Bureau of Economic Geology


Geothermal

The Bureau of Economic Geology has a long history of working on geothermal energy research, from initial reconnaissance of conventional geothermal resources and analysis of development potential in Texas in the 1970’s to present-day work on applying the new paradigm of deep closed-loop systems. These new engineering approaches (fig. 1), some of which are being developed in the UT Cockrell School of Engineering, in combination with conventional hydrothermal systems hold the promise of making geothermal energy available anywhere, which could dramatically change the global energy status quo.

 

Geothermal

Figure 1. The deep, closed-loop geothermal energy generation concept. Unlike conventional geothermal energy generation, which must be located where nature concentrates heat (i.e., shallow magma bodies), the new paradigm will enable drilling almost anywhere to reach deep enough to get to sufficiently high temperatures.

 

The Bureau is on the forefront of the resurgence of geothermal-resources innovation, exploration, and assessment. We are part of a major Department of Energy project to spur innovation in geothermal technology and are applying new analytic approaches, including big data and machine learning, to significantly improve our knowledge of the resource in Texas, the United States, and beyond.

Vast amounts of geothermal energy are stored in the crust of the Earth, renewed constantly by the heat flowing from the 6,000°C (~11,000°F) core. Traditionally, this heat was only able to be exploited where nature concentrates the resource—shallow magma bodies or deep fluid circulation in the crust. These conventional geothermal resources are generally located in the western United States. But new engineering can access heat anywhere in the crust. Current technology can generate economically viable electricity off temperatures of around 120°C (~250°F), with emerging work pushing that temperature limit below 100°C (~210°F). Figure 2 shows that this temperature is present across all of Texas at 6.5 km (~21,000 ft) depth (well within current oil and gas drilling depths). In some areas, this temperature is only a few kilometers below the surface.

 

Geothermal

Figure 2. Temperature at 6.5 km (~21,000 feet) below the surface of the conterminous United States. This illustrates the immense amount of untapped energy that continually flows out of the Earth. Current technology allows for viable electricity generation from temperatures as low as 120°C (~250°F), but the much greater energy density at higher temperatures and depth holds even more promise and motivation for advancing the field of geothermal generation.

 

Geothermal power plants require at least moderately greater up-front investment (in the drilling of wells) than a fossil fuel plant. However, over the long term, these issues are offset by the significant advantages of geothermal power:

  • Baseload energy supply—Unlike solar and wind, geothermal power is always available and can be load-following.
  • Self-contained and renewable—No consumables (fossil fuel) needed, indefinite lifetime, minimal maintenance.
  • Scalable—If more power is needed, another well can be drilled locally.
  • Distributed—Geothermal plants, generally in the 10–100 MW range, can be built near where the power is needed.
  • Safe—No combustion or radioactivity involved.
  • Green—No pollution/greenhouse gas emissions, and even the potential to be slightly carbon negative.

Many variations exist on the main idea of geothermal energy. Using the Earth as a battery could allow for wind and solar to become baseload power without the heavy environmental cost of batteries. Geothermal is already widely used for building heating and cooling, and the final stage of any geothermal power plant will likely use “waste” heat for this purpose.

Looking beyond Earth, as humanity expands into the solar system, we will need safe, practical power systems. As you move out from the sun, solar power becomes less practical, and fission has significant drawbacks—geothermal power has the potential to become the best power source on some worlds. In particular, multiple moons of Jupiter and Saturn have active geyser systems, indicating geothermal activity on a planetary scale (fig. 3). Bureau researchers are beginning to assess this potential.

 

Geothermal

Figure 3. Multiple icy moons in the outer solar system appear to have vast subsurface oceans, as indicated by surface features including geysers hundreds of kilometers high. Settings such as these may be suitable for developing geothermal power. Illustration courtesy of NASA.

 

References

Blackwell, D. D., Richards, M., Frone, Z., Batir, J., Dingwall, R., Ruzo, A., and Williams, M., 2011, 2011 geothermal heat flow map of the U.S.: Southern Methodist University Geothermal Lab, Dallas, Tex. in Chokshi, P., “A new geothermal map of the United States”: The official google.org blog, http://blog.google.org/2011/10/a-new-geothermal-map-of-united-states_25.html (accessed July 2, 2021).


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