A method for enhancing in-situ combustion fracturing of methane

Abstract

A method for strengthening methane in-situ combustion fracturing, liquid carbon dioxide is pressurized and heated to form supercritical carbon dioxide, which is then sent into the fracturing channel to form a complex fracture network around the fracturing channel; mixed fracturing fluid formed by mixing supercritical carbon dioxide and fly ash is injected into the well bottom; combustion-supporting agent is injected into the wellbore and mixed with the mixed fracturing fluid at the well bottom to enter the complex fracture network together, so that a multiphase mixed fluid is formed in the complex fracture network; the annulus valve is closed to promote mineralization reaction of supercritical carbon dioxide and fly ash under the temperature and pressure conditions of the reservoir, and to form high-strength minerals; the mineralization reaction is used to promote the desorption of methane in the reservoir and into the complex fracture network, so that methane-combustion-supporting agent mixed gas is formed in the complex fracture network; the combustion process is used to promote the dust cloud formed by the mixing of fly ash and gas in the complex fracture network, to strengthen the effect of methane in-situ combustion; and the fracturing reconstruction of all layers is completed. The fracturing effect of the method is ideal.

Description

A method for enhancing in-situ combustion and detonation fracturing of methane Technical Field

[0001] This invention belongs to the field of unconventional oil and gas reservoir production enhancement and coal-based solid waste utilization technology, specifically a method for enhancing in-situ combustion and fracturing of methane. Background Technology

[0002] Natural gas, as a clean energy source, is expected to become an important alternative to coal in the future. However, its low reservoir permeability leads to low extraction efficiency, necessitating fracturing followed by proppant injection to support the fractures and prevent them from closing due to stress release. To improve the fracturing effect of unconventional natural gas reservoirs, some researchers have proposed using in-situ methane combustion to fracture the formation, thereby creating a complex three-dimensional fracture network. This technology uses reservoir methane as fuel, creating a methane-proppant mixture at the bottom of the well or within the reservoir by introducing an oxidizer on the surface. The methane combustion generates instantaneous high pressure at the bottom of the well, fracturing the reservoir and forming impact fractures. Because in-situ methane combustion creates numerous shear fractures, which are narrow and complex in shape, they are prone to closure. Therefore, improving the fracturing effect of in-situ methane combustion and preventing fracture closure after fracturing is a key challenge that this technology needs to address. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for enhancing in-situ combustion and explosion fracturing of methane. This method has simple implementation steps, low implementation cost, and improved permeability and production. While completing reservoir fracturing and transformation, it can effectively dispose of wastes such as fly ash and carbon dioxide. It has many advantages such as low carbon, environmental protection and waste utilization, and is conducive to the formation of an integrated technology of coal-based solid waste treatment, carbon dioxide mineralization and storage, and reservoir fracturing and production enhancement.

[0004] To achieve the above objectives, the present invention provides a method for enhancing in-situ combustion and explosion fracturing of methane, specifically comprising the following steps:

[0005] Step 1: Install ground equipment and fracturing devices;

[0006] S11: Install the fly ash storage tank, liquid carbon dioxide storage tank, combustion aid storage tank, fracturing truck and mixing system in sequence on the ground, and connect the output end of the liquid carbon dioxide storage tank to the input end of the fracturing truck, connect the input end of the mixing system to the output end of the fracturing truck and the output end of the fly ash storage tank respectively, connect the output end of the mixing system to the input end of the high-pressure oil pipe, connect the output end of the combustion aid storage tank to the annulus inlet between the wellbore and the high-pressure oil pipe, and connect the fracturing device to the output end of the high-pressure oil pipe;

[0007] S12: The fracturing device is lowered to the target formation by lowering the high-pressure tubing;

[0008] Step 2: Reservoir fracturing and fracture creation;

[0009] S21: Inject the liquid carbon dioxide from the liquid carbon dioxide storage tank into the fracturing truck, pressurize the liquid carbon dioxide using the fracturing truck, and heat the liquid carbon dioxide using the heating device in the fracturing truck. When the pressure and temperature of the liquid carbon dioxide reach the supercritical state, supercritical carbon dioxide is formed.

