The Role of Dolomitization and Clay Rims in Shaping Sandstone Evolution: Insights from the Groningen Gas Field

The Groningen gas field, Europe’s largest onshore gas reservoir, has undergone extensive compaction due to prolonged gas extraction, leading to surface subsidence and seismicity. Understanding the diagenetic processes controlling reservoir quality is essential for managing these risks. This study investigates the role of dolomitization and associated diagenetic alterations in shaping the petrophysical and geomechanical properties of the Rotliegend sandstones. Detailed petrographic analysis, incorporating optical and scanning electron microscopy, reveals that early dolomite cementation significantly reduced primary porosity while preserving intergranular volume (IGV) and enhancing mechanical stability by inhibiting grain rearrangement and compaction during burial. Dolomite cementation was particularly prominent in zones proximal to mudstone interbeds, indicating its strong depositional and diagenetic control. Authigenic clays, including illite, smectite, and chlorite, were found to inhibit late-stage quartz cementation, preserving reservoir quality in specific zones. Burial depth and prolonged thermal exposure intensified quartz overgrowths and illite development, particularly in deeper sections of the reservoir. Clustering patterns among authigenic minerals revealed strong positive and negative associations: Illite, illite-smectite, and chlorite frequently co-occur in fine-grained sandstones, particularly in northern wells, where their abundance reduces pore space and permeability. Conversely, high dolomite content negatively correlates with clay minerals and quartz cement, reflecting the inhibitory role of early dolomitization on subsequent diagenetic mineral development. Quartz cementation plays a minor role in compaction due to shallow burial conditions and the presence of clay rims around grains, which limited growth of quartz cements. Mechanical compaction primarily affected sandstones lacking dolomite, where authigenic clay content and quartz cementation are higher, correlating with higher porosity and permeability than sandstones that are dolomitized. This study highlights the interplay between depositional setting, diagenetic timing, and burial history in shaping reservoir quality and stability. By linking petrographic trends to geomechanical behavior, these findings provide critical insights into mitigating subsurface risks associated with gas extraction in Groningen and analogous reservoirs worldwide.