Dual Perspectives

By Alexis Madrigal | 04.06.09

What if, instead of relying on Mother Nature, we could engineer our own geysers? Then we could put geothermal energy plants next to cities, where they are needed, instead of building them in the often remote parts of the West where they are now. The idea is not as far-fetched as it may seem. In 2007 the Department of Energy recruited scientists at the Massachusetts Institute of Technology to look into the idea. MIT's feasibility study concluded that "most of the key technical requirements to make [the engineered-geyser scheme] work economically over a wide area of the country are in effect, with remaining goals easily within reach.”

An engineered geyser is called an "enhanced geothermal system," or EGS for short, and here's how you go about making one. First, you drill a pair of wells, one a little deeper than the other. Then you crack the hot rock at the bottom of the deeper well and inject water (or another liquid) into it. Fracture the rock in just the right way, and the water will come up the shallower well as steam—which turns your turbine, and voila! Electricity.

Or rather, that's how one would make an artificial geyser, in theory. "In reality, there's never been an enhanced geothermal project that's worked, " reports Ernie Majer, the Energy Resources program head at the Department of Energy's Lawrence Berkeley Lab.

That may be about to change, however. Ever since the MIT feasibility report, money has been gushing into EGS. The Department of Energy's Geothermal Technologies Program just received $90 million in stimulus money to play with, up from $5 million two years ago when the MIT report first came out. And last year Google invested $10 million in venture capital money in EGS, split between two EGS technology startups, Potter Drilling and AltaRock.

Potter is developing a new bit that should make it possible to drill deeply relatively cheaply. Drilling costs can skyrocket when boring to the extreme depths necessary for EGS. Increasingly hard rock can slow progress to a crawl, and a broken bit will junk a multimillion-dollar hole. Potter's idea is to replace physical drill bits with jets of extremely hot water to bore through rock, a process called “hydrothermal spallation.” The company plans to drill its first test well later this year in Northern California.

After reaching the hot rock layer, several thousand meters down, the next challenge is getting the rock to fracture in just the right way. You need the correct size and number of fractures to allow just the right amount of liquid to move: Too little permeability is bad—as is too much. Though it's a tough problem, it's not completely unknown. Petroleum engineers have mastered the technique cracking shale to get at natural-gas deposits.

"It's a highly refined technology in the oil business, the gas people know how to do it. And they do it very well," says Chip Groat, the former head of the U.S. Geological Survey, and a geoscientist at the University of Texas–Austin. "But they are not operating at [EGS] temperatures."

Learning to fracture rock "very well" at great depths and high temperatures is exactly what the other Google-funded geothermal startup, AltaRock Energy, is working on. While they are secretive about the exact nature of their technology, they claim to be able to map and even direct the cracking of the rock that they induce. Soon the company will put its ideas to the test at California's Geysers, the largest geothermal plant in the world, in an effort to increase the production of the existing plant.

And if it works, there's no telling where the drilling might stop.

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