Shale gas reservoir fracturing method based on in-situ methane explosion

Abstract

The invention provides a shale gas reservoir fracturing method based on in-situ methane explosion, and belongs to the technical field of shale gas exploiting.The shale gas reservoir fracturing method comprises the steps that original modifier crystals are subjected to mechanical grinding treatment to obtain particles with specific physical characteristics, and an ignition modifier is prepared; oxygen is injected into the shale gas exploitation pipeline, and meanwhile hydrogen is doped into reservoir methane to form CH4-O2-air mixed gas; a plurality of groups of high-pressure injection devices are arranged in the mining pipeline and are respectively filled with an ignition improver and improver particles, and high-pressure air is injected as a driving air source; the power controller synchronously triggers the high-pressure jetting device to jet materials and the ignition assembly to ignite, so that the mixed gas is burnt and exploded, and explosion parameters are monitored; and after burning explosion is finished, residual substances in the pipeline are removed, waste gas is discharged, and fracturing operation is completed. According to the method, remarkable synergistic improvement of explosion overpressure and explosion velocity is achieved, and the method has the advantages of being efficient, clean, safe and the like, is environmentally friendly and economical, and is suitable for development of deep and high-ground-stress reservoirs.

Description

Technical Field

[0001] This invention relates to the field of shale gas extraction technology, and in particular to a shale gas reservoir fracturing method based on in-situ methane explosion. Background Technology

[0002] Currently, shale gas, as an abundant unconventional natural gas resource, has become an important direction in the global energy sector. Among shale gas extraction technologies, hydraulic fracturing is the most widely used mainstream method. This technology injects high-pressure fluids (including water and chemical additives) into the reservoir to create a network of fractures in the shale, releasing natural gas. Meanwhile, to address the inherent limitations of hydraulic fracturing, in-situ methane explosive fracturing technology is gradually emerging. This technology utilizes the overpressure shock wave generated by the explosion of a mixture of methane and oxidizer in the reservoir to fracture the shale. It has potential advantages such as zero water consumption, the ability to achieve multi-stage pulse blasting, and environmental friendliness, making it an emerging research direction in the industry.

[0003] With the increasing demand for developing deep, high-stress, and low-permeability shale reservoirs, the limitations of traditional hydraulic fracturing technology in terms of water consumption, environmental pollution, and fracture formation effectiveness are becoming increasingly apparent, driving the industry towards waterless fracturing technology. In-situ methane explosive fracturing technology, due to its suitability for deep reservoir characteristics and minimal environmental impact, has become a key research focus as an alternative to hydraulic fracturing. Research efforts primarily focus on increasing explosion pressure, optimizing ignition efficiency, and improving the performance of combustion modifiers. For example, enhancing the explosion effect by increasing ignition energy, incorporating hydrogen, or adding solid fuels (such as aluminum powder and potassium permanganate) to meet the fracturing requirements of deep reservoirs.

[0004] Despite the development potential of in-situ methane explosive fracturing technology, it still faces significant technical bottlenecks: First, the explosion pressure is insufficient. Current technologies, by increasing the ignition energy (e.g., from 1 kJ to 10 kJ), can only raise the methane explosion overpressure to 1.78 bar, which is far from the high pressure required for deep reservoirs (e.g., 100 MPa). Furthermore, further increasing the ignition energy would reduce the safety of the equipment. Second, there are issues with ignition efficiency and energy transfer. While simply adding hydrogen can improve ignition efficiency, it cannot solve the problem of directional release and homogenized transfer of explosion energy, resulting in insufficient energy utilization. Third, modifiers have limitations. Although aluminum powder can increase overpressure, the increase in detonation velocity is limited and it is prone to causing secondary pollution. Potassium permanganate, on the other hand, has problems such as unclear explosion mechanism, risk of heavy metal residue (e.g., manganese) pollution, and insignificant increase in initiation velocity, making it difficult to meet the requirements of efficient and clean development.

