A coal seam fracturing method coupling liquid nitrogen and static crushing agent

Abstract

This invention discloses a coal seam fracturing method coupled with liquid nitrogen and a static fracturing agent. First, frozen static fracturing agent particles are prepared using liquid nitrogen. These particles are then injected into the borehole along with the liquid nitrogen. Due to the low temperature and gradually increasing pressure, the liquid nitrogen drives the coal seam to generate and expand fractures. The frozen static fracturing agent particles flow into these fractures along with the liquid nitrogen. After liquid nitrogen fracturing, as the coal seam temperature gradually recovers from the influence of geothermal activity, the frozen static fracturing agent particles begin to dissolve. At this point, the static fracturing agent reacts chemically with water, expanding in volume. This expansion forms a static fracturing agent expansion zone within the fracture, performing secondary expansion fracturing. Simultaneously, the expansion zone supports the fracture, preventing it from closing due to geostress, thus completing the coal seam fracturing. This method not only achieves efficient coal seam fracturing but also effectively supports the fractures, reducing the likelihood of subsequent closure and ultimately improving the efficiency of coalbed methane extraction.

Description

Technical Field

[0001] This invention relates to a coal seam fracturing method coupled with liquid nitrogen and a static fracturing agent, belonging to the field of coalbed methane extraction technology. Background Technology

[0002] As shallow coal resources are gradually depleted, coalbed methane extraction is increasingly moving towards deeper deposits. my country's coalbed methane resources are generally characterized by low porosity and low permeability; these extremely poor porosity and permeability characteristics hinder effective seepage of coalbed methane and severely restrict the rapid development of the coalbed methane industry.

[0003] To extract coalbed methane (CBM), coal seams need to be fractured, currently primarily using hydraulic fracturing. However, hydraulic fracturing technology suffers from low efficiency and high cost, limiting the effective extraction of CBM. Liquid nitrogen, with a temperature of -196℃ at normal pressure, can rapidly lower the temperature of solids upon contact, causing them to contract and creating thermal stress along their internal radial direction. Simultaneously, liquid nitrogen vaporizes and expands to 696 times its original volume when it reaches 21℃, generating enormous pressure within a confined space. If water is present in the pores of the solid, a water-ice phase transition occurs, resulting in approximately 9% volume expansion, theoretically generating a frost heave force as high as 207 MPa. Therefore, liquid nitrogen has begun to be used in coal seam fracturing, and its permeability-enhancing effect is relatively good. Although liquid nitrogen fracturing technology can improve fracturing efficiency and effectiveness, the lack of effective fracture support after fracturing leads to the closure of fractures due to geostress, ultimately resulting in low CBM extraction efficiency.

[0004] Therefore, the research direction of this invention is to provide a new method that can not only achieve efficient fracturing of coal seams, but also effectively support the formed fractures, thereby reducing the likelihood of subsequent closure and ultimately improving the extraction efficiency of coalbed methane. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a coal seam fracturing method coupled with liquid nitrogen and a static fracturing agent. This method not only enables efficient fracturing of coal seams but also effectively supports the formed fractures, thereby reducing the likelihood of subsequent closure and ultimately improving the efficiency of coalbed methane extraction.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a coal seam fracturing method coupled with liquid nitrogen and a static fracturing agent, the specific steps of which are as follows:

[0007] Step 1: Preparation of frozen static breaker particles: Pour a certain amount of liquid nitrogen into an insulated tank. Install a sieve plate with multiple sieve holes inside the insulated tank, with the sieve plate positioned above the liquid nitrogen surface. Prepare a static breaker solution by mixing the static breaker agent and water in the required ratio. Pour the static breaker agent solution into the insulated tank. At this time, the static breaker agent solution first flows through the sieve plate and forms static breaker agent droplets through each sieve hole. The static breaker agent droplets fall into the liquid nitrogen and freeze rapidly to form frozen static breaker particles.

[0008] Step 2: Drilling holes in the coal seam: Drill holes into the coal seam using a drilling rig. After completion, a sealing device is installed in the hole to seal it. The sealing device is equipped with a nitrogen injection pipe and a vent pipe. One end of the nitrogen injection pipe and one end of the vent pipe are inside the hole, while the other ends of the nitrogen injection pipe and the vent pipe are outside the hole and are respectively equipped with a nitrogen injection shut-off valve and a vent shut-off valve.

