A method for stimulating shale gas production from multi-stage fractured shale

Abstract

This invention discloses a method for increasing shale gas production from multi-stage fracturing shale formations. First, water containing water-absorbing resin is intermittently injected into the shale gas well, impacting the shale layer and creating multiple fractures, forming a primary fracturing process. Next, liquid nitrogen and sodium particles are injected into the shale gas well. The resin, already saturated with water, remains within the fractures. At this point, the liquid nitrogen cools the shale layer below its freezing point, causing the saturated resin to freeze and rapidly expand, forming a secondary fracturing process. Then, as the injected liquid nitrogen continues to vaporize, it further freezes the water and water-absorbing resin adsorbed by the shale, forming a tertiary fracturing process. When the temperature of the shale layer exceeds its freezing point, the expanded ice on the water-absorbing resin melts into water. At this point, the sodium particles react with the water, releasing a large amount of heat, causing the shale layer temperature to rise rapidly, creating a thermal shock to the low-temperature shale layer, forming a quaternary fracturing process. This completes the multi-stage fracturing process of the shale layer, effectively improving the extraction efficiency of shale gas.

Description

Technical Field

[0001] This invention relates to a method for fracturing shale, specifically a method for increasing shale gas production from multi-stage fracturing shale, belonging to the field of shale gas extraction technology. Background Technology

[0002] Shale gas is natural gas extracted from shale formations, primarily composed of methane, and is an important unconventional natural gas resource. my country possesses abundant shale gas reserves, with an onshore geological resource potential of 134.42 trillion cubic meters and a recoverable resource potential of 25.08 trillion cubic meters. Furthermore, shale gas has a relatively long extraction lifespan and growth cycle. Therefore, the commercial exploitation of shale gas is expected to improve the current situation where my country cannot be self-sufficient in conventional natural gas resources.

[0003] The current main method of shale gas extraction relies on its own desorption. After a period of extraction, shale gas production drops sharply, resulting in unsatisfactory extraction performance, low and unstable production, and failure to meet industrial development standards. Therefore, it is necessary to wait for a period of time to allow for natural desorption before extraction resumes. To improve the recovery rate of shale gas, extraction can be carried out even when the shale gas production is below the industrial development standard (1000m³ per well). 3 At any given time (per day), measures are taken to enhance shale gas extraction. Existing enhancement measures mainly employ hydraulic fracturing for reservoir stimulation. The principle is to pump fracturing fluid into the bottom of the well using a high-pressure pump truck. The high-pressure fracturing fluid creates one or more fractures in the shale gas reservoir, thereby providing more channels for shale gas seepage and desorption. However, this method does not generate a dense fracture network, and the production enhancement effect is limited. Other methods include using steam for gas-driven fracturing of shale reservoirs, or first using hydraulic fracturing followed by steam fracturing within the same shale gas well. While these multiple methods can partially improve fracturing efficiency, they are independent of each other, meaning they do not interact with subsequent fracturing. Therefore, while using multiple methods improves fracturing efficiency, it also increases the fracturing process, ultimately not improving shale gas extraction efficiency. Thus, developing a method for multi-stage fracturing of shale gas reservoirs that, compared to other existing methods, achieves higher shale gas extraction yields within the same construction time, thereby effectively improving shale gas extraction efficiency, is one of the research directions in this industry. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for multi-stage fracturing of shale to increase shale gas production. This method can perform multi-stage fracturing on shale gas reservoirs, and compared with other existing methods, it can achieve a higher shale gas production rate under the premise of enhanced shale gas extraction within the same construction time, thereby effectively improving the shale gas extraction efficiency.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for increasing shale gas production from multi-stage fractured shale, the specific steps of which are as follows:

[0006] A. Construct a vertical section of the shale gas well from the ground into the shale layer until the vertical section extends into the shale layer and stops. Then, construct a horizontal section of the shale gas well from the current position into the shale layer and stop. Next, insert a sealing pipe into the vertical section of the shale gas well to support the vertical section and seal it for later shale gas extraction. Finally, install a shale gas well sealing cap at the wellhead to seal the shale gas well, thus completing the construction of the shale gas well.

