Heading-on advanced hydraulic fracturing pressure relief and scour prevention method for coal roadway tunneling

Abstract

The invention discloses a tunneling coal roadway head-on advanced hydraulic fracturing pressure relief and scour prevention method. The method comprises the following steps: S1, rapid diagnosis of geological conditions; measuring the direction of the maximum principal stress within the range of 20m in front of the head-on, and taking a coal core to measure the tensile strength of the coal seam; s2, small-aperture fracturing drill holes are constructed; a small-aperture drill hole is constructed to the designed maximum depth along the tunneling axis of the roadway; s3, performing segmented mechanical reaming and cavity construction; after the operation of the mechanical reaming section is completed, the reaming drill bit executes radial retraction action; then the drill rod is withdrawn to an orifice at a constant speed; s4, performing targeted hole sealing hydraulic fracturing; positioning and hole sealing are conducted at a target point n + 1 m away from a hole opening, and pulse type high-pressure water is injected into the coal seam to implement hydraulic fracturing; s5, circulating construction and effect acceptance; and S2 to S4 are repeated according to the tunneling requirement to complete porous construction. According to the invention, the risks of abnormal coal dust gushing, drilling tool clamping stagnation and even in-hole rock burst induction in subsequent mechanical reaming operation in a high-stress and strong-disturbance environment are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine rock burst prevention and control, in particular to a method for preventing rock burst by hydraulic fracturing in advance during coal tunneling. Background Art

[0002] With increasing coal mining depths, rock burst hazards are becoming increasingly severe, particularly in tunneling tunnels facing high static stresses. Rock burst prevention and control presents significant challenges. Large-diameter drilling is the preferred pressure-relief technology for rock burst prevention and control at tunneling faces, but its application often fails to effectively prevent rock bursts. Pre-construction of large-diameter boreholes, due to the rheological or time-dependent self-stabilization of the surrounding rock, results in excessively rapid stress recovery in the pressure-relief zone. This prevents the expected weakening zone from developing sufficiently to bear and transfer high stresses during subsequent tunneling. Furthermore, drilling in high-stress core areas carries inherent risks, posing a high risk of coal dust outflow and absorption, drill tool jamming, and even directly contributing to rock bursts. Despite widespread implementation of large-diameter drilling pressure-relief measures in mines, rock burst accidents remain uncontrolled, highlighting the inadequate effectiveness of current large-diameter drilling pressure-relief methods in addressing complex stress environments at depth. Therefore, identifying and developing new approaches to effectively address these technical challenges is a critical challenge facing the industry.

[0003] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for unloading pressure and preventing impact by hydraulic fracturing in advance in coal tunneling. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for unloading pressure and preventing impact by hydraulic fracturing in advance in coal tunneling, so as to solve the problems existing in the prior art.

[0005] To achieve the above-mentioned object, the present invention provides the following solution: The present invention provides a method for unloading pressure and preventing impact by hydraulic fracturing in a coal tunnel, comprising the following steps: S1, rapid diagnosis of geological conditions; A portable ground stress measuring instrument is used to measure the maximum principal stress direction within 20m ahead of the head, and coal cores are taken to measure the tensile strength of the coal seam; S2, construction of small-diameter crack-inducing drilling holes; Drill small-diameter holes along the tunneling axis to the designed maximum depth; S3, segmented mechanical cavitation and expansion; After the hole reaches the designed depth, a high-pressure hydraulically driven reaming drill bit is used to carry out segmented reaming of the predetermined reaming section. The water pressure and propulsion parameters are dynamically adjusted until a reaming and pressure relief cavity of the designed diameter is finally formed. After the mechanical reaming section is completed, the reaming drill bit performs a radial retraction action to fully retract the cutting blades to the initial transport state. The drill pipe is then withdrawn at a uniform speed to the hole mouth. S4, targeted sealing hydraulic fracturing; Position and seal the hole at a target point n+1 meters away from the hole mouth, and inject pulsed high-pressure water into the coal seam to perform hydraulic fracturing; S5, cyclic construction and effect acceptance; Repeat S2 to S4 to complete multi-hole construction according to excavation requirements; Among them, n is the daily footage, which is 6-8m.

[0006] According to the method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling provided by the present invention, in S2, after the drilling is completed, a drilling trajectory meter is used to detect the deflection and confirm the thickness of the sediment at the bottom of the hole. If it is unqualified, correction or hole washing is required.

