Alex Mills
By Alex Mills
Almost two years ago the news that the possible link of oil and gas activity to earthquakes in North Texas made the national news. Television stations sent camera crews to town hall meetings in Azle in January 2014. Citizens in the area called for a ban on drilling. Newspapers ran front page stories alleging a link between hydraulic fracturing and the tremors.
Scientists from the Huffington Department of Earth Sciences at Southern Methodist University joined the U.S. Geological Survey and the Institute of Geophysics and Department of Petroleum and Geosystems Engineering at the University of Texas at Austin to conduct a study of the seismic activity. They issued a paper, “Causal Factors for Seismicity near Azle, Texas”, on April 21, 2015 that concluded, “brine production combined with wastewater disposal represented the most likely cause of recent seismicity near Azle.”
Three days later the Railroad Commission (RRC), which regulates oil and gas in Texas, ordered the companies that had operations near Azle to appear before a hearing of the RRC to consider the report’s findings. On June 10, the first hearing was held, and XTO Energy in Fort Worth made a comprehensive and technical presentation regarding the geology in the area and the company’s activities.
On Aug. 31, RRC Technical Examiner Paul Dubois and Administrative Law Judge Marshall Enquist issued their findings that the XTO well “is not contributing to seismic activity in the Azle-Reno area.” They also said that the seismic activity is not solely the result of natural tectonic process.”
In other words, the examiners did not believe the Causal Factors report that oil and gas production and disposal by XTO most likely caused the earthquakes near Azle. The examiners also rejected XTO’s suggestion that the seismic active in North Texas was natural, solely.
The examiners’ 30-page report detailed the geology in the area and the operations of XTO Energy. A summary of other findings of fact by the examiners are:
- The salt water disposal well operated by XTO was constructed and operated according to the RRC permit.
- There is no evidence that injected fluids are escaping from the permitted disposal zone.
- There is no evidence that seismic activity originated in the Fort Worth Basin prior to 2008.
- The earthquakes that occurred in December 2013 near Azle occurred at a depth of about 20,000 feet. The well was completed at 9,334 feet in the Ellenburger Formation, where water was being injected.
- The evidence does not support a finding that XTO’s well likely contributed to seismic activity.
The Causal Factors report acknowledged that many of the earthquakes (larger magnitude events, especially) occurred in the basement rock along the primary fault, and that “the deeper earthquakes are due to downward pressure transfer within the fault system.”
However, XTO testified that the Causal Factors report “does not accurately represent the progression of earthquakes, which originated on the primary Azle fault at depths of about 20,000 feet and then generally spread to shallower locations on the antithetic fault.” XTO’s disposal well was completed into the Ellenburger Formation to a total depth of 9,334 feet on May 23, 2009. It was permitted to inject up to 25,000 barrels per day at a surface injection pressure of 2,600 psi, and initially the average injection volume was 16,977 barrels per day in September 2009 with maximum average monthly surface injection pressure of 1,198 psi in August 2010.
The well currently serves 233 XTO gas wells completed in the Newark, East (Barnett Shale) Field. From March through May 2015 the well injected an average of 6,646 barrels per day with an average daily surface injection pressure of 442 psi.
The second company to respond to the hearing request is EnerVest, Ltd. RRC examiners have not issued their findings from their hearing, yet.
The examiners’ report on XTO now lies in the hands of the three commissioners.
Alex Mills is President of the Texas Alliance of Energy Producers. The opinions expressed are solely of the author.
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