Researchers at the University of Bristol have established a direct link between man-made earthquakes in Oklahoma and the depths at which wastewater is injected into the ground by the oil and gas industry.
Damaging earthquakes have become a fact of life in Oklahoma, impacting residents and even leading to legal charges against well operators. Induced earthquakes pose a growing threat to commercial infrastructure, such as the oil storage facility at Cushing.
Although the connection between earthquakes and deep water injection has been previously established, an unprecedented surge in earthquake activity has raised serious concern.
At the peak of seismic activity in Oklahoma since 2011, the annual number of earthquakes increased by 800 times. During this same time frame, well operators injected an average of 2.3 billion barrels of wastewater each year.
Fluids are typically disposed of at depths far below the level of freshwater sources, one or two kilometers beneath the ground. As a result of the current study, researchers have determined that the frequency of Oklahoma’s earthquakes is strongly linked to the depth of wastewater injection.
“Our new modelling framework provides a targeted, evidential basis for managing a substantial reduction in induced seismicity in Oklahoma, with extensive possibilities for application elsewhere in the world,” said lead author Dr. Thea Hincks. “This marks a step forward in understanding the evolution of seismicity in the Oklahoma region.”
The research team investigated the connection between injection volume, depth, and location over the course of 6 years. They used an advanced computer method to combine data on wastewater injection with earthquake data from the U.S. Geological Survey.
The team discovered that the depth and volume of the injections have a critical influence on potential seismic activity. Injection volume becomes more significant at depths where layered sedimentary rocks meet crystalline basement rocks because fractured basement rocks are much more susceptible to earthquakes.
“The underlying causes of Oklahoma’s induced earthquakes are an open and complex issue, not least because there are over 10,000 injection wells, with many different operators and operating characteristics, all in an area of complex geology,” explained co-author Dr. Tom Gernon.
“Thanks to an innovative model capable of analysing large and complex data sets, our study establishes for the first time a clear link between seismicity and fluid injection depth.”
The study is published in the journal Science.
By Chrissy Sexton, Earth.com Staff Writer