Home – Home – Jornals – Advanced Search

An integrated lithofacies analysis of the Middle-Upper Bathonian petroleum horizon J₂ in the northeastern part of the latitudinal Ob’ region was carried out. The new data were used to supplement and refine the available data. The recognized lithofacies and their associations clearly mark off the boundaries of reconstructed sedimentation conditions. A petrographical study of the silt-sandy rocks of the horizon was carried out with a detailed calculation of their grain size and petrographic compositions. Grain size coefficients were analyzed with the use of genetic, dynamic, and dynamogenetic diagrams. The new data permitted a considerable refinement of the reconstructed sedimentation conditions of the horizon. It has been found that the transgressive change of sedimentation conditions is reflected in regular changes in some characteristics of the studied sediments: a decrease in the total number and thickness of coal interbeds, an increase in the degree of sediment bioturbation, a change of ichnofossils, and an increase in the amount of pyrite. More detailed paleogeographical schemes have been constructed for the formation of the lower (continental), middle (transitional), and upper (littoral marine) parts of the horizon. They provide a better understanding of the regularities of development of the Middle–Late Bathonian sedimentary basin in the study area.

Based on results of deep drilling and the CDP-2D seismic profiling, the relations between the Early and Middle Cambrian carbonaceous rocks and the underlying, overlying, and synchronously formed deposits in the Siberian Platform are analyzed, and the lithologo-paleogeographic, paleotectonic, and tectonic conditions of their formation are considered. It is shown that these carbonaceous rocks are intimately related to the Cambrian organogenic structures, up to their mutual transitions.

Stable carbon isotope variations in primarily offshore Proterozoic carbonates of the Eselekh, Neleger, and Sietachan Formations in the Kharaulakh Range of northern East Siberia provide important information on the depositional history of the Riphean complexes and allow an age estimate to be made for potentially petroliferous Precambrian strata in the northeast of the Siberian Platform. The results of petrographic, geochemical, and isotopic studies of the measured samples demonstrate that the carbonates recrystallized without substantial postdepositional alteration of the carbon isotope system and that the acquired δ¹³С values are accurate and can be used for the purposes of chemostratigraphy. The Riphean strata of the Kharaulakh Range are characterized by mostly high (5.5–8.6‰) δ¹³С values. Based on the carbon isotope data, the studied section could not be correlated with Mesoproterozoic strata of the Anabar and Olenek uplifts but occupies a rather higher stratigraphic position. It can be correlated with the Baikal Group of the West Pre–Baikal Area and the Dal’nyaya Taiga Group of the Patom upland; specifically, the negative shift in the uppermost Sietachan Formation possibly corresponds to the Zhuya negative excursion. Comparison with the model curve of carbon isotope evolution in the Precambrian ocean suggests that the age of the studied section does not exceed 820 Ma. Most likely, the studied strata are younger than 635 Ma (i.e., postdate the Marino glaciation) but older than the Gaskiers glaciation (580 Ma).

Consolidated crust in the North Barents basin with sediments 16–18 km thick is attenuated approximately by two times. The normal faults in the basin basement ensure only 10-15% stretching, which caused the deposition of 2–3 km sediments during the early evolution of the basin. The overlying 16 km of sediments have accumulated since the Late Devonian. Judging by the undisturbed reflectors to a depth of 8 s, crustal subsidence was not accompanied by any significant stretching throughout that time. Dramatic subsidence under such conditions required considerable contraction of lithospheric rocks. The contraction was mainly due to high-grade metamorphism in mafic rocks in the lower crust. The metamorphism was favored by increasing pressure and temperature in the lower crust with the accumulation of a thick layer of sediments. According to gravity data, the Moho in the basin is underlain by large masses of high–velocity eclogites, which are denser than mantle peridotites. The same is typical of some other ultradeep basins: North Caspian, South Caspian, North Chukchi, and Gulf of Mexico basins. From Late Devonian to Late Jurassic, several episodes of rapid crustal subsidence took place in the North Barents basin, which is typical of large petroleum basins. The subsidence was due to metamorphism in the lower crust, when it was infiltrated by mantle–source fluids in several episodes. The metamorphic contraction in the lower crust gave rise to deep–water basins with sediments with a high content of unoxidized organic matter. Along with numerous structural and nonstructural traps in the cover of the North Barents basin, this is strong evidence that the North Barents basin is a large hydrocarbon basin.

