Study on Gas Control Methods Optimization for Mining Safety

Effective gas control is of significance for safe efficient coal mining in Haizi Coal Mine and other mines with similar geological conditions. This study concentrates on gas control theories and techniques in multiple coal seams of Haizi Coal Mine (No. 7, No. 8, No. 9, and No. 10 coal seam from top to bottom). To minimize risk of high gas emission and outburst hazard, No. 10 seam was mined first as a protective seam prior to the mining of its overlying outburst-prone No. 7, No. 8, and No. 9 seam. Four gas drainage measures were determined for gas control, including cross-measure boreholes into overlying coal seams, surface goaf wells, roof boreholes, and roof gas drainage roadway. These gas control measures, if implemented through entire coal seam extraction, would be possibly uneconomic. An investigation was undertaken to analyze effects of those four measures on gas emission, methane concentration, and gas drainage quantity in No. 2 1024 mining panel of No. 10 seam. Results indicate that the highly expensive gas drainage measure of a roof roadway has poor drainage performance and could be effectively replaced by roof boreholes. When adopting the optimized combination of gas drainage measures, drainage efficiency of No. 7 seam, No. 8 seam, and No. 9 seam could reach 58.64% and decrease gas pressure to be below 0.74 MPa. Outcomes of this study could provide beneficial guidance not only for gas drainage design optimization in Haizi Coal Mine but also for other multiple-seam mines with similar mining and geological conditions, for increasing gas drainage efficiency and guaranteeing mining safety.

INFLUENCE OF TECTONIC DISTURBANCES OF COAL LAYER ON HIS GAS DYNAMIC STATE

Problem Statement and Purpose. At one of the coal mines of the Donetsk basin, there was a sudden release of coal and gas. The peculiarity of this case is that the accident happened in the place of the alleged development of a geological disturbance, but without any visible signs of this. Inspection of the ejection site and adjacent horizons made it possible to conclude that the emergency site is located in the place of the plicative disturbance development. Thus, it is necessary to study in more detail the influence of disturbed zones hidden nature on the gas-dynamic state of the reservoir, as well as to develop and implement methods for determining such zones. Data & Methods. To achieve this goal, a new method was tested, based on the property of structureless substances to form crystal-like units. This phenomenon has been studied for decades; therefore, such new formations have long been given the name quasicrystals. It was noted that the increase in the concentration of such forms is associated with the presence of geological disturbances. Consequently, the increase in quasicrystals in the rock is an indicator of its disturbance due to the influence of tectonic pressure. Thus, in order to test the technique and reveal the hidden geological disturbance of the coal seam, coal samples were taken, microstructural features were studied, and the strength of the coal seam was measured at 56 points. Result. As a result the values of the concentration of quasicrystals, data on the strength of the formation were obtained, a schematic map of the development of the disturbance in this area was built, its contours were determined, the center of the disturbed zone was identified and the role of such disturbances in the outburst hazard of the formation was substantiated. It has been established that geological disturbances, even of plicative nature, have a high degree of fracturing. Such pores and cracks in coal reduce the strength properties and are able to concentrate sufficient volumes of gas for manifestation of GDP.

Fundamentals of Creating a Subsystem for the Forecast of Outburst Hazard of the Multifunctional Safety System of a Coal Mine

Substantiation of the feasibility of incorporating the methods and means of the forecast of outburst hazard as a subsystem for forecasting outburst hazard into a multifunctional safety system of the coal mine is given. This is due to the reduction in economic costs for increasing the reliability of the forecast, since in this case the forecast can be carried out considering the information received by other subsystems of the multifunctional safety system. As such an outburst monitoring subsystem integrated with a multifunctional safety system, the combination of the spectral-acoustic forecasting method with the mine air-gas control system is justified. It is shown that for the efficient operation, the outburst hazard forecasd subsystem must meet the following requirements: be based on the geophysical methods for monitoring the stress state of the bottomhole space, control the main outburst hazard factors, have an operational method for determining the outburst hazard criterion for the planned development of a reservoir section, have a scientifically substantiated «depth of sensitivity» hazard ahead of the face, be computerized and have a dedicated infrastructure unit to maintain the system. The latter should include geophysicists trained in the physics of wave processes in the anisotropic media. It is shown that the outburst hazard forecast subsystem should include functional and supporting parts. Functional part responsible for the information processing algorithm to determine the indicator and criterion of the outburst hazard should be based on the outburst preparation model, which considers the main outburst hazard factors: rock pressure, in-situ gas pressure, and the coal strength. As such, the model of two-stage preparation of an outburst is considered. In accordance with this model, at the first stage, a block structure of coal is formed in the bottomhole space of the working due to the growth of cracks under the influence of rock and gas pressure. On the second stage, the destruction of a relatively thin layer of coal at the mouth of the outburst cavity and the squeezing of the formed pieces of coal into the working. After that, the actual outburst begins.

Outburst hazard of little-studied lakes assessment at the Mongun-Taiga massif

There is a reduction in the area of glaciation of mountain massifs as a result of climate warming, which leads to the formation of lake-glacial complexes in areas of glaciation degradation. These complexes are dynamic systems that are rapidly changing over time, therefore, unstable and potentially outburst. Moraine and periglacial lakes outbursts are dangerous hydrological phenomena. As a result of outbursts catastrophic floods and mudflows can form, causing serious damage to the infrastructure of settlements located downstream and often leading to human toll. Therefore, the study of outburst-hazardous lakes is necessary and is an important applied problem associated with forecasting natural hazards. In this paper an the outburst hazard of little-studied moraine and periglacial lakes at the Mongun-Taiga mountain massif (Tyva Republic, Russian Federation) assessment was carried out using the scoring method, supplemented taking into account regional characteristics, using data from remote sensing of the Earth. The performed assessment according to satellite images showed that most of the massif's lakes have a high outburst hazard. Based on the assessment results a group of lakes was selected located in the right branch upstream of the river “Tolaity” for the purpose of a more detailed field survey (hydrological and geophysical studies were carried out). Field work carried out on the selected group of lakes allowed us to correct the performed assessment. In paper the applicability of the method based on comparing field data and data obtained from satellite images was estimated.