GoEffective - Geomechanical assessment and well design for geothermal sites based on effective stress: GFZ

GoEffective - Geomechanical assessment and well design for geothermal sites based on effective stress

Duration : 2023-2026

Funding: BMWK

Principle investigators: Oliver Heidbach and Steffi Lammers

Project partners: Michael Drews, Florian Duschl (TU München) Birgit Müller (KIT), Rene Kahnt (G.E.O.S), Mojtaba Rajabi (Univ. Brisbane)

Deep geothermal energy in Germany has the potential to play an important role in order to achieve the climate protection goals - especially in the field of heat transition. For this reason, all possible risks concerning deep drilling, exploration and production have to be further reduced. In this regard, the geomechanical integrity of the subsurface is of crucial importance as it significantly influences reservoir quality, wellbore stability and occurrence of induced seismicity. Apart from geomechanical rock parameters, the geomechanical integrity of the subsurface is mostly controlled by the difference between the minimum principal stress magnitude and the pore pressure, also known as effective stress.

The project is intended to help reduce both, risks and production costs of deep geothermal projects in Germany. Therefore, a comprehensive database on pore pressure and thus effective stresses is supposed to be presented within the World Stress Map project for the first time. Pore pressure data and minimum effective stresses are of utmost importance for well design in deep drilling, especially when optimal mud weight, casing landing depth and wellbore integrity need to be defined. In a next step this database is supposed to be used for developing the new well management toolkit EFFECT. This toolkit should enable to automatically predict minimum effective stresses and wellbore integrity using data on wellbore location and well design only. The toolkit will therefore be validated through an industry partner regarding its suitability and sensitivity with respect to real data. Besides, its manageability will be optimized as well. The availability of a database which covers both, pore pressures and effective stresses as well as the provision of a toolkit which allows for standardized high-quality parameter prediction would not only be unique in the world. It would thereby also provide socio-economic and safety-relevant benefits to the deep geothermal industry in Germany.

GoEffective — Relationship between stress, pore pressure, effective stress and borehole stability. A: Pressure and stress as a function of depth. Sv = vertical stress, FG = fracture gradient, or minimum principal stress, SFG = shear failure gradient, which causes well blowouts, σmin' = minimum effective stress, OP = overpressure, Hyd = hydrostatic pore pressure. B: As A, but stresses and pore pressure are shown as equivalent mud weight. C: Borehole stability as a function of mud weight, stresses and pore pressure. If the mud weight is too low, inflows, borehole collapse or blowouts may result. Too high a mud weight can generate mud losses. *(Drews et al. (2022))*

Referenzen:

Altmann, J. B., T. M. Müller, B. I. R. Müller, M. R. P. Tingay, and O. Heidbach (2010), Poroelastic contribution to the reservoir stress path, Int. J. Rock. Mech. & Min. Sci., 47, 1104-1113. http://doi.org/10.1016/j.ijrmms.2012.08.001

Drews, M.C., Bauer, W., Caracciolo, L., Stollhofen, H., 2018. Disequilibrium compaction overpressure in shales of the Bavarian Foreland Molasse Basin: results and geographical distribution from velocity-based analyses. Marine and Petroleum Geology 92, 37–50. https://doi.org/10.1016/j.marpetgeo.2018.02.017

Drews, M.C., Hofstettter, P., Zosseder, K., Shipilin, V., Stollhofen, H., 2020. Predictability and mechanisms of overpressure in the Bavarian Foreland Molasse Basin: an integrated analysis of the Geretsried GEN-1 Deep Geothermal Well. Geotherm. Energy 8, 20. https://doi.org/10.1186/s40517-020-00175-8

Drews, M.C., Seithel, R., Savvatis, A., Kohl, T., Stollhofen, H., 2019. A normal-faulting stress regime in the Bavarian Foreland Molasse Basin? New evidence from detailed analysis of leak-off and formation integrity tests in the greater Munich area, SE-Germany. Tectonophysics 755, 1–9. https://doi.org/10.1016/j.tecto.2019.02.011

Drews, M.C., Shatyrbayeva, I., Bohnsack, D., Duschl, F., Obermeier, P., Loewer, M., Flechtner, F., Keim, M., 2022. The role of pore pressure and its prediction in deep geothermal energy drilling – examples from the North Alpine Foreland Basin, SE Germany. Petroleum Geoscience 28. https://doi.org/10.1144/petgeo2021-060

Heidbach, O., Rajabi, M., Cui, X., Fuchs, K., Müller, B., Reinecker, J., Reiter, K., Tingay, M., Wenzel, F., Xie, F., Ziegler, M.O., Zoback, M.L., Zoback, M., 2018. The World Stress Map database release 2016: crustal stress pattern across scales. Tectonophysics 744, 484–498. https://doi.org/10.1016/j.tecto.2018.07.007

Müller, B., F. Schilling, T. Röckel, and O. Heidbach (2018), Induced Seismicity in Reservoirs: Stress Makes the Difference, Erdöl Erdgas Kohle, 134(1), 33-37. https://doi.org/10.19225/180106

Reinecker, J., Tingay, M., Müller, B., Heidbach, O., 2010. Present-day stress orientation in the Molasse Basin. Tectonophysics 482, 129–138. https://doi.org/10.1016/j.tecto.2009.07.021

Reiter, K., O. Heidbach, J. Reinecker, B. Müller, and T. Röckl (2015), Spannungskarte Deutschland 2015, Erdöl Erdgas Kohle, 131(11), 437-442.

Seithel, R., Steiner, U., Müller, B., Hecht, C., Kohl, T., 2015. Local stress anomaly in the Bavarian Molasse Basin. Geotherm. Energy 3. https://doi.org/10.1186/s40517-014-0023-z

Ziegler, M. O., Heidbach, O., 2020. The 3D stress state from geomechanical–numerical modelling and its uncertainties: a case study in the Bavarian Molasse Basin. Geothermal Energy, 8(1). https://doi.org/10.1186/s40517-020-00162-z