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February 2018

Vol. 23, No.7 Week of February 11, 2018

Northstar-Kuparuk oil pool rules approved

Hilcorp producing from shallower pool above Ivishak formation where production began in 2001; Kuparuk identified by some 30 wells

Kristen Nelson

Petroleum News

The Alaska Oil and Gas Conservation Commission has approved pool rules for the Northstar-Kuparuk oil pool at the North Slope Northstar unit, which straddles state and federal leases in the Beaufort Sea. Hilcorp Alaska, which took over Northstar as part of North Slope acquisitions from BP at the end of 2014, applied in October 2016 for an order defining a new pool within the Northstar unit and for rules governing pool development and operation.

BP, the former Northstar operator, began producing from the Ivishak formation at Northstar in 2001 and in 2006 began testing natural gas and condensate from the shallower Kuparuk sands, with sustained Kuparuk production beginning in 2010.

In 2012 BP applied for designation of the Kuparuk producing area at Northstar as the Hooligan participating area. That original PA included only the Kuparuk C sands. In 2016 another Northstar well began gas and condensate production from the deeper Kuparuk A sands and Hilcorp applied for an expansion of the PA, which was granted in early 2017.

Northstar

Northstar lies offshore the North Slope some 12 miles northwest of Prudhoe Bay and is developed from the Northstar artificial island drill site. Hilcorp is 100 percent working interest owner and operator at Northstar.

Shell Oil Co. drilled the Northstar discovery well in 1983, encountering oil indicators in the Kuparuk formation. A number of confirmation wells were drilled through 1986, the commission said, with some 30 wells to date having been logged across the Kuparuk reservoir within Northstar. The geologic structure and reservoir have been determined using 3-D seismic survey and well log data.

The Northstar-Kuparuk oil pool is the accumulation common to and correlating with the interval between measured depths of 12,156 and 12,446 feet in the Northstar NS-15 development well, the commission said.

Gas, condensate

The Kuparuk A sands contain a gas-condensate cap with an oil rim; the overlying Kuparuk C sands contain only gas condensate.

The commission said Hilcorp considers the Kuparuk C and A sands to be a gas-condensate reservoir, but said they are considered oil reservoirs because the producing gas oil ratio is less than 100,000 standard cubic feet per stock tank barrel. The API gravity of oil recovered from the Northstar Kuparuk pool is 38 degrees to 53 degrees, with an average of 47.6 degrees API.

Three wells are currently producing from the Northstar Kuparuk pool.

Estimated volumes are 500 to 550 billion cubic feet of gas and 22 million to 25 million stock tank barrels of original oil, with primary recovery estimated at 40 percent and primary recovery plus waterflood at 46 percent. The commission said no new wells are planned and the project is expected to continue until about 2030.

The majority of the Northstar Kuparuk reserves are assigned to less compartmentalized C sands where wells will drain larger areas. Hilcorp is continuing to gather data on the C sands and is evaluating the potential of implementing a gas reinjection project to improve ultimate recovery from the C sand. The commission said the A sand does not appear to be a good candidate for enhanced recovery due to limited reserves and compartmentalization.

The commission approved pool rules, including commingling of production from the C and A sands due to the small size of the A sand and proximity to the C sand.

Hilcorp will continue to collect reservoir performance data to determine whether an enhanced oil recovery project will work for the C sand, and the commission is granting a temporary waiver, through Dec. 31, 2019, to the gas-oil-ratio in its regulations for the collection of additional reservoir performance information.






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