Coal bed gas yield increasing system and method

Abstract

The invention relates to the technical field of coal bed gas exploitation, and discloses a coal bed gas yield increasing system and method, and the coal bed gas yield increasing system comprises a fracturing channel which is drilled in a coal bed of a coal bed gas exploitation area; the nitrogen generation mechanism communicates with the first end of the fracturing channel, and the nitrogen generation mechanism generates high-pressure nitrogen and conveys the high-pressure nitrogen to the fracturing channel through an N2 injection pipeline; the carbon dioxide generating mechanism communicates with the first end of the fracturing channel, and the carbon dioxide generating mechanism can generate carbon dioxide and convey the carbon dioxide to the fracturing channel through a CO2 injection pipeline; and the extraction mechanism communicates with the second end of the fracturing channel through an extraction pipeline, and the extraction mechanism can extract coal bed gas. Nitrogen and carbon dioxide are injected into the coal seam alternately and circularly, and the yield of the coal seam gas can be increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal bed methane mining, in particular to a coal bed methane production system and a production method. BACKGROUND

[0002] Coal bed methane is mainly composed of methane, and its combustion product is mainly water vapor and carbon dioxide, without sulfur, nitrogen and other pollutant emissions, which is a clean energy. At present, the coal seams of some coalfields in China are deformed under the action of intense tectonic activity. The coal seams with serious tectonic damage usually contain abundant coal bed methane, but the permeability and mechanical strength thereof are low, resulting in low methane recovery rate. Methane is a strong greenhouse gas, and if it is leaked to the atmosphere due to unreasonable extraction, not only the resources will be wasted, but also pollution will be caused.

[0003] At present, the technology of injecting carbon dioxide into coal seams to promote carbon dioxide geological storage and improve coal bed methane recovery rate (CO2-ECBM) can effectively solve the above problems. Since the adsorption potential of carbon dioxide on coal is greater than that of methane, the adsorbed methane is induced to change into free-state methane under competitive adsorption, thereby effectively improving the methane recovery rate. This technology has the dual advantages of energy saving and environmental protection. However, in practical application, the effect of CO2-ECBM technology is affected by many factors, and sometimes the expected effect cannot be achieved. The reason is that the major difficulty of CO2-ECBM technology lies in that the swelling of coal body will reduce the carbon dioxide injectability, carbon dioxide is easy to produce acidification reaction with water and minerals in coal, carbon dioxide is easy to form hydrogen bond or charge transfer with coal, and coal structure reorganization occurs, which causes swelling of coal and affects the mining of coal bed methane. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a coal bed methane production system and a production method.

[0005] In a first aspect, the present application provides a coal bed methane production system, comprising: a fracturing channel drilled in a coal seam of a coal bed methane mining area, comprising a first end and a second end opposite to each other; a nitrogen gas generating mechanism in communication with the first end of the fracturing channel through an N2 injection pipeline, the nitrogen gas generating mechanism being capable of generating high-pressure nitrogen gas and delivering the high-pressure nitrogen gas to the fracturing channel through the N2 injection pipeline to fracture the coal seam and flush out free-state methane; a carbon dioxide generating mechanism in communication with the first end of the fracturing channel through a CO2 injection pipeline, the carbon dioxide generating mechanism being capable of generating carbon dioxide and delivering the carbon dioxide to the fracturing channel through the CO2 injection pipeline, the carbon dioxide competing with the methane in the coal seam to convert the adsorbed methane into free-state methane; and an extraction mechanism in communication with the second end of the fracturing channel through an extraction pipeline, the extraction mechanism being capable of extracting coal bed methane.

[0006] Optionally, the system further comprises a gas separator capable of separating nitrogen, carbon dioxide and methane, wherein the gas separator comprises a mixed gas inlet, a nitrogen outlet, a carbon dioxide outlet and a methane outlet, the mixed gas inlet is communicated with the outlet of the extraction mechanism, the nitrogen outlet is communicated with the inlet of the nitrogen generating mechanism, the carbon dioxide outlet is communicated with the inlet of the carbon dioxide generating mechanism, and the methane outlet is connected with a CH4 storage tank.

