December 1, 2009

The Future of Geothermal

Sonal Patel

Oil and Gas Field Waters

Hot water produced with deep drilling for oil or gas or from depleted oil/gas wells is being used more and more. But though it poses few technical challenges, the power cost using this process may not always be attractive.

Geopressured Systems

Geopressured geothermal resources consist of hot brine, saturated with methane, found in large, deep aquifers under high pressure. The water and methane are trapped in sedimentary formations at a depth of about 3 km to 6 km, and the temperature of the water is in the range of 90C to 200C. Three forms of energy can be obtained from geopressured resources: thermal energy, hydraulic energy from the high pressure, and chemical energy from burning the dissolved methane gas. The major region of geopressured reservoirs discovered to date is in the northern Gulf of Mexico.

The method consists of drilling a bore into a geopressured-geothermal reservoir, allowing the fluid within the reservoir to escape through the bore, and using the fluid to turn an electricity-generating turbine. The concept has not been commercially proven yet, though a demonstration has shown technical feasibility. Even so, it poses a variety of technical challenges to making power at a cost that is commercially viable, not to mention that its distribution is very restricted, Sanyal says.

Magma Energy

Magma, the largest geothermal resource, is molten rock found at depths of 3 km to10 km and deeper. It has a temperature that ranges from 700C to 1,200C. The concept of using this heat source theorizes that thermal energy contained in magmatic systems could represent a huge potential resource of energy. In the U.S., for example, useful energy contained in molten and partially molten magma within the upper 10 km of Earth’s crust has been estimated at 5 to 50 x 10 to the 22 power J (50,000 to 500,000 quads). This technology is far from becoming commercially viably, however, says Sanyal. Not only is it extremely localized, but it also poses a host of technical challenges, including developing drilling and completion techniques as well as developing a technology for extracting heat from magma.