A system and method for fracturing and enhancing the permeability of coal seams based on chemical thermal cycling.

Abstract

This invention discloses a chemical thermal cycling fracturing and permeability enhancement system and method for coal seams. It relates to an apparatus that improves the gas permeability and desorption capacity of coal seams while reducing blockage during drainage. The apparatus mainly includes: a drill bit at the front end of the drill rod; a locator inside the drill bit; a sealing device at the rear end of the drill rod; a gas supply pipe, a carbon gas pipe, a liquid nitrogen pipe, and a hydrochloric acid pipe on the drill rod; a perforation string behind the drill bit; and related auxiliary facilities. This system utilizes liquid nitrogen to absorb heat and fracture the coal seam, transforming it into nitrogen gas which mixes with the injected carbon dioxide to displace the gas. The nitrogen-carbon dioxide mixture is more effective at displacing gas than a single gas. Furthermore, perforation enhances the diffusion effect of liquid nitrogen in subsequent steps, increasing the fracturing range and improving coalbed methane production. The steps are effectively connected, utilizing the residues from previous steps and reducing the risk of coal mine gas deterioration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas extraction, in particular to a coal seam system and method for increasing permeability based on chemical cold and hot cycle fracturing. BACKGROUND

[0002] Coal mine gas extraction is to drill into coal seams and gas accumulation areas, connect the drill holes to special pipelines, and use extraction equipment to extract the gas in the coal seams and goaf to the ground for utilization or discharge into the total return air flow. Gas extraction is not only an important measure to reduce gas emission during mining, prevent gas overrun and accumulation, and prevent gas explosion and coal and gas outburst accidents, but also can be developed and utilized as a resource associated with coal. However, in reality, gas is often stored in coal seams and is difficult to be fully utilized under the closure of dense coal seams, and will cause serious mine disasters during the later mining process. Therefore, how to extract and remove the gas accumulated in the coal seams is an urgent problem to be solved. SUMMARY

[0003] The present application aims to provide a coal seam system and method for increasing permeability based on chemical cold and hot cycle fracturing to solve the problems existing in the prior art.

[0004] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0005] A coal seam system and method for increasing permeability based on chemical cold and hot cycle fracturing, comprising a cracking section, a perforating pipe column and a drill bit, the cracking section comprising a fixed column, a pipe group for pouring different liquids into the coal seam being arranged inside the fixed column, and the pipe group penetrating one end face and a side face of the fixed column; a hole sealing assembly for sealing the coal seam bottom hole is arranged on the outer side face of the fixed column; one end face of the fixed column is fixedly connected and communicated with an external drilling machine, the other end face of the fixed column is fixedly connected and communicated with one end face of the perforating pipe column, and the other end face of the perforating pipe column is fixedly connected and communicated with the fixed end of the drill bit; a positioner for positioning the position of the drill bit is fixedly installed in the inner cavity of the perforating pipe column; the excavating end of the drill bit is used for excavating the coal seam bottom hole; a cleaning pipe is arranged in the center of one end face of the fixed column, one end of the cleaning pipe penetrates the perforating pipe column and the drill bit and is communicated with the external atmosphere; a first one-way valve is connected in series on the cleaning pipe; and a temperature sensor is fixedly installed on the side face of the fixed column.

[0006] Preferably, the pipeline set comprises a gas supply pipe, a carbon gas pipe, a liquid nitrogen pipe and a hydrochloric acid pipe; the gas supply pipe, the carbon gas pipe, the liquid nitrogen pipe and the hydrochloric acid pipe are arranged radially from the outer side of the fixed column body to the center in sequence; the gas supply pipe, the carbon gas pipe, the liquid nitrogen pipe and the hydrochloric acid pipe are respectively connected with a second one-way valve, a third one-way valve, a fourth one-way valve and a fifth one-way valve; the gas supply pipe is further connected with an electric heating unit for heating water; the electric heating unit is arranged in the fixed column body.

[0007] Preferably, the electric heating unit comprises a heating cavity, a heating assembly and a pressure sensor; the fixed column body is provided with the heating cavity; the heating cavity is connected with the gas supply pipe at both ends; the inner wall of the heating cavity is fixedly connected with the heating assembly; the pressure sensor is fixedly installed on one side of the heating assembly; and the outlet end of the heating cavity is connected with a sixth one-way valve.

[0008] Preferably, the hole sealing assembly comprises a hole sealer and a water supply pipe; the hole sealer is sleeved on the outer side of the fixed column body; the hole sealer is fixedly connected with one end of the water supply pipe and is in communication with the water supply pipe; the water supply pipe is arranged in close contact with the outer side of the fixed column body and is connected with a seventh one-way valve.

