New coal mine gas control system and method based on carbon dioxide phase change cracking

Abstract

The present invention discloses a novel coal mine gas control system and method based on carbon dioxide phase change fracturing, including drilling construction, assembly and delivery of carbon dioxide fracturing devices, temporary plugging of carbon dioxide phase change fracturing, permeability enhancement of carbon dioxide phase change fracturing, removal and recovery of carbon dioxide fracturing devices, and fixed sealing of drilling holes and connection and extraction. In the novel coal mine gas control method based on carbon dioxide phase change fracturing provided by the present invention, when carbon dioxide phase change fracturing is used to enhance permeability of soft coal seams, since the assembled carbon dioxide fracturing device is sent into the borehole through the inside of the drill rod, even if the coal quality is soft and the tunnel excavation and drilling disturbance effects occur, resulting in the situation that the coal body is easy to cross the hole and collapse after the hole is formed, the carbon dioxide fracturing device can still be sent to the deep bottom of the borehole, thereby realizing coal seam gas phase fracturing and permeability enhancement in the entire hole section, and improving the extraction effect of soft coal seams.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mining, and in particular to a novel coal mine gas control system and method based on carbon dioxide phase change cracking. Background Art

[0002] For soft and low-permeability coal seams in coal mines, the low permeability coefficient means that gas extraction alone cannot efficiently achieve extraction standards, so coal seam permeability must be increased. Common coal seam permeability increase measures include mechanical vibration permeability increase, hydraulic permeability increase, and gas phase fracturing permeability increase. Mechanical vibration permeability increase measures are represented by deep hole pre-splitting blasting. Since the application of pyrotechnic products underground is extremely risky, strictly controlled, and prone to "duds" that are difficult to handle, their practicality is limited. Hydraulic permeability increase measures are represented by hydraulic fracturing and hydraulic slitting, but the implementation of hydraulic permeability increase requires the introduction of a large amount of water. For soft coal seams, they are more likely to collapse when exposed to water, resulting in problems such as difficulty in drainage and slag removal and poor extraction effects. Gas-phase fracturing and permeability enhancement measures are represented by carbon dioxide phase change fracturing, which has good adaptability in soft coal seams. However, the soft coal quality and the disturbance effect of tunneling and drilling construction make it easy for the coal body to cross the hole and collapse after drilling. It is difficult to send the fracturing device down the bare hole to the deep of the borehole. Therefore, carbon dioxide fracturing cannot achieve uniform permeability enhancement of the entire hole section along the layer or simultaneous permeability enhancement of multiple coal seams.

[0003] Therefore, how to improve the permeability enhancement effect of soft coal seams has become a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0004] The present invention proposes a novel coal mine gas control system and method based on carbon dioxide phase change fracturing to improve the permeability enhancement effect of soft coal seams.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a novel coal mine gas control method based on carbon dioxide phase change cracking, comprising the following steps:

[0007] Drilling construction: Use a complete set of drilling equipment equipped with hollow drill rods and open and close drill bits to drill holes in coal lanes along coal seams or in rock lanes through multiple coal seams, and record the drilling conditions; when the hole is drilled to the designed depth, stop drilling, withdraw the drill, and remove several drill rods;

[0008] Assembly and delivery of the CO2 fracturing device: assemble the bottom hole fixture, the CO2 fracturing device and the connecting rod in sequence to form a fracturing tool string, and install the bottom hole fixture on the CO2 fracturing device at the head end; send the assembled fracturing tool string through the inside of the drill pipe, push open the drill bit crossbeam, and continue to send it to the bottom of the borehole, ensure that the umbrella claws of the bottom hole fixture are open, and pull back until they are stressed, ensure that the umbrella claws of the bottom hole fixture are upside down on the coal wall, and check the safety performance of the CO2 fracturing device; withdraw all drill pipes and drill bits;

[0009] Temporary blocking of carbon dioxide phase change fracturing: connect the temporary blocking device and the carbon dioxide fracturing device, send them to the predetermined position, lead the water inlet pipe of the temporary blocking device and the busbar of the fracturing device out of the hole to avoid getting stuck in the hole after blocking; connect the water inlet pipe to the water tank, press the rubber bag of the temporary blocking device until it expands and gets stuck on the hole wall to form a temporary blockage. At the same time, use a push rod outside the hole to support the temporary blocking device with one end and the other end on the wall of the tunnel opposite the drill hole to ensure that the temporary blocking device will not be pressed out by high pressure during carbon dioxide phase change fracturing, thereby improving the quality of temporary blocking;

[0010] Carbon dioxide phase change fracturing and permeability enhancement: After checking that the fracturing device has no explosion failure, the detonator is started, and the carbon dioxide fracturing device releases high-pressure carbon dioxide gas to fracture the coal seam. After fracturing, a preset pressure holding time is set. During the fracturing process, the pins at the connection between the carbon dioxide fracturing device and the bottom hole fixing device are opened by the shock wave, and the carbon dioxide fracturing device is separated from the bottom hole fixing device.

