Sedimentary heterogeneity and rock mechanical controls on reservoir compaction in the Groningen gas field

Induced seismicity associated with gas production in the Groningen gas field, north-eastern Netherlands, underscores the need for improved forecasting of reservoir compaction and stress redistribution during long-term subsurface exploitation. While current geomechanical models typically assume laterally homogeneous reservoir properties, growing evidence suggests that sedimentary heterogeneity exerts a first-order control on sandstone compactional behaviour. This contribution integrates field-scale petrographic analysis with laboratory geomechanical experiments to quantify how inherited geological heterogeneity governs the mechanical response of the Permian Rotliegend reservoir.

A quantitative petrographic dataset of more than 300 samples from fifteen wells demonstrates that porosity loss across the field is overwhelmingly dominated by mechanical compaction associated with rapid Late Permian burial beneath the Zechstein evaporites, accounting for 55–95% of total porosity reduction. However, compaction efficiency varies systematically with depositional texture and early cementation rather than burial depth alone. Grain size, sorting, lamination, and early dolomite and anhydrite cementation controlled initial packing density and grain-contact geometry, leading to strong spatial heterogeneity in preserved intergranular volume and inferred mechanical properties.

To directly test the mechanical implications of this heterogeneity, we conducted triaxial deformation experiments on Rotliegend sandstones with comparable porosity (~12%) but contrasting cementation styles and clay contents. Experiments performed under reservoir-relevant stress and temperature conditions show that approximately 30% of total strain is inelastic, with time-dependent deformation occurring during stress relaxation phases. Samples containing higher clay contents accumulated the largest inelastic strain, while strongly dolomite- and quartz–anhydrite-cemented sandstones exhibited higher stiffness but still significant non-elastic deformation. Microstructural analyses using SEM reveal grain-scale damage patterns consistent with cement- and clay-controlled deformation mechanisms.

Together, these results demonstrate that reservoir compaction in Groningen is strongly conditioned by inherited sedimentary and diagenetic heterogeneity that is not captured in conventional homogeneous models. Incorporating these controls into geomechanical frameworks is essential for more realistic prediction of reservoir deformation and associated induced seismic hazard during subsurface resource exploitation.