N. I. Korobova

The main types of sections of the oil-bearing Bazhenov Formation on the Northeastern Surgut Arch

The lithological study of the core samples of the Bazhenov Formation that are exposed on the northeastern Surgut arch allowed us to distinguish three types of sections, which are ascribed to the different parts of an ancient intrabasin uplift. Moving from the arch to its peripheral parts, these types demonstrate a successive change in the prevailing sedimentation type from carbonate–clayey–siliceous via siliceous to clayey–siliceous types

The structure and genesis of limestones at the boundary between the Abalak and Bazhenov formations in Central West Siberia

In the central West-Siberian basin, fractured and cavernous carbonate rocks that are often oilbearing, which are referred to as correlation layer 1 (CL1), are frequently present at the top of the Abalak formation and/or at the bottom of the Bazhenov formation. They are sporadically distributed over the profile and the area; their genesis is still not completely clear. The structural features and oil-bearing capacity of carbonate rocks have been studied, as well at the distributions of carbon and oxygen stable isotopes from bulk rocks and calcite filling fractures in the CL1 layer that was penetrated by six wells. The spherolitic microstructure of limestones together with the carbon and oxygen isotope distributions (δ13C =–14 to–26‰ VPDB; δ18O = 0 to–5‰ VPDB) indicate the precipitation of carbonate material due to microbial activity on the surface and/or in the upper part of sediments at high methane concentrations. The fractures and caverns in limestones are frequently oil-bearing; they contain coarse crystals of calcite, pyrite, quartz, and, more rarely, barite. This degree of mineralization and the isotope composition of calcite oxygen (up to–18‰ VPDB) indicate that calcite precipitates at elevated temperature (up to 120°C) from the hydrothermal fluids that could migrate from underlying strata.

On the estimation of shale-oil resources and reserves

At present, the proven oil reserves from traditional Russian reservoirs are decreasing, leading to a steady fall in oil production. One of the possible ways to maintain the oil production at the present level is to produce tight oil, which is regarded as the category of oil from the Bazhenov Formation in the Kanty-Mansiysk region of Western Siberia, Domanik deposits in the Volga–Ural province, and Maikop deposits in the Fore-Caucasus.

New data on the biostratigraphy and facies types of upper carboniferous Domanik sections in the Volga–Ural basin

New data on the biostratigraphy and facies types of Domanik sections in the Volga–Ural basin are discussed with the description of four types of sections that reflect different depositional environments: the shelf of a carbonate platform, biogenic buildups (bioherms) of its outer zone, slopes of depression, depression. Paleontological remains made it possible to determine the age of the host rocks. Such information serves as a basis for modeling the formation of Domanik deposits and reconstructing their paleogeographic settings.

Late Vendian-Early Cambrian formations of the north-west Siberian Craton

The composition and structure of principal key-sections for the Tira (Late Vendian) and Danilovo (Late Vendian-Early Cambrian) Horizons were characterized on the basis of deep-drilling data and studies of natural outcrops along the peripheries of the Kureika syneclise. The typical sedimentary formations/associations were recognized, their vertical and lateral successions were distinguished, and their deposition environments were interpreted. A distribution pattern scheme of thicknesses and depositional environments of Upper Vendian-Lower Cambrian deposits was compiled at the 1: 1000000 scale. The reservoir characteristics of the formations are discussed and forecasted for poorly studied areas of the northwestern Siberian platform.

Cenozoic complex in the Upper Telekai oil-and-gas field in the Chukchi Peninsula (results of petrographic examination of the succession penetrated by well 10)

The paper discusses new data resulting from petrographic examination of the composition and structure of Cenozoic sediments penetrated by Well 10 to a depth of 2350 m in the Upper Telekai oil-and-gas field within the Anadyr Basin. An alluvial-deltaic sedimentation environment of tuffaceous-sedimentary and terrigenous producing Lower Miocene rocks was found and their secondary alterations examined, including formation of clay minerals, carbonates, and zeolite. The vitrinite reflectance indices allowed determination of the catagenic zoning of the Miocene succession, and a significant catagenic unconformity related to pre-Pliocene erosion was recorded at its top.

The Composition and Reservoir Properties of the Deposits of the Bazhenov Formation in the Central Part of the Tundrin Depression

The section structure was characterized according to the lithological and petrophysical studies of the core from the Bazhenov Formation that has been uncovered in the central part of the Tundrin Depression. The productive oil intervals where the reservoirs of the pore and fissure-pore types occur were identified.

Fracturing in the high-carbon formation of the northern flank of the South-Tatar arch

The problem of studying the Domanik deposits and their reservoir potential is among the most important ones. The discovery of hydrocarbon deposits in similar rocks at various depths, the considerable variability of reservoir properties, and ambiguity in establishing the values of the effective thickness set the task for researchers to estimate them more reliably. The high-carbon kerogenic-carbonate-siliceous stratum that is characterized by the development of differently-oriented systems of fractures is of outstanding interest.

The phosphate-containing interlayers of the Bazhenov Formation as potential reservoirs

The possible reservoir type of the Bazhenov Formation relative to the intervals enriched in phosphates (apatite varieties) is described in this work. The phosphate rocks are characterized by a highly developed pore space; their porosity can reach up to 14%. Along with this, these rocks have explicit geochemical characteristics of oil-reservoir rocks in comparison with other rock samples in the well. As an example, the productivity index and oil-saturation index for phosphates are twice as high as the background values. The composition of such rocks can slightly vary: fluorine can be observed in phosphate minerals, while the rock is always enriched in organic matter (>8 wt %).

The lithological–geochemical characteristics for the Permian oil-and-gas bearing complex of the Lena-Anabar trough (based on the example of Ust’-Olenekskaya well no. 2370)

Lithofacies of different geneses are identified in a section of Permian deposits based on the study of the core material; the best reservoirs in the Permian complex of the Lena-Anabar trough are related to the sand bodies of the delta system. The Permian oil-source strata, where organic matter was accumulated under marine conditions, are recognized, the initial characteristics of organic matter are estimated, and the initial high oil-generation potential is substantiated. The results of the lithological–geochemical studies of the samples from one of the northernmost wells in the Laptev Sea coast have been published for the first time.