Mining for heat

Oilfield Review Winter 2009/2010: 21, no. 4. Copyright © 2010 Schlumberger. For help in preparation of this article, thanks to Mo Cordes, Houston; and Stephen Hallinan, Milan, Italy. GeoFrame and TerraTek are marks of Schlumberger. The mechanics of harvesting the Earth’s natural subsurface heat seem to be familiar petroleum engineering tasks: drill and complete wells and produce fluids from wells landed in targeted formations beneath the surface. But the prize in geothermal energy production is not fluids. It is heat. So while there is considerable potential for technology transfer from the oil and gas upstream business—drilling rigs, bits, pressure control and other basic practices and technologies—the specifics of hydrocarbon and geothermal energy production diverge. For example, ultrahigh temperature represents an obvious problem in bringing oil industry technology to bear on geothermal exploration and production: It renders useless the sophisticated tools and sensors that are dependent on pressuretight seals and electronics. The industry, however, is continually overcoming temperature limitations. In reality, the accurate characterization of geothermal reservoirs is a more fundamental obstacle to realizing the full energy potential from the Earth’s heat. Constructing geothermal reservoir models and simulations using seismic surveys and logging data will require more innovation than adaptation such as increases in hardware temperature tolerances. Still, the comparison between heat and hydrocarbon exploitation remains compelling. Many of the geothermal wells currently feeding power plants have been constructed by oilfield workers using essentially traditional drilling and completion equipment and techniques. Today, those efforts have resulted in geothermal or, more accurately, hydrothermal fields that feed power plants producing about 10,000 megawatts (MW) of electricity in 24 countries (below).