Method for injecting hot flue gas to displace gas through kilometer directional drilling
The injection of hot flue gas through kilometer directional drilling technology solves the problems of low breathability and difficulty in gas desorption and flow in coal seam gas extraction, and achieves efficient gas extraction and energy utilization, reducing environmental impact.
Patent Information
- Application Number
- CN202411606649.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-12
- Publication Date
- 2025-02-18
AI Technical Summary
In the prior art, in the coal seam gas extraction, there are problems such as low permeability of coal seam, difficulty in desorption and low extraction rate, resulting in most of the gas remaining in the coal seam.
The kilometer directional drilling technology is used to inject hot flue gas, which promotes the formation of coal pore cracks and gas desorption flow through the high temperature effect of the hot flue gas, and improves the gas extraction efficiency.
Accurate control of drilling trajectory is achieved, gas extraction efficiency and energy utilization are improved, and the impact on the environment is reduced.
Smart Images
Figure CN119466690A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of gas control, and particularly relates to technical research on coal seam permeability enhancement, and specifically is a method for injecting hot flue gas to displace gas through a kilometer-long directional drilling hole. Background Art
[0002] Based on the national energy structure of "rich in coal, poor in oil, and little gas", coal accounts for more than 50% of my country's energy consumption. Among them, coal-fired power plants are the main way of coal consumption. The annual average emission of CO2 in hot flue gas from coal-fired power plants accounts for about 30% to 50%. In order to reduce the emission of CO2 into the atmosphere, CO2 storage is generally considered to be the most effective potential solution to achieve carbon neutrality; Coalbed methane (gas) is one of my country's main strategic mineral resources, with a total reserve of 70 trillion m 3 About 80% of the total gas reserves are in deep coal seams. The gas in deep coal seams is characterized by high stress, low permeability, micropores, and strong adsorption. The main technical bottlenecks faced by mining are low coal seam permeability, difficult gas desorption and flow, and low extraction rate, which results in most of the gas remaining in the coal seam. In order to improve the extraction rate of coal seam gas, scholars at home and abroad have developed many coal seam enhanced permeability technologies, such as hydraulic fracturing, hydraulic cutting, and coal seam gas injection (CO2, N2, etc.). The main components of the high-temperature hot flue gas generated by gas power generation are N2, CO2, and H2O (g). If they are captured and injected into underground gas extraction boreholes or coalbed methane wells, on the one hand, they can displace and replace the gas in the coal seam; on the other hand, the thermal effect produced can promote the desorption and flow of gas in the pores and fissures of the coal body, thereby improving the efficiency of gas extraction. Studies have shown that the adsorption capacity of gas decreases with increasing temperature. The high temperature of hot flue gas can cause the coal body to expand and deform and induce secondary pores and cracks, which helps to form new channels for gas migration.
[0003] Directional long drilling technology is an inevitable trend in the development of coal mine gas control in the future. The kilometer-long directional drilling technology has the advantages of long drilling holes, large flow rate of 100 meters, long effective extraction time, uniform hole distribution, small engineering volume and high gas extraction concentration. It can achieve precise control of long drill directional drilling, improve the efficiency of borehole gas extraction, effectively solve the hazards of high gas, increase gas utilization rate, and create huge environmental benefits while creating economic benefits. Summary of the invention
[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a method for injecting hot flue gas to displace gas through a kilometer-long directional borehole based on directional long drilling technology.
[0005] The present invention is achieved through the following technical solutions: A method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole comprises the following steps: A. Well drilling construction and borehole arrangement: first determine the location of the coal seam and its rock and soil cover, then construct vertical shafts and extraction-monitoring combined wells from the ground through the rock and soil cover to the deepest coal seam; after the vertical shafts are formed, arrange kilometer-level directional hot flue gas injection holes along the coal seam of the coal mining face; before the production of the coal mining face, construct several groups of in-layer extraction fan-shaped drilling sites in the horizontal direction toward the coal seam in the intake and return air lanes. The in-layer extraction fan-shaped drilling sites at the intake and return air lanes are placed on both sides of the hot flue gas injection hole. Each group of in-layer extraction fan-shaped drilling sites includes flow measurement holes, extraction and discharge holes, gas pressure measurement holes and coal seam deformation measurement holes.
