Method for hot flue gas displacement of coal seam methane extraction and closed-loop carbon sequestration

Abstract

The application discloses a method for hot flue gas displacement and closed-loop carbon sequestration of superimposed coal seam methane extraction, which adopts CH4 combustion and explosion fracturing technology to generate gas impact fracturing coal seam section to form a crack network in situ in each coal seam section, then hot flue gas is injected into each coal seam section, the high temperature of the hot flue gas can promote the desorption of CH4 gas in the coal body, and CO2, SO2 and NO2 in the hot flue gas can replace a large amount of CH4 gas adsorbed in the superimposed coal seam due to the competitive adsorption advantage and closed-loop utilization, thereby realizing the hot flue gas storage and improving the coal seam methane extraction efficiency. In addition, the multi-source monitoring data inversion and intelligent control system can design the best combustion and explosion gas injection parameters and the best hot flue gas injection parameters according to the changes of the physical parameters of the current different coal seam sections, thereby performing layered dynamic and accurate regulation and control on the gas injection parameters of each coal seam section, and maximizing the methane combustion and explosion fracturing, hot flue gas storage and CH4 extraction efficiency of each coal seam section of the superimposed coal seam.

Description

Technical Field

[0001] This invention relates to a method for hot flue gas storage and CH4 extraction, specifically a method for CH4 extraction and multi-directional closed-loop carbon fixation in superimposed coal seams driven by hot flue gas, belonging to the technical field of carbon fixation and CH4 extraction. Background Technology

[0002] Given China's national energy structure characterized by "abundant coal, scarce oil, and limited gas," coal accounts for more than 50% of my country's energy consumption. Coal-fired power plants are the main mode of coal consumption, and CO2 accounts for approximately 30% to 50% of the annual emissions of hot flue gas from coal-fired power plants. To reduce CO2 emissions into the atmosphere, CO2 sequestration is widely considered the most effective potential solution for achieving carbon neutrality. my country's deep unminable coal seams have a huge volume of CH4 adsorption and storage, and have great potential for CH4 resource utilization. In addition, these coal seams are buried deep underground and are generally difficult to mine directly, which can provide good geological conditions for hot flue gas sequestration. Some scholars predict that the CO2 sequestration capacity of unminable coal seams at a depth of 1500 to 2000 meters is about 55.8 billion tons. However, deep unminable coal seams are generally characterized by high ground stress, low porosity, and low permeability, which increases the difficulty of hot flue gas injection and CH4 extraction. It is necessary to use fracturing and permeability enhancement measures to promote the development of coal seam pore and fracture structure, and provide efficient transport channels for hot flue gas sequestration and CH4 extraction.

[0003] Hydraulic fracturing is currently the most widely used reservoir fracturing and permeability enhancement method for CO2 sequestration and CH4 extraction. However, hydraulic fracturing generally suffers from problems such as high water consumption and limited fracture propagation, resulting in a limited range for hot flue gas sequestration and CH4 extraction. Currently, hydraulic fracturing technology cannot achieve closed-loop construction in hot flue gas sequestration and CH4 displacement in coal seams. That is, after the injected H2O and fracturing fluid complete fracturing and permeability enhancement in the coal seam, they need to be extracted before subsequent hot flue gas sequestration and CH4 extraction can be carried out, making a closed-loop reuse process impossible. In contrast, combustion-explosive fracturing technology utilizes in-situ desorption of CH4 from the coal seam. The high-temperature, high-pressure gas generated by the synergistic combustion of O2 and CH4 impacts and fracturing deep, unmineable coal seams, thereby efficiently creating a three-dimensional fracture network. While this technology significantly improves the thermal gas storage and CH4 extraction rates in deep, unminable coal seams, there is still no research combining combustion-explosive fracturing with CH4 extraction from superimposed coal seams driven by thermal gas storage. Furthermore, the properties of different coal seam segments within superimposed coal seams vary considerably. Traditional multi-layer injection techniques use uniform injection parameters across horizontal wells, leading to low injection efficiency in individual wells. Throughout the combustion-explosive fracturing-thermal gas storage-CH4 extraction process, failure to effectively monitor changes in the physical properties of each coal seam segment can result in low efficiency in combustion-explosive fracturing, thermal gas storage, and CH4 extraction. Furthermore, the failure to detect excessive fracture development in coal seams can lead to caprock rupture, resulting in environmental safety issues such as thermal gas leakage.

[0004] Therefore, to address the shortcomings of current methods for hot flue gas sequestration and CH4 extraction in deep superimposed coal seams, a new approach is proposed. This approach combines combustion-explosion fracturing and hot flue gas sequestration technologies to achieve efficient closed-loop extraction of CH4 in each coal seam segment of the superimposed coal seam. This achieves efficient closed-loop utilization of combustion-explosion fracturing, hot flue gas, and extracted CH4 resources throughout the entire process of "combustion-explosion fracturing - hot flue gas sequestration - methane extraction," thereby reducing the cost of deep, unminable coalbed methane extraction, maximizing the utilization of deep, difficult-to-mine or unminable superimposed coal seam resources, and improving the efficiency of hot flue gas sequestration and CH4 extraction in deep, unminable, extra-thick coal seams. This provides a new research approach to support carbon neutrality and the development of the coalbed methane industry. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for methane extraction and closed-loop carbon fixation in stacked coal seams using hot flue gas displacement. By combining combustion and explosive fracturing technology and hot flue gas storage technology, it simultaneously achieves efficient closed-loop extraction of CH4 from stacked coal seams, thereby reducing the cost of deep, unminable coalbed methane extraction, maximizing the utilization of deep, difficult-to-mine or unminable stacked coal seam resources, and improving the efficiency of hot flue gas storage and CH4 extraction in deep, unminable, extra-thick coal seams.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for methane extraction and closed-loop carbon fixation in coal seams driven by hot flue gas displacement, the specific steps of which are as follows:

[0007] A. Drilling construction: First, determine the location of each coal seam segment and its rock capping layer in the superimposed coal seam. Then, drill vertical shafts and extraction-monitoring wells from the ground through each rock capping layer to the deepest coal seam segment. After the vertical shafts are formed, use a directional drilling rig to drill a horizontal well from the vertical shaft along the direction of each coal seam segment. After completion, stop drilling work.

