Nanushuk Formation

{{Short description|Geologic formation in the US state of Alaska}}

{{Infobox rockunit

| name = Nanushuk Formation

| image = Kaolinite - USGS bws00008.jpg

| caption = Kaolinite in sandstone from the Nanushuk Group

| type = Group

| age = Cretaceous

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| region = Alaska

| country = United States

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The Nanushuk Formation or Nanushuk Group is a geologic group in Alaska in westernmost National Petroleum Reserve in Alaska (NPR-A). Petroleum in these rocks likely was generated beneath Western Alaska North Slope and migrated northeastward into NPR-A. The formation preserves fossils dating back to the Albian-Cenomanian ages of the Cretaceous period. Its thickness varies from about 1500 to about 250 meters. Underneath the Nanushuk lies the Torok Formation.

Until 2015, for more than 50 years about 150 oil exploration wells had had almost zero success; However, in 2015, Repsol announced the Pikka oil pool and in 2016, ConocoPhilips announced the Willow project.

As of 2017, the U.S. Geological Survey estimated that there were 8.7 billion barrels of oil and 25 trillion cubic feet of natural gas in the Nanushuk and Torok Formations, much more than previously estimated.

File:Kokolik River Oil Sand.jpg

Geology

The Nanushuk Formation together with the Torok Formation below it forms a huge wedge of sediment deposited in a deep water basin and stretches from north of the Brooks Range beneath the Alaska North Slope to the adjacent offshore. It was deposited in shallow water and includes potential reservoirs in deltaic, shoreface, and fluvial sandstones. The USGS found large-scale folds and faults in the South of the formation and evidence, that the rocks have been heated to temperatures at which oil is converted to natural gas.{{Cite journal |last=David W. Houseknecht, Richard O. Lease, Christopher J. Schenk, Tracey J. Mercier, William A. Rouse, Palma J. Botterell, Katherine J. Whidden, Christopher P. Garrity, Kristen A. Lewis, Samuel J. Heller, William H. Craddock, Timothy R. Klett, Phuong A. Le, Rebecca A. Smith, Marilyn E. Tennyson, Stephanie B. Gaswirth, Cheryl A. Woodall, Michael E. Brownfield, Heidi M. Leathers-Miller, Thomas M. Finn |date=2017 |title=Assessment of undiscovered oil and gas resources in the Cretaceous Nanushuk and Torok Formations, Alaska North Slope, and summary of resource potential of the National Petroleum Reserve in Alaska, 2017 |url=https://www.usgs.gov/publications/assessment-undiscovered-oil-and-gas-resources-cretaceous-nanushuk-and-torok-formations |language=en |doi=10.3133/fs20173088 |journal=U.S. Geological Survey|series=Fact Sheet |doi-access=free |url-access=subscription }}{{rp|2}}

The thickness of the Nanushuk Formation varies from about 1500 to about 250 meters.{{cite journal|author=Anthony R. Fiorillo, Paul J. McCarthy, Grant Shimer, Marina B. Suarez, Ryuji Takasaki, Tsogtbaatar Chinzorig, Yoshitsugu Kobayashi, Paul O’Sullivan, Eric Orphys|year=2024|url=https://www.researchgate.net/publication/377809922|title=New Dinosaur Ichnological, Sedimentological, and Geochemical Data from a Cretaceous High-Latitude Terrestrial Greenhouse Ecosystem, Nanushuk Formation, North Slope, Alaska|journal=Geosciences|volume=14|issue=2|page=36|doi=10.3390/geosciences14020036|doi-access=free |bibcode=2024Geosc..14...36F }}

Paleontology

The formation preserves fossils dating back to the Albian-Cenomanian ages of the Cretaceous period. Many fossilized dinosaur footprints and wood fragments have been found in this formation. Some tree trunks reached up to 58 cm in diameter. Ichnotaxa of Nanushuk Formation include avian and non-avian theropods, quadrupedal ornithischians and bipedal ornithischians. The latter make up a noticeable majority, 59% of the finds near the Kukpowruk River.

History of oil discoveries

Before 2015, over a period of more than 50 years about 150 oil exploration wells had been drilled into the Nanushuk and Torok Formations, yet oil production had had almost zero success finding one small oil pool with less than 50 million barrels in place.

However, as of 2017, the U.S. Geological Survey estimated that there were 8.7 billion barrels of oil and 25 trillion cubic feet of natural gas in the Nanushuk and Torok Formations, much more than previously estimated. These discoveries were possible, because of technological advancements like three-dimensional seismic data processing, extended reach drilling.{{Cite journal |last1=Masterson |first1=W. Dallam |last2=Holba |first2=Albert G. |date=June 2021 |title=North Alaska Super Basin: Petroleum systems of the central Alaskan North Slope, United States |url=http://archives.datapages.com/data/doi/10.1306/01282120057 |journal=AAPG Bulletin |language=en |volume=105 |issue=6 |pages=1233–1291 |doi=10.1306/01282120057 |bibcode=2021BAAPG.105.1233M |issn=0149-1423|url-access=subscription }}

