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Alaska Oil and Gas Conservation Commission

Alaska Department of Administration, Alaska Oil and Gas Conservation Commission
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AOGCC Pool Statistics
Northstar Unit, Northstar Oil Pool
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Operator: BP Exploration (Alaska) Inc. .
Index map for the Colville River Unit, Nanuq Oil Pool showing it’s general location with respect to other North Slope oil fields.
Discovery Well: Shell Western E&P Inc.
  Seal Island BF-47 No. 1
  Permit No. 183-074
  API No. 50-029-20954-00-00
  Sec. 2, T13N, R13E, UM

Depth: 14,541’ MD / 12,461' TVD

January 30, 1984

Status: Producing
Location: Central Arctic Slope Area Location Map Pool Location Map DNR Unit Map
References: List of Orders Summary - Annotated Reference List  
Summary:

Northstar Island is a five-acre, man-made island located in the Beaufort Sea, 12 miles northwest of Prudhoe Bay and 6 miles offshore. Discovered by the Shell Island BF-47 No. 1 exploration well in 1984, construction of the development island began during the winter of 1999-2000, and the first production modules were installed during 2000. Northstar is connected to onshore processing facilities by a pipeline that is buried 7 to 11 feet below the seafloor to avoid ice impacts. This pipeline has a wall thickness triple those of typical onshore North Slope pipelines, and three separate leak detection systems.

Regular production began in November 2001, and climbed rapidly, regularly exceeding 50,000 barrels of oil per day (“BOPD”) by June 2002 and 70,000 BOPD by June 2003. During the first five months of 2011, the pool averaged 14,735 BOPD with a 51% water cut. The Northstar development area spans the boundary between State of Alaska and Federal waters, and the Federal percentage of Northstar production is allocated at 17.84%.

Geology:

The Northstar Oil Pool is defined as the accumulation of hydrocarbons common to and correlating with the interval between measured depths of 12,418 feet and 13,044 feet the Seal A-01 well. The reservoir interval consists of the Sag River, Shublik, and Ivishak Formations. The Sag River Formation is typically 100 feet thick in this area, and it was deposited as Triassic-aged, transgressive marine sandstone, siltstone and shale. The sandstone mineralogy is mature: quartz with minor amounts of feldspar and authigenic clay. The primary cementing agents are calcite, silica and siderite. Sag River Formation porosity ranges from 6.8% to 22.8% and averages 13%. Permeability ranges from 0.01 to 28.0 millidarcies and averages 0.86 millidarcies. Calculated water saturation values range from 50% to 65%. The net-to-gross ratio for the Sag River Formation varies from 15% to 20%.

The Shublik Formation is also Triassic-aged, and is stratigraphically complex, being characterized by marine siltstone, shale, sandstone and phosphatic limestone. Within the Shublik Formation, reservoir quality rock is limited to a basal sandstone member, the Shublik D. Porosity and permeability for the Shublik D are typically less than 10% and 1 millidarcy, respectively. The net-to-gross ratio for the Shublik D is about 50%.

The Ivishak Formation comprises a series of Permian and Triassic-aged delta-front sandstones and shales that grade upward to fluvial sandstone and medium to coarse-grained pebbly conglomerates. Within the pool, the Ivishak is about 325 feet thick, and it is more proximal, coarser grained, more deeply buried and cemented than at the Prudhoe Bay Field. Here, the Ivishak is primarily cemented with calcite, silica and siderite. The lower sand unit of the Ivishak Formation has an average porosity of about 18%, and the overlying conglomerate unit averages about 14%. However, laboratory studies show that about 40% of the total porosity within the lower sand unit is non-effective micro-porosity, and within the conglomerate unit, about 50% of the total porosity is non-effective micro-porosity. Core permeability ranges from 0.01 to 808 millidarcies, with a stress-corrected mean value of 53 millidarcies. The net-to-gross ratio for the Ivishak is 93% to 95%. The average oil saturation of the Ivishak is 42%, and the maximum oil column is estimated to range from 270 to 300 feet.

The pool structure consists of a faulted anticline defined by three-way dip closure on west, south and east. Closure to the north is obtained through fault seal or structural dip. Faults within the pool have interpreted maximum vertical displacements of less than 200 feet, and they are not expected to significantly affect reservoir performance. The oil-water contact is placed at 11,100 feet true vertical depth subsea, based on core, RFT, MDT and well test data.

  Strat Column Type Log
Production: Prod Chart        
  Oil (bbls) NGL (bbls) Gas (mcf) Water (bbls)
Cumulative 152,708,126 0 1,354,934,416 39,967,502
2005 Total
22,241,483 0 142,131,405 4,361,019
2006 Total
18,877,092 0 142,192,520 5,103,452
2007 Total
13,877,273 0 151,144,906 4,835,708
2008 Total
11,440,424 0 175,958,065 5,123,801
2009 Total
7,980,198 0 167,618,464 5,384,807
2010 Total
6,084,741 0 169,470,496 5,582,485
2011 Total
4,812,211 0 180,872,405 5,705,395
2007 Rate (b/d)
38,020 0 414,096 13,249
2008 Rate (b/d)
31,344 0 482,077 14,038
2009 Rate (b/d)
21,864 0 459,229 14,753
2010 Rate (b/d)
16,671 0 459,229 14,753
2011 Rate (b/d) 13,184 0 495,541 15,631
2008 Change (%)
-18 0 16 6
2009 Change (%)
-30 0 -5 5
2010 Change (%)
-30 0 -5 5
2011 Change (%)
-18 0 8 6

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