The aim of this article is the identification and characterization of complex factors acting simultaneously on forming large sized reservoirs in the deep South Caspian Basin, as well as the development of a model based on a combination of synchronous natural processes of the formation of hydrocarbon deposits. The article analyses reasons for high layer pressures in the hydrocarbon fields of the South Caspian Depression (SCD), impacting factors. The tectonic factor and density-barometric model can become the main criterion for selection of priority projects for exploration and site selection for drilling wells. Obtained results allow conducting effective studies of the exploration and development of oil and gas condensate fields in the SCD area. El objetivo de este artículo es la identificación y caracterización de los complejos factores que actúan en la formación de depósitos de gran tamaño en lo profundo de la cuenca al sur del Mar Caspio, al igual que el desarrollo de un modelo de formación de depósitos de hidrocarburos basado en la combinación de procesos naturales sincrónicos. Este artículo analiza las causas de la presión de las capas altas en los campos de hidrocarburos ubicados al sur de la depresión cáspica y sus factores de impacto. Además, se propone el componente tectónico y el modelo de densidad barométrico como los criterios más importantes para la selección de proyectos prioritarios de exploración y la escogencia de lugares para perforación de pozos. Los resultados obtenidos permiten realizar estudios de exploración y desarrollo en los campos de petróleo y gas condensado en el sur de la depresión cáspica.

The South Caspian Basin (SCB), including the Lower Kura Depression (LKD), was one of the deep‐sea basins of Tethys before the Late Palaeogene. During the Late Palaeogene, due to the convergence of the Iranian‐Afghan and Anatolian plates with the Eurasian Plate, the SCB was transformed into a marginal sea. By the end of the Miocene, the Arabian Plate converged between Anatolian and Irano‐Afghan, which contributed to fold deformations of north‐eastern orientation in the north‐western part of the Iranian‐Afghan Plate. It led to the development of the western side of SCB and drainage of Kura Depression; since then, the LKD became a western onshore continuation of SCB. A compressive stress regime, established there since the end of the Miocene, directly influenced the structures development process in LKD and Baku Archipelago (BA). Although LKD is located onshore and its eastern edge belongs to SCB west board, together with BA they form a single structural and tectonic zone, which is evidenced by the evolution, spatial orientation of local structures and anticlinal zones. To establish the correlation of the evolution features of LKD and BA, we performed the palaeoanalysis on the basis of reconstructed palaeoprofiles for several LKD and BA structures. From palaeoprofiles, we constructed diagrams of fold growth intensity. The results of the correlation of these diagrams indicate at the consedimentational and continuous character of the development of structures in both zones (except for the buried structures) but featuring different intensity at different intervals of geological time. During the formation time of the Lower Production Series (LPS), both zones were characterized by a relatively rapid growth of the folds. At the time of formation of the Upper Production Series (UPS), Absheron‐Aghjagil structures growth intensity was roughly the same but lower than that of LPS. The most intense growth of folds in both zones occurred in Quaternary time.

We study the mechanisms of migration and spacial distribution of hydrocarbon deposits along a regional 1000 km long SW - NE seismic cross section of the South Caspian Basin. A retrospective 2D geological simulation of basin subsidence and sediment filling history is performed taking into account accompanying processes of thermal and catagenetic transformations of organic matter, and subsequent migration and accumulation of hydrocarbons. The start of the basin opening with accumulation of considerable sedimentary mass can be dated as middle Mesozoic (Triassic or Jurassic), and hydrocarbon prone horizons can now be located at depths of 12 km. The hydrocarbon saturation of the Pliocene Productive Series is of epigenetic (allochtonous) nature, which is also confirmed in literature by geochemical data from mud volcanoes and by other facts. Geochemical age, depth of provenance and reworking degree of hydrocarbons point at generation sources in Mesozoic (gas) and Paleogene-Miocene formations (oil) with only subordinate participation of the lower "Productive Series" Pliocene suites. The dominant migration pattern of fluids is interformational (interstratal) intermittent injective subvertical flow along disjunctive planes, zones of increased fracturing and loose rocks, diapir intrusion contacts, eruptives of mud volcanoes, lithofacial unconformities and other structures, breaking the rocks continuity. This implies the possibility of commercial-scale accumulations of hydrocarbons at ultra high depths, if trap structures of sufficiently large sizes are available, comparable with already discovered giant oil and gas fields (Shah-Deniz, Azeri-Chirag-Gyuneshli etc).

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