Numerical and experimental simulation of fault reactivation and earthquake rupture applied to induced seismicity in the Groningen gas field

Abstract

In recent years, earthquakes with magnitudes up to 3.6 occurring in the Groningen gas field (The Netherlands), have resulted in >50,000 damage claims, local unrest and political upheaval. The events are induced by gas production from the Slochteren sandstone reservoir, a 200 m thick, porous rock layer at 3 km depth. Gas production reduces gas pressure, leading to compaction of the sandstone and to changes in the stresses acting on ancient faults cutting the reservoir. When the stresses exceed fault strength, rapid fault slip can occur, producing seismicity. In my thesis, I investigate the conditions under which seismic events originate on such faults, as well as the factors that control event size. I use computer models of the subsurface that include laboratory-measured properties of the different rock formations and faults and that account for fault weakening with progressive slip. The models show that offset of the reservoir layer and changes in rock composition, along pre-existing faults, cause stress concentrations that can initiate seismic slip. For the stress states and fault properties that I investigated, fault slip mostly remains confined to the reservoir. The results contribute to a physics-based understanding of how seismicity works in the Groningen field and help determine the gas pressures at which earthquakes occur, their likely locations, and the event magnitudes. The data obtained and the approach developed offer important input for future seismic hazard assessment, not only in Groningen, but also in the context of geothermal energy production and geological storage of energy or CO2.