Coal seam gas control method coordinated with microorganism and hydraulicization combined with permeability enhancement technology

Abstract

The application discloses a coal seam gas control method in cooperation with a microbial and hydraulic joint permeability enhancement technology, and comprises the following steps: step 1, drilling groups are respectively constructed in the coal body, and hydraulic slotting is performed on each drill hole after the drilling construction is completed to form a slot; step 2, a fracturing fluid is configured, the fracturing fluid is a mixed solution of water and an anaerobic methane-oxidizing bacteria solution, hydraulic fracturing is performed on the fracturing drill holes of each drill hole group, and a segmented fracturing mode is adopted for each fracturing drill hole, and the segmented fracturing is sequentially performed in segments from inside to outside in the drill hole; and step 3, after the fracturing drill holes are completed, the equipment is recovered, ball valves on the outer connecting pipes of the fracturing drill holes, the guide drill holes and the control drill holes are closed, and the drill holes and the internal cracks of the coal body are prevented from communicating with the external air. The application can effectively relieve the situation that the mine extraction capacity is tight or insufficient, can fundamentally eliminate the methane in the coal body, effectively reduces the amount of methane discharged into the atmosphere, and protects the ecological environment.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine gas control, in particular to a coal seam gas control method using a microbial and hydraulic combined permeability enhancement technology. Background Art

[0002] Gas extraction, as one of the fundamental technical measures that can effectively solve coal mine gas problems, has been widely used in various coal mines. However, due to geological conditions, the occurrence conditions of most coal seams in my country are relatively complex and the permeability is relatively poor, resulting in low coal seam gas extraction efficiency, which in turn seriously affects the safe and efficient mining of coal. Therefore, in order to control the gas in low-permeability coal seams, many scholars at home and abroad have conducted extensive research on coal seam permeability enhancement technology. Relevant research results include hydraulic permeability enhancement technology (hydraulic fracturing, hydraulic cutting, hydraulic punching, etc.), blasting permeability enhancement technology (deep hole pre-splitting blasting, loosening blasting, CO2 phase change fracturing, etc.), chemical modification permeability enhancement technology (coal seam acidification, permeability enhancement fluid, etc.), etc. Among the above-mentioned coal seam permeability enhancement technologies, hydraulic permeability enhancement technology is widely used. However, for coal seams with small amounts of resolvable gas and strong gas adsorption, after hydraulic permeability enhancement measures are implemented, although the fracture network inside the coal seam is effectively enriched, the contact area between the coal seam and the outside world through the borehole is effectively increased, but the amount of resolvable gas released by the coal seam is very limited. Even if a negative pressure extraction system is connected, the extraction effect is not ideal, resulting in a very limited reduction in the gas content of the coal seam, and thus the purpose of effectively shortening the extraction time and reducing the drilling workload cannot be achieved. In addition, due to the limitations of the comprehensive extraction capacity of the mine pump station and the insufficient inventory of extraction equipment, the installation of the extraction equipment may lag far behind the tunnel excavation or working face mining. At this time, relying solely on the discharge borehole to release the gas in the coal seam will seriously affect the tunnel excavation speed and the safe mining of coal, especially for mines with relatively tight mining succession. Furthermore, methane is a greenhouse gas, and most coal mines currently release methane directly into the atmosphere after extracting it from coal seams, polluting the atmosphere. Therefore, an environmentally friendly gas control method is needed that can effectively manage gas within low-permeability coal seams, even when extraction efficiency is low or impossible. Summary of the Invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a coalbed gas control method that combines microbial and hydraulic permeability enhancement technology.

[0004] To achieve the above-mentioned object, the present invention provides the following technical solution: a coalbed gas control method using microbial and hydraulic combined permeability enhancement technology, comprising the following steps:

[0005] Step 1: First, drill groups are constructed in the coal body. Each drill group includes one fracturing borehole, two pilot boreholes, and two control boreholes. After the drilling is completed, each borehole is hydraulically cut to form slots. Main fractures are formed between the slots, and multiple micro fractures are formed along the main fractures. Each fracturing borehole, pilot borehole, and control borehole is connected to an external pipe, each of which is equipped with a ball valve.

[0006] Step 2: preparing a fracturing fluid, which is a mixture of water and anaerobic methane-oxidizing bacteria liquid, and hydraulically fracturing the fracturing boreholes of each drilling group. Each fracturing borehole is subjected to staged fracturing, wherein the staged fracturing is performed step by step from the inside to the outside of the borehole;

[0007] Step 3: After the fracturing drilling is completed, the equipment is recovered and the ball valves on the external pipes of each fracturing borehole, pilot borehole and control borehole are closed to ensure that the borehole and the internal cracks of the coal body are not in communication with the outside air. Anaerobic methane oxidizing bacteria are adsorbed on the surface and pores of the coal, and the CH4 adsorbed in the coal micropores is driven away and replaced, so that the adsorbed CH4 becomes free CH4, thereby facilitating the conversion of the anaerobic methane oxidizing bacteria, thereby expanding the scope of the anaerobic methane oxidizing bacteria to eliminate CH4 inside the coal body.

