Bureau of Economic Geology


Geothermal

The Bureau has a long history of work on geothermal energy and resources, from initial reconnaissance of conventional geothermal resources and development potential of Texas in the 1970s to present day work on applying the new paradigm of deep closed loop system. These new engineering approaches (Figure 1.), some of which are being developed in the UT Cockrell School of Engineering, combined with conventional hydrothermal systems, hold the promise of “geothermal anywhere” which could change the world energy picture.

 

Geothermal

Figure 1. The deep, closed-loop geothermal concept. Unlike “conventional” geothermal which goes to where nature concentrates heat (i.e. shallow magma bodies), the new paradigm will enable drilling almost anywhere, deep enough to get to 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 US and beyond.

Vast amounts of geothermal energy are stored in the crust of the Earth, renewed constantly by the heat flowing from the 6000°C 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” resources are generally located in the western US. But new engineering can access heat anywhere in the crust. Current technology can generate economically viable electricity off temperatures of around 150°C. In the figure below, you see that this temperature is present across large areas of Texas by 6.5km depth (well within current oil and gas drilling depths). In some areas this temperature is only a few kilometers down.

 

Geothermal

Figure 2. Temperature at 6.5 km (~21,000 feet) below the lower forty-eight states in the US. This illustrates the immense amount of untapped energy that continually flows out of the Earth. Note: current technology allows for viable electricity generation from temperatures as low as 150°C (300°F), but the much greater energy density at higher temperatures and depth hold even more promise and motivation for advancing the field.

 

Geothermal power plants require moderate or greater up-front investment in the drilling of wells, that is not required for 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 on” and dialable up to maximum capacity.
  • Self-contained and renewable: no consumables (fossil fuel) needed, indefinite lifetime, minimal maintenance.
  • Scalable: Need more power, drill another well.
  • Distributed: Geothermal plants, generally in the 10-100MW range, can be built near where the power is needed and will be more “organic” to civilization.
  • Safe: no combustion or radioactivity involved.
  • Green: no pollution/greenhouse gas emissions and even the potential to be slightly carbon-negative.

There are many variations 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 – geothermal power has the potential on some worlds to become the best power source. In particular, multiple moons of Jupiter and Saturn have active geyser systems – indicating geothermal activity on a planetary scale (Figure 3). Bureau researchers are beginning to assess this potential.

 

Geothermal

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


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