Coupled THMC processes in Geological Media using Stochastic Discrete Fractured Network. Application to HDR Geothermal Reservoirs
Abstract
Hot Dry Rock (HDR) fractured geological formations, where the assumption of homogeneity is restrictive, are very important thermo-hydrological reservoirs. In the present study, the fractured media was treated as a heterogeneous network of stochastically generated discrete fractures (SDFN). The flow at the fracture scale was derived analytically using Laplace transform. Flow at the formation level was then achieved by combining the solution of the generated individual fractures. To validate the proposed model, one-, two- and three- dimensional problems were investigated. An experimental high pressure water injection test conducted at Soultz-sous-Forêts in Alsace, France, was simulated. Results indicated that the mechanical properties of the media influenced by the injection pressure must be incorporated into the proposed model. In particular, changes in the hydraulic conductivity and the storage coefficient as function of the effective stresses appear to be quite significant. Consequently, the model was extended to take into account the mechanical stresses and was reapplied to the flow injection test. The hydro-mechanical model results showed significant improvements between the simulated and observed pressure time series. Heat extraction from HDR is not limited however to the hydrological phenomena discussed thus far, and therefore, thermal and geochemical processes must be included. A one-dimensional model was developed which takes into account the equilibrium and/or non-equilibrium transport of the chemical species and the water-rock interaction. Thermal processes were modeled using a double porosity approach. The hydrothermal and chemical transport at the formation level was obtained by simultaneously combining the solution of the stochastically generated individual fractures. Finally to demonstrate the applicability of the proposed hydro-thermo-mechanical and chemical (THMC) model, a calcite precipitation example is presented.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H41A0845E
- Keywords:
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- 1009 Geochemical modeling (3610;
- 8410);
- 1822 Geomechanics;
- 1832 Groundwater transport;
- 1847 Modeling;
- 1869 Stochastic hydrology