[0008] Furthermore, after the drilling construction in step 1 is completed, the hydraulic fracturing of each borehole is performed using an integrated fracturing-fracture device.

[0009] Furthermore, the arrangement of each drilling group in step 1 is as follows: the fracturing drilling hole is located in the middle, and the pilot drilling hole and the control drilling hole are located on both sides of the fracturing drilling hole in sequence.

[0010] Furthermore, the fracturing boreholes, pilot boreholes and control boreholes in each group of boreholes in step 1 are all installed with casings at the hole openings. The outside of the casings is fixed to the coal body by cement mortar, and the casings are fixed to the external pipes by flanges and bolts.

[0011] Furthermore, the length L9 of the sleeve is not less than 3m.

[0012] Furthermore, the arrangement of each drilling group in step 1 includes the arrangement of coal seam drilling holes at the coal mining face and the arrangement of coal seam drilling holes at the tunneling face:

[0013] (1) Coal mining face

[0014] In a coal mining face, two adjacent drilling groups share one control borehole. The lengths of the pilot borehole, control borehole, and fracturing borehole are determined based on the inclination length L1 of the coal mining face. The lengths of the control borehole and fracturing borehole are equal, and the length L2 should be at least 30m less than the inclination length of the coal mining face, i.e., L2 ≤ L1-30. The length of the pilot borehole is shorter than that of the control borehole or fracturing borehole.

[0015] The number of construction slots in each fracturing borehole is determined by L2 and the distance L8 between the outermost slot in the borehole and the borehole opening. The distance L8 between the outermost slot in the borehole and the borehole opening is at least 30m, and the distance L7 between adjacent slots in the fracturing borehole is 20-30m. The width L3 of a single slot is 2-4m.

[0016] The number of slots inside each control borehole, the axial position of the slots, and the distance L7 between adjacent slots are the same as those in the fracturing borehole;

[0017] The number of slots in each pilot borehole is the same as that in the fracturing borehole, but the axial position of the slots is different from that in the fracturing borehole and the control borehole. The slots in the pilot borehole are spaced L7 / 2m apart from the slots corresponding to the fracturing borehole and the control borehole in the borehole axial direction. The aperture of each pilot borehole, control borehole, and fracturing borehole is not less than 94mm. All boreholes are drilled perpendicular to the coal wall of the roadway and in the same inclination as the coal seam.

[0018] (2) Excavation working face

[0019] The fracturing borehole is constructed vertically to the excavation working face, and the control borehole and the pilot borehole have an angle with the central axis of the roadway. The length of the pilot borehole, the control borehole and the fracturing borehole is mainly determined according to the excavation plan; the length of the fracturing borehole L 11 100-140m;

[0020] At the same time, in order to ensure the overall excavation efficiency, the excavation efficiency of the excavation construction team can be guaranteed by increasing the number of excavation working faces. That is, when gas control is being carried out at one excavation working face, the excavation construction team can go to another excavation working face to excavate, and then return to the excavation working face to carry out construction when gas control is carried out at the other excavation working face.

[0021] There needs to be a certain amount of stubble between each borehole in the current excavation cycle and each borehole in the next excavation cycle. The stubble length L 10 20-40m;

[0022] The number of slots, slot width and distance between adjacent slots in each guide drill hole, control drill hole and fracturing drill hole shall be the same as those in the coal mining working face.

[0023] Furthermore, the step 2 of fracturing each fracturing borehole in sequence from the inside to the outside specifically includes steps 201 to 207:

[0024] Step 201: After the fracturing drilling, pilot drilling, and control drilling are completed, a fracturing fluid is first prepared. The fracturing fluid is a mixture of water and anaerobic methane-oxidizing bacteria liquid. The preparation method is to fill a water tank with water and then pour the anaerobic methane-oxidizing bacteria liquid into the water tank.

[0025] Step 202: Then, sequentially place the front high-pressure capsule, the rear high-pressure capsule, and the connecting rod into the fracturing borehole, with the front high-pressure capsule and the rear high-pressure capsule respectively placed on both sides of the first slot counted from the inside to the outside of the fracturing borehole, to perform the first stage of fracturing; the front high-pressure capsule and the rear high-pressure capsule are spaced apart and sleeved on the connecting rod, the end of the connecting rod is connected to the emulsion pump via a high-pressure hose, the emulsion pump is connected to the water tank via a liquid inlet pipe and a liquid return pipe, and the front high-pressure capsule and the rear high-pressure capsule are also connected to a manual pressure pump via injection pipes;

[0026] Step 203: Connect the front high-pressure capsule and the rear high-pressure capsule to a manual pressure pump through injection pipes, add water to the manual pressure pump, and use the manual high-pressure pump to inject water and pressurize the front high-pressure capsule and the rear high-pressure capsule respectively to expand and squeeze the borehole wall;

