A method for treating hard roof of tunnel by directional block hydraulic fracturing

Abstract

The present invention discloses a method for treating hard roof of tunnel by directional block hydraulic fracturing, and belongs to the technical field of coal mining. According to the tunnel data and surrounding rock properties for hydraulic fracturing, the arrangement position of the fracturing boreholes is planned and the parameters thereof are designed; the fracturing boreholes are arranged as vertical boreholes arranged along the horizontal direction of the working face and horizontal boreholes perpendicular to the working face direction, and after the construction of all the fracturing boreholes is completed, a criss-cross "well" shaped hydraulic fracturing network is formed above the coal seam roof, and after hydraulic fracturing, the hydraulic fracturing cracks expanded by the fracturing divide the hard coal seam roof into blocks, so that the hard coal seam roof is fully broken and softened. The present invention fully fracturifies the roof through the "well" shaped fracturing boreholes, and the cracks generated can separate the roof into block structures, so that the mining face can fall as it is mined, and at the same time, the block roof can reduce the impact of the collapsed roof on the working face and the tunnel. The problem of low roof weakening efficiency is solved.

Description

Technical Field

[0001] The invention relates to a method for treating a hard roof of a tunnel by directional block hydraulic fracturing, and belongs to the technical field of coal mining. Background Art

[0002] In the coal mining process, the hard roof seriously restricts the production efficiency. The high ground stress caused by the hard roof hanging but not spanning in the goaf increases the difficulty of supporting the working face and adjacent tunnels. When a large area of ​​the hanging roof suddenly collapses, it will seriously impact the coal mining working face and threaten the safety of the mining face production. The current advanced hydraulic fracturing method used to treat the hard roof is to hydraulically fracture the hard roof through the drill holes arranged in the working face tunnel. After fracturing, only a single crack can be generated in the roof, and the roof weakening efficiency is low. Summary of the invention

[0003] The purpose of the present invention is to provide a method for treating hard roof of a tunnel by directional block hydraulic fracturing. In the method of the present invention, the roof is fully fractured by fracturing holes arranged in a "well" shape, and the resulting cracks can separate the roof into block structures, so that the mining face can fall as it is mined, and at the same time, the block roof can reduce the impact of the collapsed roof on the working face and the tunnel.

[0004] The technical solution of the present invention is a method for treating hard roof of a tunnel by directional block hydraulic fracturing, which is characterized by: planning the layout position of the fracturing boreholes and designing the parameters of the fracturing boreholes in advance according to the geological data of the tunnel to be hydraulically fractured and the properties of the surrounding rocks; the layout of the fracturing boreholes is divided into two parts, namely, vertical fracturing boreholes arranged along the horizontal direction of the working face and horizontal fracturing boreholes perpendicular to the direction of the working face, and after the construction of all fracturing boreholes is completed, a criss-crossing "well" shaped hydraulic fracturing network is formed above the coal seam roof, and then after hydraulic fracturing, the hydraulic fracturing cracks expanded by the fracturing divide the hard coal seam roof into blocks, so that the hard coal seam roof is fully broken and softened, reducing the impact of the collapsed coal seam roof on the working face and the tunnel.

[0005] The aforementioned method for treating hard roof of a tunnel by directional block hydraulic fracturing specifically comprises the following steps:

[0006] S1: Determine the fracturing range and determine the fracturing drilling layout parameters according to the rock mechanical properties of the coal seam roof and the layout of the tunnels around the working face;

[0007] S2: construct vertical fracturing boreholes parallel to the working face;

[0008] S3: drilling and cutting grooves in the fracturing borehole;

[0009] S4: hydraulic fracturing of the coal seam roof using a packer in a fracturing borehole;

[0010] S5: Repeat step S2 to drill a new vertical fracturing borehole next to the hydraulic fracturing borehole, and repeat steps S3 to S4;

[0011] S6: After completing hydraulic fracturing of all vertical fracturing boreholes, construct transverse fracturing boreholes perpendicular to the working surface, and repeat steps S3 to S5 until hydraulic fracturing of all transverse fracturing boreholes is completed.

[0012] In the aforementioned method of treating hard roof of a tunnel by directional block hydraulic fracturing, the layout of the fracturing boreholes is planned in advance according to the geological data of the tunnel to be hydraulically fractured and the properties of the surrounding rock, and the parameters of the fracturing boreholes are designed as follows: the spacing of the fracturing boreholes is determined by the mechanical properties of the roof rock, and the tunnel position of the fracturing boreholes is determined by the tunnel data.

