Multi-purpose method for ground gas pre-pumping well in coal face

Abstract

The invention discloses a method for achieving multiple purposes of a ground gas pre-pumping well in a coal face, and belongs to the technical field of coal mine area gas extraction, goaf filling and CO2 goaf storage. A plurality of ground gas extraction wells are constructed in a coal face to pre-extract coal seam gas, before the working face is extracted to the positions of the gas pre-extraction wells, perforation is conducted on a sleeve section within the mining disturbance range, and after pipe cutting and plugging are conducted on an underground gas pre-extraction coal seam section, negative pressure extraction is conducted on a pressure relief coal seam and goaf gas; after the working face goaf is completely formed and sealed, coal gangue and fly ash mixed paste and CO2 are injected into the goaf and the mining disturbance space at high pressure through the well, and efficient linkage of coal face gas pre-extraction, pressure relief coal seam and goaf gas extraction, goaf filling and goaf CO2 mineralization and storage is achieved. According to the method, the coal face gas pre-pumping well can be used for multiple purposes, the comprehensive cost of gas pre-pumping, pressure relief, goaf gas extraction, goaf filling and coal gangue treatment is reduced, and the method has safe, environmental and social benefits.

Description

Technical Field

[0001] The present invention relates to a method for using a ground gas pre-extraction well in a coal mining face for multiple purposes, in particular to a method for transforming a ground gas pre-extraction well into a pressure-relieving coal seam and goaf gas extraction well, a goaf and a mining disturbance range grouting filling and CO 2 Mineralized sealing wells can realize gas pre-extraction in coal mining working faces, gas extraction in depressurized coal seams and goafs, goaf filling and goaf CO 2 The efficient connection of mineralization sealing reduces the comprehensive cost of gas pre-extraction, pressure relief, gas extraction in goaf, filling in goaf and gangue treatment, which belongs to the gas extraction, filling in goaf and CO2 treatment in coal mining areas. 2 The field of goaf sealing technology. Background Art

[0002] In my country's energy industry structure, coal is an important traditional energy source, and its mining process faces many complex technical challenges and safety and environmental risks. With the continuous exploitation of coal resources, coal and gas protrusion problems have always been a major hidden danger to coal mine safety production. Traditional gas extraction methods are often inefficient and costly. In order to effectively reduce the gas content and gas pressure in coal seams and improve the safety of coal mine production, ground gas pre-extraction technology has gradually been applied. On the one hand, a large number of goafs will be formed during coal mining. Goafs may not only lead to desorption of gas from the adjacent coal seams, but also cause geological disasters such as surface collapse, and provide storage space for the accumulation of gas from coal seams within the range of coal mining disturbance. On the other hand, coal mining produces a large amount of coal gangue, and coal-fired power plants consume a large amount of coal and produce a large amount of fly ash. The accumulation of these solid wastes on the surface has created serious potential environmental pollution risks. In order to achieve low-cost treatment of solid waste in the coal mining and utilization industry, solid wastes such as coal gangue and fly ash are filled into coal mining areas, and injected with CO 2 The mixed CO 2 - Water-rock geochemical reaction, to achieve rapid consolidation of the mixed paste of gangue and fly ash, support the goaf and CO 2 Mineralized geological storage.

[0003] For a long time, due to the significant differences in the wellbore structure and completion methods of the surface gas pre-extraction wells, pressure relief gas extraction wells, and gas extraction wells in the goaf constructed in the coal mining face, it is impossible to achieve the "one well for multiple uses" of the surface gas pre-extraction wells in the coal mining face, resulting in high construction costs and large capital investment for gas surface extraction projects, making it difficult to promote gas surface extraction work on a large scale. In addition, the current integration of gas surface extraction, grouting filling in goafs and mining disturbance areas with CO 2The technical research and engineering demonstration work combined with mineralization sealing work has resulted in the single function of ground gas pre-extraction wells, high comprehensive costs, and poor economic benefits of project implementation. In order to solve the above problems, it is necessary to effectively transform the ground gas pre-extraction wells during the mining process of the working face, and use the constructed ground gas pre-extraction wells to successively extract gas from the depressurized coal seam and goaf, fill the goaf with coal gangue and fly ash paste, and CO 2 Mineralization sealing can achieve a win-win situation in terms of economic, safety, environmental and social benefits. Summary of the invention

[0004] Technical problem: The purpose of the present invention is to overcome the problems of high construction cost, large capital investment, single function and poor economic benefits of traditional ground gas pre-extraction well projects, and to provide a method for multi-purpose ground gas pre-extraction wells in coal mining working faces.

