Seismic shift: Oklahoma’s earthquakes triggered by wastewater disposal wells
THIS IS FROM YAHOO NEWS: Geologists, industry reps and regulators sound off on scientific data
Drilling rigs dot the landscape in northern Oklahoma on Nov.17, 2013. (Les Stone/Corbis)
The onslaught of seismic activity in Oklahoma in recent years has captured the attention of the nation.
State scientists say they have
uncovered the root cause of the majority of the state’s earthquakes: the
oil and gas industry’s disposal of billions of barrels of water
underground.
Now, as the public absorbs this information, Oklahoma’s regulatory
bodies are keeping a watchful eye on these disposal wells and planning
their next moves.Link between earthquakes and industry
On Tuesday, the Oklahoma Geological Survey (OGS) issued its most strongly worded statement yet linking the oil and gas industry to the state’s earthquakes.
State geologist Richard D. Andrews and state seismologist Austin Holland say the spike in earthquakes — particularly in central and north-central areas of the state — is “very unlikely to represent a naturally occurring process.”
“The primary suspected source of triggered seismicity is not from hydraulic fracturing but from the injection/disposal of water associated with oil and gas production,” the report from the Oklahoma Geological Survey (OGS) reads.
The seismicity rate in Oklahoma is about 600 times greater than it was before 2008, around the time dewatering started in the state.
Oklahoma Geological Survey seismologist, Austin Holland, installs a seismometer in southwest Oklahoma City, Okla., …
“The rates have increased phenomenally since just a few years ago,” Andrews said in an interview with Yahoo News. “We feel we had to make a statement.”
For the dewatering process, extremely salty water, which coexists with oil and gas below the Earth’s surface, is separated from those substances after extraction. Then barrels of wastewater are deposited into wells far deeper than their point of origin.
Some of this wastewater is a byproduct of hydraulic fracturing, or fracking: a process in which high-pressure liquids are blasted beneath the ground to fracture rock, releasing natural gas. But fracking only accounts for a small percentage of the water deposited in these wells.
How this happens
The majority of the state’s wastewater is deposited in the Arbuckle formations, which are underground reservoirs of dolomite, limestone and other rocks.
Parts of the Arbuckle are highly fractured with expansive systems of cavities and caverns that the energy sector found perfect for dumping wastewater.
“It is known to have bulk porosity, voids in the rocks that can hold fluids,” Andrews said. “They don’t need to inject the water under any other pressure. They just funnel it in. It will take as much water as you can put into it.”
Much of the wastewater, with much higher salinity levels than ocean water, travels many miles away from its injection site and seeps into the underlying crystalline basement; such permeability makes it difficult to link a specific well with seismic activity.
It can take anywhere from weeks to more than a year of this water pouring in before it triggers naturally occurring stresses in the Earth — causing earthquakes.
“There are faults pretty much all across the country. It doesn’t take much change to the system to cause those faults to slip. Those wells are providing the little bits of change needed,” Briana Mordick, a staff scientist for the Natural Resources Defense Council, told Yahoo News.
Most of the earthquakes have occurred within the crystalline basement, on faults within Oklahoma’s tectonic stress regime, according to the OGS.
“Water and fault zones are a formula for seismicity,” Andrews said. “We do have the science to back it up.”
