A Texas crew was scheduled to arrive at Alaska's North Slope on Thursday to control an exploratory well that apparently blew out.
No workers were injured or oil spilled at the well near the mouth of the Colville River when drilling hit a natural gas patch about 2,600 feet deep Wednesday, forcing mud back up the rig, Alaska Department of Environmental Conservation spokesman Ty Keltner said in a release.
About 42,000 gallons of drilling mud were released on the gravel pad and snow-covered tundra, he said.
Drilling mud and methane gas shot from the well through a diverter pipe, the Anchorage Daily News reported. Additional mud was pumped into the borehole in an effort to "kill" the well, but that mud was also blown out, Keltner said.
Spanish oil company Repsol evacuated workers from the site over concerns about the methane gas.
By Wednesday evening, Repsol reported that the flow of gas appeared to have nearly stopped and drilling mud was no longer flowing from the well, Keltner said. However, the well was not under control, he said.
Repsol has hired Wild Well Control Inc. of Houston to assist with controlling the well. That crew is expected to arrive Thursday.
Once the well is controlled, the North Slope company Alaska Clean Seas will begin to clean up the mud.
A state and a North Slope Borough official were also expected to be onsite Thursday. A command incident team was being arranged.
The spill was at the Qugruk 2 drill site near Nuiqsut, about 625 miles north of Anchorage.
Drilling mud, or drilling fluid, is a term for liquids used in drilling that lubricate the drill shaft and cool the hole.
Repsol E&P USA Inc., a subsidiary of Spain energy company Repsol-YPF, announced in March that it would invest at least $768 million in North Slope oil exploration and development. At the time, Repsol said it was working with 70 & 148 LLC and GMT Exploration LLC to develop leases over a 772-square mile area. It began exploratory work this winter.