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The Dallas Morning News: Earthquakes at DFW Airport continued for years after oil and gas wastewater well was shut

“Faults are not like a light switch – you don’t turn off a well and automatically stop triggering earthquakes.” — Heather DeShon, SMU seismologist.

Science journalist Anna Kuchment covered the earthquake research of a team of SMU seismologists led by SMU Associate Professor Heather DeShon and SMU Post-doctoral Researcher Paul Ogwari, who developed a unique method of data analysis that yielded the study results.

Kuchment wrote Earthquakes at DFW Airport continued for years after oil and gas wastewater well was shut for The Dallas Morning News.

The results of the analysis showed that efforts to stop human-caused earthquakes by shutting down wastewater injection wells that serve adjacent oil and gas fields may oversimplify the challenge. The seismologists analyzed a sequence of earthquakes at DFW Airport and found that even though wastewater injection was halted after a year, the earthquakes continued.

The sequence of quakes began in 2008, and wastewater injection was halted in 2009. But earthquakes continued for at least seven more years.

“This tells us that high-volume injection, even if it’s just for a short time, when it’s near a critically stressed fault, can induce long-lasting seismicity,” said Ogwari. The earthquakes may be continuing even now, he said.

The article by Kuchment, “Earthquakes at DFW Airport continued for years after oil and gas wastewater well was shut,” published Feb. 21, 2018.

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By Anna Kuchment
The Dallas Morning News

Earthquakes beneath DFW International Airport continued for seven years after an oil and gas company shut a nearby wastewater injection well that had been linked to the quakes, according to a new study by scientists at Southern Methodist University.

A wastewater well that continues to operate at the northern end of the airport – and which some area residents have said should be closed — was probably not involved in the events and poses little earthquake hazard, the researchers concluded.

“Faults are not like a light switch – you don’t turn off a well and automatically stop triggering earthquakes,” said Heather DeShon, a seismologist at Southern Methodist University and co-author of the paper, in an email.

The earthquakes at DFW Airport started on Halloween 2008, seven weeks after Chesapeake Energy began injecting wastewater into a well at the southern end of the airport. Scientists at SMU and the University of Texas at Austin investigated the quakes at the time and concluded they were most likely associated with the well.

Though Chesapeake shut its well in August 2009, earthquakes continued through at least the end of 2015. The largest, a 3.4-magnitude event, struck three years after the well was closed.

“It’s very surprising that one year of injection could produce earthquakes running for more than seven years,” said Paul Ogwari, the study’s lead author and a post-doctoral researcher at SMU. The paper was published in the Journal of Geophysical Research.

While earthquake magnitudes did not decline, Ogwari said, earthquake rates did: More than 80 percent of quakes in the sequence occurred during the first seven months of seismicity.

The DFW quakes are significant, because they mark the start of an unprecedented surge of earthquakes in North Texas and across the middle of the country.

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SMU study finds earthquakes continue for years after gas field wastewater injection stops

High rates of injection and large volumes can perturb critically stressed faults, triggering earthquakes years after wastewater wells are shut in.

Efforts to stop human-caused earthquakes by shutting down wastewater injection wells that serve adjacent oil and gas fields may oversimplify the challenge, according to a new study from seismologists at Southern Methodist University, Dallas.

The seismologists analyzed a sequence of earthquakes at DFW Airport and found that even though wastewater injection was halted after a year, the earthquakes continued.

The sequence of quakes began in 2008, and wastewater injection was halted in 2009. But earthquakes continued for at least seven more years.

“This tells us that high-volume injection, even if it’s just for a short time, when it’s near a critically stressed fault, can induce long-lasting seismicity,” said SMU seismologist Paul O. Ogwari, who developed a unique method of data analysis that yielded the study results.

The earthquakes may be continuing even now, said Ogwari, whose analysis extended through 2015.

The study’s findings indicate that shutting down injection wells in reaction to earthquakes, as some states such as Oklahoma and Arkansas are doing, may not have the desired effect of immediately stopping further earthquakes, said seismologist Heather DeShon, a co-author on the study and an associate professor in the SMU Earth Sciences Department.

“The DFW earthquake sequence began on Halloween in 2008 — before Oklahoma seismicity rates had notably increased,” said DeShon. “This study revisits what was technically the very first modern induced earthquake sequence in this region and shows that even though the wastewater injector in this case had been shut off very quickly, the injection activity still perturbed the fault, so that generated earthquakes even seven years later.”

That phenomenon is not unheard of. Seismologists saw that type of earthquake response from a rash of human-induced earthquakes in Colorado after wastewater injection during the 1960s at the Rocky Mountain Arsenal near Denver. Similarly in that case, injection was started and stopped, but earthquakes continued.

