Key layer pressure blasting device under coupling of water pressure and carbon dioxide blasting and construction method

Abstract

The invention discloses a key layer pressure blasting device under coupling of water pressure and carbon dioxide blasting and a construction method, and the device comprises a blasting column in which high-pressure carbon dioxide is stored, a fracturing pipeline and an elastic bag body which are sequentially connected with the blasting column to form a rod body structure, a water injection pipe and a water injection assembly, one end of the water injection pipe is connected with the elastic bag body, the other end of the water injection pipe is connected with the water injection assembly, and the water injection assembly is connected with the controller, controlled by the controller and used for injecting high-pressure water into the elastic bag body and the fracturing pipeline from the water injection pipe. According to the method, local lithology can be fully changed, local gas is promoted to be fully released, the problems that a single plane crack is formed, and a complex crack net is difficult to form are solved, and repeated fracturing or multi-layer fracturing construction can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mines, and in particular to a key layer blasting device and a construction method under the coupling of water pressure and carbon dioxide blasting. Background Art

[0002] During coal mining, the stability of key layers (such as the roof) directly affects underground safety. For example, traditional passive support methods are difficult to cope with complex geological conditions. Coalbed methane (gas) is stored in the micropores of the coal body in an adsorbed state, and conventional extraction efficiency is low. However, hydraulic fracturing technology can actively transform the rock structure, release pressure in advance, shift stress peaks (the location of maximum stress concentration), relieve pressure in the roadway, and reduce the risk of rock bursts. In addition, fracturing creates a fracture network in the coal seam and adjacent rock formations through high-pressure fluid injection, increasing permeability.

[0003] Hydraulic fracturing technology has the advantages of releasing rock stress, reducing the risk of tunnel deformation, and improving coalbed methane extraction rate. It can also flexibly respond to different rock types (such as hard coal or soft coal) by using indirect fracturing, volumetric acid fracturing and other technologies. However, for medium and thick rock formations, there are still the following defects: high-pressure fluid injection forms a fracture network in the key layer, and the expansion of this fracture network is single, that is, the cracks formed by hydraulic fracturing usually extend in the direction perpendicular to the minimum principal stress. When the rock formation stress field shows obvious anisotropy (such as horizontal stress dominance), the cracks will preferentially extend along the direction of the maximum principal stress, resulting in a single plane crack, which is difficult to form a complex fracture network. Summary of the Invention

[0004] The purpose of the present invention is to provide a key layer blasting device under the coupling of water pressure and carbon dioxide blasting, which can not only fully change the local rock properties and promote the full release of local gas, avoid the problems of single plane cracks and difficulty in forming complex fracture networks, but also reduce repeated fracturing or multi-layer fracturing construction.

[0005] To achieve the above purpose, the present invention provides a key layer blasting device coupled with water pressure and carbon dioxide blasting, comprising:

[0006] A blasting assembly comprising a blasting column, a fracturing pipe, and an elastic capsule;

[0007] There is high-pressure carbon dioxide inside the blasting column; the fracturing pipe, elastic capsule and blasting column are connected in sequence and gradually move away from the bottom of the borehole;

[0008] A water injection pipe, one end of which is connected to the elastic bladder and the other end of which is connected to the water injection assembly;

[0009] The water injection assembly is connected to and controlled by the water injection controller. The water injection assembly is used to inject high-pressure water from the water injection pipe into the elastic sac and the fracturing pipe.

[0010] In one example of the present invention, the pressure explosion assembly further includes a converter having a three-way structure;

[0011] The three interfaces of the converter are connected to the water injection pipe, elastic bladder and fracturing pipe respectively;

[0012] In one example of the present invention, a pressure sensor for monitoring water pressure is provided in the elastic bladder;

[0013] After receiving the water pressure signal, the water injection controller can be controlled to switch the connection between the water injection pipe and the elastic bladder, and between the water injection pipe and the fracturing pipe.

