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Introduction & Study Area
The Kuparuk River Oil Field is located upon the Alaskan Arctic plain roughly 260 miles north of the Arctic Circle. The field covers about 300 mi^2 and is described as a frontier field, as it is relatively inaccessible. The field was discovered in April 1969 following the drilling of multiple exploration wells in the nearby vicinity as the neighboring Prudhoe field targeting Pre-Cretaceous reservoirs which sub-cropped a major unconformity. The BP Alaska/Sinclair Oil Ungu well was drilled about 30 miles to the west of the Prudhoe field and drill-stem test 1 flowed oil at a rate of 1,056 bbl/day from porous Cretaceous sandstones, thus marking the discovery of the Kuparuk River Oil Field.

The field was leased out by BP Alaska Exploration Inc., Atlantic Field Rich Co., and Sohio Alaskan Petroleum Co. Between 1970 and 1980, more than 25 wells have been drilled in this oil field and additionally connects to the Trans-Alaska Pipeline System via 26 miles of direct Kuparuk pipeline.



Regional Geology & Basin Development
The Kuparuk River Oil Field is found in the Colville-Prudhoe Basin. It lies just near the Barrow Arch structure, north of the Brooks Mountain Range and south of the Canada Basin.

The dominant trapping mechanism for hydrocarbons in this oil field is Stratigraphic pinch-out and truncation of the reservoir at a local unconformity near the southern and western flanks of a southeast plunging antiform.

Rifting began within the basin in the early Cretaceous prior to the deposition of the Ugnuravik Group. The region is upon a passive continental margin and the rifting sequence is broken up into three stages of development: the rift onset phase, the infra-rift phase, and the breakup phase.

The rift onset phase occurred roughly ~50 Ma years prior to continental breakup and is attributed to crustal doming of the incipient rift. The uplift is a result of thermal activity in the upper mantle which left behind a resultant rift onset phase unconformity at the base of the Ugnuravik Group.

The infra-rift phase produced axial metamorphism in the deep crust which lead to a large collapse of the central graben block. Rates of deposition for continental, fluvial-deltaic and marginal marine environments increased following the collapse, along with minor angular unconformities. The Ugnuravik Group and Kuparuk reservoir are considered to be infra-rift sediments as they were deposited during early development stages of the continental margin.

About 5-10 Ma years prior to the breakup phase, the intensity of relative uplift and subsidence increases with a breakup unconformity marking the onset. This results in a large-scale marine transgression followed by a subsidence-induced migration of depocenters in the progradational overlying wedge. The hiatus at the top of the Ugnuravik Group has been interpreted to be the breakup unconformity in the Colville-Prudhoe Basin.

Infilling of the Colville-Prudhoe Basin began during the infra-rift phase following the collapse of the central graben block. After the collapse and when subsidence begins, the basin is infilled over time with continental, fluvial-deltaic, and marine sediments.

Faulting and uplift then occurs as rifting begins to conclude near the truncating flanks of the antiform structure, which then acts as a trapping mechanism for hydrocarbons and kerogens of the Kuparuk pool.

Stratigraphy & Depositional Environment
Stratigraphic Units and Lithologies table The units above can be grouped together into four distinct mega-sequences:

Brookian Mega-Sequence
The Brookian mega-sequence contains units from the early Cretaceous to the Holocene. The mega-sequence records stratigraphic response to convergent tectonism associated with thrusting of the Brooks Mountain Range and Colville-Prudhoe Basin in the early Cretaceous. The basin depocenters shift positions multiple times between the Cenomanian and Holocene and are described as hydrocarbon kitchens. Hydrocarbons in the depocenter eventually mature and migrate under burial weight and compaction.

Beaufortian Mega-Sequence
The Beaufortian mega-sequence contains units from the late Triassic to early Cretaceous. The mega-sequence records the major rifting event in the middle Jurassic within the prograding Kingak shale formation. The upper portion of the mega-sequence describes the basin response to the final stages of rift tectonics during the opening of the northbound Canada basin and widespread development of the Lower Cretaceous Unconformity.

