Vol 73, No 1 (2018)

In this paper 2D and 3D modeling of thermal evolution of sedimentary cover and OM evolution of the source-rock sequences (SRSs) of the East Siberian Sea were conducted. The distribution of the temperature and reflection of vitrinite in sedimentary cover is presented along the composite seismic profile of the section. Maps of the distribution of the temperature of sedimentary sequences, reflection of vitrinite of the SRSs for various temporal boundaries, and the degree of OM transformation of the SRSs for the presentday stage of evolution were plotted. The evolution of OM maturity and possible processes of hydrocarbon generation of the SRSs were analyzed on the basis of modeling results.

The compositions of approximately 70 naturally quenched melt inclusions in olivine, clinopyroxene, orthopyroxene, and plagioclase phenocrysts from tephra of the soil–pyroclastic cover of Simushir Island (Central Kuril Islands) were studied. The concentrations of the major rock-forming components, H₂O, S, and Cl were analyzed in inclusions. The reconstructed melts contain 48.6–78.4 wt % SiO₂, 0.3–8.26 wt % MgO, and 0.12–1.72 wt % K₂O. The concentration of S and Cl in the melts changes regularly with increasing SiO₂ content: from 0.14 to ~0.02 wt % S and from ~0.05 to ~0.28 wt % Cl. The content of H2O in parental melts is 4.2–4.5 wt %.

Based on the experience of developing an oil field on the Caspian Sea shelf, which was initially exploited with injection of seawater into the oil-bearing beds to maintain reservoir pressure, the deposition of sulfate salts under reservoir conditions is predicted. The prediction of sulfate deposition is made in two ways: analytical calculations according to the method of J.E. Oddo and M.B. Thomson and computer modeling. The prediction took the strontium content in the formation waters of the oil-field into account, which is usually ignored in production practice. It has been established that the prediction by computer modeling is more accurate; in particular, it considerably expands the temperature limits of anhydrite precipitation. The amount of potentially precipitable sulfate salts found by computer modeling has shown that the mass of deposited calcium and strontium sulfates is rather large, which can significantly reduce the permeability of the reservoir.

Experiments were carried out on the leaching of trace elements (Li, Rb, Cs, Sr, Ba, V, Mn, Fe, Co, Ni, Cu, Tl, Y, La, Ce, Th, and U) from unmodified ashes of Karymsky volcano (the Kamchatka Peninsula) under the interactions with 0.01 M oxalic, salicylic, tartaric, citric, and acetic acids at various proportions of solid and liquid phases. Based on the data we obtained, it was concluded that the trace elements were mainly mobilized owing to the destruction of crystalline structures of rock-forming minerals, as well as to the reduction of Fe(III) and Mn(IV) oxide–hydroxides into soluble Fe(II) and Mn(II) compounds (in the case of oxalic acid). The formation of organic complexes increased the stability of metals in a solution and provided the attainment of higher concentrations of the dissolved forms compared to the case without organic ligands.

The variation in the microstructure of clay soils during their deformation under triaxial compression conditions is considered. A comprehensive procedure for the numerical description of variations in the structural features of clay soils during their deformation under triaxial compression conditions is proposed. The research results suggest that major variations in the sample structure occur at the time of deformation instability. These variations include the redistribution of the pore space and the pronounced orientation of the structural elements of the soil. Further deformation of the soil does not change the ratio of the number of pores, but the orientation of the structural elements increases throughout the entire deformation process.

This article presents the results of long-term field studies on methane in the upper part of the permafrost for different geomorphological levels of Central Yakutia. Patterns of the spatial distribution of the methane content across different landscapes were found. The difference in the methane content in sediments of the Late Pleistocene ice complex on the left and right banks of the Lena River was found for the inter-alas areas. This was caused by different conditions of formation: the formation of a thin cover of deposits occurred under sub-aqua conditions favorable for methanogenesis on the left bank and in more dry aerobic conditions on the right bank. The highest concentrations of methane were found in alas deposits, where the major role belongs to the duration of freezing after draining the thermokarst lake in subaerial conditions. The methane content is highly variable both laterally and with depth in the studied deposits, but there is no redistribution after freezing; this allows one to use methane as a paleo indicator of the conditions of accumulation and freezing of sediments.