Such a possibility has not been well understood outside scientific circles, said DeShon. She is a member of the SMU seismology team that has studied and published extensively on their scientific findings related to the unusual spate of human-induced earthquakes in North Texas.

“The perception is that if the oil and gas wastewater injectors are leading to this, then you should just shut the injection wells down,” DeShon said. “But Paul’s study shows that there’s a lot to be learned about the physics of the process, and by monitoring continuously for years.”

Ogwari, DeShon and fellow SMU seismologist Matthew J. Hornbach reported the findings in the peer-reviewed Journal of Geophysical Research in the article “The Dallas-Fort Worth Airport Earthquake Sequence: Seismicity Beyond Injection Period.”

Known DFW Airport quakes number more than 400
The DFW Airport’s unprecedented earthquake clusters were the first ever documented in the history of the North Texas region’s oil-rich geological system known as the Fort Worth Basin. The quakes are also the first of multiple sequences in the basin tied to large-scale subsurface disposal of waste fluids from oil and gas operations.

The DFW Airport earthquakes began in 2008, as did high-volume wastewater injection of brine. Most of the seismic activity occurred in the first two months after injection began, primarily within .62 miles, or 1 kilometer, from the well. Other clusters then migrated further to the northeast of the well over the next seven years. The quakes were triggered on a pre-existing regional fault that trends 3.7 miles, or 6 kilometers, northeast to southwest.

Ogwari, a post-doctoral researcher in the SMU Roy M. Huffington Earth Sciences Department in Dedman College, analyzed years of existing seismic data from the region to take a deeper look at the DFW Airport sequence, which totaled 412 earthquakes through 2015.

Looking at the data for those quakes, Ogwari discovered that they had continued for at least seven years into 2015 along 80% of the fault, even though injection was stopped after only 11 months in August of 2009.

Rate of quakes declined, but magnitude has never lessened
In another important finding from the study, Ogwari found that the magnitude of the DFW Airport earthquakes didn’t lessen over time, but instead held steady. Magnitude ranged from 0.5 to 3.4, with the largest one occurring three years after injection at the well was stopped.

“What we’ve seen here is that the magnitude is consistent over time within the fault,” Ogwari said. “We expect to see the bigger events during injection or immediately after injection, followed by abrupt decay. But instead we’re seeing the fault continue to produce earthquakes with similar magnitudes that we saw during injection.”

While the rate of earthquakes declined — there were 23 events a month from 2008 to 2009, but only 1 event a month after May 2010 — the magnitude stayed the same. That indicates the fault doesn’t heal completely.

“We don’t know why that is,” Ogwari said. “I think that’s a question that is out there and may need more research.”

More monitoring needed for human-induced quakes
Answering that question, and others, about the complex characteristics and behavior of faults and earthquakes, requires more extensive monitoring than is currently possible given the funding allotted to monitor quakes.

Monitoring the faults involves strategically placed stations that “listen” and record waves of intense energy echoing through the ground, DeShon said.

The Fort Worth Basin includes the Barnett shale, a major gas producing geological formation, atop the deep Ellenberger formation used for wastewater storage, which overlays a granite basement layer. The ancient Airport fault system extends through all units.

Friction prevented the fault from slipping for millions of years, but in 2008 high volumes of injected wastewater disturbed the Airport fault. That caused the fault to slip, releasing stored-up energy in waves. The most powerful waves were “felt” as the earth shaking.

“The detailed physical equations relating wastewater processes to fault processes is still a bit of a question,” DeShon said. “But generally the favored hypothesis is that the injected fluid changes the pressure enough to change the ratio of the downward stress to the horizontal stresses, which allows the fault to slip.”

Earthquakes in North Texas were unheard of until 2008, so when they began to be felt, seismologists scrambled to install monitors. When the quakes died down, the monitoring stations were removed.

“As it stands now, we miss the beginning of the quakes. The monitors are removed when the earthquakes stop being felt,” DeShon said. “But this study tells us that there’s more to it than the ‘felt’ earthquakes. We need to know how the sequences start, and also how they end. If we’re ever going to understand what’s happening, we need the beginning, the middle — and the end. Not just the middle, after they are felt.”

Innovative method tapped for studying earthquake activity
Monitors the SMU team installed at the DFW Airport were removed when seismic activity appeared to have died down in 2009.

Ogwari hypothesized he could look at historical data from distant monitoring stations still in place to extract information and document the history of the DFW Airport earthquakes.

The distant stations are a part of the U.S. permanent network monitored and maintained by the U.S. Geological Survey. The nearest one is 152 miles, 245 kilometers, away.

