Taranaki basin

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Map and Cross Section of Taranaki Basin
History of Formation

The Taranaki Basin is located on the west coast of New Zealand and covers an area of about 100,000 square kilometers[1]. The Taranaki is a Cretaceous rift basin that underwent fore-arc and intra-arc development which is associated with volcanic arc. The basin consists of marine sediment, with significant amounts of terrestrial sediment from the late cretaceous. This play is one of the only producing developments in New Zealand and where the majority of the country's oil and gas is produced. Over 400 onshore and offshore exploration and production wells have been drilled in Taranaki to date of which the majority are offshore.

Provincial Geology

Tectonic History

The Taranaki Basin was formed in the Late Cretaceous due to rifting associated with the breakup of Gondwana and the separation of New Zealand and Australia. This extension created a series of half-graben depocentres that were progressively filled with non-marine syn-rift strata followed by later marine transgression. The basin was part of a large passive margin setting during the Paleocene and Eocene that culminated in maximum marine transgression in the Oligocene with widespread limestone deposition. Tectonic compression and major uplift occurred during the Miocene and parts of the Taranaki Basin were inverted. The Pliocene to Recent has featured rapid progradation of the shelf and the development of thick clinoforms.[2]

Petroleum Geology

Reservoir Rocks

Potential reservoir rocks are present throughout the stratigraphic record. Discoveries from the Galleon-1 and Kawau-1A exploratory wells in the Canterbury and Great South Basin, respectively consists of non marine and shallow marine sandstones. Production from these wells also proved the reservoir to be a gas condensate. The most productive Taranaki Basin reservoir rocks are in Paleogene transgressive shoreline systems, as in the Kupe, Maui and Pohokura fields, and a variety of facies belts within Tertiary Neogene clastic depocentres. Oligocene to Early Miocene limestone with high fracture permeability is the reservoir in the Waihapa Field. Petroleum is also produced from Miocene and younger, deep-water turbidite sandstones in the Maari, Kaimiro and Ngatoro fields. Oil is known from Miocene volcaniclastics in the Kora-1 well and gas is present in Pliocene sands at Karewa; similar Neogene slope and basin floor fans are present in many New Zealand basins and gas shows have been encountered in East Coast Basin Miocene turbidites at Titihaoa-1. In the East Coast region, Pliocene and Pleistocene coquina limestone has favourable reservoir characteristics.[2][3]

Migration

Vertical fluid escape and lateral drainage through high permeability pathways is the main driver throughout the Taranaki. The flow of acidic rich fluids is also an important driving mechanism by the dissolution of carbonate cements creating very large pores in most Taranaki reservoirs

Seals

Seals are abundant in all potential petroleum basins and overpressures, indicative of fluid confinement within the stratigraphic sequence, are sometimes encountered during drilling. Seal rocks in most basins are marine mudstones deposited during both the passive margin transgressive phase and the regressive convergent margin phase. Those Oligocene and Early Miocene limestones which were not fractured during Neogene tectonism may also provide seals in many basins.

Traps

Traps are primarily structural collision Related late Tertiary tectonics created three primary structural trap types—faulted anticlines, overthrusts, and tilted fault blocks formed in the Neogene, though the Kupe Field also has elements of stratigraphic trapping.

Source Rock

Jurassic, mid-to Late Cretaceous and Paleogene coaly rocks, Cretaceous and Paleocene marine shales. Oil and gas generation started as early as the late creatoucus in the deep water of the Taranaki basin. This basin has had a varied burial history intermittently in different parts of the basin throughout the Cenozoic and is ongoing today in parts of the basin. The source rocks of Taranaki Basin consist of hydrogen-rich coals and terrigenous carbonaceous mudstones of the upper Cretaceous.[4]

Primary Geologic risks and uncertainties

Using a geology-based assessment methodology, the USGS estimated mean volumes of 487 million barrels of oil, 9.8 trillion cubic feet of gas, and 408 million barrels of natural gas liquids.[5] There is also considerable uncertainty with what the basement is composed of in the Taranaki Basin. (Basement)

Petroleum and Facility Engineering

Production is 80% from the Maui field which is a conventional reservoir that was founded in 1969 by a joint venture of Royal Dutch/Shell, British Petroleum and Todd Petroleum. Austrian oil company OMV is now owns and operates this conventional formation. With primary production coming from two platforms the Maui A and Maui B oil is then transported onshore for refining. Currently OMV is the only company that can explore for new oil and gas developments due to government restrictions.

Future Assessment

The Taranaki Basin produces from about 20 fields, from the giant Maui gas-condensate field (original gas reserves 3.4 tcf), to a number of small oil and gas fields of about 10 mmboe. Some 418 mmbbl of oil and 6190 bcf of gas had been produced by the end of 2011. All wells drilled so far have been onshore or on the shelf. Exploration has focused on four-way dip closures, horsts, rotated fault blocks, foreland folds and detached thrust sheets along the overthrust eastern margin of the basin. Petroleum has been encountered on a commercial scale at every stratigraphic level from Pliocene to Paleocene. Structural, stratigraphic and diagenetic trapping mechanisms have yet to be fully evaluated. Cretaceous reservoirs, especially those in the deepwater province, have not been drilled, with the first well in the deepwater province scheduled to be drilled in 2013/14.[6][7] With the drainage experience near shore the future of hydrocarbon development in the Taranaki is deepwater.

References

  1. [PDF]. (n.d.). Ministry of Business, Innovation and Employment. https://www.nzpam.govt.nz/assets/Uploads/doing-business/nz-petroleum-basins-part-one.pdf
  2. 2.0 2.1 Taranaki Basin. (n.d.). Retrieved from https://www.beachenergy.com.au/new-zealand/
  3. NZ-Petroleum-Basins-Part-One. (n.d.). Retrieved from https://www.nzpam.govt.nz/assets/Uploads/doing-business/nz-petroleum-basins-part-one.pdf
  4. Asquith, G., V. Bolandi, A. K., V. Bolandi, A. K., Breiman, L., B. Carpentier, A. H., Elkatatny, S., . . . P. Zhao, Z. M. (1982, January 01). Thermal maturity and TOC prediction using machine learning techniques: Case study from the Cretaceous–Paleocene source rock, Taranaki Basin, New Zealand. Retrieved from https://link.springer.com/article/10.1007/s13202-020-00906-4#Sec25
  5. Craig J. Wandrey, C. J. (n.d.). USGS Fact Sheet 2012–3139: Assessment of Undiscovered Oil and Gas Resources of the Cretaceous-Tertiary Composite Total Petroleum System, Taranaki Basin Assessment Unit, New Zealand. Retrieved from https://pubs.usgs.gov/fs/2012/3139/
  6. Taranaki Basin. (2020, July 09). Retrieved November 16, 2020, from https://en.wikipedia.org/wiki/Taranaki_Basin
  7. Science, G. (n.d.). Taranaki Basin. Retrieved November 16, 2020, from https://www.gns.cri.nz/Home/Our-Science/Energy-Futures/Oil-and-Gas/Products/Taranaki-Basin