellent reservoir characteristics encountered in Bridgewater Bay-1 support this. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 30

Seal potential Vertical and lateral seal for this reservoir is provided by the Pember Mudstone. The Pember Mudstone provides vertical and cross-fault seal for the Lindon-1 oil accumulation. The formation is well developed and thick (up to 160 m) in many parts of the basin, but thins southwards and basinward with overall progradation of the Wangerrip Group. The development of thin porous sandstones within the Pember Mudstone may also limit its sealing capability in some areas. Mudstones in the Mepunga Formation associated with Eocene channelling also offer sealing potential. The presence of downlapping progrades, which may be associated with sand stringers in the Pember Mudstone, poses a top seal risk on the northern flank of the Bridgewater High. In the northeast of 04-1(v), topset beds of the Wangerrip Group (Dilwyn Formation) apparently overlie the play (Fig. 10). Pember Mudstone may be relatively thin and an ineffective seal to this play. Tertiary channelling poses a top seal risk where lowstand system tracts may have been developed. Elsewhere, channel fill is expected to be fine- grained.

Charge Hydrocarbon charge from oil and gas mature Waarre Formation and gas mature Eumeralla Formation source rocks may be expected to be focused along Sherbrook Group carrier beds and up faults reaching the Late Maastrichtian Unconformity level before migrating into potential Pebble Point Formation reservoirs along the Bridgewater High.

Trap styles Potential trap styles associated with this play include: • tilted fault-blocks, and • anticlines with four-way dip closure.

Risks The principal risk associated with this play is reservoir quality. Tabassi & Davey (1986) believe the lower than expected flow rate associated with the Lindon-1 DST was due to smectite in the pore spaces absorbing water from the drilling mud and expanding, thereby reducing the permeability of the unit.

6. Prospects and Leads

No structural mapping has been undertaken specifically in the gazettal block, however maps over the adjacent areas can be found in earlier VIMP reports. A compilation Top Sherbrook regional map, shown in Figure 8, illustrates the morphology of this key horizon. It can be seen from this map that 04- HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 31

1(v) lies on the north flank of the Normanby High straddling the western end of the Portland Trough, a Tertiary syncline overlying the hanging wall of the Tartwaup-Mussel Fault Zone.

South of the Tartwaup-Mussel Fault Zone, the Eumeralla and overlying Waarre and Flaxman formations are generally regarded as too deeply buried to provide a viable target. However, parts of the Bridgewater High in the western parts of 04-1(v) may be shallow enough for adequate reservoir development down to the Waarre level.

Although detailed mapping has not been undertaken a series of tilted fault-blocks visible on seismic (Fig. 10) present the possibility of closures on the north flank of the Normanby High in the western part of 04-1(v). In this area the main targets are likely to be sands of the Pebble Point, Timboon and Paaratte formations sealed within, or draped over, tilted fault-blocks and associated horsts. Deeper plays within the Waarre and Flaxman formations provide alternate, albeit deeper, targets. Play types are shown schematically in Figure 9.

7. Summary

Area 04-1(v) lies in shallow water within the three nautical mile coastal area administered by the State of Victoria. The block, covering an area of 260 km2, is located over the north flank of the Bridgewater High at the westernmost Victorian part of the basin adjacent to the South Australian border. No wells have been drilled in the block; however, four offshore and numerous onshore petroleum and water wells have been drilled nearby. Of these only Glenelg-1 reached the base of the Tertiary and many of the petroleum wells were drilled on the basis of poor quality or non-existent seismic data. Offshore, until the recent Essential Petroleum VIC/P46 survey, the pre-existing Phillips OP80 survey provided only a coarse 2 km x 5 km grid of seismic data on which Normanby-1, Bridgewater Bay-1 and Discovery Bay-1 were based. Although no commercial accumulations of hydrocarbons have yet been discovered in the area, numerous oil and gas shows have been recorded, the most significant being in Lindon-1 which intersected a 3 m oil column in the Early Paleocene Pebble Point Formation

South of the Tartwaup-Mussel Fault System, which underlies the northern flank of the Portland Trough, the Eumeralla and overlying Waarre and Flaxman formations are generally regarded as too deeply buried to provide a viable target. However, parts of the Bridgewater-Normanby High in the western part of 04-1(v) may be shallow enough for adequate reservoir development. This report has identified the nature of the leads that can be expected in the gazettal area. The northern flank of the Bridgewater High has the potential for closures in Cretaceous and Early Tertiary fault bounded structures. Here the principal plays are Tertiary sandstones of the Pebble Point Formation and the HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 32

Cretaceous Timboon and Paaratte sandstones sealed in tilted fault-blocks and NW-SE trending horsts by Pember mudstones or intraformationally.

No wells have been drilled in the gazetted area and the seismic data 04-1(v) is limited to the tails of offshore surveys. Detailed mapping of the Cretaceous fault-blocks, which comprise the most common leads in the area, will require additional seismic data to facilitate ties between the offshore and onshore geology and to delineate prospects.

8. References

ABELE, C., KENLEY, P.R., HOLDGATE, G. & RIPPER, D., 1976. Otway Basin (Tertiary). In Douglas, J.G. and Ferguson, J.A. (eds) Geology of Victoria, Geological Society of Australia Special Publication 5, pp. 198-229. ARDITTO, P.A., 1995. The eastern Otway Basin Wangerrip Group revisited using an integrated sequence stratigraphic methodology, Australian Petroleum Exploration Association Journal, 35(1), pp. 372-384. BLAKE, W.J.R., 1980. Geology and hydrology of the early Tertiary sediments of the Otway Basin. MSc Thesis, La Trobe University, Melbourne (unpublished). BRADSHAW, M., 1993. Australian petroleum systems. Petroleum Exploration Society of Australia Journal, 21, pp. 43-53. BRYAN, S.E., CONSTANTINE, A., STEPHENS, C.J., EWART, A., SCHON, R.W. & PARIANOS, J., 1997. Early Cretaceous volcano-sedimentary successions along the eastern Australian continental margin: Implications for the break-up of eastern Gondwana. Earth and Planetary Science Letters 153, pp. 85-102. BUFFIN, A.J., 1989. Waarre Sandstone development within the Port Campbell Embayment. Australian Petroleum Exploration Association Journal, 29(1), pp. 299-311. COOPER, G.T. & HILL, K.C., 1997. Cross-section balancing and thermochronological analysis of the Mesozoic development of the eastern Otway Basin. Australian Petroleum Production and Exploration Association Journal, 37(1), pp. 390-414. CONSTANTINE, A.E., 2000. Petroleum systems, play fairways and prospectivity of the Gazettal areas V00-1 and V00-2, offshore Otway Basin, Victoria. Victorian Initiative for Minerals and Petroleum Report 66, Department of Natural Resources and Environment. DUDDY, I.R., GREEN, P.F., HEGARTY, K.A. & BRAY, R., 1991. Reconstruction of thermal history in basin modelling using apatite fission track analysis: What is Really Possible? Offshore Australia Conference Proceedings 1, III, pp. 49-61. DUDDY, I.R., 1994. The Otway Basin: Thermal, structural and tectonic and hydrocarbon generation histories. Compiled by Finlayson, D.M., NGMA/Petroleum Exploration Society of Australia Otway Basin Symposium, Melbourne, April 20, 1994: extended abstract, Australian Geological Survey Organisation Record, 1994/14, pp. 35-42 DUDDY, I.R., 1997. Focussing exploration in the Otway Basin: Understanding timing of source rock maturation. Australian Petroleum Production and Exploration Association Journal, 37(1), pp. 178-191. EDWARDS, D.S., STRUCKMEYER, H.I.M., BRADSHAW, M.T. & SKINNER, J.E., 1999. Geochemical characteristics of Australia’s southern margin petroleum systems. Australian Petroleum Exploration Association Journal, 39 (1), pp. 297-320. FOSTER, D.A. & GLEADOW, A.J.W., 1992. Reactivated tectonic boundaries and implications for the reconstruction of southeastern Australia and northern Victorialand, Antarctica. Geology, 20, pp. 267-270. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 33