[0009] Preferably, the tip side of the drill bit is provided with a plurality of spray outlets for washing liquid to flow out.

[0010] A method for increasing the permeability of a coal seam based on chemical cold and hot cycle fracturing, comprising the following steps:

[0011] S1, drilling into the target coal seam and processing a bottom hole by using the system;

[0012] S2, starting the perforating string to crack the coal seam near the perforating string, and simultaneously using liquid nitrogen to further fracture the cracked coal seam;

[0013] S3, controlling the system to drill into the bottom hole by Xm, X is 4.5-5; repeating S2 until the drill bit is less than 5m away from the other side of the coal seam, and repeating S2 again;

[0014] S4, controlling the system to retreat to a position 5m away from the opening of the bottom hole, and sealing the bottom hole by using the hole sealing assembly;

[0015] S5, pouring carbon dioxide, high-temperature steam into the closed bottom hole several times in sequence, then pouring liquid nitrogen containing quicklime, and finally pouring hydrochloric acid.

[0016] Preferably, the number of times in step S5 is determined by dividing the thickness of the coal seam by Xm and taking the integer.

[0017] Preferably, in step S1, the depth of the bottom hole is Xm.

[0018] Preferably, in step S5, the particle size of the quicklime is determined according to the temperature of the liquid nitrogen induced cracking.

[0019] The present application has the following technical effects:

[0020] The present application improves the production of coalbed methane, effectively connects each step, and effectively utilizes the residues of previous steps, thereby reducing the risk of coal mine gas. The perforating string can enhance the diffusion effect of liquid nitrogen and increase the cracking range. After the liquid nitrogen endothermic fracturing of the coal seam, it becomes a mixed gas with the injected carbon dioxide in the next step, which has a better effect on gas displacement than single gas displacement. Injecting high-temperature steam can promote methane desorption, increase the temperature of the coal seam, and improve the temperature difference to enhance the fracturing effect of liquid nitrogen. The increase of water content in the coal seam can improve the effect of liquid nitrogen fracturing of the coal seam. Liquid nitrogen carrying quicklime powder can temporarily prevent quicklime from reacting with liquid water, thereby increasing the dispersion range of quicklime, and liquid nitrogen can also perform secondary fracturing of the coal seam. After the temperature returns to normal, the liquid water in the coal body reacts with the quicklime carried into the coal body fissure by liquid nitrogen to generate heat, which can promote methane desorption and fissure development again. The generated slaked lime reacts with the carbon dioxide in the coal seam fissure to generate calcium carbonate, which has a larger molecular size than calcium oxide and slaked lime, and can expand the fissure to make it expand. The injected hydrochloric acid can react with the calcium carbonate generated in the previous step and the carbonate substances originally existing in the coal seam to remove the blockage of the coal seam seepage channel. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0022] Fig. 1 It is a schematic view of the front structure of the present application;

[0023] Fig. 2 It is a schematic view of the coal seam section structure using the present application;

[0024] Fig. 3 It is a schematic view of the connection structure of the present application and external equipment;

[0025] The components include: 1. Fixed column; 2. Perforation string; 3. Drill bit; 4. Positioner; 5. Cleaning pipe; 6. First check valve; 7. Gas supply pipe; 8. Carbon gas pipe; 9. Liquid nitrogen pipe; 10. Hydrochloric acid pipe; 11. Second check valve; 12. Third check valve; 13. Fourth check valve; 14. Fifth check valve; 15. Heating chamber; 16. Heating assembly; 17. Pressure sensor; 18. Sixth check valve; 19. Sealer; 20. Water supply pipe; 21. Seventh check valve; 22. Spray outlet; 23. Temperature sensor. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Depend on Figs. 1-3 The illustrated coal seam fracturing and permeability enhancement system based on chemical thermal cycling includes a fracturing section, a perforation string 2, and a drill bit 3. The fracturing section includes a fixed column 1, inside which is a pipeline assembly for injecting different liquids into the coal seam. The pipeline assembly passes through one end face and the side face of the fixed column 1. Several sealing components for sealing the bottom holes of the coal seam are fitted on the outer side of the fixed column 1. One end face of the fixed column 1 is fixedly connected to and communicates with an external drilling rig, and the other end face of the fixed column 1 is fixedly connected to and communicates with one end face of the perforation string 2. The other end face of the perforation string 2 is fixedly connected to and communicates with the fixed end of the drill bit 3. A positioner 4 for positioning the drill bit 3 is fixedly installed in the inner cavity of the perforation string 2. The excavating end of the drill bit 3 is used to excavate the bottom holes of the coal seam. A cleaning pipe 5 is opened at the center of one end face of the fixed column 1. One end of the cleaning pipe 5 passes through the perforation string 2 and the drill bit 3 and is connected to the external atmosphere. A first one-way valve 6 is connected in series on the cleaning pipe 5. The sealing assembly includes a sealing device 19 and a water supply pipe 20. The sealing device 19 is sleeved on the outer side of the fixed column 1. The sealing device 19 is fixedly connected to one end of the water supply pipe 20 and is in communication with it. The water supply pipe 20 is set to fit against the outer side of the fixed column 1 and is connected in series with a seventh one-way valve 21.

