RESEARCHERS say injecting wastewater deep underground as a byproduct of oil and gas extraction processes, which include fracking, causes human-made earthquakes.
The US study also offers a solution on how the risk can be mitigated through monitoring, and the results have the potential to change oil and gas industry practices, says lead author Manoochehr Shirzaei, an assistant professor in geophysics from Arizona State University.
“It's a hot topic [because] injection and fracking is extremely important in terms of jobs, money and independence,” said Shirzaei, “So now the goal, the scope of every scientist…is to make that injection safer [by] reducing the number of earthquakes as much as we can.”
The technique to extract oil and gas from rock uses a high-pressure mix of water, sand or gravel and chemicals, which produces wastewater. This wastewater is disposed through underground injections that “have led to an increase in earthquakes across the US,” he said.
The study shows that the team can estimate how pressure increases underground, which provides a chance for wastewater injections to be halted before the buildup becomes critical. The team say the pressure eventually returns to normal, allowing the injections to resume.
The researchers used space-borne Interferometric Synthetic Aperture Radar (InSAR), a remote satellite-based sensing technique, to measure the surface uplift of an area near four high-volume wells used for disposing wastewater near Timpson, Texas – an area which has not experienced much seismic activity historically. The researchers chose this site, as a 4.8 magnitude earthquake hit Timpson in May 2012 – the largest event ever monitored in the region. Several more quakes hit the area over the next 16 months.
The InSAR technique uses highly accurate radar to measure the change in distance between the satellite and ground surface, allowing the team to show that injecting water into the wells at high pressure caused ground uplift near the shallower wells. From this, the team calculated the strain and pore pressure underneath. They also found that seismic activity increased, even when water injection rates declined, due to pore pressure continuing to diffuse throughout the area from earlier injections.
“Monitoring surface deformation using these remote sensing techniques is a proactive approach to managing the hazards associated with fluid injection, and can help in earthquake forecasting,” said Shirzaei.
The data shows less seismic activity in denser rock where pore pressure was prevented from disseminating into basement rock. The team say this helps to explain why injection can, but does not always, cause earthquakes.
The team say they have provided a definitive link between wastewater injection and earthquake activity in Texas by integrating seismic data, injected water histories, and geological and hydrogeological information with surface deformation observations.
“This research opens new possibilities for the operation of wastewater disposal wells in ways that could reduce earthquake hazards,” Shirzaei added.
There are currently 180,000 disposal wells in the US – primarily in Texas, California, Oklahoma and Kansas – injecting a total of around 9bn l/d of wastewater underground.
Shirzaei said that no one from the oil and gas industry has seen the work yet, but he plans to present the findings to the scientific community at the Geological Society of America meeting in Colorado – taking place between the 25–28 September – and to state and industry leaders in Texas and other affected states..
When asked by The Chemical Engineer how industry may respond to the findings Shirzaei said he hopes it will welcome findings that offer a working solution.
“Industry is usually reluctant to acknowledge there is a problem, but given our approach to tell the story, [and] focus on making injection safer…it is a win for everyone,” he said.
He added that the next research step for the team will be to use the collected data in an earthquake-forecasting model to calculate the time-dependent probability of earthquake on nearby faults as a result of injection.
Science, DOI: http://doi.org/bqzk
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