Features of filling reservoirs with hydrocarbons in the territories with a low maturity of the oil and gas parent rocks (a case study of Jurassic hydrocarbon traps in the Uvat district)

The article is devoted to the results of an analysis of geological factors that had a great influence on the filling of Jurassic traps with hydrocarbons. Based on the results of paleotectonic analysis, three key stages of reconstructions of the structural plans of sedimentary cover deposits were identified. Each stage was characterized not only by the appearance of new traps in the interval of Jurassic deposits, but also by the sinking of rocks of Bazhenov formation to a certain depth. It is revealed that in most of the territory of the Uvat district, Bazhenov formation didn't have time to fully realize its hydrocarbon-generating potential. In the Central and Eastern regions it entered the main zone of oil formation only in the Paleogene. Since the development of the relief of modern structural plans of Jurassic deposits in this area occurred in several stages, both the formation of traps and the lateral migration of hydrocarbons also occurred in stages. The first stage of migration occurred at the boundary of the lower and upper Cretaceous, the second stage occurred at the beginning of the Paleogene. As a result, the combined influence of lateral migration of hydrocarbons and the gradual formation of local structures in different areas of the Uvat district led to selective filling of Jurassic hydrocarbon traps.

Prospects for the oil and gas content of the Upper Permian deposits of the southwestern part of the Vilyui syneclise based on the analysis of sedimentary environments and geochemical conditions of oil and gas content

The article discusses the prospects for the oil and gas content of the Upper Permian deposits in the southwestern marginal part of the Vilyui syneclise. In this margin, the Permian terrigenous complex with proven oil and gas productivity in the central part of the syneclise, pinches out. The study area, represented by the monoclinal slopes of the Vilyui syneclise, is considered a promising area for the exploration of non-structural hydrocarbon traps in the Upper Paleozoic sediments. The objectives of the study include identifying general patterns of sediment formation, associated mainly with the development of the alluvial complex, and substantiating the potential opportunities of migration and accumulation of hydrocarbons in the predicted traps. The research is based on the interpretation of the latest seismic surveys and prior-years geological and geophysical data. Authors carried out structural and paleo-structural analysis, identified lithofacies in the well log, generalized and analyzed the geochemical conditions of the oil and gas content of the Upper Permian deposits, traced the pinching out of the Upper Permian deposits on the southwestern margin of the syneclise, and also outlined areas of river valleys development that form zones of advanced reservoirs. The results of the studies have validated promising oil and gas accumulation zones on the southwestern slopes of the syneclise associated with non-anticlinal hydrocarbon traps. Authors also drew up a diagram of the oil and gas potential of the Upper Permian deposits. The obtained results are of interest for prospecting for oil and gas in the area under study.

Upper Paleozoic reef systems of the Rubezhinsky Trough (southern part of the Buzuluk Depression)

