State approves adding 4 leases to Prudhoe Bay unit, 9,053 acres
How does a large oil and gas unit grow? Typically, by absorbing acreage on its edges. In the case of a new Prudhoe Bay expansion, by absorbing acreage which was previously part of smaller and now defunct units.
The Prudhoe Bay unit, Alaska’s most prolific field, and at 254,235.32 acres, also the largest physically, has just been expanded by 9,053.11 acres, four leases.
(See map in the online issue PDF)
In a Jan. 12 approval of an application by Prudhoe operator Hilcorp North Slope, the Department of Natural Resources’ Division of Oil and Gas said, “lands included in the expansion area were part of the now terminated Gwydyr Bay, Beechey Point, or Dewline Units.”
One of the leases, ADL 47466, was issued in 1969 and was most recently held by ConocoPhillips Alaska. The other three leases were most recently acquired by Hilcorp North Slope in 2021 and cross assigned in 2022 to ConocoPhillips Alaska, ExxonMobil Alaska and Chevron U.S.A. ADL 47466 has also been cross assigned and is now held jointly by the Prudhoe working interest owners, ConocoPhillips, ExxonMobil, Hilcorp and Chevron.
The four leases are west and northwest of the Point McIntyre drill pad, adjacent to the north-central edge of Prudhoe, the division said.
ADL 47466ADL 47466 was committed to the Gwydyr Bay unit in 1979. A well, Gwydyr Bay State 2A, was drilled on the lease in 1981, and certified capable of producing following plugging and abandonment. The division no longer recognizes P&A’s wells as capable of producing and ordered the lease - then held by ConocoPhillips Alaska - into production in 2013.
The company requested a 5-year extension in 2014, a request the division denied, but the date to bring the well into production was extended to 2016. ConocoPhillips appealed and a decision, issued in 2020, required the company to submit a plan to bring the lease into production by May 2021. ConocoPhillips submitted a plan in April 2020 and has since fulfilled requirements of that plan, the division said.
Potential on the acreageThe Prudhoe Bay unit was formed in 1977 to develop oil discovered in 1968 at Prudhoe Bay State No. 1 in the Triassic Ivishak and Sag sandstones of the Sadlerochit Group, with eight expansions approved since then, the most recent in 2009, the division said.
Hamilton Brothers Oil Co.’s Point Storkersen 1 exploration penetrated the Kuparuk, Sag, Ivishak and Lisburne reservoirs in the expansion area in 1969, the division said, on what is now ADL 393965, one of the three issued to Hilcorp in 2021.
ExxonMobil took over as operator of the Point Storkersen 1 well in 1973, and initial P&A work began in 1974 with final closure of well site remediation in 2004. Drill stem testing of the Ivishak and Sag reservoirs at the well had yielded rates of 735 and 312 stock tank barrels per day, the division said.
Three additional exploration wells penetrated the Kuparuk, Sag and Ivishak reservoirs in the expansion area, the division said: Kuparuk Delta 51-1, Kuparuk Delta 51-2 (both drilled by Hamilton Brothers) and Gwydyr Bay State 2 (drilled by Conoco in 1980).
The division said the Gwydyr Bay well only penetrated the Brookian formation before requiring sidetrack operations.
The four wells are all on ADL 47466.
The Kuparuk Delta 51-1 had flows only from the Ivishak, which had a very high water cut, 95%, with no flow rates recorded, the division said.
Kuparuk Delta 51-2 had Kuparuk flows of 350 bpd and no water, Ivishak flows of 695 bpd at 59% water-cut and no flows for the Sag.
Gwydyr 2A (the sidetrack) had Kuparuk flows of 740 bpd with no water, Ivishak flows of 3,540 bpd at 28% water-cut and no flow test for the Sag.
The division said the commercial oil rates from the Ivishak allowed the Gwydyr 2A to be certified.
BP Exploration (Alaska) drilled the Point McIntyre 12 in 1991 from the Point McIntyre pad. The division said the well penetrated the Kuparuk reservoir in ADL 393966 (one of the three leases issued to Hilcorp in 2021) and was logged but not flow tested.
BP (then the Prudhoe operator) acquired high density broadband 3D seismic over the expansion area in 2019, the division said.
Hilcorp provided confidential data, but the division said that based on non-confidential data “there are multiple reservoirs and potential hydrocarbon accumulations located in the proposed PBU expansion area.”
Potential hydrocarbonsIvishak is the primary producing formation at Prudhoe, the division said, and in addition to producing from both the initial participating area and Raven participating area at Prudhoe, it is also in production at Duck Island and Northstar.
“Hilcorp integrated available subsurface control from well data with seismic attributes to predict the presence of Ivishak sands within the proposed expansion area. Ivishak sand structure and net pay maps were created and one distinct Ivishak potential hydrocarbon accumulation target was identified within the proposed expansion area,” the division said.
The division said the Sag River reservoir has diminished quality compared to the Ivishak with permeability the greatest challenge. Sag River is in production at Milne Point and at the IPA in Prudhoe.
Hilcorp has identified one distinct Sag River potential accumulation within the proposed expansion area, the division said.
“The Kuparuk sandstone is one of the most prolific oil-bearing reservoirs on the North Slope,” the division said, and is in production at the Kuparuk River, Oooguruk, Milne Point and Colville River units, in addition to the Aurora, Borealis and Midnight Sun participating areas at Prudhoe.
Hilcorp has identified three distinct Kuparuk potential hydrocarbon accumulations within the proposed expansion area.
Exploration planHilcorp submitted an initial plan of exploration for the expansion area as part of the application and proposes to drill one well within three years targeting one of the five described bottomhole locations, with any future development and drilling to depend on results from the initial well.
The division said the initial plan of exploration is effective Jan. 12, 2023, through Jan. 12, 2026, with a second POE due Nov. 13, 2025.
In its POE for the expansion area, Hilcorp said plans for the fourth quarter of 2023 “currently include targets within potential hydrocarbon accumulations extending across the northern two leases, ADL 47466 and ADL 393965” in the Kuparuk (at an approximate depth of -8,850’ TVDSS), in the Sag River and the Ivishak (at an approximate depth of -10,600’ TVDSS), and potential targets within potential hydrocarbon accumulations extending across the southern two leases, ADL 393966 and ADL 393967, in the Kuparuk (at an approximate depth of -8,900’ TVDSS).”
Hilcorp said preparation of a comprehensive drilling plan for an extended reach appraisal/development well, Gwydyr 1, is underway, along with regional analysis of reservoir quality for both the Sag and Kuparuk formations, and stimulation plans for Gwydyr 1.