[0009] Step 3, Equipment Installation: Connect the mixer to the inlet of the high-pressure nitrogen injection pump via a connecting pipe. Connect the outlet of the high-pressure nitrogen injection pump to the other end of the nitrogen injection pipe via a pressure-resistant pipe and a connector. Install a pressure gauge at the outlet of the high-pressure nitrogen injection pump to monitor the nitrogen injection pressure.

[0010] Step 4: Coal Seam Liquid Nitrogen Fracturing: First, open the nitrogen injection shut-off valve and the venting shut-off valve. Pour liquid nitrogen into the mixer and start the high-pressure nitrogen injection pump. At this time, the liquid nitrogen in the mixer is pumped by the high-pressure nitrogen injection pump, causing the liquid nitrogen to be injected into the borehole through the pressure-resistant pipe and the nitrogen injection pipe. Due to the high temperature inside the borehole, the liquid nitrogen entering the borehole continuously vaporizes, reducing the borehole temperature and producing nitrogen gas. The nitrogen gas is discharged from the borehole through the venting pipe. As the borehole temperature continues to decrease, liquid nitrogen gradually accumulates in the borehole, gradually filling the borehole. When liquid nitrogen is observed flowing out from the other end of the venting pipe, close the venting shut-off valve. The borehole is kept in a sealed space. Simultaneously, the frozen static fracturing agent particles prepared in step one are added to the mixer. These particles are injected into the borehole along with liquid nitrogen. As the liquid nitrogen is continuously pressurized and injected into the borehole, the low temperature freezes the coal body, increasing its brittleness. Simultaneously, the increasing pressure of the liquid nitrogen in the borehole drives the formation and expansion of cracks in the coal body. The frozen static fracturing agent particles flow into the cracks formed in the coal seam along with the liquid nitrogen. Within the cracks, the frozen static fracturing agent particles act as a proppant, promoting the flow of liquid nitrogen and further increasing the crack propagation length.

[0011] Step 5: Secondary fracturing with static fracturing agent: After the liquid nitrogen fracturing is completed, the high-pressure nitrogen injection pump and nitrogen injection shut-off valve are shut off, and the frozen static fracturing agent particles remain in the fracture. As the coal seam temperature gradually recovers due to the influence of geothermal temperature, the remaining liquid nitrogen in the borehole continues to vaporize, causing the temperature in the borehole to rise continuously. When the melting point of the frozen static fracturing agent particles is reached, they begin to dissolve. At this time, the static fracturing agent and water begin to react chemically and expand in volume, thus expanding in the fracture to form a static fracturing agent expansion zone, which performs secondary expansion fracturing on the fracture, creating secondary fracturing fissures around the fracture. At the same time, the static fracturing agent expansion zone supports the fracture, preventing the fracture from closing under the action of geostress, thus completing the coal seam fracturing process.

[0012] Furthermore, the sieve holes on the sieve plate are evenly distributed, and the sieve hole diameter is determined according to the particle size of the frozen static breaking agent particles to be prepared.

[0013] Furthermore, one end of the vent pipe is positioned inside the borehole near the bottom, and the other end of the nitrogen injection pipe is positioned inside the borehole near the sealing device. This arrangement ensures that liquid nitrogen can only enter the vent pipe after the borehole is essentially filled with liquid nitrogen, making it easy to determine the accumulated amount of liquid nitrogen inside the borehole by observing whether liquid nitrogen is being discharged from the vent pipe.

[0014] Furthermore, the static fracturing agent contains calcium oxide. Calcium oxide reacts chemically with water to form calcium hydroxide, which expands in volume by approximately 100%. This property is utilized to achieve secondary expansion fracturing of the static fracturing agent.

[0015] Furthermore, the borehole is drilled upwards. This facilitates the injection of liquid nitrogen and the assessment of the injection status.

