Dynamic drainage method for close-range coal seam

Abstract

The invention discloses a dynamic drainage method for a close-range coal seam, which comprises the following steps of: obliquely drilling roadways on two sides of a target working face to corresponding upper-layer goaf along the advancing direction at equal intervals to obtain initial drainage holes; an adjacent roadway of a to-be-mined working face adjacent to the target working face is obliquely drilled to an upper-layer goaf of the target working face at equal intervals, and monitoring holes are obtained; sensors are arranged in the monitoring holes, the hole distance of the initial drainage holes is adjusted in real time according to data obtained by the sensors, and dynamic drainage of the close-range coal seam is achieved. Accurate water control and timely hole patching of key drainage areas are realized, and possible water flow channels are effectively blocked, so that water inrush accidents are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining and water hazard prevention and control, and in particular relates to a dynamic water drainage method for a close-range coal seam. Background Art

[0002] During the mining process of close-range coal seams, as the upper coal layer is mined, large amounts of water often accumulate in the goaf. This water remains in the roof cracks and rock cavities for a long time. As the lower working face gradually advances directly below it, if its dynamic evolution is not monitored and discharged promptly, it can easily form a water channel that penetrates the roof, causing water inrush accidents or flooding the working face, posing a serious threat to personnel safety and equipment stability. Traditional drainage technology for the lower working face of close-range coal seams typically relies on vertical or high-angle drilling in tunnels on both sides of the target working face to centrally pump out the accumulated water before mining or at specific stages. However, this method is limited by long drilling distances and difficult to control formation guidance errors. This often results in inaccurate alignment between the hole mouth and the goaf, resulting in drainage efficiency and coverage that cannot meet the requirements of continuous advancement. Furthermore, the lack of online monitoring methods has led to a significant disconnect between drainage and mining, making it difficult to achieve a dynamic balance between "draining water as it appears" and "controlling water as it arrives," resulting in a serious blind spot for water hazard risks.

[0003] Therefore, a new dynamic and precise water drainage method is urgently needed to solve the water drainage problem in the process of close-range coal seam mining. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a dynamic water drainage method for close-range coal seams to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above-mentioned purpose, the present invention provides a dynamic water drainage method for a close-range coal seam, comprising:

[0006] Drill holes at equal intervals along the advancing direction in the tunnels on both sides of the target working face to the corresponding upper goaf to obtain initial drainage holes;

[0007] Drill holes obliquely and equidistantly in the adjacent lanes of the working face to be mined adjacent to the target working face to the upper goaf of the target working face to obtain monitoring holes;

[0008] Sensors are arranged in the monitoring holes, and the hole spacing of the initial drainage holes is adjusted in real time based on the data obtained by the sensors, so as to realize dynamic drainage of the coal seam at a close distance.

[0009] Optionally, the hole spacing of the initial drainage holes is smaller than the hole spacing of the monitoring holes.

[0010] Optionally, the inclination angle of the initial drainage hole is greater than the inclination angle of the monitoring hole.

[0011] Optionally, the process of placing sensors in the monitoring holes includes:

[0012] A water level sensor is installed 2.0m away from the orifice, a flow sensor is installed 1.0m away from the bottom of the hole; a water pressure sensor is installed in the middle of the hole 5.0m away from the bottom of the hole.

[0013] Optionally, the data obtained by the sensor is used to determine whether the monitoring hole flow exceeds the single hole flow threshold. If it exceeds the single hole flow threshold, the drainage holes are increased in density; if it does not exceed the single hole flow threshold and the change in the monitoring hole flow value meets the preset conditions, the initial drainage hole arrangement is maintained.

[0014] Optionally, if the drainage holes are increased, the new hole spacing L is calculated based on the real-time flow of the monitoring hole and the single hole flow threshold. new , the formula is as follows:

[0015]

[0016] Where Q th is the single hole flow threshold, Q i is the real-time flow rate of the ith monitoring hole, L0 is the initial hole spacing, and γ is the empirical coefficient, where K is the equivalent permeability coefficient of the fracture, A is the effective seepage cross-sectional area; Δh is the water head difference between the hole and the goaf; L is the shortest flow distance between the hole and the goaf.