[0007] According to the method for hydraulic fracturing and pressure relief to prevent impact in coal tunneling provided by the present invention, in S4, the pressure and flow curves are monitored in real time during the fracturing process. When a sudden pressure drop and an increase in flow rate occur, it is determined that the main fracture is connected. At the same time, it is ensured that the total water injection volume is not less than 90% of the design value. If it does not meet the standard, pressure supplementation is required.

[0008] According to the method for head-on hydraulic fracturing and pressure relief and anti-blowout in coal tunneling provided by the present invention, in S2, the design depth of the small-diameter fracturing borehole is 50-100m and the diameter is 130mm.

[0009] According to the method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling provided by the present invention, in S3, the drill is withdrawn at a uniform speed of 0.5-0.8 m / min.

[0010] According to the method for head-on hydraulic fracturing and pressure relief and anti-blowout in coal tunneling provided by the present invention, in S4, MKY series packers are used for positioning and sealing.

[0011] According to the method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling provided by the present invention, in S4, water injection is continued for not less than 20 minutes during hydraulic fracturing.

[0012] According to the method for hydraulic fracturing and pressure relief and anti-bumping in coal tunneling provided by the present invention, in S3, the diameter of the expanded section during mechanical expansion is 350 mm, the length of the expanded section is 5 m, and the length of the unexpanded section is 3 m.

[0013] According to the method for head-on hydraulic fracturing and pressure relief and anti-blowout in coal tunneling provided by the present invention, in S2, a mechanical rack-and-pinion structured drilling-while-drilling drill bit is selected to carry out the construction of aperture-induced fracturing drilling.

[0014] The present invention discloses the following technical effects: The present invention firstly releases the energy of the local high stress concentration area and guides the direction of crack expansion by drilling a small diameter hole, which significantly reduces the risk of subsequent mechanical hole expansion operations encountering abnormal coal powder outflow, drill bit jamming, and even inducing rock burst in the hole under high stress and strong disturbance environment.

[0015] The present invention can achieve an efficient drilling mode of "one-time drilling and simultaneous hole expansion", avoiding the tedious process of frequent replacement of drilling tools in traditional large-diameter drilling, and significantly improving construction efficiency and hole quality. The regular annular slot structure formed by mechanical hole expansion can construct a continuous, through-hole and morphologically controllable weakening zone in the coal rock mass, which not only effectively reduces the near-field surrounding rock stress level, but also promotes the deep transfer of high stress and the gradient release of elastic energy by optimizing the stress distribution gradient. After the drill is withdrawn, the hole is sealed to complete a one-time coal seam water injection fracturing, thereby achieving a more stable, longer-lasting and spatially better distributed pressure relief effect.

[0016] The present invention constructs a protection system of "local weakening-regional pressure relief-system stabilization", which breaks through the limitations of single large-diameter drilling pressure relief, realizes the maximization of the tunnel head pressure relief range, long-term anti-bumping time, and coordinated energy management, and is particularly suitable for the safe and efficient mining of deep high-ground pressure and low-permeability coal seams. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 The present invention is a flow chart of the method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Reference Figure 1 The present invention provides a method for unloading pressure and preventing impact by hydraulic fracturing in a coal tunnel, comprising the following steps: S1, rapid diagnosis of geological conditions; A portable ground stress measuring instrument is used to measure the maximum principal stress direction within 20m ahead of the head, and coal cores are taken to measure the tensile strength of the coal seam; S2, construction of small-diameter crack-inducing drilling holes; Drill small-diameter holes along the tunneling axis to the designed maximum depth; S3, segmented mechanical cavitation and expansion; After the hole reaches the designed depth, a high-pressure hydraulically driven reaming drill bit is used to carry out segmented reaming of the predetermined reaming section. The water pressure and propulsion parameters are dynamically adjusted until a reaming and pressure relief cavity of the designed diameter is finally formed. After the mechanical reaming section is completed, the reaming drill bit performs a radial retraction action to fully retract the cutting blades to the initial transport state. The drill pipe is then withdrawn at a uniform speed to the hole mouth. S4, targeted sealing hydraulic fracturing; Position and seal the hole at a target point n+1 meters away from the hole mouth, and inject pulsed high-pressure water into the coal seam to perform hydraulic fracturing; S5, cyclic construction and effect acceptance; Repeat S2 to S4 to complete multi-hole construction according to excavation requirements; Among them, n is the daily footage, which is 6-8m.

