ConocoPhillips says gas release in North Slope field may be coming from shallow underground gas pocket

ConocoPhillips says it now believes a shallow gas pocket is the source of a troublesome release of methane on the CD-1 drill pad in the Alpine field, on the North Slope.

Detection of the gas last week prompted the company to temporarily relocate workers and to suspend operations on the pad, also curtailing production.

The company has also activated a drill rig to test for the source of the gas, which is coming from an underground source.

Gas was detected in four well houses on the production pad in the field. It is likely migrating through rock to the surface.

“We now believe the source to be a low-pressure gas pocket at the 2,000 foot to 4,000 depth range,” a ConocoPhillips spokesperson said last week. The gas appears to be reaching the production pad through cracks one eighth to one quarter of an inch wide.

The rig now activated has pulled production tubing from one well to the diagnostic tests, according to a report issued late Tuesday by the Alaska Oil and Gas Conservation Commission, a state regulatory agency in charge of well safety.

ConocoPhillips first detected the gas March 3 in well house and then subsequently in others. The gas is still present but is now at low trace levels at the threshold of detection, the company spokesperson said.

Personnel temporarily relocated are now being returned to work. Meanwhile, some of the gas has been captured and sent to a nearby oil and gas processing facility.

“We want to emphasize that there have been no injuries due to the gas release and no harm to the environment. Also, there have been no effects on the nearby Inupiat village of Nuiqsut, which is eight miles away,” the spokesperson said.

Although an apparent minor issue the gas release caused a great deal of concern when it was first detected because the CD 1 production pad is adjacent to a major field processing plant that is a hub for moving crude oil from the field to Pump Station One at the Trans Alaska Pipeline System, which is further east in the Prudhoe Bay field.

The nature of the release, from an apparent source several thousand feet underground, and its migration to the surface and at a production pad, is also unusual and is being investigated by the company and state regulatory officials.

Seepage of oil from shallow oil deposits is common on the North Slope and elsewhere, however.

Had the gas caused a fire field production facilities could have been damaged, causing the 50,000 barrels per day of Alpine production to be shut in until repairs were made, state of Alaska officials said.

As it is, the shutdown of production from CD 1 has resulted in a reduction of Alpine production by about 8,000 barrels per day, ConocoPhillips said. The field was producing at 43,700 barrels per day on March 23.

Shallow gas pockets are common on the North Slope and can be drilling hazards if drillers unexpectedly encounter high pressures in one of them.

ConocoPhillips believes this one to be low pressure, however.

It’s also possible the gas may be coming from a gas hydrate, which are known to exist in and near the producing North Slope fields in the permafrost layer of frozen rock that begins 2,000 feet underground on the slope.

Gas hydrates exist when conventional gas is frozen into the permafrost, and they can hold very large quantities of methane, the main component of natural gas.

Gas can be released from a hydrate if warming occurs, such as from contact during well drilling. A drilling operation was underway at CD 1 when the gas release was first detected.