With oil production from Alaska's North Slope in continuous decline for many years, Alyeska Pipeline Service Co., the operator of the trans-Alaska oil pipeline, has been upgrading the line and taking other actions to accommodate the technical issues caused by declining pipeline throughput. An overview of the latest status of Alyeska's efforts to deal with the slowing flow of oil is a core component of the 2012 State Pipeline Coordinator's Annual Report, published in October by the Alaska Department of Natural Resources.
Pipeline throughput peaked at more than 2 million barrels per day in 1988 but had dropped to around 600,000 barrels per day in 2012, the report says. The State Pipeline Coordinator's Office oversees the construction and operation of pipelines, including the trans-Alaska pipeline, on state right-of-way leases.
The key issue for the trans-Alaska pipeline is the speed at which oil flows down the line. With less and less oil entering the upstream end of the line, oil filling the line takes longer and longer to travel from the North Slope to Valdez.
With the slowing oil flow, the original pipeline pump systems, designed to handle relatively high rates of oil throughput, became inefficient and unsuitable for flexibly handling the lower flow rates.
And, with the oil taking longer to travel the pipeline's 800-mile length, the oil, warm as it exits the oil fields, becomes increasingly cold along the pipeline route, raising risks associated with the freezing of water carried along with the oil and potentially increasing the clogging of the pipeline walls with wax deposits.
In the early 2000s, to address the increasing inefficiency of the pumping systems as oil volumes declined, Alyeska initiated what it termed "strategic reconfiguration," a massive project involving the replacement of the original turbine driven pumps by new state-of-the-art electrically powered pumps -- variable frequency drives on the new pumps would enable the pumps to operate over a relatively wide range of pump speeds. And as part of its reconfiguration, Alyeska installed new remotely operated pipeline control and monitoring equipment, using modern digital technology.
Alyeska completed the electrification upgrades at pump stations 3, 4 and 9 in the years 2005 to 2009. Upgrade work started on pump station 1 in the 2000s but Alyeska subsequently put this upgrade on hold, the report says.
With fewer pump stations needed at lower oil throughputs, Alyeska shut in the remaining pump stations, apart from pump station 5, which acts a pressure relief station on the south downslope of the Brooks Range and does not pump oil.
During the financial year that ended June 30, 2011, Alyeska restarted the upgrade at pump station 1 in a phase of reconfiguration that the company called the electrification and automation project, the report says. That project involves the installing three new mainline pumps, with electric motors and variable frequency drives; installing a 12-megawatt turbine-powered electrical generator; and modifying two of the three booster pumps at the pump station for electrical service. In January 2011 an oil leak at pump station 1 on the North Slope triggered an extended pipeline shutdown, with the oil temperature dipping to 26 F.
Since that incident Alyeska has been recycling oil at pump stations 3, 4, 7 and 9 to warm the oil when oil temperatures in the pipeline drop, the report says.
By ALAN BAILEY