Science and technics

The article analyzes the amplitude spectra of audio magnetotelluric sounding (AMTs) data. Particular attention is focused on the frequency range from 1 to 5 kHz, which is called dead band. We analyzed the data of base stations used in the fieldwork during the summer and autumn seasons in 2013, 2014, and 2017. The area of work is located in the Chukotka Autonomous Area beyond the Arctic Circle. Previous researchers noted that a reliable signal in the dead band can only be obtained at nighttime. The authors of the article found that in Chukotka region in the daytime against the minimum signal within the dead band there is a local maximum at a frequency of 2.4 kHz. When registering a field for more than 3 hours during daytime, in most cases, it is possible to restore the frequencies of 2.2 and 2.6 kHz. These frequencies are reliable benchmarks, allowing in some cases to restore the AMT curve using the correlation between amplitude and phase. We have proposed ways to improve data quality in the dead band when measured during the daytime.

The article suggests the method for forecast of surface deformation during excavation operations in restraint urban conditions using the slurry trench technique based on FEM simulation. The results of numerical simulation of the construction of a semi-underground structure with slurry trench technique are given. The regularities of the change in the stress-strain state are determined depending on the trench parameters and the physical-mechanical properties of the soils. The work presents the troughs of surface subsidence during the construction of an excavation using the slurry trench technique, the diagrams of bending moments, transverse and longitudinal forces arising in the trench. Numerical experiments in Plaxis 2D and 3D were performed to estimate the discrepancy between modeling results in a plane and volumetric formulation of the problem.

The object of study is the system of hydrotransport of iron ore processing tailings at JSC «EVRAZ Kachkanarsky GOK». The aim of the work was to determine the parameters of the hydraulic transport of tailings of the iron ore enrichment at weight concentrations of the solid phase from 30 to 70 % and to develop recommendations for the industrial operation of hydraulic transport systems of highly concentrated slurries of the Tailing Facilities of the Kachkanarsky GOK. Laboratory studies of the parameters of hydrotransport of thickened tail pulps were carried out with the development of a calculation method; pilot tests of the hydrotransport system under the conditions of the Tailing Facilities of the Kachkanarsky GOK. It has been established that using polyurethane coatings on the inner surface of the slurry lines significantly (1.75 times) decrease the specific pressure loss on the hydrotransport of thickened fluids. This allows to significantly increase the range of transportation for placing tailings in the distant parts of the storage zone. The introduction of research results is in the project of reconstruction and development of the tailing facility of the TF of the Kachkanarsky GOK for the period 2018-2020. It is proposed to use the results of work in the project of reconstruction of the hydraulic transport system at the TF of the Kachkanarsky GOK by switching to the hydraulic transport of slurries thickened to weight concentrations of 35-40 % in the slurry pipes with an internal polyurethane coating, which will ensure energy saving in the hydraulic transport process.

The paper discusses the peculiarities of structural modelling (forecast of the depths of the reflecting horizons) based on the seismic and drilling data system. Seismic data are represented by vertical time values and the stacking velocity of borehole data that are the depth marks of the reflecting horizons. Vertical time and the depth of the reflecting horizons are bound by the equation of average velocity but the average velocity is not determined in a seismic experiment, therefore an issue of choosing a velocity model of a complex natural object arises. The task of structural modelling is solved by the selection of formal expressions containing correlations between the parameters of the underlying model and kinematic parameters of the wave field. The optimal decision on model selection is determined by the minimum discrepancy between the predicted and actual values of the depth of the sample boreholes. A practical example shows possible variants of the interpretation model. An inverse kinematic problem on converting the vertical time of the reflected waves at the depth of horizons is solved in each production report on the results of seismic work and is probably the most common objective of seismic exploration. Considering the variety of research objects and the apparent obviousness of the solution, this topic is underrepresented in scientific literature.

GEOLOGY Aleksey Egorov, Doctor of Geological and Mineralogical Sciences, Head of Department, Saint-Petersburg Mining University, Russian Federation; Ilya Vinokurov, Candidate of Geological and Mineralogical Sciences, Deputy Head of Department, A.P.Karpinsky Russian Geological Research Institute (VSEGEI); Alexander Telegin, Doctor of Geological and Mineralogical Sciences, Professor, Saint-Petersburg Mining University.

