A thermo-hydro-mechanical coupled model in local thermal non-equilibrium for fractured HDR reservoir with double porosity

• Published in: Journal of Geophysical Research Vol. 117; no. B7; pp. 1 - n/a
• Main Authors: Gelet, R., Loret, B., Khalili, N.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.07.2012; American Geophysical Union
• Subjects: Civil Engineering; dual porosity; Earth sciences; Earth, ocean, space; Engineering Sciences; enhanced geothermal system; Exact sciences and technology; fluid loss; heat exchange; mass exchange; thermo-hydro-mechanical couplings; Sandoval County New Mexico; United States; New Mexico; Fenton Hill; stress; skeletons; porosity; finite element analysis; North America; mass transfer; fluid pressure; geothermal reservoirs; circulation; displacements; temperature; Chemical potential; equilibrium; Diffusion; fractures; theory; energy; hot dry rocks; constitutive modeling; Hot Dry Rock; geothermal energy; dual-porous media; local thermal non-equilibrium
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2012JB009161

The constitutive thermo‐hydro‐mechanical equations of fractured media are embodied in the theory of mixtures applied to three‐phase poroelastic media. The solid skeleton contains two distinct cavities filled with the same fluid. Each of the three phases is endowed with its own temperature. The constitutive relations governing the thermomechanical behavior, generalized diffusion and transfer are structured by, and satisfy, the dissipation inequality. The cavities exchange both mass and energy. Mass exchanges are driven by the jump in scaled chemical potential, and energy exchanges by the jump in coldness. The finite element approximation uses the displacement vector, the two fluid pressures and the three temperatures as primary variables. It is used to analyze a generic hot dry rock geothermal reservoir. Three parameters of the model are calibrated from the thermal outputs of Fenton Hill and Rosemanowes HDR reservoirs. The calibrated model is next applied to simulate circulation tests at the Fenton Hill HDR reservoir. The finer thermo‐hydro‐mechanical response provided by the dual porosity model with respect to a single porosity model is highlighted in a parameter analysis. Emphasis is put on the influence of the fracture spacing, on the effective stress response and on the permeation of the fluid into the porous blocks. The dual porosity model yields a thermally induced effective stress that is less tensile compared with the single porosity response. This effect becomes significant for large fracture spacings. In agreement with field data, fluid loss is observed to be high initially and to decrease with time. Key Points Thermo‐hydro‐mechanical equations of fractured media The model is calibrated from the thermal outputs of two HDR reservoirs Simulation of circulation tests at Fenton Hill HDR reservoir