[0027] Step 204: Connect the liquid inlet pipe and liquid return pipe between the water tank and the emulsion pump, and the high-pressure hose between the emulsion pump and the connecting rod;

[0028] Step 205: A front high-pressure capsule and a rear high-pressure capsule are also placed on both sides of the first slot, counted from the inside to the outside, in the pilot boreholes on both sides of the fracturing borehole. The front high-pressure capsule and the rear high-pressure capsule are spaced apart and sleeved on a connecting rod. The front high-pressure capsule and the rear high-pressure capsule are also connected to a manual pressure pump via an injection pipe. Water is added to the manual pressure pump, and the manual high-pressure pump connected to the rear high-pressure capsule is used to inject water and pressurize only the rear high-pressure capsule, causing it to expand and squeeze the borehole wall to complete the borehole sealing.

[0029] Step 206: After everything is ready, the emulsion pump is started to start the first stage of fracturing the fracturing borehole. During the fracturing process, as the fracturing fluid in the water tank continuously enters the fracturing borehole along the inside of the connecting rod, water and anaerobic methane oxidizing bacteria liquid need to be continuously added to the water tank. When water flows from the control borehole of the current drilling group, it indicates that the cracks generated in the coal body due to hydraulic fracturing have extended to the position of the control borehole. At this time, the fracturing can be stopped, and the pressure of the liquid in the connecting rod and high-pressure hose in the fracturing borehole is relieved. Then, the pressure of the front high-pressure capsule, the rear high-pressure capsule of the fracturing borehole, and the rear high-pressure capsule in the pilot borehole are relieved. Thus, the first stage of fracturing of the fracturing borehole is completed.

[0030] Step 207: Fracturing the second and subsequent sections of the fracturing borehole.

[0031] The front high-pressure capsule and the rear high-pressure capsule in the fracturing borehole and the pilot borehole are sequentially moved to both sides of the second slot and each subsequent slot from the inside to the outside of the fracturing borehole and the pilot borehole, and water is injected and pressurized respectively; then, the above steps 201 to 206 are repeated to complete the staged fracturing work from the inside to the outside of the fracturing borehole;

[0032] During step 205, manual high-pressure pumps connected to the front high-pressure capsule and the rear high-pressure capsule are used to simultaneously inject water and pressurize the front high-pressure capsule and the rear high-pressure capsule, so that they expand and squeeze the borehole wall to complete the sealing of the borehole.

[0033] Furthermore, the pressure of the water injection in step 203, step 204 and step 205 is not less than 15 MPa.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) The present invention combines a drilling group (fracturing drilling, pilot drilling, and control drilling), staggered slot arrangement within each drilling hole, and staged hydraulic fracturing to make the cracks generated by hydraulic fracturing in the coal body controllable and uniform, effectively increasing the permeability of the coal body;

[0036] 2) By using a fracturing fluid made by mixing water and anaerobic methanotrophic bacteria liquid during the hydraulic fracturing process, the anaerobic methanotrophic bacteria that enter the coal body can convert CH4 into CO2. The CO2 can then replace the CH4 inside the coal body, further expanding the range of CH4 elimination within the coal body by anaerobic methanotrophic bacteria. In addition, anaerobic methanotrophic bacteria can partially degrade the coal body, increase the pore volume of the coal body, enhance the connectivity between the cracks and pores inside the coal body, and further increase the permeability of the coal body.

[0037] 3) The coal seam gas control method of the present invention, which combines microorganisms with hydraulic permeability enhancement technology, can effectively alleviate the situation of tight or insufficient mine extraction capacity, and can also fundamentally eliminate methane inside the coal body, while effectively reducing the amount of methane emitted into the atmosphere and protecting the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic plan view of the arrangement of the drilling groups in the coal seam of the coal mining working face of the present invention and the distribution of cracks after fracturing;

[0039] Figure 2 This is a schematic cross-sectional view of the connection between the fracturing drilling orifice casing and the external pipe of the present invention;

[0040] Figure 3 Layout plan of each drill hole in the coal seam of the excavation working face;

[0041] Figure 4 This is a schematic diagram of the installation structure of the front high-pressure capsule, the rear high-pressure capsule and the connecting rod in the fracturing drilling of the present invention;

[0042] Figure 5 This is a schematic diagram of the arrangement of the front high-pressure capsules and the rear high-pressure capsules in the fracturing boreholes and the pilot boreholes when fracturing is performed in different fracturing sections in different borehole groups of the present invention. The black color in the front high-pressure capsules and the rear high-pressure capsules in the figure represents water injection pressurization.