[0013] In the aforementioned method for treating hard roof of a roadway by directional massive hydraulic fracturing, the arrangement of the fracturing boreholes is determined by the roadway drawings, and the horizontal fracturing boreholes are drilled from the stone gates above the coal seam roof and parallel to it, at a horizontal angle to the fracturing area of ​​the coal seam roof; the vertical fracturing boreholes are preferably drilled from the roadways and stone gates located at the coal seam roof above the coal seam and close to the roof of the fracturing area, at a horizontal angle to the fracturing area of ​​the coal seam roof. If there is no roadway that meets the conditions, holes are drilled from the roadways on both sides of the working face along the horizontal direction of the working face at a certain angle to the fracturing area of ​​the coal seam roof, and the angle size is:

[0014] , ,

[0015] In the formula, α1 is the layout angle of the lower roadway, α2 is the layout angle of the upper roadway, h is the top cutting height, L is the length of the working face, and β is the inclination of the coal seam.

[0016] In the aforementioned method of treating hard roof of a tunnel by directional massive hydraulic fracturing, the spacing between adjacent fracturing boreholes in the same direction is 10 to 15 m; the spacing between adjacent fracturing borehole isolation sections in the fracturing borehole is 5 m.

[0017] In the aforementioned method of treating hard tunnel roof by directional block hydraulic fracturing, the drilling grooves are divided into cross grooves and vertical grooves. When the thickness of the same lithology in the coal seam roof exceeds 10m, cross grooves are arranged in all fracturing boreholes; when the thickness of the same lithology in the coal seam roof is less than or equal to 10m, vertical grooves are arranged in all fracturing boreholes.

[0018] In the aforementioned method for treating hard roof of a tunnel by directional block hydraulic fracturing, the drilling and grooving length is ≤10cm, the depth is ≤3cm, the width is ≤2cm, and the shape is diamond-shaped.

[0019] In the aforementioned method for treating hard roof of a tunnel by directional block hydraulic fracturing, in step S4, the hydraulic fracturing process is to send the packer to the fracturing section in the fracturing borehole, and continue to pressurize for hydraulic fracturing after the water pump is pressurized to seal the hole, and then retreat to fracture the next section after the pressure is released until all the fracturing sections of the entire fracturing borehole are fractured, and the fracturing time of each fracturing section should be ≥20min.

[0020] In the aforementioned method for treating hard roof of a tunnel by directional massive hydraulic fracturing, in step S4, during the hydraulic fracturing process, the fracturing section in the fracturing borehole should avoid the part that crosses and overlaps with other fracturing boreholes.

[0021] In the aforementioned method for treating hard roof of a tunnel by directional block hydraulic fracturing, in step S3, the selection of drilling and grooving should avoid the weak and broken parts of the surrounding rock in the fracturing borehole.

[0022] Beneficial effects of the present invention: Compared with the prior art, in the method of the present invention, by setting vertical fracturing holes arranged along the horizontal direction of the working face and horizontal fracturing holes perpendicular to the working face, a criss-crossing "well"-shaped hydraulic fracturing network is formed above the coal seam roof after the construction of all fracturing holes is completed. After hydraulic fracturing, the hard coal seam roof is divided into blocks through hydraulic fracturing cracks expanded by fracturing. This method can effectively weaken and break the hard roof, so that the hard coal seam roof is fully broken and softened, and the efficiency of coal seam roof collapse is improved, and the mining face can be collapsed as the mining progresses. At the same time, the blocky coal seam roof can reduce the impact of the collapsed roof on the working face and the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the plan layout of the fracturing drilling of the present invention;

[0024] Figure 2 It is a schematic diagram of vertical grooving of the present invention;

[0025] Figure 3 It is a schematic diagram of the cross groove of the present invention;

[0026] Figure 4 It is a schematic diagram of the hydraulic fracturing operation in the fracturing borehole according to the present invention.

[0027] In the figure: 1- goaf, 2- working face, 3- coal seam roof, 4- transport tunnel, 5- return air tunnel, 6- fracturing borehole, 7- drilling groove, 8- return air stone gate, 9- transport stone gate, 10- packer connecting rod, 11- packer, 12- fracturing borehole isolation section, 13- hydraulic fracturing crack. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0029] The embodiment of the present invention is a method for treating a hard roof of a tunnel by directional block hydraulic fracturing. The arrangement position of the fracturing borehole 6 is planned and the parameters of the fracturing borehole 6 are designed in advance according to the geological data of the tunnel to be hydraulically fractured and the properties of the surrounding rock. That is, the spacing distance of the fracturing borehole 6 is determined by the mechanical properties of the roof rock, and the tunnel position of the fracturing borehole 6 is determined by the tunnel data, that is, the position from which the fracturing borehole 6 is to be drilled.