Earthquake waveforms, like human fingerprints, are unique. Ogwari used the local station monitoring data to train software to identify DFW earthquakes on the distant stations. Ogwari took each earthquake’s digital fingerprint and searched through years of data, cross-correlating waveforms from both the near and regional stations and identified the 412 DFW Airport events.

“The earthquakes are small, less than magnitude three,” DeShon said. “So on the really distant stations it’s like searching for a needle in a haystack, sifting them from all the other tiny earthquakes happening all across the United States.”

Each path is unique for every earthquake, and seismologists record each wave’s movement up and down, north to south, and east to west. From that Ogwari analyzed the evolution of seismicity on the DFW airport fault over space and time. He was able to look at data from the distant monitors and find seismic activity at the airport as recent as 2015.

“Earthquakes occurring close in space usually have a higher degree of similarity,” Ogwari said. “As the separation distance increases the similarity decreases.”

To understand the stress on the fault, the researchers also modeled the location and timing of the pressure in the pores of the rock as the injected water infiltrated.

For the various earthquake clusters, the researchers found that pore pressure increased along the fault at varying rates, depending on how far the clusters were from the injection well, the rate and timing of injection, and hydraulic permeability of the fault.

The analysis showed pore-pressure changes to the fault from the injection well where the earthquakes started in 2008; at the location of the May 2010 quakes along the fault; and at the northern edge of the seismicity.

Will the DFW Airport fault continue to slip and trigger earthquakes?

“We don’t know,” Ogwari said. “We can’t tell how long it will continue. SMU and TexNet, the Texas Seismic Network, continue to monitor both the DFW Airport faults and other faults in the Basin.” — Margaret Allen, SMU

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Scientific American: Drilling Reawakens Sleeping Faults in Texas, Leads to Earthquakes

For 300 million years faults showed no activity, and then wastewater injections from oil and gas wells came along. Study authors took a different approach in the new work — they hunted for deformed faults below Texas.

Science journalist Anna Kuchment covered the landmark earthquake research of a team of SMU geophysicists led by SMU Associate Professor Beatrice Magnani in the SMU Department of Earth Sciences. Kuchment wrote Drilling Reawakens Sleeping Faults in Texas, Leads to Earthquakes for Scientific American.

The SMU researchers tapped seismic data to analyze earthquakes in Texas over the past decade.

The results of the analysis showed that human activity is causing the earthquakes as a result of movement in faults that have been silent for at least 300 million years, until recent injection of oil and gas wastewater.

The article by Kuchment, “Drilling Reawakens Sleeping Faults in Texas, Leads to Earthquakes,” published Nov. 24, 2017.

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EXCERPT:

By Anna Kuchment
Scientific American

Since 2008, Texas, Oklahoma, Kansas and a handful of other states have experienced unprecedented surges of earthquakes. Oklahoma’s rate increased from one or two per year to more than 800. Texas has seen a sixfold spike. Most have been small, but Oklahoma has seen several damaging quakes stronger than magnitude 5. While most scientists agree that the surge has been triggered by the injection of wastewater from oil and gas production into deep wells, some have suggested these quakes are natural, arising from faults in the crust that move on their own every so often. Now researchers have traced 450 million years of fault history in the Dallas-Fort Worth area and learned these faults almost never move. “There hasn’t been activity along these faults for 300 million years,” says Beatrice Magnani, a seismologist at Southern Methodist University in Dallas and lead author of a paper describing the research, published today in Science Advances. “Geologically, we usually define these faults as dead.”

Magnani and her colleagues argue that these faults would not have produced the recent earthquakes if not for wastewater injection. Pressure from these injections propagates underground and can disturb weak faults. The work is another piece of evidence implicating drilling in the quakes, yet the Texas government has not officially accepted the link to one of its most lucrative industries.

Magnani and her colleagues studied the Texas faults using images of the subsurface similar to ultrasound scans. Known as seismic reflection data, the images are created by equipment that generates sound waves and records the speeds at which the waves bounce off faults and different rock layers deep within the ground. Faults that have produced earthquakes look like vertical cracks in a brick wall, where one side of the wall has sunk down a few inches so the rows of bricks no longer line up. Scientists know the age of each rock layer—each row of bricks–based on previous studies that have used a variety of dating techniques.

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The Washington Post: Oil and gas industry is causing Texas earthquakes, a ‘landmark’ study suggests

The study authors took a different approach in the new work — they hunted for deformed faults below Texas.

The Washington Post covered the landmark earthquake research of a team of SMU geophysicists led by SMU Associate Professor Beatrice Magnani in the SMU Department of Earth Sciences.

The researchers tapped seismic data to analyze earthquakes in Texas over the past decade.

