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Spill analysis focuses on flowlines Long-awaited North Slope Spills Analysis points to three-phase flowlines as a culprit for spills, suggests augmented regulations Eric Lidji Petroleum News
Responding to a major oil spill caused by corrosion in March 2006, former Gov. Sarah Palin told the Alaska Department of Environmental Conservation in early 2007 to take a comprehensive look at the risks facing Alaska oil and gas infrastructure. Now that the study is complete, albeit with a narrower scope, that big spill looks to be an outlier.
The North Slope Spills Analysis released on Dec. 2 shows that two major spills, including the largest in the history of the North Slope, skew the dataset. Without them, flowlines prove to be responsible for most of the oil spills on the North Slope.
DEC is now recommending that regulators and operators use the dataset to improve mitigation measures to reflect the leading causes and locations of past oil spills.
The North Slope Spills Analysis looked for trends among the causes of spills on North Slope oil infrastructure, including wells, processing centers and storage tanks, and various pipelines, from gathering lines to flowlines to major crude oil transmission lines.
The analysis categorized 640 spills reported to the DEC between July 1995 and December 2009 by infrastructure, size and cause. Of the six types of infrastructure considered, spills from flowlines tend to be larger and more common than spills on other infrastructure, like process pipeline, facility pipeline, crude oil transmission lines, wells and storage tanks.
Two large spills in dataset In March 2006, internal corrosion caused a Prudhoe Bay transmission pipeline to spill 212,252 gallons of oil. In December 2006, a Prudhoe Bay separation tank spilled 255,152 gallons of produced water and 126 gallons of crude oil. Those are the two largest spills in the report, but hardly typical. The analysis found that valve and seal failures are the most likely cause of spills, while transmission lines and storage tanks are the infrastructure least likely to see spills.
However, corrosion, a much-discussed issue following the March 2006 spill, continues to be an important factor. Corrosion is the most common cause of spills greater than 10,000 gallons and is the most dominate cause of spills on flowlines, according to the analysis.
Flowlines typically carry three-phase fluid from a drill site to a processing center and that mixture of oil, natural gas and produce water can be highly corrosive to pipelines.
If there is a silver lining to the finding that flowlines might be the biggest culprit for spills, it’s that the state took the unusual step of regulating flowlines back in 2008.
“As far as I can tell, we’re the only government entity to attempt to regulate this particular pipeline,” DEC Director of Spill Prevention and Response Larry Dietrick said on Dec. 2.
As a result, the report recommends that the state augment its existing regulatory framework for flowlines by bringing in elements from other state and federal programs, as well as improving reporting requirements to make the database of spills more complete and to work to improve leak detection technology that could help prevent spills.
Fields, age and detection The 260-page report analyzes spill trends in a number of different ways.
It compares various North Slope fields by adjusting for production rates and pipeline mileage. It found that Endicott appears to have the lowest leak rates, while Milne Point appears to have the highest, and that Alpine, Endicott and Northstar appear to have consistently lower leak rates than Kuparuk River, Milne Point and Prudhoe Bay.
The analysis did not include Badami in the comparison because the on-again off-again eastern North Slope field has had a patchy production history over the past dozen years.
When the Legislature funded the study, it wanted to know what role age played in spills. The analysis found a “significant correlation” between age and probability of a spill, with the likelihood of a spill increasing 10-fold between five- and 30-year-old pipelines.
Dietrick noted that spill trends tend to follow a bathtub shaped curve, with incidents more likely in the early and later years of the life of a piece of infrastructure. Alaska is still “in the bottom of the bathtub,” he said, but needs to stay vigilant as facilities age.
Spills are primarily noticed by on-site crews, rather than leak detection devices. In fact, leaks are most commonly detected in June, when the sun never sets on the North Slope, making it easier for crews to spot leaks. As a result, the analysis concluded that reducing the time it takes to detect spills could significantly reduce the severity of spills.
The analysis did not look at the consequences of spills, but suggested it as a future topic.
A project years in the works The North Slope Spills Analysis grew out of a much larger project, a comprehensive assessment of the risks facing all oil and gas infrastructure in Alaska. The state narrowed the scope after the National Academy of Sciences found that project problematic.
The DEC announced this new approach in March and in August announced that it had completed the report, but did not ultimately release it to the public until early December.
Dietrick said the final report took longer than expected because the DEC needed approval from the DEC commissioner and Gov. Sean Parnell, and to get insights from a five-member “expert panel” convened to guide and review the North Slope Spills Analysis.
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