[0010] S22: Supercritical carbon dioxide is delivered to the fracturing device downhole through a high-pressure tubing and then injected into the fracturing channel in the reservoir that is connected to the wellbore through the fracturing device.

[0011] S23: Continuous supercritical carbon dioxide pumping causes the pressure in the fracturing channel to rise continuously until it exceeds the fracturing pressure of the reservoir, forming a complex network of fractures around the fracturing channel.

[0012] Step 3: Add combustion aid and fly ash;

[0013] S31: After pumping supercritical carbon dioxide into the reservoir for a period of time, fly ash is injected into the mixing system. The mixing system is used to fully mix the supercritical carbon dioxide and fly ash that have entered the system to form a mixed fracturing fluid.

[0014] S32: The fracturing truck pumps the mixed fracturing fluid from the mixing system into the high-pressure tubing and outputs it through the fracturing device; at the same time, the combustion aid in the combustion aid storage tank is injected into the wellbore through the annulus, so that the injected combustion aid reaches the bottom of the well and is further mixed with the mixed fracturing fluid at the bottom of the well before entering the complex fracture network together, so that a multiphase mixed fluid of supercritical carbon dioxide, combustion aid and fly ash is formed in the complex fracture network;

[0015] Step 4: Mineralization reaction of fly ash with supercritical carbon dioxide;

[0016] After the combustion aid and fly ash have been added, the annulus valve at the fracturing truck and the annulus inlet is closed to promote the mineralization reaction between supercritical carbon dioxide and fly ash under the high temperature and high pressure conditions of the reservoir. This causes some of the supercritical carbon dioxide and fly ash to form high-strength minerals. The high-strength minerals increase the bonding strength between fly ash particles and further improve the support effect of fly ash on complex fracture networks.

[0017] Step 5: In-situ combustion and detonation fracturing of methane;

[0018] S51: Utilizing the characteristic of supercritical carbon dioxide and fly ash undergoing mineralization reaction and consuming gas, the gas volume in the complex fracture network is reduced, and the pressure of the fluid in the complex fracture network is further reduced, so that the gas pressure in the complex fracture network is lower than the reservoir pressure, and a pressure difference is formed between the reservoir and the complex fracture network.

[0019] S52: Utilize pressure difference to promote the desorption of methane in the reservoir and its entry into the complex fracture network, thereby increasing the methane content within the complex fracture network; as methane continues to desorb, the methane content within the complex fracture network continuously increases, thus forming a methane-fuel mixture.

[0020] During this process, the methane content at the bottom of the well is monitored by sensors inside the fracturing unit;

[0021] S53: When the methane content at the bottom of the well reaches the conditions for combustion and explosion, the methane-combustion oxidizer mixture is ignited and detonated; the combustion and explosion process of the methane-combustion oxidizer mixture causes the fly ash to mix with the gas in the confined space where the complex fracture network is located to form a dust cloud, further enhancing the in-situ combustion and explosion effect of methane, and promoting the further extension and expansion of the complex fracture network to form a three-dimensional network of cracks.

[0022] At the same time, the high temperature and pressure generated by the in-situ combustion of methane promotes the further mineralization reaction between fly ash and supercritical carbon dioxide, generating a large amount of carbonate minerals, which further increases the support effect on the three-dimensional network cracks.

[0023] Step Six: Complete the fracturing and modification of all sections;

[0024] After the fracturing of the first reservoir is completed, move the fracturing device to the next segment and repeat steps two to five until the fracturing of all segments is completed.

[0025] Furthermore, to ensure safety during the construction process, the high-pressure oil pipe in step one must be able to withstand a pressure of at least 60 MPa.

[0026] Furthermore, to ensure the fracturing effect, the final heating temperature of the supercritical carbon dioxide in step two is greater than 40 °C, and the initial injection pressure is greater than 60 MPa.

