Winner: Hot Rocks

December 31, 2008

Four kilometers down below the orange earth of Australia’s Cooper Basin lies some of the hottest nonvolcanic rock in the world—rock that the geothermal industry had never seriously considered using to make electricity. But next month Geodynamics, an eight-year-old company based in Milton, Queensland, will prove otherwise when it turns on its 1‑megawatt pilot plant here. The company has done more to harness this unconventional form of geothermal energy than anyone else in the world.

Geodynamics picked a place in the middle of Australia with a smattering of trees, a mostly dry riverbed, and a town with a population of about 14. Even in the best circumstances, building a geothermal power plant is a risky endeavor: drilling costs money, and divining what’s going on in the depths of the Earth is still something of a black art. Here, geothermal companies must clear yet another hurdle. The world’s 10 000-MW collection of geothermal power plants exploits existing underground reservoirs of water and steam. Australia’s geoscientists, by contrast, must create their own.

This very experimental technology is known as an engineered geothermal system, or EGS. If it works—and the finances and expertise at Geodynamics’ disposal suggest that it will—heat from deep under the outback could contribute a few gigawatts of clean round-the-clock power, up to 20 percent of Australia’s capacity today. And if it works here, many other countries will want to give it a whirl.

In the last few years, the concept of geothermal energy has undergone a dramatic reshaping to include a broad range of geological conditions not normally deemed useful. In the United States, for example, EGS could potentially contribute as much as 100 000 MW of electricity in the next 50 years, according to an MIT report released in 2006. Today conventional geothermal capacity in the United States amounts to about 3000 MW, less than half of a percent of the country’s total electric capacity. In famously geothermal Iceland it comes to 450 MW—about one-fourth of the island’s total. Australia’s use of geothermal heat is basically nil.

If the three dozen geothermal ventures now trolling the Australian continent are any indication, that situation is about to change. But there’s a catch. Only a couple of EGS projects have ever produced power, and those are in Germany and France, where the rock is considerably more pliant than Australia’s granite underpinnings. That hasn’t stopped Geodynamics, whose managing director, Gerry Grove-White, contends that the system he is shepherding into existence is the first with real commercial promise. “None of those hold the prospects of ours, with our massive [geological] resource and much higher temperatures,” says Grove-White, a power engineer and former executive at Tata Power, India’s largest private utility. The reasons for his optimism have everything to do with the unique conditions into which Geodynamics has plunged itself.

Today virtually all geothermal systems are in volcanic regions, near the boundaries of tectonic plates. When two plates heave into each other, one tends to buckle under the other, creating openings in the mantle through which magma can seep up, heating the rock above. Mining the underground heat, however, requires a carrier. Today’s systems rely on rainwater, which collects in fractures in the crust and drips several kilometers down, pooling in cracks and porous rock. A geothermal company drills a well, builds a power plant above it, and starts pumping water. The water comes to the surface and explodes into steam, which turns a turbine, which drives a generator, producing electricity. The hotter the rock and the larger the buried reservoir of water, the better the system should perform.

Now eliminate from that picture much of the water and shrink the fractures where the water pools to millimeter-wide slivers. Move the system to the middle of a desert, 500 kilometers from the closest grid connection. Those are the circumstances that Geodynamics chose to face in the Cooper Basin.

Australia’s granite is a natural nuclear pile, warmed by the decay of uranium, thorium, and potassium isotopes. The result is some of the hottest nonvolcanic rock in the world, with temperatures in the range of 200 to 300 ˚C not uncommon a few kilometers below the surface.

Geodynamics was offered a rare glimpse of the deep Earth and its temperatures thanks to an Australian oil and gas company called Santos, which has been drilling its way through the Cooper Basin for decades. Where it didn’t find fossil fuels, Santos did uncover remarkably hot granite, and its abandoned wells have served as windows into the underground. “In our case, figuring out where to drill was easy. We went right alongside wells that Santos had drilled in the past,” says Grove-White.

Geodynamics’ first big stroke of luck came early, when it drilled a well and hit hot water that seemed to be trapped in place rather than leaking down into harder-to-reach crevices. “Nobody had ever realized that such conditions existed—an environment a long way away from volcanoes and full of high-temperature waters,” says geoscientist Doone Wyborn, who is Geodynamics’ executive director.

Granite generally fractures horizontally in this geological environment, so the lack of downward cracks wasn’t a complete surprise; even so, more water seemed to be pooling than anyone had anticipated. The discovery made all the difference, because it meant that water injected into the ground would stay there to soak up heat rather than trickling uselessly away. Even better, such water-holding conditions might well apply in much of the rest of the continent, whose geological conditions are more uniform than just about anywhere else.

“Now it turns out that virtually none of the systems we’re looking at are dry,” says John Garnish, an EGS consultant based in the UK. That was pretty good news for Geodynamics, which subsequently abandoned the idea of diverting large quantities of water to the desert of a drought-ridden nation. “Frankly, if it was hot dry rock, I wouldn’t be here,” says Grove-White, who joined the company two years ago.

