Variations in fracture distribution across Northern Bavaria – Towards large-scale geothermal fracture models

Natural faults and fractures form a critical component of fluid flow in low permeable reservoirs such as tight carbonates for a wide variety of applications including geothermal energy extraction. Fractured systems often control permeability in these reservoirs at the first order where properties of these networks are defined by fracture orientation, intensity, aperture, and connectivity. Accurately quantifying these network properties is vital in generating representations of the fracture networks at reservoir depth.

In regions with limited subsurface data (borehole and seismic), field data and outcrop analogues become an important source for characterising the fracture networks for modelling reservoirs at depth. Outcrops can be used to define several properties of the networks and information on the variation in the fracture distribution across defined areas.

The Franconian Basin is a major tectonic structure in Northern Bavaria containing Mesozoic sediments up to 3500m thick. It is a relatively under-researched region where limited subsurface data is available in comparison to the south in the Molasse Basin where geothermal exploration and production is well established with extensive subsurface datasets widely distributed. Increased geothermal gradients have been identified in Northern Bavaria, including surrounding the major urban areas presenting an opportunity to improve the understanding of the geothermal potential of the region. Several of the identified reservoir units in this region are primarily composed of low permeable carbonates where faults and fractures control primary reservoir flow. These units are also present as outcrop analogues in the Franconian Alb which can be utilised for surface fracture characterisation.

We present results analysing the variations in the fault and fracture systems from across the region captured from 1D measurements and 2D and 3D imaging of quarry and cave outcrops. Using these results, stochastic fracture models of the parts of the region can be generated, providing realisations of the fracture networks which can contribute to assessing the permeability and geothermal potential of the reservoirs in Northern Bavaria.