[0043] In the picture:

[0044] 1-coal body; 2-fracturing drill hole; 3-pilot drill hole; 4-control drill hole; 5-slot; 6-main fracture; 7-micro fracture; 8-external pipe; 9-ball valve; 10-casing; 11-cement mortar; 12-flange; 13-bolt;

[0045] 14-Front high-pressure capsule; 15-Rear high-pressure capsule; 16-Connecting rod; 17-Injection pipe; 18-Manual pressure pump; 19-High-pressure hose; 20-Emulsion pump; 21-Liquid inlet pipe; 22-Liquid return pipe; 23-Water tank; 24-Excavation working face; 25-Tunnel. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] Example 1

[0048] See also Figure 1 The coal seam gas control method using microbial and hydraulic combined permeability enhancement technology includes the following steps:

[0049] Step 1: First, drill groups are constructed in the coal body 1. Each drill group includes one fracturing borehole 2, two pilot boreholes 3, and two control boreholes 4. After the drilling is completed, each borehole is hydraulically slotted to form slots 5 (hydraulic slotting is performed from the inside to the outside of the borehole). Main cracks 6 are formed between the slots 5, and multiple micro cracks 7 are formed along the main cracks 6. Each fracturing borehole 2, pilot borehole 3, and control borehole 4 is connected to an external pipe 8, each of which is equipped with a ball valve 9.

[0050] Wherein, after the drilling construction in step 1 is completed, hydraulic slotting of each borehole is performed by using an integrated slotting-fracturing device.

[0051] Among them, the function of the fracturing borehole 2 is to perform high-pressure fracturing on the coal body 1, so as to generate cracks in the coal body 1; the function of the guide borehole 3 is to use the slot 5 to induce and control the generation and expansion of cracks around the fracturing borehole 2; the control borehole 4 is mainly used to control and monitor the expansion range of the cracks generated by the fracturing borehole 2 under the action of the fracturing fluid, and at the same time to induce the expansion direction of the cracks through its own slot 5.

[0052] In step 1, the arrangement of each set of drill holes is as follows: the fracturing drill hole 2 is located in the center, with the pilot drill hole 3 and the control drill hole 4 located on either side of the fracturing drill hole 2. To reduce the number of times the overall construction equipment is moved, the control drill hole 4 and the pilot drill hole 3 can be constructed first, followed by the fracturing drill hole 2. The slots 5 within each drill hole should be constructed backwards as much as possible to facilitate the removal of coal slag from the borehole during the slotting process.

[0053] Reference Figure 2 In step 1, the fracturing borehole 2, the pilot borehole 3, and the control borehole 4 in each group of boreholes are all installed with a casing 10 at the position located at the hole mouth. The outside of the casing 10 is fixed to the coal body 1 by cement mortar 11, and the casing 10 is fixed to the external pipe 8 by a flange 12 and bolts 13.

[0054] The length L9 of the casing 10 is not less than 3 m.

[0055] Reference Figure 1 and Figure 3 In step 1, the arrangement of each drilling group includes the arrangement of coal seam drilling holes at the coal mining face and the arrangement of coal seam drilling holes at the tunneling face:

[0056] (1) Coal mining face

[0057] In a coal mining face, two adjacent drilling groups share one control borehole 4. The lengths of the pilot borehole 3, the control borehole 4, and the fracturing borehole 2 are determined based on the coal mining face inclination length L1. The control borehole 4 and the fracturing borehole 2 are equal in length, and the length L2 should be at least 30 meters less than the coal mining face inclination length, i.e., L2 ≤ L1-30. The pilot borehole 3 is shorter than the control borehole 4 or the fracturing borehole 2 by a length difference of L6 (in meters). Specifically, L6 is 2-10 meters. The horizontal distance L4 between the fracturing borehole 2 and the pilot borehole 3 is 5-20 meters, and the horizontal distance L5 between the pilot borehole 3 and the control borehole 4 is 5-15 meters.

[0058] The number of construction slots 5 in each fracturing borehole 2 is determined by L2 and the distance L8 between the outermost slot 5 in the borehole and the borehole opening. Generally, the distance L8 between the outermost slot 5 in the borehole and the borehole opening is at least 30m, and the distance L7 between adjacent slots 5 in the fracturing borehole 2 is 20-30m. The width L3 of a single slot 5 is 2-4m.

[0059] The number of slots 5 inside each control borehole 4, the axial position of the slots 5 and the distance L7 between adjacent slots 5 are the same as those of the fracturing borehole 2;

[0060] The number of slots 5 inside each guide borehole 3 is the same as that of the fracturing borehole 2, but the axial position of the slots 5 is different from that of the fracturing borehole 2 and the control borehole 4. The slots 5 inside the guide borehole 3 and the slots 5 corresponding to the fracturing borehole 2 and the control borehole 4 are spaced L7 / 2m (i.e., 10-15m) apart in the axial direction of the borehole. The purpose of this arrangement is to ensure that the cracks generated by the fracturing borehole 2 during the fracturing process are as uniform as possible and that there are fewer "blank zones" in gas control. In addition, the aperture of each guide borehole 3, control borehole 4, and fracturing borehole 2 is not less than 94mm, and the boreholes are all constructed perpendicular to the coal wall of the roadway and have the same inclination angle as the coal seam. At the same time, the control boreholes 4 in each group of boreholes can be shared with the adjacent group of boreholes, that is, each control borehole 4 can control the fracturing boreholes 2 on both sides of it separately.

