A North Slope well spill is bigger than originally thought

More than 7,000 gallons of petroleum products leaked from a North Slope well operated by Caelus Energy Alaska, state environmental regulators said this week, more than doubling the original estimate of the size of the spill.

The release consisted of diesel fuel and mineral oil, products refined from crude oil that are used as antifreeze in the well. In July, the month after the leak was initially discovered, Caelus had reported it was smaller, at 2,900 gallons, with most of it contained to a metal well cellar rather than escaping onto the surrounding gravel pad.

But further investigation by Caelus showed that the metal cellar, a large metal container around the well, did not contain plugs to hold the spilled material, said Tom DeRuyter, state on-scene coordinator for Alaska Department of Environmental Conservation.

The missing plugs allowed liquids to move between the cellar and the surrounding pad, and some of the oil product to escape the cellar.

A small amount of the spilled material is believed to have reached the tundra. Caelus “estimates that about 3 gallons of the oil leaked” off the pad, DeRuyter said.

The spill occurred at the Nuna drill site gravel pad about 45 miles west of Deadhorse. Caelus has delayed development at the Nuna project amid low oil prices and uncertainty over state payment of cash credits. The state has said top production at Nuna could reach 25,000 barrels daily. Caelus says the state owes it $75 million in tax credits convertible to cash payments.

DeRuyter said the Nuna well was not in production.

At the Nuna spill, Caelus “estimates 4,200 gallons (100 barrels) of diesel freeze-protect fluid and 2,940 gallons (70 barrels) of mineral oil” were released from the well, a DEC statement said.

At some point, water entered the cellar at the Nuna well and froze, damaging a valve and assembly on the well, DeRuyter said. That allowed the oil, used as antifreeze in open spaces outside pipes, to escape the well into the well cellar.

Later, Caelus cleaned out the well cellar and discovered the missing plugs. Excavation work outside the cellar revealed the release onto the pad, DeRuyter said.

The DEC is continuing to investigate the release, he said. And Commissioner Cathy Foerster of the Alaska Oil and Gas Conservation Commission said her agency was also investigating.