Is up to 10 percent of increased earthquake activity in the central United States related to hydraulic fracturing?
And does that present a risk for oil and gas operators?
Hydraulic fracturing could have contributed to the dramatic increase in Oklahoma’s earthquake activity in recent years, said Austin Holland, seismologist for the Oklahoma Geological Survey in Norman.
Holland said earthquake activity in the state has increased about 80-fold since he joined the Survey in January 2010. That reflects a general increase in mid-continent earthquake activity dating back to 2009.
He said his preliminary analysis of Oklahoma quake data indicated that hydraulic fracturing might have been a factor in as much as 10 percent of the activity, although he noted the actual percentage could be lower.
“It may not be as rare as once thought to have these felt earthquakes resulting from hydraulic fracturing,” Holland said.
The strength of the earthquakes potentially related to hydrofracturing ranged up to 3.6 magnitude, Holland said, which generally agrees with the findings of other scientists who have been researching recent quake activity in the central United States.
That level of earthquake is just strong enough to be felt, but not strong enough to cause meaningful damage.
If a magnitude of 3.6 was the actual, upper limit for the induced quakes, it would eliminate any direct tie between hydraulic fracturing and the much stronger earthquakes that shook Oklahoma in 2011.
Rob Habiger is a consultant for Spectraseis Inc. in Denver and serves on the company’s board of directors. He has a doctorate in physics and worked in geophysics for Phillips Petroleum and ConocoPhillips for 28 years.
Habiger also served as a member of the National Research Council committee on “Induced Seismicity Potential in Energy Technologies.” That committee issued a report in 2012 identifying wastewater injection wells as a much more likely source of induced seismic events than hydraulic fracturing operations.
“There’s always a discussion around these issues,” he said, “but despite those discussions, there are going to be consequences any time induced seismicity is connected to operations.”
Induced seismicity can be defined as earthquakes and tremors resulting from human activity that alters stresses in the earth. Links between hydraulic fracturing and induced seismicity do carry risks for operators, including potential regulatory limitations on hydrofracturing activities.
Most operators aren’t capturing information relevant to any seismicity induced by their operations, Habiger noted. That can leave the industry vulnerable when questions arise about hydraulic fracturing and earthquakes.
“They don’t have the data to answer those questions,” he said. “Then they’re stuck.”
Holland said operators can monitor to what extent their activities might be causing induced seismicity, and alter their operations accordingly.
“The things we know can be problematic are the things you want to keep track of” in assessing the likelihood of subsurface failure and resulting quakes, he said.
“If you start monitoring a field when you begin developing it, and you see this (induced seismic) activity start happening, you might look at what you’re doing and see that as a sign of failure,” he said.
Brad Artman, chief technology officer for Spectraseis, designs surveys for operators to monitor induced seismicity.
“What we want the operators to do is to use the data on a daily basis to look for trends,” he said. “If a magnitude 4.0 quake will shut down operations, you want to know how many 2.0 and 3.0 quakes are happening.”
Spectraseis uses equipment and processes that will capture information to augment data gathered by government and academic seismic arrays, Artman said.
“There are so many issues about equipment compatibility,” he noted. “You can go out with a little geophone that might be convenient, but it won’t be compatible.”
At the same time, operators will have much more subsurface information about a specific lease area than academic or governmental groups, Artman said.
“Our solution is meant to be as precise as possible and to utilize all of the information the operator has at its disposal,” he said. “One of the biggest risks for operators is ambiguous answers.”
Lack of sufficient seismic data for evaluation is a common lament at the state level. Holland has been gathering more data to rework his study on earthquake activity and hydraulic fracturing in Oklahoma.
“We clearly don’t have enough permanent monitoring stations in the state,” Holland said. “Our aim is to get to a point where when we have a felt earthquake we can say with some level of confidence where it’s occurring, and to say something about this felt or damaging earthquake.”
Oklahoma is now refurbishing its seismic monitoring capability and will be adding eight new stations, Holland said.
The Oklahoma Geological Survey sponsored a workshop on “Fluid Injection Induced Seismicity” in July. A goal was to develop best practices for industry, with feedback gathered from participants, Holland said.
“Right now we’re putting this feedback together in a document and then sending that back to the people who attended the workshop,” he said. “Then we will put together a document for public comment. OGS has never sent out a document for public comment before, so we are breaking new ground.”
Any resulting list of best practices will be issued as guidelines or suggestions, because the Survey is not a regulatory agency.
Induced seismicity typically produces seismic activity – tremors and quakes – of low magnitude, although some stronger, damaging events have occurred.
“We don’t want to be fear mongers,” Habiger said. “We just want to lay the facts out.”
Because of the possible connection between hydraulic fracturing and induced seismicity, some oil and gas operators that utilize hydrofracturing are beginning to monitor seismic activity in their operating areas, he noted.
“Sometimes the technical people bring it up,” he said. “Sometimes the board of directors brings it up because they’re worried about the risk side.”
A series of small but noticeable earthquakes in the Dallas-Fort Worth area five years ago first touched off speculation about a connection between oil and gas operations and induced seismicity (October 2010 EXPLORER). Now other states are looking at induced seismic events.
“We see Texas as different from Oklahoma, because there’s not that much interest in it in Texas. Oklahoma is much more seismically active,” Habiger said. “Canada, on the other hand, is very tuned into this, because of activity in the Horn River Basin and other areas.”
Artman said operators should define their risks from induced seismicity, then decide whether to implement monitoring.
“The most important thing for us as a service company is for an operator or group of operators to figure out their needs, and then to have me sit down and figure out how to meet those needs,” he said.
Over the past three years, the focus on induced seismicity in oil and gas producing areas has shifted away from hydraulic fracturing and toward injection wells. But trying to identify a connection between injection wells and earthquakes in Oklahoma is difficult, Holland said.
In studying a potential connection, scientists have looked at quake origins within five kilometers of an injection well. Oklahoma’s seismic monitoring system has a 10-kilometer uncertainty in identifying the location of a quake origin, according to Holland.
“If you draw a 15-kilometer circle around every injection well in the state, you’re going to cover 80 percent of the state,” he said.
Put another way, any earthquake that occurs in Oklahoma is likely to have an origin near an injection well.
In July, researchers at the Lamont-Doherty Earth Observatory in New York released findings that seismic events in the United States could be triggered by major earthquakes thousands of miles away, and cited increased risks from injection-well induced seismicity.
Holland said the remote-triggering effect “has long been recognized, and it doesn’t just happen around injection wells.”
With so much current speculation about the causes of induced seismicity, the oil and gas industry’s attention has expanded beyond geophysical analysis of prospects to the geophysics of the planet itself.
“The oil and gas industry today,” Habiger said, “is rediscovering global geophysics, meaning earthquakes and how they happen, and how you measure them.”