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Abstract

Significant pressure and temperature changes can occur within geothermal reservoirs caused by injection and production of fluid which can affect transport properties of the rocks and therefore alter reservoir performance and sustainability. To understand the coupling between transport properties evolution and state variable changes, a complete description of the mechanical behavior of the reservoir is required which should consider thermo- and poroelastic effects. This study aims to integrate transport properties evolution for coupled thermo-hydro-mechanical (THM) process modelling of fluid-bearing reservoirs. This approach is here applied to the geothermal research site of Groß Schönebeck (40 km north of Berlin, Germany) which consists of a doublet system at a target depth of about − 4100 m in which both injection and production wells have been hydraulically stimulated. A 3D reservoir model including the main geological units, major natural fault zones and hydraulic fractures is integrated in the finite-element method-based simulator OpenGeoSys for modelling coupled THM processes during geothermal activity. One challenge of this study is to integrate both hydro-geological and physical complexity to better describe the dynamic behavior of the geothermal reservoir. From the results of the simulation, thermal breakthrough is observed after 18 years of injection and life time of the system has been evaluated as 50 years. Furthermore, a 5.5% increase of porosity around the injection well is observed as well as an increase of the anisotropy ratio for permeability (kz/kxy) of about 2%. These transport properties enhancements lead to a decrease of the thermal breakthrough time (around − 8%) and life time of the system (− 14%) compared to classic thermo-hydro simulations with constant transport properties. The results presented here provide therefore valuable insights for understanding porosity and permeability distributions and evolutions during injection and production of geothermal fluids and related impacts on reservoir performance.