[0027] Furthermore, in order to ensure that the fly ash can penetrate deep into the complex mesh and to enable a more complete mineralization reaction with supercritical carbon dioxide in the subsequent process, the maximum particle size of the fly ash in step three is 0.3 mm.

[0028] Furthermore, in order to improve the combustion and explosion effect of methane and the pressure generated, in step three, the combustion accelerant is oxygen.

[0029] Furthermore, in order to obtain better combustion and explosion effects in the future, in step three, the amount of supercritical carbon dioxide injected is 50% to 60% of the amount of combustion accelerant injected.

[0030] Furthermore, in order to obtain better combustion and explosion effects, and at the same time, more ideal support effects, in step three, the volume fraction of fly ash in supercritical carbon dioxide is 7%~10%.

[0031] Furthermore, in order to achieve better combustion and explosion effects, in step five, ignition is performed when the methane gas concentration is 20% to 60%.

[0032] Furthermore, for ease of operation, electronic ignition is used in step five for ignition.

[0033] In this invention, the method first uses supercritical carbon dioxide to create a complex fracture network through fracturing. Then, supercritical carbon dioxide carrying fly ash is injected into the fracturing channels of an unconventional natural gas reservoir through a high-pressure tubing. Simultaneously, a combustion accelerant is injected into the fracturing channels through the wellbore annulus to generate the complex fracture network. This complex fracture network is filled with a multiphase mixture of supercritical carbon dioxide, combustion accelerant, and fly ash. Next, the high temperature and pressure conditions of the reservoir induce a mineralization reaction between the injected carbon dioxide and fly ash, generating carbonate minerals. Since the strength of the fly ash particles increases after the mineralization reaction, the resulting high-strength minerals can serve as a proppant with better load-bearing capacity. Furthermore, the mineralization reaction consumes the supercritical carbon dioxide within the complex fracture network. This process also achieves the sequestration of supercritical carbon dioxide mineralization. Furthermore, the consumption of supercritical carbon dioxide within the complex fracture network leads to a decrease in gas pressure within the network, thereby increasing the pressure difference between the reservoir and the network. This pressure difference effectively promotes methane desorption. In addition, excess carbon dioxide can displace adsorbed methane, further increasing methane release. After the carbon dioxide mineralization reaction and methane desorption, a methane-oxidizer mixture forms within the complex fracture network. When the mixture reaches the conditions for combustion and explosion, the methane within the network undergoes in-situ combustion and explosion by igniting the methane-oxidizer. This effectively shatters the reservoir surrounding the fractures, further promoting the expansion of the complex fracture network and significantly increasing fracture complexity, thus greatly improving permeability and production. Due to the injection of fly ash, the combustion and explosion of the methane-oxidizer mixture causes the fly ash to mix with the gas in the confined space of the complex fracture network, forming a dust cloud, which further enhances the in-situ combustion and explosion fracturing effect of methane. The high-temperature environment generated by in-situ methane combustion further promotes the mineralization reaction between fly ash and supercritical carbon dioxide, improving the supercritical carbon dioxide sequestration effect. Simultaneously, it generates a large amount of carbonate minerals, which can significantly increase the support effect on the three-dimensional fracture network. Furthermore, the high-strength carbonate minerals generated by the mineralization reaction of fly ash and supercritical carbon dioxide can improve the cementing strength of fly ash, thereby significantly enhancing the support effect of complex fracture networks and improving methane extraction efficiency. This method is simple to implement, low in cost, and highly effective in increasing permeability and production. Compared to conventional hydraulic fracturing, it not only avoids the large consumption of water resources during fracturing but also effectively disposes of waste such as fly ash and carbon dioxide while completing reservoir fracturing and stimulation. It also achieves highly efficient production enhancement operations in unconventional natural gas reservoirs, possessing numerous advantages such as low carbon footprint, environmental friendliness, and waste utilization. This is conducive to the formation of an integrated technology encompassing coal-based solid waste treatment, carbon dioxide mineralization and sequestration, and reservoir fracturing for enhanced production. Attached Figure Description

[0034] Figure 1 is a schematic diagram of the state of supercritical carbon dioxide fracturing in this invention.

