A federally coordinated effort to determine whether oil and gas activities are related to growing reports of induced seismic activity has identified several information gaps that need to be closed, speakers said during an Oct. 30 briefing at the US Energy Association.
“Not all the activity is related to hydraulic fracturing,” noted William Leith, the US Geological Survey’s senior science advisor for earthquake and geological hazards. “A lot has to do with stripping and dewatering. Production waste fluid injections have caused more quakes in the US than fracing. Not having good injection data is a real problem.”
But another speaker noted that while fracing may not be responsible for much of the reported induced seismicity, it potentially could provide more information initially. Quakes from fracing produced much more information than tremors from dewatering because investments are so much greater, Oklahoma Geological Survey (OGS) State Seismologist Austin Holland said.
Having so much more data could help the OGS identify much broader conditions, but only to a point because distances are greater, Holland said. Still, finding out how pressure can be transmitted over those distances is promising, he said. “We’re working with the Oklahoma Corporation Commission and operators to share more data consistently with us,” he said.
Putting puzzle together
Their remarks came more than 3 months after the US Department of Energy announced plans to mobilize federal, state, industry, and academic experts to address subsurface engineering challenges, particularly controlling fracture propagation and fluid flow (OGJ Online, July 22, 2014).
The oil and gas industry recognizes the need for collaboration across a broad range of stakeholders and disciplines to meet this challenge, according to a third speaker, K.J. Nygaard, a senior stimulation consultant at ExxonMobil Upstream Research Co. “It’s important to understand surface stress relative to tectonic concerns,” he said. “Multiple technical disciplines are required to put the puzzle together.”
In one respect when it comes to managing risk, what matters in the Dallas-Fort Worth Metroplex doesn’t in Alberta’s Horn River basin where operations are much more remote, Nygaard said. “In our company, however, if there’s a situation in West Texas, it’s as important as Dallas-Fort Worth,” he said. “Someone’s house anywhere shouldn’t be damaged if it can be avoided.”
The ExxonMobil Corp. division is interested in faults of concern that are optimally oriented to a stress area and located near a tipping point that’s sufficiently large to cause a significant earthquake, Nygaard said. “Being able to identify where these fault patches exist is important,” he said.
As researchers identify information gaps, key research opportunities are emerging, he said. These include improving knowledge of natural tectonics and subsurface stress which can create pressure conditions, and identifying significant fault systems which are prone to slip, Nygaard said. Basically, the goal is to improve understanding of ground shaking behavior, he added.
Meanwhile, Leith said, “Faults that are slipping are well oriented to the stress field. We’re seeing earthquakes triggered at great distances that are a long way from injection sources. It’s pressure, not fluid flow.”
Determine background seismicity
It’s also essential to fully consider an area’s background seismic activity, observed a fourth speaker, Thomas H.J. Goebel, an applied seismology consult at the University of Southern California’s Induced Seismicity Consortium.
Noting that fault structures can limit the maximum reach of effects from injections, Goebel said: “We want to develop a method that works with both plate boundary regions in California and intraplate regions in Oklahoma.”
Holland said, “There are parts of Oklahoma where they’ve felt so many quakes that they’ve quit bothering to report them to the USGS.” Most of the state’s underlying geology is critically stressed, he indicated. “We can clearly show the vast majority of our quakes are occurring within or near the top of the crystalline basement,” he said.
Operators have started to share information they previously withheld, Holland said. “I have arranged with one of them to run radioactive tests to determine if they’re truly recycling their own waters,” he said. “In ways, we are both data-rich and data-poor in Oklahoma.”
Nygaard noted, “Ground shaking is the hazard that occurs. It’s a function of the event’s magnitude and location. We have to take a broad look across all these probability factors.”
Contact Nick Snow at [email protected].
