ConocoPhillips points to operational error as cause of gas leak at its Alaskan field

ConocoPhillips Tuesday for the first time describe which went wrong to cause an unusual natural gas leak that began in March and continued for weeks at a drilling rig in the Alpine Field on Alaska’s North Slope.

The company said the leak, detected March 4 at the CD1 drilling rig, occurred during a drilling operation that put too much pressure on the well. This caused a shaft component to fail about 800 meters below the earth’s surface, according to a nine-page technical report. report.

“The pressure limits were exceeded” during the operation, the company said. Pressure has built up during operations to pump diesel fluid into the well to provide freeze protection in an area where permafrost, or frozen ground, can damage pipes.

The company also failed to detect and respond to mounting pressure for three days before the leak was detected, missing an opportunity that would have reduced the gas leak, according to the report.

“The pressure increases…were not acknowledged and/or addressed and therefore did not lead to investigation or corrective action during this time,” he said.

The gas leak caused the temporary withdrawal of 300 people, alarmed residents of the nearby village of Nuiqsut and halted oil production from the drilling site.

It has also led to an ongoing investigation by the Alaska Oil and Gas Conservation Commission and a probe by Democrats to the US House Natural Resources Committee.

Rebecca Boys, a spokeswoman for the company, said the incident was unique.

“We’ve never seen anything like this before,” she said.

The gas was released from a shallow underground area that the company did not expect to contain significant amounts of gas. The gas took different routes to emerge on the surface of the drilling platform at different places.

The company mitigated the release on March 8 by bringing the gas to the surface through the waste disposal shaft. On April 8, he said he had mastered the source of the release.

But ConocoPhillips continued to detect traces of gas on the drilling rig for several weeks as gas trapped under underground obstructions slowly rose to the surface, the company said.

ConocoPhillips said the part of the well that failed involved a component called a casing shoe about 2,300 feet below ground.

The shoe is a structure at the end of a section of pipe, surrounded by cement that helps stabilize the pipe in the rock, said Dan Seamount, longtime commissioner of the oil and gas commission.

Seamount said Wednesday the commission continues to investigate the incident and gather information.

“We haven’t come to a conclusion as to what they’re saying is correct or not,” Seamount said.

ConocoPhillips said in its report that it followed requirements to place protective cement around the pipe in certain pipe sections.

But he did not encase the pipe in cement in the shallow underground area where the gas came from.

The company said it was not required to do so because it did not expect this area to contain significant amounts of gas.

Lack of cement around the pipe in that area and other well design factors did not cause the gas leak, the company said in its statement. eight page response letter to House legislators.

But ConocoPhillips told lawmakers that one of the future corrective actions it will take to prevent a similar incident is to take a closer look at drilling hazards and underground areas that require “cement isolation.”

Other corrective actions include developing a standard operating procedure document for freeze protection operations, improving detection and company communication when pressures increase in the space at the exterior of the pipe and improved well planning before and during drilling operations.

“We don’t expect that to happen again,” Boys said.

Seamount, along with the Oil and Gas Commission, said there was a good chance the commission would hold a hearing as part of its investigation. He said the commission was working on its own report.

“We’re trying to get it out as soon and as accurately as possible,” he said.

ConocoPhillips declared 7.2 million cubic feet of natural gas has been freed into the atmosphere between March 4 and March 8, when the company was able to begin delivering gas to the surface through the storage well.

Bonny J. Streater