A reduced degree of freedom model for thermal permeability enhancement in blocky rock

Derek Elsworth, J. Xiang

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

An upwind-weighted finite-element model is presented for the analysis of non-boiling hot dry rock geothermal systems. The model accommodates the essential mechanisms of permeability enhancement or degradation resulting from injection of fluid at a temperature different from ambient. The effects of induced thermal strains and fluid pressures in conditioning both normal and shear displacements in an ubiquitously jointed continuum are accommodated. The mass is idealized as a blocky assemblage where diffusive-advective energy transport in the fracture system is augmented by transient heat supply from intact rock blocks. The true transient nature of both energy supply from the blocks to the percolating fluid and the development of thermal strains within the medium are determined analytically. The local assumption of full lateral restraint coupled with analytical representation of thermal strains renders the nonlinear initial-value problem fully defined in terms of the two dependent variables of fluid pressure and fluid temperature only. Subject to these assumptions, complete fluid-pressure and fluid-temperature histories of large, thermally stimulated reservoirs may be determined effectively and efficiently. Results are presented for both single point injection and dual point injection-withdrawal scenarios to illustrate the possible scope of the method.

Original languageEnglish (US)
Pages (from-to)691-709
Number of pages19
JournalGeothermics
Volume18
Issue number5-6
DOIs
StatePublished - Jan 1 1989

Fingerprint

fluid pressure
Rocks
permeability
Fluids
fluid
rock
hot dry rock
rock block
temperature
geothermal system
conditioning
Initial value problems
freedom
Hot Temperature
Temperature
history
energy
Degradation

All Science Journal Classification (ASJC) codes

  • Renewable Energy, Sustainability and the Environment
  • Geotechnical Engineering and Engineering Geology
  • Geology

Cite this

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abstract = "An upwind-weighted finite-element model is presented for the analysis of non-boiling hot dry rock geothermal systems. The model accommodates the essential mechanisms of permeability enhancement or degradation resulting from injection of fluid at a temperature different from ambient. The effects of induced thermal strains and fluid pressures in conditioning both normal and shear displacements in an ubiquitously jointed continuum are accommodated. The mass is idealized as a blocky assemblage where diffusive-advective energy transport in the fracture system is augmented by transient heat supply from intact rock blocks. The true transient nature of both energy supply from the blocks to the percolating fluid and the development of thermal strains within the medium are determined analytically. The local assumption of full lateral restraint coupled with analytical representation of thermal strains renders the nonlinear initial-value problem fully defined in terms of the two dependent variables of fluid pressure and fluid temperature only. Subject to these assumptions, complete fluid-pressure and fluid-temperature histories of large, thermally stimulated reservoirs may be determined effectively and efficiently. Results are presented for both single point injection and dual point injection-withdrawal scenarios to illustrate the possible scope of the method.",
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A reduced degree of freedom model for thermal permeability enhancement in blocky rock. / Elsworth, Derek; Xiang, J.

In: Geothermics, Vol. 18, No. 5-6, 01.01.1989, p. 691-709.

Research output: Contribution to journalArticle

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