A shale gas reservoir fracturing method based on in-situ methane explosion

Abstract

The application provides a shale gas reservoir fracturing method based on in-situ methane explosion, and belongs to the technical field of shale gas exploitation, and comprises the following steps: obtaining particles with specific physical properties by mechanically grinding original modifier crystals to prepare an ignition modifier; injecting oxygen into a shale gas exploitation pipeline, and mixing hydrogen into reservoir methane to form CH4-O2-air mixed gas; arranging multiple groups of high-pressure injection devices in the exploitation pipeline, respectively filling the ignition modifier and the modifier particles, and injecting high-pressure air as a driving gas source; synchronously triggering the high-pressure injection devices to inject materials and igniting the ignition assembly by a power controller, so that the mixed gas is burned and exploded, and explosion parameters are monitored; after the burning and explosion are completed, residual substances in the pipeline are removed, waste gas is discharged, and fracturing operation is completed. The application realizes significant synergistic improvement of explosion overpressure and explosion speed, has the advantages of high efficiency, cleanness, safety, environmental protection and economy, and is suitable for deep and high ground stress reservoir development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of shale gas exploitation, in particular to a shale gas reservoir fracturing method based on in-situ methane explosion. BACKGROUND

[0002] At present, shale gas as a rich unconventional natural gas resource, its development has become an important direction in the global energy field. In the shale gas exploitation technology, hydraulic fracturing technology is the most widely used mainstream means, which can form a fracture network in shale to release natural gas by injecting high-pressure fluid (including water, chemical additives, etc.) into the reservoir. At the same time, to solve the inherent defects of hydraulic fracturing, in-situ methane explosion fracturing technology gradually emerges, which uses the overpressure shock wave generated by the explosion of methane mixed with oxidizing agent in the reservoir to fracture shale, has potential advantages such as no water consumption, can realize multi-stage pulse blasting, and is environmentally friendly, etc., and becomes a new direction of industry research.

[0003] With the increasing demand for the development of deep, high ground stress and low permeability shale reservoirs, the limitations of traditional hydraulic fracturing technology in water resource consumption, environmental pollution and fracture formation effect are increasingly prominent, which promotes the transformation of the industry to waterless fracturing technology. In-situ methane explosion fracturing technology becomes an important research hotspot to replace hydraulic fracturing due to its characteristics of adapting to deep reservoir characteristics and less environmental impact. The research focuses mainly on improving explosion pressure, optimizing ignition efficiency, and improving the performance of combustion improver, etc. For example, by increasing the ignition energy, adding hydrogen or adding solid fuel (such as aluminum powder, potassium permanganate), etc. to enhance the explosion effect to meet the fracturing needs of deep reservoirs.

[0004] Although the in-situ methane explosion fracturing technology has development potential, it still has significant technical bottlenecks: first, the explosion pressure is insufficient, the existing technology can only increase the methane explosion overpressure to 1.78 bar by increasing the ignition energy (from 1 kJ to 10 kJ), which is far from the high pressure (such as 100 MPa) required by deep reservoirs, and further increasing the ignition energy will reduce the safety of the device; second, the ignition efficiency and energy transfer problem, although hydrogen can improve the ignition efficiency, it cannot solve the problem of directional release and homogeneous transmission of explosion energy, resulting in insufficient energy utilization rate; third, the limitations of the improver, although aluminum powder can improve the overpressure, but the explosion speed is limited and it is easy to cause secondary pollution, and potassium permanganate has problems such as unclear explosion mechanism, heavy metal residue (such as manganese) pollution risk, and unclear initiation speed improvement, etc., which makes it difficult to meet the efficient and clean development needs.