[0014] In one example of the present invention, the elastic bladder is threadedly connected to the fracturing pipe through a connecting pipe;

[0015] An elastic member and a sealing head are provided in the connecting pipe;

[0016] The elastic member is located between the end of the fracturing pipe and the sealing head, and under the action of the elastic member, the sealing head seals the end of the connecting pipe close to the elastic sac.

[0017] In one example of the present invention, the lead of the blasting column is led out along the drill hole and connected to the blasting controller.

[0018] In one example of the present invention, the water injection assembly comprises a water tank, a pressure pump, and a high-pressure hose;

[0019] The input end of the pressure pump is connected to the water tank, and the output end is connected to one end of the water injection pipe through a high-pressure hose;

[0020] The hose is equipped with a stop valve, a pressure relief valve, and a pressure recorder.

[0021] A construction method for key layer blasting by coupling water pressure and carbon dioxide blasting, specifically comprising the following steps:

[0022] S1, drilling a hole in the tunnel toward the key layer, and inserting the water injection pipe into the hole so that the elastic bladder, fracturing pipe, and blasting column at one end of the water injection pipe are close to the designated position of the key layer;

[0023] S2, the water injection assembly first fills the elastic bladder with high-pressure water through the water injection pipe, and the elastic bladder expands and fits against the inner wall of the borehole, forming a local sealed space from the elastic bladder to the bottom of the borehole;

[0024] Then, high-pressure water is injected into the fracturing pipe through the water injection assembly to start the fracturing treatment of the key layer. At this time, the key layer is subjected to the action of water pressure to generate a main crack, and the fracturing is maintained for a period of time. While the high-pressure water is continuously injected, the blasting column is detonated to turn the liquid carbon dioxide into gas. The phase change causes the volume of carbon dioxide to increase rapidly, and the high-pressure carbon dioxide is discharged, causing a large number of secondary cracks around and inside the main crack, completing the blasting treatment of the key layer;

[0025] S3, then continue the fracturing treatment, stop the injection after a period of time, release the water in the elastic bladder, drain the water in the fracturing borehole, and finally withdraw the fracturing device and the blasting device from the borehole as a whole.

[0026] In one example of the present invention, the fracturing is maintained for 10-15 minutes in step S2, and the injection is stopped after the fracturing is continued for 10-30 minutes in step S3.

[0027] Compared with the existing technology, the key layer blasting device and construction method under the coupling of water pressure and carbon dioxide blasting first performs high-pressure water fracturing treatment on the key layer drill hole to generate main cracks, and while maintaining fracturing, blasting treatment is performed on the key layer drill hole to generate a large number of secondary cracks around and inside the main cracks, and high-pressure water injection is maintained for a period of time. This can not only fully change the local rock properties and promote the full release of local gas, but also avoid the problem of cracks extending along the direction of maximum principal stress and causing single plane cracks and difficulty in forming complex fracture networks when using only fracturing, but also reduce repeated fracturing or multi-layer fracturing construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is an overall schematic diagram of the present invention;

[0029] Figure 2 It is a schematic diagram of the pressure explosion assembly of the present invention;

[0030] Figure 3 is a schematic diagram of the water injection assembly of the present invention;

[0031] Figure 4 It is a schematic diagram of the first stage of the construction method of the present invention;

[0032] Figure 5 It is a schematic diagram of the second stage of the construction method of the present invention;

[0033] Figure 6 It is a schematic diagram of the third stage of the construction method of the present invention;

[0034] Figure 7 is a histogram within the fracturing height in an embodiment of the present invention;

[0035] In the figure, 10, water injection assembly, 11, water tank, 12, pressure pump, 13, hose, 14, pressure recorder, 15, stop valve, 16, pressure relief valve;

[0036] 20. Blasting controller;

[0037] 30. Compression and blasting assembly, 31. Water injection pipe, 32. Elastic capsule, 33. Fracturing pipe, 34. Blasting column;

[0038] A is the coal body, B is the non-critical layer, and C is the critical layer. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons of ordinary skill in the field to which the invention belongs. The words "first", "second" and similar terms used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "a" or "an" do not necessarily indicate a quantity limitation. Words such as "include" or "comprising" mean that the components or objects appearing before the word include the components or objects listed after the word and their equivalents, without excluding other components or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0041] like Figure 1 、 Figure 2 As shown, the key layer blasting device under the coupling of water pressure and carbon dioxide blasting includes:

[0042] The blasting assembly 30 comprises a blasting column 34, a fracturing pipe 33, and an elastic bladder 32;

[0043] High-pressure carbon dioxide is stored inside the blasting column 34; the fracturing pipe 33, the elastic capsule 32 and the blasting column 34 are sequentially connected to form a rod structure;

[0044] A water injection pipe 31, one end of which is connected to the elastic bladder 32 and the other end of which is connected to the water injection assembly 10;

[0045] The water injection assembly 10 is connected to and controlled by the water injection controller. The water injection assembly 10 is used to inject high-pressure water from the water injection pipe 31 into the elastic bladder 32 and the fracturing pipe 33;

[0046] Specifically, the blasting column 34 contains high-pressure carbon dioxide, which can be detonated to achieve blasting treatment; the blasting column 34 is threadedly connected to the fracturing pipe 33 and the elastic capsule 32 in sequence, that is, the blasting column 34 is closer to the bottom of the borehole;

[0047] The water injection pipe 31 is made of high-pressure resistant material and one end is connected to the water injection assembly 10 through a pressure-resistant hose 13. The length of the water injection pipe 31 is determined according to the drilling depth, that is, the drilling is performed in the tunnel toward the key layer of the rock formation; As explained, the determination of the key layer belongs to the existing technology and will not be further elaborated here;

[0048] The water injection assembly 10 is controlled by the water injection controller to complete automatic water injection;

[0049] When using this key layer blasting device coupled with water pressure and carbon dioxide blasting, a hole is drilled toward the key layer in the tunnel, and a water injection pipe 31 is inserted into the drilled hole, so that the elastic bladder 32, the fracturing pipe 33, and the blasting column 34 at one end of the water injection pipe 31 are close to the designated position. At this time, the position of the fracturing pipe 33 is the fracturing section, and the position of the elastic bladder 32 is the closed section.

[0050] The water injection assembly 10 connected to one end of the water injection pipe 31 first fills the elastic bladder 32 with high-pressure water, and the elastic bladder 32 expands and fits against the inner wall of the borehole, forming a local sealed space from the elastic bladder 32 to the bottom of the borehole;

[0051] The construction method of this pressure explosion device mainly includes three stages: Figures 4 to 6 As shown, the first stage is fracturing, that is, high-pressure water is injected into the fracturing pipe 33 through the water injection assembly 10. The hydraulic fracturing starting pressure is 5-50 MPa, and the radius can reach 10-50 m. The fracturing treatment of the key layer is completed. At this time, the key layer is subjected to the action of water pressure and the main cracks are generated.

[0052] The second stage is blasting, that is, while maintaining the high-pressure water flow, the blasting column 34 is detonated, and the high-pressure carbon dioxide is discharged, which applies an additional impact to the high-pressure water in the hole and vibrates the nearby rock mass, causing a large number of secondary cracks around and inside the main crack, completing the blasting treatment of the key layer. As explained, carbon dioxide blasting is to compress liquid carbon dioxide into the blasting column 34 through a high-pressure pump, and safely seal it. The liquid carbon dioxide is then instantly vaporized by remote operation. The liquid carbon dioxide absorbs heat and expands rapidly when it vaporizes to generate high pressure, causing the rock mass to crack. This is a conventional blasting structure, and the corresponding structure will not be further explained.

[0053] The third stage is re-fracturing, where high-pressure water is injected into the fracturing pipe 33 through the water injection assembly 10 to perform the fracturing process. After a period of time, the injection is stopped. At this time, the carbon dioxide blasts out secondary cracks and then re-fracturing. The extension of the secondary cracks also far exceeds 2 meters. The cracks change from being few and long in conventional fracturing to becoming dense and long. Finally, the water in the elastic bladder 32 is released, and the water injection pipe 31 is completely withdrawn from the borehole.

