Bonaparte Basin

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This page is currently being authored by a student at the University of Oklahoma. This page will be completed by December 15, 2021.

Overview

Australian petroleum exploration and production is primarily located along the western shelf of the continent. A majority of the known reserves are liquified natural gas and condensate from carbon rich source rocks. The basins located along the western shelf, specifically the Bonaparte, experienced a significant increase in exploration and drilling in the 1980s, when more modern forms of extraction began being developed. The Bonaparte Basin is located off of the Northwestern coast of Australia. The basin is fan shaped and is located over an area of 270,000 sq. km with approximately 20,000 sq. km extending onshore.[1] The formation of the basin took place during the Paleozoic extension in two parts and the latter half of the Triassic compression. The basin is characterized by its v-shape and is located between the Browse Basin to its west and the Money Shoals Basin to the northeast. Alliance Oil Developments was the first to drill a well in the 1960s. The area has had over 90 wells in the off-shore portion.

Figure 1 Location of the Bonaparte Basin

Geologic Setting

The 'v-shape' of the basin, shown in Figure 1, was developed during the late Devonian and into the earlier parts of the early Carboniferous. The area at this time was experiencing a north-opening rift. [2] Due to the compression in the Triassic period, the N-S region experienced a period of uplift and erosion. With other events, such as tectonics and inversion and anticlines were produced in the sub-basin. The uplifted areas of the region eroded and collapsed allowing the deposition of “Lower-Middle Jurassic ‘redbeds’”. There are thick marine mudstone deposits which are “flanked” by fan-delta sandstones. The convergence of the Australian and Eurasian plates during the late Miocene-Pliocene caused the fault systems to reactivate primarily among the Timor Trough, which is located just north of the basin. [3] Through several geologic processes, multiple sub-basins have formed. One of the basins that was formed is the Vulcan sub-basin, during the Callovian and Tithonian periods. It extends northeast-southwest and is characterized by various horsts, grabens, and terraces. Rock samples from this region show an abundance of type II and type III kerogen, showing a high level of marine deposits and carbon deposits. The stratigraphy of the region is shown in figure 2.

Figure 2

Seal

The three most important systems do have different seals. The first, Paleozoic Petroleum System, is a Lower Permian Treachery Shale and is a regional seal in the onshore and offshore Petrel sub-basin. The Treachery shale is found to be about 219m thick, consisting of carbonaceous shale and tillite. The treachery shale is present across the Petrel sub-basin and on the Plover-Lacrosse terrace. The second system and its seal are the Keyling, Hyland-Bay Permian. The gas reservoirs within this system are sealed by intraformational shales in the Kinmore group. In the Tern field within this system, the seal consists of overlying shallow marine Mount Goodwin Formation of the Kinmore group. The third system with its own distinct seal is the Mesozoic Petroleum System. Found within this system is top and lateral lower cretaceous claystone of the Upper Flamingo and Darwin Formations and is approximately 300m thick. The Frigate shale is a seal for the Plover and Malita formations.

Source Rock and Migration

To date, the oldest source rock that has been found is the Milligans-Carboniferous. This formation consists of marine shale that consists of both oil and gas in Carboniferous and Permian deltaic. Other findings show that there is marine shelf carbonate and shallow to deep marine sandstones. However, there is another system, the Permian Petroleum system, within the basin. Source rocks found here consist of Lower Permian Keyling Formation delta-plain coals and an abundance of marginal marine shales. The source rocks found within this system attribute to an abundance of gas an condensate for fluvial, deltaic and shallow marine sandstone reservoirs. This is primarily found along the Hyland-Bay formation.

Reservoir

Reservoirs found within the Bonaparte Province Basin are primarily of marine sandstone and date back to forming during the Jurassic and Cretaceous age. In one system the reservoir is of Permian rocks which are sources from shallow marine, coal, shale, and deltaic shale. Some of these reservoirs, specifically one located within the Milligans Formation are offshore-to-basinal shale which contain submarine fan deposits.

