Principle and engineering application of pressure relief gas drainage in low permeability outburst coal seam

With the increase in mining depth, the danger of coal and gas outbursts increases.In order to drain coal gas effectively and to eliminate the risk of coal and gas outbursts, we used a specific number of penetration boreholes for draining of pressure relief gas.Based on the principle of overlying strata movement, deformation and pressure relief, a good effect of gas drainage was obtained.The practice in the Panyi coal mine has shown that, after mining the C11coal seam as the protective layer, the relative expansion deformation value of the protected layer C13 reached 2.63%, The permeability coefficient increased 2880 times, the gas drainage rate of the C13 coal seam increased to more than 60%, the amount of gas was reduced from 13.0 to 5.2 m3/t and the gas pressure declined from 4.4 to 0.4 MPa, which caused the danger the outbursts in the coal seams to be eliminated.The result was that we achieved a safe and highly efficient mining operation of the C13 coal seam.

Patterns and security technologies for co-extraction of coal and gas in deep mines without entry pillars

Retaining gob-side entryways and the stability of gas drainage boreholes are two essential techniques in the co-extraction of coal and gas without entry pillars （CECGWEP）. However, retained entryways located in deep coal mines are hard to maintain, especially for constructing boreholes in confined spaces, owing to major deformations. Consequently, it is difficult to drill boreholes and maintain their stability, which therefore cannot guarantee the effectiveness of gas drainage. This paper presents three measures for conducting CECGWEP in deep mines on the basis of effective space in retained entryways for gas drainage, They are combinations of retaining roadways and face-lagging inclined boreholes, retaining roadways and face-advancing inclined boreholes, and retaining roadways and high return airway inclined boreholes. Several essential techniques are suggested to improve the maintenance of retained entryways and the stabilization of boreholes. For the particular cases considered in this study, two field trials have verified the latter two measures from the results obtained from the faces 1111（1） and 11112（1） in the Zhuji Mine. The results indicate that these models can effectively solve the problems in deep mines. The maximum gas drainage flow for a single hole can reach 8.1 m^3/min and the effective drainage distance can be extended up to 150 m or more.

Research on forced gas draining from coal seams by surface well drilling

Surface drilling was performed at the Luling Coal Mine,in Huaibei,to shorten the period required for gas draining.The experimental study was designed to reduce the cost of gas control by efficiently draining gas from the upper protected layer.The structural arraignment and technical principles of pressure relief via surface drilling are discussed.Results from the trial showed that gas drained from the surface system over a period of 10 months.The total amount of collected gas was 248.4 million m^3.The gas draining occurred in three stages：a growth period;a period of maximum gas production;and an attenuation period.The period of maximum gas production lasted for 4 months.During this time the methane concentration ranged from 60%to 90%and the average draining rate was 10.6 m^3/min.Combined with other methods of draining it was possible to drain 70.6%of the gas from middle coal seam groups.The amount of residual gas dropped to 5.2 m^3/ton,and the pressure of the residual gas fell to 0.53 MPa, thereby eliminating the outburst danger in the middle coal seam groups.The factors affecting pressure relief gas draining by surface drilling were analysed.

Gas Drainage Technology in Fully Mechanized Caving Face with Horizontal Sublevel Mining in Steep and Extra-Thick Coal Seam

This paper analyzes the gas source of the horizontally sectioned fully mechanized caving face in the steeply inclined and extra-thick seam of Adaohai Coal Mine, and numerically simulates the stress distribution and pressure relief of the lower section coal after the upper section working face is mined. It theoretically analyzed the reasonable layout of the drainage boreholes, and designed the drainage borehole layout accordingly. In the upper and lower section of the working face, the actual drainage effect of the boreholes was inspected, and the air exhaust gas volume in the working face was statistically analyzed. It was confirmed that the layout of boreholes was reasonable, the gas control effect of working face was greatly improved and fully met the needs of safe mining. The control effect was greatly improved and the need for safe mining was fully met, and thus a gas drainage technology suitable for the coal seam storage conditions and mining technology of the Adaohai Coal Mine was found. That is to say: the gas emission from the working face of the section mining mainly comes from its lower coal body. Pre-draining the lower coal body of the section and depressurizing gas interception and drainage are the key to effectively solve the problem of gas emission from the working face. Drainage boreholes in the working face of the section should be arranged at high and low positions. The high-level boreholes are located about 2 m from the top of the working face, and the high-level boreholes are about 9 m away from the top of the working face. Through the pre drainage of high and low-level boreholes in advance and the interception and pressure relief drainage, the gas control in the horizontal sublevel fully mechanized caving mining face in steep and extra thick coal seam can realize a virtuous cycle.

Determining the rational layout parameters of the lateral high drainage roadway serving for two adjacent working faces

To determine the rational layout parameters of the lateral high drainage roadway(LHDR) serving for two adjacent working faces, a mechanical model of the LHDR under mining influence was established, and the overburden fissure, mining-induced stress distribution rules were analyzed. First, the development characteristics of mining-induced overburden fissure and the stress distribution law of the upper section of the working face were analyzed. Second, by analyzing the distribution law of vertical stress at different layers, the lateral distance of the LHDR was determined as 25 m. Third, by analyzing the surrounding rock deformation effect, stress distribution law, and overburden fissure distribution law of the LHDR at the heights of 20, 25, and 30 m away from the roof, the rational horizon of the LHDR was determined to be 25 m. Finally, an example of a LHDR located 25 m above the roof of the No. 2 coal seam and 25 m away from the No. 2-603 working face was presented. Results show that when the No. 2-603 coalface is being mined, the surrounding rocks lag 80 m or even further and the working face tends to be stable. The relative deformations of the roof and floor of the roadway and both of its walls were 583 and 450 mm,respectively. The reduction rate of the roadway section was 21.52%–25.32%. The section of the roadway was sufficient to extract the pressure relief gas in the overburden of the No. 2-605 working face. The average gas concentration and the pure volume at the branch pipeline were 24.8% and 22.3 m^3/min,respectively, showing that the position of high-level boreholes was reasonable.