Guts, as much as luck, produced the company’s second big break. When the spike in oil and gas prices spurred exploration, making drilling rigs scarce and thus hard to lease, Geodynamics bucked the leasing trend by buying a rig from a vendor in Houston. It happens to be the largest and most powerful rig in the country. “For them to own their own rig is brilliant. Having it at their disposal is a key factor in their success in today’s market,” says Brian Anderson, an assistant professor of chemical engineering at West Virginia University.

Expert Call: “Even assuming solutions to technical difficulties, extracting geothermal energy from granite layers seems unlikely to be cost-effective without subsidies.” —Nick Tredennick, IEEE Fellow; editor, Gilder Technology Report.

The rig allows Geodynamics to drill more cheaply than its Australian peers can—but even so, at US $50 000 or more a day, the cost of operating a rig puts a major dent in any rock driller’s business plan. “Drilling under high temperatures and high pressures, in hard rock like granite and at great depth, makes this one of the most difficult onshore drilling projects in the world,” says Ralph Weidler, whose company, Q-con, in Bad Bergzabern, Germany, helped Geodynamics develop the reservoir.

But drilling wells is just the beginning. The pockets of water in the Cooper Basin are far smaller than the large reservoirs found in volcanic regions, so Geodynamics set out to create the reservoir for itself. The company needed to enlarge the cracks so that they could hold more water. It also had to intercept those cracks with a second well so that the brine could be returned to the ground, allowing the plant to operate continuously. The engineers used a massive pump to cram 20 000 metric tons of water down a well and through the fractures in the rock, prying them open. They inferred the location and the movement of the cracks from the innumerable tremblings registered by an installed network of seismometers.

The process of wedging open those rocks went better than anyone had expected. The geoengineers had generated a horizontal pancake of long, widened cracks 2 km in diameter. “If you compare it with other EGS sites, [Geodynamics’] fracture area is absolutely amazing. It’s humongous!” says Anderson.

The moment of truth came in mid-March, when the engineers trekked out to the tiny town of Innamincka to find out how thoroughly the fractures had connected the wells. They switched on the pump to see how much hot brine they could pull out of one well. “We could see pressure variations at one from the way we controlled the other,” says Grove‑White. As expected, the drop in pressure as the water rose converted it to steam, and it came billowing out of the well in a big white blast. The temperatures at the bottom of the well were measured at a heartening 244 ˚C. The rate of water gushing up from the well, a key part of a geothermal project’s economic credibility, held solidly at 27 kilograms per second—a very respectable starting point. Five months later, a four-day circulation test again produced sufficient quantities of water.

Geodynamics is the only firm out of the many drillers in Australia that has managed to artificially extend the fractures in a well, let alone complete a circulation test. For the company’s engineers, one major challenge remains. In the coming year it must triple its flow rate to the 80 to 100 kg/s that’s necessary for a large-scale plant. To do that the company must master the art of creating multiple tiers of nearly identical fractures between pairs of wells, a technique that’s well known in the oil and gas industries but terra incognita to geothermal engineers.

To push through, Geodynamics has strong financial backing, on the order of $228 million, secured in the past year. It signed a joint venture agreement with Origin Energy worth about $130 million in December 2007, and this past September Tata Power, Grove‑White’s alma mater, committed about $35 million. Another $64 million came from two Australian investment funds. “Finally people are starting to realize the potential is there. Once people registered that EGS could contribute so much more than conventional geothermal, the penny finally began to drop,” says Garnish, the EGS consultant.

Ladislaus Rybach, the president of the International Geothermal Energy Association, is a stalwart supporter of EGS, but he urges industry watchers to keep their expectations in check, pointing out that it took three decades of research to produce the paltry 1.5 MW of fractured-rock power in Germany and France. But he, too, notes that Geodynamics is in a unique position. “The main obstacle is that whatever you want to do in EGS takes a lot of money in hand. Only the Australians so far have managed to create this environment,” Rybach says.

In spite of a dismal global economic climate, other factors are also contributing to a favorable future for geothermal start‑ups. In Australia, a carbon-emissions trading scheme is expected to put a price on carbon dioxide within two years. A geothermal plant would be able to trade its carbon credits to other companies that burn fossil fuels, making it cost-competitive. More broadly, in September Google.org, the philanthropic arm of the search giant, offered its own endorsement of Geodynamics’ strategy by committing $11 million to two American companies to jump-start the technology in the United States. (Google also swung around a satellite to generate a more detailed tree-by-tree map of the Cooper Basin on Geodynamics’ behalf.).

Geodynamics will need the money and good will. In March it will begin the process of extending parallel levels of fractures between another pair of wells and then begin planning the construction of a 50-MW geothermal power plant, also in the Cooper Basin. As the only known source of clean, uninterrupted base-load power, geothermal energy could make an enormous difference. For that alone, it is well worth banking on. 

Sandra Upson
Spectrum Online - Dec 31,2008