FOSTER, J.D. & HODGSON, A.J.W., 1995. Port Campbell reviewed: methane and champagne. Australian Petroleum Exploration Association Journal, 35(1), pp. 418-435. GEARY, G.C. AND REID, I.S.A., 1998. Geology and prospectivity of the Offshore Eastern Otway Basin, Victoria - for the 1998 Acreage Release. Victorian Initiative for Minerals and Petroleum Report 55. Department of Natural Resources and Environment. HILL, A.J., 1995A. Burial and thermal history modelling and source rock distribution of the Otway Basin, South Australia. South Australia. Department of Mines and Energy. Report Book, 95/9. HILL, A.J., 1995B. Source rock distribution and maturity modelling. In Morton, J.G.G. and Drexel, J.F. (eds), 1995 Petroleum Geology of South Australia. Volume 1: Otway Basin. Mines and Energy, South Australia. Report 95/12, pp. 103-126. HILL, K.A. & DURRAND, C., 1993. The western Otway Basin: An overview of the rift and drift history using serial composite seismic profiles. Petroleum Exploration Society of Australia Journal, 21, pp. 67-68. KOPSEN, E. & SCHOLEFIELD, T., 1990. Prospectivity of the Otway Supergroup in the central and western Otway Basin. Australian Petroleum Exploration Association Journal, 30(1), pp. 263- 279. LAVIN, C.J., 1997. A review of the prospectivity of the Crayfish Group in the Victorian Otway Basin. Australian Petroleum Production and Exploration Association Journal, 37(1), pp. 232-244. LAVIN, C.J., 1998. Geology and prospectivity of the western Victorian Voluta Trough, Otway Basin, for the 1998 Acreage release. Victorian Initiative for Minerals and Petroleum Report 57. Department of Natural Resources and Environment. LAVIN, C.J. & MUSCATELLO, T., 1997. The petroleum prospectivity of the Casterton Petroleum System in the Victorian Onshore Otway Basin. Victorian Initiative for Minerals and Petroleum Report 41, Department of Natural Resources and Environment. LAVIN, C.J. & NAIM, H.M., 1995. The structure, stratigraphy and petroleum potential of the Portland Trough, Otway Basin. Victorian Initiative for Minerals and Petroleum Report 18, Department of Agriculture, Energy and Minerals. LOVIBOND, R., SUTTILL, R.J., SKINNER, J.E., & ABURAS, A.N., 1995. The hydrocarbon potential of the Penola Trough, Otway Basin. Australian Petroleum Exploration Association Journal, 35(1), pp. 358-371. LOWRY, D.C. & LONGLEY, I.M., 1991. A new model for the Mid-Cretaceous structural history of the northern Gippsland Basin. Australian Petroleum Exploration Association Journal 31(1), pp. 143-153. LUXTON, C.W., HORAN, S.T., PICKAVANCE, D.L. & DURHAM, M.S., 1995. The La Bella and Minerva gas discoveries, offshore Otway Basin. Australian Petroleum Exploration Association Journal, 35(1), pp. 405-417. MCKIRDY, D.M., SUMMONS, R.E., PADLEY, D., SERAFINI, K.M., BOREHAM, C.J. AND STRUCKMEYER, H.I.M., 1994. Molecular fossils in coastal bitumen from southern Australia: signatures of precursor biota and source rock environments. Organic Geochemistry, 21, pp. 265-286. MEHIN, K. & CONSTANTINE, A.E., 1999. Hydrocarbon Potential of the Western Onshore Otway Basin in Victoria. Victorian Initiative for Minerals and Petroleum Report 62, Department of Natural Resources and Environment. MEHIN, K. & LINK, A.G., 1994. Source, migration and entrapment of hydrocarbons and carbon dioxide in the Otway Basin, Victoria. Australian Petroleum Exploration Association Journal, 34(1), pp. 439-459. MCKIRDY, D.M., SUMMONS, R.E., PADLEY, D., SERAFINI, K.M., BOREHAM, C.J. AND STRUCKMEYER, H.I.M., 1994. Molecular fossils in coastal bitumen from southern Australia: signatures of precursor biota and source rock environments. Organic Geochemistry, 21, pp. 265-286. MEGALLAA, M., 1986. Tectonic development of Victoria’s Otway Basin: a seismic interpretation, In Glenie, R.C. (ed.) “Second South-Eastern Australian Oil Exploration Symposium”, Petroleum Exploration Society of Australia 1985, pp. 201-18. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 34

MEHIN, K. & LINK, A.G., 1996. Early Cretaceous source rock evaluation for oil and gas exploration, Victorian Otway Basin. Victorian Initiative for Minerals and Petroleum Report 31, Department of Natural Resources and Environment. MEHIN, K. & LINK, A.G., 1997a. Kitchens, kettles and cups of hydrocarbons, Victorian Otway Basin. Australian Petroleum Production and Exploration Association Journal, 37(1), pp. 285-300. MEHIN, K. & LINK, A.G., 1997b. Late Cretaceous source rocks offshore Otway Basin, Victoria and South Australia. Victorian Initiative for Minerals and Petroleum Report 43, Department of Natural Resources and Environment. MITCHELL, M.M., 1997. Elevated Mid-Cretaceous palaeotemperatures in the western Otway Basin: consequences for hydrocarbon generation models. Australian Petroleum Production and Exploration Association Journal, 37(1), pp. 505-523. MOORE, D. H. , 2002. Basement-Basin Relationships in the Otway Basin, Victoria, Australia. Victorian Initiative for Minerals and Petroleum Report 78, Department of Natural Resources and Environment. MORTON, J.G.G. & SANSOME, A., 1995. Reservoirs and seals. In: Morton, J.G.G. & Drexel, J.F., (eds.), 1995. Petroleum Geology of South Australia, Volume 1: Otway Basin. Mines and Energy, South Australia, Report 95/12, pp. 127-139. NORVICK, M. & SMITH, M.A., 2001. Mapping the plate tectonic reconstructions of southern and southeastern Australia and implications for petroleum systems. Australian Petroleum Exploration Association Journal, 41 (1), pp. 15-35. O’BRIEN, G.W., REEVES, C.V., MILLIGAN, P.R., MORSE, M.P., ALEXANDER, E.M., WILLCOX, J.B., YUNXUAN, Z., FINLAYSON, D.M. & BRODIE, R.C., 1994. New ideas on the rifting history and structural architecture of the Western Otway Basin: Evidence from the integration of aeromagnetic, gravity and seismic data. Australian Petroleum Exploration Association Journal 34 (1), pp. 529-554. PADLEY, D., MCKIRDY, D.M., SKINNER, J.E., SUMMONS, R.E. & MORGAN, R.P., 1995. Crayfish Group hydrocarbons—implications for palaeoenvironment of Early Cretaceous rift fill in the western Otway Basin. Australian Petroleum Exploration Association Journal, 35 (1), pp. 517- 537. PARKER, K.A., 1992. The exploration and appraisal history of the Katnook and Ladbroke Grove gas fields, onshore Otway Basin, South Australia. Australian Petroleum Exploration Association Journal, 32(1), pp. 67-85. PARTRIDGE, A., 1997. New Upper Cretaceous Palynology of the Sherbrook Group, Otway Basin. Petroleum Exploration Society of Australia News, Victorian Supplement April/May 1997. PRESTON, J., 1992a. Geochemical evaluation of cuttings samples from Fergusons Hill-1, Otway Basin, Victoria, Southern Australia. BHP Petroleum Report, June 1992 (unpublished). PRESTON, J., 1992b. Geochemical evaluation of cuttings samples from Ross Creek-1, Otway Basin, Victoria, Southern Australia. BHP Petroleum Report, July 1992 (unpublished). PRESTON, J., 1992c. Geochemical evaluation of an oil sample from Flaxmans-1, Otway Basin, Victoria. BHP Petroleum Report, September 1992 (unpublished). PRESTON, J., 1992D. Geochemical evaluation of an oil sample from Port Campbell-1, Otway Basin, Victoria. BHP Petroleum Report, September 1992 (unpublished). PRESTON, J., 1992E. Geochemical evaluation of cuttings samples from Windermere-2, Otway Basin, Victoria, Southern Australia. BHP Petroleum Report, September 1992 (unpublished). REID, I. S. A., GEARY, G. C. & CONSTANTINE, A. E., 2001. Hydrocarbon Prospectivity Of Areas V01-1 To V01-3, Offshore Western Otway Basin, Victoria, Australia. 2001 Acreage Release. Victorian Initiative for Minerals and Petroleum Report 68, Department of Natural Resources and Environment. SUMMONS, R.E., BRADSHAW, M., CROWLEY, J., EDWARDS D.S., GEORGE, S.C. & ZUMBERGE, J.E., 1998. Vagrant oils: geochemical signposts to unrecognised petroleum systems. In: Purcell, P.G. and R.R. (eds) “The Sedimentary Basins of Western Australia”. Proceedings of the Petroleum Exploration Society of Australia Symposium, Perth, 1998, pp. 169-84. TABASSI, A., & DAVEY, L.K., 1986. Recovery of oil from the basal Tertiary Pebble Point Formation at Lindon-1—Summary, results and implications. In: Glenie, R.C. (ed.), Second South-Eastern HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 35

Australia oil exploration Symposium, Petroleum Exploration Society of Australia, 1985, pp. 241-253. TICKELL, S.J., 1991. Colac and part of Beech Forest. 1:50 000 scale geological map. Geological Survey of Victoria. TUPPER, N.P., PADLEY, D., LOVIBOND, R., DUCKETT, A.K. & MCKIRDY, D.M., 1993. A key test of Otway Basin Potential: The Eumeralla-Sourced Play on the Chama Terrace. Australian Petroleum Exploration Association Journal, 33(1), pp. 77-93. WILLIAMSON, P.E., O’BRIEN, G.E. & FALVEY, D.A., 1990. Two-stage Early Cretaceous rifting of southeastern Australia: implications for rifting of the Australian southern margin. Geology 8, pp. 75-78. YANG, J.S., 1997. VIC/P35 Otway Basin Victoria - Nirranda and Wangerrip Groups Depositional Study. Unpublished Cultus Timor Sea Ltd report. YU, S.M., 1988. Structure and development of the Otway Basin. Australian Petroleum Exploration Association Journal, 28(1), pp. 243-253. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 36

9. Appendix

The Appendix is subdivided into three sections: • technical information of all the relevant wells, including brief summaries of reasons for well failure as well as a listing of available data sets. • graphical summaries of the relevant well data including the well-log motifs, stratigraphy, palynology and main depositional facies regime for each well • a complete listing of all previously released VIMP reports.

The following wells are described: Normanby-1 and Voluta-1

Legend for Well Summary Sheets The well summary sheets detail well-log curves, biostratigraphic/palynological sub-divisions and intervals with hydrocarbon shows/tested zones. Formation tops have been picked based on lithological and log character, and aided by biostratigraphic data. It is worth noting that the well summary sheets do not have relative sea-level curves superimposed on them. The curve merely represents the interpreted environments of deposition.