[0005] Therefore, there is an urgent need for an in-situ methane explosion fracturing method that can synergistically improve the explosion overpressure and explosion speed, optimize the energy utilization efficiency, and consider environmental friendliness and safety, to break through the technical bottlenecks of the existing technology and provide support for the efficient development of deep shale gas reservoirs. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the purpose of the present application is to provide a shale gas reservoir fracturing method based on in-situ methane explosion, which solves the problems of insufficient explosion pressure, heavy metal pollution and low energy utilization rate in the prior art, and realizes significant synergy of explosion overpressure and explosion speed, has the advantages of high efficiency, cleanliness, safety, environmental protection and economy, and is suitable for deep, high ground stress reservoir development.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following solutions:

[0008] A shale gas reservoir fracturing method based on in-situ methane explosion, comprising the following steps:

[0009] S1, mechanically grinding the original modifier crystals to obtain particles with specific physical properties to avoid reducing the reaction activity due to agglomeration;

[0010] S2, preparing an ignition improver for improving the ignition probability and promoting the methane explosion reaction;

[0011] S3, injecting oxygen into the shale gas extraction pipeline, and mixing hydrogen into the reservoir methane to form CH4-O2-air mixture gas;

[0012] S4, arranging multiple groups of pressure-driven jet devices in the extraction pipeline, wherein one group of pressure-driven jet devices is filled with the ignition improver and directly opposite the ignition assembly, and the remaining groups of pressure-driven jet devices are filled with treated modifier particles and distributed outside the ignition point, and injecting power pressure air as a driving gas source into each device;

[0013] S5, sending a synchronization signal to the electromagnetic valve of the pressure-driven jet device and the ignition assembly through the power controller, so that the pressure-driven jet device sprays the treated modifier particles and the ignition improver into the pipeline and mixes with the mixture gas, and the ignition assembly starts ignition to make the mixture gas explode, and a dynamic signal tester is used to monitor the explosion parameters in the pipeline;

[0014] S6, after the explosion is over, removing the residual substances in the pipeline of each group of pressure-driven jet devices and discharging the exhaust gas, and completing the shale gas reservoir fracturing operation.

[0015] Preferably, in S1, the implementation process of the mechanical grinding treatment comprises: placing the original modifier crystals in a mechanical grinder, grinding at a power of 1600-2000W for 2-4 seconds, to obtain particles with a particle size of not more than 100μm, a specific surface area of 0.1m 2 / g, an adsorption rate RA of less than 50% and an oxygen content of 35%-60%.

[0016] Preferably, in S2, the ignition improver is propylene oxide.

[0017] Preferably, in S3, the forming process of the CH4-O2-air mixture comprises: injecting oxygen into the production pipe to a volume fraction of 10%~15%; mixing hydrogen into the reservoir methane, so that the volume ratio of methane to hydrogen is 4:1~5:1, and the volume fraction of hydrogen is 1.3%~2.6%; and 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.

[0018] Preferably, in S4, the arrangement of the pressure-driven injection device and the injection process of the driving gas source comprise:

[0019] Each group of pressure-driven injection devices is composed of a porous nozzle, a chemical agent tank, an electromagnetic valve, and a pressure air storage tank. The front end of the chemical agent tank is connected to the porous nozzle, and the end is connected to the electromagnetic valve. One end of the electromagnetic valve is connected to the pressure air storage tank, and the other end is connected to the inlet valve.

[0020] The pressure-driven injection devices opposite to the ignition assembly are filled with ignition improver, and the remaining pressure-driven injection devices are distributed outside the ignition point and filled with modified agent particles.

[0021] 0.6~0.8MPa driving pressure air is injected into each pressure air storage tank as a driving gas source, and the aperture of the porous nozzle is 1.6~2.0mm.

[0022] Preferably, in S5, the working process of the pressure-driven injection device comprises:

[0023] The injection, ignition, and data acquisition are synchronously triggered by the power controller, and the ignition delay time is set to 50~320ms. Finally, the dynamic signal tester is used to record the explosion overpressure at different positions in the production pipe.

[0024] Preferably, in S5, the implementation process of the mixture combustion and explosion is multi-stage explosion, which comprises:

[0025] Primary ignition, the ignition assembly ignites the ignition improver and the surrounding CH4-O2 mixture to generate an initial shock wave;

[0026] Secondary enhancement, the initial shock wave acts on the modified agent particles outside the ignition point to trigger a secondary explosion.

[0027] Preferably, in S6, the implementation process of removing residual substances and discharging exhaust gas comprises: first, using the pressure air for cleaning to blow off the residual substances in the pipe and the chemical agent tank, and then discharging the exhaust gas and the residual substances through a cleaning module composed of valves, pipes, and a vacuum pump, wherein the cleaning module includes a flowback fluid recovery system for separating the decomposition products of the modified agent.

