A Conceptual Model Approach to the Geophysical Exploration of Permeable Geothermal Reservoirs That Considers Context and Uncertainty

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Conference Paper: A Conceptual Model Approach to the Geophysical Exploration of Permeable Geothermal Reservoirs That Considers Context and Uncertainty

Abstract
Geophysical exploration of geothermal resources is more effective when it is directed at constraining an integrated resource conceptual model, not at identifying an anomaly to target. Because permeable geothermal systems always leak heat by conduction and usually by advection, a temperature profile in a shallow well or the geochemistry of a hot spring are far more diagnostic than a shallow well or an oil seep would be in a petroleum context. A conceptual model approach is particularly effective in geothermal exploration because it promotes the interpretation of geophysics in the context of this wider range of geoscience information. All current commercially productive geothermal reservoirs have high temperature and permeability over an economically significant volume and so geothermal exploration programs are designed to identify prospects and constrain their temperature, permeability and volume. Although high fracture permeability is characteristic of the majority of productive geothermal wells, the fracture targets are too complex and the acquisition environment too challenging for seismic reflection to be routinely cost-effective. The geophysical parameter most commonly correlated with the overall permeability pattern of most geothermal reservoirs is resistivity. The low permeability hydrothermal smectite clays that cap most geothermal reservoirs are very low resistivity. However, to make effective use of resistivity imaging, it must be integrated with the geochemistry, shallow borehole temperatures, structure, alteration and other data to provide context for a conceptual model interpretation. The standard display of a geothermal conceptual model includes a natural state isotherm pattern in section view. The distribution of the isotherms illustrates permeability in a manner that can be directly analyzed by reservoir engineers and tested by drilling. Resource capacity and well targeting uncertainty can be assessed by preparing several conceptual models that are consistent with the data and cover a statistically representative range of outcomes and evaluating their likelihood using case histories.

Author 
William Cumming






Conference 
SEG Houston 2009 International Exposition and Annual Meeting; Houston, TX; 2009/10/25


Published 
Society of Exploration Geophysicists, 2009





DOI 
10.1190/1.3255789

Online 
Internet link for A Conceptual Model Approach to the Geophysical Exploration of Permeable Geothermal Reservoirs That Considers Context and Uncertainty

Citation

William Cumming. 2009. A Conceptual Model Approach to the Geophysical Exploration of Permeable Geothermal Reservoirs That Considers Context and Uncertainty. In: SEG Technical Program Expanded Abstracts 2009. SEG Houston 2009 International Exposition and Annual Meeting; 2009/10/25; Houston, TX. Houston, TX: Society of Exploration Geophysicists; p. 5