State proposes ROW lease for Tyonek line
Hilcorp plans a new gas pipeline under Cook Inlet from the offshore Tyonek platform to Ladd Landing on west side of inlet
The Alaska State Pipeline Coordinator’s Section has issued a notice proposing to approve the establishment of a right of way for a new Cook Inlet subsea natural gas pipeline that Harvest Alaska, a subsidiary of Hilcorp Alaska, plans to construct. The pipeline will run from the Tyonek platform, offshore in the inlet, to Ladd Landing on the inlet’s west side. Public comments on the proposed right of way are due by March 14. An open house and public hearing are scheduled March 12 in the Nikiski Community Recreation Center on the Kenai Peninsula.
Eliminate Drift River terminalThe proposed pipeline construction, scheduled to begin when ice goes out in the inlet this spring, comes as part of a plan by Hilcorp to ship oil from the west side of the inlet to Nikiski on the east side by subsea pipeline, thus eliminating the continued use of the Drift River oil terminal on the inlet’s west side. The terminal is currently used to load oil onto tankers for shipment to Nikiski, but there are safety concerns because of the terminal’s proximity to the Redoubt Volcano.
Hilcorp’s plan involves using one of the twin subsea gas pipelines that form what is called the Cook Inlet Gas Gathering System to carry oil rather than gas west to east under the inlet. A short new onshore oil line will connect the CIGGS line to the existing oil pipeline system on the west side of the inlet.
The idea behind the planned new Tyonek subsea gas line is to maintain Hilcorp’s capability to transport gas across the inlet, after one of the CIGGS lines is switched to the carriage of oil. An existing gas pipeline connects the Tyonek platform to Nikiski, although Hilcorp also plans to replace an onshore segment of that line.
The carriage of adequate volumes of gas across the inlet forms a vital component of the gas supply arrangements for gas and electricity utilities in Southcentral Alaska, especially during the winter when gas demand is high.
In addition to its application for the Tyonek pipeline right of way, Harvest has applied for authorization of a change to the CIGGS right of way lease, to allow the carriage of oil on one of the CIGGS lines. SPCS says that it is still assessing that application.
Pipeline designThe design documentation for the planned Tyonek gas pipeline, referred to as the Tyonek W 10 pipeline, says that the subsea section of the 10-inch diameter line will be 5.5 miles in length. A 1.4-mile onshore section of the line will run from Ladd landing to a junction with the existing Beluga gas pipeline. The Beluga line connects south to the gas pipeline infrastructure on the west side of the Cook Inlet, and north through Enstar Natural Gas Co.’s gas transmission line to the Wasilla and Palmer area.
The new pipeline is being designed to operate at a pressure of around 800 pounds per square inch, a similar pressure to the other gas lines in the region.
According to the design document, the concept for construction of the new subsea gas line involves assembling the line in half-mile segments onshore at Ladd Landing while using a barge to pull the pipeline out to the platform. Piles of sandbags placed at intervals along the line will pin the line to the seafloor, the design document says. The sandbag system will be maintained through annual surveys. Hilcorp’s pipeline operators will manage the pipeline use and performance through the company’s existing pipeline management computer system. Pipeline pressure and gas volume discrepancy monitoring would alert operators to any potential pipeline leaks. Annual patrols along the pipeline’s length would discover any disturbance to the line, as well as looking for any evidence of gas leaks.
Corrosion prevention would involve the use of cathodic protection and appropriate pipeline coatings.