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GMEG - Geology, Minerals, Energy, & Geophysics Science Center

Geothermal Resource Investigations





Advances in Resource Classification and Assessment Methodology

Issue: The part of the geothermal resource assessment completed in early FY09 that was focused on natural hydrothermal systems encompassed both identified and undiscovered resources. The work of assessing these resources involved both significant revisions to the original USGS "volume method" for identified resources and development of new approaches to assessing undiscovered resources. Although the new methods applied to undiscovered resources represent a substantial advance over earlier efforts, there is significant room for improvement, especially in establishing a much stronger quantitative basis in the physical, chemical and thermal processes known to control the spatial and temporal distribution of hydrothermal systems. Consequently, a major component of this task is devote to establishing a better scientific framework for undiscovered resource estimates that are currently based primarily on empirical relationships derived from exploration and production histories within a framework motivated by theory. In addition, the methodology applied in the provisional Enhanced/Engineered Geothermal Systems (EGS) assessment, although theoretically sound and consistent with existing data, is based upon a limited number of EGS projects and could be significantly improved through careful analysis of ongoing EGS-related work, particularly those projects with direct USGS involvement (see Task 4). Finally, advances in power conversion technology at lower temperatures and the expansion of geothermal development into areas (such as deep sedimentary basins) has led to much greater diversity in the nature of the exploitable geothermal resource. Consequently, in collaboration with DOE, we are embarking on an effort to revise and update geothermal resource classification schemes that date back more than 30 years to reflect the current state of knowledge and technology.


  • Develop quantitative physical, chemical and thermal models for the processes that control the formation of geothermal systems in varied tectonic and magmatic environments, such as the Great Basin, the Salton Trough, the Cascades and Aleutians volcanic arcs, the Hawaiian islands, the Rio Grande Rift, and the California Coast Ranges. Frame these conceptual models in terms of processes and properties that can be measured or estimated using existing or easily acquired data.
  • Develop improved methods for geothermal resource assessments based on these models. Systematically evaluate the parameters of older methods and update or revise them as necessary to accommodate advances in knowledge and the existence of a vastly improved database on geothermal systems.
  • In collaboration with DOE, develop and publish a new classification system that clearly defines and encompasses the varied types of geothermal resources that are available for development.

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