To frack or not to frack
New study suggests conventional ways are tougher on groundwater. Nick Carne reports.
Fracking continues to be a divisive issue, and even good science can’t always help in painting a clear picture of its overall impact on the environment.
Less than a week after one study implicated it in a significant recent increase in atmospheric methane levels, another suggests that it has a much lesser impact on groundwater than conventional oil and gas production.
"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," says Jennifer McIntosh, a hydrologist at the University of Arizona, US, and co-author of a paper published in the journal Groundwater.
"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."
Fracking is high-volume hydraulic fracturing. Water, sand and chemicals are injected under high pressure into petroleum-bearing rock formations to recover previously inaccessible oil and natural gas. It led to the shale gas boom that started about 15 years ago.
But conventional methods of oil and natural gas production also inject water underground to aid in the recovery of oil and natural gas, says McIntosh, and we’ve been using them since the late 1800s.
In their recent study, she and colleague Grant Ferguson, from Canada’s University of Saskatchewan, looked at how much water was and is being injected by petroleum industry activities in North America, how those activities change pressures and water movement underground, and how they could contaminate groundwater supplies.
They found that there is likely more water now in the petroleum-bearing formations than initially because of traditional production activities.
Conventional enhanced oil recovery injects water into petroleum-bearing rock formations to push the oil and gas toward extraction wells. Saline water produced as a by-product is then re-injected, along with additional freshwater, to extract more oil and gas.
At the end of the cycle, excess saltwater is disposed of by injecting it into depleted oil fields or deep into geological formations that don't contain oil and gas. That injection of wastewater, the researchers say, has changed the behaviour of liquids underground and increases the likelihood of contaminated water reaching freshwater aquifers.
"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 says.
Another wild card, Ferguson adds, is the 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.
"We haven't done enough site investigations and monitoring of groundwater to know what the liability really looks like," he says.
"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."