Lithogenetic aspects of oil and gas systems formation in the Volyno-Podolia Silurian deposits
Received: September 11, 2018
Institute of Geology and Geochemistry of Combustible Minerals of National Ukrainian Academy of Sciences
Institute of Geology and Geochemistry of Combustible Minerals of the National Academy of Science of Ukraine
Institute of Geology and Geochemistry of Combustible Minerals of National Ukrainian Academy of Sciences

Objective. To elucidate the dynamics of catagenetic processes that occurred in the Silurian sediments against the background of an oil and gas systems formation. Method. The method includes lithology-facies, mineralogical-petrographic, catagenetic, and litho-fluido-dynamic analyses. Results. The spatial-temporal development features of carbonate (bank-reefal facies), argillite (outer and inner shelf), and argillite-carbonate (transition facies) complexes located in the Silurian sediments (profile of boreholes: Lishchynska-1 – Peremyshlyany-1 – Baluchin-1 – Olesko-1) have been determined. The main post-sedimentary transformations of clayey compound rocks consistent in the formation of quartz, calcite, pyrite, as well in the formation of caverns and fractures, which in most cases are combined with thin channels forming a single system, have been studied. It has been established that during the Palaeozoic and Early Mesozoic, the regime of catagenesis of the Silurian sediments of the considered structures was identical. Its further differentiation caused by the individualization of various tectonic block development occurred. In the first catagenetic cycle, the Silurian deposits reached the temperature conditions of the main zone of gas formation. The hydrocarbon (HC) generation centre was located in the western part of the studied profile (the Lishynskaya area), and within the zone of hydrocarbon accumulation a number of lithogenetic reservoirs were localized, the formation of which took place at different catagenetic substages. The main phase of hydrocarbon accumulation is confined to the Late Cretaceous. At this time in the Lishchino-Peremyshlyanskaya area there was a knot of reservoirs pertaining to the heterogeneous morphology, genesis, and the time of their formation. The spatial superposition of these reservoirs and the presence of a multi-directional system of fractures led to the formation of a single fluid system. In the Palaeogene, the accumulated oil and gas accumulations were destroyed as a result of the regional fracture zone development. Hydrocarbon fluids migrated both laterally and vertically with their possible accumulation in structural or lithological traps in the Silurian and Devonian sediments. Scientific novelty. The novel periodization of the Silurian deposits catagenesis has been determined, and the difference in the regime of catagenesis which occurred in various tectonic structures has been established. Practical relevance. The hydrocarbon fluids migration stages and the history of conditions during the formation of the lithogenetic reservoirs have been determined, which allowed assessing specific aspects of the oil-and-gas potential of the Silurian and adjacent sedimentary complexes.

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