[0016] Compared with existing technologies, this invention first utilizes liquid nitrogen to prepare frozen static fracturing agent particles. In this state, water encapsulates the static fracturing agent in the form of ice. The absence of water prevents the static fracturing agent from undergoing a chemical reaction, facilitating subsequent injection into the borehole. Next, a borehole is drilled at the location of the coal seam to be fracturing, and liquid nitrogen is injected. The frozen static fracturing agent particles are injected along with the liquid nitrogen. Due to the low temperature, the liquid nitrogen freezes the coal body surrounding the borehole, increasing its brittleness. Simultaneously, the increasing pressure of the liquid nitrogen within the borehole drives the coal body to generate and continuously expand cracks. The frozen static fracturing agent particles flow into the cracks generated in the coal seam with the liquid nitrogen, and within the cracks... The liquid nitrogen acts as a proppant, promoting the flow of liquid nitrogen within the fractures and further increasing the fracture propagation length. After liquid nitrogen fracturing, the frozen static fracturing agent particles remain within the fractures. As the coal seam temperature gradually recovers from the influence of geothermal activity, the frozen static fracturing agent particles begin to dissolve. At this point, the static fracturing agent reacts chemically with water, expanding in volume and forming a static fracturing agent expansion zone within the fracture. This zone then performs secondary expansion fracturing on the fracture, creating secondary fracturing fissures around it. Simultaneously, the static fracturing agent expansion zone supports the fracture, preventing it from closing under geostress, ultimately completing the coal seam fracturing process. This method not only achieves efficient coal seam fracturing but also effectively supports the formed fractures, reducing the likelihood of subsequent closure and ultimately improving the efficiency of coalbed methane extraction. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the construction layout of the present invention;

[0018] Figure 2 This is a schematic diagram of the preparation of frozen static breaking agent particles in this invention;

[0019] Figure 3 This is a schematic diagram of secondary expansion fracturing in this invention.

[0020] In the diagram: 1-Mixer, 2-Connecting pipe, 3-High-pressure nitrogen injection pump, 4-Pressure gauge, 5-Pressure-resistant pipe, 6-Connector, 7-Nitrogen injection pipe, 8-Nitrogen injection shut-off valve, 9-Vent pipe, 10-Vent shut-off valve, 11-Sealing device, 12-Drill hole, 13-Crack, 14-Liquid nitrogen, 15-Freeze static fracturing agent particles, 16-Sieve plate, 17-Sieve holes, 18-Insulation tank, 19-Static fracturing agent solution, 20-Static fracturing agent droplets, 21-Static fracturing agent expansion zone, 22-Coal seam. Detailed Implementation

[0021] The present invention will be further described below.

[0022] like Figure 1 As shown, the specific steps of the present invention are as follows:

[0023] Step 1: Prepare frozen static breaking agent particles: such as Figure 2As shown, a certain amount of liquid nitrogen 14 is poured into the insulated tank 18. A sieve plate 16 with multiple sieve holes 17 is installed inside the insulated tank 18, and the sieve plate 16 is positioned above the liquid nitrogen 14. The static breaker agent and water are mixed in the required ratio to prepare a static breaker agent solution 19. The main component of the static breaker agent is calcium oxide, which is an existing formulation. The static breaker agent solution 19 is poured into the insulated tank 18. At this time, the static breaker agent solution 19 first flows through the sieve plate 16 and forms static breaker agent droplets 20 through each sieve hole 17. The static breaker agent droplets 20 are dripped into the liquid nitrogen 14 and rapidly frozen to form frozen static breaker agent particles 15. The sieve holes 17 on the sieve plate 16 are evenly distributed, and the pore size of the sieve holes 17 is determined according to the particle size of the frozen static breaker agent particles 15 to be prepared.

[0024] Step 2: Drilling a borehole in the coal seam 22: A drilling rig is used to drill a borehole 12 into the coal seam 22. After completion, a sealing device 11 is installed in the borehole 12 to seal it. The sealing device 11 is equipped with a nitrogen injection pipe 7 and a vent pipe 9. One end of the nitrogen injection pipe 7 and one end of the vent pipe 9 are both inside the borehole 12, while the other ends of the nitrogen injection pipe 7 and the vent pipe 9 are outside the borehole 12 and are respectively equipped with a nitrogen injection shut-off valve 8 and a vent shut-off valve 10. The borehole 12 is drilled upwards. This facilitates liquid nitrogen injection and the assessment of the injection status. One end of the vent pipe 9 is located inside the borehole 12 near the bottom, and one end of the nitrogen injection pipe 7 is located inside the borehole near the sealing device 11. This arrangement ensures that liquid nitrogen 14 can only enter the vent pipe 9 after the borehole 12 is basically filled, making it easy to determine the accumulated amount of liquid nitrogen in the borehole 12 by observing whether liquid nitrogen 14 is discharged from the vent pipe 9.