[0005] Technical solution: In order to achieve the above-mentioned purpose, a method for using a ground gas pre-extraction well in a coal mining face for multiple purposes is provided by the present invention, comprising the following steps:

[0006] (a) In the coal mining face, a gas pre-extraction well is constructed by drilling holes on the ground. After drilling the well, the pre-extraction gas coal seam is subjected to fracturing transformation. After installing the upper and lower drainage equipment of the well, drainage gas extraction is first carried out, and then negative pressure extraction is carried out to reduce the gas content and gas pressure in the pre-extraction gas coal seam, eliminate the risk of gas outburst in the coal mining face, and ensure the safe excavation and recovery of the coal mining face tunnel;

[0007] (b) When the coal mining face is mined to 30-40m before the gas pre-extraction well, the first motor and the water ring vacuum pump are turned off, and the negative pressure extraction of gas from the pre-extraction coal seam is stopped; the wellhead of the gas pre-extraction well is opened, the underground drainage device is taken out, and the perforating gun is lowered to perform segmented perforation at the casing section above the pre-extraction coal seam. The segmented perforation position is within the range of the mining disturbance height of the pre-extraction coal seam, including the caving zone, fracture zone and curved subsidence zone formed by the mining of the working face. The specific layer section of the segmented perforation is determined according to the position of the upper adjacent coal seam and non-coal gas-bearing layer within the mining disturbance height range, and is as close as possible to the position of the upper adjacent coal seam and non-coal gas-bearing layer; after perforation, the drainage device is lowered into the production casing again, and the wellhead of the gas pre-extraction well is closed, and the gas pre-extraction well is transformed into a depressurized coal seam and goaf gas extraction well;

[0008] (c) Negative pressure extraction is performed on the depressurized coal seam and the gas extraction well in the goaf. When the coal mining face is mined to 10 to 15 m in front of the depressurized coal seam and the gas extraction well in the goaf, the first motor and the water ring vacuum pump are started to depressurize and extract the pre-extracted gas coal seam and the upper adjacent coal seam within the mining disturbance height range at a wellhead negative pressure value of -0.06 to -0.08 MPa;

[0009] (d) When the coal mining face is mined to 1 to 2 m in front of the depressurized coal seam and the gas extraction well in the goaf, turn off the first motor and the water ring vacuum pump;

[0010] (e) When the coal mining face is mined to the depressurized coal seam and the gas extraction well in the goaf, the underground workers use casing cutting equipment to cut off the production casing at the goaf, and seal the bottom of the production casing with a pressurized removable plug; when a wellhead pressure greater than 5MPa is applied from top to bottom, the removable plug automatically falls off, opening the bottom channel of the production casing, providing a channel outlet for the subsequent injection of the mixed paste of coal gangue and fly ash into the goaf;

[0011] (f) After the bottom of the production casing is sealed, restart the first motor and the water ring vacuum pump to depressurize and extract the pre-extracted gas coal seam and the upper adjacent coal seam within the mining disturbance height range at a wellhead negative pressure value of -0.04 to -0.06 MPa; when a large amount of water is filled in the goaf, causing the wellbore liquid level to rise and affecting the depressurized coal seam and gas extraction in the goaf of the upper adjacent coal seam, use the underground drainage device to quickly drain the water in the goaf, so that the wellbore liquid level drops and improves the gas extraction effect of the depressurized coal seam and the goaf;

[0012] (g) When the pure amount of extracted gas is ≤100m 3 / d, and when the extracted gas concentration is ≤20%, the gas extraction work of the decompression coal seam and goaf is completed. After the decompression coal seam and goaf gas extraction work is completed, the wellhead of the decompression coal seam and goaf gas extraction well is opened, the underground drainage device is taken out, the ground drainage pipeline and negative pressure extraction pipeline are removed, and the coal gangue and fly ash mixed paste injection device and CO are assembled on the ground. 2 injection device, and inject the mixture of gangue and fly ash into the paste injection device, CO 2 The injection device is connected to the wellhead to transform the depressurized coal seam and the gas extraction well in the goaf into grouting filling and CO 2 Mineralized storage wells;

[0013] (h) After the goaf is completely formed and sealed, the coal gangue and fly ash mixture is injected into the device, CO 2 The injection device mixes the coal gangue and fly ash into paste and liquid CO 2 During the injection process into the production casing, the injection speed is increased to form high pressure at the bottom of the production casing, which will flush out the pressurized removable plug, so that the injected coal gangue and fly ash mixed paste, gaseous or liquid CO 2 Directly enter the goaf with larger storage space, coal gangue and fly ash mixed paste, gaseous or liquid CO 2 After being fully mixed on the surface, the multi-component, multi-phase injection is finally realized to achieve the paste filling and CO 2 Mineralization storage.

