The White Jurassic Limestone (Malm) below the basement of the Southern Bavarian Molasse Basin is rich in hydrothermal fluids with temperatures up to 160 °C. These hydrothermal fluids are used to gain profitable, renewable and sustainable energy. Upon now, this resource is gained and used to produce long-distance heating and electricity in several locations in the greater area of Munich (Moeck & Zimmer 2014). However, there is still an increased risk of not discovering fluids the more south the borehole is situated. A concept to reduce this risk is targeted drilling into fracture or fault zones within the Jurassic Limestone Therefore, the rock-mechanical understanding of the surrounding rock of the drilling is of major importance since stress redistribution, fracture initiation and propagation contribute to the borehole stability and the understanding of the connectivity to the aquifer in the near field of the drilling. These influences, in addition to the in-situ stresses in the White Jurassic Limestone in depths of 4000 m have not been investigated satisfyingly.
As a first approach to gain rock mechanical parameters for the characterization, so-called "analogue samples" are taken. Later, in the subsequent course of the project "Dolomitkluft", drill core samples of the deep geothermal borehole will be available. The sampling of the analogue rocks follows lithostratigraphic characteristics of an existing deep borehole and includes dolomite stones as well as limestones from quarries of the Franconian, Swabian and Helvetic White Jura (Fig. 1a). These rock samples are classified petrographically, associated with their original depth and prepared for laboratory testing such as Uniaxial Compressive Strength (UCS), Tensile Strength (BTS), Ultrasonic Velocity (USV) and Acoustic Emission (AE).
Indirect Tensile strength tests after ISRM 1978 (Fig. 1b), conducted on Dolomite stones of different quarries that differ only little in petrography already show variations in σt of more than 5 MPa. Thus, we expect that with little change in geology or rather petrography along the borehole, big fluctuations in stress change, crack propagation and borehole stability will occur. In addition, UCS, USV and AE Tests will be performed on the same rock types.