MIT-Led Study: Geothermal Could Supply Substantial Portion of Future US Power Need

22 January 2007
 Schematic of a conceptual two-well Enhanced Geothermal System in hot rock in a low-permeability crystalline basement formation. Click to enlarge.

A comprehensive new MIT-led study of the potential for geothermal energy within the United States has found that Enhanced Geothermal System (EGS) technology could supply a substantial portion of US electricity well into the future, probably at competitive prices and with minimal environmental impact.

Overall, the panel concluded that EGS can likely deliver cumulative capacity of more than 100,000 MWe within 50 years with a modest, multiyear federal investment for RD&D. The panel estimated the total EGS resource base to be more than 13 million exajoules (EJ), with an estimated extractable portion to exceed 200,000 EJ—about 2,000 times the annual consumption of primary energy in the United States in 2005.

An 18-member panel led by MIT prepared the 400-plus page study, titled The Future of Geothermal Energy. Sponsored by the US Department of Energy, it is the first study in some 30 years to take a new look at geothermal.

The goal of the study was to assess the feasibility, potential environmental impacts and economic viability of using EGS technology to greatly increase the fraction of the US geothermal resource that could be recovered commercially.

The Department of Energy defines Enhanced (or engineered) Geothermal Systems (EGS) as engineered reservoirs that have been created to extract economical amounts of heat from low permeability and/or porosity geothermal resources. EGS recovers thermal energy contained in subsurface rocks by creating or accessing a system of open, connected fractures through which water can be circulated down injection wells, heated by contact with the rocks, and returned to the surface in production wells to form a closed loop.

In its assessment, the panel adapted that definition to include all geothermal resources that are currently not in commercial production and require stimulation or enhancement. In addition, it added coproduced hot water from oil and gas production as an unconventional EGS resource type that could be developed in the short term and possibly provide a first step to more classical EGS exploitation.

The study viewed the quality of a geothermal resource as a continuum in several dimensions: temperature-depth relationship (i.e., geothermal gradient), the reservoir rock’s permeability and porosity, and the amount of fluid saturation.

High-grade hydrothermal resources have high average thermal gradients, high rock permeability and porosity, sufficient fluids in place, and an adequate reservoir recharge of fluids.

All EGS resources lack at least one of these, according to the study. For example, reservoir rock may be hot enough but not produce sufficient fluid for viable heat extraction, either because of low formation permeability/connectivity and insufficient reservoir volume, and/or the absence of naturally contained fluids.

The analysis considered three main components:

1. Resource: estimating the magnitude and distribution of the US EGS resource.

2. Technology: establishing requirements for extracting and utilizing energy from EGS reservoirs including drilling, reservoir design and stimulation, and thermal energy conversion to electricity.

3. Economics: estimating costs for EGS-supplied electricity on a national scale using newly developed methods for mining heat from the earth. Developing levelized energy costs and supply curves as a function of invested R&D and deployment levels in evolving US energy markets.

Specific findings of the report include:

1. EGS is one of the few renewable energy resources that can provide continuous base-load power with minimal visual and other environmental impacts. Geothermal systems have a small footprint and virtually no emissions, including carbon dioxide. Geothermal energy has significant base-load potential, requires no storage, and, thus, it complements other renewables—solar (CSP and PV), wind, hydropower—in a lower-carbon energy future. In the shorter term, EGS would provide a buffer against the instabilities of gas price fluctuations and supply disruptions, as well as nuclear plant retirements.

2. The accessible geothermal resource, based on existing extractive technology, is large and contained in a continuum of grades ranging from today’s hydrothermal, convective systems through high- and mid-grade EGS resources (located primarily in the western United States) to the very large, conduction-dominated contributions in the deep basement and sedimentary rock formations throughout the country. The panel estimated the total EGS resource base to be more than 13 million exajoules (EJ), with an estimated extractable portion to exceed 200,000 EJ—about 2,000 times the annual consumption of primary energy in the United States in 2005.

With technology improvements, the economically extractable amount of useful energy could increase by a factor of 10 or more, thus making EGS sustainable for centuries.

3. Ongoing work on both hydrothermal and EGS resource development complement each other. Improvements to drilling and power conversion technologies, as well as better understanding of fractured rock structure and flow properties, benefit all geothermal energy development scenarios.

