Two companies operating in the Barnet Shale have found themselves having to defend their wells from closure. Following a report from the Southern Methodist University on the alleged induced seismicity near Azle, Texas, The Railroad Commission of Texas has initiated proceedings requiring the companies to show why the wells should not be shut down.
The two wells at issue are XTO Energy Inc.’s West Lake SWD No. 1, Newark, East (Barnett Shale) Field, Parker County and Enervest Operating L.L.C.’s Briar No. 1, Caughlin (Strawn) Field, Wise County.
SMU seismologists have been studying earthquakes in North Texas since 2008, when the first series of felt tremors hit near DFW International Airport between Oct. 30, 2008, and May 16, 2009. Next came a series of quakes in Cleburne between June 2009 and June 2010, and this third series in the Azle-Reno area northwest of Fort Worth occurred between November 2013 and January 2014.
In their study, entitled “Causal Factors for Seismicity near Azle, Texas,” and published in the journal Nature Communications, the researchers have found that the earthquakes in the area were likely caused by ‘induced seismicity’ – that is, caused by something other than strictly natural forces. Such occurrences – the report states – are often associated with subsurface pressure changes.
“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,” said Heather DeShon, SMU associate professor of geophysics.
The researchers also noted that prior to the DFW Airport earthquakes in 2008, an earthquake large enough to be felt had not been reported in the Fort Worth Basin since 1950. 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. The Texas Railroad Commission reports that production in the Barnett Shale grew exponentially from 216 million cubic feet a day in 2000, to 4.4 billion cubic feet a day in 2008, to a peak of 5.74 billion cubic feet of gas a day in 2012.
While the SMU Azle study adds to the growing body of evidence connecting some injection wells and, to a lesser extent, some oil and gas production to induced earthquakes, SMU’s team notes that there are many thousands of injection and/or production wells that are not associated with earthquakes.
In response to the SMU’s publication, the Chairman of The Texas Railroad Commission, Christi Craddick, said that the Commission “has in place strong rules addressing the issue of seismicity and disposal well activity, and it is incumbent upon us to apply these rules where and when appropriate for the protection of public safety and our natural environment.”
Commissioner David Porter said, “Due to the that fact the wells were permitted prior to the Commission’s rule amendments addressing disposal well activity and seismic activity, and in light of the new research contained in SMU’s report, it’s appropriate and necessary for the Commission to consider the operation of these wells in a fully informed manner and determine the appropriate course of action.”
The study was produced by a team of scientists from SMU’s Department of Earth Sciences in Dedman College of Humanities and Sciences, the U.S. Geological Survey, the University of Texas Institute for Geophysics and the University of Texas Department of Petroleum and Geosystems Engineering. SMU scientists Hornbach and DeShon are the lead authors.
Note: This is a generic illustration, not representative of any damage caused in Azle.
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