Geothermal Energy and Earthquakes

Geothermal Energy is one of those sources that is, within normal scales, sustainable, and it is currently being drawn upon, so that relative costs and techniques don’t have to be invented for it to become a viable program. It can, however, be considered to be useful at two different levels, there is the small-scale facility, often referred to as ground source heat pumps and then there are the full-scale power plant types of operation.

We had considered putting a ground-source system into our own home, and I wrote about that, and other family reviews of the technology back in my Oil Drum days. Arising out of that discussion, and comments, it appears that the current cost of systems remain up around the $20,000 to $30,000 dollar mark, which is considerably too expensive for folks such as myself, relative to the energy and cost return that we would achieve from such an investment. However the comments on that article are informative and well worth a visit.
Ground source heat systems (Source)

It is the larger scale operations that I want to write about today. It is a system that is growing, but in the process is stirring more public controversy. Here much larger and longer pipes are drilled down into rock that is much hotter than normal, and the resulting steam/hot water is extracted back out of the ground and used both to generate electricity and for district heating. These are the systems, such as can be found at The Geysers in California, where Calpine runs 15 power plants that generate some 725 megawatts of electricity.

The Geysers meets the typical power needs of Sonoma, Lake, and Mendocino counties, as well a portion of the power needs of Marin and Napa counties. In fact, The Geysers satisfies nearly 60 percent of the average electricity demand in the North Coast region from the Golden Gate Bridge to the Oregon border. The Geysers is one of the most reliable energy sources in California delivering extremely high availability and on-line performance and accounts for one-fourth of the green power produced in California.

There are, however, different ways in which the heat can be extracted from the ground, depending on the nature of the rock which is being used as a reservoir. In the first, and simplest case the rock is already fractured and contains water, under pressure, that can be tapped by the wells that reach down into the rock. The water is refreshed, either from the surrounding volumes, or by reinjection of the spent fluids from the power plant, after the heat energy has been extracted.

How the Geysers get power

Such a system is, for example, being developed in Switzerland. But whenever fluids move and are injected, or removed from highly-pressurized systems then problems, such as earthquakes can result, and this is what generates the considerable public concern particularly when such earthquakes happen in areas that are already prone to earthquakes.

But this is part of the problem, in that the places where the hot rock comes closest to the surface lie along the boundaries of the plates that comprise the shell of the Earth. And these places already see earthquakes – whether in Japan, Iceland or Switzerland. So if one is going to drill into this rock, and then crack the rock between two wells, to provide a path for fluid to flow and gain heat, then you will affect the rock structure to the point that the change in stresses around the operation can trigger small earthquakes.
LASL plans for fracturing between wells to extract heat from geothermal wells

As the fractures grow to generate networks this weakens the rock, and the fluid lubricates the planes along which the rock can slip, so that rock which was already approaching the stress levels at which the rock would move and generate an earthquake now can, and so it does.
Concept for geothermal heating in Switzerland where they plan on using natural rock fractures

Now in almost all cases the stresses would have continued to build until an earthquake finally occurred. And at that point the energy released by the quake would be greater than that released by the geothermal operation (since the stress levels would be higher at that time, and the failure would be more violent). But it is hard to get that concept over to the public.

Basically they see that the geothermal well was drilled, and an earthquake resulted. That it ameliorated a worsening potential earthquake is something that is not easily recognized, especially since the smaller quake can still cause damage (as it has done).

The problem, and the public relations aspect is a significant part of this, is something that needs to be addressed forthwith, since at the moment the Department of Energy is gearing up for a significant investment in geothermal power including new Enhanced Geothermal Systems (EGS).

Before EGS could be implemented, scientists would need to calm concerns about insufficient technology and the possibility of earthquakes at EGS sites. The allotted $30 million would also have to increase in later years to reach the $1 billion the panel report calls for overall. Still, many scientists view the project as our best baseline energy option.

“We’re no longer limited by just discovering the Icelands of the world,” says Jefferson Tester, a professor of chemical engineering at MIT who chaired the EGS panel. The report estimates that by 2050, EGS could be implemented to a capacity of 100,000 new megawatts of power – more electricity capacity than all of the nuclear power plants in the United States combined.

At present the problem that relates earthquakes and geothermal energy extraction is known, and recognized

a major quake requires a several-kilometer-long fault, argues Ernest Majer, a seismologist at the Lawrence Berkeley National Laboratory. Engineers know not to put EGS sites near large or dangerous faults, and the small cracks created by the system itself are not dangerous. “We can’t make faults as big as Mother Nature does … and there has never been a damaging geothermal earthquake anywhere in the world,” he adds.

At Geysers in California, there are about 3,000 earthquakes per month, according to Majer. The largest, however, reached only 4.6 magnitude – big enough to be noticeable, but not dangerous.

Majer is enthusiastic about how education and community involvement can help to allay earthquake fears. The quakes at EGS plants can be controlled and monitored for safety, and better research will help scientists and engineers understand how to make EGS plants even safer, he says.

Explaining the issues to the public may, however, be another story.
(For the record I am working with Dr Majer on a program that could be funded under the EGS program).