Earthquakes often result in damage to buildings and infrastructure and sometimes loss of human lives. Induced earthquakes due to human activities like gas extraction, are the result of fast slip on powder-filled pre-existing faults in the subsurface due to a rapid breakdown of their strength. The physical mechanisms contributing to the rapid failure remain unclear. In this project we will perform experiments at scales of a single rock grain to millions of grains combined with computer models to investigate these weakening mechanisms. Our results will help to better constrain the hazard of induced earthquakes.

Surface subsidence, ground motion and induced seismicity caused by fluid extraction from geological formations frequently have significant technical, environmental and economic impact, such as seen for the Groningen gas field, the Netherlands. For the Groningen gas field, these phenomena are largely driven by reservoir compaction, resulting from gas extraction. However, time-dependent deformation, caused by slow pore pressure equilibration, of the clay- and organic-matter rich, low -permeability formations directly over- and underlying the reservoir may further contribute to subsidence and impact the state of stress on faults in the system. As these formations may transfer stress from weaker to stiffer components of the geosystem, i.e. the reservoir, changes in production rates may impact the magnitude-frequency distribution of earthquakes. Therefore, a microphysical understanding of the mechanisms operating in the over- and underburden formations enveloping the Groningen gas field is needed to further constrain the timescale upon which seismic activity and subsidence will slow down, or halt, after changes in production. We will identify and quantitatively characterise the main mechanisms causing deformation of Carboniferous shales/siltstone and the Ten Boer claystone, directly under- and overlying the Groningen reservoir, respectively, as well as being present at other Rotliegend gas fields in the Netherlands, Germany and the UK. The characteristic timescales, or rates, of the creep processes that operate in these reservoir-bounding shales will be determined, under pressure, temperature and chemical conditions relevant to fluid extraction. The project will provide a basis for improving and extending the predictive capability (currently being developed within the DeepNL programme) needed for evaluating and mitigating long-term hazards related to fluid extraction. With many smaller Rotliegend fields being considered for natural gas, hydrogen or CO2 storage in the future, potentially leading to renewed deformation and/or induced seismicity, the proposed research is also relevant beyond the lifetime of the Groningen gas field.