[0005] Therefore, there is an urgent need for an in-situ methane explosion fracturing method that can synergistically improve explosion overpressure and detonation velocity, optimize energy utilization efficiency, and take into account both environmental protection and safety, so as to break through the existing technical bottlenecks and provide support for the efficient development of deep shale gas reservoirs. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a shale gas reservoir fracturing method based on in-situ methane explosion. This method solves the problems of insufficient explosion pressure, heavy metal pollution, and low energy utilization in existing technologies. It also achieves a significant synergistic improvement in explosion overpressure and detonation velocity, and has the advantages of high efficiency, cleanliness, and safety while being environmentally friendly and economical. It is suitable for the development of deep, high-stress reservoirs.

[0007] To achieve the above objectives, the present invention provides the following solution: A shale gas reservoir fracturing method based on in-situ methane explosion includes the following steps: S1. The original modifier crystals are mechanically ground to obtain particles with specific physical properties in order to avoid agglomeration and reduced reactivity. S2. Prepare ignition modifiers to increase the ignition probability and promote the methane explosion reaction; S3. Inject oxygen into the shale gas extraction pipeline, and at the same time mix hydrogen into the reservoir methane to form a CH4-O2-air mixture. S4. Multiple pressure-driven injection devices are arranged in the mining pipeline. One set of pressure-driven injection devices is filled with the ignition modifier and is directly facing the ignition assembly. The remaining set of pressure-driven injection devices is filled with the processed modifier particles and distributed outside the ignition point. Power pressurized air is injected into each device as the driving gas source. S5. The power controller sends a synchronization signal to the solenoid valve and ignition assembly of the pressure-driven injection device, so that the pressure-driven injection device injects the treated modifier particles and ignition modifier into the pipeline to mix with the gas mixture. At the same time, the ignition assembly starts ignition to ignite the gas mixture and cause it to explode. The explosion parameters in the pipeline are monitored by a dynamic signal tester. S6. After the combustion and explosion, remove the residual material in the pipelines of each pressure-driven injection device and discharge the exhaust gas to complete the shale gas reservoir fracturing operation.

[0008] Preferably, in S1, the mechanical grinding process includes: placing the original modifier crystals in a mechanical grinder and grinding them for 2-4 seconds at a power of 1600-2000W to obtain a particle size not exceeding 100μm and a specific surface area of ​​0.1m². 2 / g of particles with an adsorption rate RA of less than 50% and an oxygen content of 35%~60%.

[0009] Preferably, in S2, the ignition modifier is propylene oxide.

[0010] Preferably, in S3, the process of forming the CH4-O2-air mixture includes: injecting oxygen into the extraction pipeline to a volume fraction of 10%~15%; adding hydrogen to the reservoir methane to make the volume ratio of methane to hydrogen 4:1~5:1, wherein the hydrogen gas fraction is 1.3%~2.6%; controlling the volume fraction of CH4 in the mixture to be 10%~20%, and the equivalent ratio of CH4-O2 mixture to be 0.6~1.25.

[0011] Preferably, in S4, the arrangement of the pressure-driven injection device and the process of injecting the driving gas source include: Each pressure-driven injection device consists of a multi-hole nozzle, a chemical reagent tank, a solenoid valve, and a pressurized air tank. The front end of the chemical reagent tank is connected to the multi-hole nozzle, and the end is connected to the solenoid valve. The solenoid valve is connected to one end of the pressurized air tank, and the air inlet valve is connected to the other end of the pressurized air tank. The pressure-driven injection device directly facing the ignition assembly is filled with ignition modifier, while the remaining pressure-driven injection device is distributed outside the ignition point and filled with modifier particles. Inject 0.6~0.8MPa of driving pressure air into each pressurized air storage tank as the driving air source, and the orifice diameter of the multi-hole nozzle is 1.6~2.0mm.

[0012] Preferably, in S5, the working process of the pressure-driven injection device includes: The injection, ignition, and data acquisition are triggered synchronously by a power controller, with the ignition delay time set to 50~320ms; finally, a dynamic signal tester is used to record the explosion overpressure at different locations within the mining pipeline.

