A composite fracturing device and fracturing method based on the superposition of electric explosion-CO2 phase change-powder deflagration sequence.

Abstract

The application discloses a composite cracking device based on electric explosion-CO2 phase change-powder deflagration time sequence superposition and a cracking method thereof. The design of the composite cracking device organically integrates electric explosion shock wave, liquid CO2 phase change expansion energy and metal powder deflagration chemical energy into three energy sources. Through special energy conversion and time sequence control structure, the three energies are sequentially superimposed and released in the order of electric explosion-CO2 phase change-powder deflagration. The composite cracking device realizes organic synthesis and time sequence control release of the three energies. The technical scheme of the application avoids the inhibition of CO2 heat absorption on powder deflagration, realizes step-by-step amplification of energy, accurately controls the time interval of energy release, ensures that shock waves chase and superimpose in space propagation process in turn, and forms a composite wave with a higher peak value.

Description

Technical Field

[0001] This invention belongs to the field of engineering blasting technology, specifically relating to a composite fracturing device and method based on the superposition of electric explosion-CO2 phase change-powder deflagration sequence. Background Technology

[0002] Liquid carbon dioxide phase change fracturing technology is a physical blasting technique with advantages such as no sparks, no toxic gases, and low vibration, and has been widely used in coal mining, tunnel excavation, and other fields. Traditional liquid CO2 fracturing devices typically use a chemical heating rod (containing flammable and explosive agents such as potassium perchlorate) that is electrically heated to vaporize and expand the liquid CO2, releasing a shock wave through a shock absorber. However, the agents in the chemical heating rod are classified as controlled explosive materials, posing a risk of premature triggering due to accidental factors such as friction and static electricity during transportation, storage, and high-pressure environments, thus requiring improved safety.

[0003] To address safety concerns, existing technologies have attempted to replace chemical heating rods with electro-explosion using metal wires. However, current technologies only utilize the thermal energy of the electro-explosion to induce the CO2 phase transition, failing to effectively utilize the shock wave energy generated by the electro-explosion itself, resulting in low energy utilization efficiency. Furthermore, research indicates that adding a suspension of metal powders such as aluminum powder to the electro-explosion environment can produce a significant secondary shock wave enhancement effect, increasing peak pressure by 2.25 times and impulse by approximately 50%.

[0004] However, the following key issues remain unresolved with existing technologies: (1) Problem of single energy source integration: Existing technologies have not organically integrated the three energy sources of electric explosion shock wave, liquid CO2 phase change expansion energy and metal powder deflagration chemical energy into a single device. Experiments of electric explosion-driven aluminum powder suspension are mostly carried out in open or semi-open water environments, while liquid CO2 phase change cracking requires a closed high-pressure cavity. The physical environments of the two are significantly different, and direct reaction faces structural compatibility problems.

[0005] (2) The physical conflict in the energy release sequence: Liquid CO2 vaporization is a strongly endothermic process, while the deflagration of metal powder is a strongly exothermic process. If the deflagration of the powder occurs before the CO2 phase change, the subsequent CO2 vaporization will absorb a large amount of heat from the deflagration products, causing a sharp drop in deflagration pressure. The total output energy will be lower than that of the CO2 phase change alone, resulting in energy cancellation rather than superposition. Therefore, precise control of the energy release sequence is the core prerequisite for achieving positive energy superposition rather than mutual cancellation.

[0006] (3) Problems with the accumulation and timing control of powder deflagration energy: When the powder suspension is placed directly in a large-volume cavity, the pressure rises slowly after the high-pressure CO2 gas enters, the powder is not evenly dispersed, the reaction degree is low, and the intensity of the shock wave is difficult to increase. Existing technologies lack effective accumulation of powder deflagration energy and dedicated timing control structures, and cannot achieve the sequential pursuit and superposition of triple shock waves in spatial propagation.

[0007] (4) On-site operation safety and adaptability issues: Most existing electric explosion-energetic material composite devices are laboratory-scale and lack modular and reusable structural designs suitable for downhole drilling; the leakage risk of powder suspension during transportation and pipe laying has not been effectively resolved; there are safety hazards in the handling of pressurized fracturing pipes in deep hole operations, and the outward protrusion of the side wall filling port can easily cause pipe laying blockage. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a composite fracturing device and method based on the superposition of the time sequence of electric explosion-CO2 phase change-powder deflagration.

[0009] To achieve the above objectives, the present invention provides the following solution: A composite fracturing device based on the superposition of electric explosion-CO2 phase change-powder deflagration sequence includes: an electric explosion excitation section (1), a liquid CO2 energy storage section (2) and a powder suspension reaction section (3) connected in series along the axial direction, and a directional energy release head (4) connected to the front end of the powder suspension reaction section. The electric explosion excitation section (1) includes: a first tube (11), a metal wire (12) disposed in the first tube (11), and an end seat (14) fixed to the rear end of the first tube (11). The end seat (14) is provided with a positive electrode seat (131) and a negative electrode seat (132). The two ends of the metal wire (12) are respectively connected to the inner ends of the positive and negative electrode seats, and the outer ends of the positive and negative electrode seats are used to connect to a high-voltage pulse power supply. The liquid CO2 energy storage section (2) includes a second tube (21), which is filled with liquid CO2 (26). The side wall of the second tube (21) is provided with a CO2 injection port (25), and a submersible one-way valve (24) is installed in the CO2 injection port (25). A first rupture disc (22) is provided between the electric explosion excitation section and the liquid CO2 energy storage section, and a second rupture disc (23) is provided between the liquid CO2 energy storage section and the powder suspension reaction section; the rupture discs make each tube independently sealed, the rupture pressure of the first rupture disc is P1, and the rupture pressure of the second rupture disc is P2, satisfying P2 < P1. The powder suspension reaction section (3) includes a third tube (31), and a constraint tube (33) is coaxially arranged inside the third tube (31). The annular gap between the constraint tube (33) and the third tube (31) or the inside of the constraint tube (33) is filled with powder suspension. The powder in the powder suspension is micron-sized aluminum powder or magnesium powder with a particle size of 5~50 μm. The liquid phase of the powder suspension is water or an aqueous solution containing 5%~20% hydrogen peroxide, and the concentration of the powder is 50~300 mg / mL. The venting hole (42) of the directional energy release head (4) includes a main energy release hole (421) and a flight stop hole (422). The main energy release hole (421) is a radial rectangular hole, and the flight stop hole (422) is an inclined hole. The angle between its axis and the axis of the release head body (41) is 30°~60°. The main energy release hole and the flight stop hole are alternately distributed along the circumference. When the fracturing tube is in operation, the three stages of energy are released in sequence in the order of electric explosion → CO2 phase change → powder deflagration.