[0035] Figure 2 is a schematic diagram showing the state of the combustion aid and fly ash in this invention.

[0036] Figure 3 is a schematic diagram of the mineralization reaction between fly ash and supercritical carbon dioxide in this invention.

[0037] Figure 4 is a schematic diagram of the state of methane-combustion accelerant mixed gas formed in the complex stitched mesh of the present invention;

[0038] Figure 5 is a schematic diagram of the combustion and explosion fracturing state of the methane-fuel mixture in this invention;

[0039] Figure 6 is a schematic diagram showing the state of fracturing modification of all segments in this invention.

[0040] In the diagram: 1. Fly ash, 2. Mixing system, 3. Liquid carbon dioxide, 4. Fracturing truck, 5. Mixed fracturing fluid, 6. High-pressure tubing, 7. Wellbore, 8. Reservoir, 9. Fracturing device, 10. Fracturing channel, 11. Annulus, 12. Combustion accelerator, 13. Annulus valve, 14. Complex fracture network, 15. High-strength mineral, 16. Methane-combustion accelerator mixed gas, 17. Three-dimensional network fracture, 18. Fly ash storage tank, 19. Liquid carbon dioxide storage tank, 20. Combustion accelerator storage tank, 21. Supercritical carbon dioxide. Detailed Implementation

[0041] The invention will now be further described with reference to the accompanying drawings.

[0042] This invention provides a method for enhancing in-situ combustion and explosion fracturing of methane. The method first creates fractures using supercritical carbon dioxide. Then, supercritical carbon dioxide carrying fly ash is injected into the fracturing channels of an unconventional natural gas reservoir through a high-pressure tubing. Simultaneously, a combustion accelerant is injected into the fracturing channels through the wellbore annulus, thereby filling the complex fracture network with a multiphase mixture of supercritical carbon dioxide, combustion accelerant, and fly ash. Next, the reservoir's temperature and pressure conditions promote a mineralization reaction between carbon dioxide and fly ash, forming carbonate minerals. The strength of the fly ash particles increases after the mineralization reaction, forming high-strength minerals with better support strength. Furthermore, the mineralization reaction consumes supercritical carbon dioxide within the fractures, leading to a decrease in gas pressure and promoting methane desorption. In addition, excess carbon dioxide can replace adsorbed methane, further increasing the amount of methane released. After the carbon dioxide mineralization reaction and methane desorption, a methane-fuel mixture is formed in the fracture. When the mixture reaches the conditions for combustion and explosion, it is ignited to carry out combustion and explosion fracturing, breaking up the reservoir around the fracture, further increasing the complexity of the fracture, and significantly improving the permeability and production enhancement effect. Specifically, it includes the following steps:

[0043] Step 1: Install ground equipment and fracturing devices;

[0044] As shown in Figure 1, before construction, ground equipment and fracturing device 9 need to be installed; the ground equipment includes fly ash storage tank 18, liquid carbon dioxide storage tank 19, combustion aid storage tank 20, fracturing truck 4 and mixing system 2.

[0045] S11: Install the fly ash storage tank 18, liquid carbon dioxide storage tank 19, combustion aid storage tank 20, fracturing truck 4 and mixing system 2 in sequence on the ground, and connect the output end of the liquid carbon dioxide storage tank 19 to the input end of the fracturing truck 4, connect the input end of the mixing system 2 to the output end of the fracturing truck 4 and the output end of the fly ash storage tank 18 respectively, connect the output end of the mixing system 2 to the input end of the high-pressure oil pipe 6, connect the output end of the combustion aid storage tank 20 to the annular inlet between the wellbore 7 and the high-pressure oil pipe 6, and connect the fracturing device 9 to the output end of the high-pressure oil pipe 6.

