Natural stress and fault controls in induced seismicity: what canwe learn from gas depletion in the Netherlands

Abstract

In this paper we present a review of controlling geological, tectonic and engineering factors for induced seismicity associated to gas depletion in the Netherlands and we place experiences from extensive Dutch geomechanical studies in the past decade in the context of recent models for EGS seismicity. The Netherlands is in a mature gas production phase, marked by excellent subsurface structural and stratigraphic characterization. Over 190 gas fields of varying size have been exploited. No more than 15% of these fields show seismicity, which is being closely monitored. Geomechanical studies show that, similar to EGS, largest seismicity is localized on pre-existing fault structures. However, the prime cause for seismicity in gas depletion is differential compaction, whereas in EGS pressure build-up and fluid pressure diffusion along the faults form the prime mechanism. Stress measurements from leak-off pressure and the accumulated pressure development prior to earthquakes consistently show that most faults showing induced seismicity are generally far from critically stressed.