VIMP Report 79 - Hydrocarbon prospectivity of areas V03-1 and V03-2, 03-1(v),03-2(v), Offshore Gippsland Basin: 2003 Acreage Release
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Product description:Download The downloadable version of this report is supplied in PDF format. Executive Summary The Gippsland Basin is situated in southeastern Australia, located about 200 km east of the city of Melbourne, and is well serviced by roads and population centres. About two thirds of the basin lies offshore representing one of Australia's most prolific hydrocarbon provinces. Initial proven reserves were estimated at 4 billion barrels of oil (Bbbl) and 10 trillion cubic feet (Tcf) of gas. The basin currently supplies (as at June 2002) 20% of the nation’s oil demand and most of the State of Victoria’s gas requirements. The remaining resources (at P50 level) have been assessed at 600 million barrels of liquids (MMbbl) and 5 Tcf gas, much of which is likely to occur in deeper stratigraphic units. Most of the discoveries to date have been hosted within the Late Cretaceous to Early Tertiary Latrobe Group. Onshore and offshore, the Gippsland Basin has over 80 000 km of 2D seismic data, more than 30 3D seismic surveys and a density of approximately one exploration well per 50 km². Although a mature basin by comparison with other Australian basins, by world standards the Gippsland Basin is still considered to be relatively under-explored. A network of pipelines brings produced hydrocarbons to the onshore petroleum processing facilities at Longford. From here, new pipelines were recently commissioned to deliver Gippsland gas to Sydney in New South Wales, to Adelaide in South Australia and to Tasmania. The potential for additional discoveries will ensure continued interest in the region, which will also be maintained by several other factors. Among these are increasing gas market demand in the SE Australian region and deregulation and reform of the upstream and downstream gas industry. Recent gazettal rounds in the Gippsland Basin have resulted in a number of new acreage awards adjacent to the production licences held by the Esso/BHP Petroleum joint venture. Increased interest is being expressed by various companies, spanning both large and small petroleum industry players and may be attributed to factors ranging from improvements in technology to the changing economic and regulatory environment. The areas described in this report were partly explored by previous operators who identified several prospects and leads. All areas offer significant opportunities for hydrocarbon entrapment in several different play types. Area V03-1, located in the basin’s northwest, lies adjacent to the 3-mile zone and approximately 10 km south of the Lakes Entrance oil field and 20 km east of Lake Wellington. Water depths are very shallow and range between 20-40 m. Petroleum geological control within the block is provided by four exploration wells: Albatross-1 (drilled by Endeavour Oil in 1970), West Seahorse-1 and West Seahorse –2 (drilled by Hudbay Oil in 1981/82) and Cuttlefish-1 (drilled by Amity Oil in 1999). The gazettal block is geologically diverse, since the southern section traverses the Rosedale Fault System across which the hydrocarbon-bearing Latrobe Group thickens southwards into the Central Deep. The heavily dissected nature of the Northern Terrace/Central Deep transition is favourable for structural traps and numerous discoveries were made near the southern segment of Area V03-1. Although the Latrobe Group thins rapidly northward, only about 35 m thick in Albatross-1, the Northern Terrace is nevertheless considered prospective and provides possible settings for structural and stratigraphic plays. Based on previous mapping, several leads have been recognised in Area V03-1. A seismic ‘mound’ lying above a strong reflector was attributed to either a top-Latrobe erosional remnant or a barrier bar lying above the Latrobe coal measures. Other leads were mapped in the hanging wall of the Rosedale Fault. These were regarded primarily as Golden Beach leads by analogy with the Kipper discovery. Other leads include a large complex Golden Beach play bounded updip by the confluence of two poorly defined faults and two poorly defined hanging wall closures adjacent to the Rosedale Fault System. More recently, a shallow top-Latrobe stratigraphic lead involving Oligocene submarine channel fill facies and a low relief structural closure were identified. Area V03-2 is located in the basin’s west and lies adjacent to the 3-mile zone extending parallel to the southern part of the Ninety Mile Beach. Water depths are generally shallow and range between 20-70 m. Approximately half of the area extends across the Southern Platform and Terrace, while the northern half lies over the Central Deep, providing access to the entire stratigraphic section that has been identified as being prospective. Good seismic coverage exists in the northern two thirds of the block, while only little data is available from the Southern Platform. Well control is provided by seven wells drilled between 1971 and 1998 (Flying Fish-1, 1971, NSW Oil and Gas Company; Kyarra-1, 1983, Aquitaine; Wyrallah-1, 1984, Aquitaine; Snook-1, 1990, Esso; Amberjack, 1990, BHP Petroleum; Tommyruff-1, 1990, BHP Petroleum; Broadbill-1, 1998, Amity Oil). Although none of these discovered any hydrocarbons, the area’s prospective status is confirmed by the oil fields at Perch, Dolphin, Torsk, Tarwhine, Mulloway and Whiptail. Previous prospectivity assessments primarily targeted top-Latrobe objectives, including a barrier bar complex in the Tommyruff area and structural closures elsewhere that were generated during Miocene basin inversion. Faulted contacts of intra-Latrobe sequences (Halibut Subgroup) against Palaeozoic basement and Latrobe Group pinch-outs were also proposed as viable objectives. Although much of the Southern Platform is unexplored, the fact that the Latrobe Group pinches out between basement and the Tertiary Seaspray Group, makes this part of Area V03-2 attractive. New palynological data from Perch-1 has revealed the presence of Turonian (P. mawsonii biozone) sediments immediately south of the Darriman Fault System, confirming that the Emperor Subgroup extends onto the Southern Terrace. It appears therefore likely that Kipper-style plays (gas-bearing sandstones sealed by volcanics and lacustrine shales) are developed along the Darriman Fault System and Longtom-type plays (gas-bearing sandstones within lacustrine Kipper Shale) exist on the terrace. In summary, the 2003 Gippsland gazettal blocks provide excellent exploration opportunities, catering for the big as well as the smaller exploration companies. The Gippsland Basin has the distinct advantage of being positioned close to expanding infrastructure and markets. The basin is currently undergoing a resurgence in exploration activity and some major efforts are being undertaken to identify the many hidden oil and gas accumulations. In this context, Esso/BHP Billiton have recently stepped up their own exploration activity with the acquisition of a 4060 km² 3D seismic survey at a cost of approximately A$60 million. This survey, the largest proprietary 3D survey ever acquired in Australia, covers the major northern producing oil and gas fields of the basin and will provide the joint venture partners with an integrated, regional, structural and stratigraphic framework on which to base their future exploration and production activity. Another large 3D survey, the Tuskfish survey, totalling around 1000 km², was completed by Esso/BHP Billiton in March 2003. Bibliographic reference Bernecker, T., Thomas, J.H., and Driscoll, J., 2003. Hydrocarbon Prospectivity of Areas V03-1 and V03-2, 03-1(v),03-2(v), Offshore Gippsland Basin, Victoria, Australia: 2003 Acreage Release. Victorian Initiative for Minerals and Petroleum Report 79. Department of Primary Industries. | ||||||