[0007] B. Assemble a multi-stage fracturing shale formation system on the ground, including a hydraulic fracturing device, a liquid nitrogen and sodium particle injection device, a gas pressure measuring device, and a laser rangefinder. The hydraulic fracturing device includes a water tank and a pulsating pump. The water tank is connected to the inlet of the pulsating pump via a water injection connection pipe. The outlet of the pulsating pump is connected to one end of the water injection pipe. The other end of the water injection pipe passes through the shale gas well sealing cap and extends into the sealing pipe. A first control valve is installed on the water injection pipe, and a second control valve is installed on the water injection connection pipe. The water tank contains water containing water-absorbing resin. The liquid nitrogen and sodium particle injection device includes a liquid nitrogen tank, a liquid nitrogen pulsating pump, a mixing container, and a T-connector. The liquid nitrogen tank is connected to the inlet of the liquid nitrogen pulsating pump via a third liquid nitrogen pipe. The outlet of the liquid nitrogen pulsating pump is connected to one port of the T-connector via a second liquid nitrogen pipe. The other two ports are connected to one end of the first liquid nitrogen pipe and one end of the sodium particle injection pipe, respectively. The other end of the first liquid nitrogen pipe passes through the shale gas well sealing cover and extends into the sealing pipe. The other end of the sodium particle injection pipe is connected to the outlet of the mixing container. A third control valve is installed on the sodium particle injection pipe. A first liquid nitrogen control valve is installed on the second liquid nitrogen pipe. A second liquid nitrogen control valve is installed on the third liquid nitrogen pipe. The temperature measuring device is installed on the first liquid nitrogen pipe. The gas pressure measuring device and the laser rangefinder are both installed on the shale gas well sealing cover. The probe of the gas pressure measuring device extends into the sealing pipe. The probe of the laser rangefinder extends into the sealing pipe and faces the deepest part of the vertical section of the shale gas well. The liquid nitrogen tank stores liquid nitrogen. The mixing container contains a mixture of kerosene and metallic sodium particles, thus completing the assembly of the multi-stage fractured shale layer system.

[0008] C. Open the first control valve and the second control valve, start the pulsating pump. The water containing water-absorbing resin in the water tank is pulsated by the pulsating pump to obtain pulsating water containing water-absorbing resin. The pulsating water containing water-absorbing resin enters the sealed pipe in the shale gas well through the water injection pipe. After continuous injection, the water containing water-absorbing resin impacts the shale layer, causing multiple cracks to be formed in the shale layer. The pulsation ends after a period of time. Close the pulsating pump, the first control valve and the second control valve to form the first-stage fracturing process.

[0009] D. The distance between the water surface and the laser rangefinder in the shale gas well is measured in real time using a laser rangefinder. When the distance measured by the laser rangefinder equals the depth of the shale gas well, it indicates that the water containing water-absorbing resin has seeped into the shale layer. Next, the first and second liquid nitrogen control valves are opened, and the liquid nitrogen pulse pump is started. Liquid nitrogen enters the sealed pipe through the third, second, and first liquid nitrogen pipes. Simultaneously, the temperature on the first liquid nitrogen pipe is measured using a temperature measuring device. When the temperature measured by the temperature measuring device is lower than the external temperature... When the temperature is above 10℃, the third control valve is opened, and the mixture of kerosene and metallic sodium particles is injected into the shale gas well along with liquid nitrogen through the sodium particle injection pipe and the tee joint. After the liquid nitrogen enters the shale gas well, it comes into contact with the shale layer. At this time, the temperature of the shale layer drops rapidly and freezes the shale layer. At the same time, the water-absorbing resin that has been injected into the shale layer cracks freezes into ice because the temperature is below the freezing point, causing its volume to expand rapidly. This puts pressure on the shale layer cracks, causing the cracks in the shale layer to expand and develop further, forming a secondary fracturing process.

[0010] E. When the distance between the laser rangefinder and the liquid nitrogen surface in the shale gas well is measured to be the depth of the shale gas well minus the thickness of the shale layer, the liquid nitrogen pulse pump, the first liquid nitrogen control valve, the second liquid nitrogen control valve, and the third control valve are closed to stop the pulse injection of liquid nitrogen and a mixture of kerosene and metallic sodium particles into the shale gas well. The shale gas well is sealed for 24–36 hours. During this period, the liquid nitrogen continues to vaporize and generate nitrogen gas, which increases the pressure inside the shale gas well. This further promotes the flow of liquid nitrogen in the various fractures of the shale layer, further freezes the water-absorbing resin, increases the fracturing effect of the shale layer, and forms a three-stage fracturing process.