Palynology (spore-pollen zones): P. tu P. tuberculatus H. un H. uniforma N. as N. asperus A. di A. distocarinatus P. as P. asperopolus P. pa P. pannosus M. di M. diversus C. pa C. paradoxa L. ba L. balmei C. st C. striatus F. lo F. longus C. hu C. hughesii T. li T. lilliei P. no P. notensis N. se N. senectus F. wo F. wonthaggiensis T. ap T. apoxyexinus C. au C. australiensis P. ma P. mawsonii R. wa R. watherooensis

Lithology CGL Conglomerate glauc Glauconite SST Sandstone pyr Pyrite SLT Siltstone calc Calcareous CST Claystone dol Dolomite MST Mudstone (if CAPITALS, major component; lower case, minor component)

Symbol

Dry hole Oil show (weak)/Gas show (weak) Fluorescence

Gas show (weak) Oil show (weak)/Gas show (strong)

Gas show (strong) Oil show (weak)/Gas zone Tested interval

Gas zone Oil show (strong)/Gas show (strong) RFT sample

Oil show (weak) Oil show (strong)/Gas zone FIT sample

Oil show (strong) Oil zone/Gas show (strong) MDT sample

Oil zone Oil zone/Gas zone HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 37

Normanby-1

KB/RT 26.8 m Water Depth 48.8 m Total Depth (dr/log) 3306 mRT (dr); 3305 mRT (log)

Operator BP Petroleum Development Ltd. 90% Partner Gas & Fuel Exploration (Victoria) 10%

Spud Date 07-03-1986 Rig Released 29-04-1986 Permit Area VIC/P14 (VIC/P46)

Long./Lat. 141º 05' 03.26"E 38º 14' 11.55"S Seismic Reference OP80-09, SP:1455

Status Weak gas show, plugged and abandoned.

Structure

Normanby-1 lies approximately 12 km offshore and 70 km northwest of Portland, within the Voluta Trough. The Normanby structure comprises a large rotated fault-block, which is bounded to the southwest by a major normal fault and in all other directions by dip-closure.

Target

Normanby-1 was primarily drilled to test the hydrocarbon potential of the Waarre Formation, whilst the underlying Eumeralla Formation was proposed as a secondary target. Pre-drill studies indicated a most likely hydrocarbon column of 180 m.

Stratigraphic tops

Heytesbury Group (undifferentiated) 75.6 mRT Nirranda Group (undifferentiated) 626 mRT Wangerrip Group 717.5 mRT Dilwyn Formation 717.5 mRT Pember Mudstone 1213 mRT Pebble Point Formation 1290 mRT Massacre Shale 1313 mRT Sherbrook Group 1317 mRT Timboon Sandstone 1317 mRT Paaratte Formation 1550 mRT Belfast Mudstone 2400 mRT Flaxman Formation 3084 mRT Waarre Formation 3113 mRT

Palynological data (from A. Partridge, 1996. All depths are measured in mRT). P. asperopolus 710.0 Upper M. diversus 910.0 Lower M. diversus 1030.0 -1250.0 Upper L. balmei 1285.0 Upper F. longus 1300.0 - 1390.0 Lower F. longus 1430.0 - 1510.0 T. lilliei 1550.0 HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 38

N. senectus 1590.0 - 1880.0 T. apoxyexinus 1923.6 - 2524.3 P. mawsonii 2580.8 - 3288.0

Reservoir

Log interpretation of the Waarre sands suggests neutron log-derived porosity values of 12-19% however, permeabilities were judged to be low as a result of high clay content (one zone with a permeability of approximately 1 mD was identified during the RFT program). The sands are described as massively bedded, quartzose, fine- to medium-grained, moderately sorted, moderately cemented by calcite and dolomite, and interbedded with siltstone and mudstone. SWCs note that visual porosity was generally fair to moderate.

Seal

The Belfast Mudstone was identified pre-drill as the sealing lithology to the target Waarre Formation sandstones (both vertical and lateral seal).

Hydrocarbon shows

No significant hydrocarbon shows were encountered. However, minor gas was detected within the Waarre Formation with a maximum of 1.23% C1 recorded within a silty sandstone unit at 3175 mRT when the well was shut-in and a 'gas bubble' in the annulus was circulated out. Neither fluorescence nor cut were recorded in any sandstone intervals, however, coals within the Waarre Formation coals displayed pale blue-white cut fluorescence. Water saturations of 63-97% were derived from log interpretation.

RFT analysis was run between 3112.5 to 3277.5 mRT. Only one valid pressure test at 3178 mRT was recorded as a result of seal failures and tight formations:

• RFT 10; 3178 mRT; 1 scf gas, 1.3 L gas cut formation water (gas analysis 71.1% C1, 20.4% C2, 6.9% C3).

The Operator concluded all sandstones were water-wet and minor gas was probably in solution.

Geochemical analysis

Rv values and the molecular maturity parameter suggest that sediments range from immature at 740 m to peak mature at 3300 m (Rv 0.4-0.73%, respectively). The molecular maturity parameter supports these results (1715 mRT immature; 3225 mRT moderately mature).

The Dilwyn and Pember formations showed moderate to good source potential for the production of gas with some condensate, at temperatures less than 150°C. A thin coal within the Dilwyn Formation at approximately 1210 mRT, indicated very good gas potential for the expulsion of gas and condensate (<150°C). The Paaratte Formation (1635-1840 mRT) showed excellent gas potential. Whereas, Waarre Formation coals (3200-3300 mRT) had excellent residual gas and condensate potential (<150°C) and were probably richer and more oil prone in the past.

The hydrocarbon characterisation study by Geotech (1996) shows that the well does not have significant source rock potential. Three samples with TOC values ranging from 0.54-1.77% (interval 1470-3300 mRT) were submitted for Rock-Eval pyrolysis. The level of free hydrocarbons is low for all samples (S1 range 0.19-0.21 mg/g), as was the hydrocarbon generating potential (S2 range 0.27-1.12 mg/g). All three samples were gas-prone (HI range 50-92), however the kerogen from the 1470 mKB sample was immature compared to those at 2900 mRT and 3300 mRT which are regarded as being mature (Rv readings for these two samples were 0.60% and 0.72% respectively). HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 39

Dunn (1986) states the Paaratte and Waarre formation coals have excellent potential/residual potential to source gas and gas/condensate respectively. The associated mudstones and siltstones however show only poor-moderate gas potential. The coals did not appear to be volumetrically significant.

Well analysis

• Geochemical analysis by Dunn (1986) concluded that the Waarre Formation coals, as with the coals penetrated in the Dunroon-1 well, did not source the weathered non-marine oil seeps of algal origin stranded along the Southern Australian margin. • Post-drill mapping suggests that Normanby-1 was drilled down-dip from the crest of the structure.

Data available

Geological and petroleum engineering completion report, August 1986 (PE900334) includes: • RFT basic data • Log interpretation report • Mud log (PE600238) • Composite log (PE600234) • Source rock quality indicators (part of report PE900354 detailed below)

Drilling completion report, April 1986 (PE900342)

End of well report by Gearhart (PE900349)

Drilling proposal, February 1986 (PE900337)

Drilling programme (PE900347)

Drilling programme (PE900344)

Well seismic processing report, April 1986 (PE900357)

Wireline log evaluation report by Jack Bowler, June 1987 (PE907270)

DLLMSFL run #3B wireline log evaluation report by Jack Bowler, July 1987 (PE907271)

Palynology of Normanby-1 by R. Morgan, July 1986 (PE900356)

Interpretation of STRATDAT datums from palaeontological range charts, by A. Partridge, 1996 (PE990778)

A geochemical study of the well Normanby-1 by M. Dunn, October 1986 (PE900354) (includes Rock-Eval pyrolysis, TOC, gas chromatography)

Analysis of organic matter by Rock-Eval pyrolysis for Normanby-1 by Geotech (PE904395) (includes Rock-Eval pyrolysis, TOC)

Hydrocarbon characterisation study Otway Basin wells, June 1996 (includes Rock-Eval pyrolysis, TOC, VR, Exinite fluorescence) (PE802297 in box PE182244)

Fission track analysis of samples from Normanby-1 by I. Duddy & A. Gleadow, August 1986 (PE900351)

Cross-sections: • Chronostratigraphy (environments, facies and resource potential) from offshore Voluta area to onshore Lindon area, February 1986 (in drilling proposal PE900337) HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 40

• Depth profile along line OP80-9 showing proposed location of Normanby-1, February 1986 (in drilling proposal PE900337)

Maps • Depth structure map Normanby Prospect top Waarre Formation, January 1986 (in drilling proposal PE900337) • Depth structure map Normanby Prospect top Waarre Formation, January 1986 (PE900343 in drilling proposal PE900337) • Depth structure map Normanby Prospect projected top Waarre Formation at Santonian time based upon isopach: top Waarre Formation-top Belfast Formation, January 1986 (PE900338 in drilling proposal PE900337) • Depth structure map Normanby Prospect projected top Waarre Formation during mid Eocene based upon isopach: top Waarre Formation-top Wangerrip Group, January 1986 (PE900340 in drilling proposal PE900337) • Normanby-1 well summary montage (PE900339 in drilling proposal PE900337)

Seismic lines • Line OP80-9 (SP 1070 to 1849) migrated stack, interpreted (in drilling proposal PE900337) • Line OP80-5 (SP 10 to 1900) filtered stack, uninterpreted (PE907272 in box PE180302) • Line OP80-5 (SP 10 to 1900) filtered stack, uninterpreted (PE907273 in box PE180302) HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 41

Voluta-1

KB/RT 34.1 m Water Depth 91.7 m Total Depth (dr/log) 3974 mRT (dr); 3784 mRT (log)

Operator Shell Development (Australia) Pty Ltd Partner Frome-Broken Hill Co Pty Ltd

Spud Date 25-08-1967 Rig Released 21-12-1967 Permit Area PEP 22 (VIC/P46)

Long. /Lat. 141º 18' 47.53"E 38º 25' 46.66"S Seismic Reference OD66-29, SP:86

Status Weak gas shows, plugged and abandoned.