[0008] B. Deployment of the hot flue gas injection and coalbed methane extraction system: An injection plug is installed in each horizontal well of the vertical shaft, creating a sealed space within each well. An extraction plug is installed at the wellhead of the extraction-monitoring combined well to seal it. A tiered injection device is installed at the connection between each horizontal well and the vertical shaft. One end of the hot flue gas injection pipe and one end of the combustion and explosive gas injection pipe extend into the vertical shaft, and the tiered injection devices are connected in series. Each injection plug is equipped with a combustion and explosive gas inlet pipe. The system includes a hot flue gas inlet pipe; the two ends of the combustion and explosive gas inlet pipe are located on either side of the gas injection plug, with one end inside the sealed space equipped with a solenoid valve and the other end connected to the nearest stratified injection device; the hot flue gas inlet pipe is located on either side of the gas injection plug, with one end inside the sealed space equipped with a solenoid valve and the other end connected to the nearest stratified injection device; the gas injection plug in the sealed space is equipped with a multi-parameter monitoring sensor and an ignition head; both the multi-parameter monitoring sensor and the ignition head are connected to the ground via a multi-parameter monitoring data transmission line. The control center is connected; on the ground, in sequence, are installed a flammable gas storage tank, a flammable gas injection pump, a hot flue gas injection pump, a hot flue gas storage tank, a hot flue gas emission device for coal-fired power plants, a power generation device for coal-fired power plants, a gas separation device, a gas filtration device, a heat exchanger assembly, and an extraction pump; the flammable gas storage tank is connected to the inlet of the flammable gas injection pump, and the outlet of the flammable gas injection pump is connected to the other end of the flammable gas injection pipe; one end of the extraction pipe passes through the extraction plug and extends into the extraction-monitoring combined well, and the other end of the extraction pipe is connected to the air inlet of the extraction pump, which is connected via... The pipelines are connected sequentially to the heat exchanger assembly, the gas filtration device, and the gas separation device. The CH4 gas passing through the gas separation device is connected to the inlet of the coal-fired power plant's power generation unit and the combustion and explosion gas storage tank via the CH4 delivery pipeline. The hot flue gas entering the gas separation device and the hot flue gas entering the coal-fired power plant's tail gas treatment system are both connected to the inlet of the hot flue gas storage tank via the hot flue gas delivery pipeline. The outlet of the hot flue gas storage tank is connected to the inlet of the hot flue gas injection pump, and the outlet of the hot flue gas injection pump is connected to the other end of the hot flue gas injection pipe, thus completing the system layout.

[0009] C. Deployment of the monitoring system: Multiple integrated multi-parameter monitoring devices are sent into the extraction-monitoring combined well. Multiple integrated multi-parameter monitoring devices are deployed at equal intervals at various coal seam sections on the wellbore of the extraction-monitoring combined well. The integrated multi-parameter monitoring devices of each coal seam section are connected to the ground control center through multi-parameter monitoring data transmission lines to obtain real-time information on fracture development and temperature changes in each coal seam section, thus completing the deployment of the monitoring system.

[0010] D. Establish a multi-source monitoring data inversion and intelligent control system: First, use various integrated multi-parameter monitoring devices to monitor the geological conditions of different coal seam sections, and image the temperature, microseismic, acoustic, and resistivity data at different depths of each coal seam section in the initial state. Then, drill coal samples at all integrated multi-parameter monitoring device locations in each coal seam section, and perform laboratory measurements on samples at different depths in each coal seam section. Combining the on-site multi-source monitoring data imaging results with the laboratory measurement results, a multi-source monitoring data inversion and intelligent control system is established by training the acquired data using a deep learning algorithm. This system can monitor the changes in physical parameters (temperature, geostress state, mechanical strength, porosity, permeability, fluid density, viscosity, and saturation, etc.) at different depths of the stacked coal seam in real time, and can provide the optimal combustion and explosion gas injection parameters and the optimal hot flue gas injection parameters for each coal seam section based on the changes in physical parameters of each coal seam section.

[0011] E. Firing and Explosion of Stacked Coal Seams: At the start of fracturing, the fibrillation gas injection pump is activated and the solenoid valves of the fibrillation gas inlet pipes for each coal seam segment are opened. This allows the fibrillation gas to be delivered through the injection pipes to each stratified injection device. Each stratified injection device, based on the optimal fibrillation gas injection parameters determined in step D, controls the amount of fibrillation gas entering its respective sealed space. The device also uses its own multi-parameter monitoring sensors to measure the fibrillation gas pressure and CH4 concentration in the sealed space in real time. When all parameters in the sealed space reach the explosion threshold, the fibrillation gas injection pump is stopped and the solenoid valves of the fibrillation gas inlet pipes are closed. Then, the ignition head is activated, causing the injected fibrillation gas in the sealed space to undergo an in-situ combustion and explosion reaction. The transient shock wave and high-temperature, high-pressure gas generated by the combustion reaction cause numerous fractures in the surrounding coal seam. This fractured rock mass desorbs large amounts of CH4 gas, which then reacts with O2 gas, creating a pulse fracturing effect within the coal seam. After the combustion reaction ends, the multi-source monitoring data inversion and intelligent control system adjusts the combustion gas injection parameters for different coal seam segments based on their specific combustion fracturing conditions. The combustion gas injection pump is restarted, and the combustion fracturing process is repeated multiple times around the horizontal wells in each coal seam segment. During this process, an integrated multi-parameter monitoring device continuously monitors the combustion fracturing situation in each coal seam segment. The combustion fracturing process is completed when the fractures in each horizontal well extend to the junction of the coal seam and the caprock.

[0012] F. Hot flue gas injection, storage, and CH4 gas desorption: Turn on the hot flue gas injection pump and the solenoid valve of the hot flue gas inlet pipe to deliver the hot flue gas in the hot flue gas storage tank to each stratified injection device through the hot flue gas injection pipe. Each stratified injection device for each coal seam section controls the amount of hot flue gas entering the sealed space of its respective coal seam section according to the optimal hot flue gas injection parameters determined in step D. The high temperature of the hot flue gas itself can promote the desorption of CH4 gas adsorbed in each coal seam section. At the same time, CO2, SO2, and NO2 gases in the hot flue gas, due to their competitive adsorption advantages, cause each coal seam section to adsorb CO2 gas and precipitate CH4 gas through displacement, thereby achieving a large output of CH4 gas in each coal seam section. This improves the CH4 mining efficiency of the coal seam while storing the hot flue gas.

