| Title | Stress, Slip, and Productivity: Integrated Geomechanical Modeling of the Þeistareykir Geothermal Reservoir – Part 1 Wellbore Scale |
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| Authors | Irene C. Wallis, Drew L. Siler, Anette Kærgaard Mortensen, Guðjón Helgi Eggertsson |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | We present an innovative multi-scale geomechanics analysis of Þeistareykir geothermal field, Iceland. Results were consistent across-scales and a good match to the distribution of reservoir productivity. Þeistareykir is a high temperature (~350°C), volcanic-hosted, two-phase geothermal system with 90 MWe of installed capacity. It is localized by an accommodation zone that consists of west-dipping normal faults to the north and east-dipping to the south. The wellbore-scale analysis, presented herein, focuses on integration of borehole image data to parameterize stress tensor models and reveal the wellbore-scale geologic controls on permeability. The reservoir-scale analysis, presented in a companion paper (Siler et al. 2026), focuses on static and dynamic geomechanical modelling of reservoir-scale faults. Existing interpretations of eleven acoustic borehole image logs (ABI) were reviewed and three selected to constrain the stress tensor and explore controls on permeability through static geomechanical modelling. Detailed reinterpretation of drilling induced damage constrained the azimuth of horizontal stresses and revealed numerous stress rotations. These rotations matched the reservoir-scale dynamic modelling, providing cross-validation. Slip and dilatation tendency results were coherent with fracture characteristics, such as width, mineralization, and openness. First-order mechanical stratigraphy for all eleven wells provided an overall explanatory model for the distribution of feedzones and fracture intensity. Despite these insights, wellbore-scale analysis alone does not account for all feedzone locations and magnitudes. This highlights the central finding of this innovative multi-scale study: fluid flux into or out of a wellbore depends jointly on the features that are intersected and their connection to the reservoir-scale network of permeability. |