[0022] To further optimize the solution, in S2, after drilling is completed, a drilling tracker is used to detect the deflection and confirm the thickness of the sediment at the bottom of the hole. If it is unqualified, correction or hole washing is required.

[0023] After mechanical drilling is complete, the entire borehole section is inspected for deflection using a drilling tracker, requiring a straightness deviation of ≤1° (per 10m section). The bottom-hole sediment thickness is measured using a bottom-hole sediment detector, requiring a thickness of ≤50mm. If the deflection or sediment thickness does not meet the standards, the drill rig angle must be adjusted to correct the deviation (if the deflection exceeds the limit) or the hole must be flushed with high-pressure water (pressure ≥10MPa) (if the sediment exceeds the limit). Drilling can only be reversed after passing the test.

[0024] To further optimize the plan, in S4, the pressure and flow curves are monitored in real time during the fracturing process. When a sudden pressure drop and an increase in flow rate occur, it is determined that the main fracture is connected. At the same time, it is ensured that the total water injection volume is not less than 90% of the design value. If the standard is not met, pressure must be supplemented.

[0025] During hydraulic fracturing, pressure and flow curves are monitored in real time using pressure sensors (accuracy ±0.1 MPa) and electromagnetic flowmeters (accuracy ±1%). A sudden drop in pressure (≥10 MPa) accompanied by a simultaneous increase in flow (≥20%) indicates that the main fracture has been broken through. The total injected water volume is also calculated, ensuring it is no less than 90% of the designed value (typically 50-100 m³, calculated based on coal seam parameters). If the total injected water volume falls short of the target, pressure replenishment procedures must be initiated immediately: maintaining the original pulse water pressure parameters and extending the injection time until the total injected volume reaches the target. Alternatively, the water pressure can be increased by 10%-20% to accelerate fracture expansion, without exceeding the equipment's rated pressure (60 MPa).

[0026] To further optimize the plan, in S2, the design depth of the small-diameter fracturing borehole is 50-100m and the diameter is 130mm.

[0027] The setting of this parameter needs to be combined with the coal seam thickness and stress distribution characteristics. When the tunnel strikes nearly horizontally, the maximum drilling depth can be appropriately increased (no more than 120m) to ensure that the drilling can cover the high-stress core area of ​​the area to be excavated.

[0028] To further optimize the solution, in S3, the drill is withdrawn at a uniform speed of 0.5-0.8m / min.

[0029] During the withdrawal process, the drill pipe tension sensor monitors the withdrawal resistance in real time. When the resistance suddenly increases (exceeds 1.5 times the normal resistance), the withdrawal is immediately suspended to check whether the hole wall has collapsed or the drill bit is stuck. After processing, the drill continues to withdraw to the hole mouth at the original speed.

[0030] To further optimize the plan, in S4, MKY series packers were used for positioning and sealing.

[0031] An MKY series packer (specific models are tailored to the borehole diameter, such as the MKY-130) is used for positioning and sealing. The sealing position is n+1m from the borehole opening (n is the daily footage, 6-8m). High-pressure water expands the packer (expansion pressure ≥15MPa), allowing the bladder (made of butyl rubber, optimized for 1.5m length) to fit tightly against the borehole wall, ensuring a pressure-bearing capacity of >70MPa. After sealing, a pressure test (injecting 5MPa of clean water and maintaining pressure for 5 minutes, with a pressure drop of ≤0.5MPa) verifies the sealing effect. Hydraulic fracturing can only be performed if the test passes.

[0032] To further optimize the scheme, in S4, water injection should be continued for no less than 20 minutes during hydraulic fracturing.

[0033] For low-permeability coal seams (permeability <0.1 mD), the duration can be extended to 30-40 minutes; for medium-to-high permeability coal seams (permeability ≥0.1 mD), the duration is maintained for 20-25 minutes. During the water injection process, a pulsed pressurization mode (pressure periodically fluctuates between 30-60 MPa, with a cycle of 30 seconds) is used to enhance the effect of fracture expansion.