[0061] (2) Excavation working face

[0062] The fracturing borehole 2 is constructed vertically on the excavation working face 24, and the control borehole 4 and the guide borehole 3 need to have a certain angle. The size of the angle needs to be determined based on the width L of the excavation required to be protected on both sides of the on-site tunnel 25. 12 And the specific parameters of the project such as the excavation direction of tunnel 25, generally L 12 20m;

[0063] The lengths of the pilot borehole 3, the control borehole 4 and the fracturing borehole 2 are mainly determined according to the excavation plan. Considering that the excavation needs to be stopped when drilling gas to be controlled at the excavation working face 24, the length L of the fracturing borehole 2 is 11 The length of the pilot borehole 3 and the control borehole 4 is generally longer than that of the fracturing borehole 2.

[0064] At the same time, in order to ensure the overall excavation efficiency, the excavation efficiency of the excavation construction team can be guaranteed by increasing the number of excavation working faces 24. That is, when gas control is being carried out at one excavation working face 24, the excavation construction team can go to another excavation working face 24 to excavate, and then return to the excavation working face 24 to carry out construction when gas control is carried out at the other excavation working face 24.

[0065] There needs to be a certain amount of stubble between each borehole in the current excavation cycle and each borehole in the next cycle to ensure that there is no "blank zone" within the excavation protection range on both sides of the tunnel 25. The stubble length L 10 20-40m.

[0066] The requirements for the number of slots 5 in each guide borehole 3 , control borehole 4 and fracturing borehole 2 , the width of the slots 5 and the distance between adjacent slots 5 are the same as those in the above-mentioned coal mining working face.

[0067] Reference Figure 4 , step 2, prepare fracturing fluid, which is a mixture of water and anaerobic methane-oxidizing bacteria liquid, and perform hydraulic fracturing on the fracturing boreholes 2 of each drilling group. To ensure the uniformity of the distribution of cracks around the fracturing boreholes 2, each fracturing borehole 2 is subjected to staged fracturing, and the fracturing is performed section by section from the inside to the outside of the borehole;

[0068] The step 2 of fracturing each fracturing borehole 2 in sequence from the inside to the outside specifically includes steps 201 to 207:

[0069] After the fracturing borehole 2, the pilot borehole 3, and the control borehole 4 are all slotted, a fracturing fluid is first prepared. The fracturing fluid is a mixture of water and anaerobic methane-oxidizing bacteria liquid. The preparation method is to fill a water tank with water and then pour the anaerobic methane-oxidizing bacteria liquid into the water tank (the concentration and amount of the anaerobic methane-oxidizing bacteria liquid added are determined according to the actual application situation);

[0070] Step 202: Then, sequentially place the front high-pressure capsule 14, the rear high-pressure capsule 15, and the connecting rod 16 into the fracturing borehole 2, and place the front high-pressure capsule 14 and the rear high-pressure capsule 15 on both sides of the first slot 5 counted from the inside to the outside of the fracturing borehole 2, respectively, to perform the first stage of fracturing; the front high-pressure capsule 14 and the rear high-pressure capsule 15 are spaced apart and sleeved on the connecting rod 16, the end of the connecting rod 16 is connected to the emulsion pump 20 via a high-pressure hose 19, and the emulsion pump 20 is connected to the water tank 23 via a liquid inlet pipe 21 and a liquid return pipe 22. The front high-pressure capsule 14 and the rear high-pressure capsule 15 are also connected to the manual pressure pump 18 via the injection pipe 17;

[0071] Step 203: Connect the front high-pressure capsule 14 and the rear high-pressure capsule 15 to the manual pressure pump 18 through the injection tube 17, add water to the manual pressure pump 18, and use the manual high-pressure pump to inject water and pressurize the front high-pressure capsule 14 and the rear high-pressure capsule 15 (pressure is not less than 15 MPa) to expand and squeeze the borehole wall;

[0072] Step 204: Connect the liquid inlet pipe 21 and the liquid return pipe between the water tank 23 and the emulsion pump 20, and the high-pressure hose 19 between the emulsion pump 20 and the connecting rod 16;

