Heterogeneity of oil and gas carbonate natural reservoirs: Exempt of intersalt reservoirs in Pripiat basin (Byelorussia)

The Pripiat basin in the southeast of Byelorussia has known Caledonian, Hercynian and Alpian cycles in the geologic history of its sedimentary formation. At the Hercynian cycle, there is a rift characterized by two evaporitic formations, which contain a Devonian carbonate complex. This last was formed in salt active tectonic with basin bottom variations and volcanism at the east of the basin. The petrographical analysis shows that the reservoir rocks are secondary carbonates (calcareous and dolomites) which are being transformed. These secondary processings intensify from the base to the fissured summit of the anticlines, and from western to eastern regions where the volcanic influence increases constantly. They modify the carbonate porosity and form the reservoir rocks. The irregular repartition of those makes them heterogeneous. The dynamic densimetry shows seven rock types with limited open porosity (2 %) between reservoir rocks and false coverings. Using geophysical porosity data allows to stand out the horizontal and vertical repartition of reservoirs and false coverings. There correlation put in a prompt position three different natural reservoirs types: tabular homogeneous in the west, tabular heterogeneous in the center and massif homogeneous in the east of the studied region.