[0010] Preferably, the rupture pressure P1 of the first rupture disc (22) is 15~20 MPa, the rupture pressure P2 of the second rupture disc (23) is 10~15 MPa, and P2 is 3~8 MPa lower than P1.

[0011] Preferably, the CO2 injection port (25) is located on the side wall of the second tube (21) near the first rupture disc (22), and the axis of the injection port is perpendicular to the axis of the second tube. A submerged one-way valve is installed inside the injection port (25). The valve body of the one-way valve is installed in the countersunk hole on the side wall of the second tube (21). The valve body is welded to the tube wall or threaded and sealed. The end face of the valve core is flush with or slightly lower than the outer wall of the second tube, and the protrusion height is ≤ 2 mm. The opening pressure of the one-way valve is 0.3~0.8 MPa, and the reverse sealing pressure is ≥ 25 MPa.

[0012] Preferably, the constraint tube (33) is an organic glass tube, a polycarbonate tube, a brittle metal tube or a glass tube, with a wall thickness of 1~5 mm and an outer diameter of 0.7~0.95 times the inner diameter of the third tube body (31). The two ends of the constraint tube (33) are sealed to the third tube body (31) to form a closed annular loading cavity.

[0013] Preferably, a directional energy release head (4) is connected to the front end of the third tube body (31), and the main energy release holes (421) and the anti-flying holes (422) are alternately distributed along the circumference of the whole directional energy release head (4); a breakable sealing film (34) is arranged at the front end of the third tube body (31), and the sealing film (34) seals the powder suspension in the third tube body (31); wherein, the material of the breakable sealing film (34) is aluminum foil, copper foil or polyester film, the thickness is 0.05-0.2 mm, and the rupture pressure is 0.5-2 MPa.

[0014] Preferably, the positive electrode seat (131) and the negative electrode seat (132) on the end seat (14) each comprise a metal electrode rod and a ceramic insulating sleeve, the ceramic insulating sleeve is embedded in the stepped hole of the end seat (14), the metal electrode rod penetrates through the ceramic insulating sleeve, and O-ring seals are arranged between the metal electrode rod and the ceramic insulating sleeve and between the ceramic insulating sleeve and the end seat.

[0015] Preferably, a cross / cross-shaped notch is arranged at the center of the second bursting disc (23), and the notch depth is 30%-60% of the thickness of the bursting disc; a central through hole (32) with a hole diameter of 10-15 mm is arranged between the second tube body and the third tube body.

[0016] The present invention also provides a sequential composite impact fracturing method for a composite fracturing device, including: Filling step: filling liquid carbon dioxide into the second tube body (21) through the CO2 injection port (25) until the pressure reaches P CO2 , and P CO2 <P2<P1; filling the powder suspension into the annular gap of the powder suspension reaction section (3) and sealing it; filling the first tube body (11) with normal pressure protective gas; Excitation step: applying a microsecond-level pulsed current to the metal wire (12) through a high-voltage pulsed power supply, the metal wire (12) undergoes electro-explosion, generating an initial shock wave and high-temperature plasma, and the pressure in the first tube body (11) suddenly rises to exceed P1; First-stage energy release: the first bursting disc (22) ruptures, the high-temperature plasma enters the second tube body (21), the liquid CO2 instantaneously vaporizes and expands, and the volume expands 400-600 times, generating a second shock wave; Second-stage energy release: when the pressure breaks through P2, the second bursting disc (23) ruptures, the high-pressure CO2 gas flows into the powder suspension reaction section (3) at high speed through the central through hole, first enters the inner cavity of the restraint tube (33) to form a local high pressure, and when the pressure exceeds the rupture strength of the restraint tube, the whole restraint tube (33) expands and ruptures, the high-speed fragments impact and disperse the powder suspension, triggering a powder deflagration reaction, generating a third shock wave; Superimposed release steps: The triple shock wave superimposed propagates along the axial direction, breaks through the ruptureable sealing membrane (34), and is directionally released to the target rock mass through the energy release hole (42) of the directional energy release head (4).

[0017] Preferably, the rupture pressure P1 of the first rupture disc (22) is the same as the liquid CO2 filling pressure P. CO2 The relation satisfies P1 = (1.5 ~ 2.5) × P CO2 The rupture pressure P2 of the second rupture disc (23) satisfies P2 = (1.2~1.8) × P CO2 The rupture pressure of the constraint tube (33) is 5~15 MPa.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The triple energy sequence significantly enhances rock-breaking effect: By forcing the sequence of electric explosion → CO2 phase change → powder deflagration, the inhibition of powder deflagration by CO2 endothermic reaction is avoided, achieving a step-by-step amplification of energy. Experimental data shows that the peak pressure of the composite shock wave of this invention can reach 10 to 15 times that of a simple electric explosion and 2 to 3 times that of a simple CO2 phase change.

[0019] 2. Precise and controllable timing: Through the design of the two-stage rupture disc rupture pressure difference (P1>P2), the time interval of each energy release (microseconds to hundreds of microseconds) is precisely controlled, ensuring that the shock wave catches up with and superimposes in sequence during the propagation in space, forming a composite wave with a higher peak value.

