Home – Home – Jornals – Russian Geology and Geophysics 2017 number 12

This study describes a new method for quantification of hypothetical oil and gas resources, which is considered to be an alternative to conventional estimates by analogy to geologically similar plays and is most appropriate for maturely explored provinces. This method is based on the size-frequency distribution of oil accumulations in sedimentary basins and has never been applied to petroleum exploration. The new approach makes it possible to assess the oil resources concentrated in small and smallest oil fields, which may become the main targets for petroleum exploration. This study reviews the discovery and exploration history of the Volga-Ural province and provides estimates of initial and hypothetical oil resources and the size distribution of undiscovered field and the number of their pools. It was shown that given the volume of exploratory drilling of 500-550 thousand m per year, it is expected that more than three billion tons of oil would be produced from small and smallest fields of this province by the mid-21st century, with a stable annual production of 40-50 million tons. It was shown that the development of small and smallest oil fields is performed by small and medium-sized oil companies, which can be delivered through a dedicated government program.

Deposition environments in the Chukchi Sea and adjacent areas of the Arctic Ocean are studied by the Q -cluster analysis of compositions, particle sizes, and other properties of surface bottom sediments. Analysis of more than 4700 numeric values allowed mapping fifteen clusters distributed over the seafloor according to deposition environments. Chemical and statistical data confirm the predominance of clastic sedimentation and mainly mechanic sorting of sedimentary material. At the same time, the major-element composition trends correspond to Si decrease and Al increase seaward. Biogenic deposition is of inferior scale and shows up as relative enrichment in total organic carbon, Ca, Mg, Ba, Sr, and some other biogenic and chemogenic components in sediments. Clastic and biogenic deposition, with accumulation of Fe, Mn, V, Ni, Cr, Co, and other elements, as well as precipitation of authigenic growths, occurs within areas of seafloor having particular water chemistry, such as the Herald Canyon, the outer shelf, and the deepwater Arctic Ocean.

Mesozoic sections in the New Siberian Archipelago are important for understanding of the geology of underexplored shelf areas in the east of the Laptev Sea and in the west of the East Siberian Sea. They are reference sections for interpretation of seismic data in these regions. However, there are still many unresolved problems concerning the lithology, lateral extent, and age of Mesozoic deposits, as the sections have a complex structure and are heavily deformed. The performed research makes a basis for the first facies zoning of Jurassic and Cretaceous deposits in the New Siberian Islands and adjacent landmasses of continental Siberia at the junction of the Laptev and East Siberian Seas. The lithostratigraphic division of the Jurassic and Cretaceous is refined, being proposed for the first time for some stratigraphic intervals, and allows updating their lithostratigraphic division (or undertaking it for the first time for some stratigraphic intervals). Facies features of Jurassic and Cretaceous deposits allow the definition of three depositional series.

Based on our new U-Pb isotope data (SHRIMP-II) for the Voronezh Crystalline Massif (VCM) and on published U-Pb data for the Archean rocks of the Ukrainian Shield (USh), we have substantiated the main stages of the Archean evolution of the Sarmatian crust, a fragment of the basement of the East European Platform. New data have been obtained for 20 indicative rocks of the Kursk block (KB) of the VCM. We compared the Eoarchean and Paleoarchean KB rocks (mafic rocks and tonalites of the Oboyan’ complex), orthogneisses of the USh Dniester-Bug province (Bug granulite complex), and tonalites and mafic rocks of the USh Azov Province and have established the existence of ancient continental crust (3.75-3.60 Ga) in Sarmatia. The presence of Paleoarchean xenogenic zircons in younger intrusions indicates a wide spread of Paleoarchean rocks in the deep VCM crust section. In the Mesoarchean (3.2-3.0 Ga), eastern Sarmatia (KB and Azov and Middle Dnieper provinces) was a single granite-greenstone terrain. Two stages of felsic magmatic activity have been dated: 3.15-3.10 Ga (volcanics in the greenstone belts and tonalite-trondhjemite granites in the VCM and USh) and 3.05-3.00 Ga (volcanics and tonalite-trondhjemite granites in the USh and granites in the VCM KB). Magmatic and tectono-metamorphic processes (2.95-2.85 Ga) have been established throughout the eastern part of Sarmatia. The latest Mesoarchean endogenic activity (2.85-2.80 Ga) testifies to the tectonic differentiation of the area. Mafic and felsic magmatism, deformations, metamorphism, and ultrametamorphism under amphibolite and granulite facies conditions took place in the most part of the KB and in the Azov and Bug areas. It is shown that ultrametamorhic granites formed fr om an ancient (3.0-3.5 Ga) protolith. The USh Middle Dnieper province had a different tectonic position. Here, intrusion of post-tectonic granites and formation of mature sediments proceeded at 2.81-2.86 Ga. Our geochronological data show that most of the Sarmatian continental crust formed in the Mesoarchean as a result of both the intrusion of juvenile material and the reworking of the older protolith rocks. Neoarchean events (2.8-2.5 Ga) are weakly expressed in Sarmatia in contrast to Baltia, another large fragment of the East European Platform basement, wh ere endogenic processes at 2.65-2.75 Ga were the major crust-forming geologic events.

