It has become accepted that a recent surge in seismic activity in Oklahoma is related to saltwater injection that has been used to increase oil and gas production, but new research from the University of Alberta says the trend is an anomaly.
In fact the team of researchers, led by U of A geophysicist Mirko Van der Baan, concluded that Oklahoma is the only region in the nine top hydrocarbon-producing places in the US and Canada where this is happening at the regional scale.
The U of A study set out to determine the relationship between hydraulic fracturing and induced seismicity, finding that this technology--unlike saltwater injection in the specific region of Oklahoma--rarely results in tremors.
Before 2009, Oklahoma might have experienced one to two low-magnitude earthquakes per year, but since 2014 the state has experienced one to two low-magnitude earthquakes per day, according to a report last week from the US Energy Information Administration (EIA).
The EIA notes that most of these earthquakes are small, measuring in the three- to four- magnitude range on the moment magnitude scale; large enough to be felt by most people but not often causing structural damage.
Since 2014 there have been a few instances of higher magnitude earthquakes in Oklahoma (between magnitude 5 and 6) that have caused some damage, the EIA reports.
The U of A says the increase in seismic activity in Oklahoma has an 85 percent correlation to increased oil production, likely primarily due to saltwater disposal.
However, after studying the last thee to five decades of data (depending on data availability), Van der Baan’s team found that Oklahoma's experience is unique.
In a two-year study, researchers examined data from Oklahoma, Ohio, Pennsylvania, Texas, West Virginia, Alberta, British Columbia and Saskatchewan.
“The other areas do not display state/province-wide correlations between increased seismicity and production, despite 8-16 fold increases in production in some states,” reads a paper by Van der Baan and U of A postdoctoral fellow Frank Calixto that appeared in the scientific journal Geochemistry, Geophysics, Geosystems. However, the researchers acknowledged that in various cases seismicity has locally increased, linked to hydraulic fracturing.
“It’s not as simple as saying ‘we do a hydraulic fracturing treatment, and therefore we are going to cause felt seismicity.’ It’s actually the opposite. Most of it is perfectly safe,” Van der Baan said in a statement released by the U of A.
“What we need to know first is where seismicity is changing as it relates to hydraulic fracturing or saltwater disposal. The next question is why is it changing in some areas and not in others,” he said.
For example, the researchers said that while data shows that human-caused seismic activity is less likely in areas with lower existing seismic risk, the opposite is not necessarily true.
“If we can understand why seismicity changes, then we can start thinking about mitigation strategies.”
Correction: A previous version of this article stated that hydraulic fracturing is the cause of increased induced seismicity in Oklahoma, which is incorrect. JWN apologies for this error.