[0013] G. CH4 Gas Extraction and Hot Flue Gas Sequestration: After a period of time, the extraction pump is started to extract the mixed gas from the extraction-monitoring well through the gas extraction pipe. The mixed gas is then passed through a heat exchanger group to lower its temperature to ambient. The mixed gas first passes through a gas filtration device to remove other gas impurities from the extracted mixed gas. These impurities include some CO2 gas generated during the combustion and fracturing process, residual CO2, SO2, NO2, and N2 from the hot flue gas sequestration and displacement process, and the original CO2, SO2, and N2 present in the coal seam. The CH4 in the extracted mixed gas originates from the CH4 component that did not undergo combustion during the fracturing process, as well as the CH4 gas displaced by hot flue gas in the coal seam. After treatment, the extracted mixed gas enters a gas separation unit, which separates it into the main components of the hot flue gas and CH4 gas. A portion of the separated CH4 gas is injected into the coal-fired power plant's generator unit through a CH4 gas pipeline to mix with coal for combustion and power generation, improving efficiency. The remaining separated CH4 gas is injected into a combustion gas storage tank. The gas is mixed with an accelerant to generate combustion and explosive gases for subsequent combustion and explosive fracturing. The main components of the separated hot flue gas are injected into a hot flue gas storage tank via a hot flue gas delivery pipeline, and then injected into the fracturing coal seam via a hot flue gas injection pump for continuous hot flue gas storage and displacement of residual CH4 gas in the coal seam. During the hot flue gas injection and storage period, temperature, acoustic wave, microseismic parameters, and resistivity data at different depths in different coal seam sections are collected in real time using an integrated multi-parameter monitoring device. Based on multi-source data inversion from the ground control center, and... The intelligent control system performs real-time inversion of the hot flue gas injection situation in different coal seam sections of the stacked coal seam, and adjusts the optimal hot flue gas injection parameters for different coal seam sections. At this time, the ground control center monitors the pressure, CH4 concentration, and temperature of the main components of the hot flue gas (i.e., CO2, SO2, NO2, N2) and CH4 mixture in each confined space in real time through multi-parameter monitoring sensors, and dynamically adjusts the hot flue gas injection parameters in each horizontal well to the optimal hot flue gas injection parameters based on the real-time monitoring data, so as to ensure the continuous and efficient injection of hot flue gas in each fractured coal seam section of the stacked coal seam.

[0014] H. When the relative content of CH4 gas in the coal seam in the mixed gas decreases to below the critical extraction CH4 concentration, repeat steps B to G, and continue the closed-loop process of multiple combustion and fracturing, hot flue gas sealing and CH4 extraction until the hot flue gas sealing amount of each coal seam section of the stacked coal seam reaches the set value or above, and the hot flue gas sealing and CH4 extraction operation is completed.

[0015] Furthermore, the multi-parameter monitoring sensor includes a pressure sensor, a gas concentration sensor, and a temperature sensor, wherein the pressure sensor monitors the pressure of the flammable gas in the flammable and explosive confined space in real time; the gas concentration sensor is used to monitor the concentration of CH4 gas in the flammable and explosive confined space in real time; and the temperature sensor is used to monitor the temperature in the flammable and explosive confined space in real time.

[0016] Furthermore, a casing is installed inside the vertical shaft, and the casing is sealed to the inner wall of the vertical shaft. Each horizontal well is equipped with a combination of screen pipe and casing, wherein the casing is installed at the connection between the horizontal well and the vertical shaft, and the remaining part is equipped with screen pipe.

[0017] Furthermore, the main components of the hot flue gas include CO2 gas, SO2 gas, NO2 gas, N2 gas and H2O(g).

[0018] Furthermore, the integrated multi-parameter monitoring device includes: a temperature sensor, an electromagnetic wave probe, a microseismic monitoring probe, and an acoustic wave sensor; the temperature sensor can monitor the temperature changes at different depths in different coal seam sections in real time, and invert the temperature field evolution of combustion and explosion gases, hot flue gas, and coal seam gas migration throughout the entire process of combustion and explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas storage based on temperature anomalies; the electromagnetic wave probe can monitor the resistivity changes at different depths in coal seam sections in real time throughout the entire process of combustion and explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas storage, reflecting the changes in lithological parameters such as coal porosity and permeability throughout the process; the microseismic monitoring probe can monitor the combustion and explosion fracturing... The intensity and frequency changes of acoustic emission events during fracturing are measured to obtain the stress changes in reservoirs at different depths in different coal seam sections, and the effect and range of combustion-explosion fracturing are inverted in real time. The acoustic wave sensor can monitor the acoustic wave velocity, attenuation and reflection characteristics at different depths in different coal seam sections in real time. Since the propagation characteristics of acoustic waves through different gas media (CH4, CO2, SO2, NO2, N2) in the reservoir are different, the relative content, distribution range and distribution characteristics of the main components of the hot flue gas (i.e. CO2, SO2, NO2, N2) and CH4 gas in the target deep superimposed coal seam can be obtained in real time throughout the entire process of combustion-explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas sealing.

[0019] Furthermore, the explosion condition thresholds are: the explosion gas pressure threshold is 10 MPa, and the explosion CH4 concentration threshold is 5%~20%.

[0020] Furthermore, the critical extraction CH4 concentration is 10-20%.

[0021] Compared with existing technologies, the present invention employs a combination of combustible fracturing of stacked coal seams and hot flue gas displacement of CH4 gas from the coal seam, along with the sealing of CO2 gas in the hot flue gas, which has the following advantages:

[0022] (1) The methane combustion and explosion fracturing technology of the present invention uses the high temperature and high pressure gas generated by the in-situ synergistic combustion and explosion reaction of O2 and CH4 gas in the stacked coal seam to impact and fracture each coal seam segment to form a large number of initial fractures. At the same time, the CO2 gas generated by the high temperature and high pressure explosion generated by the combustion and explosion reaction continues to wedge into the fractures, causing the fractures to extend and expand further. In addition, the fractured coal body desorbs a large amount of CH4 gas in situ, which continues to react with O2 gas to form a pulse fracturing effect in the coal seam, efficiently creating a complex fracture network, and providing an efficient transport channel for the storage of hot flue gas in the stacked coal seam and CH4 extraction.

