TR: But haven’t people been talking about greater use of geothermal energy for years now? What’s changed?
JT: Like many energy technologies, it had a lot of support structure back in the 70s and in the 80s, but our national priorities shifted from energy to other things, and we didn’t necessarily invest enough in it at that time to bring it to fruition.
Many [energy] technologies, whether they’re renewables or nuclear power or coal or whatever it might be, need to be continually revisited and placed in context with the current state of technology. In this case, our interest in trying to go after hydrocarbons and extract hydrocarbons has developed a lot of technology in subsurface engineering that’s useful and makes geothermal worth revisiting.
TR: How do you plan to harvest stored heat from more areas?
JT: What we’re trying to do is emulate what nature has provided in these high-grade systems. When we go very deep, [rocks] are crystalline. They’re very impermeable. They aren’t heat exchangers like we really need. We’d like to create porosity and permeability. [The rock] actually is filled with small fractures, so what you’re trying to do is find those weak zones and reopen them. We need to engineer good connectivity between an injection set of wells and a production set of wells, and sweep fluid, in this case, water, over that rock surface so that we extract the thermal energy and bring it up another well.
TR: What technology do you need to open up the rock and harvest the heat?
JT: All the technology that goes into drilling and completing oil and gas production systems, [such as] stimulation of wells, hydraulic fracturing, deep-well completion, and multiple horizontal laterals, could in principle be extended to deep heat mining. Hydraulic methods have been the ones that hold the most promise, where you go into the system and you pressurize the rock – just water pressure. If you go higher than the confinement stress, you will reopen the small fractures. We’re just talking about using a few thousand pounds per square inch pressure – it’s surprising how easy this is to do. This is a technique that’s used almost every single day to stimulate oil and gas reservoirs.
TR: What still needs to be done to make artificial reservoirs for geothermal possible?
JT: Like any new technology, there are technical issues. But I don’t see any show-stoppers. I think that the evolution of the technology, with 30-plus years of field testing, has been very positive. The basic concept has been demonstrated. We know how to make large reservoirs. We need to connect them better, to stimulate them better than we have in the past using some of these hydraulic methods and diagnostics that are now available to us.
So it’s the scale-up to a commercial-sized system that has to be done, making a heat mine that is large enough and productive enough to sustain the economic investment. But we believe that’s possible to do based on where we are now with the technology.