Hilcorp Alaska has stopped a natural gas leak in Cook Inlet that released methane for months and generated concerns about impacts to wildlife and calls for increased scrutiny of the Inlet's dated oil and gas facilities.
Dive crews on Thursday night "safely and successfully" installed a clamp on the marine pipeline, Hilcorp said in a prepared statement.
The repair required multiple dives to the seafloor over the past week. State officials have said the damaged line is 80 feet deep.
Hilcorp will continue inspecting the 52-year-old pipeline and take additional steps to stabilize and protect it, the company said.
The subsea leak was discovered Feb. 7 but Hilcorp data showed it had been occurring since late December, according to federal pipeline regulators. The leak was northwest of Nikiski, about 3 1/2 miles off the coast.
Thick sea ice presented dangers to dive crews, delaying repairs for two months.
Bob Shavelson, with watchdog group Cook Inletkeeper, said Hilcorp's inability to repair the pipeline in winter is worrisome.
"If it takes Hilcorp months and months to shut in a leaky line, we need to re-evaluate whether they can operate in the Alaska winter," he said.
With warming weather melting the sea ice enough by Saturday, divers began efforts in the murky water to find the damaged spot.
"A total of 12 dives were completed on the fuel gas line in order to locate the leak, then properly position, stabilize and prepare the pipeline for repair," Hilcorp said in the statement issued by spokeswoman Lori Nelson.
Divers installed a steel and rubber clamp over the leak, creating a seal that won't release liquids or gas, the company said. The gash, found on the bottom of the pipeline atop a boulder embedded in the seafloor, was initially estimated to be about 2 inches wide.
But closer inspection, after the pipe was lifted more than 1 foot off the seafloor, and after divers removed mineral buildup on the outside of the pipe, showed a smaller gash, less than a half-inch long and across.
The pipeline was the first installed in Cook Inlet in 1965 as the oil and gas industry was launching a rapid construction program in the basin. By the end of the decade, 14 production platforms were built.
Originally, the pipeline delivered oil to a shore-based processing facility, tapping the Middle Ground Shoal field, the first offshore discovery in Alaska, with Shell the operator at the time.
As facilities changed hands over the decades, the line in 2005 was converted to natural gas. It delivered fuel gas 7 miles to operations at Platform A, and also to other nearby production platforms at the field. Hilcorp Alaska acquired it in 2015 from XTO Energy.
Unable to immediately make dive repairs, Hilcorp, with approval from regulators, decided against completely shutting down the line. The company said it was concerned that residual oil left in the line could leak into the environment.
But after discussions with Gov. Bill Walker, Hilcorp in late March shut down the small oil production from the field. That allowed Hilcorp to significantly reduce the amount of fuel gas flowing through the line, and reduce the leak.
The 8-inch pipeline was originally installed next to an oil pipeline that still delivers crude oil today and has generated concerns among regulators and watchdogs that it too will leak, subject to the same threats that led to the gas line leak.
Hilcorp Alaska said it is taking steps to further inspect and protect the oil line from damage.
"Neither pipeline will be returned to regular service until Hilcorp, along with state and federal regulators, agree it is safe to do so," the company said.