Fracking was dealt a blow last Friday when a series of papers was released in the journal Science linking fracking with earthquakes. A team of researchers, led by Columbia University seismologist Nicholas van der Elst, found a correlation between the injection of fluids underground—a key step in the extraction of shale oil and gas (as well as the extraction of geothermal energy)—with the proliferation of thousands of relatively small-magnitude earthquakes.
These findings are not to be taken lightly, but there’s an important distinction to be made here between fracking and the disposal of wastewater. Both are steps in the extraction of shale energy, and both carry seismic risks, but of the two, wastewater disposal is the more concerning.
When wastewater is disposed of underground, pressure builds along fault lines, which can lead to earthquakes. In March we reported on a study that made a similar connection between the disposal of wastewater from oil and gas drilling with earthquakes. That study linked a 2011 5.7 magnitude earthquake in Oklahoma with the disposal of wastewater produced from nearby oil drilling.
Fracking is a different process, which involves blasting chemical-laden water into well bores at high pressure to break up shale rock, and then extracting that liquid back out, hydrocarbons and all. This process has been linked to earthquakes that are much smaller than those caused by the disposal of the wastewater. A recent study conducted by UK scientists found just three occasions when fracking produced earthquakes, the largest of which had a relatively minuscule magnitude of 3.7.
USGS seismologist William L. Ellsworth remarks on this distinction between fracking and wastewater disposal in a new paper, also released in Science last week:
More than 100,000 wells have been subjected to fracking in recent years, and the largest induced earthquake was magnitude 3.6, which is too small to pose a serious risk. Yet, wastewater disposal by injection into deep wells poses a higher risk, because this practice can induce larger earthquakes. For example, several of the largest earthquakes in the U.S. midcontinent in 2011 and 2012 may have been triggered by nearby disposal wells. The largest of these was a magnitude 5.6 event in central Oklahoma that destroyed 14 homes and injured two people.
It’s clear that we need to rethink how we’re storing the wastewater from oil and gas extraction. The industry is already working on ways to treat and recycle wastewater for future drilling operations, and in what Halliburton’s strategic business manager of water solutions recently called a “paradigm shift,” companies are finding out that this water doesn’t need to be completely clean before reuse. That discovery should make the recycling process cheaper, and as the fracking process continues to become more sophisticated, we can expect more advances that will make the reuse of these fluids more viable. Some companies are even working on fluidless fracking, using propane to blast apart underground shale.
Beyond moving away from the disposal of wastewater in wells, we should also beef up our seismic monitoring of drill sites. One of the notable findings in the van der Elst et al. study was that large earthquakes in far-off places can set off “seismic swarms” at drilling sites that can foreshadow future earthquakes:
At most well sites, these [large earthquakes] little effect, but in a few cases they produce swarms of small tremors that are followed, months later, by larger, locally generated earthquakes. Van der Elst says that this type of seismic swarm might serve as a warning that an injection-well zone is on the verge of overloading its nearby faults, potentially producing a damaging earthquake.
Fracking has given the world access to an enormous new supply of energy, and it has been particularly important to the US, which has taken the lead on its extraction. But America’s new optimism for its energy future shouldn’t blind it to the potential risks associated with the extraction process.