Fracture system influence on the reservoirs rock formation of Ordovician-Devonian carbonates in West Siberia tectonic depression

During the Paleozoic period from the beginning of the Cambrian to the end of the Carboniferous in the boundaries of the West Siberia tectonic depression there occurred the sea, where the carbonate platforms were formed by the limestones accumulation. All the area at the end of the Carboniferous period was turned to land. Resulting from Gertsynskaya folding in the times of Permian - Triassic the formed deposits were folded and denudated to a considerable extent. Besides, the reservoir rocks of the crust of weathering including redeposited one, were formed as a result of hypergenesis, during the continental stand of the area in the near-surface zone. A new geological prospecting unit has been suggested which underlies these crusts of weathering and formed during fracture tectonic processes with hydrothermal-metasomatic limestones reworking and the processes of hydrothermal leaching and dolomitization. So, in the carbonate platforms the system of fissure zones related to tectonic disturbance was formed. This has a dendrite profile where the series of tangential, more thinned fractures deviate from the stem and finish in pores and caverns. The carbonate platforms formation in the West Siberia tectonic depression has been analyzed, their dynamics and gradual increasing from the minimal in Ordovician and Silurian to maximal at the end of the Late Devonian has been shown

Localization of carbonate platforms in ordovician formations of West-Siberian geosyneclise

The relevance of the research lies in the need to increase facilities for searching oil and gas fields, one of which is a carbonate platform in the pre-Jurassic formation of West Siberia. The discovery of a number of oil and gas fields: Urmanskoye, Archinskoye and several others, are related to carbonate platforms on the territory of West Siberian geosyneclise (WSG). The aim of the research is to consider the conditions of formation of the Ordovician depositions of West Siberian geosyneclise for establishing in its territory the sites for the formation of carbonate rocks (carbonate platforms), which are transformed into rock-collectors at the appropriate studying by hydrothermal leaching and hydrothermal dolomitization. The fissure-metasomatic zones of hydrothermal study of carbonate rocks are formed. They underlie the area zones of formation of reservoir rocks in the regions of the Paleozoic formations discharge on the pre-Jurassic surface, or zones of oil and gas horizon of the contact zone, contact areas of Paleozoic (pre-Jurassic) and Mesozoic deposits. Research methods: lithological, paleontological, paleogeographic, tectonic. On the basis of complexity of the research methods by the previous researchers, the WSG territory is divided into 23 structural-facial districts (SFD), with a characteristic set of lithostratigraphic units (sweet, thick) and paleontological substantiation of the age. By the results of the study the authors have reconstructed the paleo-geographic conditions, conditions of accumulation and distribution of precipitation in the early and middle-late Ordovician time. The greatest attention is paid to the establishment of formation areas of carbonate rocks prospective for forming reservoir rocks. The tectonic analysis allowed comparing the phases of development of carbonate platforms of early and middle-late Ordovician age for determining the tectonic movements that promote the increase or reduction of carbonate platforms. Results. The paper introduces the information on distribution of lower-, middle-upper Ordovician deposits in the territory of WSG. The authors reconstructed the conditions of sedimentation during the Ordovician period, built schematic paleogeographic maps of early and middle-late Ordovician age, and a complex map of distribution of the identified carbonate platforms of early and middle-late Ordovician age. The conclusions were made on the tectonic history of WSG during the Ordovician, in particular the manifestation of the transgressive phases in the zone of formation of the carbonate platforms of the Ordovician age

Lithology and features of formation of Cambrian deposits in South-East part of the West Kiberian geosyneclise

In the South-Eastern part of West-Siberian geosyneclise in recent years the spread of the Cambrian deposits was observed on larger territory than it was considered before. The aim of the research is to study lithological composition, conditions of formation and accumulation of Cambrian formations and to identify the types of rocks that may be associated with the opening of oil and gas fields. Methods of work: The authors have applied the paleontological methods for determining organic residues studying which the early Cambrian age was determined for the rocks exposed by drilling; lithofacial research methods, which were used to determine the conditions of formation of the lower Cambrian sediments, land and distribution zoning of the revealed lithological types of rocks within the studied area. Results: The formation of the carbonate platform deposits, started in the late Wend in the South-Eastern part of West-Siberian geosyneclise, continued during the early Cambrian. The territory of carbonate platform grew at first but to the end of the early Cambrian the carbonate platform ceased to exist. The carbonate platforms deposits are represented by sedimentary Dolomites, which grade to relatively deep-water deposits in the East and in the West. Further works may establish the development areas of the carbonate platform deposits in the Northern direction from the area studied

