Calcite cementation late, mechanism

The average porosity and permeability values of the oil zone are higher than those of the water zone because of the inhibition of late calcite cementation (calcite type III) and mechanical compaction, owing to oil emplacement within the reservoir. 

The less common late ferroan calcite cement is associated with a minus-cement porosity of <15% (Fig. 13C), indicating that it was precipitated after significant mechanical compaction. It consists of pervasive sparry calcite, which completely filled the remaining reduced intergranular pore space. Fracture-filling calcite cement occurs in grain fractures (Fig. 13D) and rock fractures. It is common below the Avalon Sandstone. 

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