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In depth
| 05/16/18

Quakes, fracking and geothermal: opportunities and challenges



This spring, a pair of papers appearing in the prestigious US academic journal Science concluded that in 2017 a pilot power plant in South Korea that employed enhanced geothermal systems (EGS) triggered the most damaging earthquake since the country started monitoring seismic events in 1905. The finding prompted discussions within the clean energy community about the potential impact on the development of this renewable resource.

Ernest Majer, one of North America’s foremost experts in the subject of seismicity and geothermal systems, spoke to The Climate Examiner about EGS, how it differs from conventional geothermal, what challenges the sector faces, and his views on the events in South Korea.

Majer began his career in the 1970s exploring seismic activity at California’s Geysers geothermal field, a complex of 22 geothermal plants and the largest single geothermal power producer in the world. He has worked at the Lawrence Berkeley National Laboratory on the issue for over 40 years.

How do conventional geothermal and enhanced geothermal systems differ?

Conventional geothermal, or “hydrothermal”, involves naturally occurring geothermal resources and dates back a long time. Yellowstone is an example of this. The Geysers are an example as well, and goes back to the twenties, although they are a sort of hybrid between hydrothermal and EGS.

EGS is a relatively new term, maybe 15-20 years old. Instead of going and looking for naturally occurring geothermal resouces, in essence we create them artificially by injecting water back into the ground.

How did EGS come about?

In the early-to mid-eighties at The Geysers, they started to inject the water back into the ground because the steam pressure had been dropping. There may be a tremendous amount of heat in these areas, but you can run out of water, and if you run out of water, you run out of steam pressure, and if you run out of steam pressure, you run out of turbine capacity, and then you run out of electricity. This was the forerunner of engineered geothermal systems, in which you deliberately put water back in the ground.

About 15 years ago, people began thinking that there’s a lot of hot rock everywhere if you drill deep enough. So, what if we enhanced the hot rock with water? And if the hot rock was dry and not permeable enough, we could enhance it with fracturing just like they have been doing in the oil industry for a long time. By fracturing the rock and making it more permeable, they can get more oil out of the ground.

So that’s where EGS came about. It has a much greater potential than conventional geothermal. This is because it’s hard to find natural geothermal as it sometimes doesn’t have much “surface expression” such as hot springs to indicate where it is located underground. There’s been a lot of effort put into finding these conventional spots, what they call “blind geothermal areas” or hidden geothermal areas.

Why are energy experts enthusiastic about EGS compared to conventional geothermal?

Because the potential is much higher than from going to look for blind areas. We know that if you drill deep enough, especially in the western United States, where the heat flow is much higher than in the rest of the US, you may not have to go as deep to get hot rock. So if you could fracture up the rock by pressurizing the rock and cause the natural fractures to fail and then propagate, and put in cold water and pump hot water out, then you can have geothermal energy in many more places than if you just depended on naturally occurring resources.

If you say okay, we can drill anywhere, say 6-8,000 feet and we can fracture it up with water pressure, then that could be almost anywhere in the US. And if you go even deeper then EGS could be sited almost anywhere in the world. And so the Europeans are looking at it very seriously, and the Koreans are of course, as is the US Department of Energy.

The promise is that maybe geothermal as a whole, with EGS being a large part of this, could deliver 10-15 percent of the electricity needs of the US and the same sort of scale is probably true for Canada as well, and perhaps a good deal more if you include energy for space heating.

How far are we technologically with the development of EGS?

It’s still very early days. The challenge is really how do you cost-effectively do this? And then how do you do it safely as well, as there is an increased seismicity issue?

The US Department of Energy program is looking at systems between 175C and 225C. The only reason we can’t go any higher than this is that if we get deeper or hotter, you begin to have trouble with instrumentation and measuring whatever you want to measure. At The Geysers, they do go up well over 250C, sometimes over 350C with some of their deeper wells. At this point you start to get a lot of fluid chemistry going on, causing a lot of corrosion. There’s a lot of energy there, but there are a lot of issues with keeping your turbines and pipes alive.

I think we know how to deal with that if you go about it properly, but there could be a financial cost associated with this.

What are the differences between hydraulic fracturing for EGS and the “fracking” that people may be aware of associated with natural gas extraction?

Conceptually, they’re pretty much the same. A resource is trapped in the ground, oil or hot water, and you want to get it out. And if there isn’t enough fracture permeability to get it out, then you have to create that. There are existing fractures everywhere, but usually there isn’t much permeability in very “tight systems,” tight gas sands, tight shales, oil shales or tight rocks in the geothermal case, usually older rocks, igneous rocks. So you want to go down with higher pressure fluids and reduce the stress holding the rocks together and make them slide and connect up with existing fractures.

In the case of EGS, you then drill another well, to connect to these fractures you’ve created, and then put cold water down one well and then pump it back as hot water out the other well.

There are a couple of major differences though. With EGS, you’re putting cold water in and getting hot water out. With gas, you’re putting frac fluid in. Also, a large frack will at most take a day or two. With geothermal, it will take days if not weeks to fracture enough rock because they do it gently and slowly.

Also, a gallon of oil is worth a lot more than a gallon of hot water, so they don’t need as much volume of fluid as you need in geothermal. You need a lot of hot water to make EGS economically viable. This means you need a lot more water pressure and hydraulic fracturing for geothermal than for oil and gas.

What do you think happened in South Korea?

There is certainly very compelling evidence in the two papers suggesting the injections induced the earthquake in the two papers, but there are also a few arguments against the conclusion that the sole cause of the events was the injections.

The first is that the magnitude 5.4 and 4.7 earthquakes, both on Nov. 15, 2017, came two months after the injections had stopped. There was also another earthquake of 4.7 magnitude at the EGS site five months after the injections had stopped on Feb. 10, 2018. This is normally a very low seismicity area of Korea. But there was also 4.9, 5.4, 4.6 and 3.5 magnitude earthquakes from Sept. 12-21, 2016, 30 kilometres to the southwest along the same fault zone. The last big seismic events in the region were in 1903, and since then until now, there has been nothing. So is the seismicity due to the larger parts of the fault being naturally reactivated? Was the EGS plant just really unlucky? Was it more of a “triggered” event—meaning partially natural, partially human-caused—versus induced only by injection.

If these injections alone did indeed lead to the unexpectedly large earthquakes, then we need to determine why they did. This would prompt such questions as: How much of the fault do you need to affect before it goes off, the majority of the fault or just a pinprick? What are the critical data needed to have a successful EGS project?

In both EGS and hydrofracturing, we are still asking: What is this induced seismicity telling us? Is this really where the fluid is going? Is this where the stresses are going? How far out do the stresses go? How far away from a fault can you be before you really make it go off?

So the two papers have prompted a lot of discussion already within the energy community and elsewhere because this doesn’t just impact geothermal energy. If it is the case that our understanding of natural seismicity is lacking, then this could impact the oil and gas industry, carbon sequestration, and other activities beyond clean energy.

In depth



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