[0030] The arrangement of the fracturing boreholes 6 is divided into two parts, namely, the vertical fracturing boreholes 6 arranged along the horizontal direction of the working face 2 and the horizontal fracturing boreholes 6 perpendicular to the working face 2. The vertical fracturing boreholes 6 are arranged on both sides of the working face 2 where hydraulic fracturing is required, that is, the vertical fracturing boreholes 6 are drilled from the lanes on both sides of the working face 2. The fracturing boreholes 6 are drilled from the lanes on both sides of the working face 2 (can be drilled from any lane or from both lanes at the same time), and the fracturing boreholes 6 are arranged on the coal seam roof 3 in a direction parallel to the working face 2. The horizontal fracturing boreholes 6 are constructed from the adjacent stone gate parallel to the working face 2 where hydraulic fracturing is implemented, and the horizontal fracturing boreholes 6 are arranged on the coal seam roof 3 in a direction perpendicular to the working face 2. After all the fracturing holes 6 are constructed, a criss-cross "well"-shaped hydraulic fracturing network is formed above the coal seam roof 3. After hydraulic fracturing, the hydraulic fracturing cracks 13 expanded by the fracturing divide the hard coal seam roof 3 into blocks, so that the hard coal seam roof 3 is fully broken and softened, reducing the impact of the collapsed coal seam roof 3 on the working face 2 and the tunnel.

[0031] The specific steps include:

[0032] S1: Determine hydraulic fracturing areas based on top cutting requirements.

[0033] S2: designing reasonable layout parameters of the fracturing drilling holes 6 according to the rock properties of the target coal seam roof 3 and geological data, and determining the construction tunnel of the fracturing drilling holes 6 .

[0034] S3: The fracturing borehole 6 is arranged in front of the working face 2. The vertical fracturing borehole 6 parallel to the working face 2 is constructed first, and the fracturing borehole 6 is selected for construction according to the site conditions. After the fracturing borehole 6 is constructed, the shape of the borehole and the accumulation of debris in the hole are observed. If the borehole has no obvious deformation, the surrounding rock of the borehole is good, and there is no obvious debris in the hole, the borehole is hydraulically cut to make a borehole groove 7 at the fracturing point.

[0035] S4: Use the packer 11 to sequentially fracture the fracturing sections of the fracturing borehole 6, with the intervals between the fracturing sections being 5 m and the fracturing time being not less than 20 minutes.

[0036] S5: drilling a new vertical fracturing borehole 6 at a distance of 10 to 15 m next to the hydraulic fracturing borehole 6, and repeating the above steps until the coal seam roof 3 within the target range is completely fractured through the vertical fracturing borehole 6.

[0037] S6: Drilling a transverse fracturing borehole 6 at the stone gate adjacent to the working face 2, with the drilling direction perpendicular to the working face 2. After the drilling is completed, check whether the borehole is qualified, and then make a drilling groove 7 in the fracturing section in the borehole. The fracturing section spacing is 5m, and the fracturing section needs to avoid the fracturing section of the vertical fracturing borehole 6 parallel to the working face 2. After the fracturing of the transverse fracturing borehole 6 is completed, drill a new transverse fracturing borehole 6 at intervals of 10 to 15m, and repeat the above operation until the coal seam roof 3 within the target range is fractured through the transverse fracturing borehole 6.

[0038] The arrangement of the fracturing boreholes 6 in the above technical solution is determined by the roadway drawings. The horizontal fracturing boreholes 6 are drilled from the stone gates above the coal seam roof 3 and parallel to it. Figure 1 For example, it is possible to drill a hole at a horizontal angle toward the fracturing zone of the coal seam roof 3 from the return air stone gate 8 or the transport stone gate 9. The vertical fracturing borehole 6 is preferably drilled from a tunnel or stone gate located above the coal seam roof 3 and close to the roof of the fracturing zone, and at a horizontal angle toward the fracturing zone of the coal seam roof 3. If there is no tunnel that meets the conditions, then drill a hole from the tunnels on both sides of the working face 2 in the manner of the present application. Figure 1 For example, it is possible to drill holes into the fracturing zone of the coal seam roof 3 from the transport tunnel 4 and the return air tunnel 5 on both sides of the working face 2 at the same time. During the drilling process, holes are drilled into the fracturing zone of the coal seam roof 3 at a certain angle along the horizontal direction of the working face 2. The angle is:

[0039] , ,

[0040] In the formula, α1 is the layout angle of the lower roadway, α2 is the layout angle of the upper roadway, h is the top cutting height, L is the length of the working face, and β is the inclination of the coal seam.

