Oil and natural gas operators need to cut back on waste fluids that are injected into wells to help reduce the outbreak of small earthquakes, which are occurring with increasing frequency in the Midcontinent, according to two recent studies.

Both studies point to oil and natural gas operations involving the deep injection of wastewater as the prime cause for the surge in seismic activity, but they differ in how the industry and regulators should respond.

The studies add to the scientific literature pointing to oil and gas injection wells as the source of quake activity in the United States (see Shale Daily, Sept. 16, 2014; Sept. 9, 2013; July 15, 2013). However, other studies have found no evidence of the links (see Shale DailyJune 12June 11).

The University of Colorado (UC) and U.S. Geological Survey (USGS) study recently was published in Science, which said regulators should concentrate on the highest volume injection wells. A separate study by Stanford University focuses on increased activity in Oklahoma and suggests that the cumulative injections across broad areas should be addressed.

The UC-USGS study concluded that "high-rate injection wells” with more than 300,000 barrels/month “are much more likely to be associated with earthquakes than lower-rate wells."

"At the scale of our study, a well's cumulative injected volume, monthly wellhead pressure, depth, and proximity to crystalline basement do not strongly correlate with earthquake association," said lead author Matthew Weingarten and colleagues. "Managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes."

The UC experts concluded that the energy industry and regulatory bodies can use the study's operational parameter "to lower the likelihood of earthquakes associated with injection wells."

Stanford’s Mark Zoback, a professor in the Department of Geophysics, noted in the second study that the recent swarm of quakes in Oklahoma has not posed a danger to the general public, but there is still the possibility of the wastewater injection eventually triggering more damaging quakes.

His study was published in Science Advances. It notes that putting limits on individual wells is not the answer. The cause of the increased quake activity since 2009 is the result of "the cumulative process from so many wells over such a large area injecting such large volumes in the past five to 10 years."

The Stanford study also concluded that hydraulic fracturing (fracking) is not linked to the seismic activity. In the past, the USGS had confirmed this, while calling for more frequent seismic monitoring and studies (see Shale Daily, April 23). USGS has traditionally assessed seismic risks on a six-year schedule, but it has proposed an annual hazard model to more effectively predict earthquakes.

Oklahoma's Geological Survey has used the Stanford findings to conclude there is a link between salt water disposal injection wells and the more quakes.