Hilcorp Alaska, owner of an underwater pipeline leaking natural gas into Alaska's Cook Inlet, is now responding to a second pipeline spill in the same vicinity. That one was spewing oil.
The pipeline, which connects two oil platforms, released an unknown amount of crude oil into the inlet before the flow of oil was halted Sunday. Oil sheens appeared as far as three-and-a-half miles away from the source of the spill. The leak was discovered and reported to the state Department of Environmental Conservation (DEC) midday Saturday.
The two oil platforms, called the Anna and Bruce platforms, are on the western side of Upper Cook Inlet. The natural gas leak is on the eastern side of Upper Cook Inlet, where the company owns two pipelines and four oil platforms. The gas pipeline has been leaking almost pure methane since late December. The two leaks are unrelated.
The gas leak has raised concerns for regulators and environmentalists, particularly because the area is home to an endangered population of beluga whales. The first water samples showed levels of methane high enough to be dangerous to fish. Oil carries an even bigger environmental threat.
Hilcorp personnel aboard the Anna platform reported the oil spill on Saturday after they felt an impact around 11:20 a.m., according to a report released by the DEC. When they looked over the edge of the platform, they saw an oil sheen and bubbles surfacing near one of the platform legs, where the pipeline is located.
The cause of the impact isn't yet known.
In response to the oil leak, Hilcorp shut down oil production on both platforms, and reduced pressure on the line from 70 psi to 5 psi. The company also conducted flights around the area. On a flight at 12:30 p.m. Saturday, an hour after the spill was first observed, Hilcorp reported seeing six oil sheens. The largest was 10 feet by 12 feet. Two others were three to four feet by 20 to 25 feet, according to the DEC.
An oil spill response ship arrived to the Anna Platform to look for sheens at 12:45 p.m., but did not find any.
On Sunday, response crews sent a "pig" through the pipeline to push the remaining oil in the line past the spot where it was believed to be leaking, and then out of the line.
"The crude oil pipeline between the Anna and Bruce platforms has been shut-in and the pressure to the line has been reduced to zero pounds per square inch," the DEC said in a report released at 4.30 p.m. Sunday.
The 8-inch pipeline's capacity is 461 barrels of oil. It sits roughly 75 feet below the surface of Cook Inlet. Both leaking pipelines were built in the 1960s.
Cook Inlet poses particular challenges for oil and gas infrastructure—and for response to leaks. The inlet has brutally strong currents and tides.
The federal Pipeline and Hazardous Materials Safety Administration issued two separate orders in March related to Hilcorp's leaking gas pipeline and an adjacent oil pipeline. It said the strength of the inlet's currents can cause a vortex of water to build around a pipeline if it's not secured to the seabed. This whirlpool can cause the pipe to snap.
Last week, Hilcorp shut down production on its two oil platforms on the eastern side of the inlet and reduced the amount of gas flowing in the leaking line. When the ice in the inlet melts, expected in the next week or two, the company will repair the line.
Hilcorp began operating in Alaska in 2012 and is the main producer of oil in Cook Inlet. According to the Alaska Oil and Gas Conservation Commission, the company is responsible for more than a quarter of all 45 safety violations from 1977 through 2016.