[0020] 3. Constrained tube design achieves efficient energy conversion and timing control: Through the pressure vessel effect and energy storage-release mechanism of the constrained tube, the kinetic energy of CO2 gas flow is efficiently converted into the compressive energy of powder combustion, and the timing shaping of the triple shock wave is achieved. Experiments show that with the constrained tube, the peak pressure of the composite shock wave can reach 2.5 times that without the constrained tube, and the powder reaction rate is increased from 30% to over 85%.

[0021] 4. Sealing membrane to prevent powder leakage: The ruptureable sealing membrane at the front end of the third tube completely seals the powder suspension in the ready-to-fire state, preventing leakage during transportation and tube lowering. At the same time, it can easily rupture under the action of shock wave during excitation without affecting energy release.

[0022] 5. High safety: Utilizing a metal wire electro-explosion as the sole ignition source, it contains no flammable or explosive chemicals, ensuring safe transportation and storage. The rupture discs between the two sections remain isolated until the rupture pressure is reached, preventing accidental triggering.

[0023] 6. High energy utilization efficiency: It makes full use of the shock wave energy of the electric explosion itself, the expansion energy of CO2 phase change and the chemical energy of metal powder, and the total energy conversion efficiency is significantly higher than that of a single energy source fracturing device.

[0024] 7. Semi-repeatable design with low operating costs: The electro-explosion excitation section and liquid CO2 energy storage section can be reused more than 50 times. Only the confinement tube and powder of the powder suspension reaction section are disposable components, reducing the cost per use by about 70%.

[0025] 8. Directional energy release and recoil-induced runaway prevention: The inclined runaway prevention hole design of the energy release head uses recoil force to automatically fix the fracture tube in the borehole, eliminating the need for additional anchoring devices.

[0026] 9. Modularity and adjustability: By replacing the constraint tube with one made of a different material, the output characteristics of the fracturing tube can be adjusted without changing other components, thus achieving multiple uses for one tube.

[0027] 10. Side-wall submerged filling port and buried filling process enhance operational safety and adaptability: The CO2 injection port of this invention adopts a submerged one-way valve, with the valve core end face flush with the outer wall of the tube body and an outward protrusion height ≤ 2 mm, ensuring smooth lowering of the fracturing tube in the borehole. Combined with the buried filling process of lowering the tube first and then injecting fluid, the risks associated with transporting pre-pressurized fracturing tubes on the ground are avoided. This is particularly suitable for deep holes (>20 m) and narrow boreholes (gap ≤ 3 mm) scenarios, while also simplifying on-site operation procedures and improving operational safety. Attached Figure Description

[0028] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the overall structure of the composite fracturing device based on the superposition of the time sequence of electric explosion-CO2 phase change-powder deflagration of the present invention. Figure 2 This is a schematic diagram of the circumferential arrangement of the energy dissipation holes; Figure 3 This is a partially enlarged view of the installation structure of the first and second rupture discs; Figure 4 A schematic diagram of the CO2 injection port and one-way valve; Figure 5 This is a schematic diagram of the energy time sequence superposition of the fracture-inducing method of the present invention.

[0030] In the diagram: 1-Electro-explosion activation section, 11-First tube body, 12-Metal wire, 13-Electrode holder, 131-Positive electrode holder, 132-Negative electrode holder, 133-Ceramic insulating sleeve, 134-O-ring seal, 14-End seat, 2-Liquid CO2 storage section, 21-Second tube body, 22-First rupture disc, 221-First rupture disc notch, 23-Second rupture disc, 24-Submersible one-way filling valve, 241-One-way valve body, 242- 243 - Valve core, 244 - Spring, 245 - Sealing ring, 246 - External convex surface of valve body, 247 - Filling gun docking interface, 25 - CO2 injection port, 26 - Liquid CO2, 3 - Powder suspension reaction section, 31 - Third tube body, 32 - Central through hole, 33 - Constraint tube, 34 - Ruptureable sealing membrane, 35 - Suspended powder, 4 - Directional energy release head, 41 - Release head body, 42 - Energy release hole, 421 - Main energy release hole, 422 - Anti-flight hole Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1 like Figure 1 As shown, this invention provides a composite fracturing device based on the sequential superposition of electric explosion-CO2 phase change-powder deflagration. It employs: ① a forced sequential release mechanism of electric explosion → CO2 phase change → powder deflagration, strictly limiting the sequence through a two-stage rupture disc pressure difference (P1 > P2), first electric explosion, then CO2 vaporization, and finally powder deflagration, completely avoiding the suppression of powder deflagration by the strong endothermic effect of CO2, achieving step-by-step energy amplification and positive superposition rather than cancellation; ② a pioneering confined tube pressure vessel-energy storage blasting structure, allowing the high-pressure CO2 gas flow to first be depressurized and then released instantaneously, efficiently converting gas kinetic energy into deflagration energy, increasing the powder reaction efficiency from 30% to over 85%, and increasing the peak shock wave by 2-3 times; ③ the organic integration of three energies, breaking through the performance limit of a single energy source, coupling the electric explosion shock wave, CO2 phase change expansion energy, and metal powder chemical energy in three stages, achieving high-energy, controllable, low-cost, and repeatable composite fracturing without open flames or hazardous agents.

[0034] like Figure 1As shown, the composite fracturing device of this invention includes: an electric explosion excitation section (1), a liquid CO2 energy storage section (2) and a powder suspension reaction section (3) connected in series along the axial direction, and a directional energy release head (4) connected to the front end of the powder suspension reaction section (3).

[0035] As one embodiment of the present invention, the electro-explosion excitation section (1) includes a first tube (11), a metal wire (12) disposed in the first tube (11), and an end seat (14) fixed to the rear end of the first tube (11). The end seat (14) is provided with a positive electrode seat (131) and a negative electrode seat (132). Each electrode seat includes a metal electrode rod and a ceramic insulating sleeve. The ceramic insulating sleeve is embedded in a stepped hole in the end seat, and the metal electrode rod passes through the ceramic insulating sleeve. O-rings are provided between the electrode rod and the ceramic insulating sleeve, and between the ceramic insulating sleeve and the end seat. The two ends of the metal wire (12) are respectively connected to the inner end clamps of the positive and negative electrode seats. The metal wire (12) is straightened and located on the axis of the first tube (11). The material of the metal wire (12) is copper, aluminum, tungsten, or their alloys, with a circular or rectangular cross-section and a diameter of 0.1~0.5 mm. The first tube (11) is filled with a normal pressure protective gas such as nitrogen or air.

