Numerical Simulation of Seismicity Induced by Gas Production—Implications for the Seismic Hazard Assessment

Abstract

AbstractNumerical models reproducing the seismic evolution in gas fields can be utilized to study the characteristics of compaction‐induced seismicity during production and thus derive valuable information for the assessment of the seismic hazard. Here, we present a numerical approach for a Rotliegend gas field in Northern Germany (“reference field”), consisting of the simulation of poro‐elastic stresses within a 3D finite element model. Fault stability is controlled by Coulomb friction, whereas the post‐failure process is implemented using a slider‐block model. The model successfully computes seismic sequences, which reproduce the main characteristics of the observed seismicity in the reference field: the location, the temporal seismic evolution, including the retarded onset several years after the beginning of production, the high prevalence of moderate magnitudes, the observed maximum magnitude and cumulative seismic moment release. The numerical simulations reveal that seismicity‐driving stresses are restricted to the vicinity of fault intersections with the top and bottom of the reservoir, respectively. Slip frequently extends beyond the vertical boundaries of the reservoir, although the failure process is generally self‐arrested outside the reservoir boundaries. The magnitude frequency distribution of observed and simulated earthquakes deviates from the log‐linear behavior frequently assumed in seismic hazard assessments. Instead, the earthquake activity is consistent with a “characteristic earthquake” model, where a fault repeatedly hosts earthquakes with a specific maximum magnitude. Our analysis indicates that production‐induced seismicity is primarily controlled by poro‐elastic stress changes rather than by unknown details of subsurface conditions. This allows for a prognosis of future seismicity and associated hazard.