[0046] S12: The fracturing device 9 is lowered to the target formation by lowering the high-pressure oil pipe 6;

[0047] Step 2: Reservoir fracturing and fracture creation;

[0048] S21: As shown in Figure 1, after the ground equipment and fracturing device 9 are installed, the liquid carbon dioxide 3 in the liquid carbon dioxide storage tank 19 is injected into the fracturing truck 4. The fracturing truck 4 pressurizes the liquid carbon dioxide 3 and heats the liquid carbon dioxide 3 using the heating device in the fracturing truck 4. When the pressure and temperature of the liquid carbon dioxide 3 reach the supercritical state, supercritical carbon dioxide 21 is formed.

[0049] S22: Supercritical carbon dioxide 21 is sent into the downhole fracturing device 9 through the high-pressure tubing 6, and then injected into the fracturing channel 10 in the reservoir 8 that is connected to the wellbore 7 through the fracturing device 9.

[0050] S23: Continuous pumping of supercritical carbon dioxide 21. As supercritical carbon dioxide 21 is continuously pumped in, the pressure in the fracturing channel 10 increases continuously until it exceeds the fracturing pressure of the reservoir 8, forming a complex fracture network 14 around the fracturing channel 10.

[0051] Step 3: Add combustion aid and fly ash;

[0052] S31: As shown in Figure 2, after pumping supercritical carbon dioxide 21 into reservoir 8 for a period of time, fly ash 1 is injected into mixing system 2. The mixing system 2 is used to fully mix the supercritical carbon dioxide 21 and fly ash 1 that have entered it to form mixed fracturing fluid 5.

[0053] S32: The fracturing truck 4 pumps the mixed fracturing fluid 5 from the mixing system 2 into the high-pressure tubing 6, and outputs it through the fracturing device 9; at the same time, the combustion accelerator 12 in the combustion accelerator storage tank 20 is injected into the wellbore 7 through the annulus 11, so that the injected combustion accelerator 12 reaches the bottom of the well and is further mixed with the mixed fracturing fluid 5 at the bottom of the well before entering the complex fracture network 14 together, so that a multiphase mixed fluid of supercritical carbon dioxide 21, combustion accelerator 12 and fly ash 1 is formed in the complex fracture network 14;

[0054] Step 4: Mineralization reaction of fly ash with supercritical carbon dioxide;

[0055] As shown in Figure 3, after the combustion aid 12 and fly ash 1 are added, the annular valve 13 at the fracturing truck 4 and the annular inlet is closed, which promotes the mineralization reaction between supercritical carbon dioxide 21 and fly ash 1 under the high temperature and high pressure conditions of the reservoir. As the mineralization reaction between fly ash 1 and supercritical carbon dioxide 21 proceeds, a portion of supercritical carbon dioxide 21 and fly ash 1 form high-strength mineral 15. This high-strength mineral 15 is mainly carbonate mineral, thus achieving the preservation of supercritical carbon dioxide 21 mineralization while obtaining a high-strength proppant. The formed high-strength mineral 15 is beneficial to increasing the bonding strength between fly ash 1 and can further improve the support effect of fly ash 1 on the complex fracture network 14.

[0056] Step 5: In-situ combustion and detonation fracturing of methane;

[0057] S51: Utilizing the characteristic of supercritical carbon dioxide 21 and fly ash 1 undergoing a mineralization reaction that consumes gas, the gas volume within the complex fracture network 14 is reduced, and the pressure of the fluid within the complex fracture network 14 is further reduced, so that the gas pressure in the complex fracture network 14 is lower than the pressure in the reservoir 8, and a pressure difference is formed between the reservoir 8 and the complex fracture network 14.

[0058] S52: The pressure difference is used to promote the desorption of methane in reservoir 8 and its entry into complex fracture network 14, so as to increase the methane content in complex fracture network 14. As shown in Figure 4, as methane is continuously desorbed, the methane content in complex fracture network 14 increases continuously, thereby forming a methane-fuel mixture 16. At the same time, the excess supercritical carbon dioxide (21) can also replace the methane adsorbed by reservoir (8), further increasing the amount of methane released.

