Geochemical characteristics and origin of the inversion in underground hydrosphere of Kolvinsky megaswell

The article is devoted to clarify the nature of the phenomenon in the underground hydrosphere ancient platforms - hydrogeochemical inversion of Kolvinsky megaswell. On the basis of geochemical systematization of groundwaters of Phanerozoic sedimentary complexes (>200 analyzes of macro- and micro-components) the analysis of the deep hydrogeochemical zoning was made, the authors presented the submission concerning the formation of the material composition of the brine and salt water, their genesis. Emphasis is placed to fresh brines of Middle-Tournaisian terrigenous-carbonate deposits. It has been shown that in the inversion hydrogeochemical sections, beginning at the depth of 2-3 km, the salinity of the brines (from 200 to 15 g/dm3), their sulphate and concentration of Br- and I- sharply decrease. This preserves the chlorine-calcium type of water and the degree of metamorphism peculiar for background reservoir brine. The analysis of lithohydrogeochemistry, thermobaric and tectonic data allowed the authors to conclude that the combination of natural conditions of the region most closely corresponds to the concept of condensation. The origin of the inversion is associated with the processes of distillation of water in hydrocarbon gas phase at the depth of 7-9 km in Paleozoic complexes bordering the Baikal basement, followed by upward migration of fluid combined-cycle fault zones and condensation under low temperature and pressure parameters. The problem of inversion of hydrogeochemical phenomena Discussed in the article is one of the fundamental problems of genetic fluidgeochemistry. Research in this area is important in relation to the application, as waters of condensate origin and their derivatives - fresh brines are one of the indicators of oil and gas potential of local structures.