4. EGS technology has advanced since its infancy in the 1970s. Field studies conducted worldwide for more than 30 years have shown that EGS is technically feasible in terms of producing net thermal energy by circulating water through stimulated regions of rock at depths ranging from 3 to 5 km. Current technology can now stimulate large rock volumes (more than 2 km3), drill into these stimulated regions to establish connected reservoirs, generate connectivity in a controlled way if needed, circulate fluid without large pressure losses at near commercial rates, and generate power using the thermal energy produced at the surface from the created EGS system.

Initial concerns regarding five key issues—flow short circuiting, a need for high injection pressures, water losses, geochemical impacts, and induced seismicity—appear to be either fully resolved or manageable with proper monitoring and operational changes.

5. At this point, the main constraint is creating sufficient connectivity within the injection and production well system in the stimulated region of the EGS reservoir to allow for high per-well production rates without reducing reservoir life by rapid cooling. US field demonstrations have been constrained by many external issues, which have limited further stimulation and development efforts and circulation testing times—and, as a result, risks and uncertainties have not been reduced to a point where private investments would completely support the commercial deployment of EGS in the United States.

6. Research, Development, and Demonstration (RD&D) in certain critical areas could greatly enhance the overall competitiveness of geothermal in two ways. First, it would lead to generally lower development costs for all grade systems. Second, it could substantially lower power plant, drilling, and stimulation costs, which increases accessibility to lower-grade EGS areas at depths of 6 km or more.

In a manner similar to the technologies developed for oil and gas and mineral extraction, the investments made in research to develop extractive technology for EGS would follow a natural learning curve that lowers development costs and increases reserves along a continuum of geothermal resource grades.

The report presents the examples of impacts that would result from research-driven improvements in three areas:

• Drilling technology: both evolutionary improvements building on conventional approaches to drilling such as more robust drill bits, innovative casing methods, better cementing techniques for high temperatures, improved sensors, and electronics capable of operating at higher temperature in downhole tools; and revolutionary improvements utilizing new methods of rock penetration to lower production costs. These improvements will enable access to deeper, hotter regions in highgrade formations or to economically acceptable temperatures in lower-grade formations.
• Power conversion technology: improving heat-transfer performance for lower-temperature fluids, and developing plant designs for higher resource temperatures to the supercritical water region would lead to an order of magnitude (or more) gain in both reservoir performance and heat-to-power conversion efficiency.
• Reservoir technology: increasing production flow rates by targeting specific zones for stimulation and improving downhole lift systems for higher temperatures, and increasing swept areas and volumes to improve heat-removal efficiencies in fractured rock systems, will lead to immediate cost reductions by increasing output per well and extending reservoir lifetimes.

For the longer term, using CO2 as a reservoir heat-transfer fluid for EGS could lead to improved reservoir performance as a result of its low viscosity and high density at supercritical conditions. In addition, using CO2 in EGS may provide an alternative means to sequester large amounts of carbon in stable formations.

7. EGS systems are versatile, inherently modular, and scalable from 1 to 50 MWe for distributed applications to large power parks, which could provide thousands of MWe of base-load capacity.

8. Using coproduced hot water, available in large quantities at temperatures up to 100°C or more from existing oil and gas operations, it is possible to generate up to 11,000 MWe of new generating capacity with standard binary-cycle technology, and increase hydrocarbon production by partially offsetting parasitic losses consumed during production.
9. A cumulative capacity of more than 100,000 MWe from EGS can be achieved in the United States within 50 years with a modest, multiyear federal investment for RD&D in several field projects in the United States.

We’ve determined that heat mining can be economical in the short term, based on a global analysis of existing geothermal systems, an assessment of the total US resource and continuing improvements in deep-drilling and reservoir stimulation technology.

EGS technology has already been proven to work in the few areas where underground heat has been successfully extracted. And further technological improvements can be expected.

—Jefferson W. Tester, the H. P. Meissner Professor of Chemical Engineering at MIT, panel-leader

In its report, the panel recommends that:

• More detailed and site-specific assessments of the US geothermal energy resource should be conducted.

• Field trials running three to five years at several sites should be done to demonstrate commercial-scale engineered geothermal systems.

• The shallow, extra-hot, high-grade deposits in the west should be explored and tested first.

• Other geothermal resources such as co-produced hot water associated with oil and gas production and geopressured resources should also be pursued as short-term options.

• On a longer time scale, deeper, lower-grade geothermal deposits should be explored and tested.

• Local and national policies should be enacted that encourage geothermal development.

• A multiyear research program exploring subsurface science and geothermal drilling and energy conversion should be started, backed by constant analysis of results.