[0011] Dismantling and recycling of carbon dioxide fracturing device: ventilation dispatcher checks the first gas concentration in the tunnel. When the first gas concentration in the tunnel is less than the first threshold, the temporary plugging device is depressurized, the bag shrinks, and the gas and carbon dioxide in the borehole gush out. The second gas concentration and carbon dioxide concentration within a preset distance near the borehole are checked. When the second gas concentration is less than the second threshold, and the carbon dioxide concentration is less than the third threshold, the dismantling work is carried out;

[0012] Borehole fixed sealing and connection for extraction: After the carbon dioxide fracturing device is removed, a bag sealing device with an extraction pipe is installed. The bag sealing device has two bags at the front and rear ends. A grouting pump is used to pressurize and grout the bags at both ends of the bag sealing device. After the bags expand and support themselves on the coal wall, expansive cement is injected into the middle blank area through the grouting pipe for pressure sealing to form a fixed sealing section. After the cement solidifies, the extraction pipe is connected to the extraction system for extraction.

[0013] Preferably, in the novel coal mine gas control method based on carbon dioxide phase change cracking of the present invention, the drilling equipment is a fully hydraulic tunnel drilling equipment, the drill rod is a shallow-leaf hollow spiral drill rod, and the drill bit of the drilling equipment is a large through-hole open-and-closed PDC drill bit;

[0014] The recorded drilling conditions include coal, rock, gas and pressure;

[0015] Wei pointed out that 1-2m before the coal is seen, medium-pressure air is used to remove slag, and the air pressure is supplied by an underground explosion-proof mobile air compressor, and the medium-pressure air pressure is 1.0-1.2MPa.

[0016] Preferably, in the novel coal mine gas control method based on carbon dioxide phase change fracturing of the present invention, the sequential assembly of the bottom hole fixing device, the carbon dioxide fracturing device and the connecting rod includes: connecting the connecting rod and the carbon dioxide fracturing device while delivering; wherein, when the borehole is a layer-coarse drilling hole, a carbon dioxide fracturing device is arranged every a certain number of connecting rods; and when the borehole is a multi-coal seam through-layer hole, a carbon dioxide fracturing device is arranged in the coal seam section.

[0017] Preferably, in the novel coal mine gas control method based on carbon dioxide phase change fracturing of the present invention, the checking of the safety performance of the carbon dioxide fracturing device includes: checking whether the circuit of the carbon dioxide fracturing device is normal; and checking whether there is any gas leakage in the carbon dioxide fracturing device.

[0018] Preferably, in the novel coal mine gas control method based on carbon dioxide phase change fracturing of the present invention, the sealing depth is not less than 15m.

[0019] Preferably, in the novel coal mine gas control method based on carbon dioxide phase change cracking of the present invention, the preset time is not less than 60 minutes.

[0020] Preferably, in the new coal mine gas control method based on carbon dioxide phase change fracturing of the present invention, the first gas concentration, the second gas concentration and the carbon dioxide concentration are volume concentrations, the first threshold, the second threshold and the third threshold are 0.5%; the preset distance is 50m.

[0021] Preferably, in the novel coal mine gas control method based on carbon dioxide phase change fracturing of the present invention, the length of the extraction pipe is ≥15m; the length of the bag sealing device is ≥15m.

[0022] The present invention also discloses a novel coal mine gas control system based on carbon dioxide phase change fracturing, comprising a complete set of drilling equipment equipped with a hollow drill rod, an open and close drill bit, a bottom hole fixing device, a carbon dioxide fracturing device, a connecting rod, a temporary plugging device, a first gas concentration detector, a carbon dioxide concentration detector, a second gas concentration detector, a bag sealing device and an extraction pipe, which are executed according to the corresponding steps in the above-mentioned novel coal mine gas control method based on carbon dioxide phase change fracturing.