Using modern thermobarogeochemical methods (thermo- and cryometry, Raman spectroscopy, and LA-ICP-MS), we studied fluid inclusions in quartz from ores formed at the quartz-fluorite, pyrite-chalcopyrite, pyrite-molybdenite, and polysulfide stages of evolution of the Samolazovskoe gold deposit. We have established the fluid regime of the ore formation processes, the gas and liquid composition, main solid phases (metal sulfates, carbonates, and chlorides), homogenization temperatures of the inclusions, and the eutectic temperatures of their solutions. The obtained data helped to estimate the fluid temperatures during the formation of ores at each stage and to determine the contents of major salt components. Based on the substance solubility values given in the reference-book by V.B. Kogan, we have first constructed a phase diagram of the system Na₂SO₄-NaHCO₃-H₂O (Na₂SO₄ < 35 wt. %) at temperatures below 40 ºC. The metal contents and geochemical specifics of solutions at each stage of the ore formation were determined by LA-ICP-MS. At the quartz-fluorite stage, the solutions were enriched in B, V, Co, Ni, Zn, As, Te, Cs, Ba, and Mg; at the pyrite-molybdenite stage, they had high concentrations of Ti, Ni, Nb, and Mo; and at the polysulfide stage, the solutions were rich in Ca, As, Pb, Sb, Te, Ag, Rb, Ba, and Sr. Native sulfur found along with sulfate and sulfide sulfur in the inclusions impelled us to study the sulfur isotope composition. The research has shown a light sulfur isotope composition (δ³⁴S = -2.5 to -13.4 ‰). We believe that sulfide sulfur in the Samolazovskoe deposit formed from a fluid during high-temperature (>500-700 ºC) sulfate reduction.

We have first determined the contents of rare-earth elements and yttrium (REY) in four major mineral fractions of hydrothermal sedimentary ferromanganese crusts of the Sea of Japan. It is shown that REY are sorbed mostly by Fe oxyhydroxides (FeOOH). The REY content in the residual aluminosilicate fraction is the second most important factor determining the crust composition. The manganese fractions, composing more than 80 vol. % of the crusts, plays a subordinate role in REY accumulation. The REY pattern of hydrothermal sedimentary crusts in back-arc basins depicts the sum of the REY contents of the FeOOH fraction (hydrogenous) and residual fractions containing the total REY of the products of bedrock disintegration and endogenous (pyroclastic material) and exogenous (desert dust) components.

Integrated study of the Dyukov Log dump of sulfide-containing mine tailings of the Salair ore-processing plant (SOP) was performed using geochemical and geophysical methods. Geochemical data and results of electromagnetic-frequency sounding and electrical-resistivity tomography were used to establish the geoelectric zoning of the tailings and the relations between the electrical parameters of the environment and the chemical composition of the tailings and pore waters. The proposed approach will make it possible in the future to evaluate the amount of tailings. The drainage water flow paths were determined, and the penetration of highly saline industrial solutions into groundwaters was proved.

This paper presents the results of study of seismically induced variations in helium concentration in groundwater in the southern Baikal region. Unlike previous studies, data were obtained not only in Baikal deepwater but also in artesian wells in the southern Baikal region. The correlation coefficients between the data obtained at these observation stations, indicator functions, and an integrated indicator functions were calculated. They provide an objective assessment of time variations in concentrations due to changes in the stress-strain state of the Earth’s crust related to earthquake preparation and hence permit one to predict the time of an earthquake.

We present results of a thermomagnetic analysis of Late Pleistocene-Holocene bottom sediments from the gravity core GC-99 of the borehole BDP-99 drilled at Posolskaya Bank of Lake Baikal in the framework of the Baikal Drilling Project. The results are compared with the earlier analytical data on the samples from the lower (Miocene) section of the BDP-98 drilled on the Akademichesky Ridge. Native-iron particles were found in only 14 of 61 samples. Their content varies from ~10^-5 to 10^-4 %, and their distribution is near-bimodal, with a distinct “zero” mode. The results of the thermomagnetic analysis are confirmed by a probe microanalysis: Only occasional native-iron particles were found. Nickel was detected in only one sample. The samples have a large number of magnetite and titanomagnetite grains. It is shown that the distribution of native-iron particles in the Baikal sediments depends on the rate of sedimentation: The rate increase is accompanied by the increase in the number of the “zero” group samples (free of iron particles). The conclusion is drawn that the native-iron particles in the studied sediments are predominantly of cosmic origin.

High frequency electromagnetic technologies for subsurface formation evaluation provide high spatial resolution and new opportunities for petrophysical interpretation of data. Dispersion of rock properties and up-scaling from pore to reservoir scale (homogenization) represent the two most challenging problems. In electrodynamics of porous media, various mixing and dispersion laws are used to homogenize rock properties and describe their frequency behavior. Mixing laws and dispersion have a close link to the fundamental physical principle of causality and therefore cannot be introduced arbitrarily. For any mixing/dispersion law, we need to prove that causality holds. For testing causality, we use Titchmarsh’s theorem and, particularly, one of its modifications - Kramers-Kronig relations . Causality is discussed for Debye, Cole-Cole, Havriliak-Negami, and CRIM models. Dispersion is closely related to wave propagation. Evaluation of phase and group velocities shed new light on the physics of phase and amplitude measurements in lossy media. We evaluated various definitions of both velocities and their dependence on spatial spectra or, in other words, on the arrangement of transmitting and receiving elements. To illustrate theoretical findings, we use dielectric logging as an exemplary technology. Usually, in modern dielectric tools, amplitude and phase data are acquired, for various frequencies and sensor positions. The measured phase is discontinuous at high frequencies and requires detection of discontinuity as well as unwrapping. Remarkably, one can determine formation attenuation and loss angle based on multifrequency/multisensor amplitude data and transform them into dielectric permittivity, resistivity, and true continuous phase. Transformations of exemplary tool data used in this paper are suitable for a conceptual study and are specific for a uniform formation. We intentionally do not address the accuracy of measurements and the propagation of errors in the inversion process, since they are tool- and processing-specific. Different tools require joint analysis of all available data and special noise reduction techniques associated with the structure of the acquisition system.