[0011] F. The gas pressure in the shale gas well is monitored in real time using a gas pressure measuring device. When the pressure value of the gas pressure measuring device stops changing, it indicates that the liquid nitrogen has been completely vaporized. As time goes on, the temperature of the shale layer will gradually rise. When the temperature of the shale layer exceeds the freezing point, the ice that expands on the water-absorbing resin melts into water. At this time, the sodium particles react with the water and release a large amount of heat, causing the temperature of the shale layer to rise rapidly, forming a thermal shock to the low-temperature shale layer. At the same time, during the temperature rise, some water vaporizes into steam, forming a dual effect of thermal shock and steam shock on the cracks in the shale layer, forming a fourth-stage fracturing process. Furthermore, because the temperature rise can accelerate the desorption of shale gas from the shale layer into the shale gas well, a multi-stage fracturing process of the shale layer is completed.

[0012] G. Repeat steps C to F 5 to 10 times to carry out multiple stages of fracturing in the shale layer, including hydraulic fracturing, water-absorbing resin freezing and expansion fracturing, nitrogen gasification fracturing, and sodium reacting with water to exothermic freeze-thaw cycle fracturing. Finally, a dense fracture network is formed in the shale layer, which greatly increases the permeability of the shale layer. Finally, shale gas is extracted through shale gas wells.

[0013] Furthermore, the check valve is installed on the third liquid nitrogen pipe to prevent liquid nitrogen in the liquid nitrogen pulsating pump from flowing back into the liquid nitrogen tank.

[0014] Furthermore, the gas pressure measuring device is a gas pressure gauge. Using a gas pressure gauge not only ensures high operational stability but also facilitates installation.

[0015] Furthermore, the sodium metal particles have a particle size of 3–5 mm. This particle size allows the sodium metal particles to penetrate into smaller cracks as much as possible and react with water within the cracks, thereby improving the effect on crack propagation and development.

[0016] Furthermore, in step C, the pulsation frequency of the pulsating pump is 0.01Hz to 0.12Hz, the pulsation pressure is 25MPa to 35MPa, and the pulsation time is 6h to 8h. Using these parameters ensures the effective impact fracturing of the shale layer by the water.

[0017] Compared with existing technologies, this invention first injects water containing water-absorbing resin into the shale gas well in a pulsating manner. The continuously injected water impacts the shale layer, and because the water contains saturated resin, it also increases the impact force on the shale layer, thereby fracturing multiple cracks in the shale layer and forming a primary fracturing process. Next, a mixture of liquid nitrogen and kerosene with metallic sodium particles is injected into the shale gas well. Since metallic sodium particles are chemically reactive and easily oxidized, placing them in the kerosene not only... This process reduces oxidation and facilitates injection into shale gas wells. When liquid nitrogen enters the shale layer, the resin, already saturated with water, remains in the fractures during the primary fracturing process. The liquid nitrogen rapidly cools the shale layer; when the temperature drops below freezing, the saturated resin freezes and expands rapidly, applying pressure to the shale fractures and significantly enhancing the freezing fracturing effect, thus forming the secondary fracturing process. Then, as the injected liquid nitrogen continues to vaporize, the pressure buildup of nitrogen within the shale gas well also helps drive the liquid nitrogen to further fracture within the shale. The flow within the rock further freezes the water and absorbent resin adsorbed by the shale, increasing the fracturing effect and forming a tertiary fracturing process. Once the liquid nitrogen has completely vaporized, the temperature of the shale layer gradually rises. When the shale layer temperature exceeds its freezing point, the ice expanding on the absorbent resin melts into water. At this point, the sodium particles react chemically with the water, releasing a large amount of heat, causing the shale layer temperature to rise rapidly, creating a thermal shock to the low-temperature shale layer. Simultaneously, as the temperature rises, some water vaporizes into steam, creating thermal shock and steam impact on the cracks in the shale layer. The dual effects of shock and impact create a four-stage fracturing process, thus completing a multi-stage fracturing process for the shale layer. During this process, the shale layer undergoes hydraulic fracturing, water-absorbing resin freezing and expansion fracturing, nitrogen gasification fracturing, and sodium-water reaction exothermic freeze-thaw cycle fracturing. By combining multiple large-temperature-difference thermal shock cycles, hydraulic fracturing, freeze-expansion fracturing, and gasification fracturing, the fracturing of shale is highly targeted and effective, resulting in a dense fracture network and ultimately a significant increase in shale layer permeability. Furthermore, the exothermic reaction of sodium and water provides a heat source for shale gas desorption, accelerating the desorption rate and facilitating high-flow-rate, high-concentration, and long-term extraction of shale gas from wells. Therefore, this invention, through multi-stage fracturing of shale layers, enhances shale gas extraction and has broad applicability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the assembled structure of the multi-stage fractured shale layer system in this invention.

