The U.S. Environmental Protection Agency (EPA) has told Texas regulators that "there is a significant possibility that North Texas earthquake activity is associated with [energy industry] disposal wells." The assertion is part of a report on the state's underground injection control (UIC) program sent to the Railroad Commission of Texas (RRC) last week.
For about two years, residents in the Dallas-Fort Worth area, including such towns as Azle and Cleburne and the area around the DFW Airport, have complained of small earthquakes that they have blamed on oil and natural gas activity, specifically drilling waste injection wells (see Shale Daily, Jan. 21, 2014). Other areas have seen seismic activity, but the quaking in Barnett Shale country has received the most attention.
RRC commissioners were eventually moved to act by strengthening their oversight of underground injection wells (see Shale Daily, April 24, 2015). However, investigations into seismic activity by the RRC have found no credible link between injection wells and seismicity, according to the regulators (see Shale Daily, Sept. 11, 2015).
In its UIC report, EPA noted that RRC representatives have not acknowledged a causal relationship between injection wells and seismic activity. The EPA contradicts this assertion and said there likely is a link between the two.
"...[N]aturally fractured injection formations may transmit pressure buildup from injection for miles," EPA said. "The Ellenberger Formation, a deep naturally fractured formation, is the preferred disposal zone for most disposal wells in North Texas. This geophysical characteristic of the Ellenberger may allow pressure from authorized injection activities to follow existing fracture pathways toward existing fault zones miles away. These fractures may also be transmitting pressure buildup downward to basement rock along faults that were previously dormant."
EPA said it is "concerned" about the level of seismic activity last year in the Dallas-Fort Worth area because of the potential effects on public health, particularly drinking water. "EPA recommends close monitoring of injection activity through daily recording and reporting of accurate injection pressures and volumes from area disposal wells, coupled with appropriate data analysis methods, in a coordinated effort to detect possible correspondence with seismic activity."
In a statement, RRC said it takes the “issue of induced seismicity very seriously and has in place some of the most stringent rules on disposal wells. Since seismicity-related disposal well rules went into effect Nov. 17, 2014, as of July 1, 2016, the Railroad Commission has received 56 disposal well applications in areas of historic seismicity. Of these, 28 permits have been issued with special conditions, such as requirements to reduce maximum daily injection volumes and pressure and/or to record volumes and pressures daily as opposed to monthly. Eleven applications were returned or withdrawn. Three applications were protested and sent to hearing. Ten permits were issued without special conditions, and four applications are pending.”