Method for enhancing extraction of coal body by gas fracturing through controllable electric pulse explosion in borehole

Abstract

This invention belongs to the field of low-permeability coal seam gas extraction technology, specifically relating to a method for enhanced gas extraction from coal seams using controllable electric pulse combustion explosion. Several boreholes are drilled within the coal seam, including combustion explosion boreholes and extraction boreholes adjacent to them. A drill rod is lowered into the combustion explosion borehole through a sealing device. An electric pulse device and an injection pipe are installed inside the drill rod, and the front end of the drill rod is sealed with a constant-pressure fracturing disc. The injection pipe is connected to a gas source containing a mixture of gas and oxygen, and the electric pulse device is connected to its control circuit. The gas inside the drill rod ignites and explodes, breaking through the constant-pressure fracturing disc and igniting the gas in the combustion explosion borehole, creating a secondary combustion explosion that disturbs the gas in the surrounding coal seam. The superposition of the two explosion waves generates a larger shock wave, causing abundant cracks in the coal seam surrounding the borehole. This method ignites the entire coal seam surrounding the borehole, resulting in good fracturing effect, low cost, and simple operation, effectively improving the gas extraction efficiency around the borehole.

Description

Technical Field

[0001] This invention belongs to the field of low-permeability coal seam gas extraction technology, specifically relating to a method for enhanced extraction of coal seams fractured by controllable electric pulse combustion gas in boreholes. Background Technology

[0002] Most coal mines in my country are high-gas, low-permeability mines. Pre-drainage using negative pressure drilling can effectively prevent coal and gas outbursts. However, with the deepening of coal mining, poor coal seam permeability and unsatisfactory drainage effects have become one of the main problems restricting coal seam mining. Therefore, it is essential to explore an effective fracturing and permeability-enhancing technology for deep coal seams. For many years, the method of using explosive shock waves to create fractures in the coal seam to enhance gas drainage has proven to be effective. Traditionally, this involves filling with explosives, using the shock waves generated by the explosion to damage the coal seam and create fractures, thus increasing permeability. However, this method has many limitations: explosives and detonating cords are strictly controlled; handling misfires is extremely dangerous; and the blast radius is relatively small. Therefore, given the shortcomings of existing blasting fracturing methods, it is particularly important to propose a low-cost, safe, and reliable method for effectively enhancing permeability and fracturing deep coal seams.

[0003] When a certain concentration of methane mixed with oxygen encounters an ignition source, an explosion will occur. Different concentrations of methane mixtures will produce different results. An explosion will not occur when the concentration of the methane mixture is below 5%; the shock wave generated by a methane explosion is strongest at a concentration of 9.5%; and it lacks explosive power when the concentration exceeds 16%. Methane explosions produce high-temperature and high-pressure shock waves. If not effectively controlled, an explosion can endanger lives and damage mine equipment. Simultaneously, methane explosions produce many toxic and harmful gases, potentially causing poisoning. However, when methane explosions can be controlled, the resulting shock force can be used to fracture and increase permeability in the coal seam surrounding the borehole, thereby improving methane extraction efficiency. Summary of the Invention

[0004] The purpose of this invention is to address the issue of low permeability in underground coal seams and the unsatisfactory effect of traditional explosive fracturing methods, and to propose a low-cost, safe, reliable, and effective method for enhanced extraction of coal seams by controlled electric pulse combustion gas fracturing in boreholes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for enhanced extraction of coal seam by controlled electric pulse combustion explosion of gas within a borehole, comprising drilling several boreholes within the coal seam, the boreholes being divided into combustion explosion boreholes and extraction boreholes adjacent to the combustion explosion boreholes; a drill rod is lowered into the combustion explosion borehole through a sealing device, and an electric pulse device and an injection pipe are installed inside the drill rod, with the front end of the drill rod sealed with a constant pressure rupture disc; the injection pipe passes through a sealing plate inside the drill rod and is connected to a gas source of gas and oxygen mixture, and the line connected to the electric pulse device passes through the sealing plate and is connected to the control circuit of the electric pulse device; the gas in the drill rod ignites and explodes, breaking through the constant pressure rupture disc and igniting the gas in the combustion explosion borehole to form a secondary combustion explosion, disturbing the gas in the coal seam surrounding the combustion explosion borehole; the extraction borehole is connected to a gas extraction pipeline for extraction.

