Small Texas quakes linked to injecting CO2 underground

WASHINGTON — A cluster of earthquakes in Texas may be tied to oil companies injecting carbon dioxide into deep rock formations in the area, according to a paper released Monday.

The study, published in Proceedings of the National Academy of Sciences, is one of the first to look closely at the potentially earth-shaking repercussions of injecting carbon dioxide underground, both to store the greenhouse gas and help enhance oil recovery. And it is the first to document a correlation between earthquakes greater than magnitude 3 with the gas injection process that many believe is valuable for combating climate change.

University of Texas seismologist Cliff Frohlich, who led the research into the Texas quakes, cautions that the science is new and there is plenty more investigations to do. But similar findings could throw cold water on policymakers’ enthusiasm for capturing carbon dioxide and indefinitely storing the heat-trapping greenhouse gas underground.

Frohlich and fellow professor Wei Gan said gas injection at the Cogdell oil field north of Snyder, Texas may have sparked as many as 18 earthquakes with magnitudes of 3 and greater between 2006 and 2011 — including one that registered 4.4 on the moment magnitude scale.

“Gas injection may have contributed to triggering a sequence of earthquakes occurring since 2006,” Frohlich and Gan said. “This is an unusual and noteworthy instance where gas injection may have contributed to triggering earthquakes having magnitudes of 3 or larger.”

Enhanced oil recovery

The small temblors took place at a time when energy companies were increasingly using carbon dioxide to help extract oil from the Cogdell field, an activity that began in the area in 2001, but which Frohlich and Gan said “has been ongoing with nearly constant injection volumes since 2004.”

Oil companies can boost their recovery of crude by sending gas underground to displace crude. Although other gases can be used, carbon dioxide is favored because of the way it interacts with oil underground.

Energy Secretary Ernest Moniz has touted the potential of carbon dioxide to boost U.S. oil recovery, while at the same time indefinitely storing the greenhouse gas. While the U.S. is now producing about 300,000 barrels per day using carbon dioxide at older fields, Moniz has said that could grow to about 3 million barrels a day, as long as there’s enough CO2 captured from power plants and industrial facilities to support it.

The Energy Department is working to accelerate some enhanced oil recovery technology and operations. For instance, it has provided about $431 million toward a project at Valero’s refinery in Port Arthur, Texas, where carbon dioxide is now being extracted from two steam methane reformers, then dried, compressed and shipped to the West Hastings oil field 20 miles south of Houston.

Water injection

The area near Snyder, Texas, which Frohlich studied, is a good case study; oil and gas has been produced in that region for decades.

Earlier studies said water flooding to improve petroleum production in the Cogdell oil field between 1957 and 1982 caused earthquakes between 1975 and 1982. But the seismic activity stopped between 1983 and 2005, before jumping again a year later.

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Frohlich and Gan say the major change was the surge in gas injection. The researchers said water injection can’t explain the recent quakes.

“This sequence followed a 24-year interval when no earthquakes were detected,” the researchers said. “The post-2006 sequence followed significant increases in gas injection in the Cogdell field, and many earthquake epicenters were within two kilometers of actively injecting wells.

Different geology

But the study notes that similar gas injection at nearby oil fields haven’t been accompanied by the same seismic activity.

For instance, the nearby Kelly-Snyder and Salt Creek fields “have experienced a combination of years of sustained injection (and) extraction of water (and) oil, followed by recent increases in gas injection.” And at test injection sites in Australia, Algeria and Utah, recorded seismic activity has been negligible.

Frohlich said the disparity suggests that there are many locations where large-volume injections of carbon dioxide are okay and do not cause earthquakes. Differences in geology may make some areas more prone to the activity, and Frohlich said further study is needed.

Prominent Stanford geophysicists last year said there was a “high probability that earthquakes will be triggered” by large-scale underground carbon dioxide injections as a strategy to reduce greenhouse gases in the atmosphere. But their paper did not offer examples of earthquakes induced by carbon dioxide injections.

Frohlich urges caution, since “this is very early in the science discussion.”

“We don’t know much about injection,” he said. “A lot of this stuff is not on people’s radar.”

“Scientists have understood for a long time that anytime you are injecting anything underground — or, for that matter, producing something from underground — you can cause earthquakes,” said Briana Mordick, a San Francisco-based staff scientist with the Natural Resources Defense Council. “This is something that needs to be properly managed. At this time, it’s just not being managed properly.”

Wells where carbon dioxide is injected with the goal of sequestering and storing the gas are subject to stronger scrutiny than wells where the substance is used to enhance oil recovery. Oil and gas companies are not required to consider seismic risk in those cases, Mordick noted.

And while still-developing carbon capture and sequester technology offers the promise of cleaning up emissions from power plants and industrial facilities, it’s going to be important to properly select and manage sites where the gas is stored, Mordick said.

Hydraulic fracturing

Separate research is underway to document whether today’s drilling boom — including the use of horizontal drilling and hydraulic fracturing — may be causing quakes near oil wells. England imposed an 18-month moratorium on hydraulic fracturing after concerns about quakes from the process that involves pumping water, sand and chemicals underground to free trapped oil and gas.

But recent studies suggest that hydraulic fracturing itself is not to blame for significant earthquakes. Instead, some research suggests, quakes near oil fields are more likely to be tied to the practice of disposing of drilling wastewater in underground injection wells.