Constant-flow injection and extraction combined coal seam water injection method

Abstract

The invention relates to the field of water injection and dust prevention of fully mechanized coal mining faces, in particular to a constant-flow injection and extraction combined coal seam water injection method. The method specifically comprises the following steps: A, constructing a water injection drill hole in a coal seam, and arranging water diversion monitoring points on a roadway wall surface and in the coal seam; b, coal seam water injection is conducted in all the construction drill holes at the constant flow Q, and the time when water drops start to be hung on the wall at the wall face monitoring points is observed and recorded; c, when the water injection time reaches the latest time when water drops are hung on the wall, a water injection system is closed, water injection is stopped, and an extraction control valve is started; d, observing and recording the peak value appearing time of the monitoring points in the coal seam; and E, when the extraction time reaches the third peak value stabilization time, the extraction system is closed, extraction is stopped, and a control valve of the water injection drill hole is opened. Circularly and intermittently injecting water until the accumulated time reaches the theoretical water injection time. According to the method, the osmotic pressure in the drill hole is enhanced through constant-flow water injection, then the wetting area is enlarged in an injection and extraction combined mode, and the gas emission amount and the dust production amount of the fully-mechanized coal mining face are reduced.

Description

Technical Field

[0001] The invention relates to the field of water injection and dust prevention for fully mechanized mining working faces, and in particular to a coal seam water injection method combining constant flow injection and pumping. Background Art

[0002] In recent years, with the continuous advancement of science and technology, the degree of mechanization in coal mines has been increasing, and the concentration of coal dust in underground fully-mechanized mining faces has remained high. The key to solving this problem is to reduce the dust production of coal dust in the working face. At present, the most commonly used method is coal seam water injection, which can reduce the dust production of the working face from the source. Coal seam water injection is not only simple in device and principle, but also has multiple functions of softening coal body, preventing and controlling various disasters. However, most coal bodies are porous media with low permeability and high stress, so the water injection process inside the coal seam is very complicated. Due to the poor coupling between the current coal seam water injection parameters and the physical structure characteristics of the coal seam, the wetting effect is not ideal. Based on the defects of the currently used isobaric water injection technology, a coal seam water injection method with high adaptability and high wetting efficiency is developed to solve the problems of poor water injection effect and high dust production rate in low permeability coal seams. Summary of the invention

[0003] The present invention provides a coal seam water injection method combining constant flow injection and extraction to solve the technical problems of poor water injection effect and high dust generation rate in low permeability coal seams. By injecting water into the coal seam at a constant flow rate to enhance the osmotic pressure in the borehole, an intermittent cycle water injection mode combining water injection holes with extraction holes is adopted to promote the coal body water that has reached a saturated state to continue to diffuse in the pore channels in the coal body under the action of extraction negative pressure, thereby further wetting and softening the coal body, which can effectively improve the wetting efficiency and infiltration range of the coal seam.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a coal seam water injection method combining constant flow injection and pumping, comprising the following steps:

[0005] A. Select three boreholes B1, B2 and B3 with a continuous and equal spacing of L on one side of the tunnel, and arrange two symmetrical monitoring points 2# and 4# on both sides of the wall of the inlet of borehole B2. The distance between the 2# and 4# monitoring points and the center of the inlet of borehole B2 is greater than the radius of the borehole r; at the same time, the 3# and 5# monitoring points are arranged on the wall at the midpoint of the spacing between boreholes B1 and B2, and between boreholes B3 and B2 respectively; the 6# and 7# monitoring points are arranged on the line connecting the ends of boreholes B1 and B2 in the coal seam. The distance between the 6# monitoring point and the center line of the inlet of borehole B2 is greater than the radius of the borehole r, and the distance between the 7# monitoring point and the center line of the inlet of borehole B2 is L / 2;

[0006] B. Use a high-pressure water injection system to inject water into all boreholes at a constant flow rate Q, and record the time t1 when water droplets appear on the wall at monitoring points 2# and 4#. Continue to observe and record the time t2 when water droplets begin to appear on the wall at monitoring points 3# and 5#.

[0007] C. When the water injection time reaches T 注 =max{t1, t2}, close the water injection system, stop water injection, and open the control valve of the extraction borehole;

[0008] D. Record the time when the moisture content of monitoring points 6# and 7# first reaches its peak value, t3 and t4 respectively. Continue to observe and record the time when the moisture content of monitoring point 6# reaches its third peak value and stabilizes, t5.

