Coal seam permeability increasing type water injection method

Abstract

The invention discloses a coal seam permeability increasing type water injection method, and belongs to the technical field of coal mining. The method comprises the steps of drilling construction, primary gas extraction, acid liquid pressure operation, alkali liquid pressure operation, secondary gas extraction, drilling flushing operation and surfactant solution injection operation. According to the method, based on the advantages and disadvantages of a water injection source and drilling selection, the water injection source and the drilling selection are innovatively combined, mine water subjected to softening treatment is used, a synergistic surfactant is added, intermittent circulating water injection is adopted, the wettability of a coal seam can be improved, and the coal seam quality is improved. The pressure of part of water-deficient areas can be effectively relieved, and the utilization rate of water resources is increased. According to the method, the anti-reflection drill holes are selected, on one hand, the gas extraction rate before water injection can be improved, on the other hand, construction is flexible, and the coal seam permeability can be improved so that water can be more evenly injected into the coal seam.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mining, and in particular relates to a coal seam permeability enhancement water injection method. Background Art

[0002] As the depth of coal mining in my country continues to increase, a series of hazards have gradually emerged, such as gas problems and coal dust problems. As the depth of coal seam mining increases, the gas content and pressure of the coal seam will also increase. As the gas is extracted, the moisture in the coal seam will also be extracted, resulting in a drier coal seam, an increase in coal dust concentration and particle size, and an increase in ground temperature. These problems will cause serious damage to the production of coal mines and the health of miners.

[0003] Coal seam water injection technology can prevent and reduce the occurrence of coal mine disasters and improve the safety of coal mining operations. Water injection can increase the moisture content of the coal body, reduce the elastic properties of the coal, and reduce the stress of the coal body. During the mining process of the wet coal seam, the adhesion between the coal and the rock is reduced, which is conducive to improving the coal mining rate. In addition, water injection can pre-wet the coal body, which can effectively reduce the coal dust generated during coal mining, improve the coal mining environment, and reduce the occurrence of occupational diseases.

[0004] The traditional coal seam permeability injection method has certain limitations, such as insufficient wettability of the coal seam, low wetting range, etc., and the large water consumption may cause certain water resource pressure in water-scarce areas. Existing water injection boreholes are mostly extraction boreholes, which also have some disadvantages, such as limited water injection pressure, small water injection flow rate and limited scope of application. Summary of the invention

[0005] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a new method of water injection in each layer. The method of the present invention is based on the advantages and disadvantages of water injection water source and borehole selection, and innovatively combines the two. It uses softened mine water and adds synergistic surfactants, and adopts intermittent circulation water injection, which can not only increase the wettability of the coal seam, but also effectively alleviate the pressure in some water-deficient areas and improve the utilization rate of water resources. The method of the present invention uses permeability-enhancing boreholes to increase the gas extraction rate before water injection on the one hand, and on the other hand, it is flexible in construction and can increase the permeability of the coal seam so that water can be injected into the coal seam more evenly.

[0006] The present invention is achieved through the following technical solutions: A coal seam permeability enhancement water injection method comprises the following steps: a. Construction drilling: Use drilling and cutting equipment to construct several boreholes in the coal seam in front of the coal mining face, and select some boreholes at intervals for permeability enhancement treatment; after the permeability enhancement drilling construction is completed, the drill rod is retracted. During the retraction process of the drill rod, the high-pressure water pump is started, and the pumped water is sprayed out from the small diameter-changing holes on the drill rod. The sprayed water forms a high-pressure water jet, which cuts the coal body along the radial direction of the borehole to form an annular groove.

[0007] b. Initial gas extraction: seal the orifice of the permeability-enhancing borehole and install the first valve and the drain valve. Connect the first valve to the gas extraction device to carry out gas extraction operations. After the extraction stops, remove the gas extraction device.

[0008] c. Acid pressure operation: Connect the first valve to the pressure acid device, inject hydrochloric acid into the permeability-enhancing borehole, and remove the pressure acid device after the hydrochloric acid injection is completed; hydrochloric acid has good dissolving ability and can dissolve the minerals in the cracks and the surrounding rocks to effectively expand the cracks in the coal seam, improve the conductivity of the cracks, and thus increase the permeability of the coal seam.

