Diagenesis and reservoir quality of the Finnmark carbonate platform, Barents Sea: results from wells 7128/6-1 and 7128/4-1

The four depositional stages of this Late Carboniferous-Permian carbonate platform show different patterns of diagenesis and porosity control because of differences in sediment composition and depositional setting. Initial mixed siliciclastic-carbonate strata (Moscovian-Gzhelian) have mostly low porosity. The following shallow-water, photozoan limestone/dolomite strata (Gzhelian-early Sakmarian) contain multiple zones of high porosity, reflecting low abundance of both early-marine and late-burial calcite cement, together with early leaching of argonite and moderate degrees of dolomitization. This combination of porosity-favourable factors resulted from deposition of a platform-interior location during a time of major sea-level fluctuation and low accommodation creation. The overlying interval of open-shelf, heterozoan limestone (Late Sakmarian-Artinskian) has uniformly low porosity due to extensive late-burial calcite cementation. The final stage of deep/cold-water deposition (mid-Late Permian) culminated in high-porosity, carbonate-poor spiculite at the top of the platform succession.