Further Development of the Lower Cretaceous Clinoform Model of the North of West Siberia Based on the Sequence Stratigraphy Principles: New Possibilities of Stratification

Abstract

The clinoform concept of the Lower Cretaceous of Western Siberia was and remains the scientific basis for predicting its oil and gas potential. At the same time, new challenges and new technological opportunities require its further development. The basis for this can be a modern model independent methodology of sequence stratigraphy, the essence of which is to divide the stratigraphic section into a succession of systems tracts by mapping of all sequence stratigraphic surfaces. At the same time, the choice of the type of surfaces limiting the sequence is carried out already at the second stage on the basis of the expression of the surfaces in the stratigraphic section or the preferences of the researcher. The wide development of unconformities in the Western Siberian Lower Cretaceous clinoform complex makes it possible to subdivide clinoforms into four systemic tracts: highstand HST, falling-stages FSST, lowstand LST, transgressive TST. The subdivision is carried out by mapping sequence stratigraphic surfaces based on the analysis of stratal stacking patterns. According to the authors, the boundaries of the sequences in this case should be the tops of the TST – the downlap surfaces (DLS), traditionally interpreted as maximum flooding surfaces (MFS). This ensures the consistency of the proposed approach with the clinoform concept. The named clinoforms of Western Siberia can be considered as genetic sequences of the III order. However, the position of facies in their systems tracts is far from always predictable. For further detailing of facies models, clinoforms – III order sequences should be subdivided into clinoforms – IV order sequences, and subdivide them into systems tracts. But the latter are not always mapped by modern seismic method. Special conditions are necessary for this. Therefore, it is proposed at first to subdivide the III order sequences into systems tracts. Then – to map their thicknesses, and to allocate of their depocenters. Further, within the depocenters (under suitable seismogeological conditions), to define IV-order clinoforms – sequences and their constituent system tracts as a basis for mapping reservoirs and hydrocarbons traps.