[0036] As one embodiment of the present invention, the liquid CO2 energy storage section (2) includes a second pipe body (21). A CO2 injection port (25) is provided on the side wall of the second pipe body (21) near the first rupture disc (22). A submersible one-way valve is installed inside the injection port. The valve body is installed in a countersunk hole in the pipe wall, with the valve core end face flush with or slightly lower than the outer wall of the pipe body, and the outward protrusion height ≤ 2 mm, ensuring the fracturing tube is smoothly lowered into the borehole. The one-way valve opening pressure is 0.3~0.8 MPa, and the reverse sealing pressure is ≥ 25 MPa. During injection, an external filling gun connects to the valve port via a quick connector; after filling, the valve port automatically seals.

[0037] In one embodiment of the present invention, a first rupture disc (22) is provided between the electric explosion excitation section (1) and the liquid CO2 energy storage section (2). The first rupture disc (22) is clamped between the front flange of the first pipe body (11) and the rear flange of the second pipe body (21), and copper sealing gaskets are provided on both sides. Its installation structure is as follows: Figure 3 As shown. The first rupture disc (22) is a thin sheet of stainless steel or nickel-based alloy with a thickness of 0.3~0.8 mm. The central area has pre-made cross-shaped or star-shaped grooves with a groove depth of 40%~60% of the sheet thickness. The rupture pressure P1 of the first rupture disc (22) is set to 15~20 MPa, and P1> the liquid CO2 filling pressure P CO21.5 to 2.5 times. The concave surface of the first rupture disc (22) faces the electric explosion excitation section (1) (low-pressure side), and the convex surface faces the liquid CO2 energy storage section (2) (high-pressure side) to ensure that creep rupture does not occur when bearing the static pressure of CO2.

[0038] As an implementation mode of the embodiment of the present invention, a second rupture disc (23) is provided between the liquid CO2 energy storage section (2) and the powder suspension reaction section (3). The front end of the second pipe body (21) is connected to the rear end of the third pipe body (31) by threads or flanges. The second rupture disc (23) is clamped between the connection surfaces, and sealing washers are provided on both sides. For its installation position and structure, reference can be made to Figure 3 . The material of the second rupture disc (23) is the same as that of the first rupture disc, but the thickness is reduced to 0.2 - 0.5 mm. Its rupture pressure P2 is set to 10 - 15 MPa, and P2 < P1, and P2 is 3 - 8 MPa lower than P1. A notch is also provided in the central area of the second rupture disc (23).

[0039] A central through-hole (311) is machined behind the second rupture disc (23). The diameter of the through-hole is 10 - 15 mm. This through-hole serves as the release channel for the high-pressure CO2 gas flow. A spiral flow guide groove is machined on the inner wall of the through-hole to make the gas flow rotate and enhance the dispersion effect on the powder.

[0040] As an implementation mode of the embodiment of the present invention, the powder suspension reaction section (3) includes a third pipe body (31). The third pipe body (31) is a thin-walled stainless steel pipe with a wall thickness of 1 - 3 mm, and its inner diameter is larger than the inner diameter of the second pipe body (21). A restraint pipe (33) is coaxially arranged inside the third pipe body (31). The restraint pipe (33) is made of organic glass, polycarbonate, brittle aluminum alloy or glass pipe, with a wall thickness of 1 - 5 mm and an outer diameter of 0.7 - 0.95 times the inner diameter of the third pipe body (31). An annular gap is formed between the two. The two ends of the restraint pipe (33) are hermetically connected to the third pipe body (31) to form a closed cavity in the annular gap. The annular gap is filled with a powder suspension. The powder is micron-sized aluminum powder or magnesium powder, and the liquid phase is water or a 5% - 20% hydrogen peroxide aqueous solution. The powder concentration is 50 - 300 mg / mL. To keep the powder suspended for a long time, a small amount of surfactant, such as sodium dodecyl sulfate, with a concentration of 0.1% - 0.5% can be added.

[0041] The inner cavity of the restraint pipe (33) can be a cavity or filled with inert gas to be more easily burst under the impact of high-pressure CO₂ gas flow. The design of the restraint pipe has the following core functions: 1. Energy accumulation and pressure multiplication: The high-pressure CO2 gas flow first enters the inner cavity of the confinement tube (33). Due to its small volume, the pressure rapidly increases to 5~15 MPa, efficiently converting the kinetic energy of the CO2 gas flow into the compressibility energy and thermal energy of the powder suspension. When the pressure exceeds the rupture strength of the confinement tube, the confinement tube bursts instantly, generating a violent pressure release. The peak value of the shock wave is 2~3 times higher than that without the confinement tube.

[0042] 2. Timing control and shock wave integration: The confined tube rupture process lasts for 50~200 μs, generating a wide pulse shock wave, which, along with the electrical explosion peak pulse and the medium pulse of CO2 phase transition, chases and superimposes during propagation to form a composite shock wave with a higher peak value.

[0043] 3. Powder dispersion and reaction enhancement: The fragments of the confined tube fly out radially at high speed, impacting, breaking and dispersing the powder, generating local hot spots that directly ignite the powder, increasing the powder reaction rate from about 30% without the confined tube to more than 85%.

[0044] 4. Protecting the tube body and improving safety: The constraint tube ruptures first to release pressure, preventing the third tube body from being subjected to excessive pressure, allowing it to be reused more than 50 times.

[0045] 5. Flexibility in material selection: By changing the constraint tubes made of different materials, such as PMMA, PC, aluminum alloy, glass, etc., the intensity, pulse width and rise time of the third shock wave can be adjusted independently, achieving multiple uses with one tube.

