| Title | Combined Analyses of Hydraulic and Thermal Data at the HDR Test Site Soultz-Sous-Forets |
|---|---|
| Authors | Thomas Kohl & Ladislaus Rybach |
| Year | 1999 |
| Conference | European Geothermal Conference |
| Keywords | Heat flow, non-Darcian flow, HDR, numerical modelling, fractured rock, Soultz-sous- Forets |
| Abstract | During the exploration of the HDR test site Soultz-sous-For& (France) numerous unexpected results have been obtained. This study aims to characterise several findings by highlighting their common characteristics derived from independent measurements. It will especially focus on the data collected so far from temperature logging and on hydraulic experiments. These findings will be related to data from logging techniques and tracer tests as well as to the tectonic situation at Soultz. The HDR reservoir at the Soultz-sous-For& site is targeted in a granitic horst zone bounded by subvertical N-S trending normal faults. The high surface heat flow at HDR test site Soultz-sous-Forets being a main reason for its selection dropped from nearly 150 mW m-í at surface to e25 mW m-í in 2-3 km depth and recovers at greater depth to -70 mW m-í. In the depth range between 2-3.8 km (i.e. the range with low heat flow) numerous hydraulic experiments have been performed which highlighted the importance of far field drainage systems. In this analysis these features will be jointly investigated by numerical models. The results elucidate that the local temperature field can be explained by a convective flow pattern which develops in the area 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. Another clue to the dominant role of the ambient fracture system are provided by the numerical simulations of the numerous multiple level flow rate experiments performed in the GPKl and GPK2 borehole. These short time (te20 days) tests have highlighted the importance of turbulent-like hydraulic behaviour and could be accurately fitted by transient models of simple geometry. Herein, particular attention to the influence of geometry and of far field fault systems was paid. These results allow to derive a conceptual model of the upper reservoir (3000-3800 m) at Soultz with a dominance of the natural fracturation and fault system. It is especially demonstrated that numerical simulation of hydraulic and thermal data can yield a recognition of flow processes and of flow geometries and provides the necessary basis for more elaborated 3-D models which then will allow to predict future HDR performance. This analysis is directed towards a general optimisation of HDR operation parameters and especially to explain data collected from the Soultz site. |