[0019] In the diagram: 1. Shale layer; 2. Shale gas well; 3. Sealing pipe; 4. Shale gas well sealing cap; 5. Water injection pipe; 6. Laser rangefinder; 7. First liquid nitrogen pipe; 8. Gas pressure measuring device; 9. First control valve; 10. Pulsating pump; 11. Water injection connection pipe; 12. Second control valve; 13. Water tank; 14. Temperature measuring device; 15. T-joint; 16. Sodium particle injection pipe; 17. Third control valve; 18. Mixing container; 19. Second liquid nitrogen pipe; 20. First liquid nitrogen control valve; 21. Liquid nitrogen pulse pump; 22. Third liquid nitrogen pipe; 23. Second liquid nitrogen control valve; 24. Check valve; 25. Liquid nitrogen tank. Detailed Implementation

[0020] The present invention will be further described below.

[0021] like Figure 1 As shown, the specific steps of this invention are as follows:

[0022] A. Construct a vertical section of shale gas well 2 from the ground towards shale layer 1 until the vertical section extends into shale layer 1. Then, construct a horizontal section of shale gas well 2 of a certain length from the current position within shale layer 1 and stop. Next, insert a sealing pipe 3 into the vertical section of shale gas well 2 to support the vertical section and seal it for subsequent shale gas extraction. Install a shale gas well sealing cap 4 at the wellhead of shale gas well 1 to seal the shale gas well, thus completing the construction of shale gas well 2.

[0023] B. Assemble a multi-stage fracturing shale formation system on the ground, including a hydraulic fracturing device, a liquid nitrogen and sodium particle injection device, a gas pressure measuring device 8, and a laser rangefinder 6. The hydraulic fracturing device includes a water tank 13 and a pulse pump 10. The water tank 13 is connected to the inlet of the pulse pump 10 through a water injection connection pipe 11. The outlet of the pulse pump 10 is connected to one end of a water injection pipe 5. The other end of the water injection pipe 5 passes through the shale gas well sealing cap 4 and extends into the sealing pipe 3. A first control valve 9 is installed on the water injection pipe 5. A second control valve 12 is installed on the water injection connection pipe 11, and the water tank 13 contains water containing water-absorbing resin. The liquid nitrogen and sodium particle injection device includes a liquid nitrogen tank 25, a liquid nitrogen pulse pump 21, a mixing container 18, and a three-way connector 15. The liquid nitrogen tank 25 is connected to the inlet of the liquid nitrogen pulse pump 21 through a third liquid nitrogen pipe 22, and the outlet of the liquid nitrogen pulse pump 21 is connected to one port of the three-way connector 15 through a second liquid nitrogen pipe 19. The other two ports of the three-way connector 15 are respectively connected to the first liquid nitrogen pipe. One end of the first liquid nitrogen pipe 7 is connected to one end of the sodium particle injection pipe 16. The other end of the first liquid nitrogen pipe 7 passes through the shale gas well sealing cap 4 and extends into the sealing pipe 3. The other end of the sodium particle injection pipe 16 is connected to the outlet of the mixing container 18. A third control valve 17 is installed on the sodium particle injection pipe 16. A first liquid nitrogen control valve 9 is installed on the second liquid nitrogen pipe 19. A second liquid nitrogen control valve 23 is installed on the third liquid nitrogen pipe 22. The temperature measuring device 14 is installed on the first liquid nitrogen pipe 7. The gas pressure measuring device 8 and the laser measuring device are also included. The rangefinder 6 is installed on the shale gas well sealing cover 4, and the probe of the gas pressure measuring device 8 extends into the sealing tube 3. The probe of the laser rangefinder 6 extends into the sealing tube 3 and faces the deepest part of the vertical section of the shale gas well 3. The liquid nitrogen tank 25 stores liquid nitrogen, and the mixing container 18 contains a mixture of kerosene and metallic sodium particles. The check valve 24 is installed on the third liquid nitrogen pipe 22 to prevent the liquid nitrogen in the liquid nitrogen pulsating pump 21 from flowing back into the liquid nitrogen tank 25, thus completing the assembly of the multi-stage fractured shale layer system.