Structure

Voluta-1 is situated approximately 10 km southwest of Cape Bridgewater and approximately 29 km southeast of Normanby-1, on the Cape Bridgewater High. Interpretation from the OD-66 survey indicated that the feature trends NE-SW, with the seismic horizon 'G' culminating within the Sherbrook Group at the Voluta-1 location (with associated areal closure of approximately 52 km2 and up to 2590 m vertical closure). Closure was also anticipated at the base of the Wangerrip Group (horizon 'B'), though with reduced areal and vertical closure (26 km2 and 647 m, respectively). At the base Heytesbury level (horizon 'A1') closure is displaced north eastwards and significantly smaller.

Target

Voluta-1 targeted potential reservoirs within the lower Sherbrook Group (Waarre Formation) and Otway Group that contain known reservoir intervals within onshore wells. Secondary targets included sands of the upper Sherbrook Group and Wangerrip Group.

The Belfast Mudstone section overlying the target reservoirs was much thicker than expected. The well was subsequently deepened, however mechanical difficulties led to the well being abandoned prior to reaching the Waarre Formation and Otway Group. The mechanical difficulties also meant that the deeper part of the well could not be logged or sampled by sidewall cores.

Stratigraphic tops

Heytesbury Group (undifferentiated) 125.8 mRT Nirranda Group (undifferentiated) 726 mRT Wangerrip Group 839 mRT Dilwyn Formation 839 mRT Pember Mudstone 1276 mRT Pebble Point Formation 1303 mRT Massacre Shale 1327 mRT Sherbrook Group 1356 mRT Timboon Sandstone 1356 mRT Paaratte Formation 1563 mRT Skull Creek Mudstone 2164 mRT Nullawarre Greensand 2205 mRT Belfast Mudstone 2279 mRT Flaxman Formation 3746 mRT HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 42

Palynological data

(from R. Partridge, 1996. All depths are measured in mRT). Lower M. diversus 1265.2 Upper L. balmei 1300.6 Lower L. balmei 1332.0 Upper F. longus 1391.7 T. lilliei 1511.2 - 1670.6 N. senectus 1685.5 - 2163.8 T. apoxyexinus 2164.4 - 2713.0 P. mawsonii 3654.2

Reservoir

Good quality reservoir sands were encountered within the Tertiary and Upper Cretaceous sequences of Voluta-1.

Several sand intervals were penetrated within the Dilwyn Formation, which were generally fine-grained to pebbly, moderately sorted, unconsolidated and carbonaceous with some interbedded claystone intervals. Density log analysis of the Wangerrip group gave porosities of approximately 30%.

The Timboon sandstone was predominantly sandy with interbeds of silty claystone. Sands were fine- to coarse-grained, silty, moderately to well sorted and pyritic. Within the Paaratte Formation, sandstones became increasingly interbedded with silty shale and siltstone. Sands were generally fine- to medium-grained, moderately sorted, pyritic and glauconitic with a white clayey cement. Density log interpretation indicated approximately 27% porosity within the Timboon Sandstone and 24-30% within the Paaratte Formation.

A sandy section was encountered within the Flaxman Formation below 3746 mRT, which contained very fine- to medium-grained quartzose, feldspathic and lithic sands.

Sample derived porosities were generally described as lower than the log-derived porosities. This is probably partially due to 'impact compaction' within sidewall cores and also due to a clayey matrix within unconsolidated sands.

Seal

The Belfast Mudstone was prognosed as the sealing unit to the Waarre Formation target sands.

Hydrocarbon shows

No significant hydrocarbon shows were encountered in Voluta-1. However minor C1 shows were recorded within mud returns by a gas detector in the Belfast and Skull Creek mudstones, and the Flaxman Formation. Traces of C2 and C3 were also detected below 3307 mRT. Gas appears to be reservoired within sands of the Skull Creek Mudstone and Flaxman Formation, though gas is most likely to be generated insitu.

Geochemical analysis

A series of geochemical reports have been issued, the salient points of each is summarised below.

Cook (1980) notes Rv of 0.95% at 3653 mRT, and mineral fluorescence is a prominent feature of samples from the lower part of the sequence (Belfast Mudstone). HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 43

Rock-Eval pyrolysis by Brown & Ruth Laboratories (1981) of a series of cuttings and core between 2161-3950 mRT showed TOC levels up to 5.31% (2161 mKB) and Tmax generally in the range 435- 445°C down to approximately 3620 mKB, increasing in value to a maximum of 462 °C at 3950 mRT.

Samples at 2459.9, 2672.4 and 3036.3 mKB exhibit excellent organic richness with TOC values of 10%, 15% and 5% respectively (Beach Petroleum NL, 1988). Both the Skull Creek and Belfast mudstones are early to peak mature (Rv: 0.47-0.85%) (Beach Petroleum NL, 1988). The Paaratte Formation has mostly good to excellent organic richness but is generally immature (TOC: 0.28-10%, Rv: 0.32-0.66%) (Beach Petroleum NL, 1988).

Pyrolysis studies by Lowe & O'Reilly (1979) demonstrate none of the sediments analysed had potential to yield significant volumes of hydrocarbons. Significant quantities of inertinite found in the Belfast Mudstone seriously downgraded the source quality of these sediments, however, TOC values of up to 1.8% were recorded from the same section. The authors concluded the following thresholds within the well: • Oil generative threshold 2870-3128 mRT • Gas generative threshold 3684-4195 mRT • Maximum oil generation 4116-4805 mRT • Oil floor 5667-7040 mRT

Geohistory analysis by Middleton and Ledsam (1981) indicate the deepest part of Voluta-1 is within the condensate/wet gas zone (Ro > 1.3%); the Wangerrip and Heytesbury groups are immature (Ro < 0.5%), and the Sherbrook Group is presently in the oil-generative zone (0.5% < Ro < 0.3%).

Analysis by Amdel (1980) yielded TOC values of 0.86-2.94%, and VR values of 0.34-0.93% (interval 909-3654 mRT).

The source rock report by Shell (1971) concludes source rocks were not present in the Belfast Mudstone section (2320-3968 mRT)

Well analysis

• Post-drill analysis within the WCR stated that the well was drilled on a closed anticlinal feature, though a slight northerly dip was noticed within the Sherbrook Group. Shell also proposed that a slight angular unconformity at the top of the Sherbrook Group indicated that that the structure developed prior to the deposition of the Paleocene Wangerrip Group. More recent seismic surveys now suggest Voluta-1 was drilled off structure at the Base Tertiary level with the well situated approximately 8 km WSE from the crest of Cape Bridgewater High and that there was no obvious structural closure within the lower Sherbrook Group (Lavin, 1998). Seismic data within the Tertiary section and below the upper Sherbrook Group is very poor within this area. • The Sherbrook Group section penetrated was far thicker than anticipated from onshore wells. • Log derived porosities were similar to those observed within the equivalent formations of the Caroline-1 well.

Data available

Well completion report, April 1968 (PE900208) includes: • Petrophysical interpretation • Palaeontological report by Shell Development (Australia) Pty Ltd • Palynological report by M.E. Dettmann, March 1968 • Velocity survey report by Shell Development (Australia) Pty Ltd

Well completion report enclosures (PE904304) includes: • Composite well log (PE600602/3 & PE600623/4) • Time/depth plot (PE905975) • Mud logs (PE900392/404) • Chromatologs (PE600604, PE600407, PE600612/7) HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 44

• GC-MS analysis of saturates from core samples (PE904294/303)

Exploration well proposal by Shell, July 1967 (in folder PE900199)

Drilling programme, August 1967 (in folder PE900199)

Geological appraisal of the proposed test well Voluta-1 offshore Gambier Sub-basin, Otway Basin, Victoria, July 1967 (PE900711)

Interpretation of STRATDAT datums from palaeontological range charts by A. Partridge, 1996 (PE990778)

Source rock data report, October 1969 (includes brief source potential comments) (PE800926 in box PE182244)

Geochemistry report by Amdel, October 1980 (PE904409 in box PE182244) (includes TOC, EOM analysis, maceral counts, Rv)

Source rock analysis: fixed carbon content as a function of depth by Shell, July 1971 (PE800911 box PE182244) (includes a geochemical log)

Geochemistry of cuttings samples from Voluta-1 by S. Lowe & S O'Reilly, 1979 (PE800924 in box PE182244) (includes Rock-Eval pyrolysis, Rv)

Organic Petrology of samples from a set of twenty-one wells from the Otway Basin by A. Cook, September 1980 (PE802114 in box PE181357) (includes Rv)

Vitrinite reflectance and geohistory analysis of Voluta-1 well, Otway Basin by M. Middleton & J. Ledsam, January 1981 (PE900207) (includes Ro)

Geochemical study by Brown & Ruth Laboratories (PE801013 in box PE181357) (includes Rock- Eval pyrolysis, TOC)

PEP 105/118 & Environments, Otway Basin, Western Victoria; Hydrocarbon Potential and Concepts/Directions of the Tyrendarra Embayment by Beach Petroleum NL, January 1988 (P801285)

Cross-sections • Well correlation section showing the wells Lake Bonney-1, Mount Salt-1, Caroline-1, Glenelg-1, Voluta-1, Portland-3, Heywood-10 and Eumeralla-1, March 1968 (PE900715 in WCR enclosures folder PE904304) • Cross-section of the Gambier Sub-basin showing the wells Caroline-1, Nelson-1 and the proposed Voluta-1 (prognosis), June 1966 (PE900716 in folder PE90019)

Maps • Reflection contour map Horizon G, July 1967 (PE900707 in folder PE900199) • Isochron map mid-Sherbrook level, October 1971 (PE900708 in folder PE900199) • Time structure map Horizon S (mid-Sherbrook) (PE900704/18 in folder PE900199)

