Fracking at greater depths can lead to ten times the risk of earthquakes, study finds

Fracking operations that drill deeper into the earth can make triggering an earthquake almost ten times more likely, according to a new study.

The report, published this week in the Bulletin of the Seismological Society of America (BSSA), is based on data from more than 1,300 single well sites across Oklahoma.

The study found that in one rock layer, the likelihood that fracking triggered seismic activity increased from 5 to 50 per cent with increasingly deeper well operations, from 0.9 to 3.4 miles (1.5 to 5.5km).

Dr Michael Brudzinski, who led the research team from Miami University, Ohio, told The Independent: “The strongest trend was depth. We saw almost a factor of ten increase in the likelihood of seismic activity in deep wells compared to shallow wells.”

Fracking - hydraulic fracturing, to use its official name - is the process of recovering gas and oil from shale rock. Well operators drill vertically, or horizontally at most new US sites, through rock then force a highly-pressurised mix of sand, water and chemicals against a rock formation. The liquid breaks apart, or fractures, the rock layers to release deposits of gas and oil.

The drilling method has made the US the largest oil producer in the world. However recent price wars, plus the slash in demand caused by the Covid-19 pandemic, has left some oil and gas companies teetering on the verge of bankruptcy.

Earthquakes linked to fracking have been triggered around the world including in multiple US states. Oklahoma has seen a dramatic rise in earthquake activity in the past decade.

The new study analysed well sites in Oklahoma because the state's large number of fracking operations generated a big enough dataset of correlation between fracking and earthquakes.

But the issue is not exclusive to Oklahoma. In the Appalachian region, Texas, Arkansas, Canada's Alberta and British Columbia provinces, and recently in the UK and China, there have been earthquakes linked to fracking.

In 2019 a fracking-induced earthquake, measuring 4.9-magnitude on the Richter scale, struck a village in the Sichuan Province of China, leaving two people dead and a dozen injured. It was believed to be the first ever fracking earthquake deaths, according to Inside Science. A study following the incident noted that the fracking operation was relatively shallow - about 0.6 miles (1km) deep.

Increasingly, studies have found that fracking can induce earthquake activity large enough for people to feel. This is possibly due to increasing fluid pressures within the rock that relieve stress on faults and allow them to slip, according to the Seismological Society of America.

The new BSSA study looked at data from 929 horizontal and 463 vertical wells in Oklahoma to estimate the probability of generating earthquake activity.

Although there is ongoing research as to the exact mechanisms linking well depth and earthquake probability, the team suggested that the overpressure of fluids trapped inside the rock may be important.

“The deeper the rock layers are, the more rock that is sitting on top of a well, and that is going to potentially increase the fluid pressures at depth,” said Dr Brudzinski.

The total volume of injected liquid did not affect the probability of earthquake activity near the Oklahoma wells—a surprising finding that differs from other studies of "induced seismic events".

Some previous studies have linked earthquakes to vast, underground wastewater disposal from fracking.

The new study looked at single wells and not multiple wells clustered together on a drilling pad. In other fracking studies where a link was made between the volume of liquid injected and earthquake activity, multiple wells on a pad are more common.

Dr Brudzinki said: “So that’s where we started to think that perhaps that’s the difference between what we’re seeing in our study versus other studies. We’re proposing that multiple wells injecting next to each other may be why volume does matter in those cases, although we need to study it more.”

He added: “An isolated well with a large volume may not have nearly as much of a [seismic] risk as a large volume well that is in close proximity to other large volume wells.”

Dr Brudzinksi said the study was designed to help answer questions that public officials and regulators have around fracking and the factors that most influence the earthquake risk. Some operators are already limited in the depths they are permitted to drill.

“What we’re trying to get across to operators is being pragmatic about long-term decisions," he said. "If drilling is going to require really deep depths, they are likely to have the potential for higher seismicity. They have to factor that risk into their economic analysis."

Environmentalists have clashed with oil and gas producers over the environmental and public health risks linked to fracking.

Along with the contamination of groundwater from chemicals used in the injection solutions, activists point to the climate impacts from fracking. Methane, the primary component of natural gas, has a powerful greenhouse effect and is 25 times more effective at trapping heat in the atmosphere than carbon dioxide. A 2015 study made the conservative estimate that the Barnett Shale region in Texas leaked 544,000 tons of methane annually - equivalent to 46 million tons of CO2.

Seth Gladstone, of the NGO Food & Water Watch which has called for a ban on fracking, told The Independent: “From air and water contamination, to grave human health effects, to the disastrous climate impacts of oil and gas extraction and burning, there are numerous inherent risks of fracking.

"But among the most immediate and potentially disastrous of these risks are earthquakes. No one wants earthquakes under their feet or under their homes. And no one who has come face to face with any of the devastating effects of fracking would choose to live in proximity to them.”