[0028] Preferably, the process of removing residual substances and discharging exhaust gas further includes: purging the mining pipeline with pressurized air or inert gas to suppress the risk of spontaneous combustion.

[0029] 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%.

[0030] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0031] (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.

[0032] (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.

[0033] (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

[0034] 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.

[0035] Figure 1 This is a flowchart of a shale gas reservoir fracturing method based on in-situ methane explosion according to the present invention;

[0036] 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.

[0037] Figure 3 Structure diagram of pressure-driven jetting device provided by the present application.

[0038] Legend of reference signs:

[0039] 1, ground station; 2, ground; 3, underground water; 4, overburden; 5, shale reservoir; 6, deep formation; 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 jetting device; 131, air inlet valve; 132, pressure air storage tank; 133, electromagnetic valve; 134, chemical agent tank; 135, porous nozzle. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0041] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0042] As shown in Figure 1 , the present application provides a shale gas reservoir fracturing method based on in-situ methane explosion, comprising the following steps:

[0043] S1, mechanically grinding the original modifier crystals to obtain particles with specific physical properties to avoid reducing the reaction activity due to agglomeration.

[0044] Specifically, the implementation process of the mechanical grinding treatment includes: placing the original modifier crystals in a mechanical grinder, grinding at a power of 1600-2000W for 2-4 seconds to obtain particles with a particle size of not more than 100μm, a specific surface area of 0.1m 2 / g, an adsorption rate RA of less than 50% and an oxygen content of 35%-60%.

[0045] S2, preparing an ignition improver for increasing the ignition probability and promoting the methane explosion reaction.

[0046] Specifically, the ignition improver is propylene oxide, and the amount thereof is 20ml.

[0047] S3, injecting oxygen into the shale gas extraction pipeline, and mixing hydrogen into the reservoir methane to form CH4-O2-air mixed gas.

[0048] Specifically, the forming process of the CH4-O2-air mixture includes: injecting oxygen into the production pipeline to a volume fraction of 10% to 15%; mixing hydrogen into the reservoir methane, so that the volume ratio of methane to hydrogen is 4:1 to 5:1, and the volume fraction of hydrogen is 1.3% to 2.6%; and controlling the volume fraction of CH4 in the mixture to be 10% to 20%, and the equivalent ratio of the CH4-O2 mixture to be 0.6 to 1.25.

[0049] S4, arranging a plurality of groups of pressure-driven jet devices in the production pipeline, wherein one group of pressure-driven jet devices is filled with the ignition improver and faces the ignition assembly, and the remaining groups of pressure-driven jet devices are filled with the treated modified agent particles and distributed outside the ignition point, and power pressure air is injected into each device as a driving gas source.

[0050] Specifically, the arrangement and driving gas source injection process of the pressure-driven jet device includes:

[0051] As shown in Figure 3 Each group of pressure-driven jet devices 13 is composed of an air inlet valve 131, a porous nozzle 135, a chemical agent tank 134, an electromagnetic valve 133, and a pressure air storage tank 132. The front end of the chemical agent tank 134 is connected to the porous nozzle 135, and the end is connected to the electromagnetic valve 133. The electromagnetic valve 133 is connected to one end of the pressure air storage tank 132, and the air inlet valve 131 is connected to the other end of the pressure air storage tank 132 as the air inlet end of the pressure-driven jet device 13.

[0052] The pressure-driven jet device facing the ignition assembly is filled with the ignition improver, and the remaining pressure-driven jet devices are distributed outside the ignition point and filled with modified agent particles.

[0053] 0.6 to 0.8 MPa of power pressure air is injected into each pressure air storage tank 132 as a driving gas source, and the porous nozzle aperture is 1.6 to 2.0 mm.

[0054] S5, sending a synchronization signal to the electromagnetic valve of the pressure-driven jet device and the ignition assembly through the power controller, so that the pressure-driven jet device sprays the treated modified agent particles and the ignition improver into the pipeline to mix with the mixture, and the ignition assembly starts ignition to make the mixture explode, and a dynamic signal tester is used to monitor the explosion parameters in the pipeline.