Resources:

_This may well be a partial medium term solution. Unless we face a dire need for energy, in which other sources cannot feasibly replace, we should keep this as an Ace up our sleeves.
_As rock cools/heats up, it shrinks/expands, and may crack if cooled/heated too fast/unevenly. Long-term concerns include sinking land, new cracks in (overlaying) rock formations, water table disturbance and contamination.
_Perhaps we could use very large footprint (shallow-medium depth) geothermal as a large-scale solar energy storage reservoir. During the summer, the system pumps the heat down, to cool indoor living/working spaces. During cooler months, the stored heat is available to draw upon. Of course, to eliminate the risk of damagingly uneven, and abrupt heating, and cooling of rock formations, precise management is required.

Sounds like a natural for big oil companies. (They have the drilling technologies and imaging tech required)

I think there was an article in the news in regards the Swiss test plant has resulted in two significant earthquakes. If the problems there are not resolved, I'm not sure if the idea will fly with commercial interests.

http://uk.news.yahoo.com/16012007/323/swiss-geothermal-drilling-upsets-neighbours.html

I guess this means the US should be more than a little careful if trying this out around old faithful. (I understand that area has the potential to be a super volcano).

90 percent of icelands power is generated by using geothermal.

Iceland also has a population that is about three orders of magnitude smaller than ours, and they sit atop an area that is very geologically active.

I do not know if this resource is properly termed renewable. Reading between the lines, it appears as if this technology would be capable of drawing heat out of the earth's crust faster than it is produced by the decay of natural isotopes embedded in the rocks. In this way it is simlar to petroleum. Both nuclear decay and the transformation of buried organic matter slowly recharge these resources, but at rates that are too insignificant to matter.

All the same, exploiting this resource would seem to have virtually no CO2 footprint, which makes it attractive. The whole earthquake business needs looking into, though.

I wouldn't discourage this research, since breaking fossil fuel's monopoly is so difficult it needs to be attacked from many directions at once. But we shouldn't let this take away from more promising sources. It should be understood that the total energy flux to the earth's surface coming from the sky is on the order of 5,000 times what it is coming from below. Other than that, we are talking about non-renewable energy with geothermal, and that means many of the same kinds of depletion (and other) problems we are familiar with from petroleum.

Also, I would be concerned about disturbing earthquake patterns and thus blowing our ability to eventually predict earthquakes. I would also be concerned about disturbing aquifers and causing bad things to leach into groundwater that had been stable for eons.

The technology will have several spinoffs. I fear the unspoken most motivating of these will be for oil barrel-scraping which could only hinder the rise of renewables.

I think this study refers to granite type rocks not leaky volcanic rocks as in Iceland and elsewhere. The incident near Basel, Switzerland suggests the plants have to be well away from population centres. Moreover if the hot zone is overcooled new boreholes will have to be drilled some distance away. The rock may not be suitable for this and longer surface pipes to the turbines will lose heat. Maybe MIT's optimistic estimate is right but for practical purposes very few locations will prove suitable.

No good technological solutions will be allowed until all the bad technologies are used up; because you can’t have benign geothermal energy (with potentially centuries of power production) undercutting Bush/Cheny’s breeder reactor nuclear plans. They won't allow it. Too much money to be made...

Has anybody compared the global risk factor of geothermal versus getting energy from messy Alberta Tar sands?

Personnally, I agree with MIT, USA should rely more or such clean energy sources and stop/reduce OIL imports.

To date, geothermal power has been cost-effective in just a few locations, e.g. Iceland and New Zealand. Both of these are located in highly active volcanic zones.

Except for a very few locations, geothermal wells tend to yield low-exergy heat at just 90-120 degC. Unless you're prepared to use a heat pump powered by fossil fuels to concentrate the exergy, that means you need to resort to fairly exotic and expensive technology such as the Kalina process. If you happen to have a ready source of fresh water, it becomes much easier aka cheaper to reject the waste heat from such a process.

The Western US has a lot of volcanic zones out West but few of them have plentiful available water - a direct consequence of overly generous water rights allocations. Also note that geothermal wells can have long useful lives but are not strictly speaking considered renewable sources.

On the other hand, the $300+ billion poured into Iraq so far, plus the many more that will need to be spent just to get the US armed forces to replace their lost equipment and ordinance, could easily have paid for a significant expansion of geothermal power plus a large fleet of PHEV vehicles to take advantage of it. The best thing is that the report used SI units. I'm not sure that water availability is a particular problem for the implementation listed here which seems to recycle the water in a closed loop. Neil - water is needed for the initial drilling and stimulation (hydraulic rock fracturing) of the site. Certain power station designs operating at elevated temperature levels rely on periodic flashing of superheated steam, which involves emissions of low-grade waste steam. On the other hand, the$300+ billion poured into Iraq so far...

