Thermal recovery from a fractured medium in local thermal non-equilibrium
Article first published online: 15 NOV 2012
Copyright © 2012 John Wiley & Sons, Ltd.
International Journal for Numerical and Analytical Methods in Geomechanics
Volume 37, Issue 15, pages 2471–2501, 25 October 2013
How to Cite
Gelet, R., Loret, B. and Khalili, N. (2013), Thermal recovery from a fractured medium in local thermal non-equilibrium. Int. J. Numer. Anal. Meth. Geomech., 37: 2471–2501. doi: 10.1002/nag.2145
- Issue published online: 11 SEP 2013
- Article first published online: 15 NOV 2012
- Manuscript Accepted: 15 AUG 2012
- Manuscript Revised: 2 AUG 2012
- Manuscript Received: 28 FEB 2012
- enhanced geothermal system;
- hot dry rock;
- coupled problems;
- thermal stress;
- local thermal non-equilibrium
Thermal recovery from a hot dry rock (HDR) reservoir viewed as a deformable fractured medium is investigated with a focus on the assumption of local thermal non-equilibrium (LTNE).
Hydraulic diffusion, thermal diffusion, forced convection and deformation are considered in a two-phase framework, the solid phase being made by impermeable solid blocks separated by saturated fractures. The finite element approximation of the constitutive and field equations is formulated and applied to obtain the response of a generic HDR reservoir to circulation tests. A change of time profile of the outlet fluid temperature is observed as the fracture spacing increases, switching from a single-step pattern to a double-step pattern, a feature which is viewed as characteristic of established LTNE. A dimensionless number is proposed to delineate between local thermal equilibrium (LTE) and non-equilibrium. This number embodies local physical properties of the mixture, elements of the geometry of the reservoir and the production flow rate. All the above properties being fixed, the resulting fracture spacing threshold between LTNE and LTE is found to decrease with increasing porosity or fluid velocity. The thermally induced effective stress is tensile near the injection well, illustrating the thermal contraction of the rock, while the pressure contribution of the fracture fluid is negligible during the late period. Copyright © 2012 John Wiley & Sons, Ltd.