Extra golden egg
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Oil Search adds seawater plan to Pikka; AIDEA might finance roads and bridges
Development of one of Oil Search’s big Nanushuk oil discoveries on Alaska’s North Slope has laid another golden egg: The construction of a seawater treatment plant for use in the Pikka unit.
Construction is expected to start in November 2021 and be complete by April 2024, per an application for a 35-year easement for the plant filed by Oil Search on June 23 and public noticed by Alaska’s Division of Oil and Gas on Aug. 6.
The company told the division that another application for a “makeup” water pipeline easement would follow.
When Oil Search filed its first plan of development for the Pikka unit on Nov. 4, infrastructure and facilities within the unit included the Nanushuk processing facility, or NPF, infield pipelines, import and export pipelines, infield and access roads, a boat ramp, and a potable water system.
The company said the development will also include facilities and infrastructure outside of the unit and that they will be authorized under separate permits. While a seawater treatment plant, or STP, was not specifically mentioned, the company did say that makeup water, “likely seawater,” will be needed for production and injection well stimulation.
Some of that water, at least initially, will likely be purchased from a third party, which is still the case, per the recent easement application.
Water quality importantThe STP will be located on state tidelands adjacent to Oliktok Point in Simpson Lagoon in the Kuparuk River unit.
Oil Search said it is “engaged in discussions with interested parties related to access to the proposed easement area and minimizing impacts related to simultaneous use of areas adjacent to the proposed easement area.”
The Pikka unit development will initially be targeting oil in the Nanushuk and Alpine C reservoirs.
Production of oil from these reservoirs requires a supply of makeup water with “sufficient reliability and water quality assurance to allow Oil Search to optimize production efficiency,” the company said in its easement application.
Construction of the STP is necessary, the company said, “in order to provide a long-term supply of makeup water with sufficient reliability and water quality assurance … for improved hydrocarbon extraction efficiency from the Pikka unit reservoirs.”
Work force and pipelinesSeasonal peak workforce during STP-related construction will vary from 50-350 individuals. Once the plant is in operation, six to seven fulltime workers will be needed.
An 18.4-mile-long makeup water pipeline and fuel gas pipeline will be permitted and constructed from the treatment plant to the development’s Tie-in Pad, or TIP, northwest of the Kuparuk Central Processing Facility. The yet-to-be constructed fuel gas pipeline will transport gas from the TIP to the plant. The pipelines will tie into the Pikka project makeup water and fuel gas pipelines that were permitted with the Pikka development, which is approximately 7 miles northeast of the community of Nuiqsut, west of the central North Slope.
STP construction will involve driving sheet pile, driving piles, trenching, excavating, placing gravel fill, screeding, installing vertical support members and pipelines, and constructing ice roads and pads.
The application requests an exclusive easement authorization for the placement of the plant over an approximately 6.8-acre area east of, and adjacent to, the east side of gravel fill at Oliktok Point.
The total requested initial construction easement is approximately 30.3 acres.
After the initial winter construction season, the easement area will be reduced to a smaller, interim construction easement of approximately 14.8 acres. The total requested operations phase easement is approximately 13 acres.
Built on a submersible bargeThe seawater treatment plant will be built off-site in modules on a submersible barge and transported via sealift to the North Slope during the open water season. Upon arrival, the barge will be positioned by tugboats into its final location and ballasted down to rest on the ocean floor.
Gravel fill will be discharged over the area surrounding the barge. Screeding of the seafloor will occur initially during the open water season when the plant arrives; after installation screeding may occur annually in the same area for plant maintenance operations.
The STP will be fully functional upon arrival following connection to the yet-to-be constructed TIP fuel gas pipeline and the STP pipeline; the STP will be equipped with a seawater intake structure, filtration system, power generation, and heating system.
One standby diesel generator and diesel fuel storage tanks will be on-site, internal to the STP, for backup power.
Any waste generated during construction or STP operations will be hauled off-site for proper disposal.
Initial sheet pile installationBefore the STP barge arrives, sheet pile will be installed to form the dock face and enclose the barge location.
Approximately 2,218 linear feet of sheet pile will be installed during winter. All the sheet piling will be installed below MHW, or mean high water. The approximate water depth where sheet pile will be installed is 3 to 7.25 feet.
