Print this pageApplication of High Resolution Sequence Stratigraphy and a Quantified Eustatic Curve to Mid-Upper Jurassic Productive Units of the Nyurolskaya Depression, West Siberia, Russia
SAHAGIAN DORK, PINOUS OLEG., and SHURYGIN BORIS
The Nyurolskaya depression is located in the south-eastern part of West Siberia. A large proportion of the petroleum accumulations discovered in this region is concentrated in Callovian-Oxfordian deposits of the Vasyugan Formation. The depositional setting was a low ramp that was periodically flooded and exposed during frequent sea-level changes. As a result, individual producing zones represent a variety of facies and locally demonstrate interruptions and internal heterogeneity. The productive sandstone units range in thickness from 3 to 20 meters which is beyond the usual resolution of the seismic stratigraphic methods which have been applied to the region. Our high resolution sequence stratigraphic analysis based on data from 190 well logs and 64 cores assisted in understanding the depositional histories and preserved facies architecture, and resulted in improvement of the previously existing local and regional correlations. Four distinct depositional sequences were identified including transgressive systems tracts, lowstand complexes, incised valley fills, and highstand deposits. Comparison of the sea-level events interpreted from Nyurolskaya with those of our Quantified Eustatic Curve generated from the Russian Platform (APPG Bulletin, vol. 80, p. 1433-1458, 1996), reveal close correspondence (>90%) of timing of sea-level events. This suggests that eustasy was the main factor controlling sedimentation in the Nyurolskaya depression during that interval (the rate of eustatic changes overwhelmed tectonic subsidence). Thus, the interpretation of eustatically forced sequence boundaries and maximum flooding surfaces permits reliable correlation within the basin. In addition, it supports the utility of our Quantified Eustatic Curve as a tool for correlation.