Geothermal well drilling near Reno, Nevada.
Is There Room for Geothermal Energy?
December 2006 / January 2007
Volume 4 Number 6
Despite the potential to provide a significant percentage of the nation's electrical energy needs, geothermal energy technologies often are not part of the discussion. No one knows that better than the researchers at the geothermal research department at Sandia National Laboratories. Despite breakthroughs that could enable geothermal energy to provide a sizable portion of the nation's energy, the Department of Energy's geothermal program is scaling down and funding for fundamental research is in jeopardy.
"Do we let geothermal mature to be only natural geothermal systems, or do we go after the big prize—€”Engineered Geothermal Systems (EGS)?" asked Sandia researcher Chip Mansure. "Now we don't have the money to find out."
That big prize could be a virtually non-polluting energy source good for as much as 20 percent or more of the nation's total electrical energy needs. Western states, where geologic conditions are most favorable for geothermal development, would realize the biggest impact of such technology development. Hawaii, sitting as it does on top of the magmatic hot spot that created it, could have all of its electrical energy needs met by geothermal power. And energy-starved California could meet as much of half of its needs through geothermal. But in a telling irony, that state's recent Proposition 87 to provide funding for alternative energy research did not even mention geothermal energy.
Geothermal energy uses heat produced by the Earth to produce steam that then powers generators in the same way as traditional power plants. The planet produces the energy deep in its mantle, where radioactive decay releases the heat that drives convection currents responsible for plate tectonics. The borders of the plates that make up the Earth's crust are the prime regions for tapping into geothermal energy. The Earth's crust is thinnest in those zones, and magma often is able to push its way close to the surface. The extreme heat of the magma transfers to the surrounding rocks. Any groundwater that is present also becomes heated, and turns to steam when relieved of its natural pressure.
The steam can be drawn up in much the same fashion as water in a conventional water well, and then used to drive a conventional turbine-based power plant located adjacent to the well.
Temperature, permeability and fluid availability are the primary factors that make or break a geothermal well. The temperature at the bottom of the well is driven solely by forces of nature, but the latter factors sometimes can be enhanced. Hydrofracturing of rock, a process of forcing water into the earth under high pressures to fracture solid rock, can sometimes be used to increase the ability of fluids to circulate and become heated. And when water is not present naturally in wells, it can be sent down into the earth by a series of injection wells, heated, and then drawn back to the surface by a production well.
But drilling is difficult in the igneous or metamorphic rocks that often are present at the edges of the tectonic plates. Drill bits often fail during well development that traditionally has been as much as art as it is science. The hard rock, extreme temperature and harsh geochemical environment combine to make geothermal well emplacement one of the toughest challenges in the field of geology.
"The geothermal energy industry today has picked the low-hanging fruit," notes department manager Doug Blankenship. "But the potential that could be developed is astronomical." To realize that potential, Blankenship's department has been developing drilling and high-temperature electronics technologies that are finding commercialization potential in geothermal and traditional energy applications, and possibly in non-energy venues, as well. One technology is the polycrystalline diamond compact (PDC) drill bit, which can cut through the hard rock as much as twice as effectively as traditional roller-cone bits and potentially eliminate as much as 15 percent of geothermal well development costs.
The Achilles' heel of PDC bits is their sensitivity to bit vibration, known to drillers as "chatter." The Sandia geothermal researchers have developed technologies that attack the issue from two angles. First, they have developed a magneto-rheological (MR) damper system that mitigates chatter. And as part of their considerable body of work in the field of high-temperature electronics, they have developed downhole drilling sensors that can provide real-time information on critical parameters such as vibration and forces at the drill bit. One area of future development would be to integrate the PDC bits, MR dampers and downhole drilling sensors to create a smart system that would automatically adjust drilling parameters as conditions change.
"The role for Sandia is to reduce the drilling risks to keep geothermal energy competitive with other resources such as natural gas and steam power plants," said Bill Livesay, a San Diego-based drilling consultant working with the Sandia geothermal department. Livesay added that much of the technology developed by Sandia for geothermal wells also benefits other drilling operations including environmental drilling.
Sandia researchers have set a goal of lowering the cost of well development by 25-50 percent. They also hope to see their EGS technologies being used to sink geothermal wells that are twice as deep as today's wells.
But the ability to develop more efficient geothermal wells will be wasted without a concerted effort to better utilize the energy resource.
"The bigger issue is energy security," argued Livesay. "Just being able to generate the amount of energy available through EGS technology is significant to the country. As we use up our oil and gas resources, it bothers me that we are ignoring the potential for geothermal development."
Mansure and Livesay recently participated in an EGS feasibility study, led by Massachusetts Institute of Technology professor Jeff Tester, that looked at the potential for EGS development in this country. The results of that work are much more encouraging than anyone expected. The final report, to be published soon by the university and presented to the Department of Energy, is expected to indicate that geothermal energy is a grossly underdeveloped renewable energy resource.
Blankenship noted that while geothermal energy will not address all of the nation's energy concerns, it would greatly reduce our dependence on non-renewable resources. "Accessing that resource could have a substantive impact on the energy portfolio of this country," said Blankenship.
G. Jeffrey Hoch reports on Sandia National Laboratories for Innovation.
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