Alyeska Pipeline Service Co. — and the North Slope producers — are dealing with a winter shutdown of the trans-Alaska oil pipeline, a shutdown which for four days beginning the morning of Jan. 8 forced producers to cut back production to 5 percent, an amount which could be stored in tanks at Pump Station 1.
The pipeline was restarted on a temporary basis late Jan. 11, but plans were for a 36-hour shutdown targeted to begin Jan. 14 for installation of a bypass line.
The pipeline is shut down regularly for maintenance but those shutdowns occur in the summer, when North Slope weather is at its mildest and lines and equipment aren’t threatened by the brutal cold of winter.
This unplanned shutdown occurred after Alyeska personnel at Pump Station 1 discovered oil leaking into what the Alaska Department of Natural Resources described as a concrete “sump” in the station’s booster pump building, a leak coming from a section of piping encased in concrete adjacent to the building.
The oil was discovered at about 8:15 a.m. Jan. 8; the pipeline was shut down at 8:50 a.m.
Production was prorated to 5 percent; it took producers until the evening of Jan. 9 to reach that level.
Oil recovery began the afternoon of Jan. 8, after the building had been vented sufficiently that it was safe for crews to work. DEC said the oil was half an inch to an inch deep on the approximately 30-by-40-foot floor of the basement.
Alyeska will install a bypass around the affected piping during the 36-hour shutdown.
Emergency responseAlyeska established a full incident management team at the Fairbanks Emergency Operations Center, DEC said. State and federal representatives were notified and joined the response.
Engineers and technical specialists arrived at Pump Station 1 the evening of Jan. 8 to design a temporary pipe plan.
DEC said there was no damage to booster pumps or other facility infrastructure from the oil release.
Vacuum trucks are being used to remove the oil, some 52 barrels prior to the Jan. 11 restart and an additional 55 barrels by 4 p.m. Jan. 12, day two of the restart. The oil will be reinjected into the pipeline and DEC said it would be measured at the reinjection point. Workers installed an 800-gallon containment vault at the seep site in the booster pump building to facilitate oil collection.
DEC said no oil has been observed during ongoing surface and subsurface monitoring of soil in the vicinity of the booster pump building or during inspections of the perimeter of the pump station’s gravel pad.
Temperature issuesAlyeska took steps to prevent problems with the line due to cold temperatures and the length of the shutdown, including installing temperature sensors at numerous points on the line and periodically circulating oil within the pump stations to keep pumps, oil and facility piping warm.
DEC said Alyeska staff planned for both a normal restart and a cold restart. A cold restart could be required after an extended winter shutdown, and is a more complex restart process involving temperature monitoring of the pipe, periodically circulating oil through equipment, implementing various freeze-up prevention measures and installing additional piping and equipment at pump stations and other locations on the pipeline.
Cold weather shutdown risks include ice formation and buildup of paraffin wax within the pipe, which can damage or disable the system, DEC said.
Ice and wax could impede the progress of a cleaning pig that stopped near mile 420 of the line at shutdown and cause interference with the flow of oil and damage to the pipeline, valves and other critical equipment.
“Such damage could result in a more extended TAPS shutdown, with subsequent impacts to other North Slope facilities, including production facilities,” DEC said.
Restart Jan. 11The startup sequence began at about 7 p.m. Jan. 11.
DEC said regulators approved the restart plan because of weather concerns and because of the time Alyeska estimated it would take to fabricate and install the 157-foot, 24-inch bypass line needed to move oil around the area of the leak.
Alyeska-chartered C-130s began delivering parts and equipment for the bypass to the North Slope Jan. 9.
The temporary restart would increase the temperatures of oil and equipment and move the pig at mile 420 to Pump Station 8 where it can be removed from the pipeline.
DEC said the restart “will entail pumping oil through the compromised underground discharge piping, which may increase the flow of oil into the booster pump building and increase the potential for soil contamination.”
The agency said that aerial and ground-based monitoring of the main line would continue and normal operation would allow installed leak monitoring systems to resume functioning.
The restart was authorized by the unified command at 5:20 p.m. Jan. 11; restart procedures began at 5:30 p.m.; oil began flowing just after 9 p.m.
By noon Jan. 12, DEC said the rate of flow through the line was approximately 400,000 barrels per day. North Slope producers were providing oil at a rate of 330,000 to 350,000 bpd with the remaining volume coming from the Pump Station 1 storage tanks.
North Slope production was at 647,255 bpd Jan. 1 and dropped to 298,856 bpd Jan. 7. Northstar production dropped to zero; other fields remained some production level throughout the shutdown.
The cleaning pig which was of concern was expected to reach Pump Station 8 on Jan. 13. DEC said it would be trapped between two valves in the main line while oil flows around it through a bypass pipe. A second pig, in a warmer section of the line near Valdez, was expected to arrive at the Valdez Marine Terminal around midday Jan. 13.
DEC said Alyeska is planning for the upcoming shutdown and continues to prepare for a cold restart, should that be necessary. Field crews have installed 95 temperature monitors on the main line and plan to add up to 18 more. DEC said crews also continue to install additional piping and equipment at pump stations, including Pump Station 12, which is normally inactive but could play a role in a cold restart.
AOGCC emergency orderThe shutdown was also affecting the North Slope’s producing fields, and on Jan. 11 the Alaska Oil and Gas Conservation Commission issued an emergency order allowing BP Exploration (Alaska) to pump oil into specified development wells at the Badami, Endicott, Milne Point and Prudhoe Bay fields so that it could produce fuel gas and keep equipment and lines from freezing while the pipeline was shut down.
The commission said that while “normal production is not possible, some amount of production must be maintained to protect the safety of operating personnel in the fields and Deadhorse by providing fuel gas.”
It also said that if production equipment and pipelines are damaged due to freezing, state resources are at risk of environmental damage and public safety will be further threatened.
BP proposed a plan to maintain a minimum production rate to produce fuel gas and prevent freezing in field lines.
“In order to prevent waste, oil can be pumped into development wells to be later produced,” the commission said.
Since the unavailability of the pipeline “constitutes an emergency situation that may result in harm to public health and safety,” the commission issued the emergency order to allow pumping crude oil into development wells at the listed fields.