Technical Committee Earth Sciences

Development of an Evaluation Matrix of Geological Control Factors for Production-Induced Seismicity in North German Gas Fields

Production-induced seismicity is observed only in some North German natural gas fields, but not in the majority of fields. The causes for the occurrence or absence of seismicity during pore pressure drawdown are investigated for 25 reservoirs. For each field, about 30 parameters related to geology, petrophysical properties and production history are ranked according to their more or less favoring a production-induced seismicity. The resulting evaluation matrix shows that the combination of reservoir thickness, lateral stiffness contrast, field size, and cumulative production parameters can explain the occurrence or absence of seismicity for 88% of the fields studied. In addition, differences in the controlling factors for seismicity between Rotliegend and Zechstein fields become apparent. In the second part of the project, four scenarios with reservoir geometries typical for northern Germany are considered. Using 2D poroelastic finite element modeling, the reactivation potential of faults is investigated. The numerical simulations validate both the qualitative findings from the assessment matrix and the working hypothesis that several factors need to be considered together to understand production-induced seismicity in northern Germany. This validation against observational data is an important step towards more reservoir-specific geomechanical modeling.