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Standardized Definitions and Permeability Regimes for the Characterization and Capacity Estimation of Geothermal Systems
Ryan LIBBEY, John MURPHY
[Ormat, USA]
Key geothermal resource parameters such as Area, Thickness, and Temperature play an important role in the characterization of resources, the identification of appropriate analogs, and the calculation of resource capacity estimates. There is currently no industry-wide standard for the definition of resource geometry, i.e., resource Area and Thickness, which can result in confusion when communicating such parameters with non-specialists and inconsistent approaches to resource capacity estimations. The definitions presented herein focus on a conceptual model approach to Area and a Thickness parameter rooted in the concept of heat-sweeping in a hypothetical or realized development. In addition to resource parameters such as temperature, area, and thickness, there is the ability to characterize geothermal resources based on Permeability Regime; a resource descrptor that is controlled by geologic setting and that influences parameters such as area, well permeability, feedzone distributions, recovery factors, and post-development cooling trends. Four end-member Permeability Regimes are proposed to describe all naturally-occurring geothermal systems: Discrete, Limited Distributed, Enhanced Distributed, and Stratigraphic, and their relationship to well productivity index values are described herein. This paper outlines an approach to standardize the documentation of key resource characteristics and Permeability Regimes for all geothermal systems, regardless of temperature or geologic setting. A companion paper reviewing the reservoir engineering characteristics of geothermal Permeability Regimes is provided by Murphy and Libbey (2026).
Topic: Geology