| Title | Pressure Dependent Hydraulic Flow, Heat Transport and Geo-thermo-mechanical Deformation in HDR Crystalline Geothermal Systems: Preliminary Application to Identify Energy Recovery Schemes at Urach Spa |
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| Authors | C. I. McDermott, A. L. Randriamanjatosoa, H. Tenzer, M. Sauter, O. Kolditz |
| Year | 2005 |
| Conference | World Geothermal Congress |
| Keywords | Reservoir, Modeling, Finite-element method, HTM, Heat Flow, Geomechanics, Optimization |
| Abstract | Understanding flow and heat transport pressure and temperature dependent parameters of crystalline rock coupled with geomechanical deformation is particularly important in crystalline geothermal reservoirs. The permeability of these reservoirs is dominated by the fracture systems found within them. In-situ stress conditions have a significant impact on the flow, transport and exchange characteristics of the three dimensional fracture networks. Hydraulic, Thermal and Mechanical coupling (HTM) occurs as a result of the extraction of heat from the reservoirs utilizing high pressure injection and extraction of in situ geofluids. These coupled processes significantly effect the characteristics of heat extraction from the geothermal reservoir. Based on a newly developed and experimentally calibrated geomechanical model, the changes in the flow and transport parameters within crystalline fractures due to changes in local effective stress as a result of the reservoir fluid draw down, water injection and thermal stresses can be estimated. Using a finite element model of the Bad Urach (South West Germany) potential Hot Dry Rock (HDR) geothermal reservoir comprising tetrahedral elements, this mechanical deformation and alteration of fracture parameters is coupled with state of the art fluid parameter functions dependent on pressure, temperature and salinity for heat capacity, conductivity, viscosity and density. The effects of HTM coupled flow and heat extraction on the reservoir characteristics are investigated to assist in the identification of heat recovery schemes for the long term economical operation of the HDR plant. |