Expert opinions vary on earthquake risk from enhanced geothermal systems

25 Sep 2018

(Courtesy: iStock/doguhakan)

Enhanced geothermal systems (EGS) that retrieve heat from dry rock could add to the renewable energy mix but we don’t fully know the geological impact of pumping water deep underground. Given that the systems could lie close to large populations, it’s prudent to solicit expert opinion on the risk of inducing seismic activity. The range of responses from such a panel, however, can be surprisingly diverse.

Scientists in Switzerland and the US convened a panel of 14 international experts and presented them with a hypothetical EGS plant and its geological context. The experts provided their individual judgements in one-on-one interviews with a member of the research team.

“Best-guess” probabilities for the likelihood of a magnitude three, or larger, earthquake occurring during six days of stimulation to create an 80 million m3 reservoir at a depth of 5 km ranged from 0.2% to 95%. When considering 30 years of plant operation, the range of “best-guess” estimates for induced seismicity widened even further.

“As the [EGS] technology is relatively new and there are still deep uncertainties about induced seismicity, we wanted to complement the usual approach of quantitative risk assessment with insights from expert elicitation,” says Evelina Trutnevyte, now at the University of Geneva, Switzerland. “By observing the discussions among seismologists, we had already sensed that some judgements on how high the induced seismicity hazard and risk are would be different. However, we were still very much surprised how different the judgements were for the same hypothetical scenario.”

As well as observing a wide range of probability estimates, Trutnevyte and colleagues noted that responses also diverged on what influences induced seismicity and how it could be better assessed and managed. Based on these findings, the researchers have the following advice for those reviewing a potential EGS project.

“This diversity [in the range of responses] has important implications on how induced seismicity is managed,” says Trutnevyte. “For example, multiple experts should be recruited to make sure that different perspectives are represented, or induced seismicity hazard and risk assessments should be commissioned from several sources that use different methodologies.”

For the study, the team recruited experts working in science, consultancy, public administration and industry. More than half of the recruits reported their primary or secondary disciplines as seismology. Other specialisms included geotechnical and structural engineering; petroleum and production engineering; and rock physics.

“When looking for the experts to participate in our study, we found that we could recruit seismologists relatively easily, perhaps because induced seismicity is a hot topic in their field at the moment,” says Trutnevyte. “However, it was harder for us to find structural engineers who had experience working on induced seismicity damage to buildings, infrastructures and populations nearby.”

Organizations such as the Swiss Competence Center for Energy Research – Supply of Electricity have set up work packages to extend fundamental knowledge of geothermal power production, which could help in bringing opinions closer together.

Trutnevyte and colleagues described their study in Environmental Research Letters (ERL).

25/9/2018 from physicsworld.com