NSBís unique gas fields
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Producers Magazine Preview: Fields power Utqiagvik, the northernmost city in U.S.
Near Point Barrow in northern Alaska, natural gas has accumulated in Jurassic-aged sandstone reservoirs that lie along the western and eastern margins of a buried, ancient meteorite impact crater, which is on the northern flank of the east-trending Barrow High.
In the aftermath of World War II, the federal government sponsored exploration in the National Petroleum Reserve-Alaska in a bid to improve domestic energy security. Drilling by U.S. Navy contractors began in the winter of 1948 and continued through 1987.
One impact of that activity was the discovery of three gas fields - South Barrow, East Barrow and Walakpa - near the community of Barrow (renamed Utqiaġvik in 2016), the North Slopeís biggest economic hub and population center (4,383 in 2017 Census).
According to the U.S. Department of Energyís National Energy Technology Laboratory, the Barrow Gas Fields Hydrate Study provided very strong evidence for the existence of hydrates updip of the East Barrow and Walakpa gas fields.
The South Barrow and East Barrow reservoirs have a stratigraphic setting similar to the Alpine oil field.
Walakpa, the most productive of the Barrow gas fields, is in the Pebble shale unit, a major North Slope source rock.
Walakpa has been proven to be methane-bearing at depths of 2,000-2,550 feet below sea level. The producing formation is a laterally continuous, south-dipping, Lower Cretaceous shelf sandstone.
Minimal investmentThe Barrow gas fields are unique in Alaskaís oil and gas industry because they are operated by a public entity - and because they are the only fields on the North Slope where natural gas is being used for something other than oil field operations.
The Barrow Gas Field Transfer Act of 1984 directed the Secretary of the Interior to convey subsurface estates of the South Barrow and East Barrow gas fields and the Walakpa gas discovery site, related support facilities, funds and other surrounding land interests to the North Slope Borough. This subsurface land transfer gave the NSB ownership of and authorization for exploration and harvesting of oil and gas within 320 acres of land.
Entitlements to energy transportation easements were provided within the Barrow Gas Field Transfer Act, allowing for easements of all purposes associated with the operation, maintenance, development, production, operation or transport of energy (including electricity) from the Barrow gas fields and Walakpa discovery site to Utqiaġvik, Wainwright and Atqasuk.
NSB has operated the gas fields for decades. The fields have generally required minimal development work, aside from a $92 million rejuvenation program launched in 2011 to combat declining production.
With that effort, the NSB commissioned three wells at the East Barrow field and three wells at the Walakpa field. By improving deliverability, the city of Utqiagvik could rely on natural gas for its energy needs even during cold snaps or during maintenance activities, instead of switching to diesel as an alternative.
Other improvements were also made, such as in 2017, NSB selected Taku Engineering to develop the design and construction bid package for work at the Walakpa gas field. The design included the replacement of the three generators, gas turbine heat recovery, fuel gas process improvements, supervisory control and data acquisition, remote operator controls and all other ancillary systems.
Taku also provided construction administration services for the project including owner representation and full-time on-site construction oversight. The design was completed in early 2018 and construction was completed in April 2019.
South Barrow gas fieldThe accumulation on the western margin of the meteorite impact crater is named the South Barrow gas pool, per the Alaska Oil and Gas Conservation Commission, or AOGCC. The South Barrow field was discovered by the Navy with the 2,505-foot South Barrow No. 2 well in 1949.
From 1948 through 1987, the commission reported that 13 wells were drilled, and one well, South Barrow 7, was subsequently deepened approximately 64 feet.
The South Barrow gas fieldís main natural gas reservoir is the Barrow sandstone, an informal member of the Kingak formation. This sandstone lies between the measured depths of 1,900 feet and 2,150 feet.
According to the commissionís records, regular production from the pool began in August 1949, peaked at 3.6 million cubic feet of gas per day in November 1981, and began to decline.
In 1990, the borough began to sporadically suspend production at South Barrow.
For the first half of 2011, the pool produced an average of 1.1 million cubic feet of gas per day from five wells.
Since July 2012, the pool produced only during winter months.
In November 2015, South Barrow averaged 461,000 cubic feet of gas per day from three wells.
After nearly six years of inconsistent production, South Barrow has now been producing regularly since May 2018.
In the year ending June 1, 2021, the South Barrow gas field produced some 199 thousand cubic feet per day, averaging 198.6 thousand cubic feet per day.
Cumulative production from South Barrow through 2020 was 24.0 billion cubic feet, according to the AOGCC.
East Barrow gas fieldThe U.S. Geological Survey discovered the East Barrow field with the South Barrow No. 2 well in 1949 at a measured and true vertical depth of 2,505 feet.
According to AOGCC, the main gas reservoir for the East Barrow field is the Barrow sandstone, an informal member of the Kingak formation. In South Barrow No. 12 well this sandstone lies between the measured depths of 1,940 feet and 2,132 feet.
It deposited in a marine environment, and it consists of silty, very fine to fine grained, moderately sorted sandstone that contains pyrite, siderite, glauconite and calcite and is commonly interbedded with siltstone and shale.
In the East Barrow field, porosity for the Barrow sandstone ranges from 2% to 28%, averages 18% and has a median value of 18%. Permeability for the sandstone ranges from 0.01 to 3295 millidarcies, averages 133 millidarcies, and has a median value of 13 millidarcies.
Reservoir quality rock also occurs within the Walakpa sandstone, Pebble shale, Torok formation, and the Sag River sandstone.
Drilling and testing of the East Barrow gas field began in 1974 and continued through 1990, the commission reported. During this time eight wells were drilled in the field: South Barrow 12, 14, 15, 17, 18, 19, 20, and East Barrow 21, per AOGCC.
Regular gas production from the pool began in December 1981, peaked at about 2.75 million cubic feet of gas per day in early 1983, and then began to decline, AOGCC said.
During the first quarter of 2011, the East Barrow gas pool produced an average of 448 thousand cubic feet of gas per day, and for 2015 the pool averaged 442 thousand cubic feet of gas per day. During the first six months of 2019, the pool averaged 392 thousand cubic feet of gas per day.
In the year ending June 1, 2021, the East Barrow gas field was producing an average of 334 thousand cubic feet per day.
Through the end of 2020, cumulative production from the field was 9.8 billion cubic feet, AOGCC reported.
Walakpa gas fieldWorking under a U.S. Navy contract, Husky Oil discovered the Walakpa field with the 3,666-foot Walakpa No. 1 well in the 1980s.
Southwest of Utqiaġvik, Walakpa has peaked above 5 million cubic feet per day numerous times in the decades since it went online in late 1992. In the year ending June 1, 2020, the field produced 1.3 billion cubic feet or nearly 3.6 million cubic feet per day, according to AOGCC, up from 12.8 billion cubic feet or more than 3.5 million cubic feet per day in the year prior.
In the year ending June 1, 2021, the Walakpa gas field produced an average of 3.7 million cubic feet per day, per AOGCC.
Cumulative production from Walakpa was 35.1 billion cubic feet through the end of 2020.