Examining the effect of fluid flow on the stress and strain evolution of Dutch geothermal reservoirs and the implications for induced seismicity

Abstract

Geothermal energy is expected to produce 23% of the total heat demand in the Netherlands by 2050. As geothermal energy production is known to induce seismicity, risk assessment is crucial for a safe transition to new energy sources. The exact mechanisms inducing seismicity in geothermal reservoirs are, however, very complex and poorly understood. In this thesis, a fully coupled seismo-hydro-mechanical numerical code by Petrini (2019) is adapted to work for a geothermal setting with a set-up that represents the Dutch subsurface. The main goal is to investigate whether this code is suited for studying such a setting and to debug any potential mistakes in the code. Furthermore, the aim is to investigate how stress and strain build-up due to geothermal energy production in the Dutch subsurface. Lastly, a parameter study is executed to examine the effect of operational parameters (injection and production rates) and fault material parameters. The adapted code successfully triggers multiple (seismic) events, giving insight into the relationship between fluid flow and solid deformation during multiple phases: 1) inter-seismic, 2) nucleation, 3) propagation, and 4) post-seismic. The seismicity that was triggered, however, was very mild (ML<2.0), meaning that it would not be felt at the surface. While the code is very efficient in examining the short-term effects (i.e. less than a year) of geothermal energy production, it requires too much computational time to see what happens if geothermal energy were to be produced long-term (i.e. for decades of production). Insights are offered into why the computational time is so long and solutions are offered for future work.