[0014] In step (a), the fracturing transformation of the pre-gas-extracted coal seam (9) needs to control the fracturing scale according to the real-time microseismic monitoring results on the ground, and by reducing the fracturing construction pressure, it is avoided that the artificial cracks formed by the fracturing extend to the roof of the pre-gas-extracted coal seam (9), so as to reduce the difficulty of roof management during the recovery process of the coal mining face.

[0015] In step (b), the downhole drainage device comprises, from bottom to top, a sand settling pipe (17), a suction port screen pipe (16), an electric submersible pump (15), a drainage pipe (28), a downhole thermometer (26) for monitoring the bottom hole temperature and pressure, and a thermometer cable (27).

[0016] In step (b), the perforating gun is a 102 gun and a 107 bullet, the perforating fluid is formation water, the perforating bullet arrangement is a 60° phase spiral arrangement, and the perforating density is 16 holes / m.

[0017] In step (c), the wellhead negative pressure value is based on the gas production rate, the produced gas CH 4 The concentration is adjusted in time, and a step-by-step change method is adopted. When the gas production rate gradually decreases during the negative pressure extraction process, the produced gas CH 4 When the concentration gradually increases, the negative pressure should be adjusted to -0.08MPa in a step-by-step manner. When the gas production rate gradually increases during the negative pressure extraction process, the produced gas CH 4 As the concentration gradually decreases, the extraction negative pressure should be adjusted in steps to -0.06MPa.

[0018] In step (d), the first motor and the water ring vacuum pump are turned off, and then the gas outburst situation of the coal mining face should be monitored more frequently, and the ventilation intensity of the coal mining face should be adjusted in time according to the change of the gas outburst rate to ensure the safe recovery of the working face.

[0019] In step (e), the pressurized detachable wire plug is a temporary plugging device for sealing the bottom of the production casing under normal pressure and low pressure conditions.

[0020] In step (f), the wellhead negative pressure value is based on the gas production rate, the produced gas CH 4 The concentration is adjusted in time, and a step-by-step change method is adopted. When the gas production rate gradually decreases during the negative pressure extraction process, the produced gas CH 4 As the concentration gradually increases, the negative pressure is adjusted to -0.06 MPa in a step-by-step manner. During the negative pressure extraction process, the gas production rate gradually increases, and the produced gas CH 4 When the concentration gradually decreases, the extraction negative pressure is adjusted in steps to -0.04MPa.

[0021] In step (g), the coal gangue and fly ash mixed paste injection device comprises a first motor, a paste injection pump, a paste storage tank, a first rotary valve, and a wellhead pressure gauge. The first motor drives the paste injection pump to suck the coal gangue and fly ash mixed paste in the paste storage tank into the paste injection pump, and injects it into the wellbore after pressurization. The injection pressure change is monitored by the wellhead pressure gauge installed on the wellhead to achieve continuous injection of the coal gangue and fly ash mixed paste material under the conditions of 5-15MPa injection pressure and 40-80L / min injection speed at the wellhead. 2 The injection device includes CO 2 Injection pump, second motor, liquid CO 2 Storage tank, second rotary valve, wellhead pressure gauge, second motor drives CO 2 The injection pump injects liquid CO 2 Liquid CO in tanks 2 Inhaled CO 2 The injection pump is pressurized and injected into the wellbore. The injection pressure change is monitored by the wellhead pressure gauge installed on the wellhead to achieve liquid CO at a wellhead injection pressure of 5 to 15 MPa and an injection rate of 20 to 40 L / min. 2 continuous injection of.

[0022] In step (h), the coal gangue and fly ash are mixed into a paste, liquid CO 2 During the injection process into the production casing, the injection is performed at the same pressure and different speeds, or alternately at different pressures and different injection speeds.