[0006] B. Arrange the hot flue gas injection system, coalbed methane extraction system and nitrogen injection system: set an extraction plug at the wellhead of the extraction-monitoring well to prevent gas leakage; set a gas injection plug at the mouth of the hot flue gas injection hole, so that a closed space is formed inside the hot flue gas injection hole; one end of the extraction pipe located in the air intake lane is connected to the extraction-monitoring well, and the other end is connected to the boreholes of each layer extraction fan-shaped drilling field at the air intake lane; one end of the extraction pipe located in the return air lane is connected to the extraction-monitoring well, and the other end is connected to the boreholes of each layer extraction fan-shaped drilling field at the return air lane; the ground is equipped with a gas thermal power plant power generation device, a hot flue gas emission device, a gas extraction pump, a hot flue gas storage device, a gas drying and filtering device, a gas separation device, a CO2 gas storage tank, and a gas pressurizing device in sequence; the gas thermal power plant power generation device is connected to the hot flue gas emission device, and the hot flue gas is discharged from the gas extraction pump, and the hot flue gas storage device is connected to the gas extraction pump. The flue gas discharge device is connected to the hot flue gas storage device, the hot flue gas storage device is connected to the gas drying and filtering device, and a hot flue gas storage tank valve is arranged between the two, the gas drying and filtering device is connected to the gas separation device, one path of the gas separation device is connected to the gas pressurizing device through the N2 pipeline, and the N2 pipeline is provided with an N2 valve, the other path of the gas separation device is connected to the CO2 gas storage tank, the CO2 gas storage tank is connected to the gas pressurizing device through the CO2 pipeline, and the CO2 pipeline is provided with a CO2 valve, the gas pressurizing device is connected to the hot flue gas injection pipe, the hot flue gas injection pipe is placed in the vertical shaft, the other end of the hot flue gas injection pipe is connected to the gas injection plug and communicated with the hot flue gas injection hole; one end of the gas extraction pump is connected to the extraction plug and communicated with the extraction-monitoring combined well, and the other end of the gas extraction pump is connected to the power generation device of the gas thermal power plant.
[0007] C. Arrangement of monitoring and surveillance system: Arrange integrated multi-parameter monitoring devices at the extraction-monitoring combined wells and gas injection plugging devices. The integrated multi-parameter monitoring devices are connected to the ground control center through multi-parameter monitoring data transmission lines to obtain the changes in hot flue gas injection time, temperature and pressure at each stage of each coal seam in real time, thus completing the arrangement of the monitoring system.
[0008] D. The first stage of hot flue gas displacement and pre-extraction before mining: The hot flue gas generated by the power generation device of the gas thermal power plant enters the hot flue gas storage device through the hot flue gas discharge device. At this time, the valve of the hot flue gas storage tank is in a closed state. After the pressure of the hot flue gas storage device reaches 0.9MPa and the hot flue gas flow is stable, the hot flue gas storage tank valve is opened, and the hot flue gas enters the gas drying and filtering device to filter out the high-temperature water vapor. The hot flue gas after impurity removal flows into the gas separation device. The gas separation device mainly separates N2 and CO2 in the hot flue gas. Open the N2 valve, The CO2 valve is closed, and the separated CO2 is stored in the CO2 gas storage tank to collect enough CO2 for the next downhole gas injection displacement; the separated N2 enters the gas pressurizing device through the N2 pipeline, and the gas pressurizing device is pressurized to 1.6MPa. The pressurized N2 is passed through the hot flue gas injection pipe to the hot flue gas injection hole. The pressure and concentration difference replaces the adsorbed CH4, and the high mobility washes away the free CH4. The high-pressure flushing can not only support the channel with high pore pressure, but also reduce the effective stress of the coal seam, thereby improving the efficiency of the coal seam. High permeability; while injecting N2, turn on the gas extraction pump, and start the first stage of pre-extraction in the extraction pipes located in the intake and return air lanes; determine the duration of high-pressure N2 injection into the closed coal seam based on the volume capacity of CO2 in the CO2 gas storage tank, and when the pressure in the CO2 gas storage tank reaches 1.6MPa, close the N2 valve to stop N2 injection, close the hot flue gas storage tank valve, and continue to collect hot flue gas in the hot flue gas storage device, open the CO2 valve, and pressurize the CO2 in the CO2 gas storage tank to 1.6MPa through the gas pressurizing device, and then pass the hot flue gas through the hot flue gas storage device. The gas injection pipe is transported to the hot flue gas injection hole to displace the coal seam that has been flushed by N2 at a high speed. CO2 has a stronger adsorption capacity in the coal seam than CH4, and the CH4 in the coal matrix with smaller porosity in the coal seam is replaced. At the same time, the higher temperature of CO2 itself can promote the desorption of CH4 gas adsorbed by the coal seam, and on the other hand, it also realizes the storage of CO2. A large amount of CH4 is produced in the coal seam section, which improves the CH4 mining efficiency of the coal seam. The extracted CH4 is returned to the power generation device of the gas thermal power plant through the extraction-monitoring combined well and the gas extraction pump to continue generating electricity.