[0055] Specifically, the working process of the pressure-driven jet device includes:

[0056] The jet, ignition, and data acquisition are triggered synchronously through the power controller, and the ignition delay time is set to 50 to 320 ms; finally, a dynamic signal tester is used to record the explosion overpressure at different positions in the production pipeline.

[0057] Further, the implementation process of the mixed gas explosion is multi-stage explosion, including:

[0058] Primary ignition, the ignition assembly ignites the ignition improver and the surrounding CH4-O2 mixed gas to generate an initial shock wave;

[0059] Secondary reinforcement, the initial shock wave acts on the improved agent particles outside the ignition point to initiate a secondary explosion.

[0060] Further, the implementation process of removing residual substances and discharging waste gas includes: first, using the pressure air for blowing to remove the residual substances in the pipeline and the chemical agent tank, and then discharging the waste gas and the residual substances through a cleaning module composed of a valve, a pipeline and a vacuum pump, wherein the cleaning module includes a flowback fluid recovery system for separating the improved agent decomposition products. In addition, the mining pipeline is also swept by using the pressure air or inert gas for blowing, so as to inhibit the risk of spontaneous combustion.

[0061] The effect parameters of the mixed gas explosion are as follows: explosion overpressure 30-50 MPa, explosion speed 1.2-1.5 km / s, and ignition efficiency 80%-90%.

[0062] S6, after the explosion, the residual substances in the pipeline of each group of pressure-driven jetting devices are removed, and the waste gas is discharged, so as to complete the shale gas reservoir fracturing operation.

[0063] According to the above content, the structure layout for implementing the above method is as shown in the figure. Figure 2 The ground station 1 is located above the ground 2; the underground water 3, the overburden 4, the shale reservoir 5, the deep rock layer 6, the cementing casing 7, the gas inlet pipe 8, the shale gas pipeline 9 and the like penetrate through the underground layers, the chemical ignition port 10, the sealing wall 11, the horizontal branch well 12 and the pressure-driven jetting device 13 are mainly laid in the shale reservoir 5 and the related wellbore structure. Specifically, the ground station 1 is connected with the underground gas inlet pipe 8, the shale gas pipeline 9 and the like through pipelines and the like to realize control and data, material transmission; the gas inlet pipe 8, the shale gas pipeline 9 and the like penetrate into the cementing casing 7 and extend to the shale reservoir 5 area; the chemical ignition port 10, the pressure-driven jetting device 13 and the horizontal branch well 12 are connected; the sealing wall 11 is used to separate the related wellbore space; all the components jointly constitute an underground-ground connection system for the shale gas mining fracturing operation, which cooperates to complete the fracturing operation based on the in-situ methane explosion; the overburden 4, the shale reservoir 5, the deep rock layer 6 and the like serve as geological bearing layers, which are spatially nested with various wellbores, devices and operation associations.

[0064] The above content will be further verified through specific embodiments, and the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0065] Embodiment 1

[0066] The present embodiment is based on Figures 1 to 3 The steps for fracturing the shale gas reservoir are as follows:

[0067] First, the original NaClO3 crystal is placed in a mechanical grinder and ground for 2 seconds at a power of 1600W to obtain particles with a particle size of 22.4μm, a specific surface area of 0.1m 2 / g, and an adsorption rate (RA) of less than 50%. Then, a protective cementing casing 7 is pre-installed in the shale gas well, the methane in the reservoir is released by desorption technology, and 50L of oxygen is injected into the gas pipeline 8 to a volume fraction of 10%, and 80L of methane is injected to a volume fraction of 16% to form a CH4-O2-air mixture, ensuring that the equivalent ratio of the mixture is 1.25.

[0068] Secondly, a chemical ignition port 10 and 17 groups of pressure-driven injection devices 13 are arranged in a 500L shale gas pipeline 9 with a length of 16m and a diameter of 0.2m. Each group of pressure-driven injection devices 13 is composed of a pressure air storage tank 132, an electromagnetic valve 133, a chemical agent tank 134, and a porous nozzle 135 with a pore size of 1.6mm. The first group of pressure-driven injection devices 13 is directly opposite the chemical ignition port 10 and sprays 20mL of propylene oxide as a combustion aid, and the remaining 16 groups of pressure-driven injection devices 13 are evenly distributed at an interval of 0.74m outside the area 5.0m away from the chemical ignition port 10, and are used to spray the prepared NaClO3 modifier particles, so that the loading concentration of NaClO3 modifier particles in the pipeline reaches 0.2g / L.

