Multi-section controllable hydraulic fracturing and cave forming coupling method for top coal weakening and pressure relief

Abstract

The invention discloses a multi-section controllable hydraulic fracturing and caving coupling method for top coal weakening and pressure relief. The multi-section controllable hydraulic fracturing and caving coupling method comprises the steps of roadway advanced fracturing drill hole arrangement, segmented hydraulic fracturing, coal seam caving and the like. According to the multi-section controllable hydraulic fracturing and cave forming coupling method for top coal weakening and pressure relief, rock stratum pressure can be reduced through rock stratum fracturing, then stress distribution can be changed, favorable conditions are created for coal seam cave forming, coal seam strength can be further weakened through coal seam cave forming, top coal caving is promoted, overall uniform weakening and effective pressure relief of the top coal are achieved through combination of the two methods, and the coal seam strength is improved. The weakening device is simple in structure, safe, reliable, controllable in cost and good in weakening effect, stress concentration in the top coal can be effectively reduced, overall uniform weakening of the top coal of the large-dip-angle fully mechanized caving face is achieved, and then the caving performance of the top coal is improved.

Description

Technical Field

[0001] The present invention relates to a method for weakening and relieving pressure on the top coal of a fully-mechanized caving working face, specifically a multi-stage controllable hydraulic fracturing and cavitation coupling method suitable for weakening and relieving pressure on the top coal of a fully-mechanized caving working face with a large dip angle, belonging to the technical field of safe coal mining. Background Art

[0002] In recent years, the high production, high efficiency and safety issues in the mining process of thick coal seams have been two major problems that have plagued my country's coal enterprises. The fully mechanized top coal caving mining technology, with its comprehensive advantages of high production, high efficiency and safety, is currently the main technical means for mining thick coal seams in my country. In the mining of high-angle fully mechanized top coal caving working faces, the poor collapse of the top coal is one of the important factors restricting production efficiency and safety. Due to the large inclination of the coal seam in the high-angle working face, the top coal is affected by multiple factors such as its own gravity and the pressure of the overlying rock strata, which easily forms a high stress concentration area, resulting in the top coal being hard and difficult to collapse, seriously affecting the coal caving effect and even causing safety accidents. Traditional top coal weakening methods mainly include: blasting loosening, hydraulic cutting, hydraulic cavitation and hydraulic fracturing. The above methods can improve the collapse of the top coal to a certain extent, but due to the complex geological conditions of the high-angle fully mechanized top coal caving working face, there are still problems such as uneven weakening effect, low pressure relief efficiency, high construction cost and high safety risks. Therefore, there is an urgent need for a safe, efficient and economical top coal weakening and pressure relief method to improve the top coal collapse of large-angle fully-mechanized caving working faces and improve production efficiency and safety. Summary of the Invention

[0003] In response to the problems existing in the above-mentioned prior art, the present invention provides a multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief, which is safe and reliable, cost-controlled and has good weakening effect. It can effectively reduce the stress concentration in the top coal and achieve overall uniform weakening of the top coal in the high-angle fully-mechanized caving working face, thereby improving the collapse resistance of the top coal.

[0004] To achieve the above objectives, the multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief specifically includes the following steps:

[0005] Step 1: Arrangement of advance fracturing drilling holes in the tunnels above and below the working face: construct multiple groups of fracturing drilling holes in advance of the coal seam to be mined in the coal caving section;

[0006] Step 2, staged hydraulic fracturing: According to the characteristics of the rock and coal seams, different fracturing section lengths and intervals are set, and retreat fracturing is used to perform staged fracturing on each fracturing borehole;

[0007] Step 3, coal seam cavitation: After hydraulic fracturing is completed, different cavity lengths and cavity spacings are set according to the characteristics of the coal seam, and the coal seam is cavitated using a hydraulic coal breaking device with a backward coal breaking method.

[0008] Furthermore, in Step 1, according to the distribution characteristics of the specific rock layer and coal seam, the drilling has an elevation angle and an internal staggered angle so that the fracturing range covers the entire working face end.

[0009] Furthermore, the drill holes in the upper and lower drift crossways of the working face are arranged in a staggered manner.

[0010] Furthermore, in Step 2, a long fracturing section is used in the rock layer portion, and a short fracturing section is used in the coal layer portion.

[0011] Furthermore, in Step 3, when the hydraulic coal breaking device retreats to a position close to the roadway, short-type coal breaking and hole making are performed.

[0012] Compared with existing technologies, this top coal weakening and pressure relief multi-stage controllable hydraulic fracturing and cavitation coupling method adopts a combined pressure relief method of "rock layer fracturing + coal seam cavitation", which has the following advantages:

[0013] 1. Uniform weakening effect of top coal: Through the combined action of rock stratum fracturing and coal seam cavitation, the overall uniform weakening of top coal can be achieved, significantly improving the collapse resistance of top coal.

[0014] 2. High pressure relief efficiency: effectively reduce stress concentration in the top coal, especially in key areas such as the end of the working face, and improve the stress state of the top coal.

[0015] 3. High safety: The use of hydraulic fracturing and hydraulic coal breaking technology avoids high-risk operations such as blasting, and reduces safety hazards such as gas explosions and coal dust explosions.

[0016] 4. Low construction cost: The use of mechanized drilling and fracturing equipment improves construction efficiency and reduces labor costs.

[0017] 5. Strong adaptability: The process parameters can be flexibly adjusted according to different coal seam geological conditions and working face conditions, and it has strong adaptability.