[0009] E. Coal seam mining in the first stage: After the completion of the pre-extraction in the first stage, the second stage of coal seam mining begins to achieve extraction of residual CH4 in the coal seam while mining; with the recovery of the coal mining face, a T-valve is installed every 30-50m on the extraction pipe located in the return air lane. The T-valve is placed in the extraction chamber, and one end of the extraction pipe is gradually buried in the goaf. The T-valve in the previous extraction chamber of the buried part is closed to ensure the airtightness of the extraction. This process is repeated until the mining task of this coal seam is completed.
[0010] F. Nitrogen injection in goaf: a gas injection plug is installed at the entrance of the air inlet tunnel, a vortex tube and two nitrogen injection pipelines are buried in the air inlet tunnel, the hot flue gas injection pipe is connected to one end of the vortex tube, and the other end of the vortex tube is connected to two nitrogen injection pipelines respectively, and each nitrogen injection pipeline is provided with a valve; when the pressure in the hot flue gas storage device reaches 0.9MPa again, the hot flue gas storage tank valve is opened, and the hot flue gas is processed by the gas drying and filtering device and the gas separation device in turn, the N2 valve is opened, and the CO2 valve is closed. The separated N2 is pressurized to 1.6MPa by the gas pressurizing device and then enters the vortex tube through the hot flue gas injection pipe for cooling. The high-temperature N2 is cooled by the vortex tube and then enters the goaf through the nitrogen injection pipeline for fire prevention and extinguishing.
[0011] Furthermore, in step A, when arranging kilometer-scale directional hot flue gas injection holes, the technical parameters of the hot flue gas injection holes, including layer position, length, and number of groups, are analyzed based on the mining conditions of the coal mining face and the gas occurrence rules, including ash content, gas content, permeability, and gas pressure. The construction position of the hot flue gas injection holes is determined based on the technical parameters and then construction is carried out.
[0012] Furthermore, in step C, the integrated multi-parameter monitoring device includes a temperature sensor, a gas pressure sensor and a gas concentration detector; the temperature sensor monitors the changes in the temperature of the coal seam and the hot flue gas in real time, and the temperature sensor also detects the temperature of N2 during the nitrogen injection process; the gas pressure sensor detects the changes in CH4 pressure; the gas concentration detector monitors the changes in CH4 concentration during the displacement process and the nitrogen injection process.
[0013] Furthermore, in step D, the pre-extraction time of the first stage is 3-6 months. After the extraction is completed, the CO2 valve and the gas pressurizing device are closed to complete the hot flue gas sealing and perform the hole sealing operation.
[0014] Furthermore, in step F, after the high-temperature N2 is transported to the vortex tube, the high-temperature N2 enters the nozzle of the vortex tube, generating a rotating airflow, causing the high-temperature N2 to undergo adiabatic expansion, the temperature to drop, and the heat to be taken away and transferred to the surrounding coal environment.
[0015] Furthermore, in step F, the two nitrogen injection pipelines in the goaf adopt the buried pipe nitrogen injection method. After the pre-set first nitrogen injection pipeline is buried for a certain length, fire-proof nitrogen injection begins, and the second nitrogen injection pipeline is pre-buried at the same time; when the outlet of the first nitrogen injection pipeline is at the junction of the oxidation zone and the cooling zone of the goaf, the goaf between the outlets of the two nitrogen injection pipelines is the oxidation zone, the second nitrogen injection pipeline starts to inject nitrogen, and the nitrogen injection of the first nitrogen injection pipeline is stopped at the same time, and the nitrogen injection pipeline is pre-buried again; such a reciprocating cycle allows nitrogen to be continuously injected into the spontaneous combustion zone of the goaf, thereby achieving the purpose of isolating and suffocating the remaining coal.
[0016] Compared with the prior art, the method of the present invention has the following beneficial effects: 1) The method of the present invention can realize the precise control of the drilling trajectory. The kilometer-long directional drilling ensures the effective extension of the drilling trajectory in the predetermined layer. This precise control can improve the effectiveness and efficiency of drilling.
[0017] 2) The method of the present invention increases the effective extraction distance of the borehole, thereby increasing the gas extraction volume of the borehole. The thermal effect generated by the injection of hot flue gas can promote the desorption and flow of gas in the pores and fissures of the coal body. The combination of the two greatly improves the gas extraction efficiency.