[0069] An ignition generator is arranged at the front end of the pipeline, and an activation signal is sent to the ignition generator and the pressure-driven injection devices 13 through a power controller, so as to trigger the ignition and injection simultaneously. 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 positions. After the explosion is completed, the residual substances in the chemical agent tank 134 are blown away by using clean-up pressure air, and the waste gas and residues are discharged together with the residues in the pipeline through a cleaning module including valves, pipelines and vacuum pumps. In the present embodiment, an explosion overpressure of up to 33.197MPa is generated in the pipeline, the rising rate is 2.221GPa / s, and the explosion speed is 1.359km / s.

[0070] Example 2

[0071] In this embodiment, the original KMn04crystal is placed in a mechanical grinder and ground for 4 seconds at a power of 1600W to obtain particles with a particle size of 20μm. A protective cementing casing 7 is then pre-installed in the shale gas well, the methane in the reservoir is released by desorption technology, and 50L of oxygen is injected through the air inlet pipe 8 to a volume fraction of 10%, 50L of methane is injected to a volume fraction of 10%, forming a CH4-O2-air mixture, and ensuring that the equivalent ratio of the mixture is 0.75.

[0072] A chemical ignition port 10 and 17 groups of pressure-driven injection devices 13 are arranged in a 500L shale gas pipeline 9 with a length of 16m and a diameter of 0.2m, each group of pressure-driven injection devices 13 consisting of a pressure air storage tank 132, an electromagnetic valve 133, a chemical agent tank 134 and a porous nozzle 135 with a pore size of 1.6mm. The first group of pressure-driven injection devices 13 is directly opposite the chemical ignition port 10, and sprays 40mL of propylene oxide as a combustion improver, and the remaining 16 groups of pressure-driven injection devices 13 are evenly distributed at an interval of 0.74m in the area 5.0m away from the chemical ignition port 10, and are used to spray the prepared KMn04modifier particles, so that the loading concentration of KMn04modifier particles in the pipeline reaches 0.5g / L.

[0073] An ignition generator is arranged at the front end of the pipeline, and an activation signal is sent to the ignition generator and the pressure-driven injection devices 13 through a power controller, so as to trigger ignition and injection synchronously, 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 positions. After the explosion is completed, the residual substances in the chemical agent tank 134 are blown away by using clean-up pressure air, and the waste gas and residues are discharged together with the residues in the pipeline through a cleaning module including valves, pipelines and vacuum pumps. In this embodiment, an explosion overpressure of up to 30.64MPa is generated in the pipeline, the pressure rise rate is 20.78GPa / s, and the explosion speed is 1km / s.

[0074] Example 3

[0075] In this embodiment, the original NaClO4crystal is placed in a mechanical grinder and ground to obtain particles with a particle size of 26.6μm. A protective cementing casing 7 is pre-installed in the shale gas well, the methane in the reservoir is released by desorption technology, and 50L of oxygen is injected through the air inlet pipe 8 to a volume fraction of 10%, 50L of methane is injected to a volume fraction of 10%, forming a CH4-O2-air mixture, and ensuring that the equivalent ratio of the mixture is 0.75.

[0076] A chemical ignition port 10 and 17 sets of pressure-driven injection devices 13 are arranged in a 500L shale gas pipeline 9 with a length of 16m and a diameter of 0.2m, each set of pressure-driven injection devices 13 is composed of a pressure air storage tank 132, a solenoid valve 133, a chemical agent tank 134 and a porous nozzle 135 with a hole diameter of 1.6mm. The first set of pressure-driven injection devices 13 is directly opposite the chemical ignition port 10, and sprays 40mL of propylene oxide as a combustion improver. The remaining 16 sets of pressure-driven injection devices 13 are evenly distributed at an interval of 0.74m in the area 5.0m away from the chemical ignition port 10, and are used to spray prepared NaClO4 modifier particles, so that the loading concentration of NaClO4 modifier particles in the pipeline reaches 0.15g / L.