[0006] Specifically, the following steps are included:

[0007] a: Construct combustion and extraction boreholes in low-permeability coal seams; the front end of the drill rod is sealed with a constant pressure rupture disc and the rear side is sealed with a sealing plate; the electric pulse device is fixed in the sealed cavity between the constant pressure rupture disc and the sealing plate; one end of the gas injection pipe is connected to the gas injection pump and the other end passes through the sealing plate into the sealed cavity; the gas injection pipe is equipped with a gas injection valve and a pressure gauge; the gas injection pump is connected to both a gas storage tank and an oxygen storage tank.

[0008] b: Connect the drill rod to the sealing device and send it into the explosive borehole. The gas sensor probe of the gas sensor is sent into the explosive borehole after passing through the sealing device. Activate the sealing device to seal the explosive borehole.

[0009] c: After completing the sealing of the explosion borehole, inject a mixture of gas and oxygen into the explosion borehole, observe the gas sensor, and stop the gas injection when the gas concentration is between 9-10% and the gas injection pressure reaches 1-2 MPa.

[0010] d: The electric pulse device discharges and ignites the gas; the gas explosion pressure in the drill pipe exceeds the fixed pressure and the maximum shear stress of the rupture disc is destroyed, the gas that explodes in the drill pipe enters the explosion borehole, and then ignites the gas in the explosion borehole for secondary explosion, causing cracks in the coal body around the borehole.

[0011] e: After the gas explosion is over, the extraction borehole is connected to negative pressure for extraction. After a period of extraction, the gas concentration in the extraction borehole is measured with a gas meter.

[0012] f: When the gas concentration in the extraction borehole is below 30%, inject a mixture of gas and oxygen into the combustion borehole and observe the gas sensor. Stop injecting gas when the gas concentration is between 9-10%.

[0013] g: The electrical pulse device discharges and ignites the gas, causing the gas explosion inside the borehole to further expand the cracks around the borehole.

[0014] Repeat step e.g. multiple times to induce gas explosion and fracturing in the explosive borehole, expanding the fractures around the borehole.

[0015] Furthermore, the diameter of the combustion and extraction boreholes is 120mm, the borehole length is 90m, the combustion and extraction boreholes are parallel, and the parallel spacing is 5-10m.

[0016] Furthermore, the first gas sensor probe was inserted into the bottom of the combustion borehole, and a gas sensor probe was arranged at 30cm intervals along the depth of the borehole.

[0017] Furthermore, the sealing device is used to seal the borehole at a distance of 25m from the opening of the explosive borehole.

[0018] Furthermore, a sealing ring is installed at the connection between the constant pressure rupture disc and the front end of the drill pipe.

[0019] Furthermore, the control circuit of the electric pulse device includes a capacitor charging switch, a capacitor, a capacitor discharging switch, and a capacitor charging power supply; closing the capacitor charging switch charges the capacitor, and after charging is completed, opening the capacitor charging switch stops charging, closing the capacitor discharging switch discharges the ignition gas mixture through the positive and negative terminals of the capacitor discharge in the electric pulse device.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] This method involves inserting a drill pipe into a combustion borehole and sealing it with a constant-pressure fracturing disc. Under the action of an electric pulse device, the gas mixture inside the drill pipe is ignited, generating a combustion explosion and creating an explosive shock wave—this is the primary explosion. After the shock wave breaks the constant-pressure fracturing disc, the combusting gas in the drill pipe enters the combustion borehole, igniting the mixed gas mixture for a secondary combustion explosion. The superposition of the two explosion waves creates an even larger shock wave, causing abundant cracks in the coal seam surrounding the borehole. This method ignites the entire coal seam surrounding the borehole, resulting in good fracturing effect, low cost, and simple operation, effectively improving the gas extraction efficiency around the borehole. The traditional method involves filling the borehole with gas and sealing it for combustion. Compared to the traditional method, this method improves coal seam gas extraction efficiency by more than 30%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a method for enhanced extraction of coal seams by controlled electrical pulse combustion and gas fracturing in boreholes, according to the present invention.