[0018] 3) The method of the present invention has strong adaptability to strata. It can be used for both hard and intact strata and for breaking soft, medium-hard, and unevenly hard and soft strata. The holes drilled in the fan-shaped drilling field can evenly cover the entire working surface. It has the advantages of high drilling efficiency, multi-hole combination, centralized extraction, etc., and can significantly improve the effect of coal seam gas control.
[0019] 4) The method of the present invention improves the utilization rate of gas energy, reduces the impact and damage to the environment, and is of great significance to the safe and efficient production of coal mines. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] 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.
[0021] Figure 1 This is a schematic diagram of hot flue gas displacement and pre-extraction before mining in the first stage of the method of the present invention.
[0022] Figure 2 Schematic diagram of coal seam mining in the second stage of the method of the present invention.
[0023] In the figure: 1-gas thermal power plant power generation device, 2-hot flue gas emission device, 3-gas extraction pump, 4-hot flue gas storage device, 5-hot flue gas storage tank valve, 6-gas drying and filtering device, 7-gas separation device, 8-N2 valve, 9-CO2 gas storage tank, 10-CO2 valve, 11-gas pressurizing device, 12-vertical shaft, 13-gas injection plugger, 14-seam extraction fan-shaped drilling site, 15-flow measurement hole, 16-extraction drilling hole, 17-gas pressure measurement hole, 18-coal seam deformation measurement hole, 19-hot flue gas injection hole, 20-extraction pipe, 21-T-valve, 22-extraction chamber, 23-vortex tube, 24-nitrogen injection pipeline, 25-extraction plugger, 26-extraction-monitoring combined well, 27-hot flue gas injection pipe. DETAILED DESCRIPTION
[0024] 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.
[0025] This embodiment provides a method for injecting hot flue gas into a kilometer-long directional borehole to displace gas, such as Figure 1 and Figure 2 As shown, the following steps are included: A. Drilling construction and drilling arrangement: First, determine the location of the coal seam and its rock and soil cover layer, and then construct a vertical shaft 12 and an extraction-monitoring combined well 26 from the ground through the rock and soil cover layer to the deepest coal seam; after the vertical shaft 12 is formed, arrange kilometer-scale directional hot flue gas injection holes 19 along the coal seam of the coal mining face; when arranging the kilometer-scale directional hot flue gas injection holes 19, analyze the technical parameters of the hot flue gas injection holes 19, including: layer position, length, number of groups, according to the mining conditions of the coal mining face and the law of gas occurrence, including: ash content, gas content, permeability and gas pressure, and determine the construction position of the hot flue gas injection holes 19 according to the technical parameters before construction. The above analysis method is a conventional method in the field, and the technicians in this field are clear and can implement it.
[0026] Before the coal mining face is put into production, several groups of in-layer extraction fan-shaped drill sites 14 are constructed horizontally toward the coal seam in the intake and return air tunnels. The in-layer extraction fan-shaped drill sites 14 at the intake and return air tunnels are placed on both sides of the hot flue gas injection hole 19. Each group of in-layer extraction fan-shaped drill sites 14 includes a flow measurement hole 15, an extraction borehole 16, a gas pressure measurement hole 17 and a coal seam deformation measurement hole 18.
[0027] B. Arrangement of hot flue gas injection system, coalbed methane extraction system and nitrogen injection system: An extraction plug 2533 is provided at the wellhead of the extraction-monitoring combined well 26 to prevent air leakage; an injection plug 13 is provided at the mouth of the hot flue gas injection hole 19, so that a closed space is formed inside the hot flue gas injection hole 19; one end of the extraction pipe 20 located in the air intake lane is connected to the extraction-monitoring combined well 26, and the other end is connected to the boreholes of each layer extraction fan-shaped drilling field 14 at the air intake lane; one end of the extraction pipe 20 located in the return air lane is connected to the extraction-monitoring combined well 26, and the other end is connected to the boreholes of each layer extraction fan-shaped drilling field 14 at the return air lane; a gas thermal power plant power generation device 1, a hot flue gas exhaust device 2, a gas extraction pump 3, a hot flue gas storage device 4, a gas drying and filtering device 6, a gas separation device 7, a CO2 gas storage tank 9, and a gas pressurizing device 11 are provided on the ground in sequence; the gas thermal power plant power generation device 1 is connected to the hot flue gas exhaust device 2, and the hot flue gas exhaust device 2 is connected to the hot flue gas storage device 4, the hot flue gas storage device 4 is connected to the gas drying and filtering device 6 and a hot flue gas storage tank valve 5 is arranged between the two, the gas drying and filtering device 6 is connected to the gas separation device 7, one way of the gas separation device 7 is connected to the gas pressurizing device 11 through the N2 pipeline, and the N2 pipeline is provided with an N2 valve 8, the other way of the gas separation device 7 is connected to the CO2 gas storage tank 9, the CO2 gas storage tank 9 is connected to the gas pressurizing device 11 through the CO2 pipeline, and the CO2 pipeline is provided with a CO2 valve 10, the gas pressurizing device 11 is connected to the hot flue gas injection pipe 27, the hot flue gas injection pipe 27 is placed in the vertical shaft 12, the other end of the hot flue gas injection pipe 27 is connected to the gas injection plug 13 and communicated with the hot flue gas injection hole 19; one end of the gas extraction pump 3 is connected to the extraction plug 2533 and communicated with the extraction-monitoring combined well 26, and the other end of the gas extraction pump 3 is connected to the power generation device 1 of the gas thermal power plant.