You know, for once I'd like to enjoy a purely technical discussion on the merits without politics coming into it. Please?

Raser Technologies, known to GCC readers for their innovative Symetron motor-generators, currently aqquired couple of geothermal properties and planning to build geothermal power stations. Raser has rights to employ Kalina cycle technology, which is best suited to generate electricity from low-temperature heat sources.

The deeper you drill, the hotter it gets. I think we presently have the technology to get down where there is plenty of heat. Oil and gas companies sometimes drill to the 30,000 foot level. We might even think of redrilling some of our old oil wells for this purpose to cut down costs. You need two deep wells with cracked rock in between. It seems practical. Send down water on one well, bring up steam under pressure with the other well.

I think this technology has a lot of potential. The article just released probably has a lot of information, but there is already a lot out there if you Google "hot dry rock geothermal". I spent some time looking at this a couple of months ago and there was no lack of information.

The earthquake issue will have to be dealt with either by more study or by concentrating on areas with low potential for earthquakes (lower than Basel). The other issue is the limited life of each area IIRC reservoirs are expected to last about 40 years, then take 100-150 years to get hot enough to be useful again. However, they cover a fairly small area, so wells could be capped and plants moved a short distance to start again.

The process does require some water, but as it is a closed loop when operating the requirements are quite low once the reservoir is developed and the system running. I don't think anyone has a full-scale plant up an running yet, but once numbers come in from the plant in Australia there will probably be a lot of interest.

I don't understand the extreme pessimism about this source of energy. This is about as good as it gets. Even hypothesizing a short 25 year useful life for a given site the ROI (figuring in maintenance and disposal of equipment) has to dwarf that of solar or wind - and the plants would be much more unobtrusive than wind turbines. Oh, and the two words that put this in a whole different league: Base Load.

"Personnally, I agree with MIT, USA should rely more or such clean energy sources and stop/reduce OIL imports."
I doubt that making electricity from geothermal (or anything) will have the slightest effect on oil imports.
All of the oil we import is used for transportation and to heat homes, neither of which will bein the least bit affected in any way shape or form by the method we decide to use to create electricity. This comment was almost as bad as that by our lowly regarded Sen Max Baucus, who said during a windfarm installation that it was good that the wind would replace oil. And this guy's up there in D.C. voting on laws for our country! I suppose he figures energy is energy, what's the difference. Yeah, right.

More government handouts. We already are spending
money without a whole lot of thinking. Wind is getting massive subsidies and it, quite frankly, sucks as an energy source. Geoexchange heat pump subsidies would be
both a lot more effective in helping our energy situation and would reduce utility bills as well. Geothermal is very attractive when compared to wind (as is EVERY alternative energy source) - it is controllable, very dense (windfarms extend over hundreds of acres), NOT outlandishly visible, unlike those turbines that have had virtually no effect on our energy situation (case in point - last year saw the largest number of new wind turbines - 2700 megawatt nameplate capacity, but only able to produce around 800 megawatts, while 16,000 megawatts of new natural gas powerplants were built). As I said before, wind sucks. As of
today, wind power accounts for less than 1/4 of one percent of power generated. Should a cheap power storage device be invented, wind would benefit, but it would remain an expensive and ineffective method of producing electricity.

Kent: Electricity production can have an effect on oil demand. Since I got my BEV I've used half the gas I used to.

Given how much money big oil gets in subsidies why not spend a little on renewables.

Wind generators just need to get off the ground and into the jet stream.

Atlantic Geothermal has posted a survey of blog headlines from the first week following the publication of the MIT-led study, "Future of Geothermal Energy."

An 18-member panel led by MIT prepared 400-plus pages of pure FICTION! What a load of PR rubbish.

There is only one commercial 2.5MW partial EGS plant in operation and MIT already declares "the technology could supply a substantial portion of US electricity well into the future, probably at competitive prices and with minimal environmental impact" Do earth quakes qualify as "environmental impact"??

There isn’t a SINGLE commercial full EGS plant on the planet. This report is like announcing commercial space flights will soon be a reality when they haven't figured out how to get into space yet and first space mission hasn't even happened. From what I've read in most cases the technology is still at the early R&D phase so 'engineered' geothermal, as a commercial replacement for fossil fuels, is just 400 pages of wishful thinking masquerading as an MIT 'report'

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