The results of the analysis showed that human activity is causing the earthquakes as a result of movement in faults that have been silent for at least 300 million years, until recent injection of oil and gas wastewater.

The article by journalist Ben Guarino, “Oil and gas industry is causing Texas earthquakes, a ‘landmark’ study suggests,” published Nov. 24, 2017.

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By Ben Guarino
The Washington Post

An unnatural number of earthquakes hit Texas in the past decade, and the region’s seismic activity is increasing. In 2008, two earthquakes stronger than magnitude 3 struck the state. Eight years later, 12 did.

Natural forces trigger most earthquakes. But humans are causing earthquakes, too, with mining and dam construction the most frequent suspects. There has been a recent increase in natural gas extraction — including fracking, or hydraulic fracturing, but other techniques as well — which produces a lot of wastewater. To get rid of it, the water is injected deep into the ground. When wastewater works its way into dormant faults, the thinking goes, the water’s pressure nudges the ancient cracks. Pent-up tectonic stress releases and the ground shakes.

But for any given earthquake, it is virtually impossible to tell whether humans or nature triggered the quake. There are no known characteristics of a quake, not in magnitude nor in the shape of its seismic waves, that provide hints to its origins.

“It’s been a head-scratching period for scientists,” said Maria Beatrice Magnani, who studies earthquakes at Southern Methodist University in Dallas. Along with a team of researchers at the U.S. Geological Survey, Magnani, an author of a new report published Friday in the journal Science Advances, attempted to better identify what has been causing the rash of Texas quakes.

A cluster of earthquakes around a drilling project can, at best, suggest a relationship. “The main approach has been to correlate the location to where there has been human activity,” said Michael Blanpied, a USGS geophysicist and co-author of the new study.

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SMU seismology research shows North Texas earthquakes occurring on “dead” faults

Study by Beatrice Magnani, USGS and other SMU scientists shows recent seismicity in Fort Worth Basin occurred on faults not active for 300 million years

Recent earthquakes in the Fort Worth Basin — in the rural community of Venus and the Dallas suburb of Irving – occurred on faults that had not been active for at least 300 million years, according to research led by SMU seismologist Beatrice Magnani.

The research supports the assertion that recent North Texas earthquakes were induced, rather than natural – a conclusion entirely independent of previous analyses correlating seismicity to the timing of wastewater injection practices, but that corroborates those earlier findings.

The full study, “Discriminating between natural vs induced seismicity from long-term deformation history of intraplate faults,” was published online Nov. 24, 2017 by the journal Science Advances.

“To our knowledge this is the first study to discriminate natural and induced seismicity using classical structural geology analysis techniques,” said Magnani, associate professor of geophysics in SMU’s Huffington Department of Earth Sciences. Co-authors for the study include Michael L. Blanpied, associate coordinator of the USGS Earthquake Hazard program, and SMU seismologists Heather DeShon and Matthew Hornbach.

The results were drawn from analyzing the history of fault slip (displacement) over the lifetime of the faults. The authors analyzed seismic reflection data, which allow “mapping” of the Earth’s subsurface from reflected, artificially generated seismic waves. Magnani’s team compared data from the North Texas area, where several swarms of felt earthquakes have been occurring since 2008, to data from the Midwestern U.S. region that experienced major earthquakes in 1811 and 1812 in the New Madrid seismic zone.

Frequent small earthquakes are still recorded in the New Madrid seismic zone, which is believed to hold the potential for larger earthquakes in the future.

“These North Texas faults are nothing like the ones in the New Madrid Zone – the faults in the Fort Worth Basin are dead,” Magnani said. “The most likely explanation for them to be active today is because they are being anthropogenically induced to move.”

In the New Madrid seismic zone, the team found that motion along the faults that are currently active has been occurring over many millions of years. This has resulted in fault displacements that grow with increasing age of sedimentary formations.

In the Fort Worth Basin, along faults that are currently seismically active, there is no evidence of prior motion over the past 300 million years.

“The study’s findings suggest that the recent Fort Worth Basin earthquakes, which involve swarms of activity on several faults in the region, have been induced by human activity,” said USGS scientist Blanpied.

The findings further suggest that these North Texas earthquakes are not simply happening somewhat sooner than they would have otherwise on faults continually active over long time periods. Instead, Blanpied said, the study indicates reactivation of long-dormant faults as a consequence of waste fluid injection.

Seismic reflection profiles in the Venus region used for this study were provided by the U.S. Geological Survey Earthquake Hazards Program.

Seismic reflection profiles for the Irving area are proprietary. Magnani and another team of scientists collected seismic reflection data used for this research during a 2008-2011 project in the northern Mississippi embayment, home to the New Madrid seismic zone. — Kim Cobb, SMU