[0025] Step 3, Equipment Installation: Connect the mixer 1 to the inlet of the high-pressure nitrogen injection pump 3 via the connecting pipe 2. Connect the outlet of the high-pressure nitrogen injection pump 3 to the other end of the nitrogen injection pipe 7 via the pressure-resistant pipe 5 and the connector 6. The outlet of the high-pressure nitrogen injection pump 3 is connected to the pressure gauge 4 for monitoring the nitrogen injection pressure.

[0026] Step 4: Coal Seam Liquid Nitrogen Fracturing: First, open the nitrogen injection shut-off valve 8 and the venting shut-off valve 10. Pour liquid nitrogen 14 into the mixer 1 and start the high-pressure nitrogen injection pump 3. At this time, the liquid nitrogen in the mixer 1 is pumped by the high-pressure nitrogen injection pump 3, causing the liquid nitrogen 14 to be injected into the borehole 12 through the pressure-resistant pipe 5 and the nitrogen injection pipe 7. Due to the high temperature inside the borehole 12, the liquid nitrogen entering the borehole 12 continuously vaporizes, reducing the borehole temperature and producing nitrogen gas. The nitrogen gas is discharged from the borehole 12 through the venting pipe 10. As the temperature of the borehole 12 continues to decrease, liquid nitrogen gradually accumulates in the borehole 12 and gradually fills the borehole 12. When liquid nitrogen is observed flowing out from the other end of the venting pipe 9, close the venting shut-off valve 10 to allow the borehole 12 to be filled with liquid nitrogen. 2. Maintain a sealed space inside, and simultaneously add the frozen static fracturing agent particles 15 prepared in step one to mixer 1. The frozen static fracturing agent particles 15 are injected into borehole 12 along with liquid nitrogen 14. As the liquid nitrogen 14 is continuously injected into borehole 12 under pressure, the liquid nitrogen 14 in borehole 12 freezes the coal body due to the low temperature, which increases the brittleness of the coal body. At the same time, the liquid nitrogen pressure in the borehole gradually increases, driving the coal body to generate cracks 13 and continuously expand and develop. The frozen static fracturing agent particles 15 flow into the cracks 13 generated in coal seam 22 along with liquid nitrogen 14. The frozen static fracturing agent particles 15 act as a proppant in cracks 13, promoting the flow of liquid nitrogen 14 in cracks 13 and further increasing the length of crack expansion 13.

[0027] Step 5, Secondary fracturing with static fracturing agent: After the liquid nitrogen 14 fracturing operation is completed, the high-pressure nitrogen injection pump 3 and nitrogen injection shut-off valve 8 are closed. The frozen static fracturing agent particles 15 remain in the fracture 13. As the temperature of the coal seam 22 gradually recovers due to the influence of geothermal temperature, the remaining liquid nitrogen 14 in the borehole 12 continues to vaporize, causing the temperature in the borehole 12 to continue to rise. When the melting point of the frozen static fracturing agent particles 15 is reached, they begin to dissolve. Figure 3 As shown, the calcium oxide in the static fracturing agent reacts with water to form calcium hydroxide, which expands in volume by about 100%. This expansion forms a static fracturing agent expansion zone 21 within the fracture 13, which performs secondary expansion fracturing on the fracture. This creates secondary fracturing fissures around the fracture 13. At the same time, the static fracturing agent expansion zone 21 supports the fracture 13, preventing it from closing under the influence of ground stress, thus completing the coal seam fracturing process.

[0028] The mixer 1, high-pressure nitrogen injection pump 3, heat preservation tank 18, sieve plate, pressure gauge 4, sealing device 11 and static crushing agent mentioned above are all existing equipment or components that can be purchased from the market. This invention only utilizes their existing functions.