[0023] Beneficial effect: Due to the adoption of the above technical solution, the present invention overcomes the problems of high construction cost, large capital investment, single function and poor economic benefit of traditional ground gas pre-extraction well engineering, and proposes a method for using a ground gas pre-extraction well in a coal mining face for multiple purposes, transforming the ground gas pre-extraction well constructed in the early stage into a gas extraction well for decompression coal seam and goaf area, grouting filling and CO2 removal in goaf area and mining disturbance range, etc. 2 Mineralized sealing wells can realize gas pre-extraction in coal mining working faces, gas extraction in depressurized coal seams and goafs, goaf filling and goaf CO 2The efficient connection of mineralization sealing can greatly reduce the comprehensive cost of gas pre-extraction, pressure relief and gas extraction in goaf, filling in goaf and treatment of coal gangue. Firstly, a perforating gun is lowered into the surface gas pre-extraction well to perform segmented perforations at the casing section above the pre-extraction coal seam and a drainage device is lowered to transform the gas pre-extraction well into a pressure relief coal seam and goaf gas extraction well, so as to achieve the goal of gas extraction in the pressure relief coal seam and goaf during the mining process of the coal face; secondly, the wellhead negative pressure value is adjusted in segments and steps to extract gas in the pressure relief coal seam and goaf, so as to achieve efficient extraction of pressure relief coal seam and gas, and reduce the adverse effects of negative pressure extraction on underground coal mining in coal mines; thirdly, the coal gangue and fly ash mixed paste is injected into the device, CO 2 The injection device is connected to the wellhead to transform the depressurized coal seam and the gas extraction well in the goaf into grouting filling and CO 2 Mineralized storage wells can realize low-cost and efficient filling of goaf with mixed paste of coal gangue and fly ash and CO 2 Mineralization storage. The main advantages compared with existing technologies are:

[0024] 1) The ground gas pre-extraction well has realized the pre-extraction of coal seam gas, pressure relief and gas extraction in goaf, filling of goaf with mixed paste of coal gangue and fly ash, CO 2 The “one well for multiple uses” of geological sealing and mine environmental governance has significantly reduced the overall cost of coal mine gas control, environmental protection, and comprehensive utilization of goaf areas;

[0025] 2) The production casing is not cemented, which significantly reduces the destructive effect of the movement of the overlying strata on the wellbore after the formation of the goaf, and provides stable wellbore conditions for the long-term extraction of gas from the depressurized coal seam and goaf;

[0026] 3) By perforating in sections within the disturbance height range of pre-gas extraction coal seam mining, the pressure relief gas extraction, coal gangue and fly ash mixed paste and CO 2 The injection provides multiple flow channels, significantly reducing the pressure relief gas extraction, paste and CO 2 The difficulty of injection engineering has improved the filling support effect of the mixed paste of coal gangue and fly ash and the CO 2 Mineralization storage capacity; ④ The surface gas pre-extraction well transformation process is simple, the project implementation cost is low, and the economic, environmental and social benefits are good. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram of the gas pre-extraction well body structure, drainage gas extraction and negative pressure extraction method in the coal mining working face of the present invention.

[0028] Figure 2 A diagram of a method for transforming a gas pre-extraction well in a coal mining face into a gas extraction well for a pressure-relieved coal seam and goaf according to the present invention.

[0029] Figure 3 The invention is to transform the decompression coal seam and gas extraction well in the goaf in the coal mining working face into grouting filling and goaf CO in the goaf and mining disturbance range. 2 Diagram of mineralized storage well method.

[0030] In the figure: 1-ground; 2-first wellbore; 3-surface casing; 4-first wellbore cement ring; 5-second wellbore; 6-production casing; 7-annular passage between second wellbore and production casing; 8-packer; 9-pre-extracted gas coal seam; 10-pre-perforated screen; 11-annular steel plate; 12-wellhead; 13-ordinary wire plug; 14-wellbore liquid level; 15-electric submersible pump; 16-inlet screen; 17-sand settling pipe; 18-sand settling during drainage and production; 19-positive and negative pressure gauge; 20-first rotary valve; 21-gas flow meter; 22-gas transmission pipeline; 23-second rotary valve; 24-liquid flow meter; 25-water pipeline; 26-downhole thermometer; 27-thermometer cable; 28-drain pipe; 29-water ring vacuum pump; 30-first motor; 31-production casing perforation position; 32-coal powder; 33-goaf; 34-mining disturbance height; 35-upper adjacent coal seam; 36-pressurized detachable plug; 37-first motor; 38-paste injection pump; 39-paste storage tank; 40-coal gangue and fly ash mixed paste; 41-first rotary valve; 42-wellhead pressure gauge; 43-CO 2 Injection pump; 44 - second motor; 45 - liquid CO 2 Storage tank; 46-Liquid CO 2 ; 47-second rotary valve. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the embodiments in the accompanying drawings:

[0032] like Figure 1 As shown, the method for using a ground gas pre-extraction well in a coal mining face for multiple purposes of one well of the present invention comprises the following specific steps:

[0033] (a) In the coal mining face, a gas pre-extraction well is drilled on the ground 1 to construct a gas pre-extraction well. After the well is drilled, the pre-extraction gas coal seam 9 is subjected to hydraulic fracturing. After the upper and lower drainage equipment of the well is installed, drainage and gas extraction are first carried out, and then negative pressure extraction is carried out to reduce the gas content and gas pressure in the pre-extraction gas coal seam 9, eliminate the risk of gas outburst in the coal mining face, and ensure the safe excavation and recovery of the coal mining face tunnel; the method of using a ground gas pre-extraction well in the coal mining face for multiple purposes, the hydraulic fracturing transformation of the pre-extraction gas coal seam 9 needs to control the scale of hydraulic fracturing to avoid the artificial cracks formed by hydraulic fracturing extending to the roof of the pre-extraction gas coal seam 9, so as to reduce the difficulty of roof management during the recovery of the coal mining face.

[0034] (b) When the coal mining face is mined to 30 to 40 m before the gas pre-extraction well, the first motor 30 and the water ring vacuum pump 29 are turned off, the negative pressure extraction of gas from the pre-extraction coal seam 9 is stopped, the wellhead 12 of the gas pre-extraction well is opened, the underground drainage device is taken out, and a perforating gun is lowered to perform segmented perforations at the casing section above the pre-extraction coal seam 9. After perforating, the drainage device is again lowered into the production casing 6, and the wellhead 12 is closed to transform the gas pre-extraction well into a pressure-relieving coal seam and goaf gas extraction well; the underground drainage device includes, from bottom to top, a sand settling pipe 17, a suction port screen pipe 16, an electric submersible pump 15, a drainage device, and a gas extraction well. The perforating gun is a 102 gun and a 107 bullet. The perforating fluid is formation water. The perforating bullet is arranged in a 60° phase spiral arrangement. The perforating density is 16 holes / m. The segmented perforating position is within the mining disturbance height 34 of the pre-gas extraction coal seam 9, including the caving zone, fracture zone and curved subsidence zone formed by the working face mining. The specific layer section of the segmented perforation is determined according to the position of the upper adjacent coal seam 35 and the non-coal gas-bearing layer within the mining disturbance height 34, and is as close as possible to the position of the upper adjacent coal seam 35 and the non-coal gas-bearing layer.

[0035] (c) When the coal mining face is mined to 10 to 15 m before the decompression coal seam and the gas extraction well in the goaf, the first motor 30 and the water ring vacuum pump 29 are started to decompress and extract the pre-extracted gas coal seam 9 and the upper adjacent coal seam 35 within the range of the mining disturbance height 34 at a wellhead negative pressure value of -0.06 to -0.08 MPa; the wellhead negative pressure value is adjusted in time according to the gas production rate and the produced gas concentration, and a step-by-step change method is adopted. When the gas production rate gradually decreases during the negative pressure extraction process, the produced gas CH 4 When the concentration gradually increases, the negative pressure should be adjusted to -0.08MPa in a step-by-step manner. When the gas production rate gradually increases during the negative pressure extraction process, the produced gas CH 4 As the concentration gradually decreases, the extraction negative pressure should be adjusted in steps to -0.06MPa.

[0036] (d) When the coal mining face is mined to 1 to 2 meters in front of the depressurized coal seam and the gas extraction well in the goaf, the first motor 30 and the water ring vacuum pump 29 are turned off; after the first motor 30 and the water ring vacuum pump 29 are turned off, the gas outburst situation of the coal mining face should be monitored more frequently, and the ventilation intensity of the coal mining face should be adjusted in time according to the change of the gas outburst rate to ensure the safe mining of the face.

[0037] (e) When the coal mining face is mined to the location of the depressurized coal seam and the gas extraction well in the goaf, the underground workers use casing cutting equipment to cut off the production casing 6 at the location of the goaf 33, and use a pressurized detachable plug 36 to seal the bottom of the production casing 6; the pressurized detachable plug 36 is a temporary plugging device, which can achieve the sealing of the bottom of the production casing 6 under normal pressure and low pressure conditions. When a wellhead pressure greater than 5MPa is applied from top to bottom, the detachable plug 36 will automatically fall off and open the bottom channel of the production casing 6, providing a channel outlet for the subsequent injection of the mixed paste 40 of coal gangue and fly ash into the goaf.