[0009] E. When the extraction time reaches T 抽 = t5, close the extraction system, stop extraction, and open the control valve of the water injection borehole;

[0010] F. Repeat steps C and E. When the cumulative injection and pumping time T = ∑(T 注 +T 抽 )When the theoretical water injection time is reached, the water injection can be stopped.

[0011] Furthermore, the constant flow rate Q of the high pressure water injection system is 0.6-7.5m 3 / h.

[0012] Furthermore, the method of combining injection and extraction is an intermittent control mode of only injection without extraction, or only extraction without injection.

[0013] Furthermore, the arrangement of the injection and extraction drilling holes is to inject water into the entire hole for the first time, and then adopt a circulating water injection method of injecting two and closing one without extraction, and then closing two and extracting one without injection.

[0014] Furthermore, the coal seam water injection method is a two-way long borehole arrangement with equal spacing on the same side of the tunnel and staggered arrangements on both sides.

[0015] Furthermore, the spacing L is 20 m and the drilling radius r is 32.5 mm.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] On the basis of traditional isobaric coal seam water injection, the present invention fully considers the structural characteristics of low permeability of coal seams, and injects constant flow pressurized water into the borehole. The low permeability coal seam will cause the diffused water to gather pressure in the borehole, thereby increasing the osmotic pressure of the water in the borehole. At the same time, an intermittent circulation water injection mode combining water injection holes and extraction holes is adopted to promote the coal body water that has reached a saturated state to continue to diffuse in the pore channels in the coal body under the action of the extraction negative pressure, thereby further wetting and softening the coal body, and can effectively improve the wetting efficiency and infiltration domain of the coal seam. The method of the present invention is simple to operate, has strong adaptability, can effectively wet and soften coal seams, and improve the wetting efficiency and infiltration domain of coal bodies, and has broad practical value in the field of this technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the coal seam water injection method combining constant flow injection and pumping of the present invention.

[0019] Figure 2 It is a schematic longitudinal section diagram of the arrangement of drilling holes and monitoring points of the present invention.

[0020] Figure 3 A schematic diagram of the relative position arrangement of monitoring points and boreholes of the present invention.

[0021] The following are marked in the figure:

[0022] 1-coal seam, 2-drill hole B m , 3-drilling hole B1, 4-drilling hole B2, 5-drilling hole B3, 6-drilling hole B n , 7-borehole A1, 8-borehole A2, 9-2# monitoring point, 10-4# monitoring point, 11-3# monitoring point, 12-5# monitoring point, 13-6# monitoring point, 14-7# monitoring point, 15-B1 flow meter, 16-B2 flow meter, 17-B3 flow meter, 18-B1 control valve, 19-B2 control valve, 20-B3 control valve, 21-B1 pressure gauge, 22-B2 pressure gauge, 23-B3 pressure gauge, AA tunnel one side wall, BB tunnel other side wall. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with specific embodiments.

[0024] Example 1

[0025] A coal seam water injection method combining constant flow injection and pumping, such as Figure 1 As shown, the specific method is as follows:

[0026] A. Select coal seam 1 of the target fully mechanized mining face with a porosity of 7.2%. Select five boreholes B13, B24, B35, A17, and A28 with a radius of r = 32.5 mm and a continuous and equidistant interval of L = 20 m. Establish a two-dimensional model. Arrange two symmetrical 2# monitoring points 9 and 4# monitoring points 10 on both sides of the inlet wall (BB) of borehole B24. The distance between 2# monitoring points 9 and 4# monitoring points 10 and the center of the inlet of borehole B24 is 35 mm. , 3# monitoring point 11 and 5# monitoring point 12 are arranged on the wall surface (BB) at the midpoint of the borehole spacing L=20m between borehole B13 and borehole B24, and between borehole B24 and borehole B35; 6# monitoring point 13 and 7# monitoring point 14 are arranged on the connecting line of the ends of borehole B13 and borehole B24 in coal seam 1, the distance between 6# monitoring point 13 and the center line of the inlet of borehole B24 is 35mm, and the distance between 7# monitoring point 14 and the center line of the inlet of borehole B24 is L / 2=10m.

[0027] B. High-pressure water injection system with constant flow rate Q = 3.83m 3 / h to carry out water injection simulation on model boreholes B13, B24, B35, A17 and A28, and adopt transient multiphase flow model to calculate the time when water droplets start to hang on the wall at 2# monitoring point 9 and 4## monitoring point 10 (t1=7.0h), and the time when water droplets start to hang on the wall at 3## monitoring point 11 and 5## monitoring point 12 (t2=18.0h).

[0028] C. When the simulated water injection time reaches T 注 =18.0h, the first simulation result shows that the water injection radius of borehole B24 is 4.72m; at this time, the water injection system is closed, the water injection is stopped, and the B2 control valve 19 of the extraction borehole B24 is opened.

