Subsurface temperatures can produce electricity

Most people associate geothermal energy with extremely high heat – think geysers.

But the Geothermal Map of North America produced by Professor David Blackwell and SMU researcher Maria Richards for the American Association of Petroleum Geologists in 2004 revealed locations all over the United States where subsurface temperatures are high enough to drive a small, binary power plant and generate electricity.

This kind of power plant is similar to an air conditioning unit run backwards, using heat to generate electricity. The hot water that runs through one chamber in the pump heats fluid with a lower boiling point in an adjacent chamber, which expands into high-pressure vapor and drives a turbine.

Blackwell’s “light bulb” moment came when he realized that oil and gas wells all over the country were spewing moderately hot wastewater, but petroleum company executives were unaware of the resource they were pumping back into the ground.

Deep drilling through hard rock is expensive: that’s one reason traditional geothermal energy development has lagged behind green technologies like wind and solar power. But Blackwell’s mapping has proven that many existing oil and gas wells in Texas, Louisiana, Mississippi, Alabama and some mid-continent states reach shallower depths where temperatures still range from 200-300 degrees Fahrenheit. That’s hot enough for a binary power plant to do its job.

“This was just a flash of light,” Blackwell says. “It seemed to me it ought to work.”

Blackwell is not trying to convince anyone that piggybacking geothermal pumps onto existing oil and gas wells is the answer to all of America’s energy needs. But the technology could generate enough electricity to power as many as 4.5 million homes, and make it possible for petroleum producers to continue pumping low-producing wells that the high cost of purchased electricity might otherwise force them to shut down.

“What is important about this work is its sense of vision of what is possible from geothermal energy,” Gawell said.

This last year has been a watershed for Blackwell’s research:

• Blackwell was recently awarded the prestigious Joseph W. Aidlin Award at the annual meeting of the Geothermal Resources Council, given annually for outstanding contributions to the development of geothermal energy.
   
• The price of oil and gas went through the roof (and will likely rise again), refocusing attention on alternative energy sources previously overshadowed by wind and solar power.
   
• The U.S. Department of Energy is working with companies like Ormat to make geothermal energy more affordable from such moderate-temperature sites, and expects the result will be about 15,000 megawatts of new electrical generating capacity within the next decade.
   
• Search engine giant Google has jumped into geothermal research, funding $10 million in studies – including a grant to SMU’s Blackwell to update and expand his 2004 Geothermal Map of North America.

Blackwell, who received his Ph.D. from Harvard University, joined SMU’s faculty in 1968 and is the Hamilton Professor of Earth Sciences in Dedman College of Humanities and Sciences.

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