Skip to comments.Abundant Power from Universal Geothermal Energy
Posted on 08/01/2006 11:15:01 AM PDT by aculeus
An MIT chemical engineer explains why new technologies could finally make "heat mining" practical nearly anywhere on earth.
A section of the geothermal plants north of San Francisco, known as The Geysers. These plants rely on relatively rare geologic formations. MIT professor Jefferson Tester believes geothermal can be much more widespread, by making artificial reservoirs for harvesting the earths heat. (Source: National Renewable Energy Laboratory)
The answer to the world's energy needs may have been under our feet all this time, according to Jefferson Tester, professor of chemical engineering at the MIT Laboratory for Energy and the Environment. Tester says heat generated deep within the earth by the decay of naturally occurring isotopes has the potential to supply a tremendous amount of power -- thousands of times more than we now consume each year.
So far, we've been able to harvest only a tiny fraction of geothermal energy resources, taking advantage of places where local geology brings hot water and steam near the surface, such as in Iceland or California, where such phenomena have long been used to produce electricity. But new oil-field stimulation technology, developed for extracting oil from sources such as shale, makes it possible to harvest much more of this energy by allowing engineers to create artificial geothermal reservoirs many kilometers underground.
Tester calls it "universal geothermal" energy because the reservoirs could be located wherever they're needed, such as near power-hungry cities worldwide.
Technology Review spoke with Tester about the potential of universal geothermal energy and what it will take to make it a reality.
Technology Review: How much geothermal energy could be harvested?
Jefferson Tester: The figure for the whole world is on the order of 100 million exojoules or quads [a quad is one quadrillion BTUs]. This is the part that would be useable. We now use worldwide just over 400 exojoules per year. So you do the math, and you know you've got a very big source of energy.
How much of that massive resource base could we usefully extract? Imagine that only a fraction of a percent comes out. It's still big. A tenth of a percent is 100,000 quads. You have access to a tremendous amount of stored energy. And assessment studies have shown that this is thousands of times in excess of the amount of energy we consume per-year in the country. The trick is to get it out of the ground economically and efficiently and to do it in an environmentally sustainable manner. That's what a lot of the field efforts have focused on.
TR: We do use some geothermal today, don't we?
JT: In some cases nature has provided a means for extracting stored thermal energy. We have many good examples. The Geysers field in California is the largest geothermal field in the world -- it's been in production for over 40 years and produces high-quality steam that can readily be converted into electric power, and it's one of the rarities nature-wise in terms of what we have worldwide. In the mineral vernacular they would be regarded as sort of high-grade gold mines.
TR: But haven't people been talking about greater use of geothermal energy for years now? What's changed?
JT: Like many energy technologies, it had a lot of support structure back in the 70s and in the 80s, but our national priorities shifted from energy to other things, and we didn't necessarily invest enough in it at that time to bring it to fruition.
Many [energy] technologies, whether they're renewables or nuclear power or coal or whatever it might be, need to be continually revisited and placed in context with the current state of technology. In this case, our interest in trying to go after hydrocarbons and extract hydrocarbons has developed a lot of technology in subsurface engineering that's useful and makes geothermal worth revisiting.
TR: How do you plan to harvest stored heat from more areas?
JT: What we're trying to do is emulate what nature has provided in these high-grade systems. When we go very deep, [rocks] are crystalline. They're very impermeable. They aren't heat exchangers like we really need. We'd like to create porosity and permeability. [The rock] actually is filled with small fractures, so what you're trying to do is find those weak zones and reopen them. We need to engineer good connectivity between an injection set of wells and a production set of wells, and sweep fluid, in this case, water, over that rock surface so that we extract the thermal energy and bring it up another well.
TR: What technology do you need to open up the rock and harvest the heat?
JT: All the technology that goes into drilling and completing oil and gas production systems, [such as] stimulation of wells, hydraulic fracturing, deep-well completion, and multiple horizontal laterals, could in principle be extended to deep heat mining. Hydraulic methods have been the ones that hold the most promise, where you go into the system and you pressurize the rock -- just water pressure. If you go higher than the confinement stress, you will reopen the small fractures. We're just talking about using a few thousand pounds per square inch pressure -- it's surprising how easy this is to do. This is a technique that's used almost every single day to stimulate oil and gas reservoirs.
TR: What still needs to be done to make artificial reservoirs for geothermal possible?
JT: Like any new technology, there are technical issues. But I don't see any show-stoppers. I think that the evolution of the technology, with 30-plus years of field testing, has been very positive. The basic concept has been demonstrated. We know how to make large reservoirs. We need to connect them better, to stimulate them better than we have in the past using some of these hydraulic methods and diagnostics that are now available to us.
So it's the scale-up to a commercial-sized system that has to be done, making a heat mine that is large enough and productive enough to sustain the economic investment. But we believe that's possible to do based on where we are now with the technology.
TR: You're working on new drilling technology. How does this fit in?
