A Geomechanical and Seismological Model for Production-Induced Seismicity at Groningen Gas Field

The Groningen Field in The Netherlands has been producing gas since 1963. Seismic events in this area have been observed since 1991. The objective of this work is to utilize advanced geomechanical modeling to (i) characterize subsurface behavior related to production-induced fault reactivation, (ii) evaluate alternate production strategies to help manage subsurface stresses to reduce fault slippage which can lead to seismicity, and (iii) integrate geomechanical results with a seismological model to forecast seismicity attributes. We utilize a 3D multi-scale modeling framework that includes a global model to capture full-field phenomena and three sub-models for regions with observed seismic activity which honor conditions of the global model, but also include explicit modeling of multiple faults. This approach considers the following features: i) irregular stratigraphy and fault surfaces including offsets of layers across faults, ii) variable reservoir rock properties according to porosity changes, iii) non-uniform depletion from reservoir simulations, iv) relaxed deviatoric salt stresses at start of production, v) salt creep effects during production, vi) Biot coefficient effects for reservoir rocks, and vii) Coulomb friction behavior to capture slippage along faults. The sub-models include nearly all mapped faults, with approximately 150 faults in each sub-model. The predicted subsidence and reservoir strains from the full-field global model match well with corresponding field data without need for calibration of material properties. Model results show that the fault offset is a key factor for production induced fault reactivation leading to more slip on more faults. Initial seismological model results based on slip data show good correlation with observed seismic activity rate. The use of quasi-static geomechanical models for predicting seismicity attributes is an evolving field and alternative correlations are being considered.