Underground coal fires are a huge problem, what could possibly go wrong with intentionally igniting oil underground?

This month, on the frozen plains of Saskatchewan in Canada, workers began to inject steam and air into the Superb field, a layer of sand 700 meters down that holds 200 million barrels of thick, viscous oil. Their goal was not to pump out the oil, but to set it on fire—spurring underground chemical reactions that churn out hydrogen gas, along with carbon dioxide (CO2). Eventually the company conducting the $3 million field test plans to plug its wells with membranes that would allow only the clean-burning hydrogen to reach the surface. The CO2, and all of its power to warm the climate, would remain sequestered deep in the earth.
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