[0054] The key layer blasting device coupled with water pressure and carbon dioxide blasting first performs high-pressure water fracturing treatment on the key layer drill hole to generate a main crack. While maintaining the fracturing, the key layer drill hole is blasted to generate a large number of secondary cracks around and inside the main crack, forming an interlaced crack network. The high-pressure water injection is maintained for a period of time. This can not only fully change the local lithology and promote the full release of local gas, but also avoid the problem of single plane cracks extending along the direction of maximum principal stress and difficulty in forming a complex fracture network when using only fracturing, and can reduce repeated fracturing or multi-layer fracturing construction.

[0055] In some examples of the present invention, the compression explosion assembly 30 further includes a converter having a three-way structure;

[0056] The three interfaces of the converter are connected to the water injection pipe 31, the elastic bladder 32, and the fracturing pipe 33 respectively;

[0057] A pressure sensor for monitoring water pressure is provided in the elastic bladder 32;

[0058] The converter is connected to the water injection controller and can be controlled to switch the connection between the water injection pipe 31 and the elastic bladder 32, and between the water injection pipe 31 and the fracturing pipe 33;

[0059] Specifically, in the initial state, the pressure sensor monitors the pressure in the elastic bladder 32. When the water injection controller controls the water injection assembly 10 to inject water into the elastic bladder 32 and the water pressure reaches the set range, the converter switches the water path, that is, closes the interface leading to the elastic bladder 32 and opens the interface leading to the fracturing pipe 33. At this time, the water pressure can be increased again by the water injection controller, for example, in the second gear, to achieve automatic injection of high-pressure water into the fracturing pipe 33 and fracturing treatment, which is simpler to operate. The switcher can be a valve structure.

[0060] In some examples of the present invention, the elastic bladder 32 is threadedly connected to the fracturing pipe 33 via a connecting pipe;

[0061] An elastic member and a sealing head are provided in the connecting pipe;

[0062] The elastic member is located between the end of the fracturing pipe 33 and the sealing head, and under the action of the elastic member, the sealing head seals the end of the connecting pipe close to the elastic bladder 32;

[0063] Specifically, the elastic sac 32 is connected between the connecting pipe and the water injection pipe 31. The outer side of the connecting pipe is threaded and sealed with the inner thread of the fracturing pipe 33. The elastic member in the connecting pipe is positioned close to one end of the fracturing pipe 33 and the other end is in contact with the head. The head can be moved inside the connecting pipe and the elastic member seals the end of the connecting pipe.

[0064] Initially, the water injection assembly 10 injects water toward the elastic sac 32 through the water injection pipe 31 to expand the elastic sac 32 and fit the inner wall of the borehole. At this time, the water pressure has not reached the set range. Under the action of the elastic member, the head remains closed to the connecting pipe; when the water injection assembly 10 continues to inject high-pressure water, the water pressure reaches the set range and squeezes the head, causing the head to open, and high-pressure water enters the fracturing pipe 33, completing the fracturing treatment of the key layer.

[0065] In some examples of the present invention, the lead wire of the blasting column 34 is led out along the drill hole and connected to the blasting controller 20;

[0066] Specifically, when the blasting column 34 is detonated, it can be electronically controlled by the blasting controller 20 .

[0067] In some examples of the present invention, Figure 3 As shown, the water injection assembly 10 comprises a water tank 11, a pressure pump 12, and a hose 13;

[0068] The input end of the pressure pump 12 is connected to the water tank 11, and the output end is connected to one end of the water injection pipe 31 through the hose 13;

[0069] The hose 13 is provided with a stop valve 15, a pressure relief valve 16, and a pressure recorder 14;

[0070] Specifically, the water tank 11 provides the necessary high-pressure water for the device, and the pressure pump 12 is used to provide the water pressure output by the water tank 11;

[0071] The stop valve 15, the pressure relief valve 16, and the pressure recorder 14 are all connected to the water injection controller, and can be opened and closed accordingly through the water injection controller. For example, when the pressure recorder 14 records that the water pressure is too high, the water injection controller controls the pressure relief valve 16 to open to complete the pressure relief process.