Seismic lines • Line OD-66-8 (SP 294 to 360) showing proposed Voluta well projected 44 yards from line OD66- 29 (PE900705 in WCR enclosures folder PE904304) • Line OD-66-29 (SP 60 to 120D) (PE900706 in box PE180044) • Line 31 (SP 44 to 104D) showing projected Voluta-1 well (PE905976 in WCR enclosures folder PE904304) • Line OD-66-8 (SP 222D to 288) showing actual Voluta-1 location (PE900719 in folder PE900197) Normanby-1

Depositional Environment NPHI Stratigraphy 0.45V/V -0.15 terrestrial marine GR Depth DT RHOB 3 0 GAPI 200 (m) 140ms/ft 40 1.95 g/cm 2.95

MARL, LST, Open undiff. glauc Marine

GRP 600

HEYT undiff. P. asperopolus SST, interbedded SST, Open 700 SLT, MST at base, glauc Marine

800

GRP

NIRR Upper 900 M. diversus SST, mst, slt, lst, mica, pyr, Prograding 1000 argillaceous Delta Plain in part

1100

GROUP Lower Dilwyn Formation M. diversus WANGERRIP 1200 Pember Mst MST, SLT, sst, dol, Prodelta Up. L. bal pyr, mica Pebble Point 1300 SST Nearshore Marine Upper Massacre MST, SLT Open Marine F. longus 1400 SST, slt, mst, Upper Delta Timboon Lower cemented in part Plain Sandstone F. longus 1500 T. lilliei 1600

1700 N. senectus 1800

1900 interbedded SST, slt, mst, dol, Lower Delta 2000 carbonaceous in Plain part, pyr, trace glauc 2100

Paaratte Formation

T. apoxyexinus 2200

2300

2400

2500

SHERBROOK GROUP

2600

2700 MST, SLT, sst, dol, carbonaceous in part, trace mica, Prodelta 2800 pyr, glauc

Belfast Mudstone 2900 P. mawsonii

3000 Flaxman SST, SLT, MST, Formation 3100 trace glauc, mica Marginal Marine interbedded SST, MST, Waarre 3200 SLT, coal, cemented Fluvial to Formation intervals, mica, partly Deltaic carbonaceous, pyr

Picks based on palynological analysis TD: 3306 mRT by A. Partridge, 1996. RT: 26.8 m Voluta-1 Depositional Environment LLD NEUT Stratigraphy 0.2ohmm 2000 0.45V/V -0.15 terrestrial marine D GR Depth T RHOB 3 0 GAPI 200 (m) 500 ms/m 100 1.95 g/cm 2.95 HEY Open GRP undiff. 700 LST, marl, dol Marine NIRR undiff. Marl, SST, SLT, Open GRP 800 dol, glauc Marine

Dilwyn 900 SST, SLT, CST, Formation 1000 Prograding pyr, glauc Delta Plain 1100

GROUP Lower 1200

Pebble

WANGERRIP

Pember M. diversus

SLT, CST, sst, dol, glauc. pyr

SST, SLT cst, glauc, pyr

Shallow Marine

Prodelta

Mudstone Point Fm. Upper L. balmei 1300 Massacre Lower L. balmei 1400 SLT, CST, pyr, glauc Open Marine Timboon Upper F. longus SST, SLT, cst, Upper Sandstone 1500 coal, pyr Delta Plain

T. lilliei 1600

1700

1800 SST, CST, SLT, dol, glauc, pyr, Lower carbonaceous, Delta Plain N. senectus 1900 mica

2000

Paaratte Formation 2100 SLT, cst, sst, Skull Creek 2200 carbonaceous, pyr Prodelta Open Nullawarre SST, sst, glauc Marine 2300

2400 T. apoxyexinus 2500

2600

2700

2800 Prodelta 2900 SLT, CST, sst, dol, SHERBROOK GROUP 3000 carbonaceous, pyr, glauc, mica 3100

3200

Belfast Mudstone

3300

3400

3500

P. mawsonii 3600

3700

3800 Flaxman SST, SLT, cst, Shallow cemented intervals, Marine Formation 3900 carbonaceous, mica, pyr Picks based on palynological analysis TD: 3975 mRT by A. Partridge, 1996. RT: 34.1 m HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 43

10. Victorian Initiative for Minerals and Petroleum (VIMP) Report Series

Petroleum Reports in bold typeface

1BUCKLEY, R.W., BUSH, M.D., O'SHEA, P.J., WHITEHEAD, M. & VANDENBERG, A.H.M., 1994. The geology and prospectivity of the Orbost Survey area. 2VANDENBERG, A.H.M., WILLMAN, C., HENDRICKX, M., BUSH, M.D. & SANDSTONES, B.C., 1995. The geology and prospectivity of the 1993 Mount Wellington Airborne survey area. 3HOLDGATE, G., 1995. The exploration potential of the Permian Numurkah Trough and Ovens Graben, Victoria. 4BUSH, M.D., CAYLEY, R.A., ROONEY, R., SLATER, K. & WHITEHEAD M.L., 1995. The geology and prospectivity of the southern margin of the Murray Basin. 5ROONEY, R., 1995. Mineral exploration history of the North West VIMP area. 6WILLOCKS, A.J., 1995. An appraisal of the new airborne surveys over the North West VIMP area. 7WHITEHEAD, M.L., 1995. Geological interpretation of geophysical data over the Dunolly 1:100 000 sheet. 8VANDENBERG, A.H.M., CALUZZI, J., WILLOCKS, A.J. & O'SHEA, P.J., 1995. The geology and prospectivity of the Mallacoota 1:250 000 sheet, Eastern Highlands VIMP area. 9SANDS, B.C., 1995. A geological interpretation of the geophysical data from the Orbost 1994 airborne survey. 10 OPPY, I.D., CAYLEY, R.A. & CALUZZI, J., 1995. The geology and prospectivity of the Tallangatta 1:250 000 sheet. 11 CALUZZI, J., 1995. Mineral exploration history of the Tallangatta 1:250 000 sheet. 12 SIMONS, B.A., 1995. An appraisal of new airborne geophysical data over the Tallangatta 1:250 000 map area, Victoria. 13 BUSH, M.D., CAYLEY, R.A. & ROONEY, S., 1995. The geology and prospectivity of the Glenelg region, North West VIMP area. 14 SLATER, K.R., 1995. An appraisal of new airborne geophysical data over the Glenelg region, North West VIMP area, Victoria. 15 RYAN, S.M., KNIGHT, L.A. & PARKER, G.J., 1995. The stratigraphy and structure of the Tyrendarra Embayment, Otway Basin, Victoria. 16 KNIGHT, L.A., MCDONALD, P.A., FRANKEL, E. & MOORE, D.H., 1995. A preliminary appraisal of the pre-Tertiary infrabasins beneath the Murray Basin, Northwestern Victoria. 17 PERINCEK, D., SIMONS, B.A., PETTIFER, G.R. & GUNATILLAKE, K., 1995. Seismic interpretation of the onshore Western Otway Basin, Victoria. 18 LAVIN, C.J. & NAIM, H.M., 1995. The structure, stratigraphy and petroleum potential of the Portland Trough, Otway Basin, Victoria. 19 SIMPSON, C.J., SIMS, J.P. & ORANSKAIA, A., 1995. The geology and prospectivity of the Mt Elizabeth area, Eastern Highlands VIMP area. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 44

20 ORANSKAIA, A., 1995. A geological interpretation of geophysical data over the Mallacoota 1:250 000 sheet, Eastern Highlands VIMP area. NOT RELEASED 21 SARMA, S., 1995. Seismic interpretation of the offshore Otway Basin, Victoria. 22 MEHIN, K. & LINK, A.G., 1995. Early Cretaceous source rocks of the Victorian onshore Otway Basin. 23 PARKER, G.J., 1995. Early Cretaceous stratigraphy along the northern margin of the Otway Basin, Victoria. 24 MOORE, D.H., 1996. A geological interpretation of the geophysical data of the Horsham 1:250 000 map sheet area. 25 VANDENBERG, A.H.M., HENDRICKX, M.A., WILLMAN, C.E., MAGART, A.P.M., ORANSKAIA, A.N., ROONEY, S. & WHITE, A.J.R., 1996. The geology and prospectivity of the Orbost 1:100 000 map area, eastern Victoria. 26 HENDRICKX, M.A., WILLMAN, C.E., MAGART, A.P.M., ROONEY, S., VAN-DENBERG, A.H.M., ORANSKAIA, A. AND WHITE, A.J.R. The geology and prospectivity of the Murrungowar 1:100 000 map area, eastern Victoria. 27 BOYLE, R.J., 1996. Mineral exploration history of the Omeo 1:100 000 map area. 28 HAYDON, S.J., 1996. An appraisal of airborne geophysical data from the 1995 Omeo survey, Victoria. 29 MAHER, S., 1996. Mineral resources of the Dunolly 1:100 000 map area. 30 CHIUPKA, J.W., 1996. Hydrocarbon Play Fairways of the Onshore Gippsland Basin, Victoria. 31 MEHIN, K. & LINK, A.G., 1996. Early Cretaceous source rock evaluation for oil and gas exploration, Victorian Otway Basin. 32 SLATER, K.R., 1996. An appraisal of new airborne geophysical data over the Dargo region, Victoria. 33 MCDONALD, P.A., 1996. An appraisal of new airborne geophysical data over the Corryong region, northeastern Victoria. 34 TWYFORD, R., 1996. An appraisal of airborne geophysical data from the Murrindal survey, Victoria. 35 HUTCHINSON, D.F., 1996. Mineral exploration history of the Dunolly 1:100 000 map area. 36 BROOKES, D.J. & BOYLE, R.J., 1996. Mineral exploration history of the Bairnsdale 1:250 000 map area. 37 MAHER, S., HENDRICKX, M.A., BOYLE, R.J. & BROOKES, D.J., 1996. Geology and prospectivity of the Bairnsdale 1:250 000 map sheet area. 38 MCDONALD, P.A. & WHITEHEAD M.L., 1996. Geological interpretation of geophysical data over the Ararat 1:100 000 map sheet. 39 MOORE D.H., 1996. A geological interpretation of the geophysical data of the Ouyen 1:250 000 map sheet area. 40 BROOKES, D.J., 1996. Mineral exploration history, Ararat and Grampians 1:100 000 map areas. 41 LAVIN, C.J., & MUSCATELLO, T., 1997. The petroleum prospectivity of the Casterton Petroleum System in the Victorian Onshore Otway Basin. 42 CHIUPKA, J.W., MEGALLAA, M., JONASSON, K.E. & FRANKEL E., 1997. Hydrocarbon plays and play fairways of four vacant offshore Gippsland Basin areas, 1997 acreage release. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 45

