Local variations in stress magnitude and $S_{Hmax}$ orientation in the Eastern Bavarian Molasse Basin: an integrated case study using legacy well data, stress measurements, and geomechanical analysis

The Eastern Bavarian Molasse Basin is used for geothermal energy, natural gas, and hydrogen storage, making constraints on the present-day stress field essential for assessing borehole stability and fault integrity. We integrate borehole breakout (BO) observations from 70 wells with formation integrity tests (FITs), an extended leak-off test (XLOT), drilling-mud pressures, RACOS® measurements, and geomechanical constraints to characterize stress orientation and magnitude. Oriented four-arm caliper data from 20 wells reveal BOs in 19 wells. The results confirm a regional N–S-oriented maximum horizontal stress ($S_{Hmax}$) but also document local stress rotations of up to 70–90° within the Aquitanian and Chattian. These rotations are associated with fault displacement, structural geometry, and the juxtaposition of mechanically contrasting units, indicating that mechanical heterogeneity can be as important as fault-related effects for local stress orientations. The XLOT at 1484 m TVD constrains $S_{Hmin}$ to approximately 28.2 MPa (~ 19 MPa/km), while S$_V$ is 33.7 MPa. Depending on pore pressure and XLOT uncertainties, $S_{Hmax}$ ranges from 34.1–42.9 MPa, consistent with an independent frictional-limit estimate of 32.4–44.8 MPa, resulting in a strike-slip regime close to normal-faulting with relatively low differential stresses. ... mehrBO formation at approximately 400 m, is facilitated by low strength. The value of integrating heterogeneous legacy datasets within a consistent geomechanical framework, providing a transferable workflow for stress characterization in mature hydrocarbon fields is demonstrated. The suggested low differential stresses in the uppermost 1.5 km provide favorable conditions for subsurface utilization of Eastern Bavarian Molasse Basin with a low likelihood of inducing significant seismicity.