[0009] d. Alkali liquid pressure operation: connect the first valve to the pressure alkali liquid device, inject liquid alkali solution into the permeability-enhancing borehole, and remove the pressure alkali liquid device after the injection of the liquid alkali solution is completed; the liquid alkali solution reacts with the acidic gas in the coal seam to form a low-viscosity liquid, further expanding the cracks in the coal seam; at the same time, the liquid alkali solution promotes the expansion and loosening of the coal seam, increasing the permeability of the coal seam.

[0010] e. Secondary gas extraction: Connect the first valve to the gas extraction device, and further improve the gas migration channel under the action of hydrochloric acid and liquid alkali solution, which is conducive to gas extraction. Continue to extract gas until the coal mining face advances to 15-20m from the borehole, stop gas extraction, and remove the gas extraction device after extraction stops.

[0011] f. Borehole flushing operation: Connect the first valve to the high-pressure mine softening water injection device, open the drain valve, and flush from the bottom of the borehole from bottom to top using a positive circulation method; after the flushing is completed, close the drain valve and remove the high-pressure mine softening water injection device.

[0012] g. Surfactant solution injection operation: connect the first valve to the alkyl phosphate device, inject the alkyl phosphate solution into the permeability-enhancing borehole, close the first valve to maintain pressure after the injection is completed, and remove the alkyl phosphate device after the pressure maintenance is completed; connect the first valve to the phenol ether phosphate device, inject the phenol ether phosphate solution into the permeability-enhancing borehole, close the first valve to maintain pressure after the injection is completed, and remove the phenol ether phosphate device after the pressure maintenance is completed.

[0013] Furthermore, in step a, a borehole is constructed 50m in front of the coal mining face; the spacing between the boreholes is 25-28m; the drilling is completed when the permeability enhancement drilling construction reaches 160m; the high-pressure water pump adjusts the pump pressure to 85-90MPa; the drill rod is slowly rotated and retracted in a "stay-retract-stay-retract..." manner, and each stay time is 15min. During each stay time period, the high-pressure water jet can cut the coal body to form an annular groove.

[0014] Furthermore, in step b, the extraction operation lasts for 2-3 days.

[0015] Furthermore, in step c, the concentration of hydrochloric acid is 3%-10%, and the injection time is 5 hours.

[0016] Furthermore, in step d, the concentration of the liquid alkali solution is 1%-5%, and the injection time is 3-4 days.

[0017] Furthermore, in step f, the injection pressure of the high-pressure mine softening water injection device is adjusted to 5-8MP; during the flushing process, the pH value and chloride ion concentration of the flushing liquid flowing out of the drain valve are regularly detected. When the pH value of the flushing liquid is between 7-8 and the chloride ion concentration is 50mg / L-200mg / L, the flushing is completed.

[0018] Furthermore, in step g, the concentration of the alkyl phosphate solution is 0.1%-1%, the injection pressure is controlled at 10-15MP, the injection time is 1.5-2h, and the pressure holding time is 6h; the concentration of the phenol ether phosphate solution is 0.1%-0.8%, the injection pressure is controlled at 10-15MP, the injection time is 1.5-2h, and the pressure holding time is 6h; and the water used to prepare the alkyl phosphate solution and the phenol ether phosphate solution is softened mine water.

[0019] Further, the concentration of hydrochloric acid is 5%.

[0020] Furthermore, the concentration of the liquid alkali solution is 4%.

[0021] Furthermore, the concentration of the alkyl phosphate solution is 0.35%, and the concentration of the phenol ether phosphate solution is 0.5%.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses acid or alkali to increase the permeability of drilling, and its beneficial effects include: 1) Improved permeability: Through the treatment of acid or alkali, the blockage in the coal seam can be effectively dissolved or softened or the coal rock layer can be weakened, thereby improving the permeability of the coal seam. This is conducive to improving the effect of water injection or gas injection, thereby better realizing the permeability increase of the coal seam; 2) Expanding the wetting range: Acid or alkali can react with minerals in the coal seam to generate new compounds, thereby changing the wettability of the coal seam. This can expand the wetting range, improve the wetting effect, and reduce the generation of dust; 3) Simple operation: The method of using acid or alkali for permeability increase is simple to operate, does not require complex equipment and piping systems, and is easy to install and maintain. At the same time, the preparation and storage of acid or alkali is also relatively convenient.

