Enhancing Geothermal Reservoirs - Modelling and Analysis of Hydraulic and Thermal Stimulation (ERiS)

Unlocking the world's vast geothermal energy resources depends on our ability to construct profitable geothermal reservoirs. These act as efficient heat exchangers in the subsurface, allowing heat from a large volume of bedrock to be extracted. The contact surface between the brine, which is to be produced to the surface, and the bedrock largely depends on natural fractures. Technology to improve flow through geothermal reservoirs is crucial for achieving sufficient production to make the resource profitable in larger regions. Hydraulic and thermal stimulation of the reservoir, by pumping water into the reservoir at elevated pressure, have proved to be promising technologies. In this project, integrated numerical modeling and data analysis tools have been developed to further enhance these technologies. In the project, different mechanisms for reactivation and propagation of fractures in the subsurface because of changes in fluid pressure, temperature and stress have been investigated. For these studies, mathematical modeling, numerical simulations, and analysis of seismic data from Iceland were utilized. The project has contributed to development and benchmarking of numerical methods for flow in fractured porous media. Methodology for simulation of thermo-poroelastic media with fractures, including deformation and tensile fracture propagation has been developed. Implementation of these methods are included in the open source platform PorePy, developed at the University of Bergen [https://github.com/pmgbergen/porepy]. Based on simulation studies using the above-mentioned tools, coupled thermo-hydro-mechanical effects in deformation and propagation of fractures and faults because of fluid injection in geothermal reservoirs have been analyzed. The project has also developed methodology for the simulation of propagation of wing-cracks because of slip and deformation of existing faults. Validation of numerical tools is done by comparing to analytical solutions and experimental data. Interpretation of seismic data from HS Orka and ÍSOR related to a period of fluid injection in a geothermal reservoir at the Reykjanes Peninsula in Iceland has been performed, and methodology for efficient analysis of seismic data is developed. Analysis of location of seismic events is done related to this study. Together with information available from previous studies from the field, and information on structural geology, this analysis is used in simulation of fluid injection in the reservoir. This has given more information on mechanisms for reactivation and deformation of fault in the field, which in turn has contributed to better understanding of observation data.

- innovative methdology for modeling and analysis of hydraulic and thermal reservoir stimulation - open source software - development of several new research projects which expand and builds on scientific results from the project - strengthening of the national research competence in modeling of analysis of hydraulic and thermal stimulation of geothermal reservoirs - strengthening of interdisciplinary and intersectoral collaboration on geothermal energy research - improvement of modeling capabilities for coupled thermo-hydro-mecanical processes in porous media, relevant for a range of subsurface applications related to injection and extraction of fluids Most of the publications documenting scientific results from the project are accompanied with the related open source software to ensure transparancy in research and allow other researchers to build on the results of the project.

Unlocking the world's vast geothermal energy resources depends on our ability to engineer profitable geothermal reservoirs, characterized by high permeability corresponding to distributed contact area between mobile fluids and reservoir rock. Geothermal resources are typically situated in igneous rocks, where the permeability of the reservoir mainly is due to discrete fractures. Hydraulic and thermal stimulation to improve the permeability of the formation by fracture opening, creating an Enhanced Geothermal System (EGS), are identified as decisive technologies in future exploitation of deep geothermal energy. Improved engineering decisions in stimulation and operation of geothermal reservoirs are closely related to understanding of subsurface dynamics when different physical processes and the underlying fractured structure of the reservoir strongly interact. Integrated numerical modelling and data interpretation tools that can identify governing mechanisms and forecast reservoir response to hydraulic stimulation are in their infancy, but will be crucial in developing sustainable and commercially competitive solutions for worldwide exploitation of deep geothermal energy. In this context, the ERiS project focus on development and integration of new analysis methods on the observational microseismic data and corresponding specialized state-of-the art numerical modelling techniques. Specifically, we will devise workflows to combine operational data (injection pressure, injection volume and temperature), interpreted data like magnitudes location and source types of microseismic events, and numerical modelling of flow in and deformation of the fractured formation. Basic research into processes that are insufficiently understood, such as fracture slip and opening due to thermal effects, supplements this activity.