Petrographic Heterogeneity and Sandstone Evolution in the Groningen Gas Field: Implications for Reservoir Geomechanics

Fluid extraction from geological formations for purposes of subsurface utilization leads to pore pressure drop in reservoirs and subsequent compaction and seismicity, especially in porous sandstones. Petrography controls the geomechanical properties of the reservoir, crucial for predicting a reservoir's response to fluid extraction and understanding its lateral variability. This study focuses on the Groningen gas field in the Netherlands, addressing its compaction-induced surface subsidence and seismic events resulting from gas depletion. Core samples were examined to delineate spatial petrographic trends and develop a microscale model of the Groningen gas field. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine mineralogical compositions, textural relationships and diagenetic processes. Predominantly constituted of sublitharenites, the sandstones exhibit dolomite and quartz cement as primary authigenic cements. Variations in clay types—kaolinite, illite, and chlorite—were observed, influencing localized pore-filling cementation processes.  Across the field, mineral relations revealed notable trends: depth-related feldspar decrease, correlation between kaolinite and feldspar abundance, and elevated chlorite content towards the northern sector together with the presence of an early quartz cementation phase, which is also observed within aquifer cores. The dissolution of feldspar potentially impacts the structural integrity of the sandstones, while authigenic mineralization appears intricately linked to depositional facies and localized fault-related fluid movements. The timing and extent of these diagenetic processes emerged as pivotal factors dictating sandstone stability within the reservoir. This comprehensive analysis enhances our understanding of Groningen's reservoir heterogeneity, offering critical insights to predict and manage subsurface responses to extraction-induced pressure changes. By providing predictive models, this study facilitates the evaluation of reservoir behavior and aids in mitigating risks associated with compaction-induced subsidence and seismicity.