Spanish oil company Repsol, which just started deep-water oil exploration off Cuba, is expecting crews from Texas to arrive Thursday to help control a blowout in one of its exploration wells in Alaska.

The North Slope well encountered a pocket of natural gas that promptly forced drilling mud to erupt out of the well bore, the Associated Press reported. The well is located near the Colville River, 625 miles from Anchorage. Alaska officials suspect 42,000 gallons of drilling mud spilled onto the tundra and gravel surrounding the well.

Drilling mud is a water-and-lubricant mixture that cuts down on friction. The fluid also helps move shavings of earth back to the surface and away from the drill so as to prevent the hole from filling back up.

The AP said an unknown amount of gas leaked through the well. No oil was leaked and no workers were injured in the blowout.