Zero-carbon method for strengthening coal seam gas recovery and CO2 storage by using flue gas residual heat

Abstract

The invention discloses a zero-carbon method for strengthening coal seam gas recovery and CO2 storage by using flue gas residual heat in the technical field of residual heat utilization, gas extraction and carbon emission reduction. The zero-carbon method comprises the following steps: step 1, collecting high-temperature flue gas in a power plant; step 2, performing high-temperature CO2 concentration-compression; step 3, reservoir evaluation and area selection; 4, designing and constructing a horizontal well; 5, high-temperature CO2 injection and joint control energy increasing are conducted, specifically, high-temperature CO2 is injected into a preset section through a pump, the injection pressure and the injection speed are adjusted through the joint control energy increasing technology, and the diffusion range and the diffusion speed of CO2 are controlled; 4, gas recovery and CO2 storage: high-temperature CO2 is used for providing energy to promote gas desorption on one hand, and the high-temperature CO2 and CH4 in the adsorption state are subjected to competitive adsorption on the other hand. The method is simple and easy to operate, the coal seam gas partial pressure is reduced through CO2 injection, the recovery efficiency is improved, CO2 can be adsorbed by a coal seam and stored in a reservoir, and geological storage of CO2 is achieved.

Description

Technical Field

[0001] This invention belongs to the field of residual heat utilization, gas extraction and carbon emission reduction technology, specifically a zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration by utilizing residual heat of flue gas. Background Technology

[0002] Coal, as a pillar industry in the energy supply sector, plays a vital role in social development. As the mining depth gradually increases, mine pressure becomes more intense, resulting in the original coal reservoir exhibiting the characteristics of "high reserves and low permeability." This leads to low gas extraction efficiency and significant challenges in managing gas disasters, seriously affecting the safe and efficient production of mines. As a highly efficient and clean resource associated with coal, efficient gas extraction is the fundamental method for preventing gas disasters and an important pathway to obtaining clean energy.

[0003] Traditional negative pressure gas extraction technology cannot overcome the problem of low permeability in coal seams. Pre-extraction is time-consuming and slow to show results, failing to meet the needs of mining succession and underground safety production. To address this problem, permeability enhancement measures such as mining protective layers, hydraulic fracturing / fracture / perforation, and loosening blasting have been implemented to improve gas extraction. While most of these measures improve permeability, the problem of a sharp decline in extraction efficiency due to reservoir pressure drop in the later stages of mining remains unresolved. There is an urgent need for a simple and effective new technology to improve coal seam permeability and increase gas extraction efficiency. With continuous advancements in science and technology, gas injection displacement technology has made breakthrough progress. This technology provides a new approach to improving underground gas extraction efficiency through gas injection displacement. This technology not only increases the internal gas pressure of the coal seam and improves the mixed gas seepage velocity, but also reduces the effective partial pressure of gas, promoting the desorption of adsorbed gas and effectively compensating for the reservoir pressure drop problem in the later stages of extraction, providing sufficient power and a reliable migration channel for the reservoir flow field.

[0004] CO2, as a low-temperature, low-viscosity, highly permeable, easily diffused, and self-pressurizing fluid with phase change properties, is injected into coal seams under pressure. Under the combined effects of low-temperature frost heave and the phase change pressure stress of heat and mass transfer between liquid CO2 and the coal body, the coal body undergoes fatigue damage, increasing its permeability. Moreover, based on the combined effects of the liquid CO2 injection pressure, the instantaneous phase change stress, the temperature gradient stress generated by the heat exchange between liquid CO2 and the coal seam, and the good adsorption potential energy of gaseous CO2 itself, it can exert a dual displacement-displacement effect on the gas in the coal seam, promoting the production of gas in the coal seam per unit time.

[0005] However, in actual mining, the coal and petrological evolution is complex, and its distribution is highly heterogeneous. Coal rank and permeability generally exhibit complex zoning characteristics. Taking coal rank as an example, in Northeast, Northwest, and North China, the coal-forming epoch is predominantly Mesozoic, with low-rank coal predominating; in Southwest China, the coal-forming epoch is predominantly Paleozoic, Cenozoic, and Paleozoic, with medium-rank coal predominating; and in Central and East China, the coal-forming epoch is predominantly Paleozoic, Mesozoic, and Paleozoic, with medium-rank and high-rank coal predominating. Taking permeability as another example, the permeability of coal seams in Northeast China is generally lower than in North China; the permeability of coal seams in South China is relatively low. This complex zoning of coal seams is not conducive to unified management of gas extraction, and consequently, insufficient CO2 concentration replacement occurs when using CO2 for displacement-reduction. Therefore, it is necessary to propose a zero-carbon method that utilizes residual heat of flue gas to enhance coal seam gas extraction and CO2 sequestration, which can adjust the gas injection values ​​according to the actual conditions of different target coal seams. Summary of the Invention

