{{Short description|Oil field in Victoria, Australia}} {{Use Australian English|date=May 2024}} {{Infobox oil field |name=Halibut Field|image=|caption=|location_map=Australia#Australia Victoria|location_map_width=|location_map_text=|relief=yes |coordinates = {{coord|38|23|56|S|148|18|59|E|type:landmark|display=inline}} |coordinates_ref=|country=[[Australia]]|region=Southeastern Australia|location=Gippsland Basin|block=|offonshore=Offshore|operator=[[ExxonMobil Australia]]|operators=|partners=[[Exxon]]|contractors=|discovery=1967|start_development=1967|start_production=1970|peak_year=|abandonment=|API=43.8|peak_of_production_oil_bbl/d=|peak_of_production_oil_tpy=|peak_of_production_gas_mmcuft/d=|peak_of_production_gas_mmscm/d=|peak_of_production_gas_bcm/y=|oil_production_bbl/d=|oil_production_tpy=|production_year_oil=|production_gas_mmcuft/d=|production_gas_mmscm/d=|production_gas_bcm/y=|production_year_gas=|est_oil_bbl=|est_oil_t=|recover_oil_bbl=|recover_oil_t=|est_gas_bft=|est_gas_bcm=|recover_gas_bft=|recover_gas_bcm=|formations=}}
The '''Halibut Field''' is an [[oil field]], within the [[Gippsland Basin]] offshore of the Australian state of [[Victoria (Australia)|Victoria]].<ref name=":2">{{Cite book|title=PETROLEUM SYSTEM OF THE GIPPSLAND BASIN, AUSTRALIA|last=Bishop|first=Michele|publisher=USGS|year=2000}}</ref> The oil field is located approximately 64 km offshore of southeastern [[Australia]].<ref name=":0">{{Cite journal|last=Clifton|first=Edwin H. Franklin, Billy B.|date=1971-01-01|title=Halibut Field, Southeastern Australia|url=http://archives.datapages.com/data/bulletns/1971-73/data/pg/0055/0008/1250/1262.htm|journal=AAPG Bulletin|volume=55|issue=8|issn=0149-1423|doi=10.1306/5d25ce4b-16c1-11d7-8645000102c1865d|url-access=subscription|doi-access=free}}</ref> The total area of this field is 26.9 km<sup>2</sup> and is composed of 10 mappable [[Geologic unit|units]].<ref name=":0" />
== Geologic history ==
During the late [[Jurassic]], a rift complex forms between the [[Australian Plate]]/[[Tasman Fold Belt]], and the [[Antarctic Plate]].<ref name=":4">Rahmanian, V. D., Moore, P. S., Mudge, W. J., and Spring, D. E., 1990, sequence stratigraphy and the habitat of hydrocarbons, Gippsland Basin, Australia; in Brooks, J., ed., Classic Petroleum Provinces, Geological Society Special Publication No. 50, p 525-541.</ref><ref>Etheridge, M. A., Branson, J. C., and Stuart-Smith, P. G., 1987, The Bass, Gippsland and Otway Basins, southeast Australia: a branched rift system formed by continental extension, ''in'' Beaumont, Christopher, and Tankard, Anthony J., eds., Sedimentary Basins and Basin-Forming Mechanisms; Canadian Society of Petroleum Geologists Memoir 12, Atlantic Geoscience Society Special Publication 5, p. 147-162.</ref><ref>Falvey, David, A., and Mutter, John C., 1981, Regional plate tectonics and the evolution of Australia’s passive continental margins; BMR Journal of Australian Geology and Geophysics, 6(1), p. 1-29.</ref> This rifting continues through the [[early Cretaceous]], and in the [[middle Cretaceous]], begins to assist in the separation of [[Gondwana]] (In is what now southern Australia).<ref name=":4" /> During this same time, ocean crust is created to the west of [[Tasmania]],<ref name=":4" /> and the separation of the Australian Plate from [[New Zealand]], the Antarctic Plate, and the Campbell Plateau occurs.<ref name=":5">Mehin, K., and Bock, M. P., 1998, Cretaceous source rocks of the onshore Gippsland Basin Victoria; Victoria Initiative for Minerals and Petroleum Report 54, 98 p.</ref> During the late [[Cretaceous]], more extension occurs in this region, which creates [[Syn-rift|syn-rift troughs]].<ref name=":2" /><ref name=":5" /> This extension forms the central depression, which is an integral part of the petroleum system, and is the location of nearly all of the oil/gas fields in the Gippsland Basin. Also during the [[late Cretaceous]], [[volcanism]] occurred due to the Tasman Sea rifting. From the [[Eocene]] to the middle [[Miocene]], a compressional tectonic period begins, and forms a series of [[anticline]]s, as well as nearly all of the [[Structural geology|structural features]] present today.<ref name=":2" /><ref>Mebberson, A. J., 1989, The future for exploration in the Gippsland Basin; The APEA Journal, v. 29, part 1, p 430-439.</ref><ref name=":6">Moore, P. S., Burns, B. J., Emmett, J. K., and Guthrie, D. A., 1992, Integrated source, maturation and migration analysis, Gippsland Basin, Australia; The APEA Journal, v. 32, part 1, p. 313-324.</ref><ref>Ozimic, S., Nicholas, E., Pain, L., and Vuckovic, V., 1987, Australian Petroleum Accumulations, Gippsland Basin, Victoria, Department of Primary Industries and Energy, Bureau of Mineral Resources, Geology and Geophysics, Canberra, 252 p.</ref>