[0013] Preferably, in S5, the combustion and explosion of the gas mixture is achieved through a multi-stage explosion, including: In the first stage of ignition, the ignition assembly ignites the ignition modifier and the surrounding CH4-O2 mixture, generating an initial shock wave. Secondary reinforcement: The initial shock wave acts on the modifier particles outside the ignition point, triggering a secondary explosion.

[0014] Preferably, in S6, the process of removing residual substances and discharging exhaust gas includes: firstly, using pressurized air for cleaning to purge the residual substances in the pipes and chemical agent tanks, and then discharging the exhaust gas and residues through a cleaning module consisting of valves, pipes and a vacuum pump, wherein the cleaning module includes a return liquid recovery system for separating the decomposition products of the modifier.

[0015] Preferably, the process of removing residual substances and discharging exhaust gases further includes: purging the mining pipeline with pressurized air or inert gas to suppress the risk of spontaneous combustion.

[0016] Preferably, in S5, the combustion and explosion effect parameters of the mixed gas are: explosion overpressure 30~50MPa, explosion velocity 1.2~1.5km / s, and ignition efficiency 80%~90%.

[0017] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: (1) This invention obtains particles with preset dispersion by grinding the original modifier crystals with specific process parameters, and at the same time prepares ignition modifiers. Combined with injecting oxygen into the mining pipeline and adding hydrogen to the reservoir methane to form a mixed gas with a specific ratio, the fuel system is optimized, laying the foundation for efficient combustion and effectively improving ignition efficiency and reactivity.

[0018] (2) This invention arranges multiple pressure-driven injection devices in the mining pipeline, fills them with ignition modifier and modifier particles respectively, and uses a power controller to synchronously trigger injection and ignition to form a multi-stage explosion, which significantly enhances the explosion overpressure and detonation velocity. The maximum explosion overpressure can reach 43.61 MPa and the detonation velocity can reach 2.91 km / s. Compared with pure methane explosion, the overpressure increase rate is 2069% and the detonation velocity increase rate is 302%, which greatly improves the reservoir fracturing effect.

[0019] (3) After the combustion and explosion, the present invention removes residual substances and discharges waste gas by purging with pressurized air and cleaning module, and separates the decomposition products of modifier by returning fluid recovery system. Pressurized air or inert gas is used to suppress the risk of spontaneous combustion, thus realizing environmental protection and safety control of the fracturing process. It is suitable for the development of deep, high-stress shale reservoirs and has both high efficiency and environmental friendliness. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be 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.

[0021] Figure 1 This is a flowchart of a shale gas reservoir fracturing method based on in-situ methane explosion according to the present invention; Figure 2 This is a schematic diagram of the overall structural layout for implementing a shale gas reservoir fracturing method based on in-situ methane explosion according to the present invention. Figure 3 A schematic diagram of the pressure-driven injection device provided by the present invention.

[0022] Explanation of reference numerals in the attached figures: 1. Surface workstation; 2. Surface; 3. Groundwater; 4. Overlying strata; 5. Shale reservoir; 6. Deep strata; 7. Cementing casing; 8. Air inlet pipe; 9. Shale gas pipeline; 10. Chemical ignition port; 11. Sealing wall; 12. Horizontal branch well; 13. Pressure-driven injection device; 131. Air inlet valve; 132. Pressurized air storage tank; 133. Solenoid valve; 134. Chemical reagent tank; 135. Multi-hole nozzle. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] like Figure 1 As shown, this invention provides a shale gas reservoir fracturing method based on in-situ methane explosion, comprising the following steps: S1. The original modifier crystals are mechanically ground to obtain particles with specific physical properties in order to avoid agglomeration and reduced reactivity.

