Assessment of the Enhanced Geothermal System Resource Base of the United States |
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Authors: | David D Blackwell Petru T Negraru Maria C Richards |
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Institution: | (1) Geothermal Lab, Department of Geological Sciences, Southern Methodist University, Dallas, TX 75275, USA |
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Abstract: | This paper describes an assessment of the enhanced geothermal system (EGS) resource base of the conterminous United States,
using constructed temperature at depth maps. The temperature at depth maps were computed from 3 to 10 km, for every km. The
methodology is described. Factors included are sediment thickness, thermal conductivity variations, distribution of the radioactive
heat generation and surface temperature based on several geologic models of the upper 10 km of the crust. EGS systems are
extended in this paper to include coproduced geothermal energy, and geopressured resources.
A table is provided that summarizes the resource base estimates for all components of the EGS geothermal resource. By far,
the conduction-dominated components of EGS represent the largest component of the U.S. resource. Nonetheless, the coproduced
resources and geopressured resources are large and significant targets for short and intermediate term development. There
is a huge resource base between the depths of 3 and 8 km, where the temperature reaches 150–250°C. Even if only 2% of the
conventional EGS resource is developed, the energy recovered would be equivalent to roughly 2,500 times the annual consumption
of primary energy in the U.S. in 2006. Temperatures above 150°C at those depths are more common in the active tectonic regions
of the western conterminous U.S., but are not confined to those areas. In the central and eastern U.S. there are identified
areas of moderate size that are of reasonable grade and probably small areas of much higher grade than predicted by this analyses.
However because of the regional (the grid size is 5′ × 5′) scale of this study such potentially promising sites remain to
be identified.
Several possible scenarios for EGS development are discussed. The most promising and least costly may to be developments in
abandoned or shut-in oil and gas fields, where the temperatures are high enough. Because thousands of wells are already drilled
in those locations, the cost of producing energy from such fields could be significantly lowered. In addition many hydrocarbon
fields are producing large amounts of co-produced water, which is necessary for geothermal development. Although sustainability
is not addressed in this study, the resource is so large that in at least some scenarios of development the geothermal resource
is sustainable for long periods of time. |
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Keywords: | Geothermal geothermal resource base renewable energy heat generation U S heat flow temperature-at-depth coproduced fluids enhanced geothermal systems (EGS) |
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