[0023] Preferably, in the above-mentioned new type of coal mine gas control system based on carbon dioxide phase change fracturing, one end of the bottom hole fixing device close to the carbon dioxide fracturing device is sleeved on the explosion vent end of the carbon dioxide fracturing device and is connected by a pin, and during the fracturing process, the pin is opened by the shock wave, and the carbon dioxide fracturing device is detached from the bottom hole fixing device.

[0024] It can be seen from the above technical scheme that in the novel coal mine gas control method based on carbon dioxide phase change fracturing provided by the present invention, when carbon dioxide phase change fracturing is used to increase the permeability of soft coal seams, the assembled carbon dioxide fracturing device is sent into the borehole through the inside of the drill pipe. Even if the coal quality is soft and the tunnel excavation and drilling disturbance effects occur, resulting in the situation that the coal body is prone to cross-hole and collapse after hole formation, the carbon dioxide fracturing device can still be sent to the deep of the borehole, thereby improving the permeability increase effect of the soft coal seam. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some examples or embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without creative work, and the present invention can also be applied to other similar scenarios based on the provided drawings. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0026] Figure 1 It is a schematic flow diagram of a novel coal mine gas control method based on carbon dioxide phase change cracking provided by the present invention;

[0027] Figure 2 It is a schematic diagram of the drilling construction provided by the present invention;

[0028] Figure 3 and Figure 4 It is a schematic diagram of the assembly and delivery of the carbon dioxide fracturing device provided by the present invention;

[0029] Figure 5 This is a schematic diagram of temporary plugging of carbon dioxide phase change fracturing provided by the present invention;

[0030] Figure 6 This is a schematic diagram of carbon dioxide phase change fracturing and permeability enhancement provided by the present invention;

[0031] Figure 7 This is a schematic diagram of dismantling the carbon dioxide fracturing device provided by the present invention;

[0032] Figure 8 It is a schematic diagram of a novel coal mine gas control system based on carbon dioxide phase change fracturing provided by the present invention;

[0033] Fig. 9 It is a schematic diagram of the connection between the carbon dioxide fracturing device provided by the present invention and the bottom hole fixing device;

[0034] Among them: 1 is drilling equipment, 2 is carbon dioxide fracturing device, 3 is bottom hole fixing device, 4 is temporary plugging device, 5 is top rod, 6 is extraction pipe, 11 is drill rod, 12 is drill bit, 13 is cross beam, 10 is coal seam, 20 is bag sealing device, and 30 is tunnel. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It will be understood that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0036] Glossary:

[0037] 1. Along-layer drilling: gas extraction drilling holes arranged along the coal seam in coal mines.

[0038] 2. Multi-coal seam drilling: drilling holes that penetrate multiple coal seams in rock tunnels underground in coal mines.

[0039] 3. Carbon dioxide phase change cracking coal seams to displace methane: Carbon dioxide exists in liquid form below 31°C and at a pressure of 7.2MPa. When the temperature exceeds 31°C, 1kg of liquid carbon dioxide absorbs 60kJ of heat and vaporizes within 40ms. Liquid carbon dioxide is filled into a carbon dioxide fracturing device and placed in a coal seam borehole. The phase change characteristics of liquid carbon dioxide, which expands 600 times in volume after being heated to become gas, are used to crack the coal seam, forming an area with high permeability and developed cracks in the coal seam around the borehole. At the same time, the coal-loving characteristics of gaseous carbon dioxide, which has an adsorption capacity 8 times higher than that of gas, are used. A large amount of adsorbed gas is displaced by gaseous carbon dioxide and converted into free gas, which improves the permeability and gas freeness of the coal seam, achieving the goal of safe and rapid extraction and sudden elimination.

[0040] See also Figure 1 The present invention provides a novel coal mine gas control method based on carbon dioxide phase change fracturing, comprising the following steps: step S100 drilling construction, step S200 carbon dioxide fracturing device 2 assembly and delivery, step S300 carbon dioxide phase change fracturing temporary plugging, step S400 carbon dioxide phase change fracturing permeability enhancement, step S500 carbon dioxide fracturing device 2 removal and recovery, and step S600 drilling fixed hole sealing and connection pumping. Figure 2 Among them, step S100 in the drilling construction includes: using a drilling device 1 equipped with a hollow drill rod 11 to drill a hole along the coal seam 10 in the tunnel 30 or to drill holes through multiple coal seams in the rock tunnel, and recording the drilling situation; when the drilling end hole reaches the designed depth, stop drilling, withdraw the drill and remove several drill rods 11.