[0023] 2. The present invention uses mine softened water with added surfactant to inject water into the coal seam, which reduces the surface tension of water in the coal seam and makes it easier for water to wet and penetrate into the coal seam; intermittent circulation water injection can expand the wetting range and improve the water injection efficiency. The moisture content of the coal seam after gas extraction is 0.3%-0.5%, and the moisture content of the coal seam after water injection can reach 8%-10%.

[0024] 3. The mine softened water used in the present invention can increase the wettability of the coal seam. By pre-wetting the coal body, the amount of coal dust generated can be reduced, and dust pollution during the operation process can be reduced. The maximum dust reduction can reach 75%-90%. Secondly, the utilization rate of mine water is improved, effectively alleviating the water shortage pressure in some areas.

[0025] 4. The present invention adopts a construction method of intermittent hole drilling to increase permeability and water injection, which can shorten the water injection operation time, has a flexible construction method, and a large coal seam pre-wetting range. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a schematic diagram of the process of the method of the present invention.

[0028] In the figure: 1-coal seam, 2-drill hole, 3-injection valve, 4-drainage valve, 5-pressure acid device, 6-pressure alkali solution device, 7-high-pressure mine softening water injection device, 8-alkyl phosphate device, 9-phenol ether phosphate device, 10-coal mining face. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention. Example 1

[0030] This embodiment provides a coal seam permeability enhancement water injection method, such as Figure 1 As shown, the following steps are included: a. Construction of borehole 2: Drilling and cutting equipment is used to sequentially construct several boreholes 2 on the coal seam 1 50 m in front of the coal mining working face 10, with the spacing of boreholes 2 being 25 m; some boreholes 2 are selected at intervals for permeability enhancement treatment, that is, one borehole 2 is selected as the borehole 2 for permeability enhancement treatment after every other borehole 2; when the permeability enhancement borehole 2 is constructed to 160 m, the permeability enhancement borehole 2 is completed and the drill rod is retracted; during the retraction of the drill rod, the high-pressure water pump is started, the pump pressure of the high-pressure water pump is adjusted to 90 MPa, and the pumped water is sprayed out from the variable diameter small hole on the drill rod, and the sprayed water forms a high-pressure water jet, which cuts the coal body along the radial direction of the borehole 2 to form an annular groove; the above-mentioned drill rod is slowly rotated and retracted in the manner of "stay-retract-stay-retract...", and the time of each stay is 15 minutes. During the time period of each stay, the high-pressure water jet can cut the coal body to form an annular groove.

[0031] b. Initial gas extraction: seal the orifice of the permeability-enhanced borehole 2 and install an injection valve 3 and a drain valve 4. Connect the injection valve 3 to the gas extraction device to carry out gas extraction. The extraction operation lasts for 2-3 days. After the extraction stops, remove the gas extraction device.

[0032] c. Acid pressure operation: Connect the injection valve 3 to the pressure acid device 5, and inject hydrochloric acid into the permeability-enhancing borehole 2. The concentration of hydrochloric acid is 5%, and the injection time is 5 hours. After the injection of hydrochloric acid is completed, remove the pressure acid device 5. Hydrochloric acid has good dissolving ability and can dissolve the minerals in the cracks and the surrounding rocks to effectively expand the cracks in the coal seam 1, improve the conductivity of the cracks, and thus increase the permeability of the coal seam 1.

[0033] d. Alkali liquid pressure operation: connect the injection valve 3 to the pressure alkali liquid device 6, inject liquid alkali solution into the permeability-enhancing borehole 2, the concentration of the liquid alkali solution is 4%, and the injection time is 3-4 days. After the injection of the liquid alkali solution is completed, remove the pressure alkali liquid device 6; the liquid alkali solution reacts with the acid gas in the coal seam 1 to form a low-viscosity liquid, further expanding the cracks in the coal seam 1; at the same time, the liquid alkali solution promotes the expansion and loosening of the coal seam 1, increasing the permeability of the coal seam 1; e. Secondary gas extraction: Connect the injection valve 3 to the gas extraction device, and further improve the gas migration channel under the action of hydrochloric acid and liquid alkali solution, which is conducive to gas extraction. Continue to extract gas until the coal mining face 10 advances to 15-20m in front of the borehole 2, stop gas extraction, and remove the gas extraction device after extraction stops.

