OREANDA-NEWS. The US Geological Survey (USGS) is advising the state of Oklahoma to distribute oil and gas wastewater injection wells over a larger area to limit potentially damaging earthquakes near cities and oil infrastructure, including the key Cushing storage hub.

The USGS and the Department of Homeland Security "are advising that wastewater injection be managed and distributed over a broader region that is far from major infrastructure, such as the Cushing storage facility, and large urban areas such as Oklahoma City," said Daniel McNamara, a research geophysicist with the USGS. He is working with the Oklahoma Corporation Commission on the issue. The commission regulates oil and gas activity in the state.

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) has concluded that the majority of recent earthquakes in central and north-central Oklahoma are likely triggered by the injection of produced water in disposal wells by the oil and gas industry. Researchers in Texas have made similar connections between the increased frequency of earthquakes and injection wells.

Oklahoma has seen more than 800 earthquakes above a magnitude 3.0 so far this year compared to 583 in 2014 and 103 in 2013. The earthquakes have become so frequent that the OGS has a Twitter account devoted solely to earthquake announcements.

Earthquakes near Cushing, Oklahoma, have been of special concern because it is a major crude storage hub, with about 60mn bl of oil stored there currently, according to the US Energy Information Administration.

There have been three earthquakes above a magnitude 4.0 near Cushing this year, compared to two in 2014, McNamara said.

McNamara and other researchers concluded in an 23 October study that a 5.6 magnitude earthquake could occur at "the conjugate fault intersection directly beneath the Cushing oil storage facility."

A 5.6 earthquake in Prague, Oklahoma, in 2011 was the strongest recorded in the state. The intensity of shaking in a similar earthquake "could cause moderate to heavy damage to storage tanks in the Cushing facility depending on the tank height, diameter, and percent full," according to the October paper.

The Oklahoma Corporation Commission immediately takes action after any earthquake above a magnitude 4.0, instructing producers to shut certain wastewater wells and cut back on others in the region. After the 4.0 magnitude earthquakes in Cushing this year the commission limited wastewater disposal in the immediate vicinity. The earthquakes rapidly died off, McNamara said.

Companies that own storage at Cushing have checked their tanks and "so far, nothing is compromised," said Matt Skinner, a spokesman for the Oklahoma Corporation Commission.

Skinner said the commission is "exploring all options" to prevent the earthquakes. He would not elaborate on possible actions.

Canadian midstream company Enbridge, which owns 20mn bl of storage at Cushing, said that all of its steel tanks have clay-lined berms which can contain 110pc of the volume of each tank should they be damaged.

SemGroup, which holds 7.6mn bl of storage at Cushing, said that its crude tanks were built after 2008 in accordance with engineering guidelines set by industry group API known as "Standard 650," which is the main standard for aboveground oil storage tanks. The company also requires all wetted surfaces of the tanks to have an additional 1/16th of an inch of steel in thickness so that they exceed industry standards.

API says it does not have separate standards for tanks that are in seismically-active areas.