[0007] Optionally, the nitrogen generating mechanism comprises an N2 storage tank, the N2 storage tank is communicated with the nitrogen outlet of the gas separator through a first pipeline, the N2 storage tank is communicated with an N2 injection pipeline, and a first high-pressure booster pump is arranged on the N2 injection pipeline.

[0008] Optionally, the carbon dioxide generating mechanism comprises a CO2 storage tank, the CO2 storage tank is communicated with the carbon dioxide outlet of the gas separator through a second pipeline, the CO2 storage tank is communicated with a CO2 injection pipeline, and a second high-pressure booster pump is arranged on the CO2 injection pipeline.

[0009] Optionally, an eighth one-way valve is arranged on the first pipeline, a first one-way valve is arranged on the N2 injection pipeline upstream of the first high-pressure booster pump, a first pressure sensor and a second one-way valve are arranged on the N2 injection pipeline downstream of the first high-pressure booster pump in sequence, a fifth one-way valve is arranged on the second pipeline, a fourth one-way valve is arranged on the CO2 injection pipeline upstream of the second high-pressure booster pump, and a second pressure sensor and a third one-way valve are arranged on the CO2 injection pipeline downstream of the second high-pressure booster pump in sequence.

[0010] Optionally, the extraction mechanism comprises a high-pressure air extraction pump communicated with the extraction pipeline, a sixth one-way valve and a third pressure sensor are arranged on the extraction pipeline in sequence along the flow direction of the gas in the extraction pipeline, the high-pressure air extraction pump is communicated with the mixed gas inlet of the gas separator through a third pipeline, and a seventh one-way valve is arranged on the third pipeline.

[0011] Optionally, the coal bed gas extraction area is drilled with an injection well and an extraction well, the first end and the second end of the fracturing channel are communicated with the injection well and the extraction well respectively, the N2 injection pipeline and the CO2 injection pipeline are inserted into the injection well, and the extraction pipeline is inserted into the extraction well.

[0012] Optionally, the wellheads of the injection well and the extraction well, and the first end and the second end of the fracturing channel are respectively provided with packers.

[0013] In a second aspect, the present application provides a coal bed gas production increasing method of the coal bed gas production increasing system, comprising: Step one, drilling a fracturing channel in the coal bed of the coal bed gas extraction area; Step two, the nitrogen generating mechanism injects high-pressure nitrogen into the fracturing channel through the N2 injection pipeline to fracture the coal bed, the time length of injecting the high-pressure nitrogen is a first preset time length, and the coal bed gas is extracted through the extraction mechanism when the high-pressure nitrogen is injected. Step three, the carbon dioxide generating mechanism injects high pressure carbon dioxide into the fracturing channel through the CO2 injection pipeline, the carbon dioxide competes with the methane in the coal seam for adsorption, converts the adsorbed methane into free methane, improves the coal seam gas recovery rate, the time length of injecting the high pressure carbon dioxide is a second preset time length, and the coal seam gas is extracted through the extraction mechanism when the high pressure carbon dioxide is injected; Step four, steps two to four are repeated until the concentration of methane in the extracted coal seam gas is lower than a preset value, and then the coal seam gas extraction operation is completed after a third preset time length.

[0014] Optionally, the pressure of nitrogen in the N2 injection pipeline is 8MPa~15MPa, the pressure of carbon dioxide in the CO2 injection pipeline is 9MPa~16MPa, the first preset time length is 15 hours~20 hours, the second preset time length is 70 hours~75 hours, the preset value is 0.08%~0.12%, and the third preset time length is 1 hour~6 hours.

[0015] Compared with the prior art, the technical scheme provided by the embodiment of the present application has the following advantages: By setting the nitrogen generating mechanism, high pressure N2 can be injected into the coal seam to fracture the coal seam, cracks are generated while the reservoir pressure is maintained in a high range, CH4 is desorbed due to the decrease in partial pressure, and free state CH4 is flushed out, thereby effectively improving the coal seam permeability and improving the CO2 injectability. After a large amount of CO2 is injected, CH4 existing in the micro pores is displaced out due to the stronger adsorption capacity of CO2 than N2 and CH4, and is converted into a free state. In this process, the coal matrix will swell and deform due to gas adsorption, the cracks will close, the permeability will decrease, and by injecting N2 again, the closed cracks caused by CO2 adsorption are opened, the number of repeated alternating gas injection is increased, and the desorption amount of coal seam gas is increased. Therefore, by injecting N2 / CO2 to provide formation energy, the formation pressure drop speed is slowed down to improve the gas reservoir recovery rate. Injecting N2 into the reservoir can effectively prevent the decrease in reservoir permeability caused by the closure of cracks, a large flow rate of injected gas carries out the free state CH4, and the purpose of promoting CH4 extraction is achieved. Since CO2 has a storage effect, the N2 / CO2 alternating injection method is adopted to effectively improve the coal seam gas production. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A structure schematic diagram of a coal seam gas production increasing system provided for the embodiment one of the present application.