[0059] During this process, the methane content at the bottom of the well is monitored by sensors inside the fracturing unit 9;

[0060] S53: When the methane content at the bottom of the well reaches the conditions for combustion and explosion, the methane-combustion oxidizer mixture 16 is ignited and detonated; as shown in Figure 5, the combustion and explosion process of the methane-combustion oxidizer mixture 16 is used to cause the fly ash 1 to mix with the gas in the confined space where the complex fracture network 14 is located to form a dust cloud, further enhancing the in-situ combustion and explosion effect of methane, and promoting the further extension and expansion of the complex fracture network 14 to form a three-dimensional network crack 17;

[0061] At the same time, the high temperature and high pressure generated by the in-situ combustion of methane promotes the further mineralization reaction between fly ash 1 and supercritical carbon dioxide 21, and generates a large amount of carbonate minerals, which further increases the support effect on the three-dimensional network crack 17.

[0062] Step Six: Complete the fracturing and modification of all sections;

[0063] As shown in Figure 6, after the fracturing of the first reservoir is completed, the fracturing device 9 is moved to the next segment, and steps two to five are repeated until the fracturing of all segments is completed.

[0064] To ensure safety during construction operations, the high-pressure oil pipe 6 in step one must be able to withstand a pressure of at least 60 MPa.

[0065] To ensure the fracturing effect, the final heating temperature of the supercritical carbon dioxide 21 in step two is greater than 40 ℃, and the initial injection pressure is greater than 60 MPa.

[0066] To ensure that fly ash can penetrate deep into the complex mesh and to allow for a more complete mineralization reaction with supercritical carbon dioxide, the maximum particle size of fly ash 1 in step three is 0.3 mm.

[0067] In order to improve the combustion effect and the pressure generated by methane, in step three, the combustion accelerant 12 is oxygen.

[0068] In order to achieve better combustion and explosion effects in the future, in step three, the amount of supercritical carbon dioxide 21 injected is 50% to 60% of the amount of combustion accelerant 12 injected.

[0069] In order to achieve better combustion and explosion effects, and at the same time, to achieve more ideal support effects, in step three, the volume fraction of fly ash 1 in supercritical carbon dioxide 21 is 7%~10%.

[0070] In order to achieve better combustion and explosion effects, in step five, ignition is performed when the methane gas concentration is 20% to 60%.

[0071] For ease of operation, electronic ignition is used in step five.

