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Eni targets ANS viscous oil Rock Flour target is shallow West Sak/Schrader Bluff; also after Ugnu, Kuparuk C By Kristen Nelson Petroleum News Editor-in-Chief
Could the North Slope’s shallowest and most viscous oil formation, the Ugnu, be commercial at depths comparable to West Sak/Schrader Bluff reservoirs now in production?
That is one proposition Eni Petroleum Exploration Co. plans to test at the proposed Rock Flour exploration unit off the southeast corner of Kuparuk, although the West Sak/Schrader Bluff accumulation is the primary objective in the unit.
Eni told the state in its unit application that it will be evaluating whether higher temperatures found in an exploration well in the area will make West Sak/Schrader Bluff oil in the proposed unit easier to produce than colder reservoirs currently under production.
Eni, which acquired acreage in Alaska when it purchased Armstrong Alaska’s assets in August, applied to the Alaska Department of Natural Resources Aug. 25 for formation of the Rock Flour unit on leases adjacent to Kuparuk and just west of the Prudhoe Bay unit. Eni will be the operator; ConocoPhillips Alaska and Pioneer Natural Resources Alaska also hold leases in the proposed 15,308-acre unit. Eni has 100 percent working interest in five of the eight leases proposed for the unit; the other three leases are held 50 percent each by ConocoPhillips and Pioneer. Two of the Eni leases (acquired by Armstrong from Anadarko Petroleum in April) expire Nov. 30; inclusion of the leases in a unit would extend them for the life of the unit. First well in 2007 The five-year exploration plan Eni submitted says an initial exploration well will be drilled in the 2007 winter drilling season, a second in the 2009 winter season and a third in 2010. Prior to that first well the company said it will reprocess existing data and finalize well designs. After the first well is drilled results will be “integrated with planned additional geologic/reservoir studies and seismic acquisition through the remainder of 2007/2008,” work which will lead to a second well in the 2009 winter drilling season, “or earlier.”
The second well would “test the limits and continuity of the primary Ugnu/West Sak/Schrader Bluff reservoirs over the southern portion of the proposed” unit; the third exploration well would “evaluate Cretaceous objectives over the northern portion of the proposed unit. It will refine Ugnu/West Sak/Schrader Bluff resource limits, as well as other potentially recoverable resources.”
Eni said it may modify the order in which the wells are drilled, and after the first well is drilled “the location and drilling depth of subsequent wells may be adjusted pursuant to the results ...”
The company’s schedule of wells includes three 7,000-foot wells, the first in ADL 389117, section 16-township 10 north, range 11 east, Umiat Meridian; the second in ADL 389118, 30-10N-11E, UM; and the third in ADL 390695, 33-11N-11E, UM.
Eni told the state intervals to be tested “may include but are not limited to” the Cretaceous Ugnu sandstone, Cretaceous West Sak/Schrader Bluff sandstone and the Kuparuk “C” sand.
ConocoPhillips produces from the shallow West Sak/Schrader Bluff and Kuparuk formations at Kuparuk; BP Exploration (Alaska) produces from the formations both at its Milne Point unit and at Prudhoe Bay satellites. The Ugnu, the shallowest and heaviest of the North Slope formations, is not yet in production anywhere on the slope. Previous drilling in the area Eni said drilling began in the vicinity of the proposed exploration unit in 1969, with wells drilled in that year and through the 1970s finding “oil saturated sands” in the West Sak interval.
Exploration in the 1980s targeted West Sak in this area, Eni said, and there was a pilot West Sak water flood project. While prices and technology didn’t allow for development of West Sak in the 1980s, Eni said, the pilot area was the basis for the West Sak 1J pad development which is currently under way.
Delineation and exploration drilling in the 1980s included production tests of the West Sak interval in one well, and a finding of tight sands in the Kuparuk “C” interval some two miles southwest of Rock Flour, although the same well had “fair to excellent shows” in sidewall cores taken in the West Sak. A 1986 well two miles west of Rock Flour found oil-saturated sands found in both the Ugnu and West Sak intervals.
Eni said these two wells found “additional prospective sand above the West Sak D that is better developed to the south of existing production.” 1991 well in proposed unit area Exploration has continued in the area.
The 9,132-foot Rock Flour No. 1 was drilled in 1991 within the area of the proposed Rock Flour unit, Eni said, and “encountered wet Ivishak sands at total depth,” and Kuparuk ‘C’ sands appeared wet by log analysis, but sidewall cores found a West Sak oil interval.
Eni said the Rock Flour No. 1 “defines the prospective West Sak section for the proposed” Rock Flour unit.
The 2002 Kuparuk River Unit 1M-17 (with a bottomhole a half mile to the north of the proposed unit), drilled to a true vertical depth of 7,009 feet, tested 1,450 barrels per day in the Kuparuk “C” sands; the well is a suspended producer.
Eni noted that ConocoPhillips in its 2002 Kuparuk River unit eighth expansion plan “described plans to add a new 1M drill site ‘with possibly 18 Kuparuk development wells and eight to 12 West Sak development wells.’”
Eni said the proposed 1M drill site “is in a structurally similar position” to the proposed Rock Flour exploration unit. Primary objectives Eni said the upper Cretaceous West Sak/Schrader Bluff sandstones are its primary objective, along with Upper Cretaceous Lower Ugnu sandstones. Based on previous drilling in the area Eni said it believes there is “an overall prospective trend for continued West Sak Sand reservoir quality and thickness to the south/southeast over our proposed Rock Flour exploration unit.”
It said the measured bottomhole temperature in the Rock Flour well (99 degrees Fahrenheit) “could significantly improve the viscosity/mobility characteristics of the crude within the West Sak reservoir interval” at Rock Flour, compared to Kuparuk West Sak field average reservoir temperatures of 65-70 degrees F.
Based on previous wells Eni said there is also “an overall prospective trend for continued Ugnu Sand reservoir quality and thickness” over the Rock Flour unit. “The targeted Ugnu sandstone depths and resultant warmer reservoir temperatures could significantly improve viscosity and resultant mobility of crude within the Ugnu reservoir interval. The Ugnu sands are expected to be encountered at roughly the equivalent subsea depth and temperature to the up-dip producing West Sak ‘D’ sandstones,” Eni said. It plans to do production testing of the Ugnu to evaluate “its commercial viability from both a reservoir deliverability and operational producibility standpoint.”
The Lower Cretaceous Kuparuk “C” sandstone is a secondary objective at Rock Flour, and is limited to the western part of the proposed unit. Eni said the size of the Kuparuk “C” at Rock Flour “is dependent on both the oil/water contact and the accuracy of the structural mapping in this area.”
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