[0046] 6. Simplified packaging and storage: The confinement tube and powder suspension can be pre-packaged into powder ammunition cartridges at the factory and directly loaded on site, avoiding the risk of dust explosion and with a storage period of more than 1 year.

[0047] As one embodiment of the present invention, to prevent the powder suspension from leaking from the vent hole (42) in the ready-to-release state, a ruptureable sealing membrane (34) is provided at the connection between the third tube and the directional venting head (4). The sealing membrane is made of aluminum foil, copper foil, or polyester film, with a thickness of 0.05~0.2 mm and a rupture pressure of 0.5~2 MPa. The sealing membrane is clamped between the front flange of the third tube and the rear flange of the venting head, or fixed to the inner wall of the tube opening by adhesive bonding. The sealing membrane completely seals the powder suspension within the annular gap of the third tube (31), ensuring no leakage during transportation, storage, and tube lowering.

[0048] As an alternative, the powder suspension can also be pre-encapsulated inside the constraint tube (33), with both ends of the constraint tube sealed with sealing films, and the inner cavity of the third tube (31) being hollow. In this case, there is no need to set a sealing film at the front end of the third tube, the structure is more simplified, and the powder suspension is double-sealed, resulting in higher reliability.

[0049] In one embodiment of the present invention, the front end of the third tube body (31) is connected to a directional energy release head (4). The release head body (41) is a conical or hemispherical closed end, and the energy release hole includes a main energy release hole (421) and a fly-off stop hole (422), and the main energy release hole (421) and the fly-off stop hole (422) are alternately distributed along the circumference of the entire directional energy release head (4); the main energy release hole is a radial rectangular hole with a width × length of 6~10 mm × 15~25 mm, used to release the main impact energy; the fly-off stop hole is an inclined hole, the angle between its axis and the axis of the release head body is 30°~60°, and its size is small, with a width × length of 3~6 mm × 10~15 mm, using the recoil force generated by the inclined hole to prevent the fracture tube from flying out of the borehole. The main energy release hole and the fly-off stop hole are alternately distributed along the circumference, with each group spaced 45° apart, such as Figure 2 As shown.

[0050] The physical basis for determining the working principle and sequence: such as Figure 5 As shown in the energy timing superposition diagram, this invention strictly limits the energy release sequence to electric explosion → CO2 phase change → powder deflagration, based on the following physical basis: 1. Avoiding Energy Cancellation: The vaporization of liquid CO2 is a strongly endothermic process, with a heat of vaporization of approximately 230 kJ / kg. If the deflagration of powder occurs before the CO2 phase transition, the CO2 will absorb a large amount of heat from the deflagration products during vaporization, causing a sharp drop in deflagration pressure. Consequently, the total energy output will be lower than that of a single CO2 phase transition. Experiments show that this reverse sequence can reduce the peak pressure by more than 30%.

[0051] 2. Utilizing CO2 gas flow to drive powder: A CO2 phase transition first occurs, generating a high-speed, high-pressure CO2 gas flow of 30-50 MPa (Mach 2-3). This gas flow breaks through the second rupture disc and impacts the powder suspension at extremely high speed, causing the powder to disperse, break up, and locally heat up, easily reaching the ignition temperature. Studies have shown that high-speed gas flow impact can increase the reaction rate of powder deflagration by 5-10 times.

[0052] 3. Step-by-step amplification effect: The electric explosion generates an initial shock wave that triggers the CO2 phase transition; the CO2 phase transition generates a stronger shock wave and drives the powder to deflagration; the powder deflagration releases chemical energy, further heating the CO2 gas, so that the peak pressure of the shock wave can be increased to 2 to 3 times that of the pure CO2 phase transition, thus achieving step-by-step energy amplification.

[0053] 4. Timing Controllability: By setting the rupture pressure of the two-stage rupture discs P1>P2, temporal separation is forcibly achieved. After the first rupture disc ruptures, the CO2 chamber pressure needs to rise from PCO2 to P2 before the second rupture disc ruptures, which takes approximately 20~100 μs. This ensures that the CO2 is fully vaporized before release. The entire timing superposition process is as follows: Figure 5 As shown.

[0054] Application Example 1 This embodiment provides a sequential composite impact fracturing tube for electro-explosive-induced liquid CO2 powder suspension suitable for hard rock fracturing.

[0055] Structural parameters: Electro-explosion excitation section (1): The first tube (11) is a 35CrMo seamless steel tube with an outer diameter of 60 mm, an inner diameter of 50 mm, a wall thickness of 5 mm, and a length of 200 mm. The metal wire (12) is a copper wire with a diameter of 200 μm and a length of 180 mm, with both ends fixed to the electrode holders. Two ceramic insulated electrode holders with a withstand voltage of 30 kV are installed on the end seat (14). The first tube is filled with atmospheric pressure nitrogen.

[0056] First rupture disc (22): Stainless steel 304, thickness 0.5 mm, cross-shaped notch depth 0.25 mm, rupture pressure P1=18MPa.

[0057] Liquid CO2 storage section (2): The second pipe (21) is a 35CrMo seamless steel pipe with an outer diameter of 60 mm, an inner diameter of 52 mm, a wall thickness of 4 mm, and a length of 300 mm. The CO2 injection port (25) is located on the side wall 50 mm from the rear end, and uses a submersible check valve with the valve core end face flush with the outer wall of the pipe. Figure 4 As shown. Fill with liquid CO2 to a pressure of 10 MPa.

[0058] Second rupture disc (23): 304 stainless steel, 0.3 mm thick, cross-shaped notch depth 0.15 mm, rupture pressure P2=12MPa. Installed in the flange between the front end of the second pipe body and the rear end of the third pipe body, with a central through hole diameter of 12 mm.