[0072] In this invention, the method first uses supercritical carbon dioxide to create a complex fracture network through fracturing. Then, supercritical carbon dioxide carrying fly ash is injected into the fracturing channels of an unconventional natural gas reservoir through a high-pressure tubing. Simultaneously, a combustion accelerant is injected into the fracturing channels through the wellbore annulus to generate the complex fracture network. This complex fracture network is filled with a multiphase mixture of supercritical carbon dioxide, combustion accelerant, and fly ash. Next, the high temperature and pressure conditions of the reservoir induce a mineralization reaction between the injected carbon dioxide and fly ash, generating carbonate minerals. Since the strength of the fly ash particles increases after the mineralization reaction, the resulting high-strength minerals can serve as a proppant with better load-bearing capacity. Furthermore, the mineralization reaction consumes the supercritical carbon dioxide within the complex fracture network. This process also achieves the sequestration of supercritical carbon dioxide mineralization. Furthermore, the consumption of supercritical carbon dioxide within the complex fracture network leads to a decrease in gas pressure within the network, thereby increasing the pressure difference between the reservoir and the network. This pressure difference effectively promotes methane desorption. In addition, excess carbon dioxide can displace adsorbed methane, further increasing methane release. After the carbon dioxide mineralization reaction and methane desorption, a methane-oxidizer mixture forms within the complex fracture network. When the mixture reaches the conditions for combustion and explosion, the methane within the network undergoes in-situ combustion and explosion by igniting the methane-oxidizer. This effectively shatters the reservoir surrounding the fractures, further promoting the expansion of the complex fracture network and significantly increasing fracture complexity, thus greatly improving permeability and production. Due to the injection of fly ash, the combustion and explosion of the methane-oxidizer mixture causes the fly ash to mix with the gas in the confined space of the complex fracture network, forming a dust cloud, which further enhances the in-situ combustion and explosion fracturing effect of methane. The high-temperature environment generated by in-situ methane combustion further promotes the mineralization reaction between fly ash and supercritical carbon dioxide, improving the supercritical carbon dioxide sequestration effect. Simultaneously, it generates a large amount of carbonate minerals, which can significantly increase the support effect on the three-dimensional fracture network. Furthermore, the high-strength carbonate minerals generated by the mineralization reaction of fly ash and supercritical carbon dioxide can improve the cementing strength of fly ash, thereby significantly enhancing the support effect of complex fracture networks and improving methane extraction efficiency. This method is simple to implement, low in cost, and highly effective in increasing permeability and production. Compared to conventional hydraulic fracturing, it not only avoids the large consumption of water resources during fracturing but also effectively disposes of waste such as fly ash and carbon dioxide while completing reservoir fracturing and stimulation. It has many advantages such as low carbon footprint, environmental friendliness, and waste utilization. At the same time, it achieves efficient production enhancement operations in unconventional natural gas reservoirs, facilitating the formation of an integrated technology of coal-based solid waste treatment, carbon dioxide mineralization and sequestration, and reservoir fracturing for enhanced production.