[0023] In the diagram: 1-Explosion borehole; 2-Extraction borehole; 3-Pressure rupture disc; 4-Gas sensor probe; 5-Electrical pulse device; 6-Cant discharge negative electrode; 7-Cant discharge positive electrode; 8-Gas injection pipe; 9-Sealing plate; 10-Gas injection valve; 11-Pressure gauge; 12-Cant discharge switch; 13-Capacitor; 14-Cant charging switch; 15-Cant charging power supply; 16-Gas sensor; 17-Gas injection pump; 18-Gas storage tank; 19-Oxygen storage tank. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0025] Please see Figure 1 It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings of this specification are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the scope of the invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0026] This invention provides a technical solution: a method for enhanced extraction of coal seam by controlled electric pulse combustion and explosion of gas within a borehole. Several boreholes are constructed within the coal seam, including a combustion and explosion borehole 1 and an extraction borehole 2 adjacent to the combustion and explosion borehole 1. A drill rod passes through a sealing device and is lowered into the combustion and explosion borehole 1. An electric pulse device 5 and a gas injection pipe 8 are installed inside the drill rod, and the front end of the drill rod is sealed with a constant pressure rupture disc 3. The gas injection pipe 8 passes through a sealing plate 9 inside the drill rod and is connected to a gas source containing a mixture of gas and oxygen. The circuit connected to the electric pulse device 5 passes through the sealing plate 9 and is connected to the control circuit of the electric pulse device. The gas combustion and explosion within the drill rod breaks through the constant pressure rupture disc 3, igniting the gas in the combustion and explosion borehole 1 to form a secondary combustion and explosion, disturbing the gas in the coal seam surrounding the combustion and explosion borehole 1. The extraction borehole 2 is connected to a gas extraction pipeline for extraction.

[0027] Specifically, the following steps are included:

[0028] a: Construct combustion and explosion borehole 1 and extraction borehole 2 in a low-permeability coal seam; the front end of the drill rod is sealed with a constant pressure rupture disc 3 and the rear side is sealed with a sealing plate 9; an electric pulse device 5 is fixed in the sealed cavity between the constant pressure rupture disc 3 and the sealing plate 9; one end of the gas injection pipe 8 is connected to the gas injection pump 17 and the other end passes through the sealing plate 9 and enters the sealed cavity; a gas injection valve 10 and a pressure gauge 11 are installed in the gas injection pipe 8; the gas injection pump 17 is simultaneously connected to a gas storage tank 18 and an oxygen storage tank 19.

[0029] b: Connect the drill rod to the sealing device and send it into the explosion borehole 1. The gas sensor probe 4 of the gas sensor 16 is sent into the explosion borehole 1 after passing through the sealing device; start the sealing device to seal the explosion borehole 1.

[0030] c: After sealing the explosion borehole 1, inject a mixture of gas and oxygen into the explosion borehole 1, observe the gas sensor 16, and stop the gas injection when the gas concentration is between 9-10% and the gas injection pressure reaches 1-2 MPa.

[0031] d: The electric pulse device 5 discharges and ignites the gas; the gas explosion pressure in the drill pipe exceeds the maximum shear stress of the rupture disc 3, causing it to break. The gas that explodes in the drill pipe enters the explosion borehole 1, which in turn ignites the gas in the explosion borehole 1 and causes a secondary explosion, resulting in cracks in the coal body around the borehole.