[0034] f. Flushing operation of borehole 2: connect the injection valve 3 to the high-pressure mine softening water injection device 7, adjust the injection pressure of the high-pressure mine softening water injection device 7 to 5MP, open the drain valve 4, and flush from the bottom of the borehole 2 from bottom to top in a positive circulation mode; during the flushing process, regularly check the pH value and chloride ion concentration of the flushing liquid flowing out of the drain valve 4. When the pH value of the flushing liquid is between 7-8 and the chloride ion concentration is 50mg / L-200mg / L, the flushing is completed; after the flushing is completed, close the drain valve 4 and remove the high-pressure mine softening water injection device 7.

[0035] g. Surfactant solution injection operation: connect the injection valve 3 to the alkyl phosphate device 8, inject the alkyl phosphate solution into the permeability-enhancing borehole 2, close the injection valve 3 after the injection is completed to maintain the pressure, and remove the alkyl phosphate device 8 after the pressure maintenance is completed; in this process, the concentration of the alkyl phosphate solution is 0.35%, the injection pressure is controlled at 13MP, the injection time is 1.8h, and the pressure maintenance time is 6h.

[0036] The injection valve 3 is connected to the phenol ether phosphate device 9, and the phenol ether phosphate solution is injected into the permeability-enhancing borehole 2. After the injection is completed, the injection valve 3 is closed to maintain the pressure. After the pressure maintenance is completed, the phenol ether phosphate device 9 is removed. In this process, the concentration of the phenol ether phosphate solution is 0.5%, the injection pressure is controlled at 13MP, the injection time is 1.8h, and the pressure maintenance time is 6h.

[0037] Softened mine water is used to prepare the alkyl phosphate solution and the phenol ether phosphate solution.

[0038] h. The coal seam water injection operation in the above steps ag shall be carried out 30 days before production until the start of production. Example 2

[0039] This embodiment provides a coal seam permeability enhancement water injection method, such as Figure 1 As shown, the following steps are included: a. Construction of borehole 2: Drilling and cutting equipment is used to sequentially construct several boreholes 2 on the coal seam 1 50 m in front of the coal mining working face 10, with the spacing of boreholes 2 being 28 m; some boreholes 2 are selected at intervals for permeability enhancement treatment, that is, one borehole 2 is selected as the borehole 2 for permeability enhancement treatment after every other borehole 2; when the permeability enhancement borehole 2 is constructed to 160 m, the permeability enhancement borehole 2 is completed and the drill rod is retracted; during the retraction of the drill rod, the high-pressure water pump is started, the pump pressure of the high-pressure water pump is adjusted to 88 MPa, and the pumped water is sprayed out from the variable diameter small hole on the drill rod, and the sprayed water forms a high-pressure water jet, which cuts the coal body along the radial direction of the borehole 2 to form an annular groove; the above-mentioned drill rod is slowly rotated and retracted in the manner of "stay-retract-stay-retract...", and the time of each stay is 15 minutes. During the time period of each stay, the high-pressure water jet can cut the coal body to form an annular groove.

[0040] b. Initial gas extraction: seal the orifice of the permeability-enhanced borehole 2 and install an injection valve 3 and a drain valve 4. Connect the injection valve 3 to the gas extraction device to carry out gas extraction. The extraction operation lasts for 2-3 days. After the extraction stops, remove the gas extraction device.

[0041] c. Acid pressure operation: Connect the injection valve 3 to the pressure acid device 5, and inject hydrochloric acid into the permeability-enhancing borehole 2. The concentration of hydrochloric acid is 3%, and the injection time is 5 hours. After the injection of hydrochloric acid is completed, remove the pressure acid device 5. Hydrochloric acid has good dissolving ability and can dissolve the minerals in the cracks and the surrounding rocks to effectively expand the cracks in the coal seam 1, improve the conductivity of the cracks, and thus increase the permeability of the coal seam 1.

