Sandia researchers test explosives and propellants to create geothermal power sites
Why are scientists setting off small-scale explosions inside 1-foot cubes of plexiglass? They’re watching how fractures form and grow in a rock-like substance to see if explosives or propellants, similar to jet fuel, can connect geothermal wells in a predictable manner.
Geothermal energy has a lot of promise as a renewable energy source that is not dependent on the sun shining or the wind blowing, but it has some challenges to wide adoption. One challenge is that there are only a few places in the U.S. that naturally have the right combinations of hot rock close to the Earth’s surface with available underground water. Another challenge is the initial start-up cost of drilling and connecting geothermal wells. Eric Robey, a Sandia National Laboratories mechanical engineer, is leading a team to explore if explosives can reduce those two challenges.
“Our goal was to come up with a new way of creating a geothermal fracture network that you have a clear idea where it is going to go — it’s steerable and manageable — and you are utilizing fewer resources and being more environmentally friendly,” Robey said. “This is where explosives and propellants come in. The idea is that they’ll allow us to get away from pumping a lot of fluid down the wells. We’re collaborating with Lawrence Livermore National Laboratory to model the explosions and improve the predictability of forming fracture networks.”
Starting with 1-foot cubes of plexiglass, which mimic many of the properties of rock, the team watched the explosion shock wave ripple through the cube and listened with specialized microphones to the formation of tiny fractures. The team is using the information on the location of the fractures and the timing of fracture formation to refine existing computer models of underground explosions.
Challenges of cracking hot rock
Because natural formations with the right combination of hot rock and underground water aren’t located throughout the U.S., the Department of Energy’s Geothermal Technologies Office supports the research, development and testing of enhanced geothermal systems. An enhanced geothermal system takes a location with hot rock and turns it into a location suitable for producing geothermal power by drilling deep wells and carefully fracturing the hot rock so that water can reach the hot rock and carry that heat up to the surface to produce power.
Enhanced geothermal systems have the potential to power 100 million homes, according to the Geothermal Technologies Office.
“They’re finding out it’s a difficult problem to get fractures to go where they want them,” Robey said. “The goal of our project is to see if we can steer the formation of fractures a bit more.”