Cheng Zhai

A new technique for preventing and controlling coal and gas outburst hazard with pulse hydraulic fracturing: a case study in Yuwu coal mine, China

Coal and gas outburst is one of the main gas hazards in coal mines, and pulse hydraulic fracturing is a new technique for preventing and controlling gas hazards in coal mines and is presented based on conventional hydraulic fracturing. S2107 is a coal seam with high gas content and coal and gas outburst hazard but with low gas concentrations when extracted. To safely drive air tunnels into S2107, the pulse hydraulic fracturing technique is used on cross-measure boreholes placed from a high-level roadway to the driving roadway to improve the effects of gas drainage and ensure safety during production. The mechanism of coal fracturing via pulsed pressure is analyzed. A variable frequency method is used to strengthen the fatigue damage effect, and the initial pressure is estimated based on previous studies. The layouts of fracturing borehole and guide borehole are designed according to the layer relation, and a new hole sealing method is developed. The results indicate the pressure changes during pulse hydraulic fracturing reflect crack extension, and it is conducive to extending and connecting cracks under pulse pressures. The initial pressure during pulse hydraulic fracturing is negatively related to the water volume and fracturing time but cannot directly influence the fracturing radius. Moreover, this pressure is 30–43xa0% less than the calculated value. After this application, the gas desorption index, K1, at the driving workface decreases to below the critical value. The gas drainage volume of fracturing boreholes and their guide boreholes increases relative to normal boreholes by 3.32-fold and 3.07-fold, respectively. The new technique is promising for preventing and controlling gas hazards in the future.

The characteristics and main influencing factors affecting coal and gas outbursts in Chinese Pingdingshan mining region

The Pingdingshan mining region in China has witnessed severe coal and gas outbursts. A total of 153 coal and gas outburst accidents have occurred in this mining region. As the mining depth progressively increase, mining conditions in the region have become more complex, and gas outburst disasters have become more severe. This research statistically analyzed the 153 outburst accidents in the Pingdingshan mining region. Additionally, based on historical data and typical outburst cases, the characteristics and primary factors affecting coal and gas outbursts within the mining region were obtained. The results indicate that the outburst accidents in this mining region were primary influenced by the following factors: geological structure, mining depth, seam thickness, the lithology of roof and floor, and the mode of operation. As mining depth increased, the geotechnical environment and the mechanical properties of coal varied. Moreover, under the combined action of high stresses and considerable amounts of high-pressure gas accumulated within the coal and rock mass, the structures of both coal seam and rock strata in the mining faces or roadways were destroyed instantly. Therefore, coal and gas outbursts occurred. The outburst intensity increased significantly when mining depth is greater than 500xa0m. Coal and gas outburst accidents happened most frequently and severely in regions with geological structures containing such features as faults and folds due to the increasing gas pressure and sharply rising ground stress. Moreover, variation of seam thickness and the lithology of the roof and floor of the seam have significant control effect on coal and gas outburst. In addition, engineering disturbance was an external factor inducing coal and gas outbursts. For example, blasting and coal cutting caused changes in the stress state in the coal at the end of excavation roadways and mining faces.

Influence factors analysis of a flexible gel sealing material for coal-bed methane drainage boreholes

Coal-bed methane (CBM) hazards are among the principal hazards in a coal mine, causing events such as coal and gas outbursts, and gas explosions. CBM drainage in underground coal mines plays a fundamental role in preventing coal mine accidents and ensuring safe production in coal mines. The effective sealing of boreholes is regarded as an important measure in the guarantee of efficient CBM drainage. Aiming at the shortcomings of conventional sealants (their poor stability, low permeability, and low adaptability), a flexible gel (FG) that adapts to borehole deformation and has preferable sealing performance was developed. In this study, the development method and the effect of the application of the FG were introduced, the effect of stirring status and the ratio of FG material to water on the water retention, hydrophobicity, and permeability of the FG were investigated; the sealing mechanism of the FG was proposed and the relationship between the stirring status, the ratio of FG material to water and its sealing effect were discussed. The results reveal that: (1) the viscosity of FG increases with time at low stirring speeds (600xa0rpm and below) and then reaches a constant viscosity. On the other hand, at high stirring speeds (800xa0rpm and above), the viscosity of FG first increases, then decreases, and finally reaches a constant viscosity. (2) The FG contains many hydrophobic groups and the surface has a protective layer structure: the main mechanisms in its borehole sealing role are the borehole deformation adaptability, high permeability, preferable water retention, and hydrophobicity. (3) The higher the ratio of material to water in the FG, the lower the hydrophobicity and permeability, and the better the water retention of the FG. (4) Once sufficiently stirred, FG has the lowest permeability, and the best water retention and hydrophobicity: excessively stirred FG is the next best option, and insufficiently stirred FG has the poorest water retention and hydrophobicity, but the greatest permeability. (5) To ensure good sealing performance, sufficiently stirred FG, with a lower ratio of material to water, is selected as the sealing material.

Coal Permeability Evolution and Gas Migration Under Non-equilibrium State

Laboratory test of coal permeability is generally conducted under the condition of gas adsorption equilibrium, and the results contribute to an understanding of gas migration in the original coal seams. However, gas flow under the state of non-equilibrium, accompanied by gas adsorption and desorption, is more common in coalbed methane (CBM) recovery and

Opposing Propagation Characteristics of Methane-Air Deflagrations in an End-to-End Pipe

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Comparative Experimental Study on Explosion Characteristics of Nano-Aluminum Powder and Common Aluminum Powder in the Explosive Device of a Long Pipeline

CO2 geological sequestration sites. Therefore, research on gas migration under the non-equilibrium state has a greater significance with regard to CBM recovery and

Mechanism of strata deformation under protective seam and its application for relieved methane control

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