Deep geothermal energy: can we defeat the exponential cost of depth?


First the bad news on EGS. There is a long list of cost issues to be overcome before Enhanced Geothermal Systems resources can complete with the proven base load generation options (hydrothermal, hydro, nuclear, etc.) There are serious problems to overcome — such as artificially stimulating sufficient permeability, increasing well bore diameter by 2 to 4 times over typical oil field practice, and drilling to the depth of economically viable heat.

I think that the most formidable economic challenge is the cost of drilling and completing geothermal wells to the depths offering high-grade heat. High-grade geothermal opportunities for electrical generation will offer injected fluid temperatures at 200°C or higher. There are almost no commercial geothermal wells that have been drilled deeper than about 1,000 meters. The bottom line is that EGS is still an R & D project, with no commercial scale successful projects to date.

Now the good news on EGS. There is risk capital being invested to tackle some of the challenges. E.g. in 2008 we wrote Geothermal energy: invests $10 million. See also this 2008 post on Deep geothermal energy via enhanced oil recovery techniques. Google spread that $10 million over three companies – one of which is Potter Drilling, who has licensed the MIT patent on Hydrothermal spallation drilling. Potter Drilling was cofounded by Bob Potter and Dr. Jefferson W. Tester, with the goal of linearizing the cost of deep drilling in hard rock. As you can see from the above cost vs. depth graphic, drilling cost today remains very much an exponential of depth. Over 6,000 meters the costs go up scary-fast. Unfortunately for the prospects of EGS, that is where the high-grade geothermal prospects are — see the following graphic showing temperatures at a depth of 10 km.

Dr. Tester is the lead author the MIT Future of Geothermal panel.