Анастасия Литвинова

In Ancient Greece, extraction of gemstones was considered a matter of national importance. At times, the war could start at the territories if they were rich in precious stones. One such location was the city of Chalcedon, situated on the shore of the Sea of Marmara. Numerous stones of various colors and shades were mined there. Local people called them "chalcedony", which gave the name to the mineral itself.

The balance of electricity consumption a significant part is occupied by the production of compressed air at the mining enterprises. Many compressor stations of enterprises are equipped with automated parameter management systems that allow reliable, uninterrupted and safe operation of the compressor facilities. But the majority of automation systems at compressor stations do not perform the function of monitoring the energy efficiency indicators of the operation of a compressor station.

The paper addresses issues of using the active rectifier in partially loaded variable frequency drive as active filter in the conditions of non-sinusoidal current and voltage disturbances caused by the presence of high-power nonlinear load in the grid. The topology of transformless three-level converter for 6-10 kV suitable for proposed solution has been presented and its mathematical model has been de-rived. Based on the model, the direct power control algorithm with ability to compensate non-linear currents has been designed. The investigation of active rectifier efficiency was performed depending on the relation between linear and non-linear load currents of the grid node, as well as on active power load of the active rectifier. Efficiency analysis was based on the developed computer model of the grid node with connected non-linear load simultaneously with the variable frequency drive with active rectifier.

Creating shifts of the lyaers in a deforming workpieces improves the quality of the product produced by pressure treatment. qual-channel angular pressing and precipitations of a cylindrical billet with a rotating turnaround were developed by specialists earlier and became basic for scientists engaged in nanotechnology. One of the most modern schemes for creating nanostructures by processing on presses is the «Cyclic Extrusion Compression» scheme (in Russia – «Hourglass»), which has significant drawbacks.

Natural chalk is characterized by a fine-grained structure. The processing of chalk in conditions traditional for calcium carbonate baking is accompanied by its almost destruction and the formation of a huge amount of dust. The paper presents strength characteristics of chalk and chalky stone baking obtained with different temperature-time conditions of heating the raw material to a temperature of 450-600 C. The uniaxial compression method was used to determine the strength depending on variable factors.

The paper considers variants of lightweight cement compositions with additives of various substances, such as clay components, ash systems, silica additives, kerogen, gilsonite, microspheres, as well as the process of cement slurry aeration. Recommendations on the use of compositions in different conditions are presented. A decrease in the density of the solution is achieved not only due to the low density of the materials used, but also as a result of an increase in the water-cement ratio. In such conditions, it is not possible to ensure the formation of a durable and impermeable cement stone in the well, which creates high quality inter-reservoir insulation. The characteristics of the physical and mechanical properties of existing lightening additives are given, which allows determining the most rational conditions for the use of cement slurries for improvement of the well cementing quality.

The paper discusses the results of interpreting well tracer studies. It is shown that from the law of mass conservation it follows that when filtering a volume of an indicator, part of the injected tracer flows into the matrix. With the flow of fluid containing the indicator from the low-filtration resistance channel (LFR) into the surrounding matrix, the linear dimensions of the flow area depend on the permeability and porosity properties of the high-permeability channel and the matrix. While another part of the tracer moves toward the production well, its mass is lost due to diffusion processes. From the solution of the diffusion equation, it follows that the initial concentration of the tracer decreases in the course of filtration along the LFR channel. To interpret the results of the tracer studies, different cases of the LFR channels' location in the volume of the productive formation are considered. The varied parameter allows characterizing the presence of several peaks in the concentration of the indicator and calculation the filtration parameters of the LFR channels.

During development of drilling projects, a whole array of data is needed considering the properties of rocks and the conditions of their bedding. Accounting for geomechanical processes occurring in the near-wellbore zone allows avoiding many complications associated with the violation of the wellbore walls stability at all stages of its construction and operation. Technological and technical factors such as vibration and rotation of the drilling string, formation of launders during the descent and ascent of the assembly, pressure pulsation during the start and stop of pumps, hydrostatic and hydrodynamic pressure of the drilling fluid, its composition and properties, have a great influence on the stress-strain state of the medium opened by the well. The washing fluid circulating in the well should provide backpressure to the reservoir, not interact with the rocks chemically, colmatage channels in porous and fractured rocks, preventing penetration of the mud into the medium, by creating an impermeable barrier at drilling clay seams that are prone to swelling, cracking, etc.

During the development of minerals by the underground method, dynamic manifestations of rock pressure occur at a certain depth, which significantly reduces the safety of mining operations. Regulatory documents prescribe at the exploration and design stages to establish the critical depth for classifying a deposit as liable to rock bumps. Currently, there are a number, mainly instrumental, methods for determining the liability of rock mass to rock bumps and methods based on the determination of physical and technical properties and the stress-strain state of rock massifs.