[0023] (2) The hot flue gas used in this invention is a high-temperature mixed gas composed of N2, CO2, H2O(g), O2, SO2, and NO2, with a temperature ranging from 50 to 1500℃. After the hot flue gas is injected into the coal seam, its high temperature enhances the desorption of adsorbed CH4 and the diffusion of free CH4. The N2 in the hot flue gas can reduce the partial pressure and concentration of CH4, promoting CH4 desorption while weakening the adsorption and expansion effect of CO2, thereby improving the injectability of CO2 and enhancing reservoir permeability. CO2, SO2, and NO2 in the hot flue gas, as strongly adsorbent gases, have a competitive adsorption advantage after being injected into the coal seam, promoting the large-scale production of CH4 gas in the superimposed coal seam, thus improving the efficiency of coal seam methane extraction while achieving hot flue gas sequestration. This also achieves the large-scale sequestration of greenhouse gases and toxic and harmful gases in deep coal seams while improving the efficiency of coal seam methane extraction. The presence of H2O(g) in the hot flue gas eliminates the need for desulfurization and denitrification in coal-fired power plants, saving related costs. In addition, H2O(g) in the hot flue gas acts as a good heat transfer medium, which can greatly reduce heat loss during the transportation of hot flue gas to the coal seam, so that the hot flue gas reaching the target coal seam still has a high temperature effect on the coal seam. Compared with other components of the flue gas, H2O(g) has a higher specific heat capacity and latent heat of vaporization. Therefore, it can retain the heat energy in the hot flue gas through its high specific heat capacity during transportation, and reduce the loss of heat from the hot flue gas to the surrounding environment through its high vaporization potential. In addition, the water vapor condensed on the inner wall of the pipe will form a heat insulation layer, further reducing the heat conduction and radiation heat loss of the hot flue gas.

[0024] (3) This invention adopts extraction-monitoring combined well technology. By deploying multiple integrated multi-parameter monitoring devices at corresponding positions in different coal seam sections within the extraction-monitoring combined well, it can simultaneously realize the functions of coalbed methane extraction and distributed dynamic monitoring of coal seam physical property parameter changes, thereby improving the utilization efficiency of a single well. In addition, the extraction-monitoring combined well, combined with temperature, micro-vibration, acoustic and electromagnetic wave monitoring technologies, can realize the monitoring of the entire process of "combustion and explosion fracturing - hot flue gas storage - methane extraction". It is combined with deep learning algorithms to establish a multi-source monitoring data inversion and intelligent control system to design the optimal combustion and explosion gas injection parameters and the optimal hot flue gas injection parameters for each coal seam based on the current physical property parameter changes of different coal seam sections. This allows for layered dynamic and precise control of the gas injection parameters of each coal seam section, maximizing the efficiency of methane combustion and explosion fracturing, hot flue gas storage and CH4 extraction in each coal seam section of the superimposed coal seam.

[0025] (4) In this invention, a portion of the CH4 gas extracted from the coal seam is injected into a coal-fired power plant to mix and burn with the coal, converting it into electrical energy. The remaining extracted CH4 gas can be mixed with an oxidizer as a combustion and explosion gas and then injected back into the fracturing coal seam for multiple CH4 combustion and explosion fracturing operations. In addition, the main components of the hot flue gas extracted from the coal seam (CO2, SO2, NO2, N2) can be mixed with the hot flue gas generated by the coal-fired power plant and continuously reinjected into the fracturing coal seam, causing further desorption and displacement of CH4 in the fracturing coal seam, so as to continuously store the hot flue gas and displace the remaining CH4 gas in the coal seam. This makes the entire "combustion and explosion fracturing - hot flue gas storage - CH4 gas extraction" process form a closed loop, maximizing the amount of hot flue gas stored and CH4 extracted in the deep unminable coal seam, and realizing the efficient closed-loop utilization of extracted CH4 gas resources. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall layout of the present invention.

[0027] Figure 2 yes Figure 1 Axial sectional view of the gas injection plug.

[0028] Figure 3 yes Figure 1 Cross-sectional view of a medium-sized integrated multi-parameter monitoring device.

[0029] In the diagram: 1-1-First caprock; 1-2-Second caprock; 1-3-Third caprock; 2-1-First coal seam section; 2-2-Second coal seam section; 2-3-Third coal seam section; 3-1-First horizontal well; 3-2-Second horizontal well; 3-3-Third horizontal well; 4-Vertical shaft; 5-Drainage-monitoring combined well; 6-Combustion and explosive gas storage tank; 7-Combustion and explosive gas injection pump; 8-Hot flue gas injection pump; 9-Hot flue gas storage tank; 10-Hot flue gas emission device; 11-Coal-fired power plant generator; 12-Gas separation device; 13-Gas filtration device; 14-Heat exchanger group; 15 - Extraction pump; 16- Explosive gas injection pipe; 17- Hot flue gas injection pipe; 18- Casing; 19- Screen pipe; 20- Injection plug; 21- Layered injection device; 22- Explosive gas inlet pipe; 23- Solenoid valve; 24- Multi-parameter monitoring sensor; 25- Ignition head; 26- Multi-parameter monitoring data transmission line; 27- Ground control center; 28- Integrated multi-parameter monitoring device; 29- Extraction plug; 30- CH4 delivery pipeline; 31- Hot flue gas delivery pipeline; 32- Temperature sensor; 33- Electromagnetic wave probe; 34- Micro-vibration monitoring probe; 35- Acoustic wave sensor. Detailed Implementation

[0030] The present invention will be further described below.