[0029] The scheme is further optimized. The pipeline group includes a gas supply pipe 7, a carbon gas pipe 8, a liquid nitrogen pipe 9, and a hydrochloric acid pipe 10. Each of the gas supply pipe 7, carbon gas pipe 8, liquid nitrogen pipe 9, and hydrochloric acid pipe 10 is provided in several groups and arranged radially from the outside of the fixed column 1 towards the center. The gas supply pipe 7, carbon gas pipe 8, liquid nitrogen pipe 9, and hydrochloric acid pipe 10 are connected in series with a second one-way valve 11, a third one-way valve 12, a fourth one-way valve 13, and a fifth one-way valve 14, respectively. An electric heating unit for heating water is also connected in series inside the gas supply pipe 7. The electric heating unit is located inside the fixed column 1.

[0030] Furthermore, the cleaning pipe 5 is fixedly connected to and connected to an external cleaning liquid storage tank via a water pump; the air supply pipe 7 and the water supply pipe 20 are fixedly connected to and connected to an external water tank via water pumps; the carbon gas pipe 8 is fixedly connected to and connected to an external gas tank; the hydrochloric acid pipe 10 is fixedly connected to and connected to an external hydrochloric acid pump station; and the liquid nitrogen pipe 9 is fixedly connected to and connected to an external liquid nitrogen pump station. All of the above are existing technologies and will not be described in detail here.

[0031] Further optimization of the design: the electric heating unit includes a heating chamber 15, a heating component 16, and a pressure sensor 17. The heating chamber 15 is provided inside the fixed column 1. Both ends of the heating chamber 15 are connected to the air supply pipe 7. The inner wall of the heating chamber 15 is fixedly connected to the heating component 16. The heating chamber 15 is a cavity, and the heating component 16 will not obstruct water from passing through the air supply pipe 7. The pressure sensor 17 is fixedly installed on one side of the heating component 16, and a sixth one-way valve 18 is connected in series at the outlet end of the heating chamber 15.

[0032] Furthermore, the heating component 16 is preferably an electric heating rod, which is existing technology and will not be described in detail here.

[0033] To further optimize the design, the tip of the drill bit 3 is provided with several nozzles 22 for the outflow of cleaning fluid.

[0034] A method for fracturing and permeability enhancement of coal seams based on chemical thermal cycling includes the following steps:

[0035] S1. Use this system to drill into the target coal seam and process it to form a bottom hole, and record the coal seam temperature;

[0036] S2. Start the perforation string 2 to fracturing the coal seam near the perforation string 2, and at the same time use liquid nitrogen to further fracturing the fracturing coal seam.

[0037] S3. Control the system to drill Xm into the bottom hole again, where X is 4.5-5; repeat S2 until drill bit 3 is less than 5m away from the other side of the coal seam, and repeat S2 again.

[0038] S4. Control the system to retreat to a position 5m away from the bottom hole opening, and use the sealing assembly to seal the bottom hole;

[0039] S5. Carbon dioxide and high-temperature steam are injected into the sealed bottom hole several times in sequence, followed by liquid nitrogen containing quicklime, and finally hydrochloric acid.

[0040] To further optimize the scheme, the number of steps in step S5 is determined by dividing the coal seam thickness by Xm and taking the integer part.

[0041] To further optimize the scheme, in step S1, the depth of the bottom hole is Xm.

[0042] To further optimize the scheme, in step S5, the particle size of quicklime is determined based on the temperature at which liquid nitrogen is used for cracking.

[0043] Based on the aforementioned method for fracturing and permeability enhancement of coal seams using chemical thermal cycling, its working process is described in detail below:

[0044] 1. Before starting, the first check valve 6, the second check valve 11, the third check valve 12, the fourth check valve 13, the fifth check valve 14, the sixth check valve 18, and the seventh check valve 21 are all in the closed state.

