Manmade quakes shake the Southwest

Tremors in Colorado and New Mexico linked to coalbed methane extraction.

 

On August 22, 2011, 15 minutes before midnight, residents of southeast Colorado, northern New Mexico and even western Kansas felt their beds shake. Historic buildings crumbled and chunks of mountainsides slid onto highways, but no injuries were reported in the 5.3 magnitude quake that the New York Times deemed “the largest natural earthquake in Colorado in more than a century.”

Except that it wasn’t natural at all. A study released Monday in the Bulletin of the Seismological Society of America confirms what scientists have suspected for years: That the 2011 quake — along with dozens of others in the Raton Basin of Colorado and New Mexico — were caused by a byproduct of coalbed methane extraction.  Other studies have made similar connections in Oklahoma and Ohio, but this is the first to conclusively link oil and gas development with increased earthquake frequency in the Southwest.

It also skews the popular notion that fracking alone is responsible for tremors in oil and gas country. U.S. Geological Survey research geophysicist Bill Barnhart, who reviewed the study and has worked in the Raton Basin, emphasizes that the human-induced seismicity there is “completely unrelated” to fracking.

Instead, the culprit is coalbed methane extraction — or, more specifically, the wastewater it produces. Coalbed methane is a natural gas trapped in the seams of coal deposits, and when it’s sucked from the earth it brings up huge quantities of water so salty it can’t be legally disposed of above ground. The solution is to drill even deeper wells, up to 1.5 kilometers down, to inject the water into deeper geologic formations — where it stays, hopefully, for eternity. The only problem? 

wastewater-jpg
Oilfield waste arrives by tanker truck at a wastewater disposal facility near Platteville, Colorado, to inject into a deep well for permanent storage underground.
Bill Ellsworth, USGS

“At those depths, you have naturally occurring faults,” explains Barnhart. “You put water down there, it increases the pressure and reduces the strength and makes the fault lines less clamped together. That leads to earthquakes.”

Since 1999, 28 wastewater wells have been drilled in the Raton Basin — together injecting up to 3.6 million barrels of water per month. In roughly the same period, the number of earthquakes increased 40-fold. Each quake has been within three miles of a well; two of the biggest were in close proximity to the highest-volume wells. 

Though technology exists to map the ultra-deep fault lines that may be causing the quakes, there’s been little impetus until now to do so, and they don’t show up on USGS’s earthquake hazards map. Plus, because researchers have struggled to link specific quakes to specific wells, industry groups have been slow to respond, calling the studies “inconclusive.” In an email, the Colorado Oil and Gas Association cites several “preliminary concerns” with the latest research, including a lack of robust seismologic tracking prior to 2001.

Nonetheless, by using fluid-injection data and seismic monitoring, USGS geophysicist Justin Rubinstein and his colleagues have made the strongest argument yet that some wastewater injection wells do, in fact, cause the earth to slip and slide. Wastewater injection has been linked to earthquakes as far back as to the 1960s, when a 4.5 magnitude earthquake shook the Denver area shortly after chemical-laden water from the Rocky Mountain Arsenal was shot underground. Back then, scientists figured that injecting pressurized wastewater into hard rock like granite had caused the quake.

Today, unpressurized water injected into sedimentary rocks is causing even larger tremors, and while researchers have made strides in identifying the phenomenon, plenty of questions remain. No one knows, for example, why some wells remain benign for decades while others cause the earth to shake, or just how large an earthquake humans have the potential to cause. “That,” Barnhart says, “is the question of the day.” 

Krista Langlois is an editorial fellow at High Country News. She tweets @KristaLanglois2.  

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