Is it OK fracking ?

Is OKlahoma fracking in oil and gas wells causing all the earthquakes ?    The sudden increase in seismicity since 2009 has certainly coincided with an increase in oil and gas activities in the state.  

What is fracking?
 This is the process of pumping high pressure fluids into otherwise impermeable rock layers in order to induce small cracks (fractures) which are then held open by sand and allow fluids(gas, oil and water)  to flow.   So by definition fracking is causing microfractures deep underground, these micro-earthquakes are very very small (generally they have negative magnitudes) and are only detectable by highly specialised sensors located deep underground near the injection sites.


However the M3+ earthquakes happening in Oklahoma are releasing orders of magnitude more energy than is being put into the ground by the injection processes,  these earthquakes are fractures along pre-existing faults and are releasing existing stresses in the crust.   Scientists call these induced earthquakes.

So are the OK induced earthquakes caused by fracking ? 

Well again it is complicated, some probably are, however in the oil and gas industries several different techniques are used that involve injecting fluids deep underground.

Different oil and gas injection operations

After careful analysis of the data in Oklahoma and comparison with known wellsite activities scientists at the USGS have concluded that the vast majority of the induced earthquakes in Oklahoma are related to "wastewater disposal" rather than "fracking" .   In Oklahoma many of the producing oil wells produce a mixture of oil and (mostly) water.   The water (brine) is very salty and it would not be environmentally safe to dispose of into existing watercourses without treating first.    It is much cheaper to return this "formation fluid" to the subsurface than to treat it at the surface.  The wastewater disposal wells usually drill into a deeper formation that is highly permeable (i.e. fluids can easily flow into it).  Sometimes this water is pumped into the formation, sometimes it just naturally flows in under its own pressure.   However since 2009 the volumes of this waster water injection have increased massively and are associated with the increased seismicity.   In 2015 the authorities in Oklahoma started to restrict the volumes of wasterwater that could be injected.   Following the M5.8 Pawnee earthquake in September this year a number of wastewater injection wells were closed, however it might take months or even years before the effects of these restrictions are seen in a reduction in earthquakes.  

Scientific American Article   https://www.scientificamerican.com/article/drilling-for-earthquakes/

Lots more information on induced sesmicity is available at the USGS website

Frequently asked questions   https://www2.usgs.gov/faq/taxonomy/term/9833   
Myths about induced earthquakes https://earthquake.usgs.gov/research/induced/myths.php

A technical paper on the Oklahoma earthquakes (Science journal)

Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection