Induced seismicity in the Groningen gas field – arrest of ruptures by fault plane irregularities

Abstract

Abstract From dynamic rupture simulations, we reveal under which conditions a rupture in the Groningen gas field stops along fault dip or along fault strike after it starts on a fault in the reservoir. The simulations focus on the capabilities of fault plane irregularities to arrest ruptures. Such irregularities can be recognised in sandstone outcrops. Fault planes in the Groningen field, extracted from the 3D seismic data by seismic attribute extraction methods, show similar irregularities. A detailed surface of a major fault plane in the field indicates that steps and jogs of tenths of metres are possible. Although these irregularities are close to seismic resolution and could be partially artificial, we investigated their effect on rupture arrest. For typical current stresses in the Groningen field, jogs and steps of this length scale are found to be remarkably effective to stop ruptures in the reservoir. Also, a significant increase in the fault dip along fault strike can stop these ruptures but a kink in the fault under a constant fault dip not. Including non-planar fault features and pressure diffusion in the Carboniferous, the simulations in this paper follow trends of previous simulations in the literature using 2D planar faults. In particular, the horizontal stress in this formation and the strength of the Carboniferous fault zone are important for rupture propagation. If the fault would have been reactivated in the Neogene or Quaternary and poorly healed in clay-rich parts, rupture propagation into the Carboniferous can only be prevented by jogs of sufficient size and lateral continuity under the present estimate of the horizontal field stress.