Once temperatures are cold enough, a six-acre ice pad and an ice road of sufficient depth will be built to support pile installation and removal activities and the staging of materials and equipment.
Vibratory hammers will be used to install and remove temporary piles for the two 25-foot-long sheet pile templates, as well as to install the sheet pile to extend the dock face at Oliktok Point.
A template will be used to position the piles when the piles are being driven.
Four 12-inch-diameter, 25-foot-long, temporary round pipe piles will be used to hold the templates in position.
Templates will be installed and removed approximately 85 times, so that temporary round pipe piles will be installed and removed a total of 356 times. Sheet pile will be installed over a period of approximately 60 days, with roughly 3 to 6 hours of pile installation and removal occurring each day.
Dolphin/pile installationAlso, during winter four mooring dolphins will be installed to help guide and moor the STP barge. Each dolphin will comprise a single 48-inch-diameter 75-foot-long pile, for a total of four 48-inch-diameter round pipe piles.
Two dolphins will be installed approximately 300 feet north of the dock face, and two will be near the southwest and southeast corners of the barge berth.
The piles will be installed to a depth of approximately 50 feet below MLLW, or mean lower low water.
Installation of each pile will occur over a period of four days with an estimated two hours of vibratory hammer driving per day.
Pile installation of the two offshore dolphins will require construction of a 0.1-mile-long ice road over sea ice.
Trenching during winterThe STP outfall pipe that extends from the sheet pile will also be installed in the winter.
The 12-16-inch-diameter STP outfall pipe will extend approximately 457 feet from the dock face and be buried just below the sea floor.
An excavator will be used to dig a two-foot-wide, three-foot-deep trench of sufficient length to lay the pipe, and then cover the pipe with native material.
The native material will be sidecast on the seafloor during trenching and then placed back over the outfall pipe. The pipe outfall will be left uncovered.
Excess material will be left in place. The duration of trenching activities is expected to be five to 10 days.
Seafloor excavation site prepSeafloor excavation site preparation will continue during summer.
The 1.9-acre area designated for barge placement will be dewatered and excavated to -9.5 feet MLLW. Pumps, excavators and a crane will be required for the excavation.
Excavated material will be placed within the sheet pile enclosure located to the northeast. Placing the material in this area is so that it can be reused, reducing the amount of gravel needed, to control turbidity at the discharge site, and to reduce the footprint associated with fill slopes.
Approximately 12,000 cubic yards of material will be excavated and placed in the adjacent sheet pile enclosure. Approximately four feet of gravel will be placed on top of the excavated material.
Initial fill placementOil Search estimates a total of approximately 190,000 cubic yards of initial fill will be needed to prepare Oliktok Point for the STP and secure the plant in place. Before the STP barge arrives, approximately 165,000 cubic yards of gravel will be placed to backfill the sheet piles and create a berth and a work surface in anticipation of STP installation.
After the barge arrives, an additional 25,000 cubic yards of gravel will be placed to fill the gap between the sheet pile and the barge, thereby securing it in place. Gravel will come from one or more existing, permitted gravel mine sites, which operate independently of the project.
During initial gravel placement, gravel will be placed off the existing east side of Oliktok Point in lifts, using large-capacity dump trucks, and will be spread out with bulldozers or similar heavy earthmoving equipment.
Once placed, it will be re-graded, farmed, and re-compacted by heavy roller. Side slopes not adjacent to sheet pile will be 3H:1V and armored with geotextile bags (4 cubic yard polyester bags), with 50% overlap.
Sheet pile removal/mud gate installFollowing the initial gravel placement during the ice-covered winter season, a temporary mud gate will be installed at the entrance of the barge berth. Approximately 182 linear feet of sheet pile will be removed from the entrance of the barge berth using a crane, possibly with the assistance of a vibratory hammer. The mud gate, constructed of I-beams and plate steel, will be installed in place of the removed sheet pile, and will remain in place until just before the STP barge arrives during open-water season.
During the ice-covered season following arrival of the STP, approximately 182 linear feet of sheet pile will be installed in front of the barge berth using a crane and a vibratory hammer to protect the STP from ice damage.
Editor’s note: See map of the STP project in the pdf or print version