The purpose of this study was to obtain diagnostic features and criteria for the distribution of heavy metals in technogenically altered soils in the area of industrial facilities, depending on their altered geochemical properties, which make it possible to fix chemical elements in landscapes (the formation of geochemical barriers). On the basis of the geoecological assessment, disturbance of the soil buffer properties, which is reflected in the ionic composition change, alkalization, pH increase, and sulfate-chloride salinization have been revealed. This forms the heavy metals alkaline barrier. For example, in case of Cu, Pb, Zn, and N, it contributes to their accumulation and subsequent concentration in the soil layer due to the exchange interactions between chemical elements and Na+, K+, Ca2+ cations. Soil saturation with sulphates also increases the probability of metals demobilization in the soil layer. It has been shown that intra-sectional soil migration of oil products (one of the most common pollutants of industrial areas) and chemical elements occurs at a depth of 30-50 cm, where the oil products based on a clay sorption layer form a technogenic barrier. The direct correlation between the oil content in the soil and the amount of toxic sulphate and chloride salts was found. The set of identified factors forms technogenic geochemical barriers in the industrial production area, on which pollutants and chemical elements, including heavy metals, are demobilized. The revealed effects are the rationale for creating artificial geochemical barriers on the migration path of both pollutants and valuable components with the aim of their subsequent extraction from the soil when developing an appropriate extraction method.

GEOECOLOGY AND OCCUPATIONAL HEALTH AND SAFETY

The issue of drilling mud multiple use is problematic. To reuse, the solution must be efficiently cleaned from solid particles according to the class of 0.04-0.07 mm. An analysis of existing technologies and equipment has shown that drilling mud regeneration schemes are rather difficult to operate and expensive. In world practice there has been a tendency to create universal equipment, which allows most complete cleaning cycle for a drilling mud in fine grades. The paper proposes an innovative vibroacoustic module for cleaning drilling muds from sludge. The creative element of the proposal is the impact of vibroacoustic oscillations on the drilling mud passing through the mesh element. At the same time, specific effects arise around the mesh, which increase the productivity and efficiency of the process. The design of the vibroacoustic apparatus and the principle of its operation are presented. An important element of the proposal is that the oscillation is created by pistons interconnected by rods and located on opposite sides of the mesh. This dipole system provides the excitation of variable pressures of different polarity before the mesh and after it. The results of industrial tests of the vibroacoustic module when servicing the BU-75-BrE drilling rig are presented. The dependence of the installation performance and efficiency on the amplitude of oscillations was found. The optimal dynamic range of exposure (from 5.5 to 6.5 mm) was determined. Analysis showed that in the composition of the cleaned drilling mud, the maximum particle size of the solid phase did not exceed 0.04 mm. The conducted industrial tests confirmed the possibility of using the vibroacoustic module for cleaning the washing fluid and developing a pit-free drilling technology on its basis.

Knowledge of the current stress-strain state of any section of the pipeline allows you to make informed decisions on its operation, maintenance and repair, as well as on the prediction of the technical condition. The task of determining the characteristics of the stress-strain state of a gas pipeline section that has cold bend offsets (CBO) according to in-line inspection (ILI) is considered. The bent part of CBO is characterized by the presence of residual stresses and deformations in the wall of the offset, which contribute to the overall level of the stress-strain state of the gas pipeline operating under external and internal loads. Using the results of in-line diagnostics, numerical modeling and a solution, the change in the values of longitudinal stresses, is determined and the need to take into account residual stresses in the zone of elastic-plastic deformations of cold bend offsets is shown.

The article deals with safe operation issues of vertical steel reservoirs with an internal floating roof when storing volatile oil products. The purpose of the work is to study the influence of ventilation openings area and wind speed on the duration of explosive state of vertical reservoirs with an internal floating roof. The influence of ventilation pipes’ dimensions and the wind speed on the duration of explosive state of the reservoir has been studied. Method for calculating this time is proposed. It is shown that natural ventilation of the reservoir gas space is caused by the effect of two forces, which are formed due to: 1) the density difference between the vapor-air mixture in the reservoir and outside air; 2) wind pressure occurring on the roof of the reservoir. An algorithm for calculating the duration of reservoir being in an explosive state with wind pressure and no wind is obtained. The greater the difference in geodetic marks of the central and peripheral nozzles, the more efficient the ventilation. This distance will be greatest if the lower ventilation pipes are located on the upper belt of the reservoir or the reservoir is equipped with an air drain. Increase in wind speed of more than 10 m/s does not significantly affect the duration of the reservoir being in an explosive state. Increasing the diameter of the central nozzle from 200 to 500 mm can significantly reduce the duration of the reservoir degassing in windless weather.