[0045] 2. Using an external drilling rig to control the drill bit 3 to drill into the coal seam, open the first one-way valve 6 connected in series on the cleaning pipe 5, start the corresponding water pump, and provide cleaning fluid to the drill bit 3, which can reduce the temperature rise of the drill bit 3 during the drilling process. Until the drilling depth is X meters, close the corresponding water pump and the first one-way valve 6, and record the coal seam temperature b through the temperature sensor 23.

[0046] 3. Start the perforating gun on the perforating string 2 to perforate and fracture the coal seam near the perforating string 2.

[0047] 4. Start the liquid nitrogen pump station and open the fourth check valve 13 connected in series on the liquid nitrogen pipe 9. A large amount of liquid nitrogen will be input into the gap between the side of the fixed column 1 and the bottom hole sidewall through the liquid nitrogen pipe 9, and gradually penetrate into the coal seam near the perforated pipe string 2 to cause fracturing. After a large amount of liquid nitrogen further fracturing the coal seam, close the fourth check valve 13 and the liquid nitrogen pump station.

[0048] 5. Use an external drilling rig to control drill bit 3 to drill forward and then drill Xm further.

[0049] 6. Repeat steps 3, 4 and 5 until drill bit 3 is less than 5 meters away from the other side of the coal seam, then execute steps 3 and 4 again.

[0050] 7. Wait for the liquid nitrogen to vaporize; at this time, the coal seam still contains a small amount of nitrogen.

[0051] 8. Control the external drilling rig to pull the drill bit 3 back to a distance of Xm from the borehole opening.

[0052] 9. Start the water pump connected in series with the water tank and corresponding to the seventh check valve 21, open the seventh check valve 21, so that the water in the water tank flows to the sealing device 19 through the water supply pipe 20. After the sealing device 19 successfully seals the bottom hole, close the seventh check valve 21 and the corresponding water pump to maintain the sealing state.

[0053] 10. Start the carbon dioxide storage tank and open the third one-way valve 12 to inject carbon dioxide gas into the coal seam through the carbon gas pipe 8.

[0054] 11. After the coal seam is filled with carbon dioxide gas, close the third one-way valve 12 and the gas tank. Even after some carbon dioxide evaporates, the coal seam still adsorbs a large amount of carbon dioxide.

[0055] 12. Start the water pump connected in series with the gas supply pipe 7, open the second check valve 11 to inject water into the heating chamber 15, and close the sixth check valve 18.

[0056] 13. After injecting a certain amount of water into the heating chamber 15, record the pressure value P fed back by the pressure sensor 17, and start the heating component 16 in the heating chamber 15.

[0057] 14. After the pressure value fed back by the pressure sensor 17 reaches 950-1000 times the P value, the heating component 16 is turned off and the sixth one-way valve 18 is opened. At this time, a large amount of high-pressure water vapor enters the crack in the bottom hole sidewall.

[0058] 15. Repeat steps 12, 13, and 14, the number of times being the coal seam thickness divided by X and rounded down to the nearest integer, then close the sixth check valve 18.

[0059] 16. Add quicklime powder with a mesh size of 300-500 to the liquid nitrogen in the liquid nitrogen pump station. Open the fourth one-way valve 13 connected in series on the liquid nitrogen pipe 9 to inject liquid nitrogen carrying quicklime into the coal seam. Due to the low temperature of the liquid nitrogen, the water in the coal seam temporarily becomes solid. Solid water will not react with quicklime, and quicklime can diffuse with the liquid nitrogen to various fissures in the coal seam. Close the fourth one-way valve 13. After the coal seam temperature rises to -100℃ to -90℃, add quicklime powder with a mesh size of 1000 or higher to the liquid nitrogen in the liquid nitrogen pump station. Open the fourth one-way valve 13 again to inject liquid nitrogen carrying quicklime into the coal seam and then close the fourth one-way valve 13. After the coal seam absorbs heat from the environment, the water becomes liquid and reacts with the quicklime in the fissures, releasing heat, promoting fissure development, increasing permeability, and promoting methane desorption. The generated slaked lime then reacts with the carbon dioxide adsorbed on the coal seam to form calcium carbonate.

[0060] 17. After the temperature recovers to 0.95-1.05°C, start the hydrochloric acid pump station and open the fifth one-way valve 14 to inject a large amount of hydrochloric acid into the coal seam. The injected hydrochloric acid reacts with the calcium carbonate in the coal seam to produce calcium chloride and water. Calcium chloride is easily soluble in water, making it convenient to be discharged along with water during subsequent coalbed methane drainage.

[0061] Furthermore, the timing and flow rate of introducing high-temperature, high-pressure steam, as well as liquid nitrogen and hydrochloric acid, are determined based on the actual geological parameters of the coal seam.

