Geothermal Plant Linked To South Korean Earthquake
Thursday, May 03, 2018

A small, pilot-scale geothermal plant with a capacity of 1.2 MW is being blamed for triggering the worst earthquake in South Korea since seismic records began in 1905.

Studies by scientists at Korea and Busan universities published in the journal Science said there was a strong link between the quake last November and the operations of the Pohang plant. The project used enhanced geothermal system (EGS) drilling to reach depths of 4,000 metres. Hydraulic fracturing was used to create an artificial reservoir chamber between two boreholes, one of which was then used to draw hot water to a power plant above. Cooled water was then pumped back down the second well.

Yet last November’s 5.5-magnitude tremor – as well as a previous quake in 2016 – may have been caused by “induced seismicity” from the plant, experts said. The Pohang quake injured 90 people and caused US$52 million in damage, Yonhap news agency said, in a country that has been otherwise largely geologically stable. There are nuclear power plants (NPPs) with six reactors in a 50-km radius of the earthquake epicentre, although operator KEPCO said there was no damage.

Work on the geothermal plant was suspended by court order after protests from local residents. The South Korean Energy Ministry has begun a separate independent inquiry involving scientists from several countries.

The plant, which would eventually have a capacity of 6 MW if completed, was being built by Korean firm Nexgeo in partnership with EGS specialists DESTRESS, an international scientific consortium based in Geneva and part-funded by the European Union. The project is also backed financially by the Korean government.

“These indications combined lead to the conclusion that a connection between the magnitude 5.5 earthquake in South Korea and the nearby geothermal project is plausible,” DESTRESS said in a statement. “So far, there is no quantitative model available that relates the injection activities conducted to the occurrence of this event.”

Speaking to the BBC World Service, University of Glasgow hydraulics engineer Rob Westaway – who was involved with the project – explained the nature of the investigation. While the first earthquake occurred around 40 km from the drilling site, Westaway noted: “This second earthquake occurred in November 2017, which was much closer, within just a few hundred metres of the points at which the fluid is injected. It is possible that this was triggered by the first of the two earthquakes and would have happened anyway, in which case it is coincidence that it is close to the site.”

“On the other hand, it is possible that it may have been caused by fluid injection…and that is the point which the investigation has reached,” he added.

If the Pohang earthquake is indeed proved to have been caused by human activity, “it would be the largest earthquake known to have been associated with the exploitation of deep geothermal energy,” DESTRESS said.

This would be damaging for wider geothermal developments using EGS, especially since the Pohang project had used new “soft stimulation” technology designed to reduce subterranean disturbance, Science said.

It could also be an ironic setback for the Seoul government, which has pledged to increase its use of renewable energy as a replacement for nuclear power, which generates about 30% of the country’s electricity, in light of public concerns about nuclear safety since Japan’s Fukushima accident in 2011.

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