[0017] Explanation of reference numerals in the attached diagram: 1. N2 storage tank; 2. CO2 storage tank; 3. CH4 storage tank; 4. First high-pressure booster pump; 5. Second high-pressure booster pump; 6. First pressure sensor; 7. Second pressure sensor; 8. Third pressure sensor; 9. High-pressure suction pump; 10. Gas separator; 11-1. First check valve; 11-2. Second check valve; 11-3. Third check valve; 11-4. Fourth check valve; 11-5. Fifth check valve; 11-6. Sixth check valve; 11-7. Seventh check valve; 11-8. Eighth check valve; 12. N2 injection pipeline; 13. CO2 injection pipeline; 14. Extraction pipeline; 15. Blocker; 16. Soil layer; 17. Rock layer; 18. Coal seam; 19. Fractured area. Detailed Implementation

[0018] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.

[0019] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the technical solution of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] Example 1: like Figure 1 As shown, this embodiment provides a coalbed methane production enhancement system, including: a fracturing channel drilled in a coal seam 18 in a coalbed methane mining area, including a first end and a second end opposite to each other; a nitrogen generating mechanism connected to the first end of the fracturing channel via an N2 injection pipe 12, the nitrogen generating mechanism can generate high-pressure nitrogen and transport the high-pressure nitrogen to the fracturing channel through the N2 injection pipe 12 to fracture the coal seam 18 and flush out free methane; a carbon dioxide generating mechanism connected to the first end of the fracturing channel via a CO2 injection pipe 13, the carbon dioxide generating mechanism can generate carbon dioxide and transport the carbon dioxide to the fracturing channel through the CO2 injection pipe 13, the carbon dioxide competes with the methane in the coal seam 18 for adsorption, converting the adsorbed methane into free methane; and an extraction mechanism connected to the second end of the fracturing channel via an extraction pipe 14, the extraction mechanism can extract coalbed methane.

[0021] like Figure 1As shown, the upper layer of the coal bed gas mining area is soil layer 16, below the soil layer 16 is rock layer 17, and below the rock layer 17 is coal bed 18. When the high-pressure nitrogen gas reaches the fracturing channel, the coal bed can be fractured to generate cracks 19.

[0022] The gas separator 10 is also capable of separating nitrogen, carbon dioxide and methane. The gas separator 10 includes a mixed gas inlet, a nitrogen outlet, a carbon dioxide outlet and a methane outlet. The mixed gas inlet is in communication with the outlet of the extraction mechanism, the nitrogen outlet is in communication with the inlet of the nitrogen generating mechanism, the carbon dioxide outlet is in communication with the inlet of the carbon dioxide generating mechanism, and the methane outlet is connected with the CH4 storage tank 3.

[0023] The nitrogen generating mechanism includes an N2 storage tank 1, which is in communication with the nitrogen outlet of the gas separator 10 through a first pipeline, and is in communication with an N2 injection pipeline 12. The first high-pressure booster pump 4 is arranged on the N2 injection pipeline 12.

[0024] The carbon dioxide generating mechanism includes a CO2 storage tank 2, which is in communication with the carbon dioxide outlet of the gas separator 10 through a second pipeline, and is in communication with a CO2 injection pipeline 13. The second high-pressure booster pump 5 is arranged on the CO2 injection pipeline 13.

