Warning of quake risk from fracking operations

(National Geographic Daily News, May 4, 2014)

Tremors induced by wastewater disposal are larger and harder to predict than previously thought.

Underground disposal of wastewater from fracking may pose a much greater risk of causing dangerous earthquakes than previously believed, particularly in areas of the U.S. Southwest and Midwest where earthquake faults have not been mapped extensively, seismology researchers are warning, in a story by Patrick Kiger for National Geographic Daily News.

The warning comes as evidence continues to accumulate that the activities associated with the North American oil and gas boom can lead to unintended, man-made tremors, or “induced seismicity,” as researchers call it.

A hydraulic fracturing oil rig stands in Garfield County, Colorado. Colorado. (photo credit: National Geographic)

A hydraulic fracturing oil rig stands in Garfield County, Colorado. Colorado. (photo credit: National Geographic)

Fracking itself has been linked to quakes. More often, though, the cause is injection of fracking wastewater into disposal wells.

A paper published in the scientific journal Geology in 2013 found that the tip of the Oklahoma quake’s initial rupture plane was less than 200 meters (656 feet) away from injection wells, and concluded that years of injecting fluid into them had altered the pressure on the fault.

That paper’s lead author, Cornell University geophysicist Katie Keranen, released a new paper at the conference, which found that four high-volume wastewater injection wells in Oklahoma had triggered a swarm of small earthquakes about 9.3 miles (15 kilometers) away. It’s not necessary for wastewater in an underground reservoir to actually reach an earthquake fault directly, because “the pressure can travel,” Keranen explained.

(For the full story, please click here.)

Links between wastewater injection and 5.7 earthquake

(GeoScienceWorld)

Significant earthquakes are increasingly occurring within the continental interior of the United States, including five of moment magnitude (Mw) ≥ 5.0 in 2011 alone. Concurrently, the volume of fluid injected into the subsurface related to the production of unconventional resources continues to rise.

Waste water injection well.

Waste water injection well.

Here we identify the largest earthquake potentially related to injection, an Mw 5.7 earthquake in November 2011 in Oklahoma. The earthquake was felt in at least 17 states and caused damage in the epicentral region. It occurred in a sequence, with 2 earthquakes of Mw 5.0 and a prolific sequence of aftershocks. We use the aftershocks to illuminate the faults that ruptured in the sequence, and show that the tip of the initial rupture plane is within ∼200 m of active injection wells and within ∼1 km of the surface; 30% of early aftershocks occur within the sedimentary section.

Subsurface data indicate that fluid was injected into effectively sealed compartments, and we interpret that a net fluid volume increase after 18 yr of injection lowered effective stress on reservoir-bounding faults. Significantly, this case indicates that decades-long lags between the commencement of fluid injection and the onset of induced earthquakes are possible, and modifies our common criteria for fluid-induced events. The progressive rupture of three fault planes in this sequence suggests that stress changes from the initial rupture triggered the successive earthquakes, including one larger than the first.

(Click here for the full report.)