During the “12th Five-Year Plan” period (2011–2015), the safety production situation of coal mines in Guizhou province was generally good. The main types of accidents are gas, flood and roof accide...

Characteristics and trends of coal mine safety development

Experimental and numerical investigations on dynamic mechanical responses and failure process of gas-bearing coal under impact load

A new method for coal and gas outburst prediction and prevention based on the fragmentation of ejected coal

Large and super-large section chamber groups in coal mines are frequently affected by dynamic loads resulting from production activities such as roadway driving and blasting The stability of the surrounding rock is poor, and it is difficult to control In this paper, a similar simulation test was used to study the deformation and evolution laws of the surrounding rock of a triangle-shaped chamber group under different dynamic loads The results showed that under dynamic loading, the vertical stress of the surrounding rock of the chamber group increased in an oscillatory form The maximum stress concentration coefficient reached 409 The damage degree of the roof was greater than that of the two sides The deformation of the roof was approximately 12 times that of the two sides For the chamber closer to the power source, the stress oscillation amplitude of the surrounding rock was larger, and the failure was more serious The force of the anchorage structure showed a phased increasing characteristic; additionally, the force of the anchorage structure on the adjacent side of the chambers was greater than that on the other side This study reveals the deformation and failure evolution laws of the surrounding rock of large section chamber groups under dynamic loading

Similar simulation study on the deformation and failure of surrounding rock of a large section chamber group under dynamic loading

The reservoir permeability dominates the transport of gas and water in coal seam. However, coal seams rich in gas usually contain various pores and fractures blocked by a large amount of minerals, which leads to an ultra-low permeability and gas extraction rate, and thus an increase of drilling workload. We first propose a thermo-hydro-mechanical-chemical coupled model (THMC) for the acid fracturing enhanced coalbed methane recovery (AF-ECBM). Then, this model is applied to simulate the variation of key parameters during AF-ECBM using a 2D geometry. The effect of different extraction schedules are comparatively analyzed to give an insight into these complex coupling responses in coal seam. Result confirms that the AF-ECBM is an effective way to increase the reservoir permeability and improve the gas production using the proposed model. The range of permeability increment zone increases most dramatically in the way of acid fracturing, followed by none-acid fracturing and acidizing over time. The gas production in order is: acid fracturing (AF-ECBM) > fracturing (F-ECBM) > acidification (A-ECBM)> direct extraction (D-CBM).

A Thermo-Hydro-Mechanical-Chemical Coupling Model and Its Application in Acid Fracturing Enhanced Coalbed Methane Recovery Simulation

To explore the law of ground deformation from shallow-buried close-distance multi-seam mining, an observation station was built in the Bulianta Coal Mine to measure and record the periodic variation of related parameters about ground subsidence and surface cracks with the advancement of working face. From the data observed from the field, it can be found that, when lower seam mining, the ground subsidence above the previously mined area was deeper and steeper than that above the left pillar; besides, the influence scope of the former was larger than that of the latter. In terms of ground cracks, the ground cracks were formed ahead of the working face and developed rapidly during the period of the breakage of the immediate roof. Besides, the average interval of the ground cracks above the previous gob was 14.75 m, and still existed and hardly changed after the advancement of the working face; while that above the left pillar was 27.8 m and most of them were closed. In addition, when the advance rate of the working face was 12.8 m/day, the advance influence distance of the mining surface crack reached the minimum of 13.6 m. This finding is helpful for protecting the surficial environment in mining area during and after mining operations and is also of significance to conduct green mining in other mining areas.

Ground Subsidence and Surface Cracks Evolution from Shallow-Buried Close-Distance Multi-seam Mining: A Case Study in Bulianta Coal Mine

Environmentally friendly techniques for high gas content thick coal seam stimulation─multi-discharge CO2 fracturing system

Stress-dominated coal and gas outburst disaster has become one of the main safety problems in deep coal mines. Acoustic emission (AE) or microseismic technology has been viewed as a promising method that can effectively reflect the stress and stability status of rock mass. The AE activity precursor of coal failure is the theoretical basis of this technology. In this study, AE experiments in failure process of coal specimens with different properties and under different stress conditions were performed in laboratory to explore influence factors and their effect of AE activity, and AE activity pattern classification was proposed based on the failure type of coal. The results indicate that the AE activity of different coals under loading are associated with the failure phase, and the evolution pattern of AE activity depends on the failure type of stressed coal. Both the mechanical property and the external stress condition have an important influential effect on the failure type and AE activity pattern in coal failure process. The internal mechanical property decides the inherent tendency of stressed coals to perform brittle or ductile behavior, and the responded AE activity pattern. The contrast of fissure distribution of specimens suggested that fissure structure in coal significantly affects the fracturing mode of coal in uniaxial compression and the AE activity pattern. The external stress condition has a transition effect on AE event energy distribution and AE activity pattern. Under the effect of external stress condition, the energy distribution of AE events was transforming between relative disperse and relative concentration, the failure type and AE activity evolution pattern of coal could appear the brittle-ductile transition. Based on the view of failure type, the pattern of AE activity of coal failure can be classified into three types, i.e., ductile, brittle, and semi-brittle pattern. It is suggested that the high-level AE activity can be viewed as the precursor of brittle instability of coal, and relative quiet phenomenon of AE activity as the precursor of ductile or semi-brittle instability. The research achievement can provide a theoretical base for the prewarning criteria establishment of coal and rock dynamic disasters at depth and improve the insight of AE activity in the coal failure process.

https://www.mdpi.com/1996-1073/11/6/1414/pdf

Experimental Investigation on Influence Factors of Acoustic Emission Activity in Coal Failure Process

https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.508

Influence of water soaking on swelling and microcharacteristics of coal

Coal and gas outburst is one of the main gas hazards in coal mines. However, due to the risks of the coal and gas outburst, the field test is difficult to complete. Therefore, an effective approach to studying the mechanism and development of outburst is to conduct the similar physical simulation. However, the similarity criteria and similar materials in outburst are the key factors which restrict the development of physical simulation. To solve those problems, this paper has established similarity criteria base on mechanics model, solid–fluid coupling model and energy model, and presented high similar materials. Combining with three groups of similar number, and considering similar mechanical parameters and deformation and failure regularity, the similarity criteria of outburst is determined on the basis of the energy model. According to those criteria, we put forward a similar material consists of pulverized coal, cement, sand, activated carbon, and water. The similar material has high compressive strength and the accordant characteristics with the raw coal, include density, porosity, adsorption, desorption. The new research is promising for preventing and controlling gas hazards in the future.

/pdf/similarity-criteria-and-coal-like-material-in-coal-and-gas-3ji2l7ap7a.pdf

Guangcai Wen

Papers

Ground Subsidence and Surface Cracks Evolution from Shallow-Buried Close-Distance Multi-seam Mining: A Case Study in Bulianta Coal Mine

Environmentally friendly techniques for high gas content thick coal seam stimulation─multi-discharge CO2 fracturing system

Experimental Investigation on Influence Factors of Acoustic Emission Activity in Coal Failure Process

Influence of water soaking on swelling and microcharacteristics of coal

Similarity criteria and coal-like material in coal and gas outburst physical simulation