[0041] The drilling spacing of adjacent fracturing boreholes 6 in the same direction is 10 to 15 meters, which is specifically selected according to the hardness of the coal seam roof 3. For extremely hard rocks such as basalt roofs with a uniaxial compressive strength exceeding 60MPa, a drilling spacing of 10m is more appropriate. For relatively hard rock roofs with a uniaxial compressive strength of 30MPa to 60MPa, the drilling spacing is adjusted to 15m. According to the mechanical properties of the coal seam roof 3, a suitable fracturing drilling spacing is selected to reduce the drilling and fracturing engineering workload while ensuring sufficient crushing of the coal seam roof 3.

[0042] Each fracturing borehole 6 is divided into a plurality of fracturing sections, each of which is spaced 5 m apart. A drilling groove 7 is provided on the fracturing borehole 6 of each fracturing section, and the drilling groove 7 is made by hydraulic slitting in the fracturing borehole 6. The drilling groove 7 has a guiding effect on the expansion direction of the hydraulic fracturing cracks 13 formed after hydraulic fracturing, thereby achieving directional fracturing and crushing of the hard coal seam roof 3, and improving the fracturing efficiency. The present invention can divide the coal seam roof 3 into block rocks by the hydraulic fracturing cracks 13 through the hydraulic fracturing borehole network and directional hydraulic fracturing technology arranged in the coal seam roof 3, making the coal seam roof 3 more likely to collapse and reducing the roof pressure of the working face 2 and the roadway.

[0043] The selection of the drilling groove 7 should avoid the weak and broken parts of the surrounding rock in the fracturing borehole 6, because the drilling groove 7 in the weak and broken parts of the surrounding rock is easy to cause the hole to collapse and bury the equipment. At the same time, there are already developed cracks in this part of the surrounding rock, and the cracks generated by hydraulic fracturing will expand along the direction of the already developed cracks in the rock formation, and the guiding effect of the drilling groove 7 is not obvious.

[0044] The drilling grooves 7 are divided into cross grooves and vertical grooves. The vertical grooves are symmetrical grooves arranged at the vertical ends of the boreholes, and the cross grooves are grooves arranged at the horizontal ends based on the vertical grooves. When the thickness of the same lithology in the coal seam roof 3 exceeds 10m, cross grooves are arranged in all fracturing boreholes 6; when the thickness of the same lithology in the coal seam roof 3 is less than or equal to 10m, vertical grooves are arranged in all fracturing boreholes 6. The hydraulic fracturing fissures 13 guided by the vertical grooves to expand vertically cut the coal seam roof 3. For the roof rock with the same lithology thickness less than 10m, the contact surface between different rocks is weakly bonded, and it can collapse naturally without the need to use cross grooves to guide the expansion of transverse cracks to cut the rock. For the roof rock with the same lithology thickness greater than 10m, the bonding strength in the rock is large, and the rock blocks are thick, so it is necessary to arrange cross grooves to guide the expansion of transverse cracks to cut the rock, so as to facilitate the collapse of the coal seam roof 3.

[0045] During the production of the drilling groove 7, its length is ≤10cm, depth is ≤3cm, width is ≤2cm, and the fracturing shape is diamond-shaped. The basic parameters of the drilling groove 7 are designed according to the hydraulic fracturing equipment. Its length is equal to the sealing section of the packer 11. Too long will easily affect the sealing effect of the packer 11. Too large depth and width of the drilling groove 7 will affect the integrity of the fracturing hole and weaken the guidance of the drilling groove 7 on the expansion of the crack. The tip of the diamond groove is more likely to induce the crack to expand along the tip of the diamond groove, and the crack is single and has few crack bifurcations.

[0046] At the same time, the fracturing section needs to avoid the overlapping parts with other fracturing boreholes 6, because the overlapping parts can only be blocked by one plugger 11 for one of the fracturing boreholes 6, and the high-pressure water used for hydraulic fracturing will be discharged from the other fracturing boreholes 6, and the hydraulic fracturing effect cannot be achieved.

[0047] The hydraulic fracturing process is to send the packer 11 to the fracturing section of the fracturing borehole 6, and seal the fracturing section through the packer 11 to form a fracturing borehole isolation section 12. After the water pump pressurizes and seals the hole, it continues to pressurize the fracturing borehole isolation section 12 to hydraulically fracture. After the hydraulic fracturing is completed and the packer 11 is depressurized, it retreats 5m to fracture the next section until all the fracturing sections of the entire fracturing borehole 6 are fractured. The fracturing time of each fracturing section should be ≥20min to ensure that the best fracturing effect can be achieved.

