Geothermal Exploration in a Greenfield Environment - Seismic Interpretation, Structural Geology, and Geomechanical Modelling for Well Planning in Hagen (Southern Ruhr District, Germany)

The paper mill of Kabel Premium Pulp & Paper, located in the city of Hagen in the southern Ruhr district (Germany) decided to replace its natural gas consumption, necessary to produce heat for the paper drying process, with renewable energy sources. A promising option is the development of the hydrothermal potential of the Massenkalk reservoir at approximately 2600 to 3600 m depth with an expected temperature range of 115 to 150 °C below the paper mill. The exploration concept implies exploration of the Grossholthauser fault and its imprint on the Massenkalk carbonate reef reservoirs. The reservoir rocks were explored by 2D seismic data and by an outcrop analogue study, located about 10 km south of the paper mill, revealing structural geology, facies, and petrophysical information. With a gross thickness of approximately 700 m, a high degree of dolomitization, and an open fracture system oriented parallel to the maximum horizontal in-situ stress orientation, we found sound reservoir properties in the outcrop analogue. Since no deep exploration wells are currently available from the area of interest, the in-situ reservoir quality (i.e., widespread karst systems) is unknown. A 3D geomechanical model was developed based on the acquired 3D seismic data of moderate quality and already available geological information from the region. Results of the model allowed improved well placement design and seismic risk estimation, utilizing the regional transtensional fault system. The main result of the pre-drill modelling campaign, with limited input and calibration data, shows that the targeted faults are nearing critical stress conditions and could be reactivated during fluid circulation within a geothermal doublet system with relatively small stress perturbations when utilizing the transtentional fault system.