Following the Texas Railroad Commission's recent proposal for additional rules related to disposal wells in "high-risk" seismic areas, on Monday, August 25, members of the Texas House Subcommittee on Seismic Activity heard testimony from Dr. Craig Pearson, the seismologist hired by the Railroad Commission to investigate the possible correlation between seismic events and oil and gas activity. Pearson's hiring followed a number of small earthquakes that occurred in late 2013 near the town of Azle, Texas, which sits atop the Barnett Shale formation. Pearson testified that seismic activity has continued in the previously affected area, but the tremors have registered below 1.0 on the Richter Scale, and are unfelt by most people.
The proposed rule amendments would include a new requirement that an applicant for a disposal well determine the radius of the 10-year, five pounds per square inch (psi) pressure front boundary from the proposed disposal well location and use that radius to retrieve information from the U.S. Geological Survey regarding the locations of any historical seismic events within that radius. "When you start injecting into an underground reservoir, you begin to build the pressure anomaly within that reservoir, and there's a front that moves away from the well with time and volume," said Pearson.
Pearson believes that the key to preventing unwanted seismic activity is for an operator to understand how the increased pressure from injections to a disposal well will affect seismic activity in the surrounding area. "The rules as they exist today were written to protect our groundwater resources. Because we're now dealing with the new seismicity, we've got to worry not just about water moving up, but waters moving out to faults, old, dormant faults, perhaps, and especially those faults that are associated with the basement rock," said Pearson. Pearson testified that he has requested proprietary information from several companies operating wells in the Barnett Shale formation, and their cooperation has been "fantastic."
The Railroad Commission will accept public comment on the proposed rules until September 29. The subcommittee will report its findings to the House Committee on Energy Resources, which oversees the activities of the Railroad Commission.
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