[0041] In the novel coal mine gas control method based on carbon dioxide phase change fracturing provided by the present invention, when carbon dioxide phase change fracturing is used to enhance the permeability of soft coal seams 10, the assembled carbon dioxide fracturing device 2 is sent into the borehole through the inside of the drill rod 11. Even if the coal quality is soft and the tunnel 30 excavation and drilling disturbance effect occur, resulting in the situation that the coal body is prone to cross-hole and collapse after hole formation, the carbon dioxide fracturing device 2 can still be sent to the deep of the borehole, thereby improving the permeability enhancement effect of the soft coal seams 10.

[0042] It should be noted that the drilling equipment 1 includes a drill rod 11, a drill bit 12 and a power head, wherein the power head drives the drill bit 12 to rotate at high speed through the drill rod 11. Preferably, the drilling equipment 1 is a fully hydraulic tunnel drilling equipment, the drill rod 11 is a shallow-leaf hollow spiral drill rod, and the drill bit 12 of the drilling equipment 1 is a large through-hole open-and-closed PDC (polycrystalline diamond composite) drill bit. The drill rod 11 is a hollow drill rod. When the carbon dioxide fracturing device 2 passes through the drill bit 12, the crossbeam 13 at the drill bit 12 is lifted up, and the carbon dioxide fracturing device 2 can be drilled out. Drill rod 11: integral wide-wing spiral drill rod 11 (specifications: drill rod 11 outer diameter Φ108mm, inner hole Φ50.8mm, length 1.0m or 1.5m or customized); drill bit 12: large through-hole open and closed PDC drill bit 12 (specifications: drill bit 12 outer diameter Φ133mm, inner hole Φ50mm), medium wind pressure (wind pressure ≥1.2MPa) drilling construction.

[0043] At a position 1-2m before the coal is seen, medium-pressure air is used to remove slag. The air pressure is supplied by an underground explosion-proof mobile air compressor, and the medium-pressure air is 1.0-1.2MPa. During the construction process, the design parameters must be strictly followed. Water is used to remove slag in the rock section, and a slow-speed advancement construction method is adopted to ensure that the hole body is straight, the inner wall is smooth, and the hole is clean. During the construction process, various drilling conditions must be recorded in detail, including the presence of coal, rock, gas, and pressure. When the drilling end hole reaches the designed depth, stop drilling, withdraw the drill, and remove several drill rods 11. Among them, withdraw the drill and remove 3 to 5 drill rods 11, and withdraw the power head of the hydraulic drilling equipment 1 to the bottom of the frame to avoid affecting the lowering of the carbon dioxide fracturing device 2.

[0044] See also Figure 3 and Figure 4Step S200 of assembling and delivering the carbon dioxide fracturing device 2 includes: assembling the bottom hole fixture 3, the carbon dioxide fracturing device 2 and the connecting rod in sequence to form a fracturing tool string, and the bottom hole fixture 3 is installed on the carbon dioxide fracturing device 2 at the head end; the assembled fracturing tool string (bottom hole fixture 3, carbon dioxide fracturing device 2 and connecting rod) is sent into the drill pipe, the drill bit cross beam 13 is pushed open, and it is continued to be sent to the bottom of the borehole, ensuring that the umbrella claw of the bottom hole fixture 3 is opened, and pulled back until it is stressed, ensuring that the umbrella claw of the bottom hole fixture is upside down on the coal wall, and checking the safety performance of the carbon dioxide fracturing device 2; withdrawing all drill pipes 11 and drill bits 12.

[0045] Assembling the bottom hole fixing device 3, the carbon dioxide fracturing device 2 and the connecting rod in sequence includes: connecting the connecting rod and the carbon dioxide fracturing device 2 while delivering; wherein, when the borehole is a layer-coarse borehole, a carbon dioxide fracturing device 2 is arranged every preset connecting rod, for example, a carbon dioxide fracturing device 2 is arranged every 10 connecting rods; the carbon dioxide fracturing device 2 is delivered to the bottom of the borehole, the crossbeam 13 of the drill bit 12 is pushed open, the carbon dioxide fracturing device 2 is delivered to the bottom of the borehole, and it is pulled backward to ensure that the bottom hole fixing device 3 is fixed at the bottom of the borehole to prevent the fracturing device from being taken out during the removal of the drill rod 11. When the borehole is a multi-coal seam 10 through-layer hole, the carbon dioxide fracturing device 2 is arranged in the coal seam 10 section.

