A study has attributed the dramatic increase in earthquakes in central Oklahoma since 2009 to subsurface wastewater injection at a few wastewater disposal wells. As per researchers, Oklahoma earthquakes make up nearly half of all central and eastern U.S. seismicity from 2008 to 2013, many occurring in areas of high-rate water disposal.
Induced seismicity poses as a primary obstacle to expanded shale gas and unconventional hydrocarbon development. The study offers insight into the process by which the earthquakes are induced and suggests that sticking to standard best practices may significantly cut down the danger of inducing seismicity. The best practices include avoiding wastewater disposal near major faults and the use of suitable monitoring and mitigation schemes.
As per research, 4 of the highest-volume disposal wells in Oklahoma (about 0.05% of wells) are capable of triggering about 20% of recent central U.S. earthquakes in a series, called a swarm, spanning nearly 2,000 sq kms, as shown by the study of modeled pore pressure surge at relocated earthquake hypocenters.
Earthquakes are induced at distances more than 30 kms from the disposal wells, far away from current criteria of 5 kms from the well for diagnosis of induced earthquakes.
The area of increased pressure related to these wells keeps expanding, increasing the probability of encountering a larger fault and thus raising the risk of triggering an earthquake of higher-magnitude.