The Features of Generation-Migration Processes in Rapidly Subsiding Sedimentary Basins (The South Caspian Basin as a Case Study)

This paper examines the features of the processes of generation, migration and accumulation of hydrocarbons (HC) under conditions of rapid subsidence and high sedimentation rates based on the example of the South Caspian Basin (SCB). The purpose of the study is ranking the basin according to the degree of openness/closedness of the generation-accumulation system, identifying their distinctive features in the nature and intensity of migration of hydrocarbons and the formation of their industrial accumulations, as well as the isotope-geochemical properties of the organic matter of rocks, oils and gases. To solve the problem, we used both long-term investigations by the author and his colleagues, as well as data published on the problem for other basins of the world. Data processing and graphical plotting were performed using standard computer programs. The massive Oligocene–Miocene source rocks, which are one of the main sources of oil and gas generation in the SCB, are classified as a semi-open system with slow fluid dynamics. A characteristic feature of this system is the widespread development of overpressures and a pulse-explosive form of intrusion into the overlying layers of the fluidized mass (the development of diapirism, mud volcanism, and focused fluid flows). Pliocene deposits, which contain more than 80% of commercial hydrocarbon reserves, belong to an open/semi-open system with favorable conditions for subvertical-lateral migration of HC. Based on the above-mentioned features of fluid-dynamic processes in the section of the sedimentary complex, a model of the SCB was constructed.