[0026] Specifically, the mechanical grinding process includes: placing the original modifier crystals in a mechanical grinder and grinding them for 2-4 seconds at a power of 1600-2000W to obtain particles with a diameter not exceeding 100μm and a specific surface area of ​​0.1m². 2 / g of particles with an adsorption rate RA of less than 50% and an oxygen content of 35%~60%.

[0027] S2. Prepare ignition modifiers to increase the ignition probability and promote the methane explosion reaction.

[0028] Specifically, the ignition modifier is propylene oxide, and its dosage is 20 ml.

[0029] S3. Inject oxygen into the shale gas extraction pipeline, and at the same time mix hydrogen into the reservoir methane to form a CH4-O2-air mixture.

[0030] Specifically, the process of forming the CH4-O2-air mixture includes: injecting oxygen into the extraction pipeline to a volume fraction of 10%~15%; adding hydrogen to the reservoir methane to make the volume ratio of methane to hydrogen 4:1~5:1, wherein the hydrogen gas fraction is 1.3%~2.6%; controlling the volume fraction of CH4 in the mixture to be 10%~20%, and the equivalent ratio of CH4-O2 mixture to be 0.6~1.25.

[0031] S4. Multiple sets of pressure-driven injection devices are arranged inside the mining pipeline. One set of pressure-driven injection devices is filled with the ignition modifier and is directly facing the ignition assembly. The remaining sets of pressure-driven injection devices are filled with the treated modifier particles and distributed outside the ignition point. Power pressurized air is injected into each device as the driving air source.

[0032] Specifically, the arrangement of the pressure-driven injection device and the process of injecting the driving gas source include: like Figure 3 As shown, each pressure-driven injection device 13 consists of an intake valve 131, a multi-hole nozzle 135, a chemical reagent tank 134, a solenoid valve 133, and a pressurized air storage tank 132. The front end of the chemical reagent tank 134 is connected to the multi-hole nozzle 135, and the end end is connected to the solenoid valve 133. The solenoid valve 133 is connected to one end of the pressurized air storage tank 132, and the intake valve 131 is connected to the other end of the pressurized air storage tank 132, serving as the air intake end of the pressure-driven injection device. The pressure-driven injection device directly facing the ignition assembly is filled with ignition modifier, while the remaining pressure-driven injection device is distributed outside the ignition point and filled with modifier particles. Inject 0.6~0.8MPa of power-grade pressurized air into each pressurized air storage tank as the driving air source, and use multi-hole nozzles with an orifice diameter of 1.6~2.0mm.

[0033] S5. The power controller sends a synchronization signal to the solenoid valve and ignition assembly of the pressure-driven injection device, so that the pressure-driven injection device injects the treated modifier particles and ignition modifier into the pipeline to mix with the gas mixture. At the same time, the ignition assembly starts ignition to cause the gas mixture to explode. The explosion parameters in the pipeline are monitored by a dynamic signal tester.

[0034] Specifically, the working process of the pressure-driven injection device includes: The injection, ignition, and data acquisition are triggered synchronously by a power controller, with the ignition delay time set to 50~320ms; finally, a dynamic signal tester is used to record the explosion overpressure at different locations within the mining pipeline.

[0035] Furthermore, the combustion and explosion of the gas mixture is achieved through a multi-stage explosion, including: In the first stage of ignition, the ignition assembly ignites the ignition modifier and the surrounding CH4-O2 mixture, generating an initial shock wave. Secondary reinforcement: The initial shock wave acts on the modifier particles outside the ignition point, triggering a secondary explosion.

[0036] Furthermore, the process for removing residual substances and discharging exhaust gases includes: firstly, using purge-grade pressurized air to purge residual substances from pipelines and chemical tanks; then, discharging exhaust gases and residues through a cleaning module consisting of valves, pipelines, and a vacuum pump. This cleaning module includes a backflow liquid recovery system for separating modifier decomposition products. Additionally, it includes purging the mining pipelines with purge-grade pressurized air or inert gas to suppress the risk of spontaneous combustion.