[0031] like Figure 1 As shown, the specific steps of this invention are as follows:

[0032] A. Drilling Construction: First, determine the positions of the three coal seam segments and their rock caprocks in the superimposed coal seam, from top to bottom as the first caprock 1-1, the first coal seam segment 2-1, the second caprock 1-2, the second coal seam segment 2-2, the third caprock 1-3, and the third coal seam segment 2-3. Then, from the surface, drill vertical shaft 4 and extraction-monitoring well 5 through the three caprocks to the deepest third coal seam segment 2-3. After the vertical shaft 4 is formed, use a directional drilling rig to drill one horizontal well along the direction of each coal seam segment from the vertical shaft 4, namely the first horizontal well 3-1, the second horizontal well 3-2, and the third horizontal well 3-2. After completion, stop drilling work. Casing 18 is installed in the vertical shaft 4, and the casing 18 is sealed to the inner wall of the vertical shaft. Screen pipes 19 and casing 18 are installed in each horizontal well, with the casing 18 installed at the connection between the horizontal well and the vertical shaft, and the remaining parts are installed with screen pipes 19.

[0033] B. Deployment of the hot flue gas injection and coalbed methane extraction system: An injection plug 20 is installed in each of the three horizontal wells of shaft 4, creating a sealed space within each well. An extraction plug 29 is installed at the wellhead of the extraction-monitoring combined well 5 to seal it. A layered injection device 21 is installed at the connection point between each horizontal well and shaft 4. One end of the hot flue gas injection pipe 17 and one end of the combustion and explosion gas injection pipe 16 extend into shaft 4, and the various sub-pipes are connected in series. Layered injection device 21; each gas injection plug 20 is equipped with a combustible gas inlet pipe 22 and a hot flue gas inlet pipe; the two ends of the combustible gas inlet pipe 22 are respectively located on both sides of the gas injection plug 20, with one end in the sealed space equipped with a solenoid valve 23 and the other end connected to the nearest layered injection device 21; the two ends of the hot flue gas inlet pipe are respectively located on both sides of the gas injection plug 20, with one end in the sealed space equipped with a solenoid valve 23 and the other end connected to the nearest layered injection device 21; such as Figure 2 As shown, a multi-parameter monitoring sensor 24 and an ignition head 25 are installed on the gas injection sealing device 20 located in a confined space. Both the multi-parameter monitoring sensor 24 and the ignition head 25 are connected to the ground control center 27 via a multi-parameter monitoring data transmission line 26. The multi-parameter monitoring sensor 24 includes a pressure sensor, a gas concentration sensor, and a temperature sensor. The pressure sensor monitors the pressure of the flammable gas in the confined space in real time. The gas concentration sensor is used to monitor the concentration of CH4 gas in the confined space in real time. The temperature sensor is used to monitor the temperature in the confined space in real time. On the ground, the following components are installed in sequence: a flammable gas storage tank 6, a flammable gas injection pump 7, a hot flue gas injection pump 8, a hot flue gas storage tank 9, a hot flue gas emission device 10 for a coal-fired power plant, a power generation device 11 for a coal-fired power plant, a gas separation device 12, a gas filtration device 13, a heat exchanger assembly 14, and an extraction pump 15. The flammable gas storage tank 6 is connected to the inlet of the flammable gas injection pump 7, and the outlet of the flammable gas injection pump 7 is connected to the other end of the flammable gas injection pipe 16. One end of the extraction pipe passes through the extraction plug 29 and extends into the extraction-monitoring combined well 5; the other end of the extraction pipe is connected to the air inlet of the extraction pump 15. The extraction pump 15 is connected to the air inlet of the extraction pump 15 via a pipe. The system is connected in sequence to the heat exchanger group 14, the gas filter device 13, and the gas separator 12. The CH4 gas passing through the gas separator 12 is connected to the inlet of the coal-fired power plant generator 11 and the combustion and explosion gas storage tank 6 via the CH4 conveying pipeline 30. The hot flue gas entering the gas separator 12 and the hot flue gas of the coal-fired power plant tail gas treatment system are both connected to the inlet of the hot flue gas storage tank 9 via the hot flue gas conveying pipeline 31. The outlet of the hot flue gas storage tank 9 is connected to the inlet of the hot flue gas injection pump 8, and the outlet of the hot flue gas injection pump 8 is connected to the other end of the hot flue gas injection pipe 17, thus completing the system layout.

[0034] C. Deployment of the monitoring system: Multiple integrated multi-parameter monitoring devices 28 are sent into the extraction-monitoring combined well 5. These devices are deployed at equal intervals at three coal seam sections along the wellbore of the extraction-monitoring combined well 5. All three coal seam sections' integrated multi-parameter monitoring devices 28 are connected to the ground control center 27 via multi-parameter monitoring data transmission lines 26 to obtain real-time information on fracture development and temperature changes within the three coal seam sections, thus completing the deployment of the monitoring system. Figure 3 As shown, the integrated multi-parameter monitoring device 28 includes: a temperature sensor 32, an electromagnetic wave probe 33, a microseismic monitoring probe 34, and an acoustic sensor 35. The temperature sensor 32 can monitor the temperature changes at different depths in different coal seam sections in real time, and invert the temperature field evolution of combustion and explosion gases, hot flue gas, and coal seam gas migration throughout the entire process of combustion and explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas storage based on temperature anomalies. The electromagnetic wave probe 33 can monitor the resistivity changes at different depths in coal seam sections during the entire process of combustion and explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas storage, reflecting the changes in lithological parameters such as coal porosity and permeability throughout the process. The microseismic monitoring probe 34 can... The intensity and frequency changes of acoustic emission events during the combustion-explosion fracturing process are monitored in real time to obtain the stress changes of reservoirs at different depths in three coal seam sections, and the effect and range of combustion-explosion fracturing are inverted in real time. The acoustic wave sensor 35 can monitor the acoustic wave velocity, attenuation and reflection characteristics at different depths in the three coal seam sections in real time. Since the propagation characteristics of acoustic waves through different gas media (CH4, CO2, SO2, NO2, N2) in the reservoir are different, the relative content, distribution range and distribution characteristics of the main components of the hot flue gas (i.e. CO2, SO2, NO2, N2) and CH4 gas in the target deep superimposed coal seam can be obtained in real time during the entire process of combustion-explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas sealing.

