Oil Drilling Blamed for Rocketing Eathquake Rates in Oklahoma

The rise in number of earthquakes in the Midwest is being attributed to oil drilling. A new study claims that reinjection of brackish water into disposal wells has pressurized fault lines to release energy as quakes.

According to researchers at Stanford University, seismic activity in Oklahoma increased in recent years with the state experiencing 24 seismic events in 2014 alone as against one or two such events in 2008. Researchers have blamed wastewater disposal into the Arbuckle formation beneath the state, and that a potentially damaging quake cannot be discounted. 

"What we've learned in this study is that the fluid injection responsible for most of the recent quakes in Oklahoma is due to production and subsequent injection of massive amounts of wastewater, and is unrelated to hydraulic fracturing," said Professor Mark Zoback.

Hydraulic fracturing is a process of passing pressurized water and chemicals into deep wells to cause rock fracturing for creating channels to obtain natural gas and petroleum oil. However the water that researchers tied to earthquakes is brackish, which is the wastewater obtained during oil drilling. This water is separated from oil and re-injected into the wells.

To arrive at their findings, Zoback and team studied three areas around the towns Cherokee, Perry and Jones. They found increased incidence of earthquakes following increase in wastewater disposal compared to three nearby control areas.

Though wastewater disposal was suspected earlier, scientists could not explain the delay between disposal and occurrence of earthquakes, until now.

"The earth's crust contains many pre-existing faults, some of which are geologically active today. Shear stress builds up slowly on these faults over the course of geologic time, until it finally overcomes the frictional strength that keeps the two sides of a fault clamped together. When this happens, the fault slips, and energy is released as an earthquake," the scientists found.

While much of the seismic activity witnessed was of low magnitude, concerns have been expressed as wastewater disposal increased from 20 million barrels per year in 1997 to 400 million barrels per year in 2013.  

The study has been published in the journal Science Advances.