A string of earthquakes in Azle, Texas in 2013 and 2014 was likely caused by high volumes of brine extraction and wastewater injection at natural gas wells, according to a paper in the journal Nature Communications.
“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,” said geophysicist Matthew Hornbach of Southern Methodist University. “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.”
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“What we refer to as induced seismicity—earthquakes caused by something other than strictly natural forces—is often associated with subsurface pressure changes,” added SMU geophysicist Heather DeShon. ” While some uncertainties remain, it is unlikely that natural increases to tectonic stresses led to these events.”
The study team “developed a sophisticated 3D model to assess the changing fluid pressure within a rock formation in the affected area,” Science Daily reports. “They used the model to estimate stress changes induced in the area by two wastewater injection wells and the more than 70 production wells that remove both natural gas and significant volumes of salty water known as brine.”
The model predicted changes in stress that were “typically tens to thousands of times larger than stress changes associated with water level fluctuations caused by the recent Texas drought.”