[0028] C. Arrangement of monitoring and surveillance system: An integrated multi-parameter monitoring device is arranged at the extraction-monitoring combined well 26 and the gas injection plug 13. The integrated multi-parameter monitoring device is connected to the ground control center through a multi-parameter monitoring data transmission line to obtain the changes in the hot flue gas injection time, temperature and pressure of each coal seam at each stage in real time, thereby completing the layout of the monitoring system.
[0029] The integrated multi-parameter monitoring device includes a temperature sensor, a gas pressure sensor and a gas concentration detector; the temperature sensor monitors the changes in the temperature of the coal seam and hot flue gas in real time, and the temperature sensor also detects the temperature of N2 during the nitrogen injection process; the gas pressure sensor detects the changes in CH4 pressure; the gas concentration detector monitors the changes in CH4 concentration during the displacement process and the nitrogen injection process.
[0030] D. The first stage of hot flue gas displacement and pre-extraction before mining: The hot flue gas generated by the power generation device 1 of the gas thermal power plant enters the hot flue gas storage device 4 through the hot flue gas discharge device 2. At this time, the hot flue gas storage tank valve 5 is in a closed state. After the pressure of the hot flue gas storage device 4 reaches 0.9MPa and the hot flue gas flow is stable, the hot flue gas storage tank valve 5 is opened, and the hot flue gas enters the gas drying and filtering device 6 to filter out the high-temperature water vapor. The hot flue gas after impurity removal flows into the gas separation device 7. The gas separation device 7 mainly separates N2 and CO2 in the hot flue gas. The N2 valve 8 is opened and the CO2 valve 10 is closed. The separated CO2 O2 is stored in the CO2 gas storage tank 9 to collect enough CO2 for the next downhole gas injection displacement; the separated N2 enters the gas pressurizing device 11 through the N2 pipeline, and the gas pressurizing device 11 is pressurized to 1.6MPa. The pressurized N2 is passed through the hot flue gas injection pipe 27 to the hot flue gas injection hole 19. The pressure and concentration difference replaces the adsorbed CH4, and the high mobility washes away the free CH4. The high-pressure flushing can both support the channel with high pore pressure and reduce the effective stress of the coal seam, thereby improving the permeability; the injected N2 At the same time, the gas extraction pump 3 is turned on, and the extraction pipe 20 located in the intake and return air lanes starts the first stage of pre-extraction; the duration of high-pressure N2 injection into the closed coal seam is determined according to the volume capacity of CO2 in the CO2 gas storage tank 9, and when the pressure in the CO2 gas storage tank 9 reaches 1.6MPa, the N2 valve 7 is closed to stop the N2 injection, and the hot flue gas storage tank valve 5 is closed. The hot flue gas continues to be collected in the hot flue gas storage device 4, and the CO2 valve 10 is opened. The CO2 in the CO2 gas storage tank 9 is pressurized to 1.6MPa through the gas pressurizing device 11, and then injected into the hot flue gas storage device 4. Pipe 27 transports CO2 to the hot flue gas injection hole 19 to displace the coal seam that has been flushed by N2 at a high speed. CO2 has a stronger adsorption capacity in the coal seam than CH4, and the CH4 in the coal matrix with smaller porosity in the coal seam is replaced. At the same time, the higher temperature of CO2 itself can promote the desorption of CH4 gas adsorbed by the coal seam, and on the other hand, the storage of CO2 is also achieved; a large amount of CH4 is produced in the coal seam section, which improves the CH4 mining efficiency of the coal seam, and the extracted CH4 is returned to the power generation device 1 of the gas thermal power plant through the extraction-monitoring combined well 26 and the gas extraction pump 3 to continue to generate electricity.