[0017] Optionally, determine whether the real-time flow rate of the monitoring hole matches the geological conditions of the area where the working face is located. If not, increase the hole diameter or add drainage holes.

[0018] Optionally, when adding drainage holes, the dynamic drainage radius is calculated based on the real-time flow of the monitoring hole. If the dynamic drainage radius exceeds the preset safety radius, a new hole is arranged at the edge of the dynamic drainage radius.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] The present invention drills holes at an angle at fixed intervals in the tunnels on both sides of the lower working face to the upper goaf. At the same time, monitoring and auxiliary drainage holes are synchronously arranged in the adjacent tunnels of the lower working face to sense in advance the evolution of water volume in the goaf that may be caused by the roof fissure channel. Water level, water pressure and flow sensors are arranged in the monitoring holes to realize online monitoring of water volume in the goaf. It breaks through the limitations of traditional long-distance drilling and periodic drainage. The drainage holes and monitoring holes are arranged in coordination on both sides of the working face. It can not only accurately reduce the risk of water stagnation near the mining boundary, but also dynamically adjust the hole spacing and hole network density according to the mining speed, the evolution rate of the roof spanning cracks and the observed hydraulic parameters, thereby truly realizing the organic combination of the three core technical features of "close distance", "precision" and "dynamic". It has the advantages of simple structure, wide application range, high drainage efficiency, fast dynamic response and precise risk control. It is particularly suitable for water hazard prevention and control in close-range coal seam mining and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0022] Figure 1 This is a front view of the arrangement of inclined holes for close-range coal seam storage and drainage according to an embodiment of the present invention;

[0023] Figure 2 This is a plan view of the arrangement of the close-range coal seam occurrence and drainage inclined holes according to an embodiment of the present invention;

[0024] Figure 3 is a flow chart of a method according to an embodiment of the present invention;

[0025] Figure markings: 1. Overlying rock stratum; 2. Upper coal seam; 3. Interval rock stratum; 4. Lower coal seam; 5. Floor of lower coal seam; 6. Protective coal pillar; 7. Goaf of upper coal seam; 8. Goaf of lower coal seam; 9. Protective coal pillar of lower coal seam working face; 10. Return air lane of target working face; 11. Target working face; 12. Transport lane of target working face; 13. Return air lane of working face to be mined; 14. Working face to be mined; 15. Inclined hole for drainage of tunnel; 16. Inclined hole for drainage of adjacent tunnel; 17. Opening of cutting eye of target working face. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0027] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0028] Example 1

[0029] like Figure 3 As shown, this embodiment provides a dynamic water drainage method for a close-range coal seam, comprising:

[0030] First, using geological survey and related simulation results, the spatial relationship between the lower working face and the upper goaf, as well as the development trend of roof fractures, is determined. Directional drilling is then carried out in the roadways on either side of the target working face at an inclination of 60° to 75°. The drilling depth should ensure close contact between the hole bottom and the goaf roof, or slight penetration, to ensure the shortest possible distance and most efficient connectivity for the drainage channel. Real-time inclination and back-tilt monitoring of drilling data allows the bottom deviation to be controlled within ±0.5m. Simultaneously, co-directional monitoring holes are placed in the adjacent working face roadways. The inclination angle (β) of the monitoring holes is slightly smaller than that of the drilled holes on either side of the roadway (α). The hole diameter and depth are comparable to those of the drainage holes, and the spacing between them can be slightly lower than the density of the main drainage hole network. Water level and flow sensors are embedded in each monitoring hole and connected to a centralized underground data collection system, which monitors the dynamics of water accumulation in the goaf at a sub-second rate. When the monitoring data exceeds a pre-calibrated safety threshold or shows a sudden change in trend, the system automatically identifies key drainage zones and recommends adding drainage holes. Trained operators or automated drilling equipment can drill additional inclined holes at the recommended locations in the shortest possible time to focus the additional drainage capacity on the bulge area.