Background. The Rubezhinsky Trough has been remained one of the most poorly studied petroleum areas of the Orenburg region to date. At present, Gazprom Neft conducts systematic exploration work within the trough at five license areas of the South Orenburg Cluster. Aim. The purpose of this article is representation of preliminary new dates on a geological structure of paleozoic reef systems within the Rubezhinsky Trough. Materials and methods. The main original materials for the work are the results of the interpretation of the 3D seismic carried out at four license areas. In addition, results drilling and regional sedimentation models were involved for analysis. Results. Regional models of Upper Paleozoic reef systems of the Rubezhinsky Trough have been extensively detailed as a result of the interpretation of 3-D seismic data within the South Orenburg cluster. It was first established that isolated reefs were formed in the interval of the Ardatovian and Mullinian regional stages (Givetian Stage of Middle Devonian) of the research area. Ardatovian-mullinian isolated reefs are covered with clay deposits and represent potential lithological traps for petroleum deposits. Isolated reefs, isolated carbonate platforms and the southern margin of the vast South-Buzuluk carbonate platform with barrier reef systems have been identified for the Frasnian Stage. Isolated frasnian reefs are potential hydrocarbon traps. Barrier frasnian reefs together with increasing them early famennian ones form a series of structural hydrocarbon traps in the overlapping complexes. The significant progradation of the margin of the famennian carbonate platform towards the Pre-Caspian paleobasin is established. Famennian progradation complexes form several large clinoforms which are potentially forward looking for the search for structural-lithological petroleum traps. The barrier reef system has been confirmed for the evaporite-carbonate complex of the Okskian regional stage. Okskian reefs border the late visean epicratonic carbonate platform. Relatively large reefs of the carbonate platform barrier system were identified in the interval from Podolskian regional stage (Carboniferous) to Asselian Stage (Permian). This barrier system has progradational architectures towards the Pre-Caspian paleobasin that was formed from the end of the Middle Carboniferous to the end of the Artinskian Age of the Early Permian. Podolskian-asselian barrier buildings predefine the development of structural hydrocarbon traps of various sizes in overlapping Lower Permian deposits. Conclusions. A preliminary analysis of 3-D seismic data indicates the significant role of the paleozoic reef systems in the formation of the sedimentary complex of the Rubezhinsky trough.

Detailed investigation algorithm for hydrocarbons deposits exploration in terms of the Shebelynske gas-condensate field

In order to elaborate the neotectonic structure and improve the searching algorithm of new hydrocarbon traps at prospective areas, detailed airspace geological investigation has been carried out. For this study, the selected cross-section Dniprovsko-Donetska depression is the regional seismic profile Lozova-Shebelinka-Staropokrovka within the Shebelinska structure zone.In particular, the investigations consisted of structural and geomorphological analysis, analysis of the hourly seismic profile Lozovaya-Shebelinka-Staropokrovka and analysis of thermal anomalies and structural interpretation by using satellite images. This approach allowed to explore the Shebelinska structure zone and the East-Shebelinska depression for hydrocarbon traps feature properties detecting in Paleozoic sediments.Based on the results of the initial data processing, we established that Paleozoic complex cannot create hydrocarbon deposits, both due to low reservoir properties and due to insufficiently studied structure. Neotectonically, the Shebelinskaya structure looks like a dome-shaped uplift. This uplift is divided by a ravine-gully network into neotectonic blocks. Productive wells are located within the most active blocks.

THE GEOLOGICAL ROLE OF THE SEARCH METHOD "WILD CAT WELLS" IN THE STUDY OF THE HYDROCARBON POTENTIAL OF THE PRIPYAT TROUGH

The results of geological exploration for oil within the Elsky, Shatilkovsky, Savichsky and Petrikovsko-Shestovichsky sections of the Pripyat trough are analyzed. The analysis covers almost 70 years from the drilling of the first exploratory wells laid by the "wild cat" method to the modern comprehensive justification. During the analyzed period, from 12 to 23 deep wells were drilled with a total penetration of 42.3 thousand meters to 68.3 thousand meters in each section. The initial stage of work after the first oil inflow is characterized by a higher activity of drilling new exploratory wells, justified by the methods available at that time. The negative result of exploratory drilling in certain areas is also due to the significant fragmentation of the intrasalt perspective horizons and the areal unevenness of reservoir layers in the subsalt complex. Within the boundaries of the sites, deposits with recoverable oil reserves of no more than 450 thousand tons are established, which can be determined as a low economic efficiency of prospecting operations. However, the work has played a positive role in determining real models of hydrocarbon traps for use in the study of other sites.

