Thermoporoelastic effects during heat extraction from low-permeability reservoirs

Saeed Salimzadeh*, Hamidreza M. Nick, R. W. Zimmerman

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Thermoporoelastic effects during heat extraction from low permeability geothermal reservoirs are investigated numerically, based on the model of a horizontal penny-shaped fracture intersected by an injection well and a production well. A coupled formulation for thermo-hydraulic (TH) processes is presented that implicitly accounts for the mechanical deformation of the poroelastic matrix. The TH model is coupled to a separate mechanical contact model (M) that solves for the fracture contact stresses due to thermoporoelastic compression. Fractures are modelled as surface discontinuities within a three-dimensional matrix. A robust contact model is utilised to resolve the contact tractions between opposing fracture surfaces. Results show that due to the very low thermal diffusivity of the rock matrix, the thermally-induced pore pressure partially dissipates even in the very low-permeability rocks that are found in EGS projects. Therefore, using the undrained thermal expansion coefficient for the matrix may overestimate the volumetric strain of the rock in low-permeability enhanced geothermal systems, whereas using a drained thermal expansion coefficient for the matrix may underestimate the volumetric strain of the rock. An “effective� thermal expansion coefficient can be computed from the drained and undrained values to improve the prediction for the partially-drained matrix.
Original languageEnglish
JournalEnergy
Volume142
Pages (from-to)546-558
Number of pages13
ISSN0360-5442
DOIs
Publication statusPublished - 2018

Keywords

  • Coupled formulation
  • Enhanced geothermal systems
  • Low-permeability rock
  • Undrained thermal expansion coefficient

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