[0046] Checking the safety performance of the carbon dioxide fracturing device 2 includes: checking the circuit of the carbon dioxide fracturing device 2; and checking whether the carbon dioxide fracturing device 2 has leakage. Among them, checking the circuit of the carbon dioxide fracturing device 2 includes using a multimeter to test the circuit of the device to ensure that the resistance of the carbon dioxide fracturing device 2 used is not greater than 500Ω / piece. Checking whether the carbon dioxide fracturing device 2 has leakage to avoid using carbon dioxide fracturing devices 2 with serious leakage. After the required number of carbon dioxide fracturing devices 2 are connected one by one and the resistance is measured to be normal, the cumulative length of the carbon dioxide fracturing devices 2 should cover the coal section.

[0047] See also Figure 5 Step S300: Temporary plugging of carbon dioxide phase change fracturing: connect the temporary blocking device 4 and the carbon dioxide fracturing device 2, send them to the predetermined position, lead the water inlet pipe of the temporary blocking device 4 and the busbar of the fracturing device out of the hole to avoid getting stuck in the hole after blocking; connect the water inlet pipe to the water tank, press the rubber bag of the temporary blocking device 4 to expand, get stuck on the hole wall, and form a temporary plugging. At the same time, use a push rod outside the hole to support the temporary blocking device with one end and the other end on the wall of the tunnel 30 opposite the drill hole to ensure that the temporary blocking device will not be pressed out by high pressure during carbon dioxide phase change fracturing, thereby improving the quality of temporary plugging. Preferably, the depth of the above-mentioned plugging hole is not less than 15m.

[0048] See also Figure 6, step S400 carbon dioxide phase change fracturing and permeability enhancement: after checking that the carbon dioxide fracturing device has no explosion failure, the detonator is started, and the carbon dioxide fracturing device 2 releases high-pressure carbon dioxide gas to fracture the coal seam 10, and the pressure holding time is preset after fracturing; wherein, during the fracturing process, the pin at the connection between the carbon dioxide fracturing device 2 and the bottom hole fixing device 3 is opened by the shock wave, and the carbon dioxide fracturing device 2 is separated from the bottom hole fixing device 3. Specifically, in order to ensure safety during fracturing, other operators must be withdrawn to 100m behind the construction site during construction. When starting fracturing, a cordon must be set up, and a special person is arranged to set up a warning at the cordon. Other personnel are strictly prohibited from entering. The guard shall not remove the warning privately before receiving the order to remove the warning from the technical personnel. Before fracturing is implemented, a full-time gas inspector shall measure the gas and carbon dioxide concentrations near the work site. The operation can only be started when the gas concentration does not exceed 0.5% and the carbon dioxide concentration does not exceed 0.5%. A special person is designated to check the electrical equipment of the working face to ensure that the electrical equipment in the warning area is intact and there is no explosion failure before starting fracturing. During the implementation, all non-intrinsically safe power supplies in the drilling construction tunnel 30 are turned off. After the technicians check that the circuit system is intact and there is no explosion, the carbon dioxide fracturing device 2 is started to release high-pressure carbon dioxide gas to fracture the coal seam 10. The pin at the connection between the first fracturing device and the bottom hole fixing device 3 is opened by the shock wave, and the fracturing device is separated from the bottom hole fixing device 3. The pressure holding time after fracturing is not less than the preset time. During this time period, personnel are not allowed to enter the fracturing range and start the equipment with points. Preferably, the preset pressure holding time is 60 minutes.

[0049] See also Figure 7 , step S500, dismantling and recycling of carbon dioxide fracturing device 2: ventilation scheduling checks the first gas concentration in tunnel 30. When the first gas concentration in tunnel 30 is less than the first threshold, the temporary plugging device is depressurized, the bag shrinks, and the gas and carbon dioxide in the borehole gush out. The second gas concentration and carbon dioxide concentration within the preset distance near the borehole are checked. When the second gas concentration is less than the second threshold, and the carbon dioxide concentration is less than the third threshold, the dismantling work is carried out. Specifically, after the pressure holding time is over, the ventilation scheduling checks the probe gas concentration in tunnel 30. When the first gas concentration in tunnel 30 is below the first threshold, the full-time gas inspector can enter the working face to check the second gas concentration and carbon dioxide concentration within the preset distance near the borehole. When the second gas concentration is less than the second threshold, and the carbon dioxide concentration is less than the third threshold, the relevant technical personnel enter the fracturing site to start the dismantling work. Preferably, the first threshold, the second threshold and the third threshold are 0.5%; the preset distance is 50m. It should be noted that the above-mentioned first gas concentration, second gas concentration and carbon dioxide concentration are volume concentrations, mass concentrations or molar concentrations, preferably volume concentrations.

