Geophysical processes and biosphere: article

Аnnotation: In paper results of assessment of the depth of the diagenetic zone and biosphere in the South Caspian basin (SCB) are given based on a complex of more than 400 data (lithological composition and reservoir properties of rocks, temperature, pressure) from 41 onshore and offshore fields, as well as on about 200 isotope-geochemical analyses of gases and oils and hydrochemical analyzes of formation waters. It was established that under conditions of an avalanche sedimentation rate in the Pliocene-Quaternary time and low temperature gradients (15-21 °C/km) an extended diagenetic zone was formed in the SCB. This is confirmed by the nature of the change with depth the physical and mechanical parameters of the rock-fluid system in the SCB (water and gas saturation, porosity and permeability of sediments, temperature and pressure). From the point of view of oil and gas generation processes, the end of the stage of late diagenesis and the beginning of the early catagenetic stage in the SCB is limited by a depth of about 4.5 km, which corresponds of a vitrinite reflectance value of 0.5 % and formation temperature of about 80oC. According to isotope-geochemical parameters, a microbiological activity and biochemical processes in the sedimentary section, the lower boundary of the biosphere is outlined at a depth of about 2-2.5 km below the earth surface, which corresponds to a temperature of 45-50 °C.