[0031] The pre-extraction time of the first stage is 3-6 months. After the extraction is completed, the CO2 valve 10 and the gas pressurizing device 11 are closed to complete the hot flue gas sealing and carry out the hole sealing operation.
[0032] E. Second stage coal seam mining: After the first stage of pre-extraction is completed, the second stage of coal seam mining begins to achieve mining and extraction of residual CH4 in the coal seam; as the coal mining face is recovered, a T-valve 21 is installed every 30-50m on the extraction pipe 20 located in the return air lane, and the T-valve 21 is placed in the extraction chamber 22. One end of the extraction pipe 20 is gradually buried in the goaf, and the T-valve 21 in the previous extraction chamber 22 of the buried part is closed to ensure the extraction airtightness. This process is repeated until the mining task of this coal seam is completed.
[0033] F. Nitrogen injection in goaf: A gas injection plug 13 is arranged at the entrance of the air inlet lane, a vortex tube and two nitrogen injection pipelines 24 are buried in the air inlet lane, a hot flue gas injection pipe 27 is connected to one end of the vortex tube 23, and the other end of the vortex tube 23 is respectively connected to the two nitrogen injection pipelines 24, and valves are arranged on the two nitrogen injection pipelines 24; when the pressure in the hot flue gas storage device 4 reaches 0.9 MPa again, the hot flue gas storage tank valve 5 is opened, the hot flue gas is processed by the gas drying and filtering device 6 and the gas separation device 7 in turn, the N2 valve 8 is opened, the CO2 valve 10 is closed, and the separated N2 is discharged through the gas heating device 4; After the pressure device 11 is pressurized to 1.6MPa, it enters the vortex tube 23 through the hot flue gas injection pipe 27 for cooling. Specifically, after the high-temperature N2 is transported to the vortex tube 23, the high-temperature N2 enters the nozzle of the vortex tube 23, generating a rotating airflow, causing the high-temperature N2 to undergo adiabatic expansion, the temperature to drop, and the heat to be taken away and transferred to the surrounding coal environment; the cooled high-temperature N2 passes through the vortex tube 23 and then through the nitrogen injection pipeline 24 into the goaf for fire prevention and extinguishing; the vortex tube 23 is a prior art, and its structural structure and working principle are clear to those skilled in the art.
[0034] The two nitrogen injection pipelines 24 in the goaf adopt the buried pipe nitrogen injection method. After the pre-set first nitrogen injection pipeline 24 is buried for a certain length, fire-proof nitrogen injection begins, and the second nitrogen injection pipeline 24 is pre-buried at the same time; when the outlet of the first nitrogen injection pipeline 24 is at the junction of the oxidation zone and the cooling zone of the goaf, the goaf between the outlets of the two nitrogen injection pipelines 24 is the oxidation zone, and the second nitrogen injection pipeline 24 starts to inject nitrogen, while the nitrogen injection of the first nitrogen injection pipeline 24 is stopped, and the nitrogen injection pipeline 24 is pre-buried again; this reciprocating cycle allows nitrogen to be continuously injected into the spontaneous combustion zone of the goaf, thereby achieving the purpose of isolating and suffocating the remaining coal.
[0035] G. After the mining of this coal seam is completed, when the relative CH4 content of the coal seam drops below the critical extraction CH4 concentration, repeat steps A to F to carry out the process of hot flue gas displacement, hot flue gas sealing and CH4 extraction for the next coal seam until the hot flue gas storage volume of each horizontal drilling well reaches above the set value, completing the hot flue gas sealing and CH4 extraction operations.