43 MEHIN, K. & LINK, A.G., 1997. Late Cretaceous source rocks offshore Otway Basin, Victoria and South Australia. 44 WILLOCKS, A.J., 1997. An appraisal of airborne geophysical data from the Castlemaine- Woodend survey, Victoria. 45 HUTCHINSON, D.F., 1997. Mineral exploration history of the Heathcote and Nagambie 1:100 000 map areas. 46 MAHER, S., VANDENBERG, A.H.M., MCDONALD, P.A. & SAPURMAS, P., 1997. The Geology and prospectivity of the Wangaratta 1:250 000 map sheet area. 47 ORANSKAIA, A.N., 1997. Geological interpretation of geophysical features Bendoc 1:100 000 sheet. 48 ORANSKAIA, A.N., 1997. Geological interpretation of geophysical features Cann, Mallacoota and Victorian part of Eden 1:100 000 sheets. 49 WILKIE, J.R. & BROOKES, D.J., 1997. Mineral exploration history of the Wangaratta 1:250 000 map area. 50 MCDONALD, P.A., 1997. An appraisal of airborne geophysical data from the Yea survey, Victoria. 51 EDWARDS, J.E., WILLMAN, C.E., MCHAFFIE, I.W., OLSHINA, A. & WILLOCKS, A.J., 1997. The geology and prospectivity of the Castlemaine, Woodend, Yea and part of Bacchus Marsh 1:100 000 map sheets. 52 MAHER, S., MOORE, D.H., CRAWFORD, A.J., TWYFORD, R. & FANNING, F.M., 1997. Test drilling on the southern margin of the Murray Basin. 53 LAVIN, C.J. & MUSCATELLO, T. 1998. The Casterton Group - Otway Basin Victoria. NOT RELEASED 54 MEHIN, K. & BOCK, M.P., 1998. Cretaceous source rocks of the onshore Gippsland Basin, Victoria. 55 GEARY, G. & REID, I., 1998. Geology and prospectivity of the offshore eastern Otway Basin, Victoria, for the 1998 Acreage Release. 56 MEGALLAA, M., BERNECKER, T. & FRANKEL, E., 1998. Hydrocarbon prospectivity of the Northern Terrace, offshore Gippsland Basin, for the 1998 Acreage Release. 57 LAVIN, C., 1998. Geology and prospectivity of the western Victorian Voluta Trough - Otway Basin, for the 1998 Acreage Release. 58 EDWARDS, J., SLATER, K.R. & PARENZAN, M.A., 1998. Bendigo and part of Mitiamo 1:100 000 map area geological report. 59 RADOJKOVIC, A., 1998. Mineral exploration history of the Ballarat and Creswick 1:100 000 map areas.

60 MESSENT, B.E., COLLINS, G.I.C. & WEST, B.G., 1999. Hydrocarbon prospectivity of the offshore Torquay Sub-basin; Victoria: Gazettal Area V99-1.

61 SMITH, M.A., 1999. Petroleum systems, play fairways and prospectivity of the Gazettal area V99-2, offshore southern Gippsland Basin, Victoria.

62 MEHIN, K., & CONSTANTINE, A.E., 1999. Hydrocarbon potential of the western onshore Otway Basin in Victoria, 1999 acreage release.

63 HUTCHINSON, D.F., 1999. Mineral exploration history of the Castlemaine, Woodend, Yea and part of Bacchus Marsh 1:100 000 map areas. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 46

64 BATSON, R.A., 1999. Mineral exploration history of the Warburton 1:250 000 map area.

65 SMITH, M.A., BERNECKER, T., LIBERMAN, N., MOORE, D.H. & WONG, D., 2000. Petroleum prospectivity of the deep-water gazettal areas V00-3 and V00-4, southeastern Gippsland Basin, Victoria, Australia.

66 CONSTANTINE, A.E., 2000. Petroleum systems, play fairways and prospectivity of the Gazettal areas V00-1 and V00-2, offshore Otway Basin, Victoria.

67 WONG, D. & BERNECKER, T., 2001. Prospectivity and Hydrocarbon Potential of Area V01-4, Central Deep, Gippsland Basin, Victoria, Australia.

68 CONSTANTINE, A.E., GEARY, G.C. & REID, I.S.A., 2001. Hydrocarbon Prospectivity of Areas V01-1 to V01-3, Offshore Western Otway Basin, Victoria, Australia. 2001 Acreage Release.

69 MOORE, D. H. & WONG, D., 2001. Eastern and Central Gippsland Basin, Southeastern Australia; Basement Interpretation and Basin Links.

70 CONSTANTINE, A.E. & LIBERMAN, N., 2001. Hydrocarbon Prospectivity Package, Eastern Onshore Otway Basin: VIC/O-01, VIC/O-01 (2) and VIC/O-01 (3). 2001 Acreage Release.

71 KROKOWSKI DE VICKEROD, J., CUFFLEY, B. & EVANS, T., 2001. Tarnagulla Goldfield, Central Victoria, 1:10000 map geological report.

72 EDWARDS, J., SLATER, K. R. & MCHAFFIE, I. W., 2001. Bendigo 1:250 map area geological report.

73 MCHAFFIE, I. W. & RADOJKOVIC, A., 2001. Synthesis and evaluation of east Victorian soil and drainage geochemistry.

74 BERNECKER, T., WONG, D., DRISCOLL, J. & LIBERMAN, N., 2001. Hydrocarbon Prospectivity of Areas V02-2, V02-3 and V02-4 in the Gippsland Basin, Victoria, Australia. 2002 Acreage Release.

75 EBSWORTH, G. B. & KROKOWSKI DE VICKEROD, J., 2002. Central Maldon Goldfield 1:5000 map area.

76 RADOJKOVIC, A. & LIBBY, L., 2003. The Regolith of the Ballarat 1:100 000 map area.

77 KOTSONIS, A. & JOYCE, B.E., 2003. The Regolith of the Bendigo 1:100 000 map area.

78 MOORE, D.H., 2002. Basement-Basin Relationships in the Otway Basin, Victoria, Australia.

79 BERNECKER, T., THOMAS, H. & DRISCOLL, J., 2003. Hydrocarbon Prospectivity of Areas V03-1, V03-2, 03-1(v) and 03-2(v) Offshore Gippsland Basin, Victoria, Australia. 2003 Acreage Release.

80 THOMAS, H., BERNECKER, T., & DRISCOLL, J., 2003. Hydrocarbon Prospectivity of Areas V03-3 and V03-4 Offshore Gippsland Basin, Victoria, Australia. 2003 Acreage Release.

81 WILLIAMS, B. & RADOJKOVIC, A., 2004. The Regolith of the Ararat 1:100 000 Map Area. HYDROCARBON PROSPECTIVITY OF 04-1(v) OTWAY BASIN, VICTORIA 47

82 MOORE, D.H., 2004. St Arnaud 1:250 000 Map Sheet. A Geological Interpretation of the Geophysical Data.

83 BERNECKER, T., DRISCOLL, J., POWELL, A & THOMAS, J.H., 2004. Hydrocarbon Prospectivity of the 2004 Acreage Release Areas, Victoria, Australia. 141°E 142°E 143°E 144°E