[0073] Step 205: On both sides of the first slot 5, counted from the inside to the outside in the pilot borehole 3 on both sides of the fracturing borehole 2, a front high-pressure capsule 14 and a rear high-pressure capsule 15 are also placed. The front high-pressure capsule 14 and the rear high-pressure capsule 15 are spaced apart and sleeved on the connecting rod 16. The front high-pressure capsule 14 and the rear high-pressure capsule 15 are also connected to the manual pressure pump 18 through the injection pipe 17. Water is added to the manual pressure pump 18, and the manual high-pressure pump connected to the rear high-pressure capsule 15 is used to inject water and pressurize only the rear high-pressure capsule 15 (the pressure is not less than 15 MPa). Figure 5 As shown, at the first crack in the pilot boreholes 3 on both sides of the fracturing borehole 2, only the post-placed high-pressure capsules 15 are injected with water to increase pressure, causing them to expand and squeeze the borehole wall to complete the borehole sealing. The purpose is to artificially control the expansion of the internal cracks of the pilot borehole 3 to prevent the pilot borehole 3 from communicating with the control borehole 4 through the cracks during the first fracturing stage of the fracturing borehole 2, and then the pilot borehole 3 will no longer expand the cracks during the remaining fracturing stages of the fracturing borehole 2;

[0074] Step 206: After everything is ready, start the emulsion pump 20 and start fracturing the fracturing borehole 2. During the fracturing process, as the fracturing fluid in the water tank 23 continuously enters the fracturing borehole 2 along the inside of the connecting rod 16, it is necessary to continuously add water and anaerobic methane oxidizing bacteria liquid to the water tank 23. When water flows from the control borehole 4 of the drilling group, it indicates that the cracks generated in the coal body 1 due to hydraulic fracturing have expanded to the position of the control borehole 4. At this time, the fracturing can be stopped, and the pressure of the liquid in the connecting rod 16 and the high-pressure hose 19 in the fracturing borehole 2 is relieved. Then, the pressure of the front high-pressure capsule 14 and the rear high-pressure capsule 15 in the fracturing borehole 2 and the pilot borehole 3 are respectively relieved. Thus, the first stage of fracturing of the fracturing borehole 2 is completed.

[0075] Step 207: Fracturing the second section and subsequent sections of the fracturing borehole 2:

[0076] The front high-pressure capsule 14 and the rear high-pressure capsule 15 in the fracturing borehole 2 and the pilot borehole 3 are sequentially moved to both sides of the second slot 5 and each subsequent slot 5 from the inside to the outside of the fracturing borehole 2 and the pilot borehole 3, and water is injected and pressurized respectively; then, the above steps 201 to 206 are repeated to complete the staged fracturing of the fracturing borehole 2 from the inside to the outside;

[0077] In step 205, the front high-pressure capsule 14 and the rear high-pressure capsule 15 are respectively connected to a manual high-pressure pump to simultaneously inject water into the front high-pressure capsule 14 and the rear high-pressure capsule 15 to pressurize them, so that they expand and squeeze the borehole wall to complete the plugging of the borehole. Figure 5As shown, at the second and third cracks in the pilot boreholes 3 on both sides of the fracturing borehole 2, the front high-pressure capsule 14 and the rear high-pressure capsule 15 are both injected with water to increase pressure (and the same applies to the subsequent sections).

[0078] Step 3: After the fracturing drilling 2 is completed, the equipment is recovered and the ball valves 9 on the external pipes 8 of each fracturing drilling hole 2, pilot drilling hole 3 and control drilling hole 4 are closed to ensure that the drilling holes and the internal cracks of the coal body 1 are not in communication with the outside air. The anaerobic methane oxidizing bacteria are adsorbed on the surface and pores of the coal, and the CH4 adsorbed in the coal micropores is driven away and replaced, so that the adsorbed CH4 is converted into free CH4, thereby facilitating the conversion of the methane oxidizing bacteria, thereby expanding the range of the anaerobic methane oxidizing bacteria to eliminate the CH4 inside the coal body 1.

[0079] The specific operation steps of step 3 are as follows: after the fracturing drilling 2 is completed, each piece of equipment is recycled in order for next use; after the front high-pressure capsule 14, the rear high-pressure capsule 15, and the connecting rod 16 in the fracturing drilling 2 are all withdrawn, the ball valve 9 on the external pipe 8 of the fracturing drilling 2 is closed; similarly, after the front high-pressure capsule 14, the rear high-pressure capsule 15, and the connecting rod 16 in the pilot drilling 3 are all withdrawn, the ball valve 9 on the external pipe 8 of the pilot drilling 3 is closed; the ball valve 9 on the external pipe 8 of the control drilling 4 can be closed immediately after the fracturing is completed;

[0080] At this point, the coal body 1 will contain a large number of anaerobic methane-oxidizing bacteria. These microorganisms will be adsorbed on the surface and pores of the coal. After a series of reactions, they will convert the CH4 inside the coal body 1 into H2O, CO2, and other gases. Since the coal body 1 has a much higher adsorption intensity for CO2 than for CH4, it can dislodge and replace the CH4 adsorbed in the coal micropores, converting the adsorbed CH4 into free CH4, making it easier for the anaerobic methane-oxidizing bacteria to convert it, thereby expanding the range of anaerobic methane-oxidizing bacteria to eliminate CH4 inside the coal body 1. In addition, the anaerobic methane-oxidizing bacteria can partially degrade the coal body 1, increase the pore volume of the coal body 1, enhance the connectivity between the cracks and pores within the coal body 1, and further increase the permeability of the coal body 1.