JT: We feel that as part of a long-term view of the possibility of universal heat mining, we should also be thinking about revolutionary methods for cutting through rock and completing wells. Most of the drilling that's done today is made by crushing and grinding our way using very, very hard materials to crush through and grind through minerals in the rock. And it's been very successful. It's evolved tremendously over the past century, and we can do it, certainly, routinely, to 10 kilometers. But it costs a lot. So we're looking for a fundamental way to change the technology that would change the cost-depth relationship, and allow us to drill deeper in a much more cost-effective manner. It would open up the accessibility tremendously.
TR: What are the advantages compared with other renewable sources of energy?
JT: Geothermal has a couple of distinct differences. One, it is very scalable in baseload. Our coal-fired plants produce electricity 24 hours a day, 365 days a year. The nuclear power plants are the same way. Geothermal can meet that, without any need for auxiliary storage or a backup system. Solar would require some sort of storage if you wanted to run it when the sun's not out. And wind can't provide it without any backup at 100 percent reliability, because the typical availability factor of a wind system is about 30 percent or so, whereas the typical availability factor of a geothermal system is about 90 percent or better.
TR: What are some environmental concerns with "heat mining?"
JT: Obviously in any system where you're going underground, you need to think about are you disturbing the natural conditions in the earth that might cause bad things to happen. We have a pretty good history of knowing the effects of extraction. Nevertheless, it has to be monitored carefully and managed carefully.
In some natural systems you have to deal with the emissions -- control of hydrogen sulfide and other gases. Environmental regulations insist on full re-injection of the fluid.
This is not a free lunch, but there's virtually no carbon dioxide, so you're producing baseload electric power without generating any carbon dioxide.
TR: How fast do you think artificial geothermal systems can be developed?
JT: With sufficient financing and a well-characterized field, you can go into existing areas right now and build a plant, getting it operational within a few years. But to get universal heat mining is going to take an investment which won't be quite that quick. It might take 10 or 15 years of investment to get to the point where you have confidence that you can do this in virtually any site that you can go to. Once it gets in place, though, it can be replicated. I think it's very reproducible and expandable. That's the great hope at least.
Copyright Technology Review 2006.
I have never understood how Geothermal energy works. Theoretically, a very hot earth core would radiate heat outward until temperature throughout the crust equalized. What produces the heat? If you drain the core of heat, how is it replenished?
here's and Aussie firm working on this:
Very interesting stuff - thanks for the post
Abundant, yes. However, it's going to be very expensive to create such reservoirs in areas where near-surface geothermal sources are not available.
Many,if not most,of the buildings in the town are heated by geothermal steam (it's located in an active geothermal area).
The downside is that when you're walking down the street you can get a powerful,and unpleasant,smell of sulfur in the air.
The earth is still giving off more heat than it gets from the sun. The core won't be cooled off much by thermal mining. It should be good at least as long as the sun itself, that is, another 500 million years.
The oil industry does this already with water injection and conventional explosives - no need for nukes...
Geothermal Energy is not inexpensive due to the corrosiveness and abrasiveness of the fluid and it's effect on the equipment needed to convert this source to energy. The Geothermal Brine pumps for example are made primarily by only one company in the USA (Johnston Pumps), as such the costs are not onbly high due to materials, but unusually high due to higher then normal margins. Others have tried, but with limited success (Flowserve, Goulds, Floway).
Geothermal sounds like a good idea, but it is far more difficult then this article implies.
That's the problem. Whatever is done will take building of infrastructure and even if the energy is free the infrastructure is not. Same problem as solar cells and wind power.
I am not a geologist, so take this with a grain of salt.
Yes, the earth is cooling down, However, the process is cosmically slow, and delayed by mitigating factors such as the decay of radiactive elements in the crust and tidal convection from the Moon's gravitational field. If we had a smaller planet (that cools faster) without a significant moon, our planet would be a cold, lifeless rock (like Mars).
I'm in the renewable energy business. I think I'll start a Renewable Energy Ping list.
Who wants on?
It doesn't seem like you would need a natural geothermal source like a geyser (think Iceland or Yellowstone)...
Heck, you can get a geothermal heat pump in the middle of Ohio that is enormously efficient. While you get about 93% efficiency out of a gas furnace, you can get 300+% efficiency out of a geothermal heat pump - all that is doing is extracting heat energy from the earth. That's not that unlike what this is proposing. Just think of an open loop system rather than closed loop, and on a MUCH bigger scale...
We put in a geothermal system (four 200 foot wells under our driveway) when we built our new house five years ago. The AC is essentially free.
BTW, President Bush installed a geothermal heat pump at his new ranch house in Crawford; however, the pipes are only 300 feet deep, not anywhere near the depth proposed here, and use naturally occurring constant temperature groundwater for heat exchange.
Radioactive decay. This has been understood for nearly a hundred years.
The average geothermal gradient of the earth is 25°C/km in depth. This means that anywhere that you drill on earth over 4000 meters depth the temperature is above the boiling point of water. You drill to the proper depth, pump water down and collect the steam and recover energy from the heat.