Le Devoir : In Thetford Mines, Deep Sky is drilling to bury carbon 1000 meters underground

Alexis Riopel

October 10, 2025 – It’s official: a company is drilling a well in Quebec to try to bury carbon underground. Work begins this week in Thetford Mines, in Chaudière-Appalaches.

Just steps from the drill site, inside an abandoned asbestos mine, geologist Gregory Maidment, one of the project's architects, does not hide his enthusiasm. “This is very, very, very exciting! Proving that this idea works here will unlock mineralization in Canada and provide the country with a decarbonization solution for the rest of the planet.”

The project is by Deep Sky, a company founded in Montreal in 2022, funded with over $100 million from public and private sources. The company aims to capture CO2 from the air and then store it indefinitely in the earth’s crust—an energy-intensive, costly ambition that has never yet been realized on a large scale.

Deep Sky places great hopes on its project in Thetford Mines. In this post-industrial, lunar-like setting, the company wants to develop its first major commercial project, whose four phases could sequester 500,000 tonnes of CO2 per year: the equivalent pollution generated by an aluminum smelter.

A lot of money is at stake. Deep Sky sells carbon credits to companies like Microsoft and the Royal Bank of Canada. On this market, buyers pay hundreds, even over $1,000, to bury one tonne of CO2, a method recognized as the gold standard in carbon offsetting.

Alex Petre, Deep Sky’s CEO, traveled from Calgary to attend the start of drilling in Quebec, an important milestone. Carbon sequestration "unites the country rather than divides it," she said. "People on both sides see benefits.”

For some environmentalists, carbon sequestration is just a costly distraction while oil flows freely. Analysts argue it is an essential tool to reach carbon neutrality, even after deep emission reductions.

Though climate policies are currently being challenged in North America, Ms. Petre sees strong appetite for carbon sequestration in Europe and Asia. “We mustn’t let the American tree hide the forest...” she warns, urging Mark Carney to sign agreements with other countries to recognize Canadian carbon credits.

An extraordinary geology

Deep Sky chose Thetford Mines because of its very particular geology (once the “world capital of asbestos”), favorable to the chemical reaction that locks CO2 underground. “For what we want to do, it’s the best place in the world,” says Mr. Maidment, vice president of underground operations.

Nearby, a turquoise lake testifies to this. The water lies in an old open-pit mine, a 400-meter-deep hole. It is magnesium, abundant in the metamorphic rock underground, that gives the water its vivid color.

Over the next month, on land owned by Société Asbestos, workers will drill an 8-centimeter hole down to 1000 meters, where the drill is expected to cross a geological fault identified by magnetic and gravity surveys conducted by Deep Sky.

For now, the company’s authorization only allows “experiments.” It will inject water (taken from the mining pit) to assess rock porosity, then add a “non-toxic” carbon-containing substance to measure the rock’s reactivity.

The desired reaction is “mineralization,” where a mixture of water and CO2—like sparkling water—reacts with the rock to create a stable mineral such as magnesium carbonate. Independent experts do not doubt the permanence of mineralization. The company CarbFix uses the same method in Iceland.

At the foot of a spoil heap, a huge pile of mining waste, Mr. Maidment points to crushed rock he tested last year. Rainwater, containing dissolved carbon, reacted with the stone, leaving a white crust. “This is mineralized CO2!” he explains, hoping to replicate this magic a kilometer underground.

A new law before proceeding further

The team expects to finish testing by November. If geological potential is confirmed, it will move to the first “commercial” phase, employing about ten specialized technicians and sequestering 30,000 tonnes of CO2 annually.

This will require drilling a second, larger well connected to the first at depth by the identified fault, allowing carbon-enriched water to circulate in a loop. Crucially, the company must capture CO2 from the atmosphere.

On the rocky area near abandoned warehouses, Deep Sky would install capture modules. At its Innisfail, Alberta site, inaugurated this summer, it is testing about ten developers’ technologies to select the best.

These machines use fans to push air over a chemical capture surface, then release the captured carbon using heat. The process requires substantial energy—energy that critics say should instead replace fossil fuels.

In February, Deep Sky applied to Hydro-Québec for 145 megawatts (MW) in four phases for the Thetford Mines project, equivalent to a large wind farm. The first phase alone requires 15 MW.

No decision has been made yet.

The launch of phase 1 depends also on establishing regulations for geological carbon sequestration in Quebec—defining long-term reservoir responsibility, a requirement for carbon credit certification.

Deep Sky has pushed the Ministry of Economy, Innovation and Energy’s office for over six months for these rules. A bill is reportedly nearly ready. The regulatory framework would also give access to a refundable federal tax credit covering up to 60% of investments, contingent on projects being located where carbon storage is “permanent.”

Phase 1 must also undergo environmental impact assessments, possibly by the Bureau d’audiences publiques sur l’environnement.

“Sacrificed” sites

At the MRC des Appalaches offices, which includes Thetford Mines, Director Rick Lavergne says Deep Sky’s project is “probably the most serious” among many proposals to revitalize old asbestos mines and waste sites in the region.

“We created wealth but also environmental scars. We believe our sites can now be part of the solution,” says Mr. Lavergne, who hopes the company will continue drilling on these “sacrificed” sites, remote from housing, in coming years.