The object of study is the subsalt Paleozoic complex of the eastern and southeastern Caspian basin. It is noted that the increase of the porosity of the Visean, Serpukhovian, Bashkirian and Moscovian carbonate deposits is often associated with the secondary processes. Active leaching, as well as pervasive fractures and caverns formation, is one of the most important factors in the forming of void space in carbonate reservoir rocks. The authors assumed that there is a relationship between the hypergenesis processes and sea-level fluctuations (transgression and regression), considering that the key moment in the increase in the void space is dissolution during leaching. The formation of the border seas Caspian megabasin on the southeastern part of the East European Platform in the Late Devonian - Early Carboniferous implies the dependence of local sea-level changes on global eustatic fluctuations in the world ocean level. Changes in the porosity coefficient and intervals of increase in secondary porosity were compared with the scheme of relative changes in sea-level and coastline compiled by John W. Snedden and Chengjie Liu according to B.U. Haq, S.R. Shutter и A.M. Al-Qahtani, as well as a detailed comparison with transgressive-regressive cycles of the Upper Paleozoic, identified by J.G. Ogg, G. Ogg и Gradstein, F.M. based on the eustatic curve of B.U. Haq и S.R. Shutter in the research of core data from five wells (Akkuduk 1, Zhagabulak-Alibekmola 4, Zhanazhol 23, Karaton 1, and Tengiz 44).
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