[0034] To further optimize the solution, in S3, the diameter of the expanded section during mechanical expansion is 350 mm, the length of the expanded section is 5 m, and the length of the unexpanded section is 3 m.

[0035] The diameter of the expanded section is strictly controlled to 350mm, and the length of a single expanded section is 5m. A 3m unexpanded section (130mm diameter) is retained between adjacent expanded sections as a transition. During expansion, a "segmented advancement + real-time monitoring" model is adopted: after each meter of expanded hole, the integrity of the expanded section's wall is checked with an in-hole camera to ensure that the wall is regular and free of obvious collapse. If this is not achieved, the expansion speed is reduced (from 1m / min to 0.5m / min) and the high-pressure water assist pressure is increased (from 20MPa to 25MPa).

[0036] To further optimize the solution, in S2, a mechanical rack and pinion structured drilling bit was selected for the construction of aperture-induced cracking drilling.

[0037] To further optimize the plan, the construction parameters of anti-bumping drilling for tunnel excavation in different impact hazard areas are as follows: Weak impact danger zone: construct a pressure relief borehole head-on, and the pressure relief borehole is arranged at the center position 1.5m away from the bottom plate; Medium impact hazard area: construct two pressure relief boreholes head-on, with the pressure relief boreholes arranged at the center position 1.5m away from the bottom plate, and the distance between the two holes is 2m; Strong impact danger zone: 3 pressure relief boreholes are constructed head-on, arranged in a "three-flower" pattern, with the distance between adjacent boreholes being 1.5m, and the pressure relief borehole is arranged at the center position 1.5m away from the bottom plate.

[0038] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling, characterized in that: The steps include: S1, rapid diagnosis of geological conditions; S2, construction of small-diameter crack-inducing drilling holes; S3, segmented mechanical cavitation and expansion; S4, targeted sealing hydraulic fracturing; S5, cyclic construction and effect acceptance; Repeat S2 to S4 according to excavation requirements to complete multi-hole construction.

2. A method for unloading pressure and preventing impact by hydraulic fracturing in advance in coal tunneling according to claim 1, characterized in that: In S2, small-diameter holes are drilled along the tunnel excavation axis to the designed maximum depth. After the drilling is completed, a drilling tracker is used to detect the deflection and confirm the thickness of the sediment at the bottom of the hole. If it is unqualified, correction or hole washing is required.

3. A method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S4, the target point n+1 meters away from the orifice is positioned and sealed, and pulsed high-pressure water is injected into the coal seam for hydraulic fracturing. During the fracturing process, the pressure and flow curves are monitored in real time. When a sudden pressure drop and flow increase occur, it is determined that the main fracture is connected. At the same time, the total water injection volume is ensured to be no less than 90% of the design value. If it does not meet the standard, pressure must be increased. Among them, n is the daily footage, which is 6-8m.

4. A method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S2, the design depth of the small-diameter fracturing borehole is 50-100m and the diameter is 130mm.

5. The method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S3, after the hole reaches the designed depth, a high-pressure hydraulically driven reaming drill bit is used to carry out segmented reaming of the predetermined reaming section, and the water pressure and propulsion parameters are dynamically adjusted until a reaming and pressure relief cavity of the designed diameter is finally formed. After the mechanical reaming section is completed, the reaming drill bit performs a radial retraction action to completely retract the cutting blades to the initial transportation state; then the drill rod is withdrawn to the hole mouth at a uniform speed, and the drill is withdrawn at a uniform speed of 0.5-0.8m / min when withdrawing.

6. A method for unloading pressure and preventing impact by hydraulic fracturing in advance in coal tunneling according to claim 1, characterized in that: In S4, MKY series packers were used for positioning and sealing.

7. The method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S4, water injection is continued for no less than 20 minutes during hydraulic fracturing.

8. The method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S3, during mechanical hole expansion, the diameter of the expanded section is 350 mm, the length of the expanded section is 5 m, and the length of the unexpanded section is 3 m.

9. The method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S2, a mechanical rack and pinion structured hole-drilling drill bit was used to construct the aperture-induced cracking drilling.

10. The method for unloading pressure and preventing impact by hydraulic fracturing in coal tunneling according to claim 1, characterized in that: In S1, a portable ground stress measuring instrument was used to determine the direction of the maximum principal stress within 20 m in front of the head, and coal cores were taken to determine the tensile strength of the coal seam.

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