Vol 276 Iss. 2

A comprehensive study of the Carnian diamonds of the Bulkur anticline in the northeastern Siberian craton has been conducted. Two most common diamond types in the Bulkur area have been identified: scarred dodecahedroids and crystals of varieties V-VII according to the Yu.L.Orlov classification. These groups are characterized by a lighter carbon δ13C isotope composition from –19.6 to –24.7 ‰, differing in morphology, concentration and forms of nitrogen aggregation, and composition of melt inclusions. Submicroscopic inclusions in diamonds of these groups have been studied for the first time. Such inclusions in dodecahedroids are of less ferruginosity (12 and 31 wt.% FeO on average) and more enriched in potassium (5.5 and 1.7 wt.% K2O on average) compared to diamonds of varieties V-VII. It is concluded that the studied dodecahedroids with scars from the Carnian deposits of the Bulkur anticline represent a separate type of diamonds characteristic to the northeast of the Siberian platform. It is assumed that the primary sources are Precambrian in age and that the diamonds entered the Triassic and younger placers as a result of the erosion of Proterozoic coastal-marine deposits within the Precambrian protrusions, in particular on the Olenek uplift.

Drilling of horizontal wells with multi-stage hydraulic fracturing (MFHW) is one of the most common solutions in the development of low-permeable oil and gas reservoirs. At the same time, the estimation of the well and reservoir parameters by well test analysis is complicated due to long time response to the radial flow regime. It is possible to eliminate uncertainty dealt with the absence of radial flow response by using data from the early radial regime that occurs at early times of pressure buildup. However, its appearance is only possible if the distance between the parallel fractures is much larger than the fracture half-lengths, which is not usual in practice. At the same time, MFHW demonstrate a complex buildup behavior due to fracture interference. By analytical and numerical simulations it is shown that the early time buildup behavior depends on duration of well production before shut-in. This behavior is similar to the buildup of a vertical well near the sealed boundary. For short production times, a radial-like regime may appear at early buildup times caused by elliptical flow around the fractures. The consistency of this regime and the relation of the pressure derivative plateau level to the parameters of the elliptical flow are justified. An empirical formula of sufficient accuracy has been obtained for reservoir transmissibility (flow capacity). This formula is applicable for the most common range of parameter values of the MFHW. These results open up new opportunities for reliable assessment of the well and reservoir parameters from well tests in MFHW in low-permeability reservoirs, including new wells or wells restarted after a long inactive period.

Polymodality of statistical sand grain size distribution is due to the changes in kinematic energy of aquatic environment during the process of sediment deposition in open system-facies. Improving relevance of information about deposition paleoenvironment is of high significance in interpretation of granulometric analysis results. The paper investigates the results of granulometric analysis of sandy-aleuritic deposits confined to different formations in the wells located in the oil fields on the Yamal Peninsula. Based on the kinematic theory of open system transformation, the equation that describes the dependence of grain size on grain kinematic parameters – time period and transport distance – was developed. Therefore, it is possible to calculate these parameters within the studied facies on the basis of available grain sizes and percentage of fraction with diameter range from 0.001 to 1 mm. The aim of this study is to present a new approach to facies identification based on the calculations of kinematic parameters of sand grain flow and fine grains using the equations of open system transformation intensity within the universal kinematic theory. The parameter which was proved the most informative is sediment transport distance during deposition, which is controlled by the size of the settling grains. This parameter is influenced by bed slope angle, grain size, and deposition depth. Comparing the value of this parameter with fraction diameter, it is possible to identify the facies of the studied area.

A potential method for modifying saponite (intercalation) ensuring its high sorption capacity for gold was theoretically and experimentally substantiated. Saponite isolated from recycled water of processing plant tailings dam is modified by mixing a suspension of the mineral and acetone with the surfactant hexadecyltrimethylammonium bromide (CTAB) followed by four washings with ethanol and distilled water, and drying. The intercalation mechanism of saponite-containing product involves the introduction of positively charged cations of organic compounds into the interlayer space through cation exchange or adsorption, which leads to expansion of mineral layers and an abrupt shift in zeta potential toward the positive side. The appearance of bands in the IR spectral ranges of 1460-1490 and 2850-2920 cm^–1 related to the deformation and stretching vibrations of the CH₂ group, respectively, confirms the successful incorporation of CTAB molecules into the mineral structure. Studies of the maximum sorption capacity of modified saponite revealed that at initial gold concentration 22.6 mg/l, complete extraction is achieved after 7.5 min. The maximum static exchange capacity of modified saponite was achieved after contact with the third portion of fresh gold-bearing solution and amounted to 100.5 mg/g. Gold sorption isotherms correspond to the Langmuir model which presumes that a monomolecular sorption layer forms on the surface of the modified saponite, and all active sites have equal energy and enthalpy of sorption. The kinetic dependences of sorption are best described by a pseudo-second order model, which presumes that the chemical exchange reaction limits the sorption process. It was found that saponite intercalation with hexadecyltrimethylammonium bromide ensures a more efficient sorption of negatively charged gold complex ions ([AuCl₄]^–). The calculated equilibrium static exchange capacity of modified saponite was 92-119 mg/g, while the experimentally determined value was 102 mg/g.

