Fracture variability of the Muschelkalk aquifer of northern Switzerland and Wutach Gorge (DE); implications for permeability, Geothermal and CO2 storage potential
Project lead: Alannah C. Brett1,
Team: Anindita Samsu1, Jefter Caldiera1, Ayoub Fatihi1
Collaborators: Larryn W. Diamond2, and Herfried Madritsch3
1 Deformation and Tectonics Group, Institute of Earth Sciences, University of Lausanne, Switzerland
2 Rock-Water Interaction Group, Institute of Geological Science, University of Bern, Switzerland
3 swisstopo, Switzerland
Switzerland aims to reach net-zero CO2 emissions by 2050 (BAFU, 2021). This project is inspired by the need to implement geological storage of CO2 and geothermal heat mining to help achieve this aim. This in turn requires reservoir properties to be assessed both locally (at sub-seismic or meter scale) and regionally. The structural and permeability architectures of the target reservoirs are essential input for numerical models that can be used to assess storage and production potential, minimize fluid injection and extraction uncertainties, and reduce exploration risks (Alt-Epping et al., this meeting). The Schinznach Formation within the Middle Triassic Muschelkalk Group hosts the Muschelkalk aquifer, one of the key potential aquifers for gas storage and hydrothermal geothermal systems identified in Switzerland (Chevalier et al., 2010). Whereas its matrix permeability is relatively well known (Diamond et al., 2019), the magnitude and distribution of its fracture permeability and the structural controls on these fractures are poorly understood.
This study aims to assess the style and intensity of natural fracture networks in the Schinznach Formation at sub-seismic (or meter) scale and to describe and explain their regional variability. This ongoing work contributes regional insight into fracture networks in support of a proposed pilot CO2 injection test into the Schinznach Formation via an existing exploration borehole at Trüllikon in northern canton Zurich (see Madritsch et al. and Diamond et al., this meeting). A feasibility study (Diamond et al., 2023) assessed the reservoir properties at Trüllikon by building digital models of discrete fracture networks (DFN) and computing their permeabilities from a combination of rock-matrix properties, vertical drill hole fracture logs, a horizontal fracture log from another nearby drill hole, and results from hydraulic tests. The DeTect group project draws comparisons between these results and new field data from outcrops in the Wutach Gorge of southern Germany in terms of fracture network variations.
The Wutach Gorge is located in the Tabular Jura and provides accessible cliff exposures through the Muschelkalk aquifer along 5–12 km-long transects in E–W and N–S directions, partly crossing regional fault strands of the Freiburg–Bonndorf–Bodensee Fault zone. This works will improve the understanding of the lateral variability of sub-seismic scale structures and fracture networks within the Muschelkalk aquifer, including how they are influenced by regional structures. Outcomes should provide a more robust basis for future exploration for both CO2 storage and geothermal energy.
References
Chevalier, G., Diamond, L. W., & Leu, W. (2010). Potential for deep geological sequestration of CO2 in Switzerland: a first appraisal. Swiss Journal of Geosciences, 103, 427-455.
Diamond, L. W., Alt-Epping, P., Brett, A.C., Aschwanden, L. and Wanner, C. (2023) Geochemical–hydrogeological study of a proposed CO2 injection pilot at Trüllikon, Switzerland. Report 2023-7 submitted to the Swiss Geological Survey (swisstopo). Rock Water Interaction, University of Bern, 87 pp. https://doi.org/10.5281/zenodo.10938102
Diamond L.W., Aschwanden, L., Adams, A., and Egli, D. (2019) Revised potential of the Upper Muschelkalk Formation (Central Swiss Plateau) for CO2 storage and geothermal electricity. Slides of an oral presentation at the SCCER-SoE Annual Conference at EPFL-Lausanne, 4th Sept. 2019. 13 pp. http://static.seismo.ethz.ch/sccer-soe/Annual_Conference_2019/AC19_S3a_08_Diamond.pdf
BAFU (2021) Switzerland Long-Term Climate Strategy. 4 pp. https://www.bafu.admin.ch/dam/bafu/en/dokumente/klima/fachinfo-daten/langfristige-klimastrategie-der-schweiz.pdf.download.pdf/Switzerland’s Long-Term Climate Strategy.pdf