=Pikka and Horseshoe oil pools=

In 2013, Repsol and Armstrong Energy discovered the Pikka oil field by drilling a discovery well they called Qugruk 3.{{Cite web |date=2020 |title=Pikka Unit Nanushuk Development Project, North Slope of Alaska, USA |url=https://www.nsenergybusiness.com/projects/pikka-nanushuk-development-north-slope-alaska/ |access-date=2024-05-16 |website=NS Energy |language=en-US}}

In 2015, they announced the Pikka oil pool to the public. In 2017, an extension of the same oil pool at "Horseshoe", 21 miles south of the Pikka discovery was confirmed.{{Cite news |last=Mackenzie |first=Wood |date=2017-03-21 |title=Massive discovery breathes life into Alaska's North Slope |url=https://www.woodmac.com/news/editorial/massive-discovery-alaskas-north-slope/ |access-date=2024-05-16 |language=en}} Per USGS in 2017, industry estimated this Pikka-Horseshoe pool may hold more than {{convert|1.0|e9oilbbl|e6m3|abbr=off|spell=us}}. In 2017 Armstrong sold its interests to Oil Search, an Australian-listed oil and gas company.{{Cite news |last= Darren Barbee |date=2017-11-03 |title=Armstrong Selling Stake In Largest US Oil Discovery In Decades |url=https://www.hartenergy.com/exclusives/armstrong-selling-stake-largest-us-oil-discovery-decades-30487 |access-date=2024-05-16 |work=Hart Energy |language=en}} The so called "Nanushuk development project" is operated by Oil Search at 51% interest, and Repsol at 49% interest.

More remarkable was the pervasive presence of bioturbation with worm burrows crossing between the silts and sands. Under normal circumstances vertical flow would be much reduced in stacked silt and shale sequences but the bioturbation was sufficient to guarantee efficient vertical recovery.{{Cite web |last1=Sommer |first1=Jesse V. |last2=Dorrington |first2=Kevin |last3=VanDenburg |first3=Colby |last4=Bonelli, Jr. |first4=James R. |last5=Alonso |first5=José Luis Algibez |date=1 January 2021 |title=11 Pikka Field and the Opening of the Nanushuk Play, North Slope, Alaska |url=https://pubs.geoscienceworld.org/books/book/2360/chapter-abstract/133513125/11-Pikka-Field-and-the-Opening-of-the-Nanushuk?redirectedFrom=PDF |website=GeoScienceWorld}}

In 2020, the Pikka Unit was expected to be the first development project to begin oil production in the Nanushuk formation, when Front-end engineering and design had started, though a final investment decision on the project was still pending. In May 2024 Repsol and Santos Limited subsidiary Oil Search were looking to sell 20-25% of their non-operating interest in the Pikka unit.{{Cite news |date=May 12, 2024 |title=Oil patch insider: Santos, Repsol reportedly look to sell 20-25% Pikka; Pokon DEC head - |url=https://www.petroleumnews.com/pntruncate/814646232.shtml |access-date=2024-05-16 |work=Petroleum News}} one month after they had asked for a permit to hydraulic fracking.{{Cite news |date=May 12, 2024 |title=Part 2: Nanushuk Oil Pool AIO for Pikka enhanced oil recovery |url=https://www.petroleumnews.com/pntruncate/604148784.shtml |access-date=2024-05-16 |work=Petroleum News}}

In 2022, the Alaska Department of Natural Resources Division of Oil and Gas approved that Oil Search forms and operates the Horseshoe unit.{{Cite news |date=March 27, 2022 |title=Horseshoe unit approved |url=https://www.petroleumnews.com/pntruncate/714587339.shtml |access-date=2024-05-16 |work=Petroleum News}}

=Willow oil pool=

In 2017, ConocoPhillips announced discovery of the Willow oil pool in the Nanushuk Formation with estimated resources of more than {{convert|300|e6oilbbl|e6m3|abbr=off|spell=us}}.

Taxonomy

The Nanushuk was reduced in rank from geologic group to geological formation and many of its subunit terms were completely abandoned.{{Cite journal |last1=Mull |first1=Charles G. |last2=Houseknecht |first2=David W. |last3=Bird |first3=Kenneth J. |date=2003 |title=Revised Cretaceous and Tertiary stratigraphic nomenclature in the Colville Basin, Northern Alaska |url=http://dx.doi.org/10.3133/pp1673 |journal=Professional Paper |doi=10.3133/pp1673 |issn=2330-7102|url-access=subscription }}

The Corwin Formation, Chandler Formation along with its members the Killik Tongue, and Niakogon Tongue, were all reassigned{{when|date=May 2024}} to the upper or nonmarine section of the Nanushuk.{{cn|date=May 2024}} The Grandstand Formation and Topagoruk Formation were reassigned{{when|date=May 2024}} to the middle or transitional portion between the lower marine and upper nonmarine.{{cn|date=June 2024}} The Kukpowruk Formation, Ninuluk Formation, and Tuktu Formation were reassigned{{when|date=May 2024}} to the lower marine section. The Hatbox Tongue's name was changed{{when|date=May 2024}} to the Killik Tongue, both terms are{{when|date=May 2024}} no longer in use.{{Cite web |title=National Geologic Map Database |url=https://ngmdb.usgs.gov/Geolex/results?ageRange=-624,0&minage=holocene&maxage=archean&Unit=Nanushuk |access-date=2024-03-27 |website=ngmdb.usgs.gov}}