European concerted action for the support of the hot dry rock geothermal energy R&D activities 1998-2000

• Unité de recherche: PCRD EU
• Numéro de projet: 98.0008-1
• Titre du projet anglais: European concerted action for the support of the hot dry rock geothermal energy R&D activities 1998-2000

Mots-clé (Anglais)

HDR (Hot Dry Rock) integrated data analysis; flow zone analysis; user-friendly software development; modelling hydraulic data; reservoir characterisation; data indexing/archiving

Autre Numéro de projet (Anglais)

EU project number: JOR3-CT98-0313

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 5.1 Nonnuclear energies

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

Coordinator: EEIG HM (F)

Résumé des résultats (Abstract) (Anglais)

Fractures are the key features in any HDR reservoir. The understanding of fracture geometry, properties and behavior is decisive for conceptual models.
Data processing and integrated analysis investigated the effect of the 1993 stimulation injections in borehole GPK1 on fractures and the rock mass around the well using geophysical log data. The long-spaced sonic log identified 9 of these 18 fractures as permeable prior to stimulation. Of 9 fracture horizons that support major flow following stimulation, 6 were permeable prior to stimulation and 5 of these were identified by the long-spaced sonic tube-wave logs. Some 100 or approx. 25% of the 400 natural fractures present in the 500 m of open holein GPK1 showed evidence of permeability after stimulation. The stimulated fractures occur in clusters which is consistent with a conceptual model where the flowing pathways are defined in fracture zones that bound relatively intact blocks. The permeable fractures are thus 'critically stressed' in a Coulomb friction sense. Enhanced UBI log images prove the link between permeability and shearing. All fractures which supported major flow also suffered dislocations of the order of millimetres to centimetres during the stimulations. The mechanism underlying the transmissivity increase is aseismic, and suggest aseismic slip.
Numerical modelling and code development interpreted the hydraulic data of the Soultz reservoir at 3.5 km depth by numerical simulations using the inverse modelling technique. Multiple level flow rate injection/production experiments in GPK1 and in GPK2 identified a complex hydraulic regime. The numerical models allowed excellent fits by non-Darcian flow in the fracture network. The results also identify matrix diffusivity and fracture aperture as the most sensitive parameters. To predict the long term behaviour of the Soultz HDR reservoir, thermal, hydraulic and chemical processes have been taken into account. The results reveal that the local temperature field can be explained by a convective flow pattern which develops in the domain with the highest degree of fracturation. The convection cell can be localised between the top of the Buntsandstein at ~1000 m and a depth of ~3700 m in the granitic basement. A first thermal, hydraulic and chemical coupled model of a fracture in the granite was run using the geochemical code CHEMTOUGH: a 30 years operating time with reservoir fluid injection (65°C) at one end of the fracture and production at the other end was simulated. The calulated precipitation behaviour of minerals is reasonable, whereas the amount of precipitation or dissolution is not yet accurate. A modified version of the geochemical module of CHEMTOUGH is now integrated into the finite element code FRACTure.
With 'Project assistance to the Soultz core team' the documentation and management of the wast amount of Soultz data was implemented. All data and some of the literature on the Soultz project have been assembled on to Compact Discs. In addition, a website for the Soultz project has been implemented. Further work focussed on fracture studies with numerical codes from sources other than the EU project participants (especially by stochastic methods). With an adapted and expanded FracSim3D code all hydraulic stimulation and flow experiments on the Soultz site in the 3000 to 3600 m depth-range have been modelled. The results confirmed the conceptual model of the shallow reservoir at Soultz as a rather 'open' system; the geometrical form of the reservoir conforms well with the shapes of observed microseismic event clouds.
'Direct Support to the Project Operating Team: Co-ordination of Data Analysis and Modelling Efforts and their Interpretation' aided in gaining a fuller understanding of all the mechanisms triggered in the creation and development of an HDR reservoir - in particular of the shallow and deep reservoirs at Soultz. The results on conceptual models of the reservoirs form a part of the final report for the phase 1998-2001 submitted to the CEC.
The project work was performed by D. Bächler, K.F. Evans, Th. Kohl and L. Rybach from the Institute of Geophyics ETH Zurich, and by R.J. Hopkirk (POLYDYNAMICS ENGINEERING, Männedorf) and Th. Mégel (MÉGEL GEOWATT, Zürich).
The investigations and results are presented in the two separate reports. They demonstrate altogether the progress made towards the development of a conceptual model of the Soultz HDR reservoir.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0008-1