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ARCO says Alpine could produce more oil than originally estimated Field operator tells Alaska Oil and Gas Conservation Commission that revised development plan with more wells could be approved by summer Kristen Nelson PNA News Editor
The Alpine field could produce more than the 365 million barrels previously estimated if a proposed plan is approved and successfully implemented by field owners.
Field operator ARCO Alaska Inc. told the Alaska Oil and Gas Conservation Commission Dec. 3 that a decision could be made by this summer to switch from waterflood to miscible-water-alternating-gas flood at the 1 billion barrel reservoir west of Kuparuk on Alaska’s North Slope. Well spacing would also be tightened and the number of wells increased, with 82 wells in phase I rather than the 50 wells in the current phase I plan.
The company’s original development plan — the only plan approved to date by field owners ARCO Alaska (78 percent) and Anadarko Petroleum Corp. (22 percent) — calls for 50 wells in phase I and 42 wells in phase II for a total of 92, 32 planned as horizontal wells and 60 as vertical wells.
The approved plan calls for waterflood from the beginning of development, with water coming in from Kuparuk, possibly followed by lean gas or miscible gas injection to improve ultimate recovery. The ratio of producing wells to injecting wells is planned at one to one. ARCO said the major uncertainty in this plan was the ability to inject water at acceptable rates.
Some injection wells may be initially used as production wells, the company said, to help increase production when a limited number of wells are available.
ARCO officials said they plan to spend five years drilling development wells at Alpine, using a single rig which will be moved to the field on ice roads this winter. Wells drilled in phase I will be those expected to perform the best. In phase II, field owners will drill wells at the boundary of the field where there is poorer quality rock and the wells will be more expensive to drill. Phase I is expected to take approximately three years and phase II two years, officials said. Potential for more wells But, ARCO officials told the commission, a revised development plan is being evaluated by field owners. While the current plan calls for waterflood in the center of the field and gas re-injection around the periphery, the revised plan includes miscible-water-alternating gas throughout the field with gas enriched to become miscible with reservoir oil.
The current plan calls for 275 acre well spacing in the center of the field and 160 acre spacing around the periphery. The revised plan would include horizontal wells throughout the field on 135 acre spacing. The revised plan would include as many as 140 wells, all horizontal: 82 phase I wells in the core area and 56 phase II wells.
Asked by Commissioner David Johnston what was required to move from the current plan to the proposed plan, ARCO officials said more technical work, economic analysis and approvals from working interest owners and others involved in the unit would be required. If the economics are favorable, ARCO said, a new plan of development could be approved by summer.
Production from the field could be more than the 365 million barrels now projected if the new plan is adopted, ARCO officials said. Field optimization ARCO said it was also evaluating multiple target wells to optimize field production. One option, company officials told the commission, is to drill wells with longer horizontal sections. About 3,000 feet of horizontal section per well is drilled now. If 7,000 feet of horizontal section could be drilled it would be the equivalent of two current wells.
The same holds true for multi-laterals, wells where multiple completions are drilled out from the same wellbore. With both long horizontals and multi-laterals, ARCO officials said, the goal would be to have 6,000-7,000 feet for formation open to production from a single wellbore.
Batch drilling will be used to reduce material storage at Alpine. Five or six holes would be drilled at a time and suspended after surface casing is set while the rig moves on to the next well. All of the wells would be completed before the end of the drilling season. Alpine pool in Colville River field The reservoir under development at Alpine will be called the Alpine pool in the Colville River field, ARCO told the commission. The company said it would also be applying to the Alaska Department of Natural Resources for an Alpine participating area within the Colville River unit. Lease ownership of the state and Arctic Slope Regional Corp. lands has already been cross assigned in the Alpine area, the company said.
The Upper Jurassic Kingak formation in the Colville River delta area contains at least three oil-bearing sands, the Alpine, Nuiqsut and Nechelik. The Alpine sandstone is the uppermost of the three, and ARCO said it displays the best reservoir properties of the three sands.
The Bergschrund 1 discovery well, drilled in 1994, penetrated 48 feet of oil-bearing Alpine sandstone and tested 2,380 barrels per day of 40 degree API gravity oil.
ARCO said that the Fiord 1, approximately two miles north of the Alpine oil pool, penetrated 20 feet net of Kuparuk sandstone and tested approximately 1,000 bopd of 31.6 degree API gravity oil. ARCO characterized the shallower Kuparuk sandstone as thin discontinuous sands with overall poor reservoir quality in the Colville River unit area.
Shallower still are the Torok sandstones, which ARCO characterized as thin-bedded turbidite sandstones with generally poor reservoir quality, interbedded with mudstone up to 100 feet thick and complexly distributed across the Colville River unit area. The company told the commission that it would continue to evaluate Torok potential as it drills Alpine development wells.
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