Martin Saar: Mining the Earth for Power

Martin Saar’s process for a pollution-free source of energy emerged several years ago as he and Jimmy Randolph, then a graduate student in Earth sciences, were driving to a field research site in northern Minnesota.

Saar, an associate professor of Earth sciences and holder of the Gibson Chair of Hydrogeology and Geofluids, and Randolph were batting about ideas for Randolph’s doctoral project on geothermal energy. They were also discussing an unrelated project on geologic carbon dioxide (CO2) sequestration—a process that pumps this greenhouse gas deep into natural rock reservoirs to keep it out of the atmosphere thereby reducing global warming.

“Then the light bulb went on. We asked ourselves, ‘What happens when you combine these two processes?’” said Saar. “We had a pretty good hunch right then and there that this could be big.”

The idea was something Saar now calls “CO2 plume geothermal system,” or CPG and piggybacks on two industrial processes. The first is geologic CO2 sequestration where CO2 is captured and pumped deep into the ground before it enters the atmosphere.

"This method actually has a negative carbon footprint, thereby rendering conventional coal-fired power plants—from where the CO2 is captured—green." 
— Martin Saar

The technology captures carbon dioxide (CO2) from fossil-fuel-burning power plants and injects it deep into the earth, helping to reduce the chief greenhouse gas that causes global warming and climate change. The bulk of the CO2 becomes permanently stored as a large underground CO2 plume that is naturally heated by Earth’s abundant internal heat.

A small portion of the geothermally heated CO2 is then cycled up to the Earth’s surface through a production well, where the CO2 heat is used to generate electricity. Once used, the cooled CO2 is re-injected back into the Earth to be cycled again.

The second process is “enhanced oil recovery.” Oil companies pump CO2 into partially depleted oil reservoirs to help drive some of the remaining oil to the surface. Electricity to power the pumps is the biggest operating costs of an enhanced oil recovery operation.

Both processes create huge CO2 reservoirs, one to five kilometers below ground surface. Tremendous pressure and temperatures of up to 200 degrees C transform the CO2 into its “supercritical” state. “It has liquid-like density and gas-like viscosity,” said Saar.

“CPG is a more efficient way to produce electricity than water-based geothermal power systems,” said Saar. “This method actually has a negative carbon footprint, thereby rendering conventional coal-fired power plants—from where the CO2 is captured—green.”

The CPG system received an initial $600,000 grant from the Institute on the Environment’s Initiative for Renewable Energy and the Environment, which helped to leverage a $1.5 million grant from the U.S. Department of Energy and a $1.9 million National Science Foundation grant. Now licensed to startup company Heat Mining Company LLC, located in Rapid City, S.D., Saar is co-founder and the chief scientific officer.

Generating power from this technology would produce significant revenue—about $5 million a year for a single 10-megawatt turbine, depending on the cost of the electricity. Furthermore, multiple CPG installations could be installed. That money would help make carbon capture and storage financially viable and help reduce global warming. Or it could prolong the life of nearly depleted oil reservoirs. “If you get electricity cheaper, then the lifespan of that oil reservoir can be extended,” Saar said.

Placed on a fast track with other green energy patents, the CO2 plume geothermal technology received a U.S. patent on November 27, 2012. The international components of the patent are currently pending. Heat Mining Company has also filed patent applications for enhanced CPG technology, which will broaden the range of geologic conditions that make economic sense.

Heat Mining Company is promoting the technology on two fronts. First, it is trying to negotiate a pilot project with one of several power plants that are geologically sequestering carbon dioxide to reduce net emissions of this greenhouse gas.

The more immediate benefit is being able to produce clean, very low cost electricity at enhanced oil recovery sites in hundreds of existing oil fields worldwide. Heat Mining Company would cover all capital costs to install or operate the CPG system. The participating oil companies would receive 30 percent of the income from the electricity produced, an amount sufficient to provide a $10 to $15 per barrel pricing hedge.

Kenneth Carpenter, Heat Mining Company’s managing partner, says the company hopes to install the first plant this year and to have 15 in place within three years. Capital costs are low, and the infrastructure to carry the power exists at all the sites already. “Technology such as turbines is pretty much off the shelf,” Carpenter said.

“That’s the beauty about it,” said Saar. “It’s one of those things where you don’t have a huge amount of risk in terms of technology because all the components are fairly well known.”