[0032] e: After the gas explosion is over, the extraction borehole 2 is connected to negative pressure for extraction. After a period of extraction, the gas concentration in the extraction borehole 2 is measured with a gas meter.

[0033] f: When the gas concentration in the extraction borehole 2 is below 30%, inject a mixture of gas and oxygen into the combustion borehole 1 and observe the gas sensor 16. Stop injecting gas when the gas concentration is between 9-10%.

[0034] g: The electric pulse device 5 discharges and ignites the gas, causing the gas explosion in borehole 1 to expand the cracks around the borehole once again.

[0035] Repeat step eg multiple times to induce gas explosion and fracturing in borehole 1, thereby expanding the fractures around the borehole.

[0036] The controlled electric pulse combustion gas-induced fracturing effect on coal seams has an influence range of 6.2-7m, which is 12% larger than traditional methods. After 100 days of gas drainage using this method, the drainage efficiency decreases by no more than 20%.

[0037] The diameter of the explosion borehole 1 and the extraction borehole 2 is 120mm, and the length of the borehole is 90m. The explosion borehole 1 and the extraction borehole 2 are parallel, with a parallel spacing of 5-10m.

[0038] The first gas sensor probe 4 is inserted into the bottom of the combustion borehole 1, and a gas sensor probe 4 is arranged at 30cm intervals along the depth of the borehole.

[0039] The sealing device was used to seal the borehole 25m away from the opening of the explosion borehole.

[0040] A sealing ring is installed at the connection between the constant pressure rupture disc 3 and the front end of the drill pipe.

[0041] The control circuit of the electric pulse device includes a capacitor charging switch 14, a capacitor 13, a capacitor discharging switch 12, and a capacitor charging power supply 15. When the capacitor charging switch 14 is closed, the capacitor 13 is charged. After the charging is completed, the capacitor charging switch 14 is opened to stop the charging. When the capacitor discharging switch 12 is closed, the ignition gas mixture is discharged through the capacitor discharge positive terminal 7 and capacitor discharge negative terminal 6 in the electric pulse device 5.

[0042] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for enhanced extraction of coal seams fractured by controllable electrical pulse combustion gas in boreholes, characterized in that: Several boreholes are drilled in the coal seam, which are divided into a combustion-explosion borehole (1) and a drainage borehole (2) adjacent to the combustion-explosion borehole (1). The drill rod passes through the sealing device and is lowered into the combustion-explosion borehole (1). An electric pulse device (5) and a gas injection pipe (8) are installed inside the drill rod. The front end of the drill rod is sealed with a constant pressure rupture disc (3). The gas sensor probe (4) of the gas sensor (16) is sent into the combustion-explosion borehole (1) after passing through the sealing device. The gas injection pipe (8) passes through the sealing plate (9) inside the drill rod and is connected to the gas source of the gas and oxygen mixture. The line connected to the electric pulse device (5) passes through the sealing plate (9) and is connected to the control circuit of the electric pulse device. The sealing device seals the combustion-explosion borehole (1) and injects gas into the combustion-explosion borehole (1). A mixture of gas and oxygen is injected into the drill pipe. The gas sensor (16) is observed. When the gas concentration is between 9-10% and the injection pressure reaches 1-2 MPa, the gas injection is stopped. Under the action of the electric pulse device (5), the mixture of gas in the drill pipe is ignited to produce combustion and explosion, forming an explosion shock wave. This is the first explosion. After the gas combustion and explosion in the drill pipe breaks through the constant pressure rupture plate (3), the gas combustion and explosion in the drill pipe enters the combustion and explosion borehole (1), which then ignites the gas in the combustion and explosion borehole (1) to form a secondary combustion and explosion. Under the superposition of the two explosion waves, a larger shock wave is formed, which disturbs the gas in the coal seam around the combustion and explosion borehole (1). The extraction borehole (2) is connected to the gas extraction pipeline for extraction.

