As regulators in Oklahoma scramble to figure out what caused a swarm of earthquakes outside an “area of interest” targeting wastewater injection wells, one researcher said there is a possibility the temblors were caused by hydraulic fracturing (fracking) operations.

According to U.S. Geological Survey (USGS) data, there have been eight earthquakes measuring 2.5 magnitude or higher on the Richter scale within the last week in the Blanchard area. Four earthquakes ranging from 2.7 to 3.0 magnitude struck on July 7 at distances of 4.3-6.2 miles southeast of Blanchard. That was followed by the largest quake, a 3.4-magnitude temblor that struck 5.6 miles south-southeast of Blanchard last Friday.

Two earthquakes, measuring 2.5 and 2.8 magnitude and centered about six miles south-southeast of Blanchard, struck on Sunday. A 3.1-magnitude temblor centered five miles southeast of the town struck on Monday night, according to the USGS.

Since the beginning of the year, regulators with the Oklahoma Corporation Commission (OCC) have ordered operators of wastewater injection wells targeting the Arbuckle Formation to cease or curtail their operations. But the OCC’s area of interest covers wide areas of the north and central parts of the state, and there are no active disposal wells near Blanchard.

Oklahoma Geological Survey (OGS) Director Jeremy Boak told NGI’s Shale Daily that the only wastewater disposal well in the area of the recent earthquakes is about 20 miles away, and hasn’t been operational for at least 10 years. He added that the disposal well was small, handling only about 10,000/bbl a year, and targeted formations above the Arbuckle.

“Injection doesn’t look like a good mechanism for this, but you are on the edge of the SCOOP [South Central Oklahoma Oil Province] play, and so we’re interacting with operators in the area to see what’s going on nearby,” Boak said Thursday. “We’re also going to try to apply some software that allows us to look at the clusters of earthquakes together. We can tighten up the locations better and that will allow us to tie things more directly.”

But Boak added, “at this point we have to consider the possibility that this is something we haven’t seen before, which is a set of earthquakes that could conceivably be tied to a frack job. There are faults in the area. There’s the reasonable possibility that if the frack job spread out far enough it could conceivably initiate some [seismic] action.”

Boak said researchers must determine the depth of the earthquakes to establish a cause.

“The earthquake depths we’re seeing are kind of deep,” Boak said. “In British Columbia, where they’ve tracked a number of frack-related earthquakes, the depth is moderately close to the fracking horizon. In this cluster, we’ve got one earthquake that might be that shallow. If we can do the cluster analysis and tighten up those locations, and especially the depths, we may see that there’s some part of this is shallow enough that we could attribute it to a frack job. But that’s still highly uncertain.

“We’ve got signs in both directions. There just isn’t much injection going on in this area, so really trying to figure out what’s driving this earthquake is a significant challenge, and we have uncertainties, we’re hoping to work those out fairly quickly.”

OCC spokesman Matt Skinner said the commission’s Oil and Gas Conservation Division (OGCD) is investigating all oil and gas activity in the Blanchard area.

“Because there are no Arbuckle disposal wells within at least a 20-mile area of the earthquakes, all oil and gas operations in the area are being examined,” Skinner said Wednesday. “Relevant data is being given to the OGS for further analysis.”

Last February, the OGCD unveiled its Western Regional Reduction Plan, which called for a nearly 500,000 b/d reduction in wastewater injection volumes (see Shale Daily, Feb. 17). One month later, the agency released its Central Oklahoma Volume Reduction Plan, which called for a 300,000 b/d reduction in injection volumes (see Shale Daily, March 7).

“We’re seeing something that’s a new phenomenon — either a broader expansion of the influence of injection, or potentially this other mechanism,” Boak said. “In the background there’s still always the possibility of a natural earthquake, but our inclination is to say if we can find an operator who’s in the middle of an operation right now, where we happen to say, ”gee, this looks like it’s actually an example of a frack-related earthquake.’

“That would have significant implications. We would have to start looking around at other operators in the area, see what can we legitimately anticipate, and see what we have to do in the way of best practices on this going forward.”