[0006] To address the challenges posed by the complex zoning characteristics of coal seams and the resulting difficulties in unified gas extraction and management, this invention aims to provide a zero-carbon method for enhancing coal seam gas extraction and CO2 sequestration using residual heat from flue gas. This method involves collecting parameter information from the target coal seam and using grey theory correlation to identify factors directly influencing CO2 enrichment and adsorption. Based on these factors, corresponding hot flue gas injection data can be allocated, enabling comprehensive gas extraction and CO2 enrichment within the flue gas from target coal seams in different regions.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: a zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas, comprising the following steps:

[0008] Step 1, Power Plant Flue Gas: The hot flue gas generated by the gas power plant is collected through the flue gas collection system, and the flue gas is pretreated by dust removal, desulfurization and denitrification; at the same time, the residual heat energy in the flue gas is recovered through the waste heat boiler or heat exchanger, and the residual heat energy is used to maintain the working temperature of the adsorption bed or converted into the power energy to drive the compressor.

[0009] Step 2, High-temperature CO2 enrichment and compression: Solid adsorbent is attached to the adsorption bed, and then the pretreated flue gas is introduced. The temperature and pressure are adjusted to separate the CO2 in the flue gas to achieve enrichment. The enriched CO2 is injected into the compressor for compression to obtain the high-temperature CO2 required for subsequent injection.

[0010] Step 3, Reservoir Evaluation and Site Selection: Geological, geophysical and geochemical evaluations are conducted on the target coalbed methane reservoir to determine reservoir parameters. Gas occurrence patterns are obtained through calculations. Based on the evaluation and gas occurrence patterns, blocks with simple geological structures, good roof and floor sealing, large coal seam thickness and high gas content are selected as sites for high-temperature CO2 injection.

[0011] Step 4, Horizontal Well Design and Construction: Based on the reservoir evaluation results and geological conditions, design the trajectory, length, and segmentation scheme of the horizontal well. After segmentation, obtain the factors that directly affect CO2 enrichment and adsorption based on reservoir parameters and using the grey theory correlation method. Classify the coal seam according to the factors that directly affect CO2 enrichment and adsorption, and install casing according to the classification. Determine the sealing position based on the casing installation and determine the injection value of high-temperature CO2.

[0012] Step 5, High-temperature CO2 injection and controlled fracture energy enhancement: High-temperature CO2 is injected into the predetermined section of the horizontal well through a high-pressure pump. The injection pressure needs to be adjusted according to the reservoir pressure and permeability. Furthermore, controlled fracture energy enhancement technology is adopted to control the diffusion range and speed of high-temperature CO2 in the coal seam by adjusting the injection pressure and injection rate.

[0013] The process of controlled fracture energy enhancement technology involves calculating the downhole fracture closure pressure based on low-pressure testing, well pressure drop, and matrix adsorption-desorption-seepage model, determining the well-drainage-flow-back time, and formulating a dynamic adjustment plan for production pressure difference, thereby forming CO2 displacement and storage energy enhancement and production improvement technology.

[0014] Step 6, Gas Recovery and CO2 Sequestration: After high-temperature CO2 injection, the natural desorption and diffusion of coalbed methane, as well as the competitive adsorption of high-temperature CO2, are used to improve the gas recovery rate. In addition, high-temperature CO2 can be adsorbed by the coal seam and stored in the reservoir, thus realizing the geological sequestration of high-temperature CO2.

[0015] Step 7, CO2 and gas separation: After gas extraction, the gas extracted from the coal seam is collected through the coalbed methane extraction system, and dust, particulate matter and moisture impurities are removed. Then, CO2 and gas are selectively separated using an adsorbent. During separation, the temperature and pressure are adjusted to achieve full separation of CO2 and gas. The separated CO2 is enriched and compressed according to the technical means in Step 2 for subsequent reuse, while the gas is stored.

[0016] Step 8, Monitoring and Evaluation: Using seismic, logging and inter-well tracer monitoring technologies, the injection effect of high-temperature CO2, gas recovery and CO2 sequestration status are monitored and evaluated in real time. Based on the monitoring results, the injection strategy and recovery plan are adjusted to ensure the continuous optimization of gas recovery rate and CO2 sequestration rate.

