Fracking Most Likely to Blame for 2013-14 Earthquakes
Fracking is most likely to blame for earthquakes occurring near Azle, Texas, from late 2013 through spring 2014, according to new research.
It is no secret that fracking, or hydraulic fracturing, is suspected to play a role in earthquakes across the country, with some scientists saying it should be included in earthquake hazard assessments.
Fracking involves injecting huge volumes of wastewater, sand, and chemicals deep into underground rock formations to access valuable oil and natural gas. While this is a form of alternative energy, it also may lead to man-made earthquakes.
For example, wastewater injection allegedly triggered two earthquakes in 2011 that topped magnitude 5 - one in southern Colorado, at magnitude 5.3, and another in Oklahoma, at magnitude 5.7. More recently, last March fracking in Poland Township, Ohio activated a previously unknown fault, triggering a series of five recorded earthquakes, ranging from magnitude 2.1 to 3.0.
And now, a seismology team led by Southern Methodist University (SMU), Dallas is blaming fracking for 2013-14 earthquakes in Azle, Texas.
After identifying two intersecting faults, the team developed a sophisticated 3D model to assess the changing fluid pressure within a rock formation in the affected area. They used the model to estimate stress changes in the area, generated by two wastewater injection wells and the more than 70 production wells that remove both natural gas and significant volumes of salty water (brine).
They also took into account fluid volumes, flow parameters, and subsurface pressures in the region to provide a more accurate estimate of the fluid pressure along this fault.
"The model shows that a pressure differential develops along one of the faults as a combined result of high fluid injection rates to the west and high water removal rates to the east," Matthew Hornbach, SMU associate professor of geophysics, explained in a statement. "When we ran the model over a 10-year period through a wide range of parameters, it predicted pressure changes significant enough to trigger earthquakes on faults that are already stressed."
In fact, the stress changes on the fault were typically tens to thousands of times larger compared to stress changes associated with water level fluctuations caused by the recent Texas drought, according to their model.
"What we refer to as induced seismicity - earthquakes caused by something other than strictly natural forces - is often associated with subsurface pressure changes," said Heather DeShon, SMU associate professor of geophysics. "We can rule out stress changes induced by local water table changes. While some uncertainties remain, it is unlikely that natural increases to tectonic stresses led to these events." (Scroll to read on...)
Natural earthquakes, researchers explain, can be caused by a variety of factors. This includes stress changes related to plate tectonics, natural water table or lake level variations - caused by changing weather patterns or water drainage patterns over time - and glacial movement.
Man-made earthquakes, on the other hand, are caused by human-generated changes to the water table, such as dam construction, and industrial activities involving the injection or removal of fluids from the subsurface.
In recent years, North Texas has experienced a series of earthquakes. First, in 2008 near DFW International Airport, then in Cleburne between June 2009 and June 2010, and another series in the Azle-Reno area northwest of Fort Worth occurred between November 2013 and January 2014. Not to mention an ongoing series of earthquakes in the Irving-Dallas area that began in April 2014, which the SMU team is currently studying.
Interestingly, before 2008 an earthquake large enough to be felt had not been reported in the North Texas area since 1950. What's more, the North Texas earthquakes of the last seven years have all occurred in areas developed for natural gas extraction from a geologic formation known as the Barnett Shale.
It should be noted that some ancient faults in the region, due to their orientation and direction, are "near critically stressed" and more susceptible to movement. Therefore, fracking near these faults poses more of a risk of inducing an earthquake.
Production in the Barnett Shale has grown at an alarming rate recently, from 216 million cubic feet a day in 2000, to 4.4 billion cubic feet a day in 2008. It reached a peak of 5.74 billion cubic feet of gas a day in 2012. If fracking continues at this rapid pace, it seems that North Texas may experience even more earthquakes in the near future.
"This report points to the need for even more study in connection with earthquakes in North Texas," said Brian Stump, SMU's Albritton Chair in Earth Sciences. "Industry is an important source for key data, and the scope of the research needed to understand these earthquakes requires government support at multiple levels."
The results were published in the journal Nature Communications.
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