Characterization of carbonate cements in Upper Jurassic sandstones from the Danish Central Graben, North Sea

Aiming at predicting reservoir quality of Heno Formation sandstones, a study of its main authigenic phases has been carried out. Lowest porosities and permeabilities are found in intensively carbonate cemented sandstones. The carbonate cement can typically be described as either; early concretionary calcite cement, later patchy calcite cement or Fe-dolomite and ankerite overgrowths and cement. The early concretionary calcite cement is volumetrically very important and is typically found in sediments deposited close to sequence boundaries reflecting shell rich detrital composition, slow sedimentation and thus enabling of early diagenesis. Patchy calcite cement has typically formed later by replacement of Carich feldspar and by recrystallization of discrete carbonate particles. Fe-dolomite and ankerite cement is geographically confined and show indications of being related to late hydrothermal fluid flow.