[0017] Furthermore, in step three, the process of obtaining the gas occurrence law is as follows: first, the gas content in the coal seam is measured; then, the pore structure and fracture development of the coal seam are analyzed to determine the gas occurrence state; and combined with the influencing factors of gas migration in the coal seam, the gas migration law is obtained; finally, the gas occurrence law is obtained by combining gas monitoring and data analysis in mine production practice.

[0018] Furthermore, in step five, before high-temperature CO2 injection, a positive injection isolation slug operation is required, that is, low-temperature diesel or other low-temperature resistant media that do not damage the reservoir are injected from the wellhead or pump outlet pipeline. During high-temperature CO2 injection, the filling volume is controlled and the working pressure and temperature of the storage tank are monitored.

[0019] Furthermore, in step five, the controlled fracture energy enhancement technology process specifically involves first, based on the collected coal seam geological parameters and monitoring and recording the pressure and flow rate during the high-temperature CO2 injection process, and then preprocessing the collected data to establish a matrix adsorption-desorption-seepage model.

[0020] The small-pressure test and well-sealing pressure drop are then conducted as follows: First, a local CO2 injection test is performed in the coal seam, the pressure response is observed and recorded, the small-pressure test data is analyzed, and the pressure sensitivity and fracture development of the coal seam are assessed. At the same time, after CO2 injection, a well-sealing operation is performed, that is, the injection is stopped and the wellhead is kept closed for a period of time. The pressure changes during the well-sealing period are monitored, the pressure drop trend and rate are analyzed, and the closure pressure and permeability changes of the downhole fractures are calculated through the well-sealing pressure drop data.

[0021] The data obtained from the low-pressure test and the pressure drop analysis of the sealed well were compared with the matrix adsorption-desorption-seepage model to correct the model parameters. Using the corrected model and the pressure drop data of the sealed well, the closure pressure of the downhole fracture was calculated, and the impact of the fracture closure pressure on CO2 storage and coalbed methane extraction was evaluated. Based on the fracture closure pressure and the coalbed methane extraction requirements, the sealed well time and flowback time were determined. Finally, the pressure changes during the production process were analyzed, and a plan for dynamically adjusting the production pressure differential was formulated.

[0022] Furthermore, in step four, the collected reservoir parameter information includes coal thickness, Protodyakonov coefficient of coal body, moisture, ash content, porosity, permeability, gas content, gas pressure, gas saturation, Langmuir pressure constant, and Langmuir volume constant.

[0023] Furthermore, in step four, the specific process of the grey theory correlation method is as follows: first, determine the reference sequence and the comparison sequence; then, perform dimensionless processing on the reference sequence and the comparison sequence to eliminate dimensional differences; calculate the grey correlation coefficient ξ between the reference sequence and the comparison sequence; then calculate the correlation degree ri; finally, rank the correlation order to obtain the factors that directly affect CO2 concentration and adsorption.

[0024] Furthermore, in step four, after obtaining the factors directly affecting CO2 concentration and adsorption, a further confidence assessment of these factors is required. The specific formula is as follows:

[0025] [Xt 0.5 (n-1)S*n -0.5 , X+t 0.5 (n-1)S*n -0.5 ]

[0026] In the formula, X is the mean of the successful sample of the influencing factors, and t 0.5 (n-1) is the upper quantile of the t-distribution with n-1 degrees of freedom about 0.5α, Xt 0.5 (n-1)S*n -0.5 , X+t 0.5 (n-1)S*n -0.5 These are the lower and upper confidence limits, respectively.

[0027] Furthermore, in step four, the coal seam grading process is as follows: First, the coal seam is divided into segments based on the parameter values ​​of factors that directly affect CO2 concentration and adsorption collected from each part of the target coal seam. The target coal seam is divided into three treatment levels: high, medium, and low. The number of casings installed is proportional to the level. The casings are equipped with several segmented gas injection holes, and the lengths of the segmented gas injection holes are all different.

[0028] Furthermore, in step five, the high-temperature CO2 injection process involves first connecting the high-temperature CO2 output device to the pressurization device, then using the pressurization device to inject the high-temperature CO2 at high pressure into the casing within the target coal seam, and using the casing to guide the high-temperature CO2. The metering device measures the injected high-temperature CO2 in real time and provides a basis for adjusting the various parameters of the high-temperature CO2. Finally, the collection device separates and collects the gas and CO2 separately.

[0029] Furthermore, in step five, as CO2 is injected, the gas change is measured in real time, using the following formula:

[0030]

[0031] In the formula, C pr ρ represents the CO2r adsorbate content. ra Let ρ be the density of CO2r under standard conditions. c Let α be the density of the coal. r b is the limiting adsorption capacity of CO2r. r p is the CO2 adsorption equilibrium constant. r The CO2r equilibrium partial pressure is represented by the subscripts r = 1 and 2, which respectively indicate the variables corresponding to gas and injected CO2.