[0072] This is a construction method for key layer blasting under the coupling of water pressure and carbon dioxide blasting. Figure 1 、 Figures 4 to 6 , specifically including the following steps:

[0073] S1, drilling a hole in the tunnel toward the key layer, the hole can pass through the coal body A, the non-key layer B, and be located in the key layer C, and the water injection pipe 31 is deeply inserted into the hole, so that the elastic bladder 32, the fracturing pipe 33, and the blasting column 34 at one end of the water injection pipe 31 are close to the designated position of the key layer C;

[0074] S2, the water injection assembly 10 first fills the elastic bladder 32 with high-pressure water through the water injection pipe 31, and the elastic bladder 32 expands and fits against the inner wall of the borehole, forming a local sealed space from the elastic bladder 32 to the bottom of the borehole;

[0075] Then, high-pressure water is injected into the fracturing pipe 33 through the water injection assembly 10 to complete the fracturing treatment of the key layer. At this time, the key layer is subjected to the action of water pressure to generate a main crack, and the fracturing is maintained for a period of time. While the high-pressure water is kept flowing, the blasting column 34 is detonated, and the liquid carbon dioxide turns into gas. The phase change causes the volume of carbon dioxide to increase rapidly. The high pressure causes a large number of secondary cracks to be generated around and inside the main crack, completing the blasting treatment of the key layer.

[0076] S3, then continue the fracturing treatment, stop the injection after a period of time, finally release the water from the elastic bladder 32, and withdraw the water injection pipe 31 from the borehole as a whole;

[0077] Furthermore, the fracturing in step S2 is maintained for 10-15 minutes, and the injection is stopped after the fracturing is continued for 10-30 minutes in step S3.

[0078] Example

[0079] Taking the hydraulic pre-fracture and roof cutting and pressure relief project of the 2303 upper working face of a coal mine as an example, there is a thick hard roof above the remaining roadway, and a pump displacement of 120L / min is selected.

[0080] The calculation formula for fracturing height is:

[0081]

[0082] Among them, M is the mining height of the working face, Kp is the initial expansion coefficient of the roof;

[0083] After time measurement and calculation, the coal seam thickness at the working face is 5.6-6.7m, with an average thickness of 6.2m. Using layered mining, the coal mining thickness is 2.45m. Therefore, the mining height M = 2.45m, and Kp is set as 1.2. Using the calculation formula for the fracturing height, the collapse zone height is 12.25m, so the fracturing height is selected as 12.25m. Considering the principle of cutting the top of the low-lying collapse zone to promote caving and cutting off the high-lying old roof to relieve pressure, the fracturing height should be adjusted to 12.25m + 10m = 22.25m.

[0084] like Figure 7 As shown in the histogram, it can be seen that the key layers within the fracturing height, that is, the roof structure above the coal seam, include 3.63 m siltstone of sequence number 10, 5.80 m medium-grained sandstone of sequence number 9, 3.20 m siltstone of sequence number 8, 1.23 m fine-grained sandstone of sequence number 6, 2.09 m siltstone of sequence number 5, 7.57 m fine-grained sandstone of sequence number 4, 1.4 m medium-grained sandstone of sequence number 3, 2.62 m mudstone of sequence number 2, and 4.2 m medium-grained sandstone of sequence number 1;

[0085] According to the lithology, the rock layers with higher elastic modulus in the continuous rock layers within the basic roof are regarded as a whole, and the fracturing layers are determined to be: 3.63m siltstone, 5.80m medium-grained sandstone, 3.20m siltstone, 1.23m fine-grained sandstone, 2.09m siltstone, 7.57m fine-grained sandstone, and 1.4m medium-grained sandstone, totaling 24.92m;

[0086] The estimated starting pressure for direct hydraulic fracturing is ρ1, that is, the calculation formula for the fracturing pressure is:

[0087] ρ1=1.3×(3σ3-σ1+R t )

[0088] Among them, σ3 is the minimum principal stress at the fracturing point, σ1 is the maximum principal stress at the fracturing point, and R t is the tensile strength of the roof rock formation at the fracturing point;

[0089] The calculation formula for vertical stress is:

[0090] Ev=ρgh

[0091] Among them, the rock density ρ is 2.5KN / m 3 ;

[0092] g is the acceleration due to gravity, which is taken as 9.8;

[0093] h is the burial depth, which is 300-350m. In this embodiment, the maximum burial depth is 350m.