[0018] 6. Improve the coal seam caving rate: Improve the coal seam caving rate by fully weakening the coal seam within the influence range of the anchor rods and cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of tunnel fracturing drilling arrangement according to an embodiment of the present invention;

[0020] Figure 2 This is a plan view of the arrangement of tunnel fracturing drilling holes according to an embodiment of the present invention;

[0021] Figure 3 is a cross-sectional view of a tunnel fracturing drilling arrangement according to an embodiment of the present invention;

[0022] Figure 4It is a schematic diagram of the rock stratum fracturing and coal seam cavitation process in a borehole according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below by taking a comprehensive top coal caving mining face of a coal mine as an example with reference to the accompanying drawings.

[0024] The multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief specifically includes the following steps:

[0025] Step 1: Arrangement of advance fracturing drilling holes in the roadway: In the upper and lower drifts of the working face, multiple sets of fracturing holes are drilled in advance of the coal seam to be mined. The holes are drilled at a specific elevation and staggered angle to ensure that the fracturing coverage covers the entire end of the working face. The holes in the upper and lower drifts are staggered to ensure a uniform fracturing effect.

[0026] like Figures 1 to 3 As shown, the drilling elevation angle of the embodiment is 42°, the internal stagger angle is 10°, the drilling length is 63m, of which the rock layer part is 24.5m, the drilling diameter is 75mm, and the spacing between different groups of fracturing boreholes is 20m.

[0027] Step 2, staged hydraulic fracturing: Based on the characteristics of the rock and coal seams, different fracturing segment lengths and segment spacings are set. Using a retreating fracturing method, each fracturing hole is staged, gradually weakening the top coal. Longer fracturing segments are used in the rock layer to create a larger fracture range; shorter fracturing segments are used in the coal seam to avoid excessive fracture.

[0028] The length of the fracturing section of the staged fracturing in a single fracturing borehole is 27m, and the fracturing spacing and number of times are adjusted according to the actual situation. Figure 4 As shown, the interval between hydraulic fracturing stages in the rock formation is 6m, the lateral impact radius of the fracturing is 10m, and the cumulative length of the fracturing interval for retreat fracturing is 43m. A high-pressure pump station is used to fracture the borehole, with fracturing occurring every 1.5m. Each fracturing stage lasts 10 to 20 minutes. The fracturing pressure is determined by the hardness of the top coal, and the holding pressure is determined by the high-pressure pump. After the pressure is maintained for a certain period of time, the high-pressure pump is turned off, ending the fracturing cycle. The sealer is then withdrawn to the next fracturing stage and fracturing is resumed until multiple fracturing operations are completed in a single hole.

[0029] Step 3: Coal Seam Hole Creation: After hydraulic fracturing is complete, different hole lengths and spacings are set based on the coal seam's characteristics. A hydraulic coal breaker is used to create holes in the coal seam using a retreating method, gradually reducing the seam's strength. When the hydraulic coal breaker retreats close to the roadway, the coal seam is within the reach of the anchor bolts and cables, allowing for short-term coal cavitation to fully weaken the top coal and increase the cavitation rate.

[0030] like Figure 4As shown, the length of the coal breaking holes in the embodiment is 2m, the hole spacing is 6m, and the cumulative length of the coal breaking intervals in the backward coal breaking method is 15m.

[0031] To address the challenges of existing top coal weakening methods in high-angle fully-mechanized caving working faces, such as uneven weakening, low pressure relief efficiency, high construction costs, and significant safety risks, this novel top coal weakening and pressure relief method utilizes a multi-stage, controllable hydraulic fracturing coupled with cavitation. This method first reduces rock formation pressure through rock fracturing, thereby altering the stress distribution and creating favorable conditions for cavitation. This cavitation further weakens the seam and promotes top coal collapse. This combination of methods achieves uniform weakening and effective pressure relief across the top coal. Based on the geological conditions and actual conditions of the coal seam at the working face, process parameters such as drill hole spacing, internal stagger, elevation angle, hole depth, fracturing stage length, stage spacing, cavity length, and cavity spacing are optimized to achieve optimal weakening and pressure relief. During the fracturing or cavitation process, pressure gauges, flow meters, and roof are monitored to monitor roof and side stability. Fracturing or cavitation is immediately stopped if any abnormalities are detected. The multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief is safe, reliable, cost-controlled and has good weakening effect. It can effectively reduce stress concentration in the top coal, achieve overall uniform weakening of the top coal in the high-angle fully-mechanized caving working face, and thus improve the collapse resistance of the top coal.

Claims

1. A multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief, characterized in that: The specific steps include: Step 1: Arrangement of advance fracturing drilling holes in the tunnels above and below the working face: construct multiple groups of fracturing drilling holes in advance of the coal seam to be mined in the coal caving section; Step 2, staged hydraulic fracturing: According to the characteristics of the rock and coal seams, different fracturing section lengths and intervals are set, and retreat fracturing is used to perform staged fracturing on each fracturing borehole; Step 3, coal seam cavitation: After hydraulic fracturing is completed, different cavity lengths and cavity spacings are set according to the characteristics of the coal seam, and the coal seam is cavitated using a hydraulic coal breaking device with a backward coal breaking method.

2. The multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief according to claim 1 is characterized in that: In Step 1, according to the distribution characteristics of the specific rock and coal seams, the drilling has an elevation angle and an internal staggered angle so that the fracturing range covers the entire end of the working face.

3. The multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief according to claim 2 is characterized in that: The drill holes in the upper and lower drift crossways of the working face are arranged in a staggered manner.

4. The multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief according to claim 1 is characterized in that: In Step 2, a long fracturing section is used in the rock layer, and a short fracturing section is used in the coal layer.

5. The multi-stage controllable hydraulic fracturing and cavitation coupling method for top coal weakening and pressure relief according to claim 1 is characterized in that: In Step 3, when the hydraulic coal breaking device retreats to a position close to the roadway, short-type coal breaking and hole making are carried out.

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