Depositional environment and cyclicity of source rocks and reservoirs formation in the Mesozoic-Cenozoic sedimentary basins of the western flank of the Caspian megadepression
Elmira H-M. Aliyeva
As a result of complex investigations using sedimentological, sequence-stratigraphic and log diagram interpretation methods a large amount of data on Mesozoic-Cenozoic sedimentary series in the western flank of the Caspian megadepression (within Middle Caspian and South Caspian depressions) were analyzed. It allowed us to determine the depositional environment in Mesozoic-Cenozoic in the region under study, to conduct a facial zonation of oil-gas bearing complexes, to study stratigraphic architecture of Mesozoic–Cenozoic sequences in the investigated area in a whole as well as separate oil fields, which together revealed facial regularities of reproduction and fossilization of organic matter is one of the important tools in prognosis of space distribution and geometry of oil hydrocarbon deposits. The basic principle used in the research is to study the deposition environment change both in the area and vertical section from the point of view of cyclicity of sedimentation and binding of depositional series to chronostratigraphic scale.
The main thesis defended in the research are: 1. binding of source rocks and reservoirs in the studied Mesozoic-Cenozoic sequence to certain depositional setting and stage of depositional cycles; 2. a key role of high frequency cycles of the closed basins level fluctuations in depositional environment change, which directly influence on the reservoirs architecture and possible formation of regional reservoirs and seals; 3. significant areal and vertical Productive Series depositional environment change, which caused reservoirs heterogeneity; 4. occurrence of large zones of hydrocarbon generation and accumulation in the South Caspian deepwater part.
Using of complex methods for solving of questions arose in the research allowed us to construct a series of facial maps designed for different Productive Series units that allows to trace a dynamics of the areal and time depositional setting change; to construct models of Productive Series reservoirs architecture in certain oil field allowing to understand the reservoirs geometry in the different parts of the basin; 3. to determine the influence of the rapid Caspian Sea level changes on the reservoirs geometry, which is an important input into hydrocarbon deposits search; to predict a possible large hydrocarbon accumulations in the deep water South Caspian part and suppose the existence of possible lateral fluid migration zones to the basins flanks that is a very important for development of the hydrocarbon search strategy in the South Caspian basin.