OREANDA-NEWS. December 21, 2016. Small earthquakes in Oklahoma's burgeoning Scoop and Stack shale regions could be linked to hydraulic fracturing operations, state officials said today.

The Oklahoma Corporation Commission and the Oklahoma Geological Survey (OGS) announced guidelines for operators in the region in the event of earthquakes of a 2.5 magnitude or higher within 1.25 miles (2km) of the operations, the first such pre-emptive regulations.

The state has previously limited wastewater disposal wells in the Arbuckle formation after large earthquakes as high as magnitude 5.6. Seismic activity has increased sharply in the state coinciding with a surge in oil and gas drilling activity.

The state agencies today cited previous research by a state seismologist as well as more recent data that showed smaller earthquakes outside of the Arbuckle area could be linked to hydraulic fracturing, a well-completion technique.

"We have enough information to develop a plan aimed at reducing the risk of these smaller events as operations commence," said OGS director Jeremy Boak.

Under the guidelines, an operator must suspend hydraulic fracturing operations after an earthquake of magnitude 3.5 or higher. If the earthquake is between 3.0 and 3.5 magnitude, the operator mush pause operations for at least six hours and hold a technical conference with state officials about mitigation practices. A 2.5 to 3.5 magnitude earthquake triggers implementation of a mitigation plan.

The Oklahoma Oil & Gas Association said its members are ready to immediately implement the guidelines. "As the data indicates, these seismic events have been small, rare and manageable," said the group's president Chad Warmington.

Seismic activity in Oklahoma is down sharply compared to last year "thanks to measures taken by the state in collaboration with the oil and natural gas industry and the scientific community," he said.

The number of earthquakes in Oklahoma above a magnitude 3.0 increased to more than 900 in 2015, compared to about 580 in 2014 and about 100 in 2013, according to the US Geological Survey. A number of studies have linked the quakes to wastewater injection wells where companies dispose of water and fluids that are generated from drilling and completion work.

The number of earthquakes has decreased this year to about 600, following efforts to limit the wastewater injection wells and a price-related slowdown in drilling.

The Oklahoma Corporation Commission implemented a large program in May that included limits on more than 600 disposal wells in the Arbuckle, the state's deepest formation. By comparison, the Scoop and Stack plays have very small amounts of produced water, state officials said.

Oklahoma regulators last month ordered oil and gas operators within 6 miles (10km) from the location of a 5.0 magnitude earthquake near the oil storage hub of Cushing to shut wastewater disposal wells. Regulators also implemented other limits on wastewater wells within 15 miles of the quake, which struck on 6 November about 2 miles (3km) west of Cushing.

Cushing is home to a massive oil storage hub, with a current total storage capacity of 66.5mn bl, according to the US Energy information Administration. Several large operators at Cushing, including Magellan Midstream Partners, Enbridge, Enterprise Products Partners and SemGroup, reported no damage to storage hubs or pipelines after the 5.0 earthquake.