[0037] The combustion and explosion effect parameters of the gas mixture are: explosion overpressure 30~50MPa, explosion velocity 1.2~1.5km / s, and ignition efficiency 80%~90%.

[0038] S6. After the combustion and explosion, remove the residual material in the pipelines of each pressure-driven injection device and discharge the exhaust gas to complete the shale gas reservoir fracturing operation.

[0039] Based on the above, the structural layout for implementing the above method is as follows: Figure 2 As shown, ground workstation 1 is located above ground 2; below ground 2 are distributed groundwater 3, overlying rock 4, shale reservoir 5, deep rock 6, cementing casing 7, gas inlet pipe 8, shale gas pipeline 9, etc., which penetrate the underground layers. Chemical ignition port 10, sealing wall 11, horizontal branch well 12, and pressure-driven jetting device 13 are mainly located in shale reservoir 5 and related well and tunnel structures. Specifically, the ground workstation 1 is connected to the underground intake pipe 8, shale gas pipeline 9, etc., through pipelines to realize control and data and material transmission; the intake pipe 8, shale gas pipeline 9, etc. penetrate into the cementing casing 7 and extend to the shale reservoir 5 area; the chemical ignition port 10 and the pressure-driven injection device 13 are connected to the horizontal branch well 12; the sealing wall 11 is used to separate the relevant well roadway space; all components together constitute the underground-surface connection system for shale gas extraction fracturing operations, and cooperate to complete fracturing operations based on in-situ methane explosion; the overlying rock layer 4, shale reservoir 5, deep rock layer 6, etc., serve as geological bearing layers, forming spatial nesting and operational association with various well roadways and equipment.

[0040] The above content will be further verified through specific implementation methods below. The implementation methods described are only some embodiments of the present invention, and not all embodiments.

[0041] Example 1 This embodiment is based on Figures 1 to 3 The steps to achieve shale gas reservoir fracturing are as follows: First, the raw NaClO3 crystals were placed in a mechanical grinder and ground for 2 seconds at 1600W power to obtain a particle size of 22.4μm and a specific surface area of ​​0.1m². 2 / g of particles with an adsorption rate (RA) of less than 50%. Then, a protective cementing casing 7 is pre-installed in the shale gas well. Methane in the reservoir is released through desorption technology, and 50L of oxygen to a volume fraction of 10% and 80L of methane to a volume fraction of 16% are injected through the air inlet pipe 8 to form a CH4-O2-air mixture, ensuring that the equivalent ratio of the mixture is 1.25.

[0042] Secondly, a chemical ignition port 10 and 17 sets of pressure-driven injection devices 13 are installed inside a 500L shale gas pipeline 9, which is 16m long and 0.2m in diameter. Each set of pressure-driven injection devices 13 consists of a pressurized air storage tank 132, a solenoid valve 133, a chemical reagent tank 134, and a multi-hole nozzle 135 with an orifice diameter of 1.6mm. The first set of pressure-driven injection devices 13 is directly facing the chemical ignition port 10 and injects 20mL of propylene oxide as a combustion aid. The remaining 16 sets of pressure-driven injection devices 13 are evenly distributed at intervals of 0.74m in an area more than 5.0m away from the chemical ignition port 10, and are used to inject prepared NaClO3 modifier particles to achieve a NaClO3 modifier particle loading concentration of 0.2g / L in the pipeline.

[0043] An ignition generator is installed at the front end of the pipeline. An activation signal is sent to the ignition generator and the pressure-driven injection device 13 via a power controller, thereby synchronously triggering ignition and injection. The ignition energy is 40J, and the delay time is 50ms. A dynamic signal tester with a frequency response of 10kHz is used to record the explosion overpressure at different pipeline locations. After the explosion, residual materials in the chemical agent tank 134 are purged using residual cleaning pressurized air, and the exhaust gas and residue are discharged along with the residue in the pipeline through a cleaning module including valves, pipelines, and a vacuum pump. In this embodiment, an explosion overpressure of up to 33.197MPa is generated in the pipeline, with a rise rate of 2.221GPa / s and an explosion velocity of 1.359km / s.