[0031] The specific steps include:

[0032] (1) Clarify the project overview and geological conditions;

[0033] like Figure 1-2 As shown, the mine utilizes a close-seam downward mining model. Both coal seams are nearly horizontal. The upper coal seam 2 is 320 meters deep, has a thickness of M1, and has been mined completely. The lower coal seam 4 is 350 meters deep, has a thickness of M2, and is separated by a 30-meter rock layer 3. The working face length is L4, and the advance length is L3. The roof of the upper coal seam 2 is the overlying rock layer 1, which has been mined completely. A protective coal pillar 6 is maintained between the upper coal seam goaf 7. Residual water accumulates in the upper coal seam goaf 7, accumulating for a long time in the roof cracks and rock cavities.

[0034] There is a horizontal tunnel on each side of the target working face 11 of the lower coal seam (hereinafter referred to as the "target working face") (i.e., the target working face return air tunnel 10 and the target working face transport tunnel 12). The elevation of the lower coal seam floor 5 is measured to be approximately -350m. Each adjacent working face is also equipped with two horizontal tunnels for ventilation and transportation. The tunnel floor elevation is approximately -350m, and the tunnel width is 5.8m and the height is 4.3m. At this time, the working face on the left side of the target working face 11 has been mined, forming a lower coal seam goaf 8, separated from the target working face by a lower coal seam working face protection coal pillar 9; to the right of the target working face 11 is the working face to be mined 14, and the target working face starts to advance from the target working face opening eye 17.

[0035] (2) Preparation before construction;

[0036] ①Geological and hydrological survey:

[0037] In the upper coal seam goaf area 7, geological radar, borehole coring, and numerical simulation were used to locate and quantitatively analyze the development of roof fractures and seepage channels. Hydrological testing of the boreholes determined the local permeability coefficient K, formation moisture content, initial water level, and pore pressure distribution. The distribution range and primary water collection points of the upper layer residual water were determined to facilitate the optimal placement of drainage holes and monitoring holes. Drill guide brackets were installed at 50-meter intervals (i.e., 0m, 50m, 100m, 150m, etc.) along the advance direction in the horizontal lanes on both sides of the target working face (i.e., the target working face return air lane 10 and the target working face transport lane 12). During installation, the brackets were installed to maintain a fixed inclination angle of 60°, and a graduated dial was provided to facilitate angle calibration. Percussive drilling and reverse circulation flushing were used to ensure borehole wall stability.

[0038] In the return airway 13 of the adjacent working face 14 to be mined, monitoring hole guide brackets were installed at intervals of 100 meters (i.e., 100m, 200m, 300m, 400m, 500m, etc.) along the advance direction, with the drilling rig maintained at a fixed inclination angle of 55°. Using the same type of hydraulic wedge drill, a 100mm hole diameter was drilled obliquely upward to the bottom of the upper goaf of the target working face, with a drilling depth of approximately 40m. The inclination error was controlled to within ±1° throughout the drilling process.

[0039] ②Determination of design parameters:

[0040] 1) Drainage holes (drainage inclined holes 15 on both sides of the lower working surface);

[0041] Inclination angle α = 60°; starting hole spacing L1 = 50m (along the working face advancement direction, a drainage hole guide line is laid out every 50m in the left and right lanes); hole diameter The estimated drilling depth H1 is ≈ 35m (converted to a vertical distance of approximately 30m / sin60°≈34.6m from the bottom surface of the upper goaf roof).

[0042] 2) Monitoring hole (slanted hole 16 for drainage near the lane);

[0043] Inclination angle β = 55° (slightly smaller than the drainage hole inclination); initial hole spacing L2 = 100m; diameter The estimated drilling depth H2 is 40m (converted to a vertical distance of approximately 30m / sin55°≈39.2m from the bottom surface of the upper goaf roof).