[0024] C. Open the first control valve 9 and the second control valve 12, start the pulsating pump 10. The water containing water-absorbing resin in the water tank 13 is pulsated by the pulsating pump 10 to obtain pulsating water containing water-absorbing resin. The pulsating water containing water-absorbing resin enters the sealed pipe 3 in the shale gas well 2 through the water injection pipe 5. After continuous injection, the water containing water-absorbing resin impacts the shale layer 1, causing multiple cracks to be formed in the shale layer 1. The pulsation frequency of the pulsating pump 10 is 0.01Hz~0.12Hz, the pulsation pressure is 25MPa~35MPa, and the pulsation time is 6h~8h. Using these parameters can ensure the impact and fracturing effect of water on the shale layer 1. Close the pulsating pump 10, the first control valve 9 and the second control valve 12 to form the first-stage fracturing process.

[0025] D. The distance between the water surface in the shale gas well 2 and the laser rangefinder 6 is measured in real time using the laser rangefinder 6. When the distance measured by the laser rangefinder 6 is equal to the depth of the shale gas well 2, it indicates that the water containing water-absorbing resin in the shale gas well 2 has all seeped into the shale layer 1. Then, the first liquid nitrogen control valve 20 and the second liquid nitrogen control valve 19 are opened, and the liquid nitrogen pulse pump 21 is started. Liquid nitrogen enters the sealed pipe 3 through the third liquid nitrogen pipe 22, the second liquid nitrogen pipe 19, and the first liquid nitrogen pipe 7. At the same time, the temperature on the first liquid nitrogen pipe 7 is measured by the temperature measuring device 14. When the temperature measured by the temperature measuring device 14 is more than 10°C lower than the outside temperature, the third control valve 17 is opened, and kerosene... The mixture of kerosene and sodium particles is injected into the shale gas well 2 along with liquid nitrogen through the sodium particle injection pipe 16 and the tee joint 15. This ensures that the liquid nitrogen is injected into the sealing pipe 3 first, and then the mixture of kerosene and sodium particles is injected, thus guaranteeing the purity of the liquid nitrogen that enters first, which is convenient for subsequent freezing work. After the liquid nitrogen enters the shale gas well 2, it comes into contact with the shale layer 1. At this time, the temperature of the shale layer 1 drops rapidly, freezing the shale layer 1. At the same time, the water-absorbing resin injected into the cracks of the shale layer 1 freezes the water it has absorbed due to the temperature being below the freezing point, causing it to expand rapidly in volume. This puts pressure on the cracks of the shale layer 1, causing the cracks in the shale layer 1 to further expand and develop, forming a secondary fracturing process.

[0026] E. When the distance between the laser rangefinder 6 and the liquid nitrogen surface in shale gas well 2 is measured to be the depth of shale gas well 2 minus the thickness of shale layer 1, the liquid nitrogen pulse pump 21, the first liquid nitrogen control valve 20, the second liquid nitrogen control valve 23 and the third control valve 17 are closed, and the pulse injection of liquid nitrogen and a mixture of kerosene and metallic sodium particles into shale gas well 2 is stopped; shale gas well 2 is sealed for 24 to 36 hours. During this period, liquid nitrogen continues to vaporize and generate nitrogen gas, which increases the pressure inside shale gas well 2, further promoting the flow of liquid nitrogen in various cracks in shale layer 1, further freezing the water-absorbing resin, increasing the fracturing effect of shale layer 1, and forming a three-stage fracturing process;

[0027] F. The gas pressure in the shale gas well 2 is monitored in real time by a gas pressure measuring device 8, which is a gas pressure gauge. Using a gas pressure gauge not only ensures high operational stability but also facilitates installation. When the pressure value of the gas pressure measuring device 8 remains unchanged, it indicates that the liquid nitrogen has completely vaporized. As time progresses, the temperature of shale layer 1 gradually rises. When the temperature of shale layer 1 exceeds the freezing point, the ice that expands on the absorbent resin melts into water. At this time, the sodium particles react with the water, releasing a large amount of heat, causing the temperature of shale layer 1 to rise rapidly, creating a thermal shock to the low-temperature shale layer 1. Simultaneously, during the temperature rise, some water vaporizes into steam, creating a dual effect of thermal and steam shock on the cracks in shale layer 1, forming a fourth-stage fracturing process. Furthermore, the temperature rise accelerates the desorption of shale gas from shale layer 1 into the shale gas well, thus completing a multi-stage fracturing process in shale layer 1.