[0077] An ignition generator is arranged at the front end of the pipeline, and activation signals are sent to the ignition generator and the pressure-driven injection devices 13 through a power controller, so as to trigger ignition and injection synchronously. 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 positions. After the explosion is completed, the residual substances in the chemical agent tank 134 are blown away by using clean-up pressure air, and the waste gas and residues are discharged together with the residues in the pipeline through a cleaning module including valves, pipelines and vacuum pumps. In this embodiment, an explosion overpressure of up to 43.61MPa is generated in the pipeline, the pressure rise rate is 20.78GPa / s, and the explosion speed is 2.91km / s.

[0078] Example 4

[0079] In this embodiment, the original barium nitrate (Ba(NO3)2) crystal is placed in a mechanical grinder and ground at a power of 1600-2000W for 3-5 seconds to obtain barium nitrate particles with a particle size of 65.3μm, a specific surface area of 0.1m 2 / g, an adsorption rate RA less than 50% and an oxygen content of 45%-55%. A protective cementing casing 7 is prearranged in a shale gas well, methane in the reservoir is released by desorption technology, and oxygen and nitrogen are injected through the gas inlet pipe 8 to form a CH4-O2-N2 mixed gas, wherein the volume fraction of CH4 is controlled to be 13%, and the equivalent specific fixed of methane is 1.25; at the same time, hydrogen is added into the methane in the reservoir, so that the volume ratio of methane to hydrogen is 4:1-5:1, and the volume fraction of hydrogen is 1.3%-2.6%.

[0080] A chemical ignition port 10 and 17 groups of pressure-driven injection devices 13 are arranged in a 500L shale gas pipeline 9 with a length of 16m and a diameter of 0.2m, each group of pressure-driven injection devices 13 is composed of a pressure air storage tank 132, a solenoid valve 133, a chemical agent tank 134 and a porous nozzle 135 with a hole diameter of 1.6mm. The first group of pressure-driven injection devices 13 is directly opposite the chemical ignition port 10, and sprays 40mL of propylene oxide as a combustion improver, and the remaining 16 groups of pressure-driven injection devices 13 are evenly distributed at an interval of 0.74m in the area 5.0m away from the chemical ignition port 10, and are used to spray prepared Ba(NO3)2 modifier particles, so that the total loading amount of Ba(NO3)2 modifier particles in the pipeline is 100g.

[0081] An ignition generator is arranged at the front end of the pipeline, and activation signals are sent to the ignition generator and the pressure-driven injection devices 13 through a power controller, so as to synchronously trigger 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 positions. After the explosion is completed, the residual substances in the chemical agent tank 134 are blown away by using clean-up pressure air, and the waste gas and residues are discharged together with the residues in the pipeline through a cleaning module including valves, pipelines and vacuum pumps. In this embodiment, an explosion overpressure of up to 22.52MPa is generated in the pipeline, and the average pressure rise rate is 2.104GPa / s.

[0082] Compared with pure methane explosion under the same conditions, the overpressure rise rate of examples 1-4 is 2069%, and the explosion velocity rise rate is 302%, which further proves that the method provided by the present application can greatly improve the reservoir fracturing effect.

[0083] Therefore, by using the above-mentioned shale gas reservoir fracturing method based on in-situ methane explosion, the problems of insufficient explosion pressure, heavy metal pollution and low energy utilization rate in the prior art are solved, and the explosion overpressure and explosion velocity are significantly improved in a coordinated manner, which has the advantages of high efficiency, cleanliness, safety, environmental protection and economy, and is suitable for deep and high geostress reservoir development.

[0084] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0085] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method of the present application and its core idea; meanwhile, for the general technical personnel in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application. In conclusion, the content of the present specification should not be understood as the limitation of the present application.

