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Borealis recovery expected to be 23 percent with water flood Original oil in place at western Prudhoe satellite field estimated at 195-277 million barrels, with 85-125 billion cubic feet of associated formation gas; field began producing in November, development from L and V pads Kristen Nelson PNA Editor-in-Chief
Borealis a Kuparuk formation western Prudhoe Bay satellite contains an estimated 195 million to 277 million barrels of original oil in place, BP Exploration (Alaska) Inc. told the Alaska Oil and Gas Conservation Commission at a pool rules and area injection order hearing April 5.
The Borealis pool was discovered in a 1969 exploration well, the West Kuparuk State No. 1, BP told the commission, and overlies Prudhoe Bay reservoirs in the vicinity of the new L and V pads in the western portion of the Prudhoe Bay unit.
The field began producing in November and is currently at 24,000 barrels per day.
BP said that recovery is estimated at 13 percent from primary depletion and an additional 10 percent from planned water flood.
Fourteen wells have been drilled at Borealis, four injectors and the rest producers. BP told the commission it is pre-producing the injectors for three to four weeks before beginning injection because that doubles the injection rate. Gathering Center 2 produced water and sea water will be used. Reservoir discontinuous The Borealis pool Kuparuk formation is stratigraphically complex, BP said, and the thickness of the upper sand, Kuparuk C, which contains the primary reservoir sands at Borealis, varies from 70 feet in the north to 180 feet in the center and 50 feet in the south and east before it thins south and east of Z pad.
The proven and potential hydrocarbon accumulations are contained in a formation BP described as having northwest-southeast trending faults intersected by north-south faults, resulting in a number of potentially isolated compartments within the field.
The oil-water contact at Borealis is estimated at 6,668 feet true vertical depth, varying from approximately 6,625 feet TVD at L pad to approximately 6,725 TVD at V and Z pads.
BP said the data suggests either a 100-foot range of oil water contact uncertainty, or compartmentalization of the Borealis fault blocks with a southeastward deepening of the OWC across the Borealis area.
Each fault block in Borealis will have to be evaluated separately, the company said.
Gravity from 25.6-27.5 degrees API L pad initial well tests show API oil gravity ranging from 25.6 degrees to 27.5 degrees. The range in estimates of original oil in place of 195 million barrels to 277 million barrels is primarily due, BP said, to uncertainty in the oil-water contact and reservoir net pay interval thickness.
The estimate for associated formation gas in place is 85-125 billion cubic feet, with no indications of a free gas column at Borealis.
Twenty to 50 production and injection wells are anticipated at Borealis, with primary production expected for 18 months with pre-production of planned injectors, followed by water injection. BP said facility modifications at Gathering Center 2 will increase deliverability and pressure of the produced water system.
Estimates are that miscible gas flood at Borealis would add approximately 5 percent to oil recovery, and BP said further evaluations of the impact of enhanced oil recovery at Borealis need to be performed. Production has begun Development drilling at Borealis began last July, and production in early November. Development will be from L and V pads, although BP said the southernmost Borealis wells may be drilled from Z pad.
Production and injection wells were first drilled at L pad and drilling will then move to V pad. Propped hydraulic fracture will be used if necessary. Injectors, the injection pipeline, manifold construction and approval to inject are necessary before injection will begin, BP said. Partial development Commissioner Dan Seamount asked BP how Borealis compares with Kuparuk reservoir analogues. He said the primary 13 percent depletion seemed low.
BP said the projected 13 percent primary depletion appears low because it represents only partial development of the Borealis participating area, the area where BP has the greatest confidence. The 23 percent depletion with water flood compares, BP said to analogues in the Kuparuk River unit with 30-40 percent recovery rates.
Seamount asked about higher than anticipated initial production rates.
BP said initial wells began at 4,000-5,000 barrels per day, which was better than anticipated, but current production rates of 2,000-3,000 bpd are in line with estimates.
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