2. The method for enhanced extraction of coal seams from boreholes by controllable electrical pulse combustion gas fracturing as described in claim 1, characterized in that, Includes the following steps: a: Construct combustion and explosion boreholes (1) and extraction boreholes (2) in low-permeability coal seams; seal the front end of the drill rod with a constant pressure rupture disc (3) and the rear side with a sealing plate (9); fix an electric pulse device (5) in the sealed chamber between the constant pressure rupture disc (3) and the sealing plate (9); connect one end of the gas injection pipe (8) to the gas injection pump (17) and the other end through the sealing plate (9) into the sealed chamber; install a gas injection valve (10) and a pressure gauge (11) in the gas injection pipe (8); connect the gas injection pump (17) to both the gas storage tank (18) and the oxygen storage tank (19). b: Connect the drill rod to the sealing device and send it into the combustion and explosion borehole (1). The gas sensor probe (4) of the gas sensor (16) is sent into the combustion and explosion borehole (1) after passing through the sealing device; start the sealing device to seal the combustion and explosion borehole (1). c: After the explosion borehole (1) is sealed, inject a mixture of gas and oxygen into the explosion borehole (1), observe the gas sensor (16), and stop the gas injection when the gas concentration is between 9-10% and the gas injection pressure reaches 1-2 MPa. d: The electric pulse device (5) discharges and ignites the gas; the gas explosion pressure in the drill pipe exceeds the constant pressure and the maximum shear stress of the rupture disc (3) is destroyed, and the gas that explodes in the drill pipe enters the explosion borehole (1), which then ignites the gas in the explosion borehole (1) for secondary explosion, causing cracks to be generated in the coal body around the borehole. e: After the gas explosion is over, the extraction borehole (2) is connected to negative pressure for extraction. After a period of extraction, the gas concentration in the extraction borehole (2) is measured with a gas meter. f: When the gas concentration in the extraction borehole (2) is less than 30%, inject a mixture of gas and oxygen into the combustion borehole (1), observe the gas sensor (16), and stop the gas injection when the gas concentration is between 9-10%. g: The electric pulse device (5) discharges and ignites the gas, and the gas explosion in the borehole (1) expands the cracks around the borehole again; Repeat step eg to repeatedly perform gas explosion fracturing on the combustion borehole (1) to expand the cracks around the borehole.

3. The method for enhanced extraction of coal seams fractured by controllable electrical pulse combustion gas in boreholes according to claim 2, characterized in that: The diameter of the combustion and explosion borehole (1) and the extraction borehole (2) is 120 mm, the length of the borehole is 90 m, the combustion and explosion borehole (1) and the extraction borehole (2) are parallel, and the parallel spacing is 5-10 m.

4. The method for enhanced extraction of coal seams fractured by controllable electrical pulse combustion gas in boreholes according to claim 2, characterized in that: The first gas sensor probe (4) is inserted into the bottom of the combustion borehole (1), and a gas sensor probe (4) is arranged at 30cm intervals along the depth of the borehole.

5. The method for enhanced extraction of coal seams fractured by controllable electrical pulse combustion gas in boreholes according to claim 2, characterized in that: The sealing device is used to seal the hole at a distance of 25m from the opening of the explosive borehole (1).

6. The method for enhanced extraction of coal seams fractured by controllable electrical pulse combustion gas in boreholes according to claim 2, characterized in that: A sealing ring is provided at the connection between the constant pressure rupture disc (3) and the front end of the drill pipe.

7. The method for enhanced extraction of coal seams fractured by controllable electrical pulse combustion gas in boreholes according to claim 2, characterized in that: The control circuit of the electric pulse device includes a capacitor charging switch (14), a capacitor (13), a capacitor discharging switch (12), and a capacitor charging power supply (15). When the capacitor charging switch (14) is closed, the capacitor (13) is charged. After the charging is completed, the capacitor charging switch (14) is opened to stop the charging. The capacitor discharging switch (12) is closed to discharge the ignition gas mixture through the capacitor discharge positive electrode (7) and capacitor discharge negative electrode (6) in the electric pulse device (5).

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