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Vol. 11, No. 8 Week of February 19, 2006
Providing coverage of Alaska and northern Canada's oil and gas industry

Alaska: BP putting new oil pool online

Raven reservoir in Sag River and Ivishak formation beneath Kuparuk formation of Niakuk field; contains 14-23 million barrels

Kristen Nelson

Petroleum News

BP Exploration (Alaska) is putting an oil pool lying under the Niakuk pool on production.

It has applied to the Alaska Oil and Gas Conservation Commission for pool rules and an area injection order for the Raven oil pool, offshore the North Slope within the geographic limits of the Niakuk participating area.

While Niakuk produces from the Kuparuk formation, Raven produces from the deeper Sag River and Ivishak formations. The latest commission records, for December, show production to date from the Niakuk oil pool of 82.9 million barrels of oil, with 356,742 barrels produced to date from the Niakuk Ivishak-Sag River undefined oil pool.

BP said 12 wells in or near the proposed Raven participating area encountered either or both of the deeper accumulations. Eight of those wells are abandoned exploration or sidetracked well bores; four are active, two at Raven pool and two at Niakuk. The NK-38A and NK-65A have open perforations in the Ivishak; the NK-43 and NK-19A are producing from the Kuparuk, but have plugged Sag River/Ivishak formations that could be used in Raven development.

The NK-38A has periodically produced from the Ivishak as a tract operation since March 31, 2005. The NK-65A was drilled and completed as a water injector to support the NK-38A producer; water injection began at the well last October.

Sag River light gravity oil and gas was produced in a long-term test from the NK-43 well within the Raven structure in 2001; the well was subsequently converted to a Kuparuk producer. BP said it is evaluating re-opening the Sag River perforations in that well and commingling production from the Kuparuk and Sag River formations.

Rules proposed for Raven

BP said the Raven owners are proposing pool rules and an area injection order for the entire stratigraphic interval of the Raven reservoir.

BP has used reprocessed seismic datasets for structural mapping and has also used fluid contacts and reservoir compartmentalization to determine the Raven pool limits. The Sag River accumulation extends over a larger area than the Ivishak, the company said, and encompasses the Ivishak accumulation.

In-place oil volumes for Raven are estimated at 14 million to 23.2 million barrels of oil and condensate. The Ivishak contains the most oil: an estimated 6.9 million to 11.4 million barrels of oil and 2.3 million to 3.8 million barrels of condensate, for a total of 9.2 million to 15.2 million barrels in place. Estimates for the Sag River are 3.5 million to 5.8 million barrels of oil and 1.3 million to 2.2 million barrels of condensate for a total of 4.8 million to 8 million barrels in place. Oil totals are estimated at 10.4 million to 17.2 million barrels and condensate totals at 3.6 million to 6 million barrels.

Gas in place is estimated at 71.5 billion to 119 billion cubic feet. Once again, the majority is in the Ivishak, with free gas estimated at 35.4 bcf to 59 bcf and solution gas at 10.4 bcf to 17.3 bcf for a total of 45.8 bcf to 76.3 bcf. The Sag River is estimated to contain 20.4 bcf to 33.9 bcf of free gas and 5.3 bcf to 8.8 bcf of solution gas for a total of 25.7 bcf to 42.7 bcf. Total free gas is estimated at 55.8 bcf to 92.9 bcf and solution gas at 15.7 bcf to 26.1 bcf.

BP said the ranges in original oil in place and original gas in place are due to “uncertainty in individual fault block oil-water contacts and gas-oil contacts where there is no well control, reservoir properties and fluid properties.”

Water injection planned

BP said the principal recovery mechanism will be voidage replacement through water injection.

Only the north fault block in the reservoir is expected to have significant recovery from the Ivishak with the two existing wells and perforations. Once the north fault block has been depleted, perforations will be added to the NK-38A wellbore in the south fault block. BP said there is also a potential for up to three sidetracks, one in the north fault block and two in the south fault block, but such future options will be based on field performance and economic factors.

The company said the Sag River reservoir at Raven is less understood and the resource is small. Plans have been approved to re-open the Sag River perforations in the NK-43 well and do a long-term test to collect reservoir performance information and study long-term production performance.

The Ivishak will be produced from the NK-38A horizontal well in the north fault block with voidage replacement from water injection at NK-65A; additional drilling options will be evaluated.

Waterflood is expected to add approximately 10-20 percent recovery to primary depletion.

Niakuk facilities to be used

BP said Raven will be developed from the Niakuk Heald Point pad and will use existing production and injection facilities at the Prudhoe Bay field; no additional pads, facilities or roads will be required.

Because of separate fault blocks, BP is asking for 20 acre well spacing.

Niakuk Kuparuk reservoir wells arc out from Heald Point, with the field’s extended reach wells to the northwest. Wells with perforations in the Raven pool lie to the north and northeast of the drill site.

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