An estimated 1,890 gallons of drilling fluid spilled at the Kuparuk oil field on Sunday, state regulators said.
Doyon Drilling Inc. told regulators that the mineral oil-based drilling mud spilled onto a snow-covered gravel pad and nearby tundra and into the rig's secondary equipment.
The contaminated mud has been shoveled off the tundra and stockpiled for off-site disposal or recycling, according to the Alaska Department of Environmental Conservation.
The accident happened at about 12:30 p.m. when a gas kick pushed up drilling mud from a well that is being developed at the Tarn oil field, a Kuparuk satellite, according to regulators and Conoco Phillips, which runs the Kuparuk field. Conoco reported the accident to state regulators about an hour and a half after it happened.
The DEC said on Monday it is sending a responder to assess the spill and monitor the cleanup.
The well, Kuparuk 2L Well 320, has been shut in, the agency said. Kuparuk is the second largest oil field on the North Slope.
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By ELIZABETH BLUEMINK