APPLICATION OF DIRECT HYDROCARBON INDICATORS FOR OIL AND GAS PROSPECTING IN THE DNIPRO-DONETS DEPRESSION

Based on the results of numerous seismic studies carried out in the areas and fields of the Dnipro-Donets depression, the strategy to identify hydrocarbon traps in this region has been developed taking into account modern requirements for prospecting and exploration of gas and oil fields. The studies are designed to determine the favorable zones of hydrocarbon accumulations based on the analysis of the structural-tectonic model. A necessary element for solving such a problem is to aaply direct indicators of hydrocarbons to predict traps of the structural, lithological or combined type. It was determined that an effective approach to identify hydrocarbon traps in the region is attribute analysis employing seismic attributes such as seismic envelope, acoustic impedance or relative acoustic impedance. In most cases of practical importance, the analysis of the distribution of the values of these attributes turned out to be sufficient for performing the geological tasks. It is given an example of extracting additional useful information on the spatial distribution of hydrocarbon traps from volumetric images obtained from seismograms of common sources with a limited range of ray angles inclinations. To analyze the distributions of seismic attribute values, it is recommended to use the Geobody technology for detecting geological bodies as the most effective when using volumetric seismic data. The distributions of various properties of rocks, including zones of increased porosity or zones of presence of hydrocarbons are determined depending on the types of seismic attributes used in the analysis,. The use of several seismic attributes makes it possible to identify geological bodies saturated with hydrocarbons with increased porosity and the like. The paper provides examples of hydrocarbon traps recognition in the areas and fields of the Dnipro-Donets depression practically proved by wells. A generalization on the distribution of promising hydrocarbon areas on the Northern flank of the Dnipro-Donets depression and the relationship of this distribution with the identified structural elements of the geological subsoil is made.

STUDY OF OIL AND GAS PROSPECTIVE STRUCTURES OF THE ARAL SEA REGION WITH THE FORECAST OF THEIR RESERVES

В начале барремского времени море отступило и до начала позднего альба территория представляла собой низменную аккумулятивную равнину, в пределах которой происходило накопление аллювиальных и озерно-аллювиальных отложений: красно-коричневых глин, алевролитов с прослоями коричневых песчаников и песков и линзами темно-серого лигнита. В основании толщи отмечаются гравелиты и конгломераты. В раннемальбе произошла кратковременная трансгрессия моря, однако территория современного Восточного Приаралья не была затоплена и представляла собой прибрежно-морскую равнину, где накапливались глины, алевролиты и песчаники. К концу позднего альба море регрессировало, и территория вновь стала представлять собой низменную аллювиально-озерную равнину. По всей территории происходило накопление пестроцветных глин, зеленовато-серых алевролитов, песков и песчаников, а также углей. При проведении иследовательских работ были обоснованы наиболее перспективные типы ловушек углеводородного сырья по стратиграфическим уровням и выявлена зональность их распространения. Дана оценка перспектив района на выявление залежей нефти и газа. Выделены информативные и качественные признаки (критерии) нефтегазоносности. Обоснованы площади и конкретные структуры для постановки детальных поисковых работ на выявление залежей нефти и газа. Рассчитана оценка потенциальных ресурсов углеводородного сырья. At the beginning of the Barremian time, the sea receded and until the beginning of the late Alb, the territory was a low-lying accumulative plain, within which the accumulation of alluvial and lacustrine-alluvial deposits occurred: red-brown clays, siltstones with layers of brown sandstones and sands and lenses of dark gray lignite. Gravelites and conglomerates are noted at the base of the strata.In the Rannemalba, there was a short-term transgression of the sea, but the territory of the modern Eastern Aral Sea region was not flooded and was a coastal-sea plain, where clays, siltstones and sandstones accumulated. By the end of the Late Alb, the sea regressed and the area again became a low-lying alluvial-lacustrine plain. There was an accumulation of variegated clays, greenish-gray siltstones, sands and sandstones, as well as coals throughout the territory. During the research work, the most promising types of hydrocarbon traps were justified by stratigraphic levels and the zoning of their distribution was revealed. The assessment of the prospects of the area for the identification of oil and gas deposits is given. Informative and qualitative signs (criteria) of oil and gas potential are identified. The areas and specific structures for setting up detailed search operations to identify oil and gas deposits are justified. The estimation of potential resources of hydrocarbon raw materials is calculated.