[0044] Example 2 In this embodiment, the raw KMnO4 crystals were placed in a mechanical grinder and ground for 4 seconds at 1600W power to obtain particles with a diameter of 20μm. Then, a protective cementing casing 7 was pre-installed in the shale gas well, and methane in the reservoir was released through desorption technology. 50L of oxygen to a volume fraction of 10% and 50L of methane to a volume fraction of 10% were injected through the air inlet pipe 8 to form a CH4-O2-air mixture, ensuring that the equivalent ratio of the mixture was 0.75.

[0045] A chemical ignition port 10 and 17 sets of pressure-driven injection devices 13 are installed inside a 500L shale gas pipeline 9, which is 16m long and 0.2m in diameter. Each set of pressure-driven injection devices 13 consists of a pressurized air storage tank 132, a solenoid valve 133, a chemical reagent tank 134, and a multi-hole nozzle 135 with an orifice diameter of 1.6mm. The first set of pressure-driven injection devices 13 is directly facing the chemical ignition port 10 and injects 40mL of propylene oxide as a combustion accelerant. The remaining 16 sets of pressure-driven injection devices 13 are evenly distributed at intervals of 0.74m in an area more than 5.0m away from the chemical ignition port 10, and are used to inject prepared KMnO4 modifier particles to achieve a KMnO4 modifier particle loading concentration of 0.5g / L in the pipeline.

[0046] An ignition generator is installed at the front end of the pipeline. An activation signal is sent to the ignition generator and the pressure-driven injection device 13 via a power controller, thereby synchronously triggering ignition and injection. The ignition energy is 40J, and the delay time is 320ms. A dynamic signal tester with a frequency response of 10kHz is used to record the explosion overpressure at different pipeline locations. After the explosion, residual materials in the chemical agent tank 134 are purged using residual cleaning pressurized air, and the exhaust gas and residue are discharged along with the residue in the pipeline through a cleaning module including valves, pipelines, and a vacuum pump. In this embodiment, an explosion overpressure of up to 30.64MPa is generated in the pipeline, with a pressure rise rate of 20.78GPa / s and an explosion velocity of 1km / s.

[0047] Example 3 In this embodiment, the raw NaClO4 crystals are placed in a mechanical grinder and ground to obtain particles with a diameter of 26.6 μm. A protective cementing casing 7 is pre-installed in the shale gas well. Methane in the reservoir is released through desorption technology, and 50 L of oxygen and 50 L of methane are injected through the air inlet pipe 8 to a volume fraction of 10%, forming a CH4-O2-air mixture with an equivalent ratio of 0.75.

[0048] A chemical ignition port 10 and 17 sets of pressure-driven injection devices 13 are installed inside a 500L shale gas pipeline 9, which is 16m long and 0.2m in diameter. Each set of pressure-driven injection devices 13 consists of a pressurized air storage tank 132, a solenoid valve 133, a chemical reagent tank 134, and a multi-hole nozzle 135 with an orifice diameter of 1.6mm. The first set of pressure-driven injection devices 13 is directly facing the chemical ignition port 10 and injects 40mL of propylene oxide as a combustion aid. The remaining 16 sets of pressure-driven injection devices 13 are evenly distributed at intervals of 0.74m in an area more than 5.0m away from the chemical ignition port 10, and are used to inject prepared NaClO4 modifier particles to achieve a NaClO4 modifier particle loading concentration of 0.15g / L in the pipeline.

[0049] An ignition generator is installed at the front end of the pipeline. An activation signal is sent to the ignition generator and the pressure-driven injection device 13 via a power controller, thereby synchronously triggering ignition and injection. The ignition energy is 40J, and the delay time is 50ms. A dynamic signal tester with a frequency response of 10kHz is used to record the explosion overpressure at different pipeline locations. After the explosion, residual substances in the chemical agent tank 134 are purged using residual cleaning pressurized air, and the exhaust gas and residue are discharged along with the residue in the pipeline through a cleaning module including valves, pipelines, and a vacuum pump. In this embodiment, an explosion overpressure of up to 43.61MPa is generated in the pipeline, with a pressure rise rate of 20.78GPa / s and an explosion velocity of 2.91km / s.