[0035] D. Establish a multi-source monitoring data inversion and intelligent control system: First, the geological conditions of the three coal seam sections are monitored using various integrated multi-parameter monitoring devices 28. Image data of temperature, microseismic activity, acoustic waves, and resistivity at different depths in the three coal seam sections under initial conditions are generated. Then, coal samples are drilled at all locations of the integrated multi-parameter monitoring devices 28 in the three coal seam sections, and laboratory measurements are performed on samples at different depths in the three coal seam sections. Combining the on-site multi-source monitoring data imaging results with the laboratory measurement results, and using existing deep learning algorithms to train the acquired data, a multi-source monitoring data inversion and intelligent control system is established. This system can monitor the changes in physical parameters (temperature, geostress state, mechanical strength, porosity, permeability, fluid density, viscosity, and saturation, etc.) at different depths of the stacked coal seam in real time, and can provide optimal combustion and explosion gas injection parameters and optimal hot flue gas injection parameters for each coal seam section based on the changes in physical parameters of each coal seam section.

[0036] E. Explosive fracturing of stacked coal seams: When fracturing begins, the explosive gas injection pump 7 is started and the solenoid valve 23 of the explosive gas inlet pipe 22 of each coal seam section is opened, so that the explosive gas is delivered to each layered injection device 21 through the explosive gas injection pipe 16. The layered injection device 21 corresponding to each coal seam section controls the amount of explosive gas entering the closed space of its respective coal seam section according to the optimal explosive gas injection parameters determined in step D, and measures the explosive gas pressure and CH4 gas concentration in the closed space in real time through its respective multi-parameter monitoring sensor 24. When the parameters in the closed space reach the explosive condition threshold, that is, the explosive gas pressure threshold is 10 MPa and the explosive CH4 concentration threshold is 5%~20%. At this point, the combustion gas injection pump 7 is stopped and the solenoid valve 23 of the combustion gas inlet pipe 22 is closed. Then, the ignition head is started, causing the combustion gas injected into the confined space to undergo an in-situ combustion reaction. The transient shock wave and high-temperature, high-pressure gas generated by the combustion reaction act on the surrounding coal body to produce a large number of cracks. The fractured rock mass can desorb a large amount of CH4 gas, which continues to react with O2 gas, thus forming a pulse fracturing effect in the coal seam. After this round of combustion reaction ends, the multi-source monitoring data inversion and intelligent control system adjusts the combustion gas injection parameters of different coal seam sections according to the different combustion fracturing conditions of the three coal seam sections, restarts the combustion gas injection pump 7, and repeats the combustion fracturing steps multiple times. Multiple combustion fracturing processes are carried out around the horizontal wells in the three coal seam sections. During this period, the combustion fracturing conditions of each coal seam section are continuously monitored by the integrated multi-parameter monitoring device 28. When the cracks in each horizontal well are detected to extend and develop to the connection between the coal seam and the caprock, the combustion fracturing process is completed.

[0037] F. Hot flue gas injection, storage, and CH4 gas desorption: The hot flue gas injection pump 8 is turned on, and the solenoid valve of the hot flue gas inlet pipe is opened. The hot flue gas in the hot flue gas storage tank 9 is transported to each stratified injection device 21 through the hot flue gas injection pipe 17. The main components of the hot flue gas include CO2, SO2, NO2, N2, and H2O (g). Each stratified injection device 21, corresponding to each coal seam segment, controls the amount of hot flue gas entering the sealed space of its respective coal seam segment according to the optimal hot flue gas injection parameters determined in step D. The high temperature of the hot flue gas itself promotes the desorption of CH4 gas adsorbed in the three coal seams. Simultaneously, due to the competitive adsorption advantage of CO2 in the hot flue gas, the three coal seams adsorb CO2, SO2, and NO2 gas through displacement, and precipitate CH4 gas, achieving a large-scale production of CH4 gas in the three coal seams. This improves the CH4 mining efficiency of the coal seams while storing the hot flue gas.

[0038] G. CH4 gas extraction and hot flue gas storage: After a period of time, the extraction pump 15 is started to extract the mixed gas from the extraction-monitoring well 5 through the gas extraction pipe. Then the mixed gas passes through the heat exchanger group 14, and the temperature of the mixed gas is reduced to room temperature after heat exchange. The extracted mixed gas first passes through the gas filtration device to remove other gas impurities in the extracted mixed gas. The sources include some CO2 gas generated during the combustion and fracturing process, residual CO2, SO2, NO2 and N2 during the hot flue gas storage and displacement process, and the original CO2, SO2 and N2 of the coal seam. The CH4 in the extracted mixed gas originates from CH4 components that did not undergo combustion during the combustion-explosion fracturing process, as well as CH4 gas displaced by hot flue gas in the coal seam. The treated mixed gas enters a gas separation device 12, which separates the treated extracted mixed gas into the main components of hot flue gas and CH4 gas. A portion of the separated CH4 gas is injected into the coal-fired power plant's generator unit 11 through a CH4 gas delivery pipeline to mix with coal for combustion and power generation, improving efficiency. The remaining separated CH4 gas is injected into the combustion-explosion gas storage tank 6 to mix with a combustion aid. (i.e., O2 gas) mixes to generate combustion and explosive gases, which are used for subsequent combustion and explosive fracturing; the main components of the separated hot flue gas and the hot flue gas from the hot flue gas emission device 10 are injected into the hot flue gas storage tank 9 through the hot flue gas delivery pipeline 31 and mixed, and finally injected into the fracturing coal seam through the hot flue gas injection pump 8, so as to continuously store the hot flue gas and displace the remaining CH4 gas in the coal seam; during the hot flue gas injection and storage, the temperature, sound wave, micro-vibration parameters and resistivity data of different coal seam sections at different depths are collected in real time by the integrated multi-parameter monitoring device 28; according to the ground control center 27, more than 10 ... The source data inversion and intelligent control system inverts the hot flue gas injection situation of different coal seam segments in real time and adjusts the optimal hot flue gas injection parameters for different coal seam segments. At this time, the ground control center 27 monitors the pressure, CH4 concentration and temperature of the main components of the hot flue gas (i.e. CO2, SO2, NO2, N2) and CH4 mixture in each sealed space in real time through multi-parameter monitoring sensors 24, and dynamically adjusts the hot flue gas injection parameters in each horizontal well to the optimal hot flue gas injection parameters based on the real-time monitoring data to ensure the continuous and efficient injection of hot flue gas in the three coal seam segments of the stacked coal seam.