[0038] (f) After the bottom of the production casing 6 is sealed, the first motor 30 and the water ring vacuum pump 29 are restarted to relieve the pressure and extract the pre-extracted gas coal seam 9 and the upper adjacent coal seam 35 within the range of the mining disturbance height 34 at a wellhead negative pressure value of -0.04 to -0.06 MPa; the wellhead negative pressure value is adjusted in time according to the gas production rate and the concentration of the produced gas, and a step-by-step change method is adopted. When the gas production rate gradually decreases during the negative pressure extraction process, the produced gas CH 4 When the concentration gradually increases, the negative pressure should be adjusted to -0.06MPa in a step-by-step manner. When the gas production rate gradually increases during the negative pressure extraction process, the produced gas CH 4 When the concentration gradually decreases, the extraction negative pressure should be adjusted in steps to -0.04MPa; when a large amount of water is filled in the goaf 33, causing the wellbore liquid level 14 to rise and affecting the gas extraction of the unloaded coal seam 35 and the goaf, the underground drainage device should be used to quickly drain the water in the goaf 33, so that the wellbore liquid level 14 will drop and the gas extraction effect of the unloaded coal seam and the goaf will be improved.

[0039] (g) When the pure amount of extracted gas is ≤100m 3 / d, and when the extracted gas concentration is ≤20%, the gas extraction work of the pressure-relieved coal seam and goaf is completed. After the gas extraction work of the pressure-relieved coal seam and goaf is completed, the wellhead 12 of the gas extraction well of the pressure-relieved coal seam and goaf is opened, the underground drainage device is taken out, the ground drainage pipeline 1 and the negative pressure extraction pipeline are removed, and the coal gangue and fly ash mixed paste injection device and CO are assembled on the ground 1. 2 injection device, and inject the mixture of gangue and fly ash into the paste injection device, CO 2 The injection device is connected to the wellhead 12, and the decompression coal seam and the gas extraction well in the goaf are transformed into the goaf 33 and the grouting filling and goaf 33CO within the mining disturbance range. 2Mineralized sealing well; the coal gangue and fly ash mixed paste injection device comprises a first motor 37, a paste injection pump 38, a paste storage tank 39, a first rotary valve 41, and a wellhead pressure gauge 42. The first motor 37 drives the paste injection pump 38 to suck the coal gangue and fly ash mixed paste 40 in the paste storage tank 39 into the paste injection pump 38, and injects it into the wellbore after pressurization. The injection pressure change is monitored by the wellhead pressure gauge 42 installed on the wellhead 12, and the continuous injection of the coal gangue and fly ash mixed paste 40 material under the conditions of 5-15MPa injection pressure and 40-80L / min injection speed at the wellhead can be achieved; CO 2 The injection device includes CO 2 Injection pump 43, second motor 44, liquid CO 2 The storage tank 45, the second rotary valve 47, the wellhead pressure gauge 42, and the second motor 44 drive the CO 2 The injection pump 43 injects liquid CO 2 Liquid CO in tank 45 2 46 Inhaled CO 2 The injection pump 43 is pressurized and injected into the wellbore. The injection pressure change is monitored by the wellhead pressure gauge 42 installed on the wellhead 12. Liquid CO can be injected at a wellhead pressure of 5 to 15 MPa and an injection speed of 20 to 40 L / min. 2 46 continuous injection.

[0040] (h) After the working face goaf 33 is completely formed and sealed, the coal gangue and fly ash paste injection device, CO 2 Injection device, mix coal gangue and fly ash paste 40, liquid CO 2 46 is injected into the production casing 6 at the same time. During the injection process, high pressure is formed at the bottom of the production casing 6 by increasing the injection speed, which flushes the pressurized removable wire plug 36, so that the injected coal gangue and fly ash mixed paste 40, gaseous or liquid CO 2 46 directly enters the goaf 33 with larger storage space to achieve filling and CO 2 Mineralization sealing; the coal gangue and fly ash mixed paste 40, gaseous or liquid CO 2 46 Goaf 33 Injection methods include coal gangue and fly ash mixed paste 40, gaseous or liquid CO 2 46 Simultaneous injection at the same pressure and different speeds, including coal gangue and fly ash mixed paste 40, gaseous or liquid CO 2 46 Alternating injection at different pressures and injection speeds, including a mixture of gangue and fly ash 40, gaseous or liquid CO 2 46 After fully mixing on the surface 1, the multi-component and multi-phase injection is finally realized to fill the closed goaf with paste and CO2 Purpose of mineralization storage.