[0025] The first pipeline is provided with an eighth one-way valve 11-8. The N2 injection pipeline 12 is provided with a first one-way valve 11-1 upstream of the first high-pressure booster pump 4, and is sequentially provided with a first pressure sensor 6 and a second one-way valve 11-2 downstream of the first high-pressure booster pump 4. The second pipeline is provided with a fifth one-way valve 11-5. The CO2 injection pipeline 13 is provided with a fourth one-way valve 11-4 upstream of the second high-pressure booster pump 5, and is sequentially provided with a second pressure sensor 7 and a third one-way valve 11-3 downstream of the second high-pressure booster pump 5.

[0026] The extraction mechanism includes a high-pressure air extraction pump 9 in communication with the extraction pipeline 14. The extraction pipeline 14 is sequentially provided with a sixth one-way valve 11-6 and a third pressure sensor 8 in the flow direction of the gas in the extraction pipeline 14. The high-pressure air extraction pump 9 is in communication with the mixed gas inlet of the gas separator 10 through a third pipeline. The third pipeline is provided with a seventh one-way valve 11-7.

[0027] The coal bed gas mining area is drilled with an injection well and an extraction well. The first end and the second end of the fracturing channel are in communication with the bottom of the injection well and the extraction well, respectively. The N2 injection pipeline 12 and the CO2 injection pipeline 13 are inserted into the injection well, and the extraction pipeline 14 is inserted into the extraction well.

[0028] The wellheads of the injection well and the extraction well, and the first end and the second end of the fracturing channel are respectively provided with a packer 15.

[0029] In the embodiment, a nitrogen backup tank, a carbon dioxide backup tank, and a controller electrically connected with the first pressure sensor 6 and the second pressure sensor 7 are further included, the nitrogen backup tank and the N2 storage tank 1 are communicated through a fourth pipeline, the carbon dioxide backup tank and the CO2 storage tank 2 are communicated through a fifth pipeline, the fourth pipeline and the fifth pipeline are respectively provided with an electromagnetic valve and a one-way valve, the two electromagnetic valves are electrically connected with the controller, when the monitoring value on the first pressure sensor 6 and / or the second pressure sensor 7 is less than a preset value, it indicates that the gas in the N2 storage tank 1 and / or the CO2 storage tank 2 is insufficient, and the controller controls the corresponding electromagnetic valve to open to supplement the corresponding gas into the corresponding storage tank.

[0030] Embodiment two: The embodiment provides a stimulation method of a coalbed methane stimulation system, which comprises the following steps: Step one, drilling a fracturing channel in a coal seam 18 in a coalbed methane mining area; Step two, injecting high-pressure nitrogen into the fracturing channel by a N2 injection pipeline 12 through a nitrogen generating mechanism to fracture the coal seam 18, the time length of injecting the high-pressure nitrogen is a first preset time length, and the coalbed methane is extracted by an extraction mechanism when the high-pressure nitrogen is injected; Step three, injecting high-pressure carbon dioxide into the fracturing channel by a CO2 injection pipeline 13 through a carbon dioxide generating mechanism, the carbon dioxide competes with the methane in the coal seam 18 to convert the adsorbed methane into free methane, thereby improving the coalbed methane recovery rate, the time length of injecting the high-pressure carbon dioxide is a second preset time length, and the coalbed methane is extracted by the extraction mechanism when the high-pressure carbon dioxide is injected; Step four, repeating steps two to four until the concentration of the methane in the extracted coalbed methane is lower than a preset value, and then completing the coalbed methane mining operation after continuously extracting for a third preset time length.

[0031] In the embodiment, the pressure of the nitrogen in the N2 injection pipeline 12 is 8 MPa to 15 MPa, the pressure of the carbon dioxide in the CO2 injection pipeline 13 is 9 MPa to 16 MPa, the first preset time length is 15 hours to 20 hours, the second preset time length is 70 hours to 75 hours, the preset value is 0.08% to 0.12%, and the third preset time length is 1 hour to 6 hours.

[0032] The above embodiment of the application is only a few specific embodiments of the application, but the embodiments of the application are not limited to this, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the application.