[0044] (3) Preparation of equipment and materials;

[0045] The working face is equipped with a hydraulic wedge drill, capable of achieving a drilling inclination accuracy of ±1°. Steel casing is installed, and depending on the construction environment, a filter screen (aperture ≥50mm) and a gravel filter layer are installed at the bottom of the borehole. After drilling is completed, the entire steel casing is lowered into the hole from the tunnel floor. The casing length must be no less than the distance from the hole opening to the bottom of the upper goaf. A filter window is reserved at the bottom of the casing to serve as a drainage channel. The upper casing section is secured to the tunnel sidewall with standard pipe clamps. A gravel filter layer is placed around the outer perimeter of the casing bottom window to prevent clogging and ensure smooth water flow. Furthermore, a water level sensor is installed in each monitoring hole 2.0m from the hole opening; a flow sensor is installed 1.0m from the hole bottom; and a water pressure sensor is installed mid-hole, 5.0m from the hole bottom. The sensors are connected to fiber optic cables via explosion-proof connectors. The fiber optic cables are routed to a manifold within the tunnel and ultimately transmitted to a ground monitoring center. After installation, signal verification and zero point calibration are immediately carried out to form a "multi-hole position, multi-parameter" synchronous monitoring network. The drainage process is based on a data acquisition unit, providing 10 times / min data sampling, supporting optical fiber transmission to the ground monitoring center. In addition, the working surface needs to be equipped with a drainage pump station, initially using 4 centrifugal pumps (single power 30kW, maximum flow 25m 3 / h, head 200m), and run in parallel to meet the initial drainage demand.

[0046] (4) Online monitoring;

[0047] After all sensors are activated, the ground monitoring center samples data from each monitoring hole and records the water level H. i (t), flow rate Q i (t), water pressure p i (t). The data is transmitted in real time via optical fiber and stored in the monitoring server database for subsequent analysis and early warning module calls. Based on the residual water volume in the upper goaf and the formation seepage characteristics, the single hole flow threshold Q is preliminarily set. th =20m 3 / h; flow rate change threshold ΔQ th : Set to 5m 3 / h; when the real-time flow rate Q of any monitoring hole i i (t)≥Q th When Qi (t) th And within 30 minutes, ΔQ i (t)<ΔQ th , it is considered to be a "locally stable" state and the existing pore density can be maintained.

[0048] (5) Dynamic hole network adjustment and water release implementation;

[0049] In the initial drainage stage, the drainage holes and monitoring holes were opened for trial drainage, and four parallel centrifugal pumps were used for drainage. At the same time, the flow data of each hole was monitored.

[0050] ① Adaptive adjustment of hole spacing;

[0051] If a monitoring hole detects flow Q i If indicators such as water level pressure exceed the preset threshold, it is necessary to increase the density of drainage holes near the area. The new drainage hole spacing (along the working face advancement direction) can be calculated using the following formula:

[0052]

[0053] Among them, L0 is the initial hole spacing, which is 50m; Q th For the preset single hole flow threshold, take 20m 3 / h;Q i is the real-time flow rate of the ith monitoring hole, taking 30m 3 / h; γ is the empirical coefficient, generally 0.5 to 0.8, this time it is 0.6, used to control the adjustment range. new It is 39.5m, so when the flow rate of the monitoring hole reaches 30m 3 / h, if the drainage holes are still arranged at a spacing of 50m, there will be a risk of the hole network being too sparse; the hole spacing in this area can be reduced to about 40m to form a denser drainage hole network.

[0054] ② Darcy's law (estimation of flow rate in the hole-goaf connection);

[0055] For the location of a monitoring hole or drainage hole, the equivalent seepage flow rate between the hole mouth and the cracks in the goaf (the maximum theoretical drainage capacity of a single hole Q) can be estimated. The calculated value Q is used to estimate the safety radius R safe :

[0056]

[0057] Where K is the equivalent permeability coefficient of the fracture (m / s), which needs to be obtained from field tests or similar formation experience; A is the effective seepage cross-sectional area of ​​the pore and fracture (m 2 ​); Δh is the difference between the water head in the hole and the water level in the goaf (m); L is the equivalent flow distance (the closest distance from the bottom of the hole to the crack in the goaf, m).