[0050] Example 4 In this embodiment, raw barium nitrate (Ba(NO3)2) crystals were placed in a mechanical grinder and ground for 3-5 seconds at a power of 1600-2000W to obtain a particle size of 65.3μm and a specific surface area of ​​0.1m². 2 / g of barium nitrate particles with an adsorption rate (RA) of less than 50% and an oxygen content of 45%~55%. A protective cementing casing 7 is pre-installed in the shale gas well. Methane in the reservoir is released through desorption technology, and oxygen and nitrogen are injected through the inlet pipe 8 to form a CH4-O2-N2 mixture, where the CH4 volume fraction is controlled at 13% and the methane equivalent ratio is fixed at 1.25. Simultaneously, hydrogen is incorporated into the reservoir methane, resulting in a methane to hydrogen volume ratio of 4:1~5:1 and a hydrogen integral of 1.3%~2.6%.

[0051] A chemical ignition port 10 and 17 sets of pressure-driven injection devices 13 are installed inside a 500L shale gas pipeline 9, which is 16m long and 0.2m in diameter. Each set of pressure-driven injection devices 13 consists of a pressurized air storage tank 132, a solenoid valve 133, a chemical reagent tank 134, and a multi-hole nozzle 135 with an orifice diameter of 1.6mm. The first set of pressure-driven injection devices 13 is directly facing the chemical ignition port 10 and injects 40mL of propylene oxide as a combustion aid. The remaining 16 sets of pressure-driven injection devices 13 are evenly distributed at intervals of 0.74m in an area more than 5.0m away from the chemical ignition port 10, and are used to inject prepared Ba(NO3)2 modifier particles, so that the total filling amount of Ba(NO3)2 modifier particles in the pipeline is 100g.

[0052] An ignition generator is installed at the front end of the pipeline. An activation signal is sent to the ignition generator and the pressure-driven injection device 13 via a power controller, thereby synchronously triggering ignition and injection. The ignition energy is 40J, and the delay time is 50ms. A dynamic signal tester with a frequency response of 10kHz is used to record the explosion overpressure at different pipeline locations. After the explosion, residual materials in the chemical agent tank 134 are purged using residual cleaning pressurized air, and the exhaust gas and residue are discharged along with the residue in the pipeline through a cleaning module including valves, pipelines, and a vacuum pump. In this embodiment, an explosion overpressure of up to 22.52MPa is generated in the pipeline, with an average pressure rise rate of 2.104GPa / s.

[0053] Compared with pure methane explosion under the same conditions, Examples 1-4 showed an overpressure increase of 2069% and a detonation velocity increase of 302%, thus proving that the method provided by the present invention can significantly improve the reservoir fracturing effect.

[0054] Therefore, the above-mentioned shale gas reservoir fracturing method based on in-situ methane explosion solves the problems of insufficient explosion pressure, heavy metal pollution and low energy utilization in the existing technology. It also achieves a significant synergistic improvement in explosion overpressure and detonation velocity, and has the advantages of high efficiency, cleanliness and safety, while also being environmentally friendly and economical. It is suitable for the development of deep and high geostress reservoirs.

