Quakes continue for weeks

KINGFISHER — Western Kingfisher County continues t o shake nearly t wo weeks after an oil and gas operator stopped trying to complete wells at one of its locations.

An ongoing swarm of earthquakes continues to impact an area about 8 miles west of the county seat, including one that happened Aug. 7 that measured 3.5 on the Richter scale. The series of quakes included a 3.6-magnitude event that is the largest temblor believed to have been associated with hydraulic fracturing that seismologists have observed.

J ake Walter, Oklahoma's state seismologist, said it isn't normal for aftershocks to last this long.

“It is unusual to see a stronger earthquake associated with completion work after operat i ons have been s t opped,” Walter said on Tuesday.

Protocol for dealing with induced seismicity suspected to be caused by comp letion activities was adopted by regulators in late 2016 for operators in the SouthCentral Oklahoma Oil Province and Sooner Trend Anadarko Basin Canadian and Kingfisher counties (STACK) plays.

Generally, it calls for pauses i n completion efforts after l ocalized seismic events to allow underground pressures t o bleed away before work resumes.

In early 2018, the protocol was tightened as regulators sought to address increased observance of seismic events in those plays. The tightened protocol requires that all operators in the defined area have access to a seismic array capable of providing them with real-time readings.

It also requires operators to notify authorities and either reduce flow or pause operations after observing a magnitude 2 or greater event during completion operations. Mandatory pauses of either six or 12 hours are required after a magnitude 2.5 or 3 strength event.

Generally, t he minimum magnitude level at which earthquakes can be felt is a 2.5.

Encana/Newfield was the oil and gas operator that ended its completion work on July 24 after the 3.6- magnitude earthquake was observed in the vicinity of its wells.

The operator previously had paused its operations twice because of other stronger temblors — once after observing an earthquake the previous day, but also after seeing earthquakes on July 8, 9 and 10.

Dozens of seismic events have continued to be observed in the general area since completion efforts ended July 24. The events have varied in strength, from as little as a 1 on the Richter scale to as big as the 3.5 magnitude event observed a week ago.

Walter said seismologists are noticing areas of subsurface Oklahoma that appear to be sensitive to completion efforts involving horizontal wells.

“I wouldn't quite call them hot spots, but they are zones of sensitivity, or areas where earthquakes are more likely to be produced,” he said.

On Tuesday, he agreed that the area west of Kingfisher may just be the latest added to scientists' lists.

He said completion operations involve significant amounts of water t hat are injected into formations to hydraulically fracture rock and then are allowed to return to the surface.

Some of what flows back is recycled so that it can be used again, while some ultimately ends up flowing down a disposal well.

“It is a risk factor in some of these areas,” he said.

Walter said scientists expect after shocks after stronger events, even those related to completion work. But ongoing research evaluating natural recovery times after completion work has been temporarily stopped had been suggesting it would be safe to resume operations, at some point.

“This is a particularly energetic sequence, and we are trying to understand exactly why that might be the case,” he said.