[0029] D. Record the time when the volume fraction of water at monitoring point 6#13 and monitoring point 7#14 first reaches its peak value, t3=1.4h and t4=2.6h respectively. Continue to observe and record the time when the volume fraction of water at monitoring point 6#13 reaches its third peak value and stabilizes, t s =6.0h.

[0030] E. When the extraction time reaches T 抽 =6.0h, the second simulation results show that the wetted area of ​​borehole B24 reaches 86% of the area occupied by a single borehole. At this time, the extraction system is closed, the extraction is stopped, and the control valve of the water injection borehole is opened.

[0031] F. Repeat steps C and E. When the cumulative injection and pumping time T = ∑(T 注 +T 抽 )When the theoretical water injection time is reached, the water injection can be stopped.

[0032] Example 2

[0033] A coal seam water injection method combining constant flow injection and pumping, the specific method is as follows:

[0034] The coal seam porosity in step A is set to 5.0% and 9.0%, and the other methods are the same as in Example 1. The water injection radius of the borehole B2 (4) in the first simulation result and the wetting area ratio of the borehole B24 in the second simulation result are shown in Table 1.

[0035] Example 3

[0036] A coal seam water injection method combining constant flow injection and pumping, the specific method is as follows:

[0037] The constant flow rate of the high-pressure water injection system in step B is set to Q = 2.4m 3 / h and Q = 6.3m 3 / h, other methods are the same as in Example 1, the water injection radius of the borehole B24 in the first simulation result and the wetted area ratio of the borehole B24 in the second simulation result are shown in Table 1.

[0038] Table 1 Simulation parameter results

[0039]

[0040]

Claims

1. A coal seam water injection method combining constant flow injection and pumping, characterized in that: The following steps are involved: A. Select three boreholes B1, B2 and B3 with a continuous and equal spacing of L on one side of the tunnel, and arrange two symmetrical monitoring points 2# and 4# on both sides of the wall of the inlet of borehole B2. The distance between the 2# and 4# monitoring points and the center of the inlet of borehole B2 is greater than the radius of the borehole r; at the same time, the 3# and 5# monitoring points are arranged on the wall at the midpoint of the spacing between boreholes B1 and B2, and between boreholes B3 and B2 respectively; the 6# and 7# monitoring points are arranged on the line connecting the ends of boreholes B1 and B2 in the coal seam. The distance between the 6# monitoring point and the center line of the inlet of borehole B2 is greater than the radius of the borehole r, and the distance between the 7# monitoring point and the center line of the inlet of borehole B2 is L / 2; B. Use a high-pressure water injection system to inject water into all boreholes at a constant flow rate Q, and record the time t1 when water droplets appear on the wall at monitoring points 2# and 4#. Continue to observe and record the time t2 when water droplets begin to appear on the wall at monitoring points 3# and 5#. C. When the water injection time reaches T 注 =max{t1, t2}, close the water injection system, stop water injection, and open the control valve of the extraction borehole; D. Record the time when the moisture content of monitoring points 6# and 7# first reaches its peak value, t3 and t4 respectively. Continue to observe and record the time when the moisture content of monitoring point 6# reaches its third peak value and stabilizes, t5. E. When the extraction time reaches T 抽 = t5, close the extraction system, stop extraction, and open the control valve of the water injection borehole; F. Repeat steps C and E. When the cumulative injection and pumping time T = ∑(T 注 +T 抽 )When the theoretical water injection time is reached, the water injection can be stopped.

2. A coal seam water injection method combining constant flow injection and pumping according to claim 1, characterized in that: The constant flow rate Q of the high-pressure water injection system is 0.6-7.5m 3 / h.

3. A coal seam water injection method combining constant flow injection and pumping according to claim 1, characterized in that: The method of combining injection and extraction is an intermittent control mode of only injection without extraction, or only extraction without injection.

4. A coal seam water injection method combining constant flow injection and pumping according to claim 1, characterized in that: The arrangement of the injection and extraction drilling holes is to inject water into the entire hole for the first time, and then adopt a circulating water injection method of injecting two and closing one without extraction, and then closing two and extracting one without injection.

5. The method for coal seam water injection combining constant flow injection and pumping according to claim 1, characterized in that: The coal seam water injection method is a two-way long drilling method with equal spacing on the same side of the tunnel and staggered layout on both sides.

6. A coal seam water injection method combining constant flow injection and pumping according to claim 1, characterized in that: The spacing L is 20m and the drilling radius r is 32.5mm.

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