The diagenetic impact on reservoir sandstones of the Heno Formation in the Ravn-3 well, Danish Central Graben, Denmark

The Upper Jurassic Heno Formation in the Ravn-3 well is the deepest producing sandstone reservoir in the Danish North Sea. A combined approach including petrography, geochemistry, porosity and permeability analysis and core description have been achieved to investigate variations in diagenesis up through the formation and how post-depositional changes impacts the sandstone reservoirs. Three depositional environments characterize the reservoir sandstones: lower shoreface, middle shoreface and foreshore. Results show that the reservoir potential of the sandstones predominantly depend on occurring digenetic phases and not depositional environment. The dominating diagenetic phases are eogenetic microcrystalline quartz, mesogenetic precipitation of illite, extensive mesogenetic quartz overgrowth and extensive Fe-dolomite and ankerite cementation. The different diagenetic phases are present in all three depositional environments. Diagenesis had a major impact on either preserving or destroying porosity, but did in all cases highly reduce the permeability. The different diagenetic phases can be recognized in the Ravn-1 well and in less degree in the Ravn-2 well.