== Stratigraphy ==
=== Strzelecki Group === The Strzelecki Group is a [[Stratigraphic unit|geologic group]] present in the Halibut Field area. The group was mainly deposited in the early Cretaceous.<ref name=":2" /> It is mainly composed of continental and [[Lacustrine deposits|lacustrine]] [[Clastic rock|clastics]].<ref name=":2" /> The lithology is predominantly nonmarine [[greywacke]]s, and [[mudstone]]s, with minor layers of [[sandstone]], [[Conglomerate (geology)|conglomerate]], [[coal]]s, and [[volcanoclastic]]s.<ref name=":2" /> [[Depositional environment]]s of this group include lakes, swamps, and floodplains. This group is the economic basement of the Halibut Field, meaning it is the stratigraphically lowest group for hydrocarbon production potential.<ref name=":2" /> This is known due to burial of 8 km or more in the offshore portion of the basin, which places the group in the [[Maturity (sedimentology)|overmature]] range.<ref name=":2" /> There is currently research being done on potential hydrocarbon reserves in the onshore portion of the Gippsland Basin.
=== Golden Beach Group === The Golden Beach Group lies unconformably above the Strzelecki Group, and was deposited in the late Cretaceous. The lithology of this group is [[shale]], and sandstone.<ref name=":2" /> In addition to these major lithologic groups, there are also volcanic flows of [[andesitic]]-[[basaltic]] composition present.<ref>Clark, A. B. S., Thomas B. M., 1988, The intra-Latrobe play: a case history from the Basker/Manta block (VIC/P19), Gippsland Basin; The APEA Journal, v. 28, part 1, p. 100-112.</ref> The depositional environments represented by this group are deep water lakes, and floodplains.<ref name=":2" /><ref>Duff, B. A., Grollman, N. G., Mason, D. J., Questiaux, J. M., Ormerod, D. S., and Lays, P., 1991, Tectonostratigraphic evolution of the south-east Gippsland Basin; The APEA Journal, v. 31, part 1, p. 116-130.</ref><ref>Partridge, Alan D., 1996, Large break-up lakes of Bass Strait; Gippsland Basin Symposium, University of Melbourn, abstract, p. 3-6.</ref> The Kipper Shale Formation within this group is a 1,0000 m thick lacustrine shale. Though this would typically make a good source rock, it is believed that oxidation of organic matter inhibited the generation of hydrocarbons.<ref name=":2" />
=== Latrobe Group === [[File:Usgs2.strat.png|thumb|Stratigraphic Column of the Halibut Field, Australia]] The Latrobe Group is stratigraphically above the Golden Beach Group, and was deposited in the late Cretaceous to the [[Eocene]].<ref name=":2" /> This group is the most valuable for hydrocarbon production, since it makes up the majority of the source rocks, and the reservoir rocks. The major rock types include sandstone, siltstone, mudstone, shale, coals, and volcanic rocks.<ref name=":2" /> These rock types are representative of alluvial, shoreline, and shallow shelf marine depositional environments.<ref name=":2" /><ref>Douglas, J. G., 1976, Gippsland Basin; ''in'' Douglas, J. G., Abele, C., Benedek, S. Dettmann, M. E., Kenley, P. R., and Lawrence, C. R., Chapter 7, Mesozoic; ''in'' Douglas, J. G., and Ferguson, J. A., eds., Geology of Victoria, Geological Society of Australia Special Publication No. 5, p. 158-176.</ref> The coals and shales of this group are the main source rock in this field, and throughout the basin.<ref name=":2" /> Sandstone from this group makes up the reservoir rocks, and exhibits a porosity of 20-25%, and a permeability of 5000-7000 millidarcies.<ref name=":3" /> This group has been subjected to much research due to its hydrocarbon implications. This has allowed researchers to reconstruct [[paleoshoreline]]s, and [[paleoflow]] directions.<ref name=":2" /> Multiple [[Marine transgression|transgressions]] and [[Marine regression|regressions]] are recorded in the rocks from the upper Paleocene to the Eocene.<ref name=":2" /> Throughout the area, the surrounding sandstones display a high amount of [[Dolomite (mineral)|dolomite]] cement present, which drastically decreases porosity (it can make up to 30% of the total rock volume). Dissolution of this cement in hydrocarbon bearing sandstones, has not been completely understood by researchers.<ref name=":2" /> The small amount of research done on this phenomenon has pointed to hydrocarbon emplacement as the reason for dissolution. This is only due to the lack of evidence for other common causes of dolomite dissolution.
