Carbonate sedimentation within the northern flank of Caspian depression is controlled by tectonic processes and eustatic sea level fluctuations, which significantly affect the reservoir properties. One of the main features of the geological structure of the study area is side ledges with a height of 400 to 1000 m. They are boundaries of different facies zones: relatively deep-sea (depression) of dark-colored clay-carbonate sediments and light colored carbonate rocks of shallow shelf edge, part of which form the barrier reef system. In recent years, a significant amount of data has been collected as a result of exploration in this area. Information can not only complete but also to clarify and develop the established notions about regional structure characteristics of study area.
The article presents the model of the Lower Permian carbonate deposits based on the interpretation of the seismic survey and well logging results with a sequent stratigraphy analysis. Work done allows to make clear about structure of Tokarevskoye and Cyganovsko-Ulyanovskoye fields, as well as to trace the zones of reef development. Based on seismic data, a chain of local elongated structures formed as a result of inherited reef formation extends along the edge of the Lower Permian ledge. Based on the results of well tests, deposits of the Artinian age contain reservoirs confined to the facies zone of the reef. The facies maps were constructed for the Asselian-Sakmarian deposits in the Cyganovsko-Ulyanovskoye and Tokarevskoye areas of the Caspian depression. The sedimentary model, which revealed eustatic cyclicity, was suggested for the carbonate deposits. Analysis of sequence stratigraphy contributed to finding of new perspective exploration objects.
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