Potential for enhanced geothermal systems in low permeability limestones – stimulation strategies for the Western Malm karst (Bavaria)

• First study investigating the potential of hydraulic stimulation in the Molasse basin.
• Stress and leak-off significantly alter stimulation results.
• Multiple fracturing treatments are needed (<10 under favorable conditions).
• If no damage zone exists the well cannot be stimulated sufficiently.
• If a damage zone can be connected to the well it may be stimulated sufficiently.

Hot water from the Malm limestone formation in the central part of the South German Molasse Basin is utilized by a number of geothermal power plants. However, in the low permeability western part of the basin geothermal systems need to be engineered in order to become commercial prospects. This study investigates the potential productivity increase resulting from hydraulic stimulation treatments for reservoir conditions typically found in the western part of the basin using commercial hydraulic fracturing software which is routinely used in the hydrocarbon industry and in addition an open source reservoir simulator. The focus of this study is to evaluate the possible dimensions of generated tensile fractures for different reservoir and stimulation parameters and to show their potential to increase the productivity of an exemplary well in that region. One single stimulation treatment does not lead to an economic productivity increase. The most promising ways to stimulate the considered low permeability well sufficiently for geothermal power production are (1) to connect the well to a higher permeable damage zone around a major fault and (2) to perform multiple stimulation treatments. Water circulation through a second well (injection well) additionally increases the productivity of the production well. Under favorable conditions less than 10 parallel hydraulic fractures need to be developed.