Alyeska Pipeline Service Co.’s proactive risk-based maintenance program’s latest construction project is designed to protect the 800-mile trans-Alaska oil pipeline from the slow pace of melting permafrost attributed to climate change.
The Trans-Alaska Pipeline System, or TAPS, was “designed and built to manage changing environmental conditions, including permafrost zones,” Alyeska’s chief communications officer Michelle Egan recently told Petroleum News in an email.
TAPS, which Alyeska has operated for more than 44 years, includes 420 miles of above-ground pipe on vertical support members, or VSMs, to accommodate permafrost conditions.
“Since the startup of TAPS operations, more than 124,000 ground-cooling thermal units called heat pipes along the pipeline have helped cool and stabilize permafrost,” Egan said.
As part of that commitment, thermal units and the VSMs are regularly monitored and when needed, Alyeska repairs or reinforces them, she said.
The latest maintenance construction project at Lost Creek Hill, which began in June, it is expected to take 120 days and will be complete yet this summer, Egan confirmed. Alyeska’s monitoring program “identified the need for maintenance” there and thus the company is replacing eight thermal VSMs and installing 60 freestanding thermosyphons to provide passive cooling to the ground.
“The project is an example of Alyeska’s proactive risk-based maintenance program,” Egan said.
About 57 miles northwest of Fairbanks near Livengood, the permafrost on Lost Creek Hill is starting to thaw which is causing the slope to creep down - the pipeline lies below that slope.
Tony Strupulis, state pipeline coordinator in the Alaska Department of Natural Resources’ Division of Oil and Gas, approved the project, which Alyeska applied for on Feb. 27, 2020. Other permits/authorizations from various agencies were also required.
Strupulis told Tracy Sinclare, the weekend meteorologist for KTUU, that no damage to the pipeline has occurred: “A little bit of tilting of the support structures, but it’s all within the allowable limits of the pipeline.”
Strupulis told Petroleum News there is no reason for panic - the support structures are not in immediate danger of collapse. But, he added, DNR remains “very mindful” about thawing permafrost for pipeline safety.
“The design philosophy is, ‘If it’s frozen, keep it frozen,’” Strupulis said.
DNR’s 2020 analysisIn DNR’s November 2020 analysis of Alyeska’s Lost Creek Hill project, the agency said the reason behind installing the passive cooling system to stabilize the ground is to protect the integrity of TAPS from permafrost degradation.
The analysis also said the new cooling system “consists of approximately 100 free-standing heat pipes” - a number with further analysis that has been dropped to 60 – “to be installed by driving steel casings 40 to 60 feet into the ground with thermosyphons inserted inside the casings. The system also includes a 3-foot layer of insulating wood chips and horizontal ventilation pipes to be placed in the thermal improvement area to assist with cooling the subsurface. The bent VSMs would be replaced and embedded to depths between 50 and 60 feet and installed with thermosyphons by driving steel casings.”
Equipment that may be used during the 120-day project timeline, DNR said, included “drill rigs, cranes, tractor sidedumps, articulated haul trucks, excavators, front-end loaders, skid steers, wood chip spreaders, dozers, a fuel truck and a water truck.”
DNR engineers headed outEngineers from DNR will soon be going out to the work site to review the progress of the project at a time when Alyeska is in the thick of construction.
DNR will also examine the project area upon completion of the construction activities to ensure all lands are in a condition acceptable to the department.
In its application, Alyeska provided the following project timeline, although the company did say that the work sequence may be altered slightly depending on field conditions at the time:
1. Mobilize personnel and equipment (around June 15).
2. Assemble heat pipes in Fairbanks.
3. Selective brushing of the work pad and temporary land use area.
4. Haul in gravel from a nearby pit.
5. Relocate the drive lane.
6. Excavate under the mainline for access to the westerly thermal improvement area.
7. Install temporary pads to support the drill rig at the bents.
8. Install new upgraded VSMs at bents 40, 41, 43 and 44.
9. Install cross beams and support structures at the bents.
10. Install … steel casings and FSHPs on the inclined slope.
11. Recharge heat pipe thermosyphons with carbon dioxide.
12. Install vent pipes and place layer of wood chips.
13. Restore and revegetate the work area as required.
14. Site clean-up and demobilize.