[0039] H. When the relative content of CH4 gas in the coal seam in the mixed gas is reduced to below 15% of the critical extraction CH4 concentration, repeat steps B to G, and continue the closed-loop process of multiple combustion and fracturing, hot flue gas sealing and CH4 extraction until the hot flue gas sealing amount of the three coal seam sections of the stacked coal seam reaches the set value or above, and the hot flue gas sealing and CH4 extraction operation is completed.

Claims

1. A method for hot flue gas displacement superimposed coal seam methane extraction and closed-loop carbon sequestration, characterized in that, The specific steps are: A, drilling construction: first determine the position of each coal seam section and its rock cap in the superimposed coal seam, then from the ground through each rock cap to the deepest coal seam section respectively construction shaft and extraction-monitoring combined well, after the formation of the shaft, using a directional drilling rig from the shaft along each coal seam section to each drill a horizontal well, after completion stop drilling work; B, layout of hot flue gas injection and coalbed methane extraction system: a gas injection packer is arranged in each horizontal well of the shaft, so that a closed space is formed in each horizontal well, an extraction packer is arranged at the wellhead of the extraction-monitoring combined well to block the extraction-monitoring combined well; a layered injection distribution device is arranged at the connection between each horizontal well and the shaft, one end of the hot flue gas injection pipe and one end of the combustion gas injection pipe are inserted into the shaft, and are connected in series with each layered injection distribution device; a combustion gas inlet pipe and a hot flue gas inlet pipe are arranged on each gas injection packer; the two ends of the combustion gas inlet pipe are respectively located on the two sides of the gas injection packer, one end of which is located in the closed space and is provided with an electromagnetic valve, and the other end is connected with the nearest layered injection distribution device; the two ends of the hot flue gas inlet pipe are respectively located on the two sides of the gas injection packer, one end of which is located in the closed space and is provided with an electromagnetic valve, and the other end is connected with the nearest layered injection distribution device; a multi-parameter monitoring sensor and an ignition head are arranged on the gas injection packer in the closed space; the multi-parameter monitoring sensor and the ignition head are connected with the ground control center through a multi-parameter monitoring data transmission line; a combustion gas storage tank, a combustion gas injection pump, a hot flue gas injection pump, a hot flue gas storage tank, a coal-fired power plant flue gas discharge device, a coal-fired power plant power generation device, a gas separation device, a gas filtration device, a heat exchanger group and an extraction pump are arranged in sequence on the ground; the combustion gas storage tank is connected with the inlet of the combustion gas injection pump, and the outlet of the combustion gas injection pump is connected with the other end of the combustion gas injection pipe; one end of the extraction pipe extends into the extraction-monitoring combined well through the extraction packer, and the other end of the extraction pipe is connected with the gas inlet of the extraction pump; the extraction pump is connected with the heat exchanger group, the gas filtration device and the gas separation device in sequence through pipelines; the CH4 gas passing through the gas separation device is connected with the gas inlets of the coal-fired power plant power generation device and the combustion gas storage tank through CH4 conveying pipelines; the hot flue gas passing through the gas separation device and the hot flue gas of the coal-fired power plant tail gas treatment system are connected with the inlet of the hot flue gas storage tank through hot flue gas conveying pipelines; the outlet of the hot flue gas storage tank is connected with the inlet of the hot flue gas injection pump, and the outlet of the hot flue gas injection pump is connected with the other end of the hot flue gas injection pipe, completing the layout of the system; C, layout of monitoring system: send multiple integrated multi-parameter monitoring devices into the extraction-monitoring combined well, and arrange multiple integrated multi-parameter monitoring devices at equal intervals on the wellbore of the extraction-monitoring combined well at the positions of each coal seam section; the integrated multi-parameter monitoring devices of each coal seam section are connected with the ground control center through multi-parameter monitoring data transmission lines, for real-time acquisition of the fracture development and temperature change in each coal seam section, completing the layout of the monitoring system. D, Establishing a multi-source monitoring data inversion and intelligent control system: First, use each integrated multi-parameter monitoring device to monitor the geological conditions of different coal seam sections, and image the temperature, microseismic, acoustic wave, and resistivity data at different depths of each coal seam section in the initial state. Then drill coal samples at each coal seam section and all integrated multi-parameter monitoring device layout points, and conduct laboratory measurements on samples at different depths of each coal seam section. Combine the imaging results of multi-source monitoring data and laboratory measurement results, use deep learning algorithm to train the obtained data, and establish a multi-source monitoring data inversion and intelligent control system; This system can monitor the changes of physical parameters at different depths of the superimposed coal seam in real time, and can give the best gas injection parameters and the best hot flue gas injection parameters according to the changes of physical parameters in each coal seam section; E, Conducting combustion and explosion fracturing in superimposed coal seams: When starting fracturing, first start the combustion gas injection pump and open the electromagnetic valve of each coal seam section combustion gas inlet pipe, so that the combustion gas is transported to each separate layer injection device through the combustion gas injection pipe. The separate layer injection device corresponding to each coal seam section controls the amount of combustion gas entering the closed space of each coal seam section according to the best combustion gas injection parameters determined in step D, and measures the combustion gas pressure and CH4 gas concentration in the closed space in real time through the multi-parameter monitoring sensor. When the parameters in the closed space reach the combustion condition threshold, stop the combustion gas injection pump and close the electromagnetic valve of the combustion gas inlet pipe, then start the ignition head, so that the injected combustion gas in the closed space occurs in situ combustion reaction. The transient shock wave and high temperature and pressure gas produced by the combustion reaction act on the surrounding coal body to produce a large number of cracks, and then the fractured rock mass can desorb a large amount of CH4 gas, which continues to react with O2 gas to form pulse fracturing effect in the coal seam. After the completion of this round of combustion reaction, the multi-source monitoring data inversion and intelligent control system adjusts the combustion gas injection parameters of different coal seam sections according to the different combustion and explosion fracturing conditions of each coal seam section, restarts the combustion gas injection pump, and repeats the combustion and explosion fracturing steps several times to perform multiple combustion and explosion fracturing processes around the horizontal drillings in each coal seam section; During this period, the integrated multi-parameter monitoring device continuously monitors the combustion and explosion fracturing of each coal seam section, and when the cracks of each horizontal drilling extend to the connection between the coal seam and the caprock, the combustion and explosion fracturing process is completed. F. Hot flue gas injection and displacement of CH4 gas desorption: open the hot flue gas injection pump and open the electromagnetic valve of the hot flue gas inlet pipe, and transport the hot flue gas in the hot flue gas storage tank to each layer injection device through the hot flue gas injection pipe. The amount of hot flue gas entering the sealed space of each coal seam section is controlled according to the optimal hot flue gas injection parameters determined in step D. The high temperature of the hot flue gas itself can promote the desorption of CH4 gas adsorbed in each coal seam section. At the same time, CO2, SO2 and NO2 in the hot flue gas can displace CH4 gas by replacing the adsorbed CO2 gas in each coal seam section, thereby achieving the production of a large amount of CH4 gas in each coal seam section. The hot flue gas is stored while the efficiency of CH4 extraction from the coal seam is improved; G. CH4 gas extraction and hot flue gas storage: after a period of time, start the extraction pump to extract the mixed gas from the extraction-monitoring combined well through the gas extraction pipe, and then pass the mixed gas through the heat exchanger group. The temperature of the mixed gas is reduced to normal temperature after heat exchange. The mixed gas first passes through the gas filtering device to remove other gas impurities in the mixed gas. The treated mixed gas enters the gas separation device. The gas separation device separates the treated mixed gas into hot flue gas main component gas and CH4 gas. A part of the separated CH4 gas is injected into the coal-fired power plant power generation device to mix and burn with coal for power generation to improve efficiency. The remaining separated CH4 gas is injected into the combustion gas storage tank to mix with the combustion aid to generate combustion gas for subsequent combustion fracturing. The separated hot flue gas main component gas and the hot flue gas of the hot flue gas discharge device are all injected into the hot flue gas storage tank through the hot flue gas conveying pipeline for mixing. Finally, the hot flue gas enters the fractured coal seam through the hot flue gas injection pump for continuous storage and displacement of the remaining CH4 gas in the coal seam. During the hot flue gas injection and storage, the integrated multi-parameter monitoring device collects temperature, acoustic wave, microseismic parameter and resistivity data along different depths of different coal seam sections in real time. The hot flue gas injection conditions of different coal seam sections in the superimposed coal seam are inversed in real time according to the multi-source data inversion and intelligent control system of the ground control center, and the optimal hot flue gas injection parameters of different coal seam sections are adjusted. At this time, the ground control center monitors the pressure, CH4 concentration and temperature of the hot flue gas and CH4 mixed gas in each sealed space in real time through the multi-parameter monitoring sensor, and dynamically adjusts the hot flue gas injection parameters in each horizontal well to the optimal hot flue gas injection parameters according to the real-time monitoring data, so as to ensure the continuous and efficient injection of hot flue gas in each fractured coal seam section of the superimposed coal seam; H. When the relative content of coal seam CH4 gas in the mixed gas is reduced to below the critical extraction CH4 concentration, repeat steps B-G to continuously close-loop the process of multiple combustion fracturing, hot flue gas storage and CH4 extraction until the hot flue gas storage amount of each coal seam section in the superimposed coal seam reaches a set value or more, and the hot flue gas storage and CH4 extraction operation is completed.

