Well activity quake risk is manageable, expert says
A Stanford University geophysicist says earthquakes triggered by oil and gas wastewater injections are cause for concern, but the risk also can be managed.
“We know how to solve this problem,” Mark Zoback said recently at the Vail Global Energy Forum. “It’s not something all that mysterious.”
He said the problem occurs when the injection wells intersect with pre-existing faults, allowing water to reach basement rocks and “unclamp” faults. The result, he said, is quakes occurring now that otherwise might not occur naturally for thousands of years.
“And this has been happening a lot,” he said.
He said the induced quakes are being widely felt, although they may cause damage only in rare circumstances.
“But everybody is aware that they are happening and they are very disturbing,” Zoback said.
He said it can be disconcerting to go through even a small quake, “and people are naturally worried.”
High-profile quakes linked to injection wells in recent years include a 5.3-magnitude one along the Colorado-New Mexico border in 2011, and other sizable temblors in the Dallas-Fort Worth area; Youngstown, Ohio; and Guy, Ark. In what Zoback calls a curious case in Oklahoma, earthquakes have increased 30-fold over the last four years, but there are several indications that the jump is a natural geological phenomenon rather than related to injection wells there, he said.
Arkansas oil and gas regulators imposed a 1,000-square-mile moratorium on injection, but he described that as a “meat-ax” approach because it resulted in a lot of costly truck hauling to other injection wells that could themselves cause problems if they are in the wrong place.
The country has about 150,000 Class 2 wastewater injection wells, as they are referred to by the Environmental Protection Agency. Zoback said most haven’t presented problems because they were located in safe areas.
He said it’s important to evaluate locations and avoid injecting wastewater in areas with potentially active faults, and such evaluations aren’t occurring now. Other approaches include limiting injection rates/pressures, monitoring seismicity and being prepared to abandon some injection wells where necessary.
Zoback said recycling rather than injecting wastewater is another important solution to the problem.
Zoback is working with fellow Stanford colleagues and with energy companies to try to come up with a protocol for evaluating possible injection sites for problems.
“If we understand the problem, what data can we obtain to manage the problem with the least disruption to activity and still protect the public?” he said, describing the team’s objective.
He said he thinks the problem can be effectively managed, and just requires more awareness and a focus on prevention.