Cross Island

Off-shore, Western North Slope

  • Key Features
    • Project lies 7 miles north of Prudhoe Bay Unit (15.2 BBO), 8 miles north of Duck Island Unit (585 MMBO), and 10 miles east of Northstar Unit (196 MMBO).
    • Upthrown to the Dinken Graben and on trend with Shell/Eni/Repsol OCS leasehold to the west.
    • Beaufort Sea #54-1/1A Wells: drilled on Cross Island; numerous oil shows in a 4,541’ interval above basement.
    • No Name Island Well had oil shows in convenional cores in the Kingak, Sag River, and Ivishak. DST in Ivishak flowed 1,263 BWPD.
  • Leases
    • ADL 391558, 391559, 391560, 391561, 391562, 391563, 391564   (9/30/2017)

Geologic Summary by: D. T. Gross (3/14/2012)

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The Donkel/Cade Cross Island Project is comprised of seven leases totaling 13,972 acres located approximately 11 miles north of the Beaufort Sea shoreline in State of Alaska waters on the north side of Cross Island. The project area lies south and upthrown to the regional NW-SE fault that defines the southern boundary of the Dinken Graben, but is immediately north and upthrown to a “mini-graben” that displaces the basement and supra-basement strata. Numerous fields are located near the Donkel/Cade leasehold with the project being only 8 miles due north of the Duck Island Unit (Endicott Field), 7 miles northeast of the Prudhoe Bay Unit, 10 miles east of the Northstar Unit, and 12 miles east-northeast of the Dewline Unit. Additionally, the Cross Island Project is 7 miles ESE along trend from the extensive 64-lease position held by Shell, ENI, and Repsol (40%, 40%, 20% respectively). Their leasehold is also upthrown to the southern boundary of the Dinken Graben and encompasses the Federal OCS acreage closest to the northern edges of the Kuparuk River / Prudhoe Bay area fields.

The Prudhoe Bay Field’s cumulative production is 12.2 billion barrels of oil from strata ranging in age from Carboniferous to Cretaceous. The Endicott Field (Duck Island Unit) has produced 471 million barrels of oil primarily from the Mississippian Kekiktik Conglomerate with a contribution from the Lower Triassic Ivishak Formation. The Northstar Field’s cumulative production is 153 MMBO from the Triassic Sag River, Shublik, and Ivishak Formations. The lithology of this section is comprised of delta-front sandstones and shales of the Ivishak that transition upwards into the shelf deposits of the Shublik and Sag River. The Northstar trap is an anticline that is bounded by a fault to the north and which displays structural closure to the east, south, and west. Though it has yet to begin production, the Dewline Unit was formed in 2009 and the Dewline #1 was drilled in March, 2009 to test the Lower Cretaceous to Lower Triassic section that contains the Kuparuk River Formation, Sag River Formation, and the Ivishak Sandstone. The objective reservoirs are structural-stratigraphic traps downthrown to the north of the Prudhoe Fault that defines the northern border of the Prudhoe Bay Field. Unit operators had announced plans to drill Dewline #2 in early 2012 and are required to drill a third well by May 2013.

Additional accumulations peripheral to the Prudhoe Bay Unit are presently being pursued by Brooks Range Petroleum Corporation (BRPC) at its proposed North Shore Development Project. They plan to produce oil from several relatively small, isolated hydrocarbon accumulations within the 15,000-foot horizontal drilling radius of their proposed pad. Two Triassic productive horizons, the Ivishak and Sag River sands, will be produced from each prospect using horizontal drilling technology and long-reach wells to recover between 5 and 10 million barrels of oil.

Two wells have been drilled previously on the Cross Island leasehold on its southern margin. The Beaufort Sea #54-1 and the Beaufort Sea #54-1A sidetrack were both drilled by Gulf Oil Corporation during the winter season of 1983-84 in the southeastern quadrant of lease ADL 391561. The wells were designed to evaluate the known Mesozoic productive interval of the area as well as the pre-Mississippian section above economic basement. The Beaufort Sea #54-1 was drilled to a depth of 14,538’ MD (14,244’ TVD) and penetrated the basement Devonian(?) argillite at 14,012’ MD. The well encountered the Jurassic Kingak Formation at 12,440’ MD, the Triassic Sag River at 13,906’ MD, and the Shublik at 13,953’ MD. (The Ivishak, Lisburne, and Kekiktuk formations were missing). One conventional core was taken in the basement argillite (14,510-38’ MD) which had neither hydrocarbon shows nor porosity. Sidewall cores were taken throughout the interval from 9,465’ to 14,500’ MD. They showed the section above basement to be a mixture of sandstones, siltstones, and shales that displayed numerous shows of yellow fluorescence, streaming cuts, and even possible dead oil. The well was plugged back to 12,550’ and the sidetrack 54-1A was drilled with a bottomhole location approximately 640’ to the northeast at a depth of 14,534’ MD (14,240’ TVD). The sidetrack encountered the basement approximately 500’ deeper at 14,209 TVD than the #54-1 well, as well as a deeper test of the Sag River at 14,059’ TVD, indicating that neither well tested strata upthrown and north of the “mini- graben” No sidewall cores were taken in #54-1A and the only log run was a GR/TDT/CCL run inside casing due to hole problems. The well was plugged and abandoned due to the lack of economic hydrocarbons.