[0081] Since anaerobic methane oxidation itself is an oxidation reaction, different electron acceptors are required to couple it with reduction. The anaerobic methane oxidizing bacteria in the present invention utilize a reduction-coupled reaction with nitric acid or nitrite. The corresponding chemical reaction formula is: CH4+4NO3 - →CO2+4NO2 - +2H2O;3CH4+8NO2 - +8H + →3CO2+4N2+10H2O.

[0082] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A coalbed gas control method using microbial and hydraulic combined permeability enhancement technology, characterized in that: The steps include: Step 1: First, drill groups are constructed in the coal body. Each drill group includes one fracturing borehole, two pilot boreholes, and two control boreholes. After the drilling is completed, each borehole is hydraulically cut to form slots. Main fractures are formed between the slots, and multiple micro fractures are formed along the main fractures. Each fracturing borehole, pilot borehole, and control borehole is connected to an external pipe, each of which is equipped with a ball valve. Step 2: prepare a fracturing fluid, which is a mixture of water and anaerobic methane-oxidizing bacteria liquid, and perform hydraulic fracturing on the fracturing boreholes of each drilling group. Each fracturing borehole is subjected to staged fracturing. The staged fracturing is performed step by step from the inside to the outside of the borehole, specifically including: Step 201: After the fracturing drilling, pilot drilling, and control drilling are completed, a fracturing fluid is first prepared. The fracturing fluid is a mixture of water and anaerobic methane-oxidizing bacteria liquid. The preparation method is to fill a water tank with water and then pour the anaerobic methane-oxidizing bacteria liquid into the water tank. Step 202: Then, sequentially place the front high-pressure capsule, the rear high-pressure capsule, and the connecting rod into the fracturing borehole, with the front high-pressure capsule and the rear high-pressure capsule respectively placed on both sides of the first slot counted from the inside to the outside of the fracturing borehole, to perform the first stage of fracturing; the front high-pressure capsule and the rear high-pressure capsule are spaced apart and sleeved on the connecting rod, the end of the connecting rod is connected to the emulsion pump via a high-pressure hose, the emulsion pump is connected to the water tank via a liquid inlet pipe and a liquid return pipe, and the front high-pressure capsule and the rear high-pressure capsule are also connected to a manual pressure pump via injection pipes; Step 203: Connect the front high-pressure capsule and the rear high-pressure capsule to a manual pressure pump through injection pipes, add water to the manual pressure pump, and use the manual high-pressure pump to inject water and pressurize the front high-pressure capsule and the rear high-pressure capsule respectively to expand and squeeze the borehole wall; Step 204: Connect the liquid inlet pipe and liquid return pipe between the water tank and the emulsion pump, and the high-pressure hose between the emulsion pump and the connecting rod; Step 205: A front high-pressure capsule and a rear high-pressure capsule are also placed on both sides of the first slot, counted from the inside to the outside, in the pilot boreholes on both sides of the fracturing borehole. The front high-pressure capsule and the rear high-pressure capsule are spaced apart and sleeved on a connecting rod. The front high-pressure capsule and the rear high-pressure capsule are also connected to a manual pressure pump via an injection pipe. Water is added to the manual pressure pump, and the manual high-pressure pump connected to the rear high-pressure capsule is used to inject water and pressurize only the rear high-pressure capsule, causing it to expand and squeeze the borehole wall to complete the borehole sealing. Step 206: After everything is ready, the emulsion pump is started to start the first stage of fracturing the fracturing borehole. During the fracturing process, as the fracturing fluid in the water tank continuously enters the fracturing borehole along the inside of the connecting rod, water and anaerobic methane oxidizing bacteria liquid need to be continuously added to the water tank. When water flows from the control borehole of the current drilling group, it indicates that the cracks generated in the coal body due to hydraulic fracturing have extended to the position of the control borehole. At this time, the fracturing can be stopped, and the pressure of the liquid in the connecting rod and high-pressure hose in the fracturing borehole is relieved. Then, the pressure of the front high-pressure capsule, the rear high-pressure capsule of the fracturing borehole, and the rear high-pressure capsule in the pilot borehole are relieved. Thus, the first stage of fracturing of the fracturing borehole is completed. Step 207: Fracturing the second and subsequent sections of the fracturing borehole. The front high-pressure capsule and the rear high-pressure capsule in the fracturing borehole and the pilot borehole are sequentially moved to both sides of the second slot and each subsequent slot from the inside to the outside of the fracturing borehole and the pilot borehole, and water is injected and pressurized respectively; then, the above steps 201 to 206 are repeated to complete the staged fracturing work from the inside to the outside of the fracturing borehole; Step 3: After the fracturing drilling is completed, the equipment is recovered and the ball valves on the external pipes of each fracturing borehole, pilot borehole and control borehole are closed to ensure that the borehole and the internal cracks of the coal body are not in communication with the outside air. Anaerobic methane oxidizing bacteria are adsorbed on the surface and pores of the coal, and the CH4 adsorbed in the coal micropores is driven away and replaced, so that the adsorbed CH4 becomes free CH4, thereby facilitating the conversion of the anaerobic methane oxidizing bacteria, thereby expanding the scope of the anaerobic methane oxidizing bacteria to eliminate CH4 inside the coal body.

