Abstract
Fluid flow in low-permeable carbonate rocks depends on the density of fractures, their interconnectivity and on the formation of fault damage zones. The present-day stress field influences the aperture hence the transmissivity of fractures whereas paleostress fields are responsible for the formation of faults and fractures. In low-permeable reservoir rocks, fault zones belong to the major targets. Before drilling, an estimate for reservoir productivity of wells drilled into the damage zone of faults is therefore required. Due to limitations in available data, a characterization of such reservoirs usually relies on the use of numerical techniques. The requirements of these mathematical models encompass a full integration of the actual fault geometry, comprising the dimension of the fault damage zone and of the fault core, and the individual population with properties of fault zones in the hanging and foot wall and the host rock. The paper presents both the technical approach to develop such a model and the property definition of heterogeneous fault zones and host rock with respect to the current stress field. The case study describes a deep geothermal reservoir in the western central Molasse Basin in southern Bavaria, Germany. Results from numerical simulations indicate that the well productivity can be enhanced along compressional fault zones if the interconnectivity of fractures is lateral caused by crossing synthetic and antithetic fractures. The model allows a deeper understanding of production tests and reservoir properties of faulted rocks.
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Acknowledgments
The authors would like to thank Matthias Klinkmüller for setting up and providing the structural geological PETREL model of the Mauerstetten reservoir. Personal credits go to Wasiu Sonnibare for sharing his expertise while carrying out the time-depth conversion of the geological model and to Dr. David Bruhn for proofreading some critical parts of the manuscript. The structural geological data and the hydraulic setting have been investigated as a part of an ongoing project (0325267B “Geothermie Allgäu 2.0”) which has been funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). Lastly, a special acknowledgement to the GeoEn project (Grant 03G0671 A/B/C) for providing a working platform cross-linking the different scientific fields, e.g. exploration, reservoir engineering, and environmental informatics. Finally, the authors would like to acknowledge three anonymous reviewers for their helpful criticisms which help improving the quality of the manuscript.
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Cacace, M., Blöcher, G., Watanabe, N. et al. Modelling of fractured carbonate reservoirs: outline of a novel technique via a case study from the Molasse Basin, southern Bavaria, Germany. Environ Earth Sci 70, 3585–3602 (2013). https://doi.org/10.1007/s12665-013-2402-3
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DOI: https://doi.org/10.1007/s12665-013-2402-3