[0042] d. Alkali liquid pressure operation: connect the injection valve 3 to the pressure alkali liquid device 6, inject liquid alkali solution into the permeability-enhancing borehole 2, the concentration of the liquid alkali solution is 5%, and the injection time is 3-4 days. After the injection of the liquid alkali solution is completed, remove the pressure alkali liquid device 6; the liquid alkali solution reacts with the acid gas in the coal seam 1 to form a low-viscosity liquid, further expanding the cracks in the coal seam 1; at the same time, the liquid alkali solution promotes the expansion and loosening of the coal seam 1, increasing the permeability of the coal seam 1; e. Secondary gas extraction: Connect the injection valve 3 to the gas extraction device, and further improve the gas migration channel under the action of hydrochloric acid and liquid alkali solution, which is conducive to gas extraction. Continue to extract gas until the coal mining face 10 advances to 15-20m in front of the borehole 2, stop gas extraction, and remove the gas extraction device after extraction stops.

[0043] f. Flushing operation of borehole 2: connect the injection valve 3 to the high-pressure mine-softening water injection device 7, adjust the injection pressure of the high-pressure mine-softening water injection device 7 to 8MP, open the drain valve 4, and flush from the bottom of the borehole 2 from bottom to top in a positive circulation mode; during the flushing process, regularly check the pH value and chloride ion concentration of the flushing liquid flowing out of the drain valve 4. When the pH value of the flushing liquid is between 7-8 and the chloride ion concentration is 50mg / L-200mg / L, the flushing is completed; after the flushing is completed, close the drain valve 4 and remove the high-pressure mine-softening water injection device 7.

[0044] g. Surfactant solution injection operation: connect the injection valve 3 to the alkyl phosphate device 8, inject the alkyl phosphate solution into the permeability-enhanced borehole 2, close the injection valve 3 after the injection is completed to maintain the pressure, and remove the alkyl phosphate device 8 after the pressure maintenance is completed; in this process, the concentration of the alkyl phosphate solution is 1%, the injection pressure is controlled at 15MP, the injection time is 1.5h, and the pressure maintenance time is 6h.

[0045] The injection valve 3 is connected to the phenol ether phosphate device 9, and the phenol ether phosphate solution is injected into the permeability-enhancing borehole 2. After the injection is completed, the injection valve 3 is closed to maintain the pressure. After the pressure maintenance is completed, the phenol ether phosphate device 9 is removed. In this process, the concentration of the phenol ether phosphate solution is 0.1%, the injection pressure is controlled at 15MP, the injection time is 1.5h, and the pressure maintenance time is 6h.

[0046] Softened mine water is used to prepare the alkyl phosphate solution and the phenol ether phosphate solution.

[0047] h. The coal seam water injection operation in the above steps ag shall be carried out 30 days before production until the start of production. Example 3

[0048] This embodiment provides a coal seam permeability enhancement water injection method, such as Figure 1 As shown, the following steps are included: a. Construction of borehole 2: Drilling and cutting equipment is used to sequentially construct several boreholes 2 on the coal seam 1 50 m in front of the coal mining working face 10, with the spacing of boreholes 2 being 27 m; some boreholes 2 are selected at intervals for permeability enhancement treatment, that is, one borehole 2 is selected as the borehole 2 for permeability enhancement treatment after every other borehole 2; when the permeability enhancement borehole 2 is constructed to 160 m, the permeability enhancement borehole 2 is completed and the drill rod is retracted; during the retraction of the drill rod, the high-pressure water pump is started, the pump pressure of the high-pressure water pump is adjusted to 85 MPa, and the pumped water is sprayed out from the variable diameter small hole on the drill rod, and the sprayed water forms a high-pressure water jet, which cuts the coal body along the radial direction of the borehole 2 to form an annular groove; the above-mentioned drill rod is slowly rotated and retracted in the manner of "stay-retract-stay-retract...", and the time of each stay is 15 minutes. During the time period of each stay, the high-pressure water jet can cut the coal body to form an annular groove.

[0049] b. Initial gas extraction: seal the orifice of the permeability-enhanced borehole 2 and install an injection valve 3 and a drain valve 4. Connect the injection valve 3 to the gas extraction device to carry out gas extraction. The extraction operation lasts for 2-3 days. After the extraction stops, remove the gas extraction device.