[0058] It can be used to evaluate the maximum drainage capacity of a single hole at a certain hole position and as a reference for adjusting the hole grid spacing.

[0059] ③Estimation of dynamic drainage radius;

[0060] Within a certain drainage time t, the drainage impact radius of a certain hole on the surrounding rock formation can be estimated using a simplified model as follows:

[0061]

[0062] Where, μ is the viscosity coefficient of water (Pa·s), which is 1.0×10 -3 Pa·s; t is the continuous drainage time of a single hole, which is 3600s (1h). When the feedback flow from the monitoring hole is high, the maximum flow rate Q of the single hole can be estimated first, and then substituted into the formula to estimate its drainage radius to determine whether it exceeds the preset safety radius R safe , take 5m. According to this estimate, if a single hole continues to drain for 1h and the equivalent permeability conditions and flow rate are similar to this value, the drainage impact radius on the surrounding rock formation is about 1.4m; if this value exceeds the preset safety radius R safe =5m (not exceeded in this example), it may be necessary to continue to increase the density of the pore network or use a larger seepage cross-section (such as increasing the pore diameter or reducing the equivalent flow distance).

[0063] ④ Supplementation of drainage holes based on monitoring data;

[0064] If the feedback flow rate of a monitoring hole continues to be higher than Q within 1 hour th =20m 3 / h, you can first calculate L according to formula (1) new ≈40m, and dynamically reduce the original 50m spacing to 40m to arrange drainage holes; combining formula (2) with the geological conditions of the area, it is possible to evaluate whether the single hole seepage capacity is insufficient. If insufficient, then focus on considering:

[0065] 1) Increase the hole diameter (e.g. increase the drain hole from 120mm to 150mm);

[0066] 2) Shorten the equivalent flow distance (① appropriately increase the angle of the inclined hole within the allowable range; ② appropriately drill drainage holes at the cracks in the floor of the upper goaf, such as drilling drainage holes from the roadway to the cracks in the floor of the upper goaf);

[0067] 3) Porous synergy: within a radius of about R safe Add several drainage holes within the range (such as 5m).

[0068] The final drainage hole arrangement can be carried out in stages:

[0069] Phase 1: Drainage holes are first placed near the initial hole placement location (e.g., 500m along the working face advancement direction) to contain the earliest high flow.

[0070] Stage 2: If the monitoring wells still maintain high flow after stage 1, the hole spacing is shortened and drainage holes are added according to formula (1) to form a "local ring" density layout;

[0071] Stage 3: If the flow rate still does not decrease significantly after the coordination of multiple holes, refer to formula (3) to evaluate the influence radius of single hole drainage and continue to add drainage holes outside the "influence radius" until the flow rate falls back to a controllable range.

[0072] Through the above ideas, even if the on-site geology is variable, the monitoring holes provide real-time data. Engineers can perform "online calculation + hypothesis testing" according to formulas (1) to (3), and then flexibly adjust the density of drainage holes based on construction conditions to achieve a dynamic drainage solution with strong versatility and good scalability.

[0073] The innovation of the method of the present invention lies in its emphasis on both "close distance" and "precision": the bottom of the drainage hole reaches directly to the boundary of the goaf, achieving the shortest drainage channel; at the same time, online monitoring and threshold control drive the hole network to adapt, which is more consistent with the hydraulic and geological evolution characteristics of the mining area; in addition, each link of the method is constructed as a continuous closed loop, so that the "dynamic" is not only reflected at the observation level, but also extends to drainage strategy and hole network optimization. This method is suitable for typical close-range coal seam lower working face mining. It can significantly improve the efficiency of water hazard prevention and control, reduce the risk of water inrush, optimize the input-output ratio of the drainage hole network, and provide paradigm-level support for intelligent water hazard management in coal mines. It has broad engineering promotion value and economic and social benefits.

