RIPHEAN HYDROCARBON RESERVOIRS OF THE YURUBCHEN-TOKHOM ZONE, LENA-TUNGUSKA PROVINCE, NE RUSSIA

The Siberian Craton covers an area of about 4.5 million sq. km in nort hern Russia, of which up to 3.5 million sq. km may be prospective for hydrocarbons. The craton was consolidated in the Early Proterozoic. an d above the basement granitoids and gneisses is a variable thickness o f sedimentary strata ranging in age from Riphean (Middle-Late Proteroz oic) to Quaternary. Reservoir rocks are known to occur in the interval between the Middle Riphean and the Upper Cretaceous; those of Riphean age have produced oil commercially since 1973. Geochemical data indic ate that the oil within the Riphean reservoir rocks was generated by s ource rocks of Riphean age. Riphean reservoir rocks include both carbo nates and siliciclastics, but commercial volumes of hydrocarbons have only been discovered within the carbonates. Three petroleum-bearing '' provinces'' or megabasins are located on the Siberian Craton: Lena-Tun guska, Lena-Vilyuy and Yenisey-Anabar. The Yurubchen-Tokhom Zone in Le na-Tunguska Province is potentially the most important oil-producing a rea in the craton, and comprises a number of distinct fields. Reservoi r rocks here consist principally of thick Riphean dolomites. Both the development of reservoir characteristics within these dolomites and th e formation of stratigraphic traps are related to an episode of emerge nce and karstification at the end of the Riphean.