Facial-Cyclostratigrapfic Model of the Berrias-Valangin Structure in Western Siberia (North-East of the Sredneobskaya Oil and Gas Province)

In this paper the structural features of berrias-valangin in the north-east of the Sredneobskaya oil and gas province of Western Siberia have been studied. These investigations are based on the detailed analysis of core from 59 wells with a total width of 1700 m involving 150 wells log data. As a result the facies-cyclostratigraphic model of the berrias-valangin structure has been developed. According to this model, 4 regional transgressive-regressive sedimentation cycles were appeared in the berrias-valanginian time. It should be noted, that the sea level rise at the beginning of the second cycle and corresponding drop by the end of I and IV cycles have an eustatic nature. The geological bodies - geoformations with a width of 60 to 220 m and hundreds kilometers long were formed as a result of four transgressive-regressive cycles of sea level fluctuations. Their distal part consist of deepwater shelf silty-pelites, in the middle part the psammites of sandbanks and deltas are dominating, and in the proximal part there are psammites of the bar and silty-pelites of lagoons. The obtained results allow us to justify the litological nature of the lower cretaceous clinoform complexes of Western Siberia. Their boundaries cross the isochronous level of the second cycle transgression maximum, which is have an eustatic nature. It is shown that the boundaries of the clinoform complexes are “sliding” along the edges of the differently aged sand lenses, creating in seismic sections a picture of the wedge-shaped bodies, inclined to the west.