[0050] When the pressure in the fracturing hole drops to 0.2Mpa, open the low-pressure test valve until it drops to less than 0.1Mpa, and start dismantling after ensuring that there is no pressure in the hole. Depressurize the temporary plugging device 4. During the depressurization period, non-related personnel are strictly prohibited from entering within 50m of the fracturing hole mouth. After the temporary plugging device 4 is depressurized, start the drilling equipment 1 to withdraw the temporary plugging device 4 and the fracturing device together, leaving the bottom fixing device 3 in the hole. If the fracturing device is stuck in the borehole, measures must be taken to deal with it, and it cannot be forcibly pulled out. Count the used "carbon dioxide fracturing device 2" and recover them to the ground.

[0051] Step S600: Drilling, fixing, sealing and connecting the hole: After the carbon dioxide fracturing device is removed, a bag sealing device with an extraction pipe is installed. The bag sealing device has two bags at the front and rear ends. A grouting pump is used to pressurize and grout the bags at both ends of the bag sealing device. After the bags expand and support themselves on the coal wall, expansive cement is injected into the middle blank area through the grouting pipe for pressure sealing to form a fixed sealing section. After the cement solidifies, the extraction pipe is connected to the extraction system for extraction.

[0052] After fracturing, the hole should be sealed and pumped in time, and the extraction pipe 6 should be installed. The length of the extraction pipe 6 should be greater than 20m. The expansion cement "two plugging and one injection" pressure sealing process should be adopted, and the fixed plugging section length should be ≥12m. Since the flow data of a single borehole is difficult to measure, a confluence pipe is used for measurement. The 5 boreholes are connected to the confluence device through a hose. The confluence device has holes and an orifice flowmeter or V-cone flowmeter is installed to facilitate the measurement of the extraction concentration and flow. The confluence pipe is connected to the extraction system for extraction, and the combined extraction negative pressure is not less than 13Kpa.

[0053] See also Figure 8 The present invention also discloses a novel coal mine gas control system based on carbon dioxide phase change fracturing, comprising a set of drilling equipment 1 equipped with a hollow drill rod 11, an open and close drill bit 12, a bottom hole fixing device 3, a carbon dioxide fracturing device 2, a connecting rod, a temporary plugging device 4, a first gas concentration detector, a carbon dioxide concentration detector, a second gas concentration detector, a bag sealing device 20 and an extraction pipe 6, which are executed according to the corresponding steps in the novel coal mine gas control method based on carbon dioxide phase change fracturing as described above. Since the above control method has the above beneficial effects, the control system executing the above control method has the corresponding effects, which will not be repeated here.

[0054] The drilling equipment 1 includes a drill rod 11, a drill bit 12 and a power head, wherein the power head drives the drill bit 12 to rotate at high speed through the drill rod 11. Preferably, the drilling equipment 1 is a fully hydraulic tunnel drilling equipment 1, the drill rod 11 is a shallow-leaf spiral drill rod, and the drill bit 12 of the drilling equipment 1 is a large through-hole open-and-closed PDC (polycrystalline diamond composite) drill bit. The drill rod 11 is a hollow drill rod 11. When the carbon dioxide fracturing device 2 passes through the drill bit 12, the crossbeam 13 at the drill bit 12 is lifted up, and the carbon dioxide fracturing device 2 can be drilled out. Drill rod 11: Integral wide-wing spiral drill rod 11 (specification parameters: drill rod 11 outer diameter Φ108mm, inner hole Φ50.8mm, length 1.0m or 1.5m or customized); drill bit 12: Large through-hole open and closed PDC drill bit 12 (specification parameters: drill bit 12 outer diameter Φ133mm, inner hole Φ50mm), medium wind pressure (wind pressure ≥1.2MPa) drilling construction. The diameter of the carbon dioxide fracturing device 2 is 40mm or customized to suit the size of the large-diameter drill rod 11, and the length is 1.0m or 1.5m or customized. The bottom hole fixing device 3 is made of PE (polyethylene) or PVC (polyvinyl chloride), and the specification parameters are: the unfolded size of the wing is Φ140mm)