[0055] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0056] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A shale gas reservoir fracturing method based on in-situ methane explosion, characterized in that, Includes the following steps: S1. The original modifier crystals are mechanically ground to obtain particles with specific physical properties in order to avoid agglomeration and reduced reactivity. S2. Prepare ignition modifiers to increase the ignition probability and promote the methane explosion reaction; S3. Inject oxygen into the shale gas extraction pipeline, and at the same time mix hydrogen into the reservoir methane to form a CH4-O2-air mixture. S4. Multiple pressure-driven injection devices are arranged in the mining pipeline. One set of pressure-driven injection devices is filled with the ignition modifier and is directly facing the ignition assembly. The remaining set of pressure-driven injection devices is filled with the processed modifier particles and distributed outside the ignition point. Power pressurized air is injected into each device as the driving gas source. S5. The power controller sends a synchronization signal to the solenoid valve and ignition assembly of the pressure-driven injection device, so that the pressure-driven injection device injects the treated modifier particles and ignition modifier into the pipeline to mix with the gas mixture. At the same time, the ignition assembly starts ignition to ignite the gas mixture and cause it to explode. The explosion parameters in the pipeline are monitored by a dynamic signal tester. S6. After the combustion and explosion, remove the residual material in the pipelines of each pressure-driven injection device and discharge the exhaust gas to complete the shale gas reservoir fracturing operation.

2. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S1, the mechanical grinding process includes: placing the original modifier crystals in a mechanical grinder and grinding them for 2-4 seconds at a power of 1600-2000W to obtain particles with a diameter not exceeding 100μm and a specific surface area of ​​0.1m². 2 / g of particles with an adsorption rate RA of less than 50% and an oxygen content of 35%~60%.

3. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S2, the ignition modifier is propylene oxide.

4. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S3, the process of forming the CH4-O2-air mixture includes: injecting oxygen into the extraction pipeline to a volume fraction of 10%~15%; adding hydrogen to the reservoir methane to make the volume ratio of methane to hydrogen 4:1~5:1, wherein the hydrogen gas fraction is 1.3%~2.6%; controlling the volume fraction of CH4 in the mixture to be 10%~20%, and the equivalent ratio of CH4-O2 mixture to be 0.6~1.

25.

5. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S4, the arrangement of the pressure-driven injection device and the process of injecting the driving gas source include: Each pressure-driven injection device consists of a multi-hole nozzle, a chemical reagent tank, a solenoid valve, and a pressurized air tank. The front end of the chemical reagent tank is connected to the multi-hole nozzle, and the end is connected to the solenoid valve. The solenoid valve is connected to one end of the pressurized air tank, and the air inlet valve is connected to the other end of the pressurized air tank. The pressure-driven injection device directly facing the ignition assembly is filled with ignition modifier, while the remaining pressure-driven injection device is distributed outside the ignition point and filled with modifier particles. Inject 0.6~0.8MPa of driving pressure air into each pressurized air storage tank as the driving air source, and the orifice diameter of the multi-hole nozzle is 1.6~2.0mm.

6. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S5, the working process of the pressure-driven injection device includes: The injection, ignition, and data acquisition are triggered synchronously by a power controller, with the ignition delay time set to 50~320ms; finally, a dynamic signal tester is used to record the explosion overpressure at different locations within the mining pipeline.

7. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S5, the combustion and explosion of the gas mixture is achieved through a multi-stage explosion, including: In the first stage of ignition, the ignition assembly ignites the ignition modifier and the surrounding CH4-O2 mixture, generating an initial shock wave. Secondary reinforcement: The initial shock wave acts on the modifier particles outside the ignition point, triggering a secondary explosion.

8. The shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S6, the process of removing residual substances and discharging exhaust gas includes: firstly, using pressurized air for cleaning to purge residual substances from pipes and chemical reagent tanks; then, discharging exhaust gas and residues through a cleaning module consisting of valves, pipes, and a vacuum pump. The cleaning module includes a return liquid recovery system for separating modifier decomposition products.

9. A shale gas reservoir fracturing method based on in-situ methane explosion according to claim 8, characterized in that, The process of removing residual substances and discharging exhaust gases also includes purging the mining pipeline with compressed air or inert gas to suppress the risk of spontaneous combustion.

10. A shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S5, the combustion and explosion effect parameters of the mixed gas are: explosion overpressure 30~50MPa, explosion velocity 1.2~1.5km / s, and ignition efficiency 80%~90%.

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