[0032] The basic scheme's principles and beneficial effects are as follows: 1. Comprehensive evaluation of geology, geophysics, and geochemistry: By conducting multi-faceted evaluations of the target coalbed methane reservoir, various reservoir parameters, such as permeability, porosity, and gas saturation, can be accurately obtained, providing a scientific basis for subsequent CO2 injection.

[0033] Determining the occurrence pattern of gas: By using geological models and data analysis techniques, the occurrence pattern of gas can be accurately calculated, thereby selecting blocks with simple geological structures, good roof and floor sealing, large coal seam thickness, and high gas content, to ensure effective adsorption after CO2 injection and efficient gas recovery.

[0034] 2. Optimization of Trajectory, Length, and Segmentation: Based on reservoir evaluation results and geological conditions, the designed horizontal well trajectory can maximize coverage of the target coal seam, improving CO2 injection efficiency and gas recovery rate. Simultaneously, a reasonable segmentation scheme can ensure uniform CO2 distribution within the coal seam.

[0035] Determining the installation location of casing and the sealing point: Using grey theory correlation analysis, factors directly affecting CO2 enrichment and adsorption are analyzed to classify the coal seam and install casing accordingly. This classification process allows for targeted injection strategies for different coal seam levels, improving CO2 utilization and gas recovery. Simultaneously, clearly defined sealing point locations ensure effective CO2 sequestration within the coal seam.

[0036] 3. Precise adjustment of injection pressure: Adjusting the CO2 injection pressure according to reservoir pressure and permeability ensures effective diffusion and adsorption of CO2 in the coal seam. At the same time, a reasonable injection pressure can also avoid excessive pressure damage to the reservoir.

[0037] Application of controlled-fracture energy enhancement technology: By adjusting the injection pressure and injection rate, the diffusion range and speed of CO2 in the coal seam can be controlled, thereby achieving uniform CO2 distribution and efficient adsorption. This technology can not only improve gas recovery rate, but also ensure the long-term sequestration of CO2 in the coal seam.

[0038] 4. Compared with existing technologies, this scheme optimizes the extraction layout and parameter settings by combining coal seam geological conditions and gas occurrence patterns to ensure the targeting and effectiveness of gas extraction. Simultaneously, it collects parameter information of the target coal seam and analyzes the factors directly affecting CO2 enrichment and adsorption using grey theory correlation analysis. Based on these influencing factors, the coal seam is classified, and casings are installed at each level to ensure the targeting and uniformity of CO2 injection. The sealing positions are clearly defined to prevent CO2 leakage and improve adsorption efficiency. Furthermore, based on the calculated factors directly affecting CO2 enrichment and adsorption, the injection pressure, flow rate, and time of the hot flue gas are precisely adjusted to ensure sufficient contact and efficient adsorption of CO2 with the coal seam. Through the refined management and precise control of the above steps, the gas extraction challenges caused by the complex zoning characteristics of coal seams are overcome, achieving unified management and efficient utilization of gas extraction.

[0039] 5. Because the service life of boreholes is short when drilling in soft coal seams, especially when implementing gas injection displacement, the borehole damage is accelerated, resulting in a significant decrease in gas injection pressure along the borehole length. Therefore, in this solution, casing is designed according to different coal seam conditions to achieve the problems of wall protection casing to prevent borehole collapse and segmented gas injection to prevent gas pressure attenuation. Segmented gas injection solves the problem of gas injection pressure attenuation along the borehole length, thereby extending the service life of the gas injection borehole and effectively improving the efficiency and effect of gas injection displacement. Furthermore, installing different numbers of casings according to different target coal seam conditions can better overcome the gas collection difficulties brought about by the complex zoning characteristics of coal seams, and realize unified management and efficient utilization of gas collection.

[0040] 6. By developing horizontal well segmented CO2 volumetric fracturing technology that effectively controls fracture length, fracture height, fracture extension direction, and fracture volume, CO2 injection capacity and sweep range can be improved, reservoir energy can be increased, and the displacement and production enhancement effect of CO2 can be strengthened, thereby achieving a dual improvement in coalbed methane recovery rate and CO2 geological sequestration rate.