[0062] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0063] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for increasing the permeability of coal seams based on chemical cold-hot cycle fracturing, based on a system for increasing the permeability of coal seams based on chemical cold-hot cycle fracturing, characterized in that, The utility model relates to a coal seam drilling system, including cracking section, perforating string (2) and drill bit (3), the cracking section includes fixed column body (1), the fixed column body (1) inside is provided with pipe group for pouring different liquid to coal seam, and the pipe group penetrates the one end surface and lateral surface of fixed column body (1), the lateral surface of fixed column body (1) is sleeved with a plurality of hole sealing components for plugging coal seam bottom hole, and one end surface of fixed column body (1) is fixedly connected with external drilling machine and communicates, the other end surface of fixed column body (1) is fixedly connected with one end surface of perforating string (2) and communicates, and the other end surface of perforating string (2) is fixedly connected with the fixed end of drill bit (3) and communicates, the positioner (4) for positioning the position of drill bit (3) is fixedly installed in the inner chamber of perforating string (2), and the excavating end of drill bit (3) is used for excavating coal seam bottom hole, and the center of one end surface of fixed column body (1) is provided with cleaning pipe (5), and one end of cleaning pipe (5) penetrates perforating string (2), drill bit (3) respectively and communicates with external atmosphere, and first check valve (6) is connected in series on cleaning pipe (5), and temperature sensor (23) is fixedly installed on the lateral surface of fixed column, The pipe group includes gas supply pipe (7), carbon gas pipe (8), liquid nitrogen pipe (9) and hydrochloric acid pipe (10), the gas supply pipe (7), carbon gas pipe (8), liquid nitrogen pipe (9) and hydrochloric acid pipe (10) are all provided with a plurality of groups and are arranged in the radial direction from the outside of fixed column body (1) to the center in turn, the gas supply pipe (7), carbon gas pipe (8), liquid nitrogen pipe (9) and hydrochloric acid pipe (10) are connected in series with second check valve (11), third check valve (12), fourth check valve (13) and fifth check valve (14) respectively, and the electric heating unit for heating water is connected in series in the gas supply pipe (7), and the electric heating unit is arranged in the inside of fixed column body (1), Further comprising the following steps: S1, using the system to drill into the target coal seam and process to form a bottom hole; S2, start perforating string (2) to crack the coal seam near perforating string (2), and at the same time use liquid nitrogen to further fracture the cracked coal seam; S3, control the system to drill into the bottom hole again by Xm, X is 4.5-5, repeat S2 until the drill bit (3) is less than 5m from the other side of the coal seam, and repeat S2 again; S4, control the system to retreat to a position 5m away from the bottom hole opening, and seal the bottom hole using the hole sealing component; S5, pour carbon dioxide, high-temperature steam into the closed bottom hole several times, then pour liquid nitrogen with quicklime, and finally pour hydrochloric acid.

2. The method for increasing the permeability of coal seams by chemical cold thermal cycling fracturing according to claim 1, characterized in that: The electric heating unit comprises a heating cavity (15), a heating assembly (16) and a pressure sensor (17), the inside of the fixed column body (1) is provided with the heating cavity (15), the two ends of the heating cavity (15) are communicated with the gas supply pipe (7) respectively, and the inner wall of the heating cavity (15) is fixedly connected with the heating assembly (16); the pressure sensor (17) is fixedly installed on one side of the heating assembly (16), and the outlet end of the heating cavity (15) is connected with the sixth one-way valve (18) in series.

3. The method for increasing the permeability of coal seams by chemical cold thermal cycling fracturing according to claim 1, characterized in that: The hole sealing assembly comprises a hole sealer (19) and a water supply pipe (20), the hole sealer (19) is sleeved on the outer side of the fixed column body (1), the hole sealer (19) is fixedly connected with one end of the water supply pipe (20) and is communicated, the water supply pipe (20) is arranged in close contact with the outer side of the fixed column body (1), and the water supply pipe (20) is connected with the seventh one-way valve (21) in series.

4. The method of claim 1, wherein the method is characterized by: The tip side of the drill bit (3) is provided with a plurality of spray outlets (22) for washing liquid outflow.

5. The method of claim 1, wherein the method is characterized by: The number of times in step S5 is determined by dividing the coal seam thickness by Xm and taking an integer.

6. The method of claim 1, wherein the method is characterized by: In step S1, the depth of the bottom hole is Xm.

7. The method of claim 1, wherein the method is characterized by: In step S5, the particle size of the quicklime is determined according to the temperature of the liquid nitrogen induced cracking. In step S1, the depth of the bottom hole is Xm. In step S5, the particle size of the quicklime is determined according to the temperature of the liquid nitrogen induced cracking.

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