Permeability measurements of fractured granite at 350-450 °C under confining stress

Tatsuya Numakura, Noriaki Watanabe, Kiyotoshi Sakaguchi, Takuma Kikuchi, Noriyoshi Tsuchiya

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

A new concept of enhanced geothermal system, in which a reservoir is created in ductile basement rocks, has been proposed recently. One of possible ways to create a fracture network in a ductile rock is thermal and/or hydraulic fracturing. Although creating fractures may be possible, there is concern about the permeability of the fractured rock after recovery of temperature and/or effective confining stress to the initial state, at which plastic deformation of fracture may occur. The present study has experimentally explored permeability of thermally fractured granite at various combinations of temperature (up to 450 °C) and effective confining stress (up to 90 MPa). It has been found that transition from elastic to plastic deformation occurs at a specific stress level (i.e., the elasticplastic transition stress), depending on temperature. The elastic-plastic transition stress decreases with increasing temperature, for which an empirical equation has been presented. At both elastic and plastic conditions, relations between log permeability and log effective confining stress are linear, and the slope of the linear curves are independent of temperature. Reduction of log permeability by increment of log effective confining stress is larger for the plastic condition. Based on these findings, a way to roughly predict permeability of fractured granite at various combinations of temperature and effective confining stress has been developed. It indicates that the method can provide reasonable prediction results at both elastic and plastic conditions.

Original languageEnglish
Title of host publicationGeothermal Resources Council Annual Meeting, GRC 2015 - Geothermal
Subtitle of host publicationAlways On
PublisherGeothermal Resources Council
Pages329-334
Number of pages6
ISBN (Electronic)9781510817241
Publication statusPublished - 2015
Event39th Geothermal Resources Council Annual Meeting - Geothermal: Always On, GRC 2015 - Reno, United States
Duration: 2015 Sep 202015 Sep 23

Publication series

NameTransactions - Geothermal Resources Council
Volume39
ISSN (Print)0193-5933

Other

Other39th Geothermal Resources Council Annual Meeting - Geothermal: Always On, GRC 2015
Country/TerritoryUnited States
CityReno
Period15/9/2015/9/23

Keywords

  • Brittle-ductile transition
  • Ductile zone
  • ECS
  • Elastic-plastic transition
  • Fracture
  • Granite
  • Permeability

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Energy Engineering and Power Technology
  • Geophysics

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