Numerical modelling of production-induced stress changes and fault reactivation in Rotliegend gas fields of the North German Basin

Production-induced seismicity is an increasing challenge to the E&P industry. Related poroelastic stress changes in reservoirs with complex geometries, their interference with tectonic stresses and their interaction with faults cannot be sufficiently explained by analytical models. Here, we develop generic numerical models to study production-induced stress changes and fault reactivation in and near compartmentalized gas reservoirs. The models are inspired by features of Rotliegend gas fields of the Northern German Basin but do not describe a specific reservoir. In a linear-elastic model series I, stress changes during pore pressure drawdown are investigated for different model parameters. Field properties leading to an increased tendency of fault reactivation are, among others, a high Biot-Willis coefficient, a locally reduced overburden load and a large reservoir thickness. In model series II a contact surface pair simulating a simplified fault is incorporated and the mechanical response of the contact surface to different schemes for absolute stress developments are simulated. For high friction coefficients the contact surface stays stable with production while for µ<0.6 the contact surface slips after a stage of poroelastic stress increase. Modelling results provide insight into the mechanisms that control production-induced poroelastic stress changes in compartmentalized reservoirs with complex geometries.