STEM 2020

What is geothermal energy? - Geothermal energy is heat (thermal) that comes from within the earth (which is what “geo” stands for). Water and steam warmed by the earth’s heat are produced from wells and used to generate electricity. In mild climates, you can heat and cool residential or commercial buildings with a ground sourced heat pump that is connected to water-filled pipes buried in the shallow subsurface.

How does geothermal heat get from the interior of the earth to the surface? - Heat is continuously generated deep in the earth’s interior, and it moves outward to the earth’s surface. Heat moves by diffusion or conduction through solid materials, but where there is magma or hot water, heat moves by convection. Convection gives rise to the very high heat flow found in the vicinity of active volcanoes and hot springs.

Where is geothermal energy found? - Since geothermal energy is heat from the earth, it can be found virtually anywhere. Rocks hot enough to be used to generate electricity are commonly found at tectonic plate boundaries where faults and volcanoes are common, like the “Ring of Fire” that borders the Pacific Ocean, or where continental crust is being broken and pulled apart like the African Rift Valley or the Basin and Range of the western US, or at “hot spots” in places like Yellowstone National Park and Hawaii. Geothermal energy can even be found in your back yard, and used to heat and cool your house!

The figure to the right shows a slice through the interior of the Earth.

This presentation provides rich and valuable information about Geothermal Energy production and uses. Access the file here.

What are Enhanced Geothermal Systems?

Most conventional geothermal power plants rely on hot rock, and a conductive channel in the crust (fracture or fault) that allows hot water to circulate through the rock. In conventional geothermal systems one or more wells are drilled to intersect these conductive channels and heated water/steam is brought to the surface to spin a turbine and generate electricity. This works effectively in parts of the country where temperature increases relatively rapidly with depth. Suppose that we can drill deeper to find hot rock but there are no conductive fractures/faults and no water can be produced? We can still create geothermal energy but we need to intervene by creating the fractures and providing an infrastructure to circulate water through this engineered reservoir. Cool water can be pumped underground down one well, where it is heated by the hot rock as it travels to the second well where it is pumped back up to the earth’s surface to the power plant. We call this Enhanced - or Engineered - Geothermal Systems (EGS).

This short animated clip shows the steps in our project over the next 3-5 years involving drilling, creating underground reservoir, and producing geothermal power at the FORGE Site. The first step is to drill the deep well that veers from vertical to sub-horizontal at about 6000 feet deep. After the well is completed, the reservoir is stimulated by injecting cold water water (blue), which opens pre-existing fractures. A second parallel well is drilled into the stimulated fractures. To produce hot water (red) and geothermal power from this second well, cold water is injected into the first well, and it heats up as the fluid moves slowly through the fractures in the stimulated reservoir.