=== Seaspray Group === The Seaspray Group lies unconformably above the Latrobe Group, and was deposited in the [[Oligocene]] to the [[Miocene]]. This group makes up the majority of the seals in the region due to the unconformity with the Latrobe Group, as well as the low [[permeability (earth sciences)|permeability]] of the rock types, which include shales, [[marl]]s, [[limestone]]s, calcareous [[claystone]]s, [[siltstone]]s, and sandstones.<ref name=":2" /> The typical depositional environments of these rock types, are [[low energy marine]] environments.
== Petroleum geology ==
=== Source rocks === The majority of the source rocks are coals, and coaly shales originating from the [[Latrobe group]].<ref name=":2" /><ref name=":6" /> The hydrocarbon formation is due to the high heat flow, and subsidence that occurred in the late Cretaceous through the early [[Paleocene]].<ref name=":2" /> The shales of the Latrobe Group display [[Total organic carbon|Total Organic Carbon]] (TOC) values of 1-3% wt.<ref name=":2" />
=== Reservoir rocks === [[File:USGS 1.png|thumb|581x581px|Critical Moment of the Halibut Field, Australia]]The reservoir rocks in this field are primarily sandstones from the Latrobe Group.<ref name=":2" /> The [[Porosity|secondary porosity]] accounts for the majority of the porosity, and therefore its ability to contain [[hydrocarbon]]s.<ref name=":2" /> The reason for this is due to the high amount of [[Dolomite (mineral)|dolomite]] cement which filled up the pores, and then was dissolved by the hydrocarbons migrating into the pores.<ref name=":2" /> The porosity of the sandstones are 20-25%, and the permeability is 5000-7000 md.<ref name=":3" />
=== Seals === The seals in this region are mainly [[marl]], [[limestone]], and sandstone from the Seaspray Group.<ref name=":2" /> These rock types are aided by being deposited on the Latrobe [[unconformity]].<ref name=":2" /> This unconformity is due to the anticlines that formed in the Latrobe group being eroded, and then the Seaspray group being deposited on top of this erosional surface.<ref name=":2" />
=== Traps === The traps in this oil field, are mainly late Eocene to middle Miocene in age.<ref name=":2" /> The traps were formed due to a small compressional event associated with the opening of the Tasman Sea. This is why [[anticline]]s, along with faults are the predominant trapping mechanism throughout the basin.<ref name=":2" /> The Halibut Field is located directly on an anticline, which serves as the trap.
=== Migration === Migration of the hydrocarbons is mainly vertical. Oil migration occurs from depths of 4–5 km, while gas migration occurs from depths of 5–6 km.<ref name=":2" />
== Production == The field was discovered in 1967, and has been producing oil and gas since 1970.<ref name=":3">Malek, R; Mehin, K, 1998 Oil and Gas Resources of Victoria Department of Natural Resources and Environment 1998 Petroleum Development</ref> The water depth is 73 m, and there are 14 producing wells.<ref name=":3" /> The oil water contact is located at approximately 2399 m depth.<ref name=":3" /> The [[porosity]] is 22%, and the [[Permeability (earth sciences)|permeability]] is 5000-7000 [[millidarcy]].<ref name=":3" /> The [[oil gravity]] is 43.3, and is [[Paraffinic hydrocarbon|paraffinic]].<ref name=":3" /> From 1970-2008 approximately 840,000,000 barrels of oil or approximately $105,000,000,000 (calculated with a price of $125.00 per barrel) was produced.<ref name=":1">{{Cite web|url=http://www.businesswire.com/news/home/20080721005836/en/Bazzard-1-Offshore-ACORs-ORRI-VICP53-Adjoins-Giant|title=Bazzard-1 Next Offshore Well on ACOR's ORRI On VIC/P53 Adjoins Giant Halibut Oil Field With Production of Approximately 840,000,000 Barrels of Oil and Is Still Producing|website=www.businesswire.com|access-date=2016-10-23}}</ref> The field is being produced by [[ExxonMobil Australia]], which is a subsidiary of [[ExxonMobil]].<ref name=":1" /> The Gippsland Basin as a whole was Australia's largest petroleum producing basin from the mid 1960s when it was discovered until 1996 when the [[North West Shelf]] surpassed it.<ref name=":2" /> The basin was integral in Australia becoming a self sufficient petroleum producing country.<ref name=":2" />
== References == {{reflist|30em}}
[[Category:Oil fields of Australia]] [[Category:Geology of Victoria (state)]]