ConocoPhillips works to seal off source of gas release on North Slope, but state reports an “unsuccessful” cement seal

ConocoPhillips is working to seal off a low-pressure gas deposit that has been releasing gas to the surface at drill site in the Alpine oil field, a company spokesperson said Tuesday in an email.

Although production wells in the CD1 drill site remain shut off production at the field has been restored to near its normal 50,000 barrels per day, according to state production data posted April 11.

“The natural gas release at Alpine CD1 has been identified and controlled within the WD-03 well, and it is being permanently isolated with cement,” spokesperson Rebecca Boys said in an email.

However, the Alaska Oil and Gas Conservation Commission reported April 14 that a pressure test on the cement plug was unsuccessful, so the work in ongoing.

Gas was detected inside well houses on seven CD1 production wells on March 4. Wells were shut in, reducing Alpine field production, normally 50,000 barrels per day, to about 36,000 barrels per day, according to state data.

Production workers were temporarily relocated to other operations in the field as a precaution, although monitoring showed no detectable levels of gas near the wells and fluctuating levels at threshold detection levels inside the well houses.

An initial estimate of gas released is 7.2 million cubic feet, ConocoPhillips told the state of Alaska. The company has meanwhile identified the source of the gas as the C10 “Halo” formation, a gas deposit previously identified at about the 4,000-foot depth level.

It is unknown how the gas migrated to the surface to be released in cracks in the well pad, however. “This was a complete surprise to us. ConocoPhillips has been drilling through that formation for a long time,” with no uncontrolled releases of gas Jessie Chmielowski, a petroleum engineer with the state of Alaska, told a state legislative committee Tuesday.

Chmielowski is one of three commissioners with the Alaska Oil and Gas Conservation Commission, or AOGCC, a state agency responsible for overseeing well safety.

Shallow gas pockets are common in and around the North Slope fields and can be a safety hazard while drilling if they are at undetected high pressures. The C-10 (Halo) deposit was known to be a low-pressure pocket, ConocoPhillips’ Boys said,

ConocoPhillips is currently working to install an open-hole cement plug in the well that would permanently seal off the C-10 Halo formation, the AOGCC said April 12 in a statement.

Although there were concerns initially for personnel safety and for residents in the nearby Iniupiat village of Niuqsut, no environmental damage has occurred.

Also, the location of the CD1 pad near the main Alpine production center was also a cause for concern.

However, “There has been no injuries,” or threats to safety or damage, ConocoPhillips spokesperson Rebecca Boys said in an interview.

The Alpine field is one of three major North Slope producing fields, and is located west of the Kuparuk River and Prudhoe Bay fields. Alpine also acts as a “hub” for crude oil produced by ConocoPhillips at three smaller production sites in the National Petroleum Reserve-Alaska, CD5, GMT1 and GMT2.

Crude oil from the NPR-A sites is processed in Alpine field facilities and shipped on to Pump Station One of the Trans Alaska Pipeline System at Prudhoe Bay.

The Alpine field was producing at 48,943 barrels per day on April 11, according to state Department of Revenue production data. Total North Slope production was at 485,715 barrels per day, the revenue department said.