Claims

1. A method for treating hard roof of a roadway by directional block hydraulic fracturing, characterized in that: The arrangement position of the fracturing boreholes (6) is planned in advance according to the geological data of the tunnel to be hydraulically fractured and the properties of the surrounding rock, and the parameters of the fracturing boreholes (6) are designed; the arrangement of the fracturing boreholes (6) is divided into two parts, namely, the vertical fracturing boreholes (6) arranged along the horizontal direction of the working face (2) and the horizontal fracturing boreholes (6) arranged perpendicular to the working face (2); after the construction of all the fracturing boreholes (6) is completed, a criss-crossing "well"-shaped hydraulic fracturing network is formed above the coal seam roof (3); after hydraulic fracturing, the hydraulic fracturing cracks (13) expanded by the fracturing divide the hard coal seam roof (3) into blocks, so that the hard coal seam roof (3) is fully broken and softened, reducing the impact of the collapsed coal seam roof (3) on the working face (2) and the tunnel; The specific steps include: S1: Determine the fracturing range, and determine the layout parameters of the fracturing drilling holes (6) according to the rock mechanical properties of the coal seam roof (3) and the layout of the tunnels around the working face (2); S2: constructing a vertical fracturing borehole (6) parallel to the working surface (2); S3: drilling and cutting grooves (7) in the fracturing borehole (6); S4: using a packer (11) to perform hydraulic fracturing on the coal seam roof (3) in the fracturing borehole (6); S5: Repeat step S2 to drill a new vertical fracturing borehole (6) next to the hydraulically fracturing borehole (6), and repeat steps S3 to S4; S6: After completing the hydraulic fracturing of all vertical fracturing boreholes (6), construct transverse fracturing boreholes (6) perpendicular to the working surface (2), and repeat steps S3 to S5 until all transverse fracturing boreholes (6) have completed hydraulic fracturing.

2. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: The arrangement positions of the fracturing boreholes (6) are planned in advance according to the geological data of the tunnel to be hydraulically fractured and the properties of the surrounding rocks, and the parameters of the fracturing boreholes (6) are designed as follows: the spacing of the fracturing boreholes (6) is determined by the mechanical properties of the top plate rock, and the tunnel positions of the fracturing boreholes (6) are determined by the tunnel data.

3. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: The arrangement of the fracturing boreholes (6) is determined by the roadway drawings. The horizontal fracturing boreholes (6) are drilled from the stone gates above the coal seam roof (3) and parallel thereto at a horizontal angle to the fracturing zone of the coal seam roof (3); the vertical fracturing boreholes (6) are selected from the roadways and stone gates located above the coal seam roof (3) and close to the roof of the fracturing zone, and are drilled at a horizontal angle to the fracturing zone of the coal seam roof (3); or from the roadways on both sides of the working face (2), along the horizontal direction of the working face (2) at a certain angle to the fracturing zone of the coal seam roof (3), and the angle size is: Where α1 is the layout angle of the lower tunnel, α2 is the layout angle of the upper tunnel, h is the top cutting height, L is the length of the working face (2), and β is the coal seam inclination.

4. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: The spacing between adjacent fracturing boreholes (6) in the same direction is 10 to 15 m; the spacing between adjacent fracturing borehole isolation sections (12) in the fracturing boreholes (6) is 5 m.

5. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: The drilling grooves (7) are divided into cross grooves and vertical grooves. When the thickness of the same lithology in the coal seam roof (3) exceeds 10m, cross grooves are arranged in all the fracturing drill holes (6); when the thickness of the same lithology in the coal seam roof (3) is less than or equal to 10m, vertical grooves are arranged in all the fracturing drill holes (6).

6. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: The drilling and cutting groove (7) has a length of ≤10 cm, a depth of ≤3 cm, a width of ≤2 cm, and is in a diamond shape.

7. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: In step S4, the hydraulic fracturing process is to send the packer (11) to the fracturing section in the fracturing borehole (6), and after the water pump pressurizes and seals the hole, continue to pressurize for hydraulic fracturing, and after the pressure is released, retreat to fracture the next section until all the fracturing sections of the entire fracturing borehole (6) are fractured, and the fracturing time of each fracturing section is ≥20 minutes.

8. The method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: In the step S4, during the hydraulic fracturing process, the fracturing sections in the fracturing borehole (6) avoid the areas where they overlap with other fracturing boreholes (6).

9. A method for treating hard roof of a tunnel by directional block hydraulic fracturing according to claim 1, characterized in that: In step S3, the drilling and grooving (7) is performed to avoid the weak and broken parts of the surrounding rock in the fracturing borehole (6).

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