A gap no wider than a human hair is allowing natural gas to migrate through a cement barrier that was supposed to seal Nalcor Energy’s first onshore exploration well at Parsons Pond.
That’s the early diagnosis, according to the province’s energy corporation which is still investigating the gas leak at its Seamus No. 1 well on the Northern Peninsula.
Nalcor estimates it could take until early January to fix the problem in the upper portion of the well.
“What we have is gas leaking through part of the first barrier, the cement,” said Jim Keating, vice-president of Nalcor’s oil and gas division.
He describes the problem as a “slow, low-volume, low-pressure leak” in the annular space between the steel casing of the drill pipe and the rock wall of the wellbore.
Nalcor has looked to other onshore oil and gas industries in Alberta and B.C. to assess the leak.
“We’re satisfied that our particular flow issue is what they call a non-serious flow,” said Keating.
A flow rate above 300 cubic metres per day, he said, is the line between serious and non-serious.
“Our flow rate that we’ve been able to measure is one-tenth that, so it’s well within the non-serious flow rate.”
Seamus No. 1 is part of three-well, $20-million exploration program at Parsons Pond.
When it suspended drilling in late May, Nalcor plugged, cemented and installed a wellhead at Seamus No. 1.
At the time, the company also reported “gas shows” at the well, and planned to return later to test and measure its potential find.
Keating said the cement barrier was also tested to ensure no leaks developed. They can occur up to 12 to 30 hours after cement is poured.
“We did the cement job, did pressure tests … and everything read zero. So we were satisfied the cement job went well.”
The gas leak was discovered Oct. 28 by a contractor during a routine well inspection.
A wellhead valve showed natural gas where it wasn’t supposed to be — the well’s cement barrier.
“The pressure’s supposed to read zero — meaning that we’ve got no flow into that space,” said Keating.
Unfortunately, he said, he suspects the cement may also contain a microscopic channel or two that is allowing the gas to migrate.
The cement is one of two barriers, along with the wellhead itself, designed to seal the well and prevent gas migration.
On a suspended or abandoned well, the wellhead performs the same function as a blowout preventer.
Blowout preventers, which are used during drilling, prevent potentially explosive surges of oil and gas by shutting down the well.
Unlike a blowout situation, Keating said the Seamus No. 1 well is under control.
“Our casing is still intact. There’s zero pressure inside the wellbore. There’s no gas inside the well.
“We’ve always had control of the well.”
For now, he said Nalcor is venting the gas through a wellhead valve and monitoring the site 24/7.
Fixing the problem means perforating the upper portion of the well’s cement barrier using an explosive charge.
Then, the company will sample and measure the gas flow and pressure-test the well.
To do this, Nalcor will borrow a rig from St. John’s-based Vulcan Minerals, one of its partners at Parsons Pond.
That specialized rig is used to test oil and gas flows at a well. Vulcan is using the rig at its exploration property south of Stephenville.
“We’re told about three weeks from now that rig should be made available to us, depending on how (Vulcan’s) operations go,” said Keating.
Once the tests are done, the rig will pump another batch of cement into the well. More pressure tests will be done to check for leaks.
“Basically, it’s a redo of the cement job in that area.”
Those repair efforts will likely focus on the first 10 metres of the well.
Keating said the company’s investigation may also point to the need for changes to future cement additives, weight and density to prevent future leaks.
“By the time we’re finished with that well it could be early January,” he said. “We would never rush any kind of repair.”