[0059] Powder suspension reaction section (3): The third tube (31) is made of 304 stainless steel, with an outer diameter of 60 mm, an inner diameter of 56 mm, a wall thickness of 2 mm, and a length of 150 mm. The constraint tube (33) is made of plexiglass (PMMA), with an outer diameter of 54 mm, an inner diameter of 48 mm, and a wall thickness of 3 mm, and three axial grooves with a depth of 1.5 mm are pre-made. The annular gap is filled with aluminum powder-water suspension: the average particle size of the aluminum powder is 10 μm, the concentration is 200 mg / mL, and 0.2% SDS surfactant is added. A ruptureable sealing membrane (34) is installed at the front end of the third tube: the aluminum foil thickness is 0.1 mm, and the rupture pressure is 0.8 MPa.

[0060] Directional energy release head (4): The release head is 120 mm long and has a cone angle of 45°. The main energy release hole (421) is 8 mm × 20 mm in size, and the anti-flying hole (422) is 4 mm × 15 mm in size, with an inclination angle of 45°. There are 4 holes in each direction around the circumference, which are alternately distributed, such as... Figure 2 As shown.

[0061] Fracturing effect: Under conditions of 200 J energy storage and 1 μs pulse width, the peak pressure of the composite shock wave at the outlet of the energy release head reached 68 MPa. Comparative experiments showed that with the confined tube, the peak pressure of the third shock wave reached 42 MPa, and the total peak pressure of the composite shock wave was 68 MPa; without the confined tube, the third shock wave was only 15 MPa, and the total peak pressure of the composite shock wave was 31 MPa. The confined tube increased the total shock wave intensity by 119%. High-speed imaging showed that the confined tube ruptured completely about 80 μs after CO2 gas injection, with fragments scattering radially. The powder suspension instantly dispersed and produced a bright deflagration flame, lasting about 200 μs. This formed a clear temporal separation and superposition with the electrical explosion (~10 μs) and CO2 phase transition (~50 μs). For details, see [link to relevant documentation]. Figure 5 The sealing membrane ruptured approximately 5 µs after the shock wave arrived, without causing a significant delay. A single blast produced 3–5 through-cracks in a 300 mm granite cube specimen, with over 70% of the fragments being <50 mm in size.

[0062] Application Example 2 This embodiment provides a fracturing tube suitable for coalbed methane permeability enhancement operations, with a focus on optimizing the powder suspension formulation.

[0063] The difference from application example 1 is: The metal wire (12) is an aluminum wire with a diameter of 150 μm and a storage capacity of 300 J. The powder suspension is composed of aluminum powder with a particle size of 5 μm and a concentration of 150 mg / mL. The liquid phase is a 10% hydrogen peroxide aqueous solution with 0.1% EDTA stabilizer added. Hydrogen peroxide decomposes and releases oxygen during the deflagration process, enhancing the deflagration intensity. The second rupture disc (23) has a rupture pressure P2 = 11 MPa. The restraint tube (33) is a polycarbonate tube with a wall thickness of 2 mm and no scoring. The sealing film (34) is a polyester film with a thickness of 0.05 mm.

[0064] Fracturing effect: In field tests at coalbed methane wells, the fracturing tubing was placed in a 75 mm diameter, 20 m deep borehole using a submerged filling process. The tubing was run first, followed by CO2 filling through a sidewall injection port. The injection port structure is as follows: Figure 4 As shown, after a single fracturing operation, the coal seam permeability coefficient increased by 8 to 12 times, and the extraction concentration increased by 30% to 50%. No powder leakage or pipe jamming occurred.

[0065] Application Example 3 This example illustrates a semi-repeatable method for using a rupture tube: 1. After the blasting is completed, the fracturing tube is removed from the borehole.

[0066] 2. Unscrew the connecting threads of each section and remove the third tube (31). The constraint tube has been broken, the powder in the annular gap has reacted, the sealing membrane has been broken, and both rupture discs (22, 23) have been deformed or sheared.

[0067] 3. Check the first tube (11) and the second tube (21) for obvious deformation or cracks, and clean the inner cavity.

[0068] 4. Replace the second rupture disc (23), the new ruptureable sealing membrane (34), and the new powder suspension reaction section (3), pre-install the constraint tube and powder suspension, and install the new first rupture disc (22).

[0069] 5. Refill with liquid CO2 and install the metal wire, and it can be used again.

[0070] Tests have shown that the first and second tubes can be reused more than 50 times, reducing the cost per use by about 70%.

[0071] Application Example 4: Sidewall Filling Port and Embedded Filling Process This embodiment provides a design scheme for fracturing tubes suitable for deep hole drilling with a depth greater than 10 m, focusing on solving the problem that the outward protrusion of the side wall filling port may affect the lowering of the tube.

[0072] Structural design: The CO2 injection port (25) is located on the side wall of the second tube (21), 60 mm from the rear end. A countersunk hole with a diameter of 12 mm and a depth of 4 mm is machined on the tube wall. The one-way valve body is installed in the countersunk hole, and the valve body is fixed to the tube wall by circumferential sealing welding. Figure 4 As shown. The valve core is made of polyetheretherketone (PEEK) material, and its end face is flush with the outer wall of the second pipe when closed, with an outward protrusion height of 0 mm. The valve body is equipped with a spring preload, and the reverse sealing pressure reaches 25 MPa.

[0073] To facilitate the submerged filling operation, an auxiliary interface is reserved at the rear end of the second tube (21), which is normally sealed with a screw plug. During filling, this interface is used to connect the long tubing.

[0074] Buried filling process: 1. The fracturing tube is assembled in an empty tube state and placed at the target drilling location. At this time, because the outer wall of the tube is smooth (the filling port has no outward protrusion), there is no obstruction during the tube lowering process.

[0075] 2. Connect one end of a 6 mm outer diameter, 30 MPa pressure-resistant high-pressure hose to the ground CO2 filling pump, and the other end through the drill hole to connect to the auxiliary interface at the rear end of the second pipe body.

[0076] 3. Start the filling pump. Liquid CO2 enters the second tube through the hose and auxiliary interface. At the same time, the one-way valve on the side wall of the second tube automatically opens under the filling pressure (0.5 MPa) to expel air from the tube. After filling to the preset pressure of 10 MPa, turn off the filling pump.

