|USGE-NEIC ComCat & Oklahoma Geological Survey; May 2, 2014|
Five years ago, Oklahoma averaged just two magnitude 3 or greater earthquakes a year. Last year there were 109. As of early July, this year’s count is already over 230 - and that’s just the magnitude 3 and above, temblors big enough to knock dishes off shelves and crack foundations. There are hundreds more low magnitude quakes, say state geologists.
Why all the quakes? They're due to increased injection of gas- and oil drilling waste fluids into disposal wells, says Cornell researcher Katie Keranen. She recently moved to Cornell from Oklahoma, where she'd been studying injection well-induced seismicity for a few years. Earlier this month she and her colleagues published a paper in the journal Sciencethat links injection wells to tremors. Their research also demonstrates that those quakes can occur up to 30 miles from the original injection well site.
Keranen got interested in the relationship between drilling and tremors after the Prague, Oklahoma quake in 2011. That 5.6-magnitude quake was centered just 45 miles northeast of Oklahoma City and was felt as far away as Texas, Arkansas, Kansas, and Missouri. Her research led her to study swarms of quakes originating near the town of that same name.
The Jones swarm began within13 miles of the highest-rate waste fluid disposal wells in Oklahoma. So the first question Keranen asked was whether the number of injection wells had increased dramatically. They hadn’t. The increase in number of injection wells was gradual.
“The thing that has changed significantly is the volume of waste fluids pumped into the disposal wells,”she says.
Of all the injection wells she looked at, the four with the highest waste-disposal injection rates are southwest of Jones, situated in southeast Oklahoma City. Between them, they accept over 4 million barrels each month, most of it from dewatering production of oil. (Dewatering production wells produce huge amounts of waste fluid, most coming from the formation – up to 200 times as much waste fluid as oil.) Disposal rates jumped after 2004, when high-rate injection wells began operating.
All of that injected fluid presses against underground rocks. Originally, geologists thought that waste fluids injected deep underground would take a long time to work its way through the formations. But Keranen finds that it’s moving faster than expected and building up pressure farther away than expected, leading to seismic events 18 to 20 miles from the original injection site.
Given the increasing number of injection-well related quakes, and that most states have lots of faults beneath the surface, there is a clear need for better regulation of the underground injection wells. Already some municipalities are requiring operators to increase seismic monitoring and monitor well pressures. But that's not enough, says Keranen. Operators must also be willing to dial down the injection volumes. Ohio is already taking steps that require injection well operators to decrease injection volumes when they see an increase in their seismic meters, she says.
“Pennsylvania, Ohio, Oklahoma – they’ve had to learn a lot over these last ten years,” says Keranen. “We can apply their lessons to New York.”
(taken from my longer article in the July 21-27, 2014 issue of Tompkins Weekly)
Post a Comment