Ellesmarian Mega-Sequence
The Ellesmarian mega-sequence contains units from the late Devonian to the late Triassic. The mega sequence contains fluvial sandstones and coals which makes up a large portion of the hydrocarbon reservoirs in this oil field. Some of the upper units within this mega-sequence were subject to erosion and were affected by the Lower Cretaceous Unconformity following basin thinning and truncation.

Franklinian Mega-Sequence
Basement units

Petroleum Systems
The seal structure within the Kuparuk River Oil Field is made up of primarily silty non-porous mudstones and marine siltstones of the HRZ Formation and in some wells the upper portion of the Kalubik Formation.

Hydrocarbon reservoirs within the Kuparuk River Oil Field consists of most of the Cretaceous Ugnuravik Group, but most prominent reservoirs are within the porous sandstones of the Kuparuk Formation. The kerogens and hydrocarbons from the underlying source rocks migrate upwards over time and eventually are sealed and trapped within the reservoir.

The source rocks for the Kuparuk River Oil Field can be broken into oil source rocks and gas source rocks. The oil source rocks are Triassic Shublik Formation and the Jurassic Kingak Shale Formation as both units have very large total organic carbon content and a large quantity of kerogens present. The Cretaceous HRZ unit as well is a source for oil, though organic content is much less than the Shublik and Kingak Formations. The gas source rocks are found deeper within the Carboniferous Kekiktuk Conglomerate Formation. The same kerogens within the oil source rocks are found in the gas source rocks, though the coal within the Kekiktuk Conglomerate Formation absorbs kerogens until further burial and maturity. The absorbed kerogens eventually crack from oil to gas at greater temperature and depth.

The trapping mechanism for the Kuparuk River Oil Field is found within the Lower Cretaceous Unconformity structure and coincides with truncation, stratigraphic pinch-out, and faulting of the Colville-Prudhoe Basin at the outer flanks of the antiform structure. Truncation and faulting of the antiform began following the breakup phase of the rifting sequence.

The petroleum migration pathway begins within the trough kitchen as petroleum from the Shublik Formation is expelled downward into the Ivishak carrier system, which is located between the Shublik Formation and the Kekiktuk Conglomerate Formation. The migrating petroleum is then mixed with the upward-migrating Kekiktuk gases. This is then followed by northward migration of the mixed oil and gas in the Ivishak, where it then contacts the Lower Cretaceous Unconformity structure and the reservoir sands of the lower Kuparuk Formation. Finally, the petroleum continues to migrate southward within the porous sandstones of the Kuparuk Formation to the Colville High and formed the Kuparuk River field accumulation.

Oil composition was determined and correlated from 15 conventional core samples from wells upon Alaska's North Slope. Using chromatographic and carbon isotopic data, most of the wells reported both low and high sulfur concentrations within the oil. Additionally, it was found that vitrinite reflectance increased more rapidly within the southern wells of the field leading up to the Brooks Mountain Range. The two sulfur concentrations allowed further classification of the oil based on δ34S to an isotopically light type known as Simpson-Umiat and a heavy type known as Barrow-Prudhoe.

Production & Business
The potential recoverable reserves of the Kuparuk River Oil Field are estimated to be about 1.0-1.5 billion stock tank bbl. The large recoverable volume of petroleum makes this oil field one of the largest in the United States.

Additionally, the oil field is connected to the Trans-Alaska Pipeline system to effectively transport the recovered petroleum to more populated regions for distribution and processing. The pipeline system was originally constructed between 1975 and 1977 during the United States Gas Crunch, and consists of about 800 miles (1,287 km) of pipeline and 12 pumping stations running from Prudhoe Bay to Valdez, Alaska. The Kuparuk River Oil Field is connected to the Trans-Alaska Pipeline System via 26 miles of direct Kuparuk pipeline to connect to the large TAPS pipeline system.