As the oil and gas industry has expanded in parts of the US, so have the number of earthquakes
Massive injections of wastewater from
the oil and gas industry are likely to have triggered a sharp rise in
earthquakes in the state of Oklahoma. Researchers say there has been a forty-fold increase in the rate of quakes in
the US state between 2008-13.
The scientists found that the disposal of water in four high-volume wells
could be responsible for a swarm of tremors up to 35km away. Their research
has been published in the journal, Science.
The US Geological Survey (USGS) has also reported on the question of seismicity induced by wastewater disposal. This new research goes further, linking a large swarm of Oklahoma tremors with a number of specific water wells, distantly located. More than 2,500 earthquakes greater than magnitude 3.0 have occurred around the small town of Jones since 2008. This represents about 20% of the total in the central and western US in this period.
According to Dr Bill Ellsworth from the USGS, the high price of oil has driven this water-based approach. But the law says that drinking water has to be protected from the salty flow.
"As part of the business model, you have to be able to dispose of these very large volumes of saline water. You can't treat it; you can't put it into the rivers. So, you have to inject it underground."
Four of the biggest of these wells in Oklahoma have been pumping around 4 million barrels of water a month to a depth of 3.5km beneath the surface.
To determine the impact of this water, the scientists developed a model that could calculate the way the underground wave of pressure from these wells spread out. By comparing this to seismic data from the Jones cluster, it was concluded that the injection of wastewater is "probably responsible" for the swarm of earthquakes.
" Pressure looks to have risen in the places where the earthquakes are occurring," said Dr Keranen.
"That pressure increase is what we see in natural triggering. So, if a fault is close to failure, the amount that the water is going to put the pressure up to at these locations in our model is enough to push them over the edge."
The four wells that are the subject of the study are owned by a company called New Dominion. It insists that it operates its wells (named Sweetheart, Chambers, Flower Power and Deep Throat) safely and within permitted parameters.
"The company notes the author did not consult with New Dominion's geologist and engineers to determine whether her premises are in any way correct," the company said in a statement.
"At best, these incorrect assumptions are irresponsible." Naturally, they would say that along with any other side-stepping and double talk they need to use to stay in business.
The authors say that they are uncertain about the potential for the large-scale disposal of wastewater to trigger events of even larger magnitude. But it is quite possible. They point to an incident in 2010 when an earthquake ruptured a portion of a 7km long fault. If the entire fault had gone, the authors write, it could have led to a magnitude 6.0 tremor.
"We often see more larger earthquakes when we see a lot of smaller ones," said Dr Keranen.
"But this is a new situation with induced seismicity and we still have a lot of questions that we are trying to address."
This view is echoed by Dr Bill Ellsworth from USGS.
"There are thousands of these wells in the US. The difficulties can be avoided but we need to know more about the process so we can give proper guidance to the authorities."
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