The earthquake risk

April 23, 2012
Much about the future of energy policy everywhere relates to balancing the promise of unconventional oil and gas resources against environmental problems associated with their development and use.

Much about the future of energy policy everywhere relates to balancing the promise of unconventional oil and gas resources against environmental problems associated with their development and use. For the oil and gas industry and environmentalists, this is new ground. Sure, the industry and those who oppose its work on environmental grounds have had to balance values in conflict in the past. But the weights haven't been as great as they are now.

Unconventional oil and gas—unconventional because of the nature of the fluids or the rocks that contain them—exist in exponentially greater amounts than do their conventional counterparts. That's the energy promise. But their development and production require far greater inputs of energy and water and can create far more surface disturbance. That's the environmental problem.

Achieving a reasonable balance, a balance both economically sound and environmentally responsible, is the largest energy challenge of the day. In addressing this challenge, there's no place for fear, which can only unbalance discourse at the outset. Indeed, there's no need for fear.

UK earthquakes

That this is so becomes clear from a UK government review of studies into earthquakes induced by hydraulic fracturing of a shale thought to contain large amounts of natural gas in Northwest England. Cuadrilla Resources Ltd., Lichfield, estimated last year that the Cretaceous Bowland shale under acreage it holds contains 200 tcf of gas in place. But it suspended development after earthquakes were detected around its Preese Hall-1 well near Blackpool during hydraulic fracturing.

It wasn't the first case of seismicity apparently induced by hydraulic fracturing. In the US, too, earthquakes have been associated with the procedure, as well as with injection into the subsurface of leftover frac water.

Without context, the link between frac jobs and earthquakes can inspire fear. And fear can make prohibition of the well-completion method seem sensible, if not obligatory. Anything that threatens to topple buildings should be banned, after all.

But earthquakes caused by hydraulic fracturing aren't that severe. And fracing isn't the only human activity that shakes the ground.

The government review of studies Cuadrilla performed of Preese Hall earthquakes makes these important points. Cuadrilla concluded that its operations caused the observed earthquakes but that work safely could proceed under a range of precautions. The government review, by a hydraulic fracturing consultant, a university professor of geophysics, and a government seismologist, generally agreed while recommending additional and in some cases stricter precautions. The UK Department of Energy and Climate Change has solicited comments on the recommendations and will make the final decision whether to allow hydraulic fracturing.

What's important to broader discussion of this issue is that the experts didn't conclude automatically that the procedure should cease because it causes earthquakes. It put the earthquakes in context, acknowledged that they present a risk, and suggested ways the risk can be managed without banning work crucial to energy supply. The balance is commendable. DECC should preserve it in its decision-making.

Mitigating risk

The review group pointed out that frac jobs don't create stresses that cause earthquakes. They release stresses that already exist, generally by introducing fluids into faults destined at some point to fail. Because of the depths and nature of faults in strata targeted by hydraulic fracturing, magnitudes of induced earthquakes are limited. The strongest earthquake around the Preese Hall well was magnitude 2.3, strong enough to be felt on the surface but not strong enough to cause damage. Seismicity induced by other human activities, such as mining of coal, salt, gypsum, anhydrite, and other minerals, is far more frequent than that caused by fracing, the reviewers said. Usually, they noted, seismic events induced by humans "are generally small in comparison to natural earthquakes."

This does not mean that hydraulic fracturing poses no risk of damaging seismicity. It does mean that the risk can be mitigated with attention, measurement, and care. This, rather than foreclosure of activity, is how environmentalism should work.

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