[0055] See also Fig. 9 , Fig. 9 In the connection structure shown, one end of the bottom hole fixing device 3 close to the carbon dioxide fracturing device 2 is sleeved on the explosion vent end of the carbon dioxide fracturing device 2 and is connected by a pin. During the fracturing process, the pin is opened by the shock wave, and the carbon dioxide fracturing device 2 is separated from the bottom hole fixing device 3.

[0056] The bottom hole fixing device 3 sleeve is sleeved on the explosion vent end of the carbon dioxide fracturing device 2, wherein the explosion vent and the bottom hole fixing device 3 have a total of 4 openings in a cross shape, and are inserted and fixed by metal pins. When the carbon dioxide fracturing device 2 is ignited and heated to detonate, the shock wave breaks through the pins, causing the fracturing device to separate and fall off from the bottom hole fixing device 3. Of course, the present invention can also have other numbers of explosion vents and openings.

[0057] In some other embodiments of the present invention, the explosion vent end of the carbon dioxide fracturing device 2 is sleeved on the bottom hole fixing device 3 and connected by a pin. During the fracturing process, the pin is opened by the shock wave and the carbon dioxide fracturing device 2 is separated from the bottom hole fixing device 3.

[0058] It should be noted that, for the convenience of description, only the parts related to the invention are shown in the drawings. In the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0059] It should be understood that the "system", "device", "unit" and / or "module" used in the present invention is a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, if other words can achieve the same purpose, the word can be replaced by other expressions.

[0060] As shown in the present invention and claims, unless the context clearly indicates an exception, the words "a", "an", "a kind" and / or "the" do not specifically refer to the singular, but may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of clearly identified steps and elements, and these steps and elements do not constitute an exclusive list, and the method or device may also include other steps or elements. The elements defined by the sentence "includes a..." do not exclude the existence of other identical elements in the process, method, commodity or device that includes the elements.

[0061] In the description of the embodiments of the present invention, unless otherwise specified, " / " means or, for example, A / B can mean A or B; "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present invention, "multiple" means two or more than two.

[0062] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0063] The present invention uses a flow chart to illustrate the operations performed by the system according to an embodiment of the present invention. It should be understood that the preceding or following operations are not necessarily performed precisely in order. On the contrary, the various steps may be processed in reverse order or simultaneously. At the same time, other operations may also be added to these processes, or one or more operations may be removed from these processes.

[0064] The above description is only a preferred embodiment of the present invention and an explanation of the technical principles used, and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. The scope of the invention involved in the present invention is not limited to the technical solution formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, the above-mentioned features are replaced with the technical features with similar functions disclosed in the present invention (but not limited to) to form a technical solution.