[0028] G. Repeat steps C to F 5 to 10 times to carry out multiple hydraulic fracturing, water-absorbing resin freezing expansion fracturing, nitrogen gasification fracturing, and sodium reacting with water exothermic freeze-thaw cycle fracturing processes on shale layer 1. Finally, shale layer 1 forms a dense fracture network, which greatly increases the permeability of shale layer 1. Finally, shale gas is extracted through shale gas wells.

[0029] As an improvement of the present invention, the particle size of the sodium metal particles is 3-5 mm. This particle size allows the sodium metal particles to penetrate into smaller cracks as much as possible and react with water within the cracks, thus improving the effect on crack propagation and development.

[0030] The aforementioned water-absorbing resin is an existing material.

[0031] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for increasing shale gas production from multi-stage fractured shale, characterized in that, The specific steps are as follows: A. Construct a vertical section of the shale gas well from the ground into the shale layer until the vertical section extends into the shale layer and stops. Then, construct a horizontal section of the shale gas well from the current position into the shale layer and stop. Next, insert a sealing pipe into the vertical section of the shale gas well to support the vertical section and seal it for later shale gas extraction. Finally, install a shale gas well sealing cap at the wellhead to seal the shale gas well, thus completing the construction of the shale gas well. B. Assemble a multi-stage fracturing shale formation system on the ground, including a hydraulic fracturing device, a liquid nitrogen and sodium particle injection device, a gas pressure measuring device, and a laser rangefinder. The hydraulic fracturing device includes a water tank and a pulsating pump. The water tank is connected to the inlet of the pulsating pump via a water injection connection pipe. The outlet of the pulsating pump is connected to one end of the water injection pipe. The other end of the water injection pipe passes through the shale gas well sealing cap and extends into the sealing pipe. A first control valve is installed on the water injection pipe, and a second control valve is installed on the water injection connection pipe. The water tank contains water containing absorbent resin. The liquid nitrogen and sodium particle injection device includes a liquid nitrogen tank, a liquid nitrogen pulsating pump, a mixing container, and a T-connector. The liquid nitrogen tank is connected to the inlet of the liquid nitrogen pulsating pump via a third liquid nitrogen pipe. The outlet of the liquid nitrogen pulsating pump is connected to one port of the T-connector via a second liquid nitrogen pipe. The other two ports of the connector are connected to one end of the first liquid nitrogen pipe and one end of the sodium particle injection pipe, respectively. The other end of the first liquid nitrogen pipe passes through the shale gas well sealing cover and extends into the sealing pipe. The other end of the sodium particle injection pipe is connected to the outlet of the mixing container. The sodium particle injection pipe is equipped with a third control valve. The second liquid nitrogen pipe is equipped with a first liquid nitrogen control valve. The third liquid nitrogen pipe is equipped with a second liquid nitrogen control valve. The temperature measuring device is installed on the first liquid nitrogen pipe. The gas pressure measuring device and the laser rangefinder are both installed on the shale gas well sealing cover. The probe of the gas pressure measuring device extends into the sealing pipe. The probe of the laser rangefinder extends into the sealing pipe and faces the deepest part of the vertical section of the shale gas well. The liquid nitrogen tank stores liquid nitrogen. The mixing container contains a mixture of kerosene and metallic sodium particles, thus completing the assembly of the multi-stage fractured shale layer system. C. Open the first control valve and the second control valve, start the pulsating pump. The water containing water-absorbing resin in the water tank is pulsated by the pulsating pump to obtain pulsating water containing water-absorbing resin. The pulsating water containing water-absorbing resin enters the sealed pipe in the shale gas well through the water injection pipe. After continuous injection, the water containing water-absorbing resin impacts the shale layer, causing multiple cracks to be formed in the shale layer. The pulsation ends after a period of time. Close the pulsating pump, the first control valve and the second control valve to form the first-stage fracturing process. D. The distance between the water surface and the laser rangefinder in the shale gas well is measured in real time using a laser