Localization of carbonate platforms in ordovician formations of West-Siberian geosyneclise

Актуальность исследования заключается в необходимости увеличения объектов для поиска месторождений нефти и газа, одним из которых являются карбонатные платформы в доюрских образованиях Западной Сибири. С карбонатными платформами на территории Западно-Сибирской геосинеклизы (ЗСГ) связано открытие ряда месторождений нефти и газа: Урманского, Арчинского и ряда других. Цель работы: рассмотрение условий формирования ордовикских образований Западно-Сибирской геосинеклизы с целью установления на ее территории участков формирования карбонатных пород (карбонатных платформ), которые при соответствующей проработке процессами гидротермального выщелачивания и гидротермальной доломитизации преобразуются в породы-коллекторы. В результате формируются трещинно-метасоматические зоны гидротермальной проработки карбонатных пород, которые подстилают площадные зоны формирования пород-коллекторов по участкам выхода палеозойских образований на доюрскую поверхность или зоны нефтегазоносного горизонта, зоны контакта палеозойских (доюрских) и мезозойских отложений. Методы исследований: литологический, палеонтологический, палеогеографический, тектонический. На основе комплексации методов исследований предыдущими исследователями, территория ЗСГ подразделена на 23 структурно-фациальных района (СФР), с характерным набором литостратиграфических подразделений (свит, толщ) и палеонтологическим обоснованием возраста. По результатам изучения реконструированы палеогеографические обстановки, условия накопления и распространения осадков в раннем и средне-позднеордовикском времени. Наибольшее внимание при этом уделено установлению зон формирования карбонатных пород, перспективных для формирования по ним пород-коллекторов. Тектонический анализ позволил провести сравнение участков развития карбонатных платформ раннеордовикского и средне-позднеордовикского возраста с целью выявления тектонических движений, способствующих увеличению или сокращению карбонатных платформ. Результаты. Приведены сведения о распространении нижнее-, средне-верхних отложений ордовика на территории ЗСГ, реконструированы условия осадконакопления в ордовикском периоде, построены схематические палеогеографические карты нижнеордовикских и средне-верхнеордовикских образований, а также совмещенная карта распространения выявленных карбонатных платформ раннеордовикского и средне-позднеордовикского возраста, и сделаны выводы о тектонической истории развития ЗСГ в течение ордовика, в частности о проявлении трансгрессивных фаз в зоне формирования карбонатных платформ ордовикского возраста.The relevance of the research lies in the need to increase facilities for searching oil and gas fields, one of which is a carbonate platform in the pre-Jurassic formation of West Siberia. The discovery of a number of oil and gas fields: Urmanskoye, Archinskoye and several others, are related to carbonate platforms on the territory of West Siberian geosyneclise (WSG). The aim of the research is to consider the conditions of formation of the Ordovician depositions of West Siberian geosyneclise for establishing in its territory the sites for the formation of carbonate rocks (carbonate platforms), which are transformed into rock-collectors at the appropriate studying by hydrothermal leaching and hydrothermal dolomitization. The fissure-metasomatic zones of hydrothermal study of carbonate rocks are formed. They underlie the area zones of formation of reservoir rocks in the regions of the Paleozoic formations discharge on the pre-Jurassic surface, or zones of oil and gas horizon of the contact zone, contact areas of Paleozoic (pre-Jurassic) and Mesozoic deposits. Research methods: lithological, paleontological, paleogeographic, tectonic. On the basis of complexity of the research methods by the previous researchers, the WSG territory is divided into 23 structural-facial districts (SFD), with a characteristic set of lithostratigraphic units (sweet, thick) and paleontological substantiation of the age. By the results of the study the authors have reconstructed the paleo-geographic conditions, conditions of accumulation and distribution of precipitation in the early and middle-late Ordovician time. The greatest attention is paid to the establishment of formation areas of carbonate rocks prospective for forming reservoir rocks. The tectonic analysis allowed comparing the phases of development of carbonate platforms of early and middle-late Ordovician age for determining the tectonic movements that promote the increase or reduction of carbonate platforms. Results. The paper introduces the information on distribution of lower-, middle-upper Ordovician deposits in the territory of WSG. The authors reconstructed the conditions of sedimentation during the Ordovician period, built schematic paleogeographic maps of early and middle-late Ordovician age, and a complex map of distribution of the identified carbonate platforms of early and middle-late Ordovician age. The conclusions were made on the tectonic history of WSG during the Ordovician, in particular the manifestation of the transgressive phases in the zone of formation of the carbonate platforms of the Ordovician age