Drillers vs. Granite Hard Rock Is Losing Its Edge

Abstract

At the Utah FORGE test site, they are drilling wells to try to accomplish something others have failed to in 50 years of trying—inject water into hot rock and produce enough steam to power a commercial electric generator. There are many reasons why it is hard, particularly finding a way to use fracturing to create what amounts to a slow-moving, high-volume waterflood that heats the water as it flows from an injection well to a production well. Multiple well pairs per power plant are likely needed, so another problem is finding a way to speed up the drilling, which at the site requires drilling through a mile of granite at temperatures exceeding 400°F. “This approach will take hundreds and hundreds of wells. The challenge is cost, like in an unconventional well,” said Fred Dupriest, professor of engineering practices at Texas A&M University, while delivering a paper at the recent SPE/IADC International Drilling Conference (SPE 208798). The comparison to shale is apt because he was brought in at Utah FORGE to teach drillers how to use the hardware and methods that speeded drilling in unconventionals to accelerate drilling through hard rock. The high cost of slow drilling in hard rock has inspired futuristic ideas such as using plasma energy to disintegrate hard rock. The technology was the basis of a startup, GA Drilling, which was recently bought by Nabors which hopes to commercialize it for hard rock sections. The challenge faced by Dupriest and his partner on the project, Sam Noynaert, an associate professor of engineering practice at Texas A&M, was to demonstrate that faster drilling methods are possible using available technology. The future of geothermal energy depends on efforts like Utah FORGE’s, which are funded by the US Department of Energy (DOE), to overcome the subsurface barriers that have limited geothermal power to less than 1% of the US electric supply. Growth has been limited by the available resources. There are so few places in the US or the world that combine geothermal heating, water, and naturally conductive fractures that make it possible to drill wells that produce superheated steam. On the other hand, it is not hard to find hot, dry rock. If profitable systems can be built to inject the water into hot formations and produce enough very hot water, geothermal power plants could be located near big, urban power markets.