rangefinder. When the distance measured by the laser rangefinder equals the depth of the shale gas well, it indicates that the water containing water-absorbing resin has seeped into the shale layer. Next, the first and second liquid nitrogen control valves are opened, and the liquid nitrogen pulse pump is started. Liquid nitrogen enters the sealed pipe through the third, second, and first liquid nitrogen pipes. Simultaneously, the temperature on the first liquid nitrogen pipe is measured using a temperature measuring device. When the temperature measured by the temperature measuring device is lower than the external temperature... When the temperature is above 10℃, the third control valve is opened, and the mixture of kerosene and metallic sodium particles is injected into the shale gas well along with liquid nitrogen through the sodium particle injection pipe and the tee joint. After the liquid nitrogen enters the shale gas well, it comes into contact with the shale layer. At this time, the temperature of the shale layer drops rapidly and freezes the shale layer. At the same time, the water-absorbing resin that has been injected into the shale layer cracks freezes into ice because the temperature is below the freezing point, causing its volume to expand rapidly. This puts pressure on the shale layer cracks, causing the cracks in the shale layer to expand and develop further, forming a secondary fracturing process. E. When the distance between the laser rangefinder and the liquid nitrogen surface in the shale gas well is measured to be the depth of the shale gas well minus the thickness of the shale layer, the liquid nitrogen pulse pump, the first liquid nitrogen control valve, the second liquid nitrogen control valve, and the third control valve are closed to stop the pulse injection of liquid nitrogen and a mixture of kerosene and metallic sodium particles into the shale gas well. The shale gas well is sealed for 24–36 hours. During this period, the liquid nitrogen continues to vaporize and generate nitrogen gas, which increases the pressure inside the shale gas well. This further promotes the flow of liquid nitrogen in the various fractures of the shale layer, further freezes the water-absorbing resin, increases the fracturing effect of the shale layer, and forms a three-stage fracturing process. F. The gas pressure in the shale gas well is monitored in real time by a gas pressure measuring device. When the pressure value of the gas pressure measuring device no longer changes, it indicates that the liquid nitrogen has been completely vaporized. As time goes by, the temperature of the shale layer will gradually rise. When the temperature of the shale layer exceeds the freezing point, the ice that expands on the water-absorbing resin melts into water. At this time, the sodium metal particles react with the water and release a large amount of heat, causing the temperature of the shale layer to rise rapidly and forming a thermal shock to the low-temperature shale layer. At the same time, during the temperature rise, some water vaporizes into steam, forming a dual effect of thermal shock and steam shock on the cracks of the shale layer, forming a fourth-stage fracturing process. Furthermore, the temperature rise can accelerate the desorption of shale gas from the shale layer to the shale gas well, thus completing a multi-stage fracturing process of the shale layer. G. Repeat steps C to F 5 to 10 times to carry out multiple stages of fracturing in the shale layer, including hydraulic fracturing, water-absorbing resin freezing and expansion fracturing, nitrogen gasification fracturing, and sodium reacting with water to exothermic freeze-thaw cycle fracturing. Finally, a dense fracture network is formed in the shale layer, which greatly increases the permeability of the shale layer. Finally, shale gas is extracted through shale gas wells.

2. The method for increasing shale gas production from multi-stage fractured shale according to claim 1, characterized in that, The check valve is installed on the third liquid nitrogen tube to prevent liquid nitrogen in the liquid nitrogen pulsating pump from flowing back into the liquid nitrogen tank.

3. The method for increasing shale gas production from multi-stage fractured shale according to claim 1, characterized in that, The gas pressure measuring device is a gas pressure gauge.

4. The method for increasing shale gas production from multi-stage fractured shale according to claim 1, characterized in that, The particle size of the sodium metal particles is 3-5 mm.

5. The method for increasing shale gas production from multi-stage fractured shale according to claim 1, characterized in that, In step C, the pulsation frequency of the pulsation pump is 0.01Hz to 0.12Hz, the pulsation pressure is 25MPa to 35MPa, and the pulsation time is 6h to 8h.

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