[0050] c. Acid pressure operation: Connect the injection valve 3 to the pressure acid device 5, and inject hydrochloric acid into the permeability-enhancing borehole 2. The concentration of hydrochloric acid is 10%, and the injection time is 5 hours. After the injection of hydrochloric acid is completed, remove the pressure acid device 5. Hydrochloric acid has good dissolving ability and can dissolve the minerals in the cracks and the surrounding rocks to effectively expand the cracks in the coal seam 1, improve the conductivity of the cracks, and thus increase the permeability of the coal seam 1.

[0051] d. Alkali liquid pressure operation: connect the injection valve 3 to the pressure alkali liquid device 6, inject liquid alkali solution into the permeability-enhancing borehole 2, the concentration of the liquid alkali solution is 1%, and the injection time is 3-4 days. After the injection of the liquid alkali solution is completed, remove the pressure alkali liquid device 6; the liquid alkali solution reacts with the acid gas in the coal seam 1 to form a low-viscosity liquid, further expanding the cracks in the coal seam 1; at the same time, the liquid alkali solution promotes the expansion and loosening of the coal seam 1, increasing the permeability of the coal seam 1; e. Secondary gas extraction: Connect the injection valve 3 to the gas extraction device, and further improve the gas migration channel under the action of hydrochloric acid and liquid alkali solution, which is conducive to gas extraction. Continue to extract gas until the coal mining face 10 advances to 15-20m in front of the borehole 2, stop gas extraction, and remove the gas extraction device after extraction stops.

[0052] f. Flushing operation of borehole 2: connect the injection valve 3 to the high-pressure mine softening water injection device 7, adjust the injection pressure of the high-pressure mine softening water injection device 7 to 5-8MP, open the drain valve 4, and flush from the bottom of the borehole 2 from bottom to top in a positive circulation mode; during the flushing process, regularly check the pH value and chloride ion concentration of the flushing liquid flowing out of the drain valve 4. When the pH value of the flushing liquid is between 7-8 and the chloride ion concentration is 50mg / L-200mg / L, the flushing is completed; after the flushing is completed, close the drain valve 4 and remove the high-pressure mine softening water injection device 7.

[0053] g. Surfactant solution injection operation: connect the injection valve 3 to the alkyl phosphate device 8, inject the alkyl phosphate solution into the permeability-enhancing borehole 2, close the injection valve 3 after the injection is completed to maintain the pressure, and remove the alkyl phosphate device 8 after the pressure maintenance is completed; in this process, the concentration of the alkyl phosphate solution is 0.1%, the injection pressure is controlled at 10MP, the injection time is 2h, and the pressure maintenance time is 6h.

[0054] The injection valve 3 is connected to the phenol ether phosphate device 9, and the phenol ether phosphate solution is injected into the permeability-enhancing borehole 2. After the injection is completed, the injection valve 3 is closed to maintain the pressure. After the pressure maintenance is completed, the phenol ether phosphate device 9 is removed. In this process, the concentration of the phenol ether phosphate solution is 0.8%, the injection pressure is controlled at 10MP, the injection time is 2h, and the pressure maintenance time is 6h.

[0055] Softened mine water is used to prepare the alkyl phosphate solution and the phenol ether phosphate solution.

