High-volume hydraulic fracturing, commonly known as fracking, injects water, sand and chemicals under high pressure into petroleum-bearing rock formations to recover previously inaccessible oil and natural gas. This method led to the current shale gas boom that started around 15 years ago.
Conventional methods of oil and natural gas production, which have been in use since the late 1800s, also inject water underground to aid in the recovery of oil and natural gas.
“If we want to look at the environmental impacts of oil and gas production, we should look at the impacts of all oil and gas production activities, not just hydraulic fracturing,” said Jennifer McIntosh, a University of Arizona professor of hydrology and atmospheric sciences.
“The amount of water injected and produced for conventional oil and gas production exceeds that associated with fracking and unconventional oil and gas production by well over a factor of 10.”
A team looked at how much water was being injected underground by petroleum industry activities, how those activities change pressures and water movement, and how those practices could contaminate groundwater supplies.
While groundwater use varies by region, about 30 per cent of Canadians and more than 45 per cent of Americans depend on the resource for their municipal, domestic and agricultural needs.
“There’s a critical need for long-term – years to decades – monitoring for potential contamination of drinking water resources, not only from fracking, but also from conventional oil and gas production,” McIntosh said.
“What was surprising was the amount of water that’s being produced and re-injected by conventional oil and gas production compared to hydraulic fracturing.
“In most of the locations we looked at – California was the exception – there is more water now in the subsurface than before. There’s a net gain of saline water.”
Oil and gas production activities can have environmental effects far from petroleum-producing regions.
For example, previous studies show that operating disposal wells can cause detectable seismic activity more than 90km away. Conventional activities inject lower volumes of water and at lower pressure, but take place over longer periods of time, which may cause contamination over greater distances.
There are also thousands of active, dormant and abandoned wells across North America. Some are leaky or were improperly decommissioned, providing possible pathways for contamination of freshwater aquifers.
There is little consensus as to the scale of the problem and decommissioning can cost anywhere from a few billion to a few hundred billion dollars, depending on the size.
“We haven’t done enough site investigations and monitoring of groundwater to know what the liability really looks like,” said Grant Ferguson, University of Saskatchewan, who also worked on the project. “My guess is that some wells probably should be left as is and others are going to need more work to address migration of brines and hydrocarbons from leaks that are decades old.”
A separate study released this week by researchers from Cornell University warned that the boom in fracking for shale has ‘dramatically increased’ global emissions of methane in the past decade.