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State approves Northstar expansion Allows Hilcorp Alaska to enlarge the Hooligan participating area vertically to include the Kuparuk A sands as well as the C sands ALAN BAILEY Petroleum News
Alaska’s Division of Oil and Gas has approved an application by Hilcorp Alaska to expand the vertical extent of the Hooligan participating area in the Northstar oil field. The participating area had previously included the oil-bearing Kuparuk C sands and, with the expansion, now encompasses the deeper Kuparuk A sands.
The field straddles state and federal leases on the border of state nearshore waters and the federal outer continental shelf of the Beaufort Sea.
Since the field first came into production in 2001, oil has come from a reservoir in the Ivishak formation, equivalent to the main reservoir of the onshore Prudhoe Bay oil field. In 2006 BP, the then Northstar field operator, began testing natural gas and condensate production from shallower Kuparuk sands. Sustained production from a single well, the NS-08, in the Kuparuk started in 2010. In 2012 the company applied for the designation of the Kuparuk as the Hooligan participating area. The Kuparuk at Northstar is equivalent to the reservoir rocks of the onshore Kuparuk River field.
But the Hooligan participating area only included the Kuparuk C sands, one of three sand intervals in the Kuparuk formation. In August 2016 another of the Northstar wells, the NS-18 well, began gas and condensate production from the deeper Kuparuk A sands: Hence the need for a participating area expansion.
Gas injected in Ivishak The Kuparuk gas is injected into Northstar’s Ivishak reservoir for enhanced oil recovery from that reservoir. Petroleum News understands from Hilcorp that the Kuparuk condensate is separated from the gas and exported from Northstar along with the liquids from the field’s Ivishak production.
Given that the Kuparuk A is capable of hydrocarbon production or of contributing to production in paying quantities, the division has decided that the expansion of the Hooligan participating area is appropriate and has backdated the expansion to Aug. 1, the first day of the month when Kuparuk A production began.
Cumulative gas production from the NS-08 well through December 2016 was 78.07 billion standard cubic feet, while the well has produced about 3 million barrels of condensate during that time, the approval document says. On Dec. 17, 2016, the NS-18 was perforated in the Kuparuk C, thus initiating co-mingled production from both the A and the C sands through that well - by the end of December the NS-18 well had a cumulative production of 2.25 billion cubic feet of gas, since the start of production from the A sands in August. NS-18 is currently producing condensate at the rate of 1.13 barrels per day, the approval document says.
Delineated from well penetrations The approval document also says that the more than 30 exploration and development wells that pass though the Kuparuk on their way to the deeper Ivishak have enabled a delineation of the Kuparuk hydrocarbon accumulation. The hydrocarbons lie in an area bounded by geologic faults to the north, west and south, while the structural dip or inclination of the reservoir limits the extent of the accumulation to the east. The gross thickness of the Kuparuk formation in the Northstar unit ranges from less than 200 feet to 400 feet. Oil found in the Kuparuk is relatively light, having an API gravity of 30, the approval document said. Diane Hunt, the Division of Oil and Gas external relations coordinator, told Petroleum News that the oil was encountered in sub-commercial quantities by the Northstar No. 1 well, outside the Hooligan participating area.
The Kuparuk C member, within the Kuparuk formation, ranges in thickness from 30 feet to more than 100 feet, with a highly variable ratio of net pay thickness to gross thickness. The rock unit includes sandstones, siltstones, shaley sandstones and shales. Deposition took place on a rift margin in an offshore marine or marine shelf environment. Faulting that took place at the same time that the sediments were laid down makes it difficult to correlate sandstones between wells. For the most part porosity and permeability in the reservoir rocks are good, the approval document says.
Production from anticline An interpretation of 3-D seismic data indicates that the Kuparuk C reservoir forms a northwest-to-southeast trending anticline, split into three segments by large faults and with a relatively unfaulted central segment. Faults to the south also separate Northstar from the rocks in the Prudhoe Bay unit. The NS-08 and NS-18 wells produce from the crest of the anticline, the approval document says.
The Kuparuk A member consists of three to five sand packages, separated from the Kuparuk C by 10 to 50 feet of shale. The A sands tend to show more consistent thicknesses than the C sands and appear to have been deposited from the north on a marine shelf as a results of ancient storms, the approval document says.
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