The "high-pressure gas release" took place as the four men were bringing the well onto production Wednesday afternoon, said Doug Hock, a spokesman for Encana's U.S. division.
The incident, near the town of Platteville, Colo., north of Denver, did not involve an explosion or fire, he said.
Internal and external investigations have been launched to find out what caused the accident.
"Our concern right now is with the family and those involved, both the contractor who lost his life as well as those who were injured," said Hock.
The man who died and two of those injured were contractors with BGH Gas Test Operating Inc. of Castle Rock, Colo. The third man who was hurt is a lease operator with Encana (TSX:ECA).
The accident marked the first fatality at Encana's operations, said Hock.
"We had a very good record and again that's why we want to investigate thoroughly and really understand what happened."
The well is located in the Niobrara shale formation, which stretches through parts of Colorado and Wyoming.
"This is an area where we're operating, I believe, four rigs right now," said Hock.
"It's an area where there's a lot of activity, not just Encana, but other companies as well."
Based in Calgary, Encana produces natural gas from several shale formations in North America — from the Horn River in northeastern British Columbia to the Haynesville in the southeastern United States.
In the face of low natural gas prices, the company has been looking to produce more lucrative natural gas liquids, which are plentiful in the Niobrara shale.
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