Oil and gas bearing collectors of deep-lying Lower Carboniferous complexes of the central part of the Dnieper-Donets Basin

Abstract

Deep-seated (at the depths more than 5 km) sedimentary complexes of the most deep depressions of the World (in Ukraine - the central part of the Dnieper-Donets Depression, the Donets Basin, the Black Sea, the Pre-Carpathian foredeep - Carpathians - Trans-Carpathians) which will possibly be the main hydrocarbons sources in the future. So, the studies of regularities of oil-and-gas presence in deep-seated complexes acquires a special strategic significance. Advantageous progression of this line of oil and gas exploration requires the resolution of the complex of problems. Among them the problem of reservoirs prediction is the most complicated. Its solving is possible only on the base of reliable concept of the nature of deep-seated reservoirs. In this respect very durable quartzite-sandstones of Lower Carboniferous of the central part of the Dnieper-Donets depression are of particular interest. Their primary capacity-filtration properties were completely eliminated as a result of catagenetic transformations (quartzous regenerated cementation, grain-jointing without cementation, etc.). Nontheless, 43 fields with about 100 mainly gas-condensate (and also gas, oil and oil-gas) pools at the depths more than 5 km have been discovered here just in this Lower Carboniferous sandstones. They are the substratum for fracture-secondary-porous reservoirs of metasomatic nature. Their formation is connected with ascending migration of (super) deep fluids and their percolation through crystalline basement and sedimentary cover. Reasonable essential reservoir properties are characterized by pillar-tessellated distribution of capacity-filtration properties. High and even super-high current yields of gas and condensate at the depths more than 5 km, together with very changeable distribution of commercial reservoirs, bear witness, on the one hand, to irregularities of metasomatic transformations, and on the other - to absence of direct relationship between productivity and depth.