[0094] Therefore, the vertical stress is: 2.5 × × 9.8 × 350 ≈ 8.58 MPa; according to the lateral pressure coefficient of 0.7, the minimum principal stress σ3 is: 8.58 × 0.7 MPa ≈ 6 MPa;

[0095] The maximum principal stress σ1 at the fracturing point is 15 MPa, obtained based on local data;

[0096] The uniaxial compressive strength is 70MPa and the tensile strength R t Calculated as 1 / 10 of the uniaxial compressive strength, the value is 7MPa;

[0097] According to the σ3 is 6MPa, σ1 is 15MPa, and the tensile strength R t Substituting 7 MPa into the above formula, the hydraulic fracturing pressure is obtained as: 1.3×(3×6-15+7)MPa=13MPa; therefore, the hydraulic fracturing pressure in this embodiment is 13MPa.

[0098] The calculation formula for ordinary fracturing time is:

[0099]

[0100] Where a is the radius of the main fracture of ordinary hydraulic fracturing, which is 10m;

[0101] B is the width of the crack, which is 0.02m;

[0102] H is the crack height, which is 4.5m;

[0103] n is the number of cracks, which is 3;

[0104] Q is the flow rate of the fracturing device, which can be 7.2m 3 / h;

[0105] Therefore, the calculated fracturing time T is 0.3925 hours, which is 23.6 minutes. Therefore, the total fracturing time should not be less than 24 minutes, and 25-30 minutes is sufficient.

[0106] According to the method of this embodiment, hydraulic fracturing can be performed first for 1 / 3-1 / 2 of the total fracturing time, and then carbon dioxide blasting can be performed. After the abundant secondary fractures are generated, hydraulic fracturing construction can be carried out, and the time can be appropriately extended in the fracturing process.

[0107] Therefore, when the water injection pipe 31 is pushed deeper into the borehole, the elastic bladder 32, the fracturing pipe 33 and the blasting column 34 at one end of the water injection pipe 31 are close to the designated position of the key layer;

[0108] The water injection assembly 10 first fills the elastic bladder 32 with high-pressure water through the water injection pipe 31, and the elastic bladder 32 expands and fits against the inner wall of the borehole, forming a local sealed space from the elastic bladder 32 to the bottom of the borehole;

[0109] Then, high-pressure water is injected into the fracturing pipe 33 through the water injection component 10. The hydraulic fracturing starting pressure is 13 MPa, and the fracturing treatment of the key layer is completed. At this time, the key layer produces a main crack under the action of water pressure, and the fracturing is maintained for 10-15 minutes. While maintaining the high-pressure water flow, the blasting column 34 is detonated, and the liquid carbon dioxide becomes gaseous. The phase change causes the volume of carbon dioxide to increase rapidly. The high pressure causes a large number of secondary cracks to be generated around and inside the main crack, completing the blasting treatment of the key layer; then the fracturing treatment is continued, and the subsequent fracturing time is determined according to the effect of the secondary cracks after the carbon dioxide blasting. For example, the total fracturing time is calculated to be not less than 24 minutes. The time can be appropriately extended in the fracturing link, for example, the injection is stopped after 15-60 minutes. Finally, the water in the elastic bag 32 is released, and the water injection pipe 31 is withdrawn from the borehole as a whole.

[0110] The above describes in detail an exemplary implementation of a key laminate explosion device coupled with water pressure and carbon dioxide blasting proposed by the present invention with reference to a preferred embodiment. However, it can be understood by those skilled in the art that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the scope of protection of the present invention, which is determined by the appended claims.