PEL 136 Bool Lagoon 1 Melba 1 Robertson 2 Lavers 1 PPL9 Robertson 1 Enlargement Port Campbell Area Mcintee 1 PEL 27 PrincesKYNETON 1 ARARAT PPL6 PEL 32 PRL1 PPL7 PPL4 Viewbank 1 Tilbooroo 1 Sawpit 1 Penola 1 PPL11 PPL3 Fenton Creek 1 Tregony 1 PPL5 PEL PEL 83 Buttress 1 66 Zema 1 Pyrus 1 Wynn 1 Penryn 2 Laira 1 Haselgrove 2 Boggy Creek 1 Penryn 1 Redman 1 Haselgrove 1 Naylor 1 Mylor 1 K3 K2 Haselgrove Sth 1 PEP160 PPL10 K4 K1 Naylor Sth 1 Hungerford 1 Ladbroke Grove 1 Vaughan 1 Braeside 1 Port Campbell 4 Bus Swamp 1 Croft 1 Blackwood 1 Vogel 1 Tullich 1 Dunbar 1 Wild Dog Road 1 BALLARATN Paaratte 1,4,5 PPL12 Mceachern 1 Curdie 1 Nth Paaratte 2 Nth Paaratte 3 Kalangadoo 1 Gordon 1 CASTERTON Port Campbell 3 PPL1 Skull Creek West 1 Seamer 1 Casterton 1 Curdievale 1 Dunbar East 1 Namgib 1 Skull Creek 1 Skull Creek Nth 1 Heathfield 1 Wallaby Creek 2 PEL 156 Casterton 2 Wallaby Creek 1 Iona 1 Iona 2 Port Campbell 1PPL2 HAMILTON PPL1Grumby 1 PEL 57 Mocamboro 11 MELBOURNE Burrungule 1 PPL8 PPL1 Compton 1 Langley 1 PEL 154 0 1 2 Port Campbell 2 PEP151 Digby 1 Mcnamara 1 Mcnicol 1 Squatter 1 Km PPL 21 Najaba 1a Hotspur 1 PEL 72 Kentgrove 1 Wilson 1 Caroline 1Caroline1Fahley 1 Mount Salt 1 Pine Lodge 1 Fahley 2 PEP150 South Caramut 1 PEL 82 Henke 1 LARA 38°S 38°S Douglas Point 1 PEL 57 Greenbanks 1 Northumberland 1 Moyne Falls 1 Glenelg 1 Lindon 1&2 Nelson 1 Hawkesdale 1 Woolsthorpe 1 Geelong Oil Bore 04-1(v) Nth Eumeralla 1 Greenslopes 1 Warracbarunah 2 GEELONG Breaksea Reef 1 Killara 1 Eumeralla 1 Pretty Hill 1 Banganna 1PEP159 EPP 27 Ballangeich 1 Normanby 1 Windermere 1 Shaw 1 Taralea 1 WINCHELSEA PEP163 100m Windermere 2 PEP164 Koroit West 1 154b Hindhaugh Creek 1 Irrewarra 1 VIC/P46 Portland Nth 1 PEP152 Garvoc 1 COBDEN Geelong Flow Oil Co 1 PORTLAND Port Fairy 1 Stoneyford 1 COLAC Torquay 1 200m PEP154a Purrumbete 1 300m VIC/P37(v)WARRNAMBOOL Tirrengowa 1 PORT FAIRY Barton Corner 1 Anglesea 1A 400m Discovery Bay 1 PEP153 Voluta 1 Naringal 1 Rowans 1 500m Westgate 1a Callista 1 1000m HowmainsMelba 1 1 Ross Creek 1 Bridgewater Bay 1 Champion 1 LORNE Flaxmans 1 Seaview 1 Sherbrook 1 VIC/P44 PORT Fergusons Hill 1 CAMPBELL Nerita 1 Olangolah 1 Pecten 1A Minerva 1 La Trobe 1 2000m M3 VIC/P51 Minerva 2a M4 V04-2 VIC/P50 APOLLO BAY Casino 3 VIC/ Casino 1 Casino 2 L22 VIC/P38(v) Wild Dog 1 Hill 1 Conan 1 VIC/P43 V04-1 Snail 1 VIC/RL7 Loch Ard 1 Nautilus 1 Mussel 1 Triton 1 La Bella 1 Eric The Red 1 39°S 3000m 39°S Geographe North 1 050 Geographe 1 km Victoria Thylacine 2 Thylacine 1 Tasmania VIC/P52 Legend Prawn A1 4000m Gas Pipeline Oil & Other Pipeline 2004 Acreage Release Proposed Gas Pipeline Gas Field Current Exploration Permit Oil/Gas Field Production Licence Marine National Park Retention Lease Marine Sanctuary

141°E 142°E 143°E 144°E 145°E

Figure 1 Otway Basin permit map showing the location of the 2004 gazettal blocks and pipeline infrastructure 141 E 142 142 E 143 E 144144 E

VIMP 41 VIMP 55 VIMP 66 Otway Basin Acreage Release VIMP 57 VIMP Reports 1997 - 2004 VIMP 60 VIMP 62 VIMP 68 VIMP 70 VIMP 83

VIMP 41 Gas Field (1997) VIMP 41 Oil Field (1997)

3838 S VIMP 62 3838 S VIMP 62 (1999) (1999)

VIMP 57 (1998)

VIMP 83 VIMP 70 (2004) (2001) VIMP 70 (2001) VIMP 57 VIMP 55 (1998) (1998) Port Campbell VIMP 55 (1998) Gas Fields VIMP 66 (2000) VIMP 68 VIMP 70 VIMP 60 (2001) VIMP 55 Minerva (2001) (1999) (1998) Casino VIMP 55 (1998) VIMP 83 VIMP 55 (2004) VIMP 68 (1998) (2001) VIMP 66 La Bella VIMP 55 (2000) (1998) 3939 S 3939 S VIMP 83 (2004) Geographe Victoria Thylacine Tasmania VIMP 68 (2001)

025 km

141141 E 142 142 E 143 143 E 144 144 E 145 145 E Figure 2 Otway Basin Acreage Release VIMP Reports 1997-2004 PETROLEUM SYSTEMS ELEMENTS EPOCH AGE STRATIGRAPHIC TECTONIC

T

N UNITS HISTORY N

SEAL

TRAP SEAWARD LANDWARD OVER-

BURDE SOURCE

MOME

CRITICAL

ACCUMULT.

EXPULSION

RESERVOIR

FORMATION PLEISTOCENE Calabrian Newer Volcanics PLIOCENE L Piacenzian E Zanclean COMPRESSION / INVERSION Messinian Hanson L - major NE - SW folding Tortonian Port Plain Sand 10 Campbell - sea-level changes -> channeling Lst - uplift Otway Ranges MIOCENE M Serravallian Langhian - downward propagating NW-SE Burdigalian Gellibrand Marl ? detachment normal faulting 20 E - reverse faulting Aquitanian Clifton L Chattian Fm

OLIGOCENE MINOR COMPRESSION 30 E Rupelian MINOR INVERSION Narrawaturk L Priabonian Marl Demons Bluff Bartonian Fm THERMAL SUBSIDENCE 40 Mepunga EOCENE M Fm Eastern Lutetian View Fm MINOR INVERSION 50 Dilwyn E Ypresian Fm

Thanetian Pember Eastern THERMAL SUBSIDENCE L Mudstone View Fm PALEOCENE Selandian 60 Pebble E Danian Point Fm Cret / Tert Boundary Shale Member CONTINENTAL SEPARATION Maastrichtian - uplift / erosion 70 Paaratte Timboon Sst Formation

Campanian Skull Creek RIFTING: NE-SW EXTENSION 80 LATE Mudstone - E-W to NW-SE faulting Nullawarre - down to S normal faulting Santonian Belfast Greensand - transpressional folding Mudstone Coniacian Flaxman Fm - reduction in heat flow 90 Turonian COMPRESSION / INVERSION Cenomanian Waarre Formation - differential uplift / erosion - uplift of Otway Ranges / Stawell Block 100 - high heat flow Albian Eumeralla Formation RIFTING / SAG - rift to thermal subsidence 110 Aptian MINOR STRUCTURING Katnook EARLY Barremian Sst 120 Laira Fm RIFTING: N-S EXTENSION Hauterivian Pretty Hill - E-W to NW-SE faulting 130 Formation - dominantly down to N normal faulting Valanginian

MINOR STRUCTURING Berriasian 140 Casterton Tithonian Formation RIFTING: N-S EXTENSION Kimmeridgian - E-W to NW-SE faulting 150 LATE

Oxfordian RIFT INCEPTION

160 MIDDLE Callovian Folding Style Tectonic Regime Depositional Regime L 300 shallow to open shallow marine and E marine limestones nearshore sandstones

major major G minor minor open marine fluviodeltaic and lower coastal E Normal Transtensional 500 N marls plain sandstones, mudstones D Reverse Compressional prodeltaic sandstones fluvial volcanoclastics, Figure 3 and marine shales lithic arenites, mudstones, coal Otway Basin Tectonostratigraphy 141° E 141° 30' E 142° E 142° 30' E 143° E 143° 30' E 144° E 144° 30' E 37° 30' S

MOYST VC FAULT AVOCA GLENELG YARRAMYLJUP MERINO ZONE FAULT

ON HIGH FAULT MT WILLIAM

GRAMPIANS / STAVELY VICTORIA ZONE FAULT STAWELL

SOUTH AUSTRALIA ZONE

NO NO RT RTH BENDIGO HE ERN RN BASIN LIMIT ZONE TARTWAUP E XT EN T W A AR MUMBANNAR R MELBOURNE ZONE PORTLAND E PLATFORM 38° S F O R M A GELLIBRAND T 38° S IO TROUGH N

04-1(v) MUSSEL OTWAY

TROUGH BASIN TYRENDARRA

EMBAYMENT COLAC WARRNAMBOOL TROUGH

BRIDGEWATER HIGH PORT CAMPBELL EMBAYMENT

BAMBRA FAULT 38° 30' S Port Campbell Gas Fields TORQUAY SUB-BASIN 38° 30' S MUSSEL OTWAY PLATFORM SHIPWRECK RANGES VOLUTA SELWYN FAULT Casino NERITA MORNINGTON HIGH FAULT DEEP TROUGH Minerva SNAIL Basement faults V04-2 TERRACE La Bella Cretaceous faults V04-1

TROUGH 39° S Depositional trough

ZONE SORELL Otway Group PRAWN 39° S outcrop KING ISLAND PLATFORM HIGH BASIN LIMIT Gas field Geographe SELWYN BLOCK Major Tertiary FAULT syncline 050 submerged basement high (Otway Group and Waarre Major Late Thylacine Formation absent) Cretaceous syncline km

141° E 141° 30' E 142° E 142° 30' E 143° E 143° 30' E 144° E 144° 30' E Figure 4 Otway Basin Structural Elements 141°E 141°30'E 142°E CAROLINE 1 WILSON 1 Legend 3371 FAHLEY 1 1317 Borehole names 3211 WANWIN 1 TD PALPARA 4 1784 1460 FAHLEY 2 PINE LODGE 1 Petroleum well names 1300 2149 DRIK DRIK 1 ANNYA 2 TD 1221 885 MYAMYN 2 38°S PALPARA 1 WANWIN 3 GLENAULIN 2 722 ARDONACHIE 2 357 1852 HENKE 1 1193 1023 38°S SAOW 2 1435 SAOW 1 GREENBANKS 1 1226 MACARTHUR 3 NELSON 1 GLENELG 1 WARRAIN 7 COBBOBOONEE 4 764 468 2226 1786 1915 0 10 LINDON 1 LINDON 2 3011 970 km COBBOBOONEE 5 PEP150 PEP151 1768

