ROUGH SIZE ESTIMATION OF A THERMALLY FRACTURED ZONE IN AN INFINITE HOT ROCK MASS

Concerning the extraction of geothermal energy from a deep thermal reservoir by the downhole coaxial heat exchanger with a thermally insulated inner pipe proposed by Morita et al, we obtained rough estimates of a size of the fractured zone induced by thermal stresses due to injecting cold water into...

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Bibliographic Details
Published inJournal of thermal stresses Vol. 20; no. 7; pp. 729 - 747
Main Authors Kurashige, Michio, Furuzumi, Mitsumasa, Kamijo, Shinji
Format Journal Article
LanguageEnglish
Published Washington, DC Taylor & Francis Group 01.10.1997
Taylor & Francis
Subjects
Applied sciences
Boreholes
Energy
Exact sciences and technology
Fracture
Geothermal energy
Heat exchangers
Heat transfer
Natural energy
Rocks
Stress concentration
Temperature distribution
Thermal insulation
Thermal stress
Thermal stress
Fractured reservoir
Thermally induced fracturing
Rock mechanics
Stress distribution
Geothermal reservoir
Modeling
Heat transfer
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Summary:Concerning the extraction of geothermal energy from a deep thermal reservoir by the downhole coaxial heat exchanger with a thermally insulated inner pipe proposed by Morita et al, we obtained rough estimates of a size of the fractured zone induced by thermal stresses due to injecting cold water into the hot rock mass through the pipe. We assumed complete spherical symmetry of the temperature and stress fields. At the rough estimation, we considered three typical or extreme cases. (1) The fracturing affects neither the loading capacity of a fractured rock mass nor the temperature distribution within the formation. (2) The fractured zone completely loses its loading capacity and is fully invaded by the borehole water. No disturbance of the fracturing makes any difference in the temperature. (3) The rock formation is assumed to have an appropriately increased fictitious conduction substituted for the heat transfer enhanced by the expected convection within the fractured zone in order to discuss the effects of an occurrence of heat convection within the fractured zone on the temperature and stress distributions and the fractured zone size. As a result, the size of the zone has been estimated to be about ten or more times the borehole radius.
Bibliography:ObjectType-Article-2
SourceType-Scholarly Journals-1
ObjectType-Feature-1
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ISSN:0149-5739
1521-074X
DOI:10.1080/01495739708956126