The effect of tectonic processes on the petroleum potential of the Upper Jurassic and Cretaceous sediments is estimated by the example of the deposits in the north of the Aleksandrov arch. The formation history of the structures bearing Upper Jurassic and Cretaceous hydrocarbon (HC) pools is discussed. The results obtained lead to the conclusion that anticlinal traps complicated by faults cutting the Meso-Cenozoic sedimentary cover are the most promising for the formation of large HC pools in Cretaceous sand reservoirs. These traps serve as channels for HC migration from the oil-producing rocks of the Bazhenovo Formation into the overlying reservoirs. In the Upper Jurassic sediments, anticlinal traps free from Cenozoic faults are the most promising for HC accumulation. These conclusions are confirmed by a number of examples.

We consider the formation history of high-amplitude anticlinal trap structures for unique Cenomanian gas pools using the example of the Medvezh’e field. Analysis shows that the Turonian-Cenozoic was the most crucial stage of formation of the world’s largest gas–bearing province in northern West Siberia. This stage was marked by (1) the formation of large anticlinal traps — petroleum–promising objects; (2) the highest intensity of gas formation, which caused the filling of these traps; and (3) the formation of the Kuznetsov seal, which shields the giant Cenomanian gas pools.

We discuss the current understanding of the Vendian regional stages in the northeast of the Nepa–Botuobiya Anteclise, establish a new correlation of the Vendian sections across different facies, and propose stratotypes for the introduced stratigraphic units. A new stratigraphic chart is constructed for the Vendian terrigenous strata in the northeast of the Nepa–Botuobiya Anteclise and the adjacent territories.

A scheme is proposed for the stratigraphic division and correlation of the Cambrian sediments of the Upper Proterozoic-Paleozoic Cis-Yenisei basin. It is based on data from the drilling of parametric wells (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-1, Vostok-3, Vostok-4, and others). Two structure-facies zones are recognized in the study area: Kas zone (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-4, and Eloguiskaya-1 wells), in which the sedimentary complexes accumulated in a salt subbasin, and Ket’ zone (Vostok-1 and Vostok-3 wells) with open-sea-basin sedimentation. The boundary between the structure-facies zones passes along the reconstructed zone of a barrier reef stretching in the N-S direction. The Vostok-4 well is localized in the western Kas structure-facies zone, at the salt subbasin/barrier reef boundary. Local stratigraphic units (formations) are described and compared with the adjacent Turukhan-Irkut-Olekma facies region of the Siberian Platform.

Application of stochastic simulation to study of the lateral migration of primary hydrocarbon pools near the roof of a collector is considered. It is shown that this approach can be used for point and interval estimations of oil accumulation in a trap and the formation of residual oil saturation.

We summarize and analyze the available data on naphthide shows in continental zones of active hydrothermal and modern volcanic activity (Uzon Volcano caldera, Yellowstone National Park, and New Zealand springs) and examine their similarity and difference. The analysis demonstrated that hydrothermal naphthides formed from lipids of living matter of different nature: phytoplankton, bacterial communities, archaea, and remains of higher land plants, including spores and pollen, which might have been supplied to the sediment through eolian transportation. Hydrothermal naphthides are different in the degree of maturity, but in general they are less transformed than most of basin oils. Their group composition and distribution of n-alkanes evidence that they were subject to hypergenesis, which led to the loss of light fractions, oxidation, and biodegradation.