KENTBRUCK 3 PEP 1733 HEYWOOD 10 HOMERTON 3 1642 1578 159 COBBOBOONEE 2 HEYWOOD 13 HOMERTON 4 KENTBRUCK 4 1837 1842 04-1(v)404 1669 NTH EUMERALLA 1 NARRAWONG 16 1670 2961 EUMERALLA 1 PRETTY HILL 1 GORAE 4 GORAE 2 3139 2478 1853 1630 NARRAWONG 15 WINDERMERE 1 NORMANBY 1 MOUZIE 1 1904 1852 3308 1948 MIRAMS 1 TYRENDARRA 13 SHAW 1 GORAE 5 1406 WINDERMERE 2 1799 383 3595 CODRINGTON 1 960 NARRAWONG 13 1265 1713 PEP152 PORTLAND NTH 1 VIC/P46 TREWALLA 5 864 Victoria 1659 PORTLAND 3 PORTLAND 2 YAMBUK 2 1438 South Australia 1718 1537 TARRAGAL 3 PORTLAND 14 PORTLAND 1 1728 BELFAST 11 1420 690 1483 PORTLAND 8 PORTLAND 11 1383 1242 PORTLAND 13 PORTLAND 12 1241 VIC/P DISCOVERY BAY 1 608 PORTLAND 10 2776 1595 VOLUTA 1 37(v) 3974

38°30'S VIC/P51 VIC/P44 38°30'S BRIDGEWATER BAY 1 VIC/P50 4200

141°E 141°30'E 142°E

Figure 5 Well and Borehole location map 141°E 141°30'E 142°E CAROLINE 1 WILSON 1 Seismic Legend FAHLEY 1 All seismic lines FAHLEY 2 PINE LODGE 1 Seismic survey OP80

38°S PALPARA 1 Seismic survey OCS96 HENKE 1 38°S SAOW 2 SAOW 1 Seismic survey OEP02 GREENBANKS 1 Seismic survey AGSO Otway NELSON 1 GLENELG 1 Seismic survey UA82 LINDON 1 LINDON 2 Seismic surveys U81 & OGF Nelson 2D/3D Survey

0 10 km 04-1(v) NTH EUMERALLA 1

EUMERALLA 1 PRETTY HILL 1 NORMANBY 1 WINDERMERE 1 SHAW 1 MIRAMS 1 WINDERMERE 2

PORTLAND NTH 1

DISCOVERY BAY 1 VOLUTA 1

38°30'S 38°30'S

BRIDGEWATER BAY 1

141°E 141°30'E 142°E

Figure 6 Seismic Surveys 141°E 141°30'E 142°E CAROLINE 1 WILSON 1 Seismic Legend FAHLEY 1 All seismic lines

FAHLEY 2 PINE LODGE 1 SEGY not available confidential 38°S PALPARA 1 HENKE 1 All 2D seismic 38°S SAOW 2 SAOW 1 with SEGY GREENBANKS 1 Nelson 2D/3D Survey NELSON 1 GLENELG 1 0 10 LINDON 1 LINDON 2 km

04-1(v) NTH EUMERALLA 1

EUMERALLA 1 PRETTY HILL 1 NORMANBY 1 WINDERMERE 1 SHAW 1 MIRAMS 1 WINDERMERE 2

PORTLAND NTH 1

DISCOVERY BAY 1 VOLUTA 1

38°30'S 38°30'S

BRIDGEWATER BAY 1

141°E 141°30'E 142°E

Figure 7 Seismic Survey with SEGY data 141°E 141°30'E 142°E Thickness (m) CAROLINE 1 WILSON 1 No Legend 5 rt 0 10 FAHLEY 1 1317 00 400 300 he 0 6 3371 1 00 rn Boreholenames 0 0 5 WANWIN1 0 0 Li 1 32110 0 m TD 17840 it km 3 S

1100 0 8 7

1 0 1 9 h 250 1 400 6 1 1 0

2 1 2 0 0 0 e 0 0 1 1 0 0 r 0 0 0PINE0 0 LODGE 1 b Boreholeswith 1 FAHLEY 2 0 PALPARA3 4 0 6 r 00 5 00 oo 500 ANNYA 2 0 k TD>1200m 1460 1300 2149 DRIKDRIK 1 0 Gr 1221 885 MYAMYN 2 oup 38°S 750 PALPARA 1 ARDONACHIE2 Petroleum well names GLENAULIN2 722 38°S WANWIN3 HENKE 1 1023 5 TD 1193 0 1000 357 0 4 0 1852 0 PICKS 2 1435 7 GREENBANKS0 0 1 1250 PICKS 1 0 Lake Condah High Marine national park/

566 0 4

320 1 1226 sanctuary/ special 1500 GLENELG 1 MACARTHUR3 management area NELSON 1 WARRAIN7 COBBOBOONEE4 764 1750 2226 1915

468 1786 0

2000 1 30 LINDON 1 1 LINDON 2 4

0 2250 0 3011 970 COBBOBOONEE5 0

0

4 2 1768 25711 00 1400 KENTBRUCK3 1733 HOMERTON3 0 HEYWOOD10 50 1578 1 1642 KENTBRUCK4 COBBOBOONEE2 16 A’ 00HEYWOOD13 HOMERTON4 1 404 1837 1842 20 0 1669 70 NTH EUMERALLA 1 0 1

1 3

0 Possible Fault 1 NARRAWONG16 0 2 2961

0 04-1(v) 1670

1 1 0 30 3 0 0 0 Bounded Leads EUMERALLA 1 PRETTY HILL 1

0

0 8 GORAE4 GORAE2 14 1 2 3139 2478 0 0 0 0 0 0 1853 0 1 9 1630 NARRAWONG15 4 00 1 WINDERMERE 1

NORMANBY 1 1904 0 7

0 Portland MOUZIE1 0 8

TYRENDARRA 131852 0 1 3308 1948 3 00 MIRAMS 1 1406 WINDERMERE 2 SHAW 1 13 Trough GORAE5 0 0 1799 383 3595 CODRINGTON1 960 14 Normanby NARRAWONG13 9 00 1265 0 0 1713 0 140 High 15 00 00

4 23

1 00

5

1 PORTLAND NTH 1 0 0

0

1 TREWALLA 5 0

5 A 2 1 00 2 864 000

0 1659 0 PORTLAND3 PORTLAND2 6 YAMBUK 2 1 1 1438 60 1718 1537 0 TARRAGAL 3 PORTLAND14 PORTLAND2300 1 1728 BELFAST11 1420 690 11 1 0 3 12 0 1483

2 1 00 3 PORTLAND11 0 0 2 00 3 0 0

0 PORTLAND8 1 0 0 1242 0 3 1383 220

1 PORTLAND13 0

1500 0

PORTLAND12 0 110 0 1 1241 2 Yambuck 2 DISCOVERY BAY 1 608 PORTLAND10 100 2776 1595 Lead

VOLUTA 1 17

1 2 2 00 3 2 2 0 0 0 0 1 0 0 0 3974 0 7 0 0 0 6 1 8 0 1 4

1 0 0

4 1 0 0

0 0 1 0 0 50 0 14 1 1 2 9 00 9

0 0

0

1 1 38°30'S Cape0 1 30 5

0 4 0 00 38°30'S

0

14 0

0 1

Bridgewater 0 06 0 5 Lead BRIDGEWATER1 BAY 1 1 1 0 40

0 00 0 9

1 2 14 4200 0

0 0 0 0 0 2 2 23 0 0 0 5 00 0 1 1 1 0 817 2 2 00 0 0 0 0 4 2 16 00

141°E 141°30'E 142°E

Figure 8 Top Sherbrook Depth Structure OFFSHORE OTWAY BASIN PLAY FAIRWAY 1 : NORTHEASTERN FLANK BRIDGEWATER HIGH S N

A Tilted Fault Block B Horst Block C Palaeogeomorphic HEYTESBURY GROUP D Anticlinal E Stratigraphic Pinchout Hydrocarbon in place NIRRANDA GROUP D D DILWYN FM. C PEMBER DILWYN FM. MST. C PEBBLE POINT FM. PEMBER PEBBLE A MST. B POINT FM. B A A A

A A A A A HEYTESBURY GROUP NIRRANDA GROUP A A A A WANGERRIP GROUP BELFAST SHERBROOK GROUP MUDSTONE WAARRE OTWAY FM. OTWAY GROUP GROUP

Figure 9 Northeastern Bridgewater Bay Play types SW NE A A’ VIC/P46 04-1(v) NORMANBY-1

0.0 0.0

Top Nirranda Group

TWT Top Wangerrip TWT (s) Group Top Pember (s) Mudstone

1.0 1.0

Top Timboon Sandstone

Top Belfast Mudstone

Top Waarre Formation

2.0 2.0

2km

Figure 10 Seismic Line 80-09a through Normanby-1 DEPARTMENTof PRIMARY INDUSTRIES MINERALSand PETROLEUM DIVISION GEOSCIENCEVICTORIA -PETROLEUM P.O.BOX 500 EMAST ELBOURNE VIC. 3002 250 VVPICTORIA P ARADE EMAST ELBOURNE VIC. 3002 PP03HONE: 03 9412 5084 FF03AX: 03 9412 5156 WAEB DDRESS: www.dpi.vic.gov.au/minpet/