Claims

1. A coal bed gas stimulation system, comprising: The application relates to a coal bed methane mining device. The device comprises a fracturing channel drilled in a coal bed of a coal bed methane mining area, a nitrogen generating mechanism and a carbon dioxide generating mechanism. The nitrogen generating mechanism is connected with the first end of the fracturing channel through an N2 injection pipeline, and can generate high-pressure nitrogen and send the high-pressure nitrogen to the fracturing channel through the N2 injection pipeline to fracture the coal bed and flush out free-state methane. The carbon dioxide generating mechanism is connected with the first end of the fracturing channel through a CO2 injection pipeline, and can generate carbon dioxide and send the carbon dioxide to the fracturing channel through the CO2 injection pipeline to compete with the methane in the coal bed and convert the adsorbed-state methane into free-state methane. The device further comprises a gas separator capable of separating nitrogen, carbon dioxide and methane.

2. The coal bed gas stimulation system of claim 1, wherein, The gas separator comprises a mixed gas inlet, a nitrogen outlet, a carbon dioxide outlet and a methane outlet. The nitrogen outlet is connected with the nitrogen generating mechanism, the carbon dioxide outlet is connected with the carbon dioxide generating mechanism, and the methane outlet is connected with a CH4 storage tank.

3. The coal bed gas stimulation system of claim 2, wherein, The nitrogen generating mechanism comprises an N2 storage tank, which is connected with the nitrogen outlet of the gas separator through a first pipeline, and is connected with the N2 injection pipeline.

4. The coal bed gas stimulation system of claim 3, wherein, The carbon dioxide generating mechanism comprises a CO2 storage tank, which is connected with the carbon dioxide outlet of the gas separator through a second pipeline, and is connected with the CO2 injection pipeline.

5. The coal bed gas stimulation system of claim 4, wherein, The first pipeline is provided with an eighth one-way valve, the N2 injection pipeline is provided with a first one-way valve upstream of a first high-pressure booster pump, and is provided with a first pressure sensor and a second one-way valve downstream of the first high-pressure booster pump. The second pipeline is provided with a fifth one-way valve, the CO2 injection pipeline is provided with a fourth one-way valve upstream of a second high-pressure booster pump, and is provided with a second pressure sensor and a third one-way valve downstream of the second high-pressure booster pump.

6. The coal bed gas stimulation system of claim 2, wherein, The extraction mechanism comprises a high-pressure air extraction pump connected with the extraction pipeline, and is provided with a sixth one-way valve and a third pressure sensor along the flow direction of the gas in the extraction pipeline.

7. The coal bed gas stimulation system of claim 1, wherein, The coal bed methane mining area is provided with an injection well and an extraction well, the first end and the second end of the fracturing channel are connected with the injection well and the extraction well respectively, the N2 injection pipeline and the CO2 injection pipeline are inserted into the injection well, and the extraction pipeline is inserted into the extraction well.

8. The coal bed gas stimulation system of claim 7, wherein, The wellheads of the injection well and the extraction well, and the first end and the second end of the fracturing channel are respectively provided with a plugging device.

9. The method of stimulating production of a coal bed gas production system according to any one of claims 1 to 8, wherein, The application relates to a coal bed methane mining device. Step one, drilling a fracturing channel in a coal bed of a coal bed methane mining area. Step two, the nitrogen generation mechanism injects high-pressure nitrogen into the fracturing channel through the N2 injection pipeline to fracture the coal seam, the duration of injecting high-pressure nitrogen is the first preset duration, and the coalbed methane is extracted through the extraction mechanism when the high-pressure nitrogen is injected; Step three, the carbon dioxide generation mechanism injects high-pressure carbon dioxide into the fracturing channel through the CO2 injection pipeline, the carbon dioxide competes with the methane in the coal seam for adsorption, converts the adsorbed methane into free methane, improves the coalbed methane recovery rate, the duration of injecting high-pressure carbon dioxide is the second preset duration, and the coalbed methane is extracted through the extraction mechanism when the high-pressure carbon dioxide is injected; Step four, steps two to four are repeated until the concentration of methane in the extracted coalbed methane is lower than a preset value, and then the coalbed methane extraction operation is completed after a third preset duration.

10. The method of stimulating production of a coal bed gas stimulation system of claim 9, wherein, The pressure of nitrogen in the N2 injection pipeline is 8MPa-15MPa, the pressure of carbon dioxide in the CO2 injection pipeline is 9MPa-16MPa, the first preset duration is 15 hours-20 hours, the second preset duration is 70 hours-75 hours, the preset value is 0.08%-0.12%, and the third preset duration is 1 hour-6 hours.

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