Four miles due south of the #54-1 and #54-1A wells, Amoco Production Company (BPAP) had earlier drilled the No Name Island #1 well in April, 1982 to a depth of 14,350’ MD (11,345’ TVD). The well encountered the “Base Delta” at 9,375’ (7,486’ TVD), the “Prudhoe Bay Unconformity” at 13,200’ (10,411’ TVD), the Sag River Sandstone at 13,620’ (10,748’ TVD), the Shublik at 13,695’ (10,810’ TVD), the Ivishak at 13,800’ (10,896’ TVD), and the basement argillite at 14,200’ (11,226’ TVD). Three conventional cores were taken during drilling. The first appears to have been taken in the Jurassic Kingak Formation (12,924-53’ MD) and revealed thin shale and fine sand cycles which displayed gold fluorescence. A core in the Triassic Lower Sag River / Upper Shublik (13,667’-13,726’ MD) was comprised of very fine to fine grained sandstones with oil staining, good cuts, and fluorescence. One horizon had an erosive base overlain with rip-up conglomerates. The deepest core, cut in the Ivishak Formation (13,866’- 13,896’ MD), was composed entirely of fine to medium grained sandstone with oil staining. A drillstem test taken over this interval (Test #1, 13,849-979’ MD) revealed very good permeability with a flow rate of 1,263 BWPD. The second test (DST #2, 13,644-73’ MD) in the Sag River returned 28 barrels of gas and mud cut water with a film of oil. DST #3 (12,880-910’) was taken above the “Prudhoe Bay Unconformity” in the Kingak(?) and flowed gas at a rate of 60 MCFGPD. Though the well was plugged and abandoned due to the lack of economic hydrocarbons, the State of Alaska agreed to Amoco’s request to extend the confidentiality of its data beyond the normal 24 months until 30 days after the Federal OCS Sale 87 (held on October 1, 1984).

Continuing south-southeast another five miles, Exxon drilled both the OCS-Y-191 Beechey Point #1 and #2 wells in the 1981-82 drilling season from the same man-made island. The #1 well was a straight hole that appears to have been targeting the Ivishak, Lisburne, and Kektiktuk formations. Nine conventional cores were cut over an interval from 10,242’ to 11,638’ MD which showed oil staining from the Permian-Triassic (10,230’ MD) to the top of Pre- Mississippian basement (11,570’ MD). The well penetrated and set casing into basement and proceeded to test a thin 125’ Permian-Triassic section and the Lisburne Formation. Both formations proved to be wet as shown by DST #1 in the upper Lisburne (10,346’-412’ MD) which produced 90 BWPD and DST #2 in the Ivishak - Ledge Sandstone (10,234’-256’ MD) which produced 168 BWPD. The Beechey Point #2 well was drilled as a directional hole which deviated 6,265’ to the southeast. The well cut conventional cores in the interval below the LCU (12,490’ MD) but above the Kayak Shale (12,578’ MD) which showed the section to be composed of mudstones and oil-stained silty sandstones (12,522’-571’ MD). Similarly, a core cut in the Kekiktuk Formation showed it to be also composed of shales and oil-stained sandstones (12,736’-776’ MD). Cased-hole drillstem tests proved that the cored intervals were nonproductive. In the Kekiktuk Formation, DST #1 (12,764’-774’ MD; 12,835’-844’ MD) reversed out 76 barrels of 15 API oil and DST #2 (12,700’-716’ MD) flowed 152 BWPD. In the interval between the LCU and Kayak Shale, DST #3 (12,470’-576’ MD) reversed out only 6 barrels of water. However in an uphole section, testing did prove that the prodelta strata of the Canning Formation could be productive and the well was suspended on 3/15/82. Despite a report of borehole damage, DST #4A flowed 186 BOPD (21 API; 11,438’-458’ MD) and DST #4B flowed 224 BOPD (21 API; 11,438’-458’ MD, 11,470’-478’ MD, 11,483’-500’ MD).

Thus, well log and seismic data combined show that the Cross Island Project acreage is essentially untested. Though the missing sub-Shublik Formation strata in the Beaufort Sea #54-1 and #54-1A wells are probably due to erosion, there remains a possibility that faulting may have been a factor and that some of this section may exist upthrown to the north of the wells. A more likely target horizon would be the Upper Triassic Sag River Sandstone which had oil shows in these wells, just as it did in the No Name Island #1 well to the south. Also, the suspended Beechey Point #2 well demonstrated that the overlying prodelta Canning Formation strata are capable of production rates in excess of 200 BOPD and seismic data suggest the likelihood of both stratigraphic and fault trapping mechanisms across the project area.