Claims

1. A method for fracturing a shale gas reservoir based on in-situ methane explosion, characterized in that, The method comprises the following steps: S1, placing the original modifier crystal into a mechanical grinder, grinding for 2-4 seconds under 1600-2000W power, obtaining a particle with a particle size of no more than 100μm, a specific surface area of 0.1m 2 / g, an adsorption rate RA of less than 50% and an oxygen content of 35%-60% to avoid reducing the reaction activity due to agglomeration, wherein the original modifier crystal is an original NaClO3 crystal or an original KMnO4 crystal or an original NaClO4 crystal or an original Ba(NO3)2 crystal; S2, preparing an ignition improver for improving ignition probability and promoting methane explosion reaction, wherein the ignition improver is propylene oxide; S3, injecting oxygen into a shale gas exploitation pipeline while mixing hydrogen into reservoir methane to form CH4-O2-air mixed gas, wherein the formation process of the CH4-O2-air mixed gas comprises the following steps: injecting oxygen into the exploitation pipeline to a volume fraction of 10-15%; mixing hydrogen into the reservoir methane, so that the volume ratio of methane to hydrogen is 4:1-5:1, and the volume fraction of hydrogen is 1.3-2.6%; and controlling the volume fraction of CH4 in the mixed gas to be 10-20% and the equivalent ratio of CH4-O2 mixed gas to be 0.6-1.25; S4, arranging multiple groups of pressure-driven jet devices in the exploitation pipeline, wherein one group of pressure-driven jet devices is filled with the ignition improver and faces the ignition assembly, and the remaining groups of pressure-driven jet devices are filled with treated modified agent particles and are distributed outside the ignition point, and power pressure air is injected into each device as a driving gas source; S5, sending a synchronous signal to the electromagnetic valve of the pressure-driven jet device and the ignition assembly through a power controller, so that the pressure-driven jet device sprays the treated modified agent particles and the ignition improver into the pipeline to mix with the mixed gas, and the ignition assembly starts ignition to make the mixed gas explode, and a dynamic signal tester is used to monitor explosion parameters in the pipeline; S6, after the explosion, removing residual substances in the pipeline of each group of pressure-driven jet devices and discharging waste gas, and completing the shale gas reservoir fracturing operation.

2. A shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S4, the arrangement and driving gas source injection process of the pressure-driven jet device comprise the following steps: Each group of pressure-driven jet devices is composed of a porous nozzle, a chemical agent tank, an electromagnetic valve and a pressure air storage tank, the front end of the chemical agent tank is connected with the porous nozzle, the tail end is connected with the electromagnetic valve, one end connected with the electromagnetic valve is connected with the pressure air storage tank, and the other end connected with the pressure air storage tank is connected with an air inlet valve; The pressure-driven jet device facing the ignition assembly is filled with the ignition improver, and the remaining pressure-driven jet devices are distributed outside the ignition point and are filled with modified agent particles; 0.6-0.8 MPa driving pressure air is injected into each pressure air storage tank as a driving gas source, and the aperture of the porous nozzle is 1.6-2.0 mm.

3. A 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 jet device comprises the following steps: The jetting, ignition and data acquisition are synchronously triggered through the power controller, the ignition delay time is set to 50-320 ms, and finally the dynamic signal tester is used to record explosion overpressure at different positions in the exploitation pipeline.

4. A shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S5, the realization process of the mixed gas explosion is multi-stage explosion, which comprises the following steps: Primary ignition, the ignition assembly ignites the ignition improver and the surrounding CH4-O2 mixed gas to generate an initial shock wave; Secondary strengthening, the initial shock wave acts on the modified agent particles outside the ignition point to cause secondary explosion.

5. A shale gas reservoir fracturing method based on in-situ methane explosion according to claim 1, characterized in that, In S6, the residual material removal and exhaust gas discharge process includes: firstly, using the pressure air to blow the residual material in the pipeline and the chemical agent tank, and then discharging the exhaust gas and residual material through the cleaning module composed of valves, pipelines and vacuum pumps, wherein the cleaning module includes a flowback fluid recovery system for separating the amendment decomposition products.

6. A shale gas reservoir fracturing method based on in-situ methane explosion according to claim 5, characterized in that, The residual material removal and exhaust gas discharge process also includes: using the pressure air or inert gas to blow the mining pipeline to inhibit the risk of spontaneous combustion.

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

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