[0056] h. The coal seam water injection operation in the above steps ag shall be carried out 30 days before production until the start of production.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A coal seam permeability enhancement water injection method, characterized in that: The steps include: a. Construction drilling: Drilling and cutting equipment is used to construct several boreholes in the coal seam in front of the coal mining face, and some boreholes are selected at intervals for permeability enhancement treatment; after the permeability enhancement drilling construction is completed, the drill rod is retracted. During the retraction process of the drill rod, the high-pressure water pump is started, and the pumped water is sprayed out from the small holes with reduced diameters on the drill rod. The sprayed water forms a high-pressure water jet, which cuts the coal body along the radial direction of the borehole to form an annular cut groove; b. Initial gas extraction: The orifice of the permeability-enhanced borehole is blocked and the first valve and the drain valve are installed. The first valve is connected to the gas extraction device to perform gas extraction operations. After the extraction stops, the gas extraction device is removed; c. Acid pressure operation: connect the first valve to the pressure acid device, inject hydrochloric acid into the permeability-enhancing borehole, and remove the pressure acid device after the hydrochloric acid injection is completed; hydrochloric acid has good dissolution ability, which can dissolve the minerals in the cracks and the surrounding rocks to effectively expand the cracks in the coal seam, improve the conductivity of the cracks, and thus increase the permeability of the coal seam; d. Alkali liquid pressure operation: connect the first valve to the pressure alkali liquid device, inject liquid alkali solution into the permeability-enhancing borehole, and remove the pressure alkali liquid device after the injection of the liquid alkali solution is completed; the liquid alkali solution reacts with the acidic gas in the coal seam to form a low-viscosity liquid, further expanding the cracks in the coal seam; at the same time, the liquid alkali solution promotes the expansion and loosening of the coal seam, increasing the permeability of the coal seam; e. Secondary gas extraction: Connect the first valve to the gas extraction device, and further improve the gas migration channel under the action of hydrochloric acid and liquid alkali solution, which is conducive to gas extraction. Continue to extract gas until the coal mining face advances to 15-20m from the borehole, stop gas extraction, and remove the gas extraction device after extraction stops; f. Borehole flushing operation: connect the first valve to the high-pressure mine softening water injection device, open the drain valve, and flush from the bottom of the borehole to the top in a positive circulation mode; After flushing is completed, close the drain valve and remove the high-pressure mine softening water injection device; g. Surfactant solution injection operation: connect the first valve to the alkyl phosphate device, inject the alkyl phosphate solution into the permeability-enhancing borehole, close the first valve to maintain pressure after the injection is completed, and remove the alkyl phosphate device after the pressure maintenance is completed; connect the first valve to the phenol ether phosphate device, inject the phenol ether phosphate solution into the permeability-enhancing borehole, close the first valve to maintain pressure after the injection is completed, and remove the phenol ether phosphate device after the pressure maintenance is completed.

2. A coal seam permeability enhancement water injection method according to claim 1, characterized in that: In step a, a borehole is constructed 50m in front of the coal mining face; the spacing of the boreholes is 25-28m; the drilling is completed when the permeability enhancement drilling is constructed to 160m; the high-pressure water pump adjusts the pump pressure to 85-90MPa; the drill rod is slowly rotated and retracted in a "stay-retract-stay-retract..." manner, and each stay time is 15min. During each stay time period, the high-pressure water jet can cut the coal body to form an annular groove.

3. A coal seam permeability enhancement water injection method according to claim 1, characterized in that: In step b, the extraction operation lasts for 2-3 days.

4. A coal seam permeability enhancement water injection method according to claim 1, characterized in that: In step c, the concentration of hydrochloric acid is 3%-10%, and the injection time is 5 hours.

5. A coal seam permeability enhancement water injection method according to claim 1, characterized in that: In step d, the concentration of the liquid alkali solution is 1%-5%, and the injection time is 3-4 days.

6. A coal seam permeability enhancement water injection method according to claim 1, characterized in that: In step f, the injection pressure of the high-pressure mine softening water injection device is adjusted to 5-8MP; during the flushing process, the pH value and chloride ion concentration of the flushing liquid flowing out of the drain valve are regularly detected. When the pH value of the flushing liquid is between 7-8 and the chloride ion concentration is 50mg / L-200mg / L, the flushing is completed.

7. A coal seam permeability enhancement water injection method according to claim 1, characterized in that: In step g, the concentration of the alkyl phosphate solution is 0.1%-1%, the injection pressure is controlled at 10-15MP, the injection time is 1.5-2h, and the pressure holding time is 6h; the concentration of the phenol ether phosphate solution is 0.1%-0.8%, the injection pressure is controlled at 10-15MP, the injection time is 1.5-2h, and the pressure holding time is 6h; the water used to prepare the alkyl phosphate solution and the phenol ether phosphate solution is softened mine water.

8. A coal seam permeability enhancement water injection method according to claim 4, characterized in that: The concentration of hydrochloric acid is 5%.

9. A coal seam permeability enhancement water injection method according to claim 5, characterized in that: The concentration of the liquid alkali solution is 4%.

10. A coal seam permeability enhancement water injection method according to claim 7, characterized in that: The concentration of the alkyl phosphate solution is 0.35%, and the concentration of the phenol ether phosphate solution is 0.5%.

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