[0036] 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 method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole, characterized in that: The steps include: A. Well drilling construction and borehole arrangement: first determine the location of the coal seam and its rock and soil cover, then construct vertical shafts and extraction-monitoring combined wells from the ground through the rock and soil cover to the deepest coal seam; after the vertical shaft is formed, arrange kilometer-level directional hot flue gas injection holes along the coal seam of the coal mining face; before the production of the coal mining face, construct several groups of layer extraction fan-shaped drilling sites in the horizontal direction of the intake and return air lanes to the coal seam. The layer extraction fan-shaped drilling sites at the intake and return air lanes are placed on both sides of the hot flue gas injection hole. Each group of layer extraction fan-shaped drilling sites includes flow measurement holes, extraction and discharge holes, gas pressure measurement holes and coal seam deformation measurement holes; B. Arrange the hot flue gas injection system, coalbed methane extraction system and nitrogen injection system: set an extraction plug at the wellhead of the extraction-monitoring well to prevent gas leakage; set a gas injection plug at the mouth of the hot flue gas injection hole, so that a closed space is formed inside the hot flue gas injection hole; one end of the extraction pipe located in the air intake lane is connected to the extraction-monitoring well, and the other end is connected to the boreholes of each layer extraction fan-shaped drilling field at the air intake lane; one end of the extraction pipe located in the return air lane is connected to the extraction-monitoring well, and the other end is connected to the boreholes of each layer extraction fan-shaped drilling field at the return air lane; the ground is equipped with a gas thermal power plant power generation device, a hot flue gas emission device, a gas extraction pump, a hot flue gas storage device, a gas drying and filtering device, a gas separation device, a CO2 gas storage tank, and a gas pressurizing device in sequence; the gas thermal power plant power generation device is connected to the hot flue gas emission device, and the hot flue gas is discharged from the gas extraction pump, and the hot flue gas storage device is connected to the gas extraction pump. The flue gas discharge device is connected to the hot flue gas storage device, the hot flue gas storage device is connected to the gas drying and filtering device, and a hot flue gas storage tank valve is arranged between the two, the gas drying and filtering device is connected to the gas separation device, one path of the gas separation device is connected to the gas pressurizing device through the N2 pipeline, and the N2 pipeline is provided with an N2 valve, the other path of the gas separation device is connected to the CO2 gas storage tank, the CO2 gas storage tank is connected to the gas pressurizing device through the CO2 pipeline, and the CO2 pipeline is provided with a CO2 valve, the gas pressurizing device is connected to the hot flue gas injection pipe, the hot flue gas injection pipe is placed in the vertical shaft, the other end of the hot flue gas injection pipe is connected to the gas injection plug and communicated with the hot flue gas injection hole; one end of the gas extraction pump is connected to the extraction plug and communicated with the extraction-monitoring combined well, and the other end of the gas extraction pump is connected to the power generation device of the gas thermal power plant; C. Arrangement of monitoring and surveillance system: Arrange integrated multi-parameter monitoring devices at the extraction-monitoring combined well and the gas injection plugging device. The integrated multi-parameter monitoring device is connected to the ground control center through a multi-parameter monitoring data transmission line to obtain the changes in the hot flue gas injection time, temperature and pressure of each coal seam at each stage in real time, thus completing the arrangement of the monitoring system; D. The first stage of hot flue gas displacement and pre-extraction before mining: The hot flue gas generated by the power generation device of the gas thermal power plant enters the hot flue gas storage device through the hot flue gas discharge device. At this time, the valve of the hot flue gas storage tank is in a closed state. After the pressure of the hot flue gas storage device reaches 0.9MPa and the hot flue gas flow is stable, the hot flue gas storage tank valve is opened, and the hot flue gas enters the gas drying and filtering device to filter out the high-temperature water vapor. The hot flue gas after impurity removal flows into the gas separation device. The gas separation device mainly separates N2 and CO2 in the hot flue gas. Open the N2 valve, The CO2 valve is closed, and the separated CO2 is stored in the CO2 gas storage tank to collect enough CO2 for the next downhole gas injection displacement; the separated N2 enters the gas pressurizing device through the N2 pipeline, and the gas pressurizing device is pressurized to 1.6MPa. The pressurized N2 is passed through the hot flue gas injection pipe to the hot flue gas injection hole. The pressure and concentration difference replaces the adsorbed CH4, and the high mobility washes away the free CH4. The high-pressure flushing can not only support the channel with high pore pressure, but also reduce the effective stress of the coal seam, thereby improving the efficiency of the coal seam. High permeability; while injecting N2, turn on the gas extraction pump, and start the first stage of pre-extraction in the extraction pipes located in the intake and return air lanes; determine the duration of high-pressure N2 injection into the closed coal seam based on the volume capacity of CO2 in the CO2 gas storage tank, and when the pressure