Integrated Reservoir Modelling at the European Hot Dry Rock Geothermal Research Project

A suite of numerical modules has been developed, specifically devoted to the understanding of flow through faulted and fractured deep rock masses. The present application concerns the geothermal project developed at the Soultz sous Forêts site (France) in the Rhine graben geological setting. This area seems well suited for such a project, since most of the faults and fractures are nearly optimally-oriented for frictional slip in the present day stress field A 3D structural model is generated from a variety of measurements collected during the 1993-1997 experimental program at depths ranging in 2850 down to 3600 m, involving flow rates up to 70 l/s and injection pressures larger than the minimum stress in the open hole sections. These include induced microsismicity, geophysical logs, flow logs, hydraulic interference tests between wells, 500 m apart, circulation tests, and tracer tests. The numerical procedure is based on a discrete fracture network approach. Flow rules are derived from the cubic law but thermal effects, fracture normal compliance and an irreversible-dilatant shearing mechanism are accounted for. In a forward modeling sense, we show how a suitable parameter configuration can be found, that matched the stimulation treatments, the hydrodynamic measurements, and that can be use in a predictive sense to model the tracer breakthrough curve. An interesting output is that rock shrinkage due to cooling at the re-injection well is likely to happen after some months of circulation. This would be supported by the observed faster tracer breakthrough and a drop in the re-injection pressure.