Depositional settings and patterns of Chokrak sandy reservoir distribution within Dagestan shelf

Petroelum potential of the Middle Miocene Chokrak sandstones has been proven in the territory of Piedmont Dagestan, where the existence of hydrocarbon traps is predetermined by the presence of high-amplitude folds complicated by faults. The only Inchkhe-More field has been discovered in the adjacent part of the Middle Caspian. Based on top Chokrak structure map, the rest of the Dagestan offshore is a trough slightly affected by tectonic deformations, so hydrocarbon accumulations should be expected in non-structural traps here. There is virtually no well data on the Piedmont Dagestan shelf, therefore it is necessary to reconstruct depositional environments basing mainly on seismic data calibrated to onshore well columns and geological maps. In this work, the Sequence Stratigraphy methodology was applied to predict structural features. Six sequences have been identified within the of Chokrak-Karagan succession. It has been found that by the early Middle Miocene a relatively deepwater depression was situated in the study area; and the Chokrak sedimentary rocks were accumulated there because of sediment supply from the northern sources of terrigenous material and progradation of coastal depositional environments. As a result, the paleo-topography was almost completely levelled-out by the Karagan time. The final geological model of the Chokrak deposit formation made it possible to explain the sand distribution patterns, where the sand volume decreases along the Caspian coastline from northwest to southeast of the study area. Chokrak reservoirs are associated with basin-floor fans in the lower part and shelf sandstones in the upper part of the section. According to the results of sequence stratigraphy analysis, the most promising areas on the Caspian Dagestan shelf with most probable presence of lithological traps are confined to pinch-outs of fan sandbodies of B and G formations in the north and south of the study area