[0074] The present invention proposes a precise drainage method combining online monitoring with dynamic adjustment to address the hidden dangers of residual water accumulation during mining of close-range coal seams, achieving the characteristics of timely response, precise drainage, rolling linkage, etc., thereby reducing the probability of water inrush and flooding accidents, and improving the safety and continuity of mining at the lower working face. At the same time, the scheme can be extended to close-range coal seam drainage projects with different inclinations and burial depths. The following will be combined with the accompanying drawings and specific embodiments to elaborate on a dynamic and precise drainage method for close-range coal seams proposed by the present invention. It should be clearly pointed out that the examples listed are only used to specifically illustrate the technical solution of the present invention, and are not intended to limit its scope of protection. For those skilled in the art, without departing from the core idea of ​​the present invention, other implementation methods can obviously be derived based on the principles disclosed in this embodiment, and these implementation methods should also be deemed to be included in the scope of protection of the present invention.

[0075] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A dynamic drainage method for close-range coal seams, characterized in that: The following steps are involved: Drill holes at equal intervals along the advancing direction in the tunnels on both sides of the target working face to the corresponding upper goaf to obtain initial drainage holes; Drill holes obliquely and equidistantly in the adjacent lanes of the working face to be mined, adjacent to the target working face, to the upper goaf of the target working face to obtain monitoring holes; Sensors are arranged in the monitoring holes, and the hole spacing of the initial drainage holes is adjusted in real time based on the data obtained by the sensors, so as to realize dynamic drainage of the coal seam at a close distance.

2. The dynamic drainage method for close-range coal seams according to claim 1 is characterized in that: The hole spacing of the initial drainage holes is smaller than the hole spacing of the monitoring holes.

3. The dynamic drainage method for close-range coal seams according to claim 1 is characterized in that: The inclination angle of the initial drainage hole is greater than the inclination angle of the monitoring hole.

4. The dynamic drainage method for close-range coal seams according to claim 1 is characterized in that: The process of placing sensors in the monitoring holes includes: A water level sensor is installed 2.0m away from the orifice, a flow sensor is installed 1.0m away from the bottom of the hole; a water pressure sensor is installed in the middle of the hole 5.0m away from the bottom of the hole.

5. The dynamic drainage method for close-range coal seams according to claim 1 is characterized in that: According to the data obtained by the sensor, it is judged whether the flow rate of the monitoring hole exceeds the single hole flow threshold. If it exceeds the single hole flow threshold, the drainage holes are increased; If the single-hole flow threshold is not exceeded and the change in the monitoring hole flow value meets the preset conditions, the initial layout of the drainage holes is maintained.

6. The dynamic drainage method for close-range coal seams according to claim 5, characterized in that: If the drainage holes are increased, the new hole spacing L is calculated based on the real-time flow of the monitoring hole and the single hole flow threshold. new , the formula is as follows: Where Q th is the single hole flow threshold, Q i is the real-time flow rate of the ith monitoring hole, L0 is the initial hole spacing, and γ is the empirical coefficient, where K is the equivalent permeability coefficient of the fracture, A is the effective seepage cross-sectional area; Δh is the water head difference between the hole and the goaf; L is the shortest flow distance between the hole and the goaf.

7. The dynamic drainage method for close-range coal seams according to claim 6, characterized in that: Determine whether the real-time flow of the monitoring hole matches the geological conditions of the working face area. If not, increase the hole diameter or add drainage holes.

8. The dynamic drainage method for close-range coal seams according to claim 7, characterized in that: When adding drainage holes, the dynamic drainage radius is calculated based on the real-time flow of the monitoring hole. If the dynamic drainage radius exceeds the preset safety radius, a new hole is arranged at the edge of the dynamic drainage radius.

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