PHYSALIS - PHYsics-based Stability Assessment Leading to Improved Subsurface usage

• Applicant: Dr. Moritz Ziegler
• Subject Area: Geophysics ; Geology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 523456847

The need to meet climate goals and become independent from gas imports highlights the necessity to find alternative solutions to provide the required energy. One option that is locally available in abundance is the use of deep geothermal energy for district heating. A reduction of risk - both economical risk due to borehole failure or lack of public acceptance due to e.g. induced seismicity - is required for a broad application. One of the required key parameter is the initial in-situ stress state of the earth's crust. It is a decisive factor for an assessment whether the rock will break or remain stable during drilling but also later during reservoir operation. Due to the sparseness in available data numerical models are applied to simulate the stress state at prospective locations. However, these models are subject to large uncertainties which decreases their results significance. Project PHYSALIS aims at a reduction of the uncertainties in initial in-situ stress field models. The main reasons for the uncertainties in stress field models are 1) the uncertainties in stress magnitude data records, 2) the (uncertain) heterogeneity of the rock material properties, and 3) the geological model, i.e. the distribution of different rock types in the underground. The impact of these factors on the model uncertainties are evaluated. A reduction of uncertainties has to use additional indirect data since the availability of direct data is limited. Indirect data is information of phenomena which depend on the stres state but are not stress magnitude data. Indirect data originates in tests performed during drilling, observations of borehole behaviour, or observation of seismicity. They are used to assess whether a certain modelled stress state is reliable or not. This allows a weighting of different modelled stress states for their probability given the available data. Eventually, a confined range of stress states with assigned probabilities is available for analysis and allows an improved and more significant interpretation compared to a model without quantified and reduced uncertainties.

• DFG Programme: WBP Position