Formation and distribution of gas-oil accumulations in the Paleozoic subsalt deposits of the northern marginal zone of the Caspian depression

We consider the formation and distribution of the gas--oil (gas-condensate) accumulations in the upper Paleozoic subsalt deposits of the northern marginal zone of the Caspian depression. On the basis of a detailed analysis of the geological, geochemical, and other conditions of preservation and conversion of the disseminated organic matter (DOM), we conclude that the principal sources of the hydrocarbons (HC) are the Devonian--Middle Carboniferous oil-source sequences. A result of the complex (stepped) migration of the hydrocarbons from these deposits, accumulations of oil and gas (gas-condensate) were formed in the Middle Carboniferous--Lower Permian deposits. From factual geological--geophysical and geochemical data, and also the results of sampling deep exploratory wells (the West Teplovo area), there is a possibility of discovering tectonically screened deposits of oil and gas in the marginal sectors of the basin, confined to the sunken blocks of structures and associated with faults in the subsalt Paleozoic sequence.