GEOTHERMAL POWER FROM LOW TEMPERATURE RESOURCES

Electric power generation from coproduced low-temperature (150° to 300°F) geothermal resources in oil and gas settings is a significant power resource that could have significant positive impacts if developed on a large scale. Historically, this concept has not been considered economically viable primarily because of the low price received for electricity generated and the lack of commercially available electric generating equipment. However, recent commercialization of scalable organic Rankine cycle (ORC) engines changes the equation. It is estimated that an ORC engine using fluid volumes of 1000 gallons per minute at temperatures at a temperature of 92 C (192 F) can produce electricity at a cost that is competitive with power produced by coal-fired power plants. Although the power generated from such a system would be only on the order of 1 MW, the potential for development of thousands distributed power plants in existing oil and gas settings is huge. A previous estimate of the low-temperature geothermal resource in U.S. continental sedimentary basins is 100,000 exaJoules (Tester, et al., 2007). This estimate was based on only the principal water-producing formations and generally excluded petroleum-bearing formations. We find that if all formations that have potential for hot water production are included, the resource is at least 400,000 EJ. The energy potential of currently coproduced fluids has been estimated as 0.0944 to 0.4510 EJ for the central and southern U.S. (McKenna, et al., 2005). Adding the substantially greater accessible resource base in sedimentary basins in the U.S. through development of abandoned wells could increase the energy potential by several orders of magnitude. Therefore, we anticipate that demonstration of economic power production from existing wells could provide the incentive for large-scale development of tens of thousands of abandoned or capped wells in oil and gas fields. Beneficial outcomes of this development include: growth of a new energy industry to develop the larger geothermal energy resource within sedimentary basins; establishment a geothermal power infrastructure would provide a sustainable and secure domestic energy resource; a reduction in CO₂ emissions by electrical power generated from fossil fuels.