[0029] 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 coal seam fracturing method coupled with liquid nitrogen and a static fracturing agent, characterized in that, The specific steps are: Step 1: Preparation of frozen static breaker particles: Pour a certain amount of liquid nitrogen into an insulated tank. Install a sieve plate with multiple sieve holes inside the insulated tank, with the sieve plate positioned above the liquid nitrogen surface. Prepare a static breaker solution by mixing the static breaker agent and water in the required ratio. Pour the static breaker agent solution into the insulated tank. At this time, the static breaker agent solution first flows through the sieve plate and forms static breaker agent droplets through each sieve hole. The static breaker agent droplets fall into the liquid nitrogen and freeze rapidly to form frozen static breaker particles. Step 2: Drilling holes in the coal seam: Drill holes into the coal seam using a drilling rig. After completion, a sealing device is installed in the hole to seal it. The sealing device is equipped with a nitrogen injection pipe and a vent pipe. One end of the nitrogen injection pipe and one end of the vent pipe are inside the hole, while the other ends of the nitrogen injection pipe and the vent pipe are outside the hole and are respectively equipped with a nitrogen injection shut-off valve and a vent shut-off valve. Step 3, Equipment Installation: Connect the mixer to the inlet of the high-pressure nitrogen injection pump via a connecting pipe. Connect the outlet of the high-pressure nitrogen injection pump to the other end of the nitrogen injection pipe via a pressure-resistant pipe and a connector. Install a pressure gauge at the outlet of the high-pressure nitrogen injection pump to monitor the nitrogen injection pressure. Step 4: Coal Seam Liquid Nitrogen Fracturing: First, open the nitrogen injection shut-off valve and the venting shut-off valve. Pour liquid nitrogen into the mixer and start the high-pressure nitrogen injection pump. At this time, the liquid nitrogen in the mixer is pumped by the high-pressure nitrogen injection pump, causing the liquid nitrogen to be injected into the borehole through the pressure-resistant pipe and the nitrogen injection pipe. Due to the high temperature inside the borehole, the liquid nitrogen entering the borehole continuously vaporizes, reducing the borehole temperature and producing nitrogen gas. The nitrogen gas is discharged from the borehole through the venting pipe. As the borehole temperature continues to decrease, liquid nitrogen gradually accumulates in the borehole, gradually filling the borehole. When liquid nitrogen is observed flowing out from the other end of the venting pipe, close the venting shut-off valve. The borehole is kept in a sealed space. Simultaneously, the frozen static fracturing agent particles prepared in step one are added to the mixer. These particles are injected into the borehole along with liquid nitrogen. As the liquid nitrogen is continuously pressurized and injected into the borehole, the low temperature freezes the coal body, increasing its brittleness. Simultaneously, the increasing pressure of the liquid nitrogen in the borehole drives the formation and expansion of cracks in the coal body. The frozen static fracturing agent particles flow into the cracks formed in the coal seam along with the liquid nitrogen. Within the cracks, the frozen static fracturing agent particles act as a proppant, promoting the flow of liquid nitrogen and further increasing the crack propagation length. Step 5: Secondary fracturing with static fracturing agent: After the liquid nitrogen fracturing is completed, the high-pressure nitrogen injection pump and nitrogen injection shut-off valve are shut off, and the frozen static fracturing agent particles remain in the fracture. As the coal seam temperature gradually recovers due to the influence of geothermal temperature, the remaining liquid nitrogen in the borehole continues to vaporize, causing the temperature in the borehole to rise continuously. When the melting point of the frozen static fracturing agent particles is reached, they begin to dissolve. At this time, the static fracturing agent and water begin to react chemically and expand in volume, thus expanding in the fracture to form a static fracturing agent expansion zone, which performs secondary expansion fracturing on the fracture, creating secondary fracturing fissures around the fracture. At the same time, the static fracturing agent expansion zone supports the fracture, preventing the fracture from closing under the action of geostress, thus completing the coal seam fracturing process.

2. The coal seam fracturing method coupled with liquid nitrogen and static fracturing agent according to claim 1, characterized in that, The sieve holes on the sieve plate are evenly distributed, and the diameter of the sieve holes is determined according to the particle size of the frozen static breaking agent particles to be prepared.

3. The coal seam fracturing method coupled with liquid nitrogen and static fracturing agent according to claim 1, characterized in that, One end of the vent pipe is located inside the borehole near the bottom, and the other end of the nitrogen injection pipe is located inside the borehole near the sealing device.

4. The coal seam fracturing method coupled with liquid nitrogen and static fracturing agent according to claim 1, characterized in that, The static breaking agent contains calcium oxide.

5. The coal seam fracturing method coupled with liquid nitrogen and static fracturing agent according to claim 1, characterized in that, The borehole is drilled upwards.

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