G. A. Kalmykov

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

Experimental investigations of hydrocarbon fluid recovery from hydrothermally treated rocks of the Bazhenov Formation

The results of experimental shale-oil recovery from hydrothermally treated rocks of the Bazhenov Formation are discussed. It is shown that the yield depends on the duration of an experiment: the longer the hydrothermal impact is, the higher the oil yield is. The potential of oil recovery from hydrothermally treated rocks of the Bazhenov Formation is as high as 25 mg/g or 2.5 wt %. The addition of reducing agents such as aluminum or oxalic acid provides no increase in the coefficient of oil recovery. It is established that the yield of the oil fraction at 250°C is insignificant; at 300°C, it amounts to 25 mg/g, while at 350°C, it decreases up to 15 mg/g. This means that a temperature of 300°C is preferable, since it provides a higher yield of oil products and oil fractions are largely represented by normal alkanes, while chromatograms that were obtained at 350°C indicate the development of complex processes, including graphitization of kerogen.

Geochemical technique of organic matter research in deposits enrich in kerogene (the Bazhenov Formation, West Siberia)

The international interest in shale oil has recently provoked special attention to the Russian unconventional oil-source formations, including the Bazhenov Formation of West Siberia, domanik deposits in the Volga–Ural region, and the lower Maikop Group of the Cis-Caucasus. High contents of para-autochthonous soluble organic matter (bitumen) in clayey–carbonate, clayey–siliceous, carbonate–clayey–siliceous rocks with low filtration–capacity properties results in significant uncertainties in the identification of the generation potential of organic matter (OM). Examination of a large database on the OM of the Bazhenov Formation allowed us to propose an optimum complex technique for study of the source rock potential and assessment of the amount of produced hydrocarbons in the kerogen-rich sediments. The investigations include a combination of Rock Eval pyrolysis prior to and after extraction with different solvents, the comparison of bituminological and pyrolytic characteristics, and the determination of the group composition of soluble organic matter, as well as chromatography and chromato-mass spectrometry.

Siliceous reservoirs of the Bazhenov formation, the Sredny Nazym Oil Field, and the structure of their pore space

The reservoirs of the oil-bearing Tutleym formation, Bazhenov horizon (analog of the Bazhenov Formation for Middle Nazym Oil Field), are studied. Their material composition, porosity and permeability, the geochemical characteristics of their organic matter, and pore space characteristics are examined, and the factors affecting the reservoir porosity and permeability are found. The changes in the structure of the porous medium, which provide primary oil migration from oil source rocks into the Tutleym formation reservoirs, are revealed.

The reservoir properties of the rocks of the bazhenovskaya formation

This work is dedicated to interpretation of the results of complex laboratory petrophysical studies of core samples of the rocks of the Bazhenovkaya Formation from several wells at Western Siberian deposits. The major aim of this study is the comparison and substantiation of analytical results that were obtained by various methods of determination of petrophysical rock properties, which is necessary to reveal the methods of complex petrophysical studies that are the most correct and applicable for the rocks of the Bazhenovskaya Formation.

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.

The geochemical patterns of rocks of the Bazhenov and Abalak formations (Western Siberia)

The composition of rocks of the Bazhenov and Abalak formations in Western Siberia is described. Correlations of the concentrations of the major and minor components in rocks with the concentrations of minor elements and organic material are shown. Study of the concentration of minor elements allows us to determine the conditions of sedimentation: redox potential, hydrogen sulfide contamination, and the source of sedimentary material. The results show that rocks of the Bazhenov Formation were formed under the conditions of low fluxes of clastic material, a reduced environment, and a periodically occurring hydrogen sulfide mode.

The hydrocarbon-generation potential of the Domanik rocks in the Volga–Ural petroliferous basin

The factors that are responsible for the formation of the hydrocarbon-generation potential and its occurrence in the Devonian carbonate sequences (Domanik Formation) of the Volga–Ural petroliferous basin are considered. The rocks of this formation are characterized by a high generation potential that is sufficient for the formation of large oil and gas accumulations. The highly carbonaceous deposits lack reservoirs.

Cavity structure in oil-saturated Bazhenov and Abalak shale rock in the Western Siberian basin

The cavity structure in oil-saturated Bazhenov and Abalak shale rock is analyzed. The Bazhenov reservoirs are of pore and pore–microcavern type. Their cavity structure is formed as a result of the transformation of the mineral component (biogenic silica) and organic component (kerogen) in the rock. The ratio of pore types depends on the mineral composition of the reservoir rock and its degree of catagenesis. Pyrite is the main mineral filling the pore volume and impairing the filtrational properties. The reservoirs of the lower Bazhenov formation are confined to the Correlation Layer and are of fracture-cavern type.