Claims

1. A new coal mine gas control method based on carbon dioxide phase change cracking, It is characterized in that The following steps are involved: Drilling construction: Use a complete set of drilling equipment equipped with hollow drill rods and open and close drill bits to drill holes in coal lanes along coal seams or in rock lanes through multiple coal seams, and record the drilling conditions; when the hole is drilled to the designed depth, stop drilling, withdraw the drill, and remove several drill rods; Assembly and delivery of the CO2 fracturing device: assemble the bottom hole fixture, the CO2 fracturing device and the connecting rod in sequence to form a fracturing tool string, and install the bottom hole fixture on the CO2 fracturing device at the head end; send the assembled fracturing tool string through the inside of the drill pipe, push open the drill bit crossbeam, and continue to send it to the bottom of the borehole, ensure that the umbrella claws of the bottom hole fixture are open, and pull back until they are stressed, ensure that the umbrella claws of the bottom hole fixture are upside down on the coal wall, and check the safety performance of the CO2 fracturing device; withdraw all drill pipes and drill bits; Temporary blocking of carbon dioxide phase change fracturing: connect the temporary blocking device and the carbon dioxide fracturing device, send them to the predetermined position, lead the water inlet pipe of the temporary blocking device and the busbar of the fracturing device out of the hole to avoid getting stuck in the hole after blocking; connect the water inlet pipe to the water tank, press the rubber bag of the temporary blocking device until it expands and gets stuck on the hole wall to form a temporary blockage. At the same time, use a push rod outside the hole to support the temporary blocking device with one end and the other end on the wall of the tunnel opposite the drill hole to ensure that the temporary blocking device will not be pressed out by high pressure during carbon dioxide phase change fracturing, thereby improving the quality of temporary blocking; Carbon dioxide phase change fracturing and permeability enhancement: After checking that the carbon dioxide fracturing device has no explosion failure, the detonator is started, and the carbon dioxide fracturing device releases high-pressure carbon dioxide gas to fracture the coal seam. After fracturing, a preset pressure holding time is set. During the fracturing process, the pins at the connection between the carbon dioxide fracturing device and the bottom hole fixing device are opened by the shock wave, and the carbon dioxide fracturing device is separated from the bottom hole fixing device. Dismantling and recycling of carbon dioxide fracturing device: ventilation dispatcher checks the first gas concentration in the tunnel. When the first gas concentration in the tunnel is less than the first threshold, the temporary plugging device is depressurized, the bag shrinks, and the gas and carbon dioxide in the borehole gush out. The second gas concentration and carbon dioxide concentration within a preset distance near the borehole are checked. When the second gas concentration is less than the second threshold, and the carbon dioxide concentration is less than the third threshold, the dismantling work is carried out; Borehole fixed sealing and connection for extraction: After the carbon dioxide fracturing device is removed, a bag sealing device with an extraction pipe is installed. The bag sealing device has two bags at the front and rear ends. A grouting pump is used to pressurize and grout the bags at both ends of the bag sealing device. After the bags expand and support themselves on the coal wall, expansive cement is injected into the middle blank area through the grouting pipe for pressure sealing to form a fixed sealing section. After the cement solidifies, the extraction pipe is connected to the extraction system for extraction.

2. The method according to claim 1, It is characterized in that The drilling equipment is a fully hydraulic tunnel drilling equipment, the drill rod is a shallow-blade hollow spiral drill rod, and the drill bit of the drilling equipment is a large through-hole open-and-closed PDC drill bit; The recorded drilling conditions include coal, rock, gas and pressure; At a position 1-2m before the coal is seen, medium-pressure air is used to remove slag. The air pressure is supplied by an underground explosion-proof mobile air compressor, and the medium-pressure is 1.0-1.2MPa.

3. The method according to claim 1, It is characterized in that The sequential assembly of the bottom hole fixing device, the carbon dioxide fracturing device and the connecting rod comprises: connecting the connecting rod and the carbon dioxide fracturing device while delivering; wherein, when the borehole is a layer-parallel borehole, a carbon dioxide fracturing device is arranged every a certain number of connecting rods; and when the borehole is a multi-coal layer-penetrating hole, a carbon dioxide fracturing device is arranged in the coal layer section.

4. The method according to claim 1, It is characterized in that The checking of the safety performance of the carbon dioxide fracturing device includes: checking whether the circuit of the carbon dioxide fracturing device is normal; and checking whether there is a gas leakage in the carbon dioxide fracturing device.

5. The method according to claim 1, It is characterized in that The sealing depth is not less than 15m.

6. The method according to claim 1, It is characterized in that The preset pressure holding time is not less than 60 minutes.

7. The method according to claim 1, It is characterized in that The first gas concentration, the second gas concentration and the carbon dioxide concentration are volume concentrations, the first threshold, the second threshold and the third threshold are 0.5%; and the preset distance is 50m.

8. The method according to claim 1, It is characterized in that The length of the extraction pipe is ≥15m; the length of the fixed plugging section is ≥15m.

9. A new coal mine gas control system based on carbon dioxide phase change cracking, It is characterized in that It includes a complete set of drilling equipment equipped with a hollow drill rod, an open and close drill bit, a bottom hole fixing device, a carbon dioxide fracturing device, a connecting rod, a temporary plugging device, a first gas concentration detector, a carbon dioxide concentration detector, a second gas concentration detector, a bag sealing device and an extraction pipe, which are executed according to the corresponding steps in the new coal mine gas control method based on carbon dioxide phase change fracturing as described in claim 1.

10. The system of claim 9, It is characterized in that One end of the bottom hole fixing device close to the carbon dioxide fracturing device is sleeved on the explosion vent end of the carbon dioxide fracturing device and connected by a pin. During the fracturing process, the pin is opened by the shock wave and the carbon dioxide fracturing device is separated from the bottom hole fixing device.

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