Claims

1. A method for enhancing in-situ combustion and detonation fracturing of methane, characterized in that, Specifically, the following steps are included: Step 1: Install ground equipment and fracturing device; S11: Install the fly ash storage tank (18), liquid carbon dioxide storage tank (19), combustion aid storage tank (20), fracturing truck (4) and mixing system (2) in sequence on the ground, and connect the output end of the liquid carbon dioxide storage tank (19) to the input end of the fracturing truck (4), connect the input end of the mixing system (2) to the output end of the fracturing truck (4) and the output end of the fly ash storage tank (18) respectively, connect the output end of the mixing system (2) to the input end of the high-pressure oil pipe (6), connect the output end of the combustion aid storage tank (20) to the annular inlet between the wellbore (7) and the high-pressure oil pipe (6), and connect the fracturing device (9) to the ground. Connect to the output end of the high-pressure tubing (6); S12: Lower the fracturing device (9) to the target formation by lowering the high-pressure tubing (6); Step 2: Fracturing the reservoir; S21: Inject the liquid carbon dioxide (3) in the liquid carbon dioxide storage tank (19) into the fracturing truck (4), pressurize the liquid carbon dioxide (3) using the fracturing truck (4), and heat the liquid carbon dioxide (3) using the heating device in the fracturing truck (4). When the pressure and temperature of the liquid carbon dioxide (3) reach the supercritical state, supercritical carbon dioxide (21) is formed; S22: Send the supercritical carbon dioxide (21) into the fracturing device downhole through the high-pressure tubing (6). (9), and injected into the fracturing channel (10) connected to the wellbore (7) in the reservoir (8) through the fracturing device (9); S23: The continuous pumping of supercritical carbon dioxide (21) causes the pressure in the fracturing channel (10) to rise continuously until it exceeds the fracturing pressure of the reservoir (8), forming a complex fracture network (14) around the fracturing channel (10); Step 3: Add combustion aid and fly ash; S31: After pumping supercritical carbon dioxide (21) into the reservoir (8) for a period of time, start injecting fly ash (1) into the mixing system (2), and use the mixing system (2) to fully mix the supercritical carbon dioxide (21) and fly ash (1) that have entered it. Forming a mixed fracturing fluid (5); S32: Using a fracturing truck (4), the mixed fracturing fluid (5) in the mixing system (2) is pumped into the high-pressure tubing (6) and output through the fracturing device (9); At the same time, the combustion aid (12) in the combustion aid storage tank (20) is injected into the wellbore (7) through the annulus (11), so that the injected combustion aid (12) reaches the bottom of the well and is further mixed with the mixed fracturing fluid (5) at the bottom of the well and enters the complex fracture network (14) together, so that a multiphase mixed fluid of supercritical carbon dioxide (21), combustion aid (12) and fly ash (1) is formed in the complex fracture network (14); Step 4: mineralization reaction of fly ash and supercritical carbon dioxide;After the combustion aid (12) and fly ash (1) are added, the annular valve (13) at the fracturing truck (4) and the annular inlet is closed, so that the supercritical carbon dioxide (21) and fly ash (1) undergo a mineralization reaction under the high temperature and high pressure conditions of the reservoir, so that some of the supercritical carbon dioxide (21) and fly ash (1) form high-strength minerals (15). The high-strength minerals (15) increase the bonding strength between fly ash (1) and further improve the support effect of fly ash (1) on the complex fracture network (14); Step 5: Methane in-situ combustion and explosion S51: Utilizing the characteristic of supercritical carbon dioxide (21) and fly ash (1) undergoing mineralization reaction and consuming gas, the gas volume within the complex fracture network (14) is reduced, and the pressure of the fluid within the complex fracture network (14) is further reduced, so that the gas pressure in the complex fracture network (14) is lower than the pressure in the reservoir (8), and a pressure difference is formed between the reservoir (8) and the complex fracture network (14); S52: Utilizing the pressure difference to promote the desorption of methane in the reservoir (8) and its entry into the complex fracture network (14), thereby increasing the methane content within the complex fracture network (14); As methane continuously... The desorption of methane causes the methane content in the complex fracture network (14) to increase continuously, thereby forming a methane-combustion oxidizer mixture (16). During this process, the methane content at the bottom of the well is monitored by a sensor in the fracturing device (9). S53: When the methane content at the bottom of the well reaches the combustion and explosion conditions, the methane-combustion oxidizer mixture (16) is ignited and detonated. The combustion and explosion process of the methane-combustion oxidizer mixture (16) causes the fly ash (1) to mix with the gas in the confined space where the complex fracture network (14) is located to form a dust cloud, further enhancing the in-situ combustion and explosion effect of methane. This promotes the further extension and expansion of the complex fracture network (14), forming a three-dimensional network fracture (17); simultaneously, the high temperature and pressure generated by the in-situ combustion of methane promotes the further mineralization reaction between fly ash (1) and supercritical carbon dioxide (21), generating a large amount of carbonate minerals, further increasing the support effect on the three-dimensional network fracture (17); Step 6: Complete the fracturing transformation of all sections; after the fracturing transformation of the first section of the reservoir is completed, move the fracturing device (9) to the next section and repeat steps two to five until the fracturing transformation of all sections is completed.

2. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 1, characterized in that, The high-pressure oil pipe (6) in step one can withstand a pressure of at least 60 MPa.

3. A method for enhancing in-situ combustion and detonation fracturing of methane according to claim 1 or 2, characterized in that, The final heating temperature of the supercritical carbon dioxide (21) in step two is greater than 40 °C, and the initial injection pressure is greater than 60 MPa.

4. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 3, characterized in that, In step three, the maximum particle size of the fly ash (1) is 0.3 mm.

5. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 3, characterized in that, In step three, the combustion accelerant (12) is oxygen.

6. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 5, characterized in that, In step three, the amount of supercritical carbon dioxide (21) injected is 50% to 60% of the amount of combustion accelerant (12) injected.

7. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 6, characterized in that, In step three, the volume fraction of the fly ash (1) in supercritical carbon dioxide (21) is 7% to 10%.

8. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 7, characterized in that, In step five, ignition is performed when the methane gas concentration is between 20% and 60%.

9. The method for enhancing in-situ combustion and detonation fracturing of methane according to claim 7, characterized in that, In step five, electronic ignition is used for ignition.

Images