[0077] 4. Quickly disconnect the hose; the auxiliary interface plug will automatically seal, and the side wall check valve will close automatically under spring force and internal pressure. At this time, the second tube will maintain high-pressure liquid CO2, and there will be no protrusions on the outer wall of the tube.

[0078] Excitation and recovery: The subsequent activation steps are the same as in Example 1. After the blasting is completed, the fracturing tube is removed from the borehole. Since the second tube has a larger wall thickness and did not rupture, it can be reused. When reused, it only needs to be refilled with liquid CO2, which can be filled in situ downhole or on the surface after removal.

[0079] Practical benefits: The sidewall-submerged check valve ensures a smooth outer wall of the pipe, suitable for small-gap drilling (54mm diameter pipe with a 60mm diameter borehole). The submerged filling process avoids the transportation risks of pressurized fracturing pipe, making it particularly suitable for deep holes and complex downhole environments. Compared to end-filled ports, sidewall-filled ports are not affected by adjacent pipe sections when fracturing pipes are used in series, allowing for more flexible placement.

[0080] Industrial Applicability: This invention is a composite fracturing device based on the sequential superposition of electric explosion, CO2 phase change, and powder deflagration. It features a reasonable structure, high safety and reliability, and controllable cost, making it widely applicable in fields such as bench blasting in mines, tunnel excavation, coal mine gas permeability enhancement, shale gas extraction, building demolition, and underwater rock breaking. Compared to existing technologies, the triple energy sequential superposition design of this invention significantly improves rock-breaking capacity and energy efficiency. The constraint tube design solves the key technical challenges of powder deflagration energy accumulation and sequential control. The sealing membrane effectively prevents powder leakage, and the side-wall submerged filling port and buried filling process further enhance the safety and adaptability of on-site operations, demonstrating extremely high industrial application value and economic benefits.

[0081] Example 2 The present invention also provides a sequential composite impact fracturing method using a composite fracturing device, comprising the following steps: Step 1: Filling Liquid carbon dioxide is filled into the second tube (21) through the CO2 injection port (25) until the pressure P is reached. CO2 = 8~12 MPa, close the one-way valve; inject powder suspension into the annular gap of the powder suspension reaction section (3), install a ruptureable sealing membrane (34) to seal the front end of the third tube; fill the first tube (11) with atmospheric pressure nitrogen or air, install the end seat (14) and fix the metal wire (12).

[0082] Step 2: Assembly The electric explosion excitation section (1), liquid CO2 energy storage section (2), powder suspension reaction section (3) and directional energy release head (4) are connected in sequence by flanges or threads to ensure that each rupture disc is installed correctly and sealed reliably.

[0083] Step 3: Stimulation The fracturing tube is placed at the target drilling position, and the positive and negative electrode holders (131, 132) are connected to the pulse capacitor bank through high-voltage cables. A pulse current with a stored energy of 0.5~5 kJ and a pulse width of 1~5 μs is applied, and the metal wire (12) explodes instantly, causing the pressure inside the first tube (11) to rise sharply to more than P1.

[0084] Step 4: Sequential Energy Release like Figure 5 The time-series superposition diagram is shown: the first rupture disc (22) breaks, and the high-temperature plasma enters the second tube (21). The liquid CO2 instantly vaporizes and expands in volume by 400 to 600 times. When the pressure is greater than the strength of the second rupture disc, a second shock wave is generated. The second rupture disc (23) ruptures, and the high-pressure CO2 gas flow rushes into the powder suspension reaction section (3) at high speed through the central through hole (311). It first enters the inner cavity of the confinement tube (33) to form a local high pressure. When the pressure exceeds the rupture strength of the confinement tube, the confinement tube (33) expands and cracks as a whole. High-speed fragments fly out radially, impacting, dispersing and heating the powder suspension in the annular gap, triggering the powder deflagration reaction and generating a third shock wave. The triple shock wave propagates axially, breaking through the fractured sealing membrane (34) and being released directionally into the target rock mass through the energy release holes (42) of the directional energy release head (4). The energy release holes are arranged circumferentially as follows: Figure 2 As shown.

[0085] Step 5: The composite shock wave is directionally released through the main venting hole (421) and the anti-flyout hole (422), acting on the rock mass. The reverse thrust generated by the anti-flyout hole (422) will press the fracture pipe against the bottom of the borehole to prevent it from flying out.

[0086] Step Six: Recycling After the blasting is completed, the rupture tube is removed. Since the first tube (11) and the second tube (21) have large wall thicknesses, they do not rupture and can be reused. Only the first rupture disc (22), the second rupture disc (23), the ruptureable sealing membrane (34), and the constraint tube and powder suspension (disposable parts) in the powder suspension reaction section (3) need to be replaced before the next operation can be carried out.

[0087] As one embodiment of the present invention, the rupture pressure P1 of the first rupture disc (22) is related to the liquid CO2 filling pressure P CO2The relation satisfies P1 = (1.5~2.5) × P CO2 The rupture pressure P2 of the second rupture disc (23) satisfies P2=(1.2~1.8)×P CO2 The rupture pressure of the constraint tube (33) is 5~15 MPa.