Trap

Mentioned in under seals, the three systems comprise of different traps. The Paleozoic Petroleum Systems are dominated by anticlinal traps. Along with anticlines are, draping structures along fault blocks and reefs. The next system, the Keyling, Hyland-Bay Permian System are also dominated with anticlines. The traps within this system contain roughly 30% of the reported oil equivalent reserves. The third system, the Mesozoic Petroleum System, contains mostly fault-block traps. The hydrocarbons within these fault-systems were primarily formed during the Late Miocene and Pliocene during collisions. Figure 3 shows the different traps within the Vulcan sub-basin, which is located in the middle of the Bonaparte Basin

Figure 3 Vulcan sub-basin

Geologic Risk and Uncertainties

A lot of the risks and uncertainties come from geopolitical standpoints. The timor sea is primarily bound by Australia and Indonesia. The international boundaries along the Timor trough and the associated island and faults run along each other. The result of this was the 'Zone of Cooperation'. However, a specific geologic risk and uncertainty lies closer to the northern shores and islands of Australia. There are reports of numerous bitumen tar bit strands in the Money Shoal Basin Province. Out of the twenty-nine fields that have been explored, three produced oil until 1997.

Future Prospects

There are currently three parts that have the most potential for companies and petroleum production. The first is the Vulcan Sub-Basin which flanks the western part of the Bonaparte and extends NE. The Vulcan Sub-Basin is comprised of limestone formed primarily during the Cainozoic/Tertiary and a sizable portion of the basin comprising of marine claystone and shale during the Mesozoic-Cretaceous period. The second area of prospect is the Laminaria-Flamingo High, which is located in the middle of the basin. The third area of prospect is the Sahul Platform, located in the north eastern part of the basin and next the the Vulcan Sub-Basin. However, there is another sub-basin, the Petrel sub-basin, which currently hosts a majority of the drilling efforts in the region. Within this sub-basin, there is a major gas field located near the Petrel deep, in the middle of the basin. The southern end is a major producer of oil due to its proximity to Cambrian Volcanics and the Precambrian Basement. The Bonaparte Basin, as a whole produces most of its oil on the western-southern regions, while gas plays are primarily located to the northern-eastern regions.

Petroleum and Facility Engineering

Since the beginning of production in 1986 in the basin, companies have used floating production facilities. In the mid-1990s offshore production was limited to just 3 facilities. Twenty-nine total fields have been established in the Bonaparte Province. Known reserves for the basin are approximately 3.2 BBOE (billion barrels of oil equivalent). Since there has not been much new discrovery in the region, there were/are plans to incorporate new infrastucture, specifically new pipelines, and facilities that will once again tap into the older fields. [4]


References

“Bonaparte Basin.” Bonaparte Basin | Geoscience Australia, https://www.ga.gov.au/scientific-topics/energy/province-sedimentary-basin-geology/petroleum/offshore-northwest-australia/bonaparte.

“Bonaparte Basin.” Oil & Gas Today, 6 Dec. 2019, https://www.oilandgastoday.com.au/bonaparte-basin/.

Staff, PESA. “Abstract: Exploration History of the Timor Sea Area, Bonaparte Basin and Surrounds.” AAPG Datapages/Archives, Petroleum Exploration Society of Australia (PESA), 1 Jan. 1970, https://archives.datapages.com/data/petroleum-exploration-society-of-australia/news/064/064001/pdfs/50.htm.

Bishop, Michele G. 1999, USGS, https://pubs.usgs.gov/of/1999/0050p/report.pdf. Accessed 13 Dec. 2021.

“Beyond the Puffin: Australia's Vulcan Sub-Basin De-Risked through Modern Seismic.” Spectrum Geo, https://www.spectrumgeo.com/geological-resources/technical-paper-library/beyond-the-puffin-australias-vulcan-sub-basin-de-risked-through-modern-seismic.

  1. [1], additional text.