| Title | Stress, Slip, and Productivity: Integrated Geomechanical Modeling of the Þeistareykir Geothermal Reservoir – Part 2 Reservoir-Scale |
|---|---|
| Authors | Drew L. Siler, Irene C. Wallis, Guðjón Helgi Eggertsson, Anette Kærgaard Mortensen |
| 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 normal faults to the south. The reservoir-scale analysis, presented herein, focuses on static and dynamic geomechanical modelling of reservoir-scale faults. The wellbore-scale analysis, presented in a companion paper (Wallis et al. 2026), focuses on integration of borehole image data to parameterize stress tensor models and reveal the wellbore-scale geologic controls on permeability. Reservoir-scale static geomechanical analysis indicates that the rift zone-parallel (north to north-northeast striking) normal faults, which dip ~75°east and west, are best oriented to control permeability. This result is consistent with the wellbore-scale work. The dynamic modeling determines slip induced by the local stress regime, and the stress and strain effects of that modeled slip. Modeling results show relatively long and narrow permeability ‘sweet spot’ on the western side of the field. This area is coincident with the accommodation zone and includes the most productive wells. Dynamic modelling generated slip-induced counter-clockwise stress rotations at the reservoir-scale. These were co-located with similar stress rotations revealed by drilling induced damage, some of which were coincident with large feedzones. This finding links the wellbore-scale results, reservoir-scale results, and productive permeability and highlights the key innovation of this study. |