Geomechanics of Fault Stability

The current hazard & risk-assessment for Groningen earthquakes as a result of the gas production is based on reservoir compaction. However, evidence from natural earthquakes around the world as well as interpretations from the updated geophone network in Groningen suggest that earthquakes are an expression of sudden displacement along existing fault planes in the subsurface. This calls for a fault-based seismological model, which is based on the loss of stress equilibrium. Since 2013, a geomechanical research effort is ongoing to assess the stability of faults due to gas production in Groningen. This presentation focused on the early results, covering a conventional Mohr-circle approach and its performance against field observations, and the impact of reservoir formation offset on the stress distribution along a fault plane. It is shown that the generally employed Mohr-circle approach is not appropriate to assess onset of fault slip. Also, it is shown that depletion on one side of a fault is not the most critical condition from a fault stability point of view