Recent research on predicting petrophysical and mechanical properties of carbonate rocks, integrating textural and microstructural observations with geotechnical measurements, has sparked critical discussions. While some studies present robust experimental methods and fresh insights, others rely on less rigorous approaches. In the Mediterranean area, shallow-water calcarenites crop out along both the coastline and internal areas. Typically, these carbonates are soft and exhibit high porosity, open in type, controlled by the depositional fabric and post-depositional processes. Their strength primarily depends on the type and amount of calcite cement, with water presence significantly impacting their stress-strain behavior. Strength and stiffness decrease markedly in the transition from dry to saturated conditions. Well-cemented calcarenites with early and late diagenetic cement exhibit brittle behavior in both dry and saturated states, whereas poorly cemented types with early calcite cementation alone show brittle behavior when dry and pseudo-ductile to ductile behavior when saturated. Dual-porosity systems, combining micro- and macro-pores, dominate the hydraulic properties of calcarenites, playing a key role in decay mechanisms and patterns. This study compares existing literature with laboratory analyses of calcarenite lithofacies from Apulia and Basilicata (Southern Italy), yielding new insights into their mechanical and physical behavior, as well as durability.

The goal of this study is to enhance the method for predicting geomechanical processes during mine working construction in an elastoplastic rock mass with dilatancy. We present the results of experimental research into the volumetric strength of rocks and the specifics of volumetric strain development under plastic shear. We demonstrate rock dilatancy and provide diagrams showing how volumetric plastic shear strains change at different levels of accumulated shear strains. We process the rock testing results using A.N.Stavrogin’s plasticity condition. We propose a new analytical solution for predicting the stress-strain state of the rock mass in areas with inelastic strains, based on A.N.Stavrogin’s plasticity condition. This includes equations for modelling the limit state zone of rock around a mine working. We introduce an algorithm for predicting the stress-strain state of the rock mass. We investigate how the size of the limit state zone around a mine working relates to rock dilatancy parameters, lateral stress coefficient, and working depth. We examine how contour displacements develop for a circular mine working under plane strain conditions, considering various plasticity parameters and rock dilatancy indicators. We implement A.N.Stavrogin’s plasticity condition in the Abaqus software package. Our research results help define the scope of the analytical solution. The solution remains physically meaningful only when the limit state zone forms around the entire perimeter of the mine working. The proposed numerical approach removes this limitation. It applies to any geomechanical state of the rock mass and to mine workings with any cross-sectional shape.

We examine crystallization conditions for saturated brines of calcium, potassium, and magnesium chlorides from the Angara‑Lena artesian basin, Siberian Platform. The study focuses on temperatures matching actual thermal conditions in wells of the “Lithium” site at the Kovykta gas‑condensate field. This critical type of lithium‑bearing raw material is classified as hard-to-recover reserves. In most wells (depths to 2.2 km), rock temperatures in the upper geological section remain below 20 °C. During well operation, various salts precipitate from saturated magnesium-calcium chloride brines within the production line. This leads to rapid wellbore clogging and eventual production shutdown. Thermodynamic analysis of phase diagrams reveals that crystallization yields antarcticite CaCl₂·6H₂O, tachhydrite Mg₂CaCl₆·12H₂O, minor amounts of carnallite KMgCl₃·6H₂O, bischofite MgCl₂·6H₂O, and several other chlorides, depending on temperature. At temperatures above 55 °C, salt precipitation becomes negligible. Thermohydrodynamic simulations of a single flowing well under hydrogeological conditions similar to those at the Kovykta area (southern Siberian Platform) demonstrate the feasibility of long-term (1 month to 1 year) exploitation of saturated sodium-chloride and calcium-chloride lithium-bearing brines. Such operations can yield lithium production rates of 31.2 to 4.2 t per well.

This paper addresses the necessity of refining standard triaxial testing methods for characterizing the mechanical behaviour of salt rocks. Triaxial testing is a key tool for determining the strength and deformation characteristics of rocks; however, existing standards often fail to account for the unique features of salts, such as their highly plastic behaviour, creep, temperature sensitivity, and defect-healing capability. The work highlights the critical importance of considering large strains and volumetric changes of specimens during testing, as this enables a more accurate representation of the behaviour of salt rocks, as this enables a more accurate representation of the behaviour of salt rocks. It is proposed that current standards be updated by incorporating well-established correction equations for geometry evolution and volumetric strain, as well as by adopting the Hencky strain measure. Experimental results obtained on natural salt rock specimens and salt-based geomaterials demonstrate significant errors in the evaluation of the stress-strain state when traditional data-processing methods are applied without accounting for the specific properties of salts. The analysis underscores the need to revise existing triaxial testing standards in line with the proposed approaches, thereby improving the accuracy and reproducibility of data that underpin geomechanical modelling and engineering design.