Claims

1. Key layer blasting device under the coupling of water pressure and carbon dioxide blasting, characterized in that: include: A pressure explosion assembly (30) comprising a blasting column (34), a fracturing pipe (33), and an elastic bladder (32); High-pressure carbon dioxide is stored inside the blasting column (34); the fracturing pipe (33), the elastic capsule (32) and the blasting column (34) are connected in sequence and gradually move away from the bottom of the borehole; A water injection pipe (31), one end of which is connected to the elastic bladder (32) and the other end of which is connected to the water injection assembly (10); The water injection assembly (10) is connected to and controlled by the water injection controller. The water injection assembly (10) is used to inject high-pressure water from the water injection pipe (31) into the elastic sac (32) and the fracturing pipe (33).

2. The key layer pressure blasting device under the coupling of water pressure and carbon dioxide blasting according to claim 1 is characterized in that: The pressure explosion assembly (30) further includes a converter having a three-way structure; The three interfaces of the converter are respectively connected to the water injection pipe (31), the elastic bladder (32), and the fracturing pipe (33); The water injection controller controls the interface conversion of the converter.

3. The key layer pressure blasting device under the coupling of water pressure and carbon dioxide blasting according to claim 2 is characterized in that: A pressure sensor for monitoring water pressure is provided in the elastic bladder (32); After receiving the water pressure signal, the water injection controller can be controlled to switch the connection between the water injection pipe (31) and the elastic bag (32), and between the water injection pipe (31) and the fracturing pipe (33).

4. The key layer pressure blasting device under the coupling of water pressure and carbon dioxide blasting according to claim 1 is characterized in that: The elastic sac (32) is threadedly connected to the fracturing pipe (33) via a connecting pipe; An elastic member and a sealing head are provided in the connecting pipe; The elastic member is located between the end of the fracturing pipe (33) and the sealing head, and under the action of the elastic member, the sealing head seals the end of the connecting pipe close to the elastic sac (32).

5. The key layer pressure blasting device under the coupling of water pressure and carbon dioxide blasting according to any one of claims 1 to 3, characterized in that: The water injection assembly (10) comprises a water tank (11), a pressure pump (12), and a high-pressure hose (13); The input end of the pressure pump (12) is connected to the water tank (11), and the output end is connected to one end of the water injection pipe (31) through a high-pressure hose (13); The rubber hose (13) is provided with a stop valve (15), a pressure relief valve (16), and a pressure recorder (14).

6. A construction method for a key layer blasting device coupled with water pressure and carbon dioxide blasting according to claim 1, characterized in that: The specific steps include: S1, drilling a hole toward the key layer in the tunnel, and inserting the water injection pipe (31) into the hole, so that the elastic sac (32), the fracturing pipe (33), and the blasting column (34) at one end of the water injection pipe (31) are close to the designated position of the key layer; S2, the water injection assembly (10) first fills the elastic bladder (32) with high-pressure water through the water injection pipe (31), and the elastic bladder (32) expands and fits against the inner wall of the borehole, forming a local sealed space from the elastic bladder (32) to the bottom of the borehole; Then, high-pressure water is injected into the fracturing pipe (33) through the water injection assembly (10) to start the fracturing treatment of the key layer. At this time, the key layer is subjected to the water pressure to generate a main crack, and the fracturing is maintained for a period of time. While the high-pressure water is continuously injected, the blasting column (34) is detonated to convert the liquid carbon dioxide into gaseous state. The phase change causes the volume of the carbon dioxide to increase rapidly, and the high-pressure carbon dioxide is discharged, so that a large number of secondary cracks are generated around and inside the main crack, completing the blasting treatment of the key layer; S3, then continue the fracturing treatment, stop the injection after a period of time, finally release the water in the elastic bag (32), drain the water in the fracturing borehole, and finally withdraw the fracturing device and the blasting device from the borehole as a whole.

7. The construction method of the key layer pressure blasting device under the coupling of water pressure and carbon dioxide blasting according to claim 6 is characterized in that: The fracturing is maintained for 10-15 minutes in step S2, and the injection is stopped after the fracturing is continued for 10-30 minutes in step S3.

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