2. The method for hot flue gas displacement superimposed coal bed methane extraction and closed-loop carbon sequestration according to claim 1, characterized in that, The multi-parameter monitoring sensor comprises an air pressure sensor, a gas concentration sensor and a temperature sensor, wherein the air pressure sensor is used for monitoring the pressure of the explosion gas in the explosion sealed space in real time; the gas concentration sensor is used for monitoring the concentration of CH4 gas in the explosion sealed space in real time; and the temperature sensor is used for monitoring the temperature in the explosion sealed space in real time.

3. The method for hot flue gas displacement superimposed coal bed methane extraction and closed-loop carbon sequestration according to claim 1, characterized in that, The casing is arranged in the shaft and is sealed between the casing and the inner wall of the shaft, and the screen pipe and the casing are arranged in each horizontal well, wherein the casing is arranged at the connection between the horizontal well and the shaft, and the screen pipe is arranged in the remaining part.

4. The method for hot flue gas displacement superimposed coal bed methane extraction and closed-loop carbon sequestration according to claim 1, characterized in that, The main component gases of the hot flue gas include CO2 gas, SO2 gas, NO2 gas, N2 gas and water vapor.

5. The method for hot flue gas displacement interbedded coal bed methane extraction and closed loop carbon sequestration of claim 1, wherein, The integrated multi-parameter monitoring device comprises a temperature sensor, an electromagnetic wave probe, a microseismic monitoring probe and an acoustic wave sensor; the temperature sensor can monitor the temperature change of different coal seam sections along different depths in real time, and according to the temperature anomaly, the temperature field evolution of the explosion gas, the hot flue gas and the coal seam gas migration in the whole process of explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas storage can be inverted; the electromagnetic wave probe can monitor the resistivity change of different depth coal seam sections in the whole process of explosion fracturing-hot flue gas displacement-CH4 extraction-hot flue gas storage in real time, and reflect the lithology parameter change of the coal body porosity and permeability in the whole process; the microseismic monitoring probe can monitor the intensity and frequency change of the acoustic emission event in the explosion fracturing process in real time, so as to obtain the stress change of different coal seam sections at different depths, and invert the effect and range of the explosion fracturing in real time; and the acoustic wave sensor can monitor the acoustic wave velocity, attenuation and reflection characteristics of different coal seam sections along different depths in real time.

6. The method for hot flue gas displacement interbedded coal bed methane extraction and closed loop carbon sequestration of claim 1, wherein, The explosion condition threshold is that the explosion gas pressure threshold is 10 MPa, and the explosion CH4 concentration threshold is 5% to 20%.

7. The method for hot flue gas displacement interbedded coal bed methane extraction and closed loop carbon sequestration of claim 1, wherein, The critical extraction CH4 concentration is 10% to 20%.

Images