Geophysical processes and biosphere: article

Аnnotation: The paper summarizes and analyzes the results of long-term field and analytical studies, as well as petroleum field data (measurements of temperatures and productivity of wells, analyzes of the physical and chemical properties of hydrocarbons (HCs), the hydrochemical composition of waters, etc.) of onshore and offshore fields and mud volcanoes in the South Caspian basin (SCB). Research in the last 30 years has been carried out using the modern methods: 3D seismic exploration, rock pyrolysis, isotope-geochemical and biomarker studies of organic matter (OM) and HCs, reconstruction of the thermal history of the basin, basin modeling, etc. All these results, taking into account the world experience in studying oil and gas systems of other sedimentary basins, formed the basis for the developed sedimentary-condensation model of the formation of HC fields in the SCB. The model uses the forecast estimates of temperatures and the phase state of HCs at the base of various stratigraphic complexes. It is shown that under hard temperature conditions in the basal layers of the sedimentary strata (temperatures of 250-500 °C) is formed a gas (consisting mainly of methane and water vapor), as a result of the cracking of liquid HCs. The dominant role in the mass transfer of liquid HCs to traps of vapor-gas solutions (with an increased ability to dissolve high-molecular organic matter), accompanied by phase differentiation of the fluid during their ascending migration, has been substantiated. In conditions of a high degree of closure of deeply burial sediments, the main pathways of pulse-injection focused migration of fluids are deep faults, systems of crevices and channels of mud volcanoes.