in the CO2 gas storage tank reaches 1.6MPa, close the N2 valve to stop N2 injection, close the hot flue gas storage tank valve, and continue to collect hot flue gas in the hot flue gas storage device, open the CO2 valve, and pressurize the CO2 in the CO2 gas storage tank to 1.6MPa through the gas pressurizing device, and then pass the hot flue gas through the hot flue gas storage device. The gas injection pipe is transported to the hot flue gas injection hole to displace the coal seam that has been flushed by N2 at a high speed. CO2 has a stronger adsorption capacity in the coal seam than CH4, and the CH4 in the coal matrix with smaller porosity in the coal seam is replaced. At the same time, the higher temperature of CO2 itself can promote the desorption of CH4 gas adsorbed by the coal seam, and on the other hand, it also realizes the storage of CO2; a large amount of CH4 is produced in the coal seam section, which improves the efficiency of CH4 mining in the coal seam. The extracted CH4 is returned to the power generation device of the gas thermal power plant through the extraction-monitoring combined well and the gas extraction pump to continue power generation; E. First stage coal seam mining: After the first stage of pre-extraction, the second stage of coal seam mining begins, realizing extraction of residual CH4 in the coal seam while mining; with the recovery of the coal mining face, a T-valve is installed every 30-50m on the extraction pipe located in the return air lane. When the T-valve is in the extraction chamber, one end of the extraction pipe is gradually buried in the goaf, and the T-valve in the previous extraction chamber of the buried part is closed to ensure the extraction tightness. This process is repeated until the mining task of this coal seam is completed; F. Nitrogen injection in goaf: a gas injection plug is installed at the entrance of the air inlet tunnel, a vortex tube and two nitrogen injection pipelines are buried in the air inlet tunnel, the hot flue gas injection pipe is connected to one end of the vortex tube, and the other end of the vortex tube is connected to two nitrogen injection pipelines respectively, and each nitrogen injection pipeline is provided with a valve; when the pressure in the hot flue gas storage device reaches 0.9MPa again, the hot flue gas storage tank valve is opened, and the hot flue gas is processed by the gas drying and filtering device and the gas separation device in turn, the N2 valve is opened, and the CO2 valve is closed. The separated N2 is pressurized to 1.6MPa by the gas pressurizing device and then enters the vortex tube through the hot flue gas injection pipe for cooling. The high-temperature N2 is cooled by the vortex tube and then enters the goaf through the nitrogen injection pipeline for fire prevention and extinguishing.
2. The method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole according to claim 1 is characterized in that: In step A, when arranging kilometer-scale directional hot flue gas injection holes, the technical parameters of the hot flue gas injection holes, including layer position, length, and number of groups, are analyzed according to the mining conditions of the coal mining face and the gas occurrence law, including ash content, gas content, permeability, and gas pressure. The construction position of the hot flue gas injection holes is determined according to the technical parameters and then construction is carried out.
3. The method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole according to claim 1 is characterized in that: In step C, the integrated multi-parameter monitoring device includes a temperature sensor, a gas pressure sensor and a gas concentration detector; the temperature sensor monitors the changes in the temperature of the coal seam and the hot flue gas in real time, and the temperature sensor also detects the temperature of N2 during the nitrogen injection process; the gas pressure sensor detects the changes in CH4 pressure; the gas concentration detector monitors the changes in CH4 concentration during the displacement process and the nitrogen injection process.
4. The method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole according to claim 1 is characterized in that: In step D, the first stage pre-extraction time is 3-6 months. After the extraction is completed, the CO2 valve and the gas pressurizing device are closed to complete the hot flue gas sealing and perform the hole sealing operation.
5. The method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole according to claim 1 is characterized in that: In step F, after the high-temperature N2 is transported to the vortex tube, the high-temperature N2 enters the nozzle of the vortex tube, generating a rotating airflow, causing the high-temperature N2 to undergo adiabatic expansion, the temperature to drop, and the heat to be taken away and transferred to the surrounding coal environment.
6. The method for displacing gas by injecting hot flue gas through a kilometer-long directional drilling hole according to claim 1, characterized in that: In step F, the two nitrogen injection pipelines in the goaf adopt the buried pipe nitrogen injection method. After the pre-set first nitrogen injection pipeline is buried for a certain length, fire-proof nitrogen injection begins, and the second nitrogen injection pipeline is pre-buried at the same time; when the outlet of the first nitrogen injection pipeline is at the junction of the oxidation zone and the cooling zone of the goaf, the goaf between the outlets of the two nitrogen injection pipelines is the oxidation zone, the second nitrogen injection pipeline starts to inject nitrogen, and the nitrogen injection of the first nitrogen injection pipeline is stopped at the same time, and the nitrogen injection pipeline is pre-buried again; such a reciprocating cycle allows nitrogen to be continuously injected into the spontaneous combustion zone of the goaf, thereby achieving the purpose of isolating and suffocating the remaining coal.