[0088] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A composite fracturing device based on the sequential superposition of electric explosion-CO2 phase change-powder deflagration, characterized in that, include: The electric explosion excitation section (1), the liquid CO2 energy storage section (2) and the powder suspension reaction section (3) are connected in series along the axial direction, as well as the directional energy release head (4) connected to the front end of the powder suspension reaction section. The electro-explosion excitation section (1) includes a first tube (11), a metal wire (12) disposed in the first tube (11), and an end seat (14) fixed to the rear end of the first tube (11). The end seat (14) is provided with a positive electrode seat (131) and a negative electrode seat (132). The two ends of the metal wire (12) are respectively connected to the inner ends of the positive and negative electrode seats, and the outer ends of the positive and negative electrode seats are used to connect to a high-voltage pulse power supply. The liquid CO2 energy storage section (2) includes a second tube (21), which is filled with liquid CO2 (26). The side wall of the second tube (21) is provided with a CO2 injection port (25), and a submersible one-way valve (24) is installed in the CO2 injection port (25). A first rupture disc (22) is provided between the electric explosion excitation section and the liquid CO2 energy storage section, and a second rupture disc (23) is provided between the liquid CO2 energy storage section and the powder suspension reaction section; the rupture discs make each tube independently sealed, the rupture pressure of the first rupture disc is P1, and the rupture pressure of the second rupture disc is P2, satisfying P2 < P1. The powder suspension reaction section (3) includes a third tube (31), and a constraint tube (33) is coaxially arranged inside the third tube (31). The annular gap between the constraint tube (33) and the third tube (31) or the inside of the constraint tube (33) is filled with powder suspension. The venting hole (42) of the directional energy release head (4) includes a main energy release hole (421) and a flight stop hole (422). The main energy release hole (421) is a radial rectangular hole, and the flight stop hole (422) is an inclined hole. The angle between its axis and the axis of the release head body (41) is 30°~60°. The main energy release hole and the flight stop hole are alternately distributed along the circumference. When the fracturing tube is in operation, the three stages of energy are released in sequence in the order of electric explosion → CO2 phase change → powder deflagration.

2. The composite fracturing device based on the superposition of the electrical explosion-CO2 phase change-powder deflagration sequence as described in claim 1, characterized in that, The rupture pressure P1 of the first rupture disc (22) is 15~20 MPa, and the rupture pressure P2 of the second rupture disc (23) is 10~15 MPa, and P2 is 3~8 MPa lower than P1.

3. The composite fracturing device based on the superposition of the electrical explosion-CO2 phase change-powder deflagration sequence as described in claim 2, characterized in that, The CO2 injection port (25) is located on the side wall of the second tube (21) near the first rupture disc (22), and the axis of the injection port is perpendicular to the axis of the second tube. A submerged one-way valve is installed inside the injection port (25). The valve body of the one-way valve is installed in the countersunk hole on the side wall of the second tube (21). The valve body is welded to the tube wall or fixed by thread sealing. The end face of the valve core is flush with or slightly lower than the outer wall of the second tube, and the outward protrusion height is ≤ 2 mm. The opening pressure of the one-way valve is 0.3~0.8 MPa, and the reverse sealing pressure is ≥ 25 MPa.

4. The composite fracturing device based on the superposition of the electrical explosion-CO2 phase change-powder deflagration sequence as described in claim 3, characterized in that, The constraint tube (33) is an organic glass tube, polycarbonate tube, brittle metal tube or glass tube with a wall thickness of 1~5 mm and an outer diameter of 0.7~0.95 times the inner diameter of the third tube body (31). The two ends of the constraint tube (33) are sealed to the third tube body (31) to form a closed annular loading cavity.

5. The composite fracturing device based on the superposition of the electrical explosion-CO2 phase change-powder deflagration sequence as described in claim 4, characterized in that, The front end of the third tube (31) is connected to a directional energy release head (4), and the main energy release hole (421) and the anti-flight hole (422) are alternately distributed along the circumference of the entire directional energy release head (4); the front end of the third tube (31) is provided with a ruptureable sealing membrane (34), which seals the powder suspension inside the third tube (31).

6. The composite fracturing device based on the superposition of the electrical explosion-CO2 phase change-powder deflagration sequence as described in claim 5, characterized in that, The positive electrode holder (131) and negative electrode holder (132) on the end seat (14) each include a metal electrode rod and a ceramic insulating sleeve. The ceramic insulating sleeve is embedded in the stepped hole of the end seat (14), and the metal electrode rod passes through the ceramic insulating sleeve. O-rings are provided between the metal electrode rod and the ceramic insulating sleeve, as well as between the ceramic insulating sleeve and the end seat.

7. The composite fracturing device based on the superposition of the electrical explosion-CO2 phase change-powder deflagration sequence as described in claim 6, characterized in that, The second rupture disc (23) has a cross / star-shaped groove at its center, and the groove depth is 30% to 60% of the thickness of the rupture disc; a central through hole (32) with a diameter of 10 to 15 mm is provided between the second tube and the third tube.

8. A sequential composite impact fracturing method using a composite fracturing device, characterized in that, include: Filling steps: Fill the second tube (21) with liquid carbon dioxide through the CO2 injection port (25) until the pressure P is reached. CO2 And P CO2 < P2 < P1; Fill the annular gap of the powder suspension reaction section (3) with powder suspension and seal it; fill the first tube (11) with atmospheric pressure protective gas; Excitation steps: A microsecond-level pulse current is applied to the metal wire (12) through a high-voltage pulse power supply. The metal wire (12) undergoes an electrical explosion, generating an initial shock wave and high-temperature plasma. The pressure inside the first tube (11) rises sharply to more than P1. First stage energy release: The first rupture disc (22) ruptures, and high-temperature plasma enters the second tube (21). Liquid CO2 instantly vaporizes and expands, increasing in volume by 400 to 600 times, generating a second shock wave. Second stage energy release: Pressure breaks through P2, the second rupture disc (23) ruptures, and high-pressure CO2 gas flows through the central through hole into the powder suspension reaction section (3) at high speed. It first enters the inner cavity of the confinement tube (33) to form local high pressure. When the pressure exceeds the rupture strength of the confinement tube, the confinement tube (33) expands and cracks as a whole. High-speed fragments impact and disperse the powder suspension, triggering the powder deflagration reaction and generating a third shock wave. Superimposed release steps: The triple shock wave superimposed propagates along the axial direction, breaks through the ruptureable sealing membrane (34), and is directionally released to the target rock mass through the energy release hole (42) of the directional energy release head (4).

9. The sequential composite impact fracturing method of the composite fracturing device according to claim 8, characterized in that, The rupture pressure P1 of the first rupture disc (22) and the liquid CO2 filling pressure P CO2 The relation satisfies P1 = (1.5~2.5)×P CO2 The rupture pressure P2 of the second rupture disc (23) satisfies P2 = (1.2~1.8)×P CO2 The rupture pressure of the constraint tube (33) is 5~15MPa.

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