2. The method for coalbed gas control using a microbial and hydraulic combined permeability enhancement technology as claimed in claim 1, characterized in that: After the drilling construction in step 1 is completed, the hydraulic fracturing of each borehole is performed by using an integrated fracturing-fracture device.

3. The method for coalbed gas control using a microbial and hydraulic combined permeability enhancement technology as claimed in claim 1, characterized in that: The arrangement of each drilling group in step 1 is as follows: the fracturing drilling hole is located in the middle, and the pilot drilling hole and the control drilling hole are located on both sides of the fracturing drilling hole.

4. The method for coalbed gas control using microbial and hydraulic combined permeability enhancement technology as claimed in claim 1, characterized in that: In the step 1, the fracturing boreholes, pilot boreholes and control boreholes in each group of boreholes are all installed with casings at the hole openings. The outside of the casings is fixed to the coal body by cement mortar, and the casings are fixed to the external pipes by flanges and bolts.

5. The method for coalbed gas control using a microbial and hydraulic combined permeability enhancement technology as claimed in claim 4, characterized in that: The length L9 of the sleeve is not less than 3m.

6. The method for coalbed gas control using a microbial and hydraulic combined permeability enhancement technology as claimed in claim 1, characterized in that: The arrangement of each drilling group in step 1 includes the arrangement of coal seam drilling holes in the coal mining working face and the arrangement of coal seam drilling holes in the tunneling working face: (1) Coal mining face In a coal mining face, two adjacent drilling groups share one control borehole. The lengths of the pilot borehole, control borehole, and fracturing borehole are determined based on the inclination length L1 of the coal mining face. The lengths of the control borehole and fracturing borehole are equal, and the length L2 should be at least 30m less than the inclination length of the coal mining face, i.e., L2 ≤ L1-30. The length of the pilot borehole is shorter than that of the control borehole or fracturing borehole. The number of construction slots in each fracturing borehole is determined by L2 and the distance L8 between the outermost slot in the borehole and the borehole opening. The distance L8 between the outermost slot in the borehole and the borehole opening is at least 30m, and the distance L7 between adjacent slots in the fracturing borehole is 20-30m. The width L3 of a single slot is 2-4m. The number of slots inside each control borehole, the axial position of the slots, and the distance L7 between adjacent slots are the same as those in the fracturing borehole; The number of slots in each pilot borehole is the same as that in the fracturing borehole, but the axial position of the slots is different from that in the fracturing borehole and the control borehole. The slots in the pilot borehole are spaced L7 / 2m apart from the slots corresponding to the fracturing borehole and the control borehole in the borehole axial direction. The aperture of each pilot borehole, control borehole, and fracturing borehole is not less than 94mm. All boreholes are drilled perpendicular to the coal wall of the roadway and in the same inclination as the coal seam. (2) Excavation working face The fracturing borehole is constructed vertically to the excavation working face, and the control borehole and the pilot borehole have an angle with the central axis of the roadway. The length of the pilot borehole, the control borehole and the fracturing borehole is mainly determined according to the excavation plan; the length of the fracturing borehole L 11 100-140m; At the same time, in order to ensure the overall excavation efficiency, the excavation efficiency of the excavation construction team can be guaranteed by increasing the number of excavation working faces. That is, when gas control is being carried out at one excavation working face, the excavation construction team can go to another excavation working face to excavate, and then return to the excavation working face to carry out construction when gas control is carried out at the other excavation working face. There needs to be a certain amount of stubble between each borehole in the current excavation cycle and each borehole in the next excavation cycle. The stubble length L 10 20-40m; The number of slots, slot width and distance between adjacent slots in each guide drill hole, control drill hole and fracturing drill hole shall be the same as those in the coal mining working face.

7. The method for coalbed gas control using a microbial and hydraulic combined permeability enhancement technology as claimed in claim 1, characterized in that: During step 205, manual high-pressure pumps connected to the front high-pressure capsule and the rear high-pressure capsule are used to simultaneously inject water and pressurize the front high-pressure capsule and the rear high-pressure capsule, so that they expand and squeeze the borehole wall to complete the sealing of the borehole.

8. The method for coalbed gas control using a microbial and hydraulic combined permeability enhancement technology as claimed in claim 1, characterized in that: The pressure of the water injection in step 203, step 204 and step 205 is not less than 15 MPa.

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