Geomechanical characteristics of gas depletion induced seismicity in The Netherlands

Abstract

Over 190 gas fields have been exploited in The Netherlands and only 15-20% have been associated with induced seismicity. We assess the geomechanical characteristics of stress changes on faults due to gas depletion for 180 producing gas fields in the Netherlands. We confirm findings from earlier generic studies that inter-reservoir offset faults require less reservoir depletion to reach failure compared to bounding and small offset faults. However, the stress changes on the offset faults alone are not sufficient to explain the observed seismicity. We find that the presence of the visco-elastic Zechstein formation probably has a crucial influence on the in-situ stress field in the Dutch subsurface and significantly impacts the fault stability of the gas reservoirs in the Netherlands. By accounting for this influence, our results show remarkable consistency with the observed (non)occurrence of induced seismicity in the Dutch gas fields. A more detailed study taking into account the detailed geological information of reservoir and fault geometry available at the operators and the slip weakening behavior of the frictional strength is required to further refine the predictive power of our analysis.