Claims

1. A method for using a ground gas pre-extraction well in a coal mining face for multiple purposes, characterized in that: The following steps are involved: (a) In the coal mining face, a gas pre-extraction well is drilled on the ground (1), and after the well is drilled, the pre-extraction gas coal seam (9) is subjected to fracturing transformation. After the well is installed with drainage equipment above and below the well, drainage gas extraction is first performed, and then negative pressure extraction is performed to reduce the gas content and gas pressure in the pre-extraction gas coal seam (9), eliminate the risk of gas outburst in the coal mining face, and ensure safe excavation and recovery of the coal mining face tunnel; (b) When the coal mining face is mined to 30 to 40 m before the pre-gas extraction well, the first motor (30) and the water ring vacuum pump (29) are turned off, and the negative pressure extraction of gas from the pre-gas extraction coal seam (9) is stopped; the wellhead (12) of the pre-gas extraction well is opened, the underground drainage device is taken out, and a perforating gun is lowered to perform segmented perforations at the casing section position above the pre-gas extraction coal seam (9), and the segmented perforation positions are within the range of the mining disturbance height (34) of the pre-gas extraction coal seam (9), including The specific layer section for segmented perforation is determined according to the position of the upper adjacent coal seam (35) and the non-coal gas-bearing layer within the range of the mining disturbance height (34), and is as close as possible to the position of the upper adjacent coal seam (35) and the non-coal gas-bearing layer; after perforation, a drainage device is re-inserted into the production casing (6), and the wellhead (12) of the gas pre-extraction well is closed, and the gas pre-extraction well is transformed into a depressurized coal seam and goaf gas extraction well; (c) negative pressure extraction is performed on the depressurized coal seam and the gas extraction well in the goaf. When the coal mining face is mined to 10 to 15 m in front of the depressurized coal seam and the gas extraction well in the goaf, the first motor (30) and the water ring vacuum pump (29) are started to depressurize and extract gas from the pre-extracted gas coal seam (9) and the upper adjacent coal seam (35) within the range of the mining disturbance height (34) at a wellhead negative pressure value of -0.06 to -0.08 MPa; (d) when the coal mining face is mined to 1 to 2 m in front of the depressurized coal seam and the gas extraction well in the goaf, the first motor (30) and the water ring vacuum pump (29) are turned off; (e) When the coal mining face is mined to the location of the depressurized coal seam and the gas extraction well in the goaf, the underground workers use casing cutting equipment to cut off the production casing (6) at the location of the goaf (33), and seal the bottom of the production casing (6) with a pressurized removable plug (36); when a wellhead pressure greater than 5MPa is applied from top to bottom, the removable plug (36) automatically falls off, opening the bottom channel of the production casing (6), providing a channel outlet for the subsequent injection of the mixed paste (40) of coal gangue and fly ash into the goaf; (f) After the bottom of the production casing (6) is sealed, the first motor (30) and the water ring vacuum pump (29) are restarted to depressurize and extract gas from the pre-extracted gas coal seam (9) and the upper adjacent coal seam (35) within the range of the mining disturbance height (34) at a wellhead negative pressure value of -0.04 to -0.06 MPa; when a large amount of water is filled in the goaf (33), causing the wellbore liquid level (14) to rise and affecting the depressurized coal seam and gas extraction in the goaf of the upper adjacent coal seam (35), the underground drainage device is used to quickly drain the water in the goaf (33), so that the wellbore liquid level (14) drops, thereby improving the gas extraction effect of the depressurized coal seam and the goaf; (g) When the pure amount of extracted gas is ≤100m 3 / d, and when the extracted gas concentration is ≤20%, the decompression coal seam and goaf gas extraction work is completed. After the decompression coal seam and goaf gas extraction work is completed, the wellhead (12) of the decompression coal seam and goaf gas extraction well is opened, the underground drainage device is taken out, the ground (1) drainage pipeline and negative pressure extraction pipeline are removed, and the ground (1) assembles a coal gangue and fly ash mixed paste injection device and a CO2 injection device, and connects the coal gangue and fly ash mixed paste injection device and the CO2 injection device to the wellhead (12), and transforms the decompression coal seam and goaf gas extraction well into a goaf (33) and a grouting filling and goaf (33) CO2 mineralization sealing well within the mining disturbance range; (h) After the goaf (33) is completely formed and sealed, the gangue and fly ash mixed paste (40) and liquid CO2 (46) are simultaneously injected into the production casing (6) using a coal gangue and fly ash mixed paste injection device and a CO2 injection device. During the injection process, high pressure is formed at the bottom of the production casing (6) by increasing the injection speed, and the pressurized removable wire plug (36) is flushed open, so that the injected coal gangue and fly ash mixed paste (40) and gaseous or liquid CO2 (46) directly enter the goaf (33) with a larger storage space. The coal gangue and fly ash mixed paste (40) and gaseous or liquid CO2 (46) are fully mixed on the surface (1) and injected in a multi-component, multi-phase state, ultimately achieving the paste filling of the closed goaf and the mineralization and sealing of CO2.

2. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (a), the fracturing transformation of the pre-gas-extracted coal seam (9) needs to control the fracturing scale according to the real-time microseismic monitoring results on the ground, and by reducing the fracturing construction pressure, it is avoided that the artificial cracks formed by the fracturing extend to the roof of the pre-gas-extracted coal seam (9), so as to reduce the difficulty of roof management during the recovery process of the coal mining face.

3. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (b), the downhole drainage device comprises, from bottom to top, a sand settling pipe (17), a suction port screen pipe (16), an electric submersible pump (15), a drainage pipe (28), a downhole thermometer (26) for monitoring the bottom hole temperature and pressure, and a thermometer cable (27).

4. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (b), the perforating gun is a 102 gun and a 107 bullet, the perforating fluid is formation water, the perforating bullet arrangement is a 60° phase spiral arrangement, and the perforating density is 16 holes / m.

5. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (c), the wellhead negative pressure value is timely adjusted according to the gas production rate and the CH4 concentration of the produced gas, and a step-by-step change method is adopted. When the gas production rate gradually decreases and the CH4 concentration of the produced gas gradually increases during the negative pressure extraction process, the extraction negative pressure should be adjusted in a step-by-step manner to -0.08MPa. When the gas production rate gradually increases and the CH4 concentration of the produced gas gradually decreases during the negative pressure extraction process, the extraction negative pressure should be adjusted in a step-by-step manner to -0.06MPa.

6. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (d), the first motor (30) and the water ring vacuum pump (29) are turned off, and then the gas outburst situation of the coal mining face should be monitored more frequently, and the ventilation intensity of the coal mining face should be adjusted in time according to the change of the gas outburst rate to ensure the safe recovery of the working face.

7. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (e), the pressurized detachable wire plug (36) is a temporary plugging device for sealing the bottom of the production casing (6) under normal pressure and low pressure conditions.

8. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (f), the wellhead negative pressure value is adjusted in time according to the gas production rate and the CH4 concentration of the produced gas, and a step-by-step change method is adopted. When the gas production rate gradually decreases and the CH4 concentration of the produced gas gradually increases during the negative pressure extraction process, the extraction negative pressure is adjusted to -0.06MPa in a step-by-step manner. When the gas production rate gradually increases and the CH4 concentration of the produced gas gradually decreases during the negative pressure extraction process, the extraction negative pressure is adjusted to -0.04MPa in a step-by-step manner.

9. The method for using a single well for multiple purposes for ground gas pre-extraction in a coal mining face according to claim 1, characterized in that: In step (g), the coal gangue and fly ash mixed paste injection device comprises a first motor (37), a paste injection pump (38), a paste storage tank (39), a first rotary valve (41), and a wellhead pressure gauge (42). The first motor (37) drives the paste injection pump (38) to suck the coal gangue and fly ash mixed paste (40) in the paste storage tank (39) into the paste injection pump (38), and injects it into the wellbore after pressurization. The wellhead pressure gauge (42) installed on the wellhead (12) monitors the injection pressure change, so as to achieve the coal gangue and fly ash mixed paste (40) under the conditions of 5 to 15 MPa injection pressure at the wellhead and 40 to 80 L / min injection speed. 40) continuous injection of materials; the CO2 injection device comprises a CO2 injection pump (43), a second motor (44), a liquid CO2 storage tank (45), a second rotary valve (47), and a wellhead pressure gauge (42); the second motor (44) drives the CO2 injection pump (43) to suck the liquid CO2 (46) in the liquid CO2 storage tank (45) into the CO2 injection pump (43), and injects it into the wellbore after pressurization, and monitors the injection pressure change through the wellhead pressure gauge (42) installed on the wellhead (12), so as to realize the continuous injection of liquid CO2 (46) under the conditions of 5-15MPa injection pressure at the wellhead and 20-40L / min injection speed.

10. The method for using a ground gas pre-extraction well for multiple purposes in a coal mining face according to claim 1, characterized in that: In step (h), during the process of injecting the mixed paste (40) of coal gangue and fly ash and liquid CO2 (46) into the production casing (6), the injection is performed simultaneously at the same pressure and different speeds, or alternately at different pressures and different injection speeds.

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