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Stored-heat Assessments: a Review in the Light of Field Experience : Volume 2, Issue 1 (17/12/2014)

By Grant, M. A.

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Book Id: WPLBN0004009978
Format Type: PDF Article :
File Size: Pages 6
Reproduction Date: 2015

Title: Stored-heat Assessments: a Review in the Light of Field Experience : Volume 2, Issue 1 (17/12/2014)  
Author: Grant, M. A.
Volume: Vol. 2, Issue 1
Language: English
Subject: Science, Geothermal, Energy
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2014
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Grant, M. A. (2014). Stored-heat Assessments: a Review in the Light of Field Experience : Volume 2, Issue 1 (17/12/2014). Retrieved from http://www.ebooklibrary.org/


Description
Description: MAGAK, 14A Rewi Rd, Auckland 1023, New Zealand. Stored-heat or volumetric assessments of geothermal resources are appealingly simple: the resource being exploited is heat. A stored-heat calculation simply computes the amount of heat in the resource, similarly to computing the amount of ore in an ore body. The method has theoretical support in numerical simulations of resource production. While there are significant unknowns in any resource, some of these can be covered by probabilistic approaches, notably a Monte Carlo method. The Australian Geothermal Reporting Code represents one specification of such stored-heat assessments.

However the experience of recent decades, with the development of significant numbers of geothermal resources, has shown that the method is highly unreliable and usually biased high. The tendency to overestimates, in particular, has led to the reduced credibility of the method. An example is quoted where simple application of the apparently simple rules gives a ridiculous result. Much of the problem lies in the recovery factor, the proportion of the resource that can actually be exploited, where comparison with actual performance shows past values have been in all cases too high, as is the current version of the Australian code.

There are further problems, usually overlooked, in the way that the reservoir volume and cutoff temperature are defined. Differing approaches mean that results between different reports are not comparable. The different approaches also imply unrecognised assumptions about the physical processes controlling reservoir depletion. The failure of Monte Carlo methods is similarly due to unrecognised violation of logical consistency in the use of probabilities.

The net effect of these problems is that the method is not a simple means to generate a rough resource estimate, and it often generates faulty results. Usually, such results are overestimates. Monte Carlo methods do not provide a protection against these errors.

The Australian Geothermal Reporting Code should be used for hydrothermal systems with an average recovery factor of 10%. With this average, results are subject to an error of ±70%. For enhanced geothermal systems (EGS), the recovery factor should be a few percent.


Summary
Stored-heat assessments: a review in the light of field experience

Excerpt
MIT: The future of geothermal energy, 2006.; Garg, S. K. and Combs, J.: Appropriate use of USGS volumetric heat in place method and Monte Carlo calculations, Proc, 35th Workshop on geothermal reservoir engineering, Stanford University, 2010.; Garg, S. K. and Combs, J.: A re-examination of USGS volumetric heat in place, method, Proc, 36th Workshop on geothermal reservoir engineering, Stanford University, 2011.; Grant, M. A. and Garg, S. K.: Recovery factor for EGS, Proc, 37th Workshop on Geothermal Reservoir Engineering, Stanford University, 2012.; Grant, M. A.: Geothermal resource proving criteria, Proceedings, World Geothermal Congress, 2581–2584, 2000.; Lawless, J. and Lovelock, B.: New Zealand's geothermal resource, paper presented at NZ Geothermal Association, 2002.; Lund, J. W., Gawell, K., Boyd, T. L., and Jennejohn, D.: The United States of America country update 2010, World Geothermal Congress paper 0102, 2010.; AGEA AGEG: The geothermal reporting code Second edition, 2010a.; AGEA AGEG: Geothermal lexicon for resources and reserves definition and reporting, 2010b.; Clearwater, E. K., O'Sullivan, M. J., and Brockbank, K.: An update on modelling the Ohaaki geothermal system, NZ Geothermal Workshop, 2011.; GeothermEx: New geothermal site identification and qualification, Consultant report for California Energy Commission PIER report no. P500-04-051, 2004.; Muffler, L. P. J.: Assessment of geothermal resources of the United States – 1978, U.S. Geological Survey, Circular 790, 163p., 1978.; Nathenson, M.: Physical factors determining the fraction of stored energy recoverable from hydrothermal convection systems and conduction-dominated areas, USGS Open-file report 75–525, 1975.; Pálmason, G., Johnsen, G. V., Torfason, H., Sæmundsson, Ragnars, K., Haraldsson, G. I., and Halldórsson, G. K.: Mat á Jar\dhvarma Íslands, (in Icelandic) Orkustofnun report OS-85076/JHD-10, 1985.; Sanyal, S. K., Henneberger, R. C., Klein, C. W., and Decker, R. W.: A methodology for the assessment of geothermal energy reserves associated with volcanic systems, Transactions, Geothermal Resources Council 26, 59–64, 2002.; Sanyal, S. K., Klein, C. W., Lovekin, J. W., and Henneberger, R. C.: National assessment of U.S. geothermal resources – a perspective, Transactions, Geothermal Resources Council 28, 355–362, 2004.; Sanyal, S. K. and Butler, S. J.: An analysis of power generation prospects from Enhanced geothermal systems Transactions, Geothermal Resources Council, 29, 131–137, 2005.; Sarmiento, Z. F. and Björnsson, G.: Reliability of early modelling studies for high-temperature reservoirs in Iceland and The Philippines, Proceedings, 32nd Workshop on Geothermal Reservoir Engineering, Stanford University, 2007.; Stefansson, V.: World geothermal assessment, Proceedings, World Geothermal Congress paper 0001, 2005.; White, D. E. and Williams, D. L.: Assessment of geothermal resources of the United States – 1975, Geological Survey Circular 726, USGS, 1975.; Williams, C. F.: Development of revised techniques for assessing geothermal resources, Proceedings, 29th Workshop on Geothermal Reservoir Engineering, Stanford University, 276–280, 2004.; Williams, C. F.: Updated methods for estimating recovery factors for geothermal resources, Proceedings, 32nd Workshop on geothermal reservoir engineering, Stanford University, 2007.; Williams, C. F.: Thermal energy recovery from enhanced geothermal systems – evaluating the potential from deep, high-temperature resources Proceedings, 35th Workshop on geothermal reservoir engineering, Stanford University, 2010.; Wilmarth, M. and Stimac, J.: Worldwide power density review Proc., 39th Workshop on geothermal reservoir engineering, Stanford University, 2014.

 

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