OREANDA-NEWS. Oil and gas producers in central Oklahoma must reduce their drilling wastewater well injections by more than 300,000 b/d to curb potentially damaging earthquakes, according to state regulators.

The reduction plan announced today marks an expansion of Oklahoma's earthquake prevention efforts which now include an area of more than 10,000 square miles in central and western Oklahoma and more than 600 wastewater disposal wells in the Arbuckle formation. The state's total area is about 70,000 square miles.

The Oklahoma Corporation Commission, which oversees production, does not have an estimate on how much oil and gas output could be curtailed because of the new regulations. Most of the producers affected are small operators with one to four wells.

"We have no way of knowing. It's up to each operator," said spokesman Matt Skinner.

The state's crude output was about 400,000 b/d in December, down by 2pc from November, according to the latest data from the US Energy Information Administration (EIA). The drop was in par with a nationwide downward trend.

A sharp increase in earthquakes in Oklahoma has coincided with a surge in oil and gas drilling activity in recent years. The Oklahoma Geological Survey (OGS) said it believes a recent increase in earthquakes is linked to increased injection well volumes.

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. Earthquakes near Cushing, Oklahoma, have been of special concern because it is a major crude storage hub, with more than 66mn bl of oil stored there currently, according to the EIA.

The wastewater injection reduction plan for central Oklahoma includes part or all of the counties of Oklahoma, Logan, Kingfisher, Garfield, Noble, Pawnee, Payne, Lincoln, Creek, Pottawatomie, and Cleveland.

It will reduce wastewater injections in the region by 30pc from the average of about 1mn b/d in 2015. It will be phased in over two months as recommended by researchers, who caution against sudden pressure changes. The first stage starts today.

State officials today also expanded the area covered by so-called "yellow light" earthquake precautions in areas that have not yet seen major seismic activity. The precautions include daily and weekly volume recording and reporting requirements.

The expansion, which added 118 Arbuckle wells to the area, is a "proactive move to get ahead of the earthquake activity," said Oil and Gas Conservation Division director Tim Baker.

The Oklahoma Corporation Commission has previously taken action after earthquakes above a magnitude 4.0, instructing producers to shut certain wastewater wells and cut back on others in the region. But the two regional plans for western and central Oklahoma are the largest volume reduction plans so far. In total, the state has taken actions to reduce wastewater injection volumes by 1mn b/d since March 2015.