Scientists have confirmed that oil drilling wastewater disposal in off-site wells may trigger some earthquakes in California.
The research paper, published by the American Geophysical Union Researchers on February 4, documented that a “swarm of moderate earthquakes in Kern County” were tied to the filing of three wastewater disposal wells near the White Wolf fault between 2001 and 2005. Although the research could not prove a direct causal link between wastewater injections and an earthquake swarm, the statistical probability was 97 percent.
The California study followed the research published on June 19 in the journal Science Advances by Stanford geophysicists Professor Mark Zoback and doctoral student Rall Walsh. It pertains to similar seismic activity associated with oil drilling off-site waste water injections that identified differences in salinity as the triggering mechanism responsible for the recent spike of earthquakes in parts of Oklahoma.
In 2015, Oklahoma experienced 907 quakes larger than magnitude 3 on the Richter scale. Prior to 2008, the state averaged just two similarly sized quakes per year.
Once considered the most environmentally responsible way for oil companies to deal with their wastewater, the Stanford team traced Oklahoma’s rising number of earthquakes to a dramatic increase in the disposal of salty wastewater into the Arbuckle formation, a 7,000-foot-deep sedimentary formation under Oklahoma.
The Oklahoma study also showed that the primary source of the quake-triggering wastewater is not so-called “flowback water” generated after hydraulic fracturing operations. Rather, the culprit is “produced water”–brackish water that naturally coexists with oil and gas within the earth. Drilling companies separate produced water from extracted oil and gas and typically reinject the water into off-site deep disposal wells.
California was once the number two producer of oil until the 1970s. After falling to number four in the 2000s, a big increase in hydraulic fracking in California in the last year has pushed production up to the number three state.
About 350 injection wells in California are within five miles of an active fault. Several very large off-site injection wells skirt the huge San Andreas fault. Prior research had shown a causal relationship between a rise in earthquakes and off-site underground injections of water in geothermal wells. But the American Geophysical Union study was the first to link earthquakes to injection wells in California.
The California Division of Oil, Gas, and Geothermal Resources has commissioned Lawrence Berkeley National Laboratory to study the prevalence of the relationship between earthquakes and deep injection wells.