DIAGENESIS AND RESERVOIR QUALITY OF THE FINNMARK CARBONATE PLATFORM, BARENTS SEA - RESULTS FROM WELL-7128 6-1 AND WELL-7128/4-1/

The four depositional stages of this Late Carboniferous-Permian carbon ate platform show different patterns of diagenesis and porosity contro l because of differences in sediment composition and depositional sett ing. Initial mixed siliciclastic-carbonate strata (Moscovian-Gzhelian) have mostly low porosity. The following shallow-water, photozoan lime stone/dolomite strata (Gzhelian-early Sakmarian) contain multiple zone s of high porosity, reflecting low abundance of both early-marine and late-burial calcite cement, together with early leaching of aragonite and moderate degrees of dolomitization. This combination of porosity-f avourable factors resulted from deposition in a platform-interior loca tion during a time of major sea-level fluctuation and low accommodatio n creation. The overlying interval of open-shelf heterozoan limestone (Late Sakmarian-Artinskian) has uniformly low porosity due to extensiv e late-burial calcite cementation. The final stage of deep/cold-water deposition (mid-Late Permian) culminated in high-porosity, carbonate-p oor spiculite at the top of the platform succession.