[0041] 7. The competitive adsorption of CO2 at high temperatures significantly reduces the adsorption potential energy of CH4 in the coal seam, accelerating gas desorption through molecular substitution. Simultaneously, the high-temperature environment (typically >50℃) alters the expansion stress of the coal matrix, reducing gas diffusion resistance and increasing the desorption rate. Furthermore, the adsorption capacity of coal for supercritical CO2 is 2-3 times that for CH4, and injecting high-temperature, high-pressure CO2 makes it easier to reach the supercritical state. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a zero-carbon method for enhancing coalbed methane recovery and CO2 sequestration using residual heat of flue gas, as described in an embodiment of the present invention. Detailed Implementation

[0043] The following detailed description illustrates the specific implementation method:

[0044] The basic implementation examples are as follows: Figure 1 The following is a zero-carbon method for enhancing coalbed methane recovery and CO2 sequestration using residual heat from flue gas, comprising the following steps:

[0045] Step 1, Power Plant Flue Gas: The hot flue gas generated by the gas power plant is collected through the flue gas collection system, and the collected flue gas is pretreated, including dust removal, desulfurization and denitrification.

[0046] Step 2, High-temperature CO2 enrichment and compression: Solid adsorbent is attached to the adsorption bed, and then the pretreated flue gas is introduced. The temperature and pressure are adjusted to separate the CO2 in the flue gas to achieve enrichment. The enriched CO2 is injected into the compressor for compression to obtain the high-temperature CO2 required for subsequent injection.

[0047] Step 3, Reservoir Evaluation and Site Selection: Geological, geophysical and geochemical evaluations are conducted on the target coalbed methane reservoir to determine reservoir parameters. Gas occurrence patterns are obtained through calculations. Based on the evaluation and gas occurrence patterns, blocks with simple geological structures, good roof and floor sealing, large coal seam thickness and high gas content are selected as sites for high-temperature CO2 injection.

[0048] The process of obtaining the gas occurrence law is as follows: first, the gas content in the coal seam is measured; then, the pore structure and fracture development of the coal seam are analyzed to determine the gas occurrence state; and finally, the gas migration law is obtained by combining the influencing factors of gas migration in the coal seam. Finally, the gas occurrence law is obtained by combining gas monitoring and data analysis in mine production practice.

[0049] Step 4, Horizontal Well Design and Construction: Based on the reservoir evaluation results and geological conditions, design the trajectory, length, and segmentation scheme of the horizontal well. After segmentation, obtain the factors that directly affect CO2 enrichment and adsorption based on reservoir parameters and using the grey theory correlation method. Classify the coal seam according to the factors that directly affect CO2 enrichment and adsorption, and install casing according to the classification. Determine the sealing position based on the casing installation and determine the injection value of high-temperature CO2.

[0050] The collected reservoir parameter information includes coal thickness, Protodyakonov coefficient of coal body, moisture, ash content, porosity, permeability, gas content, gas pressure, gas saturation, Langmuir pressure constant and Langmuir volume constant.

[0051] The Protodyakonov coefficient reflects the compressive strength of the coal seam. A higher coefficient indicates better compressive strength, leading to higher economic benefits and safety in actual mining and utilization. Porosity and permeability reflect the permeability of the coal seam. Understanding porosity and permeability helps assess the gas occurrence conditions and gas migration patterns in the coal seam, providing guidance for gas drainage and control. Gas content and gas pressure are important parameters for assessing the gas content of the coal seam. Understanding gas content and gas pressure helps determine the feasibility of gas drainage and the setting of drainage parameters, ensuring safe production in the coal mine. The Langmuir pressure constant and Langmuir volume constant reflect the coal seam's adsorption capacity for gas.

[0052] Meanwhile, the specific process of the grey theory correlation method is as follows: first, determine the reference sequence and the comparison sequence, perform dimensionless processing on the reference sequence and the comparison sequence to eliminate the difference in dimensions, calculate the grey correlation coefficient ξ between the reference sequence and the comparison sequence, then calculate the correlation degree ri, and finally rank the correlation order to obtain the factors that directly affect CO2 concentration and adsorption.

[0053] Furthermore, after identifying the factors directly affecting CO2 concentration and adsorption, a further confidence assessment of these factors is required. The specific formula is as follows:

[0054] [Xt 0.5 (nh)S*n -0.5 , X+t 0.5 (nh)S*n -0.5 ]

[0055] In the formula, X is the mean of the successful sample of the influencing factors, and t 0.5 (n-1) is the upper quantile of the t-distribution with n-1 degrees of freedom about 0.5α, Xt 0.5 (nh)S*n -0.5 , X+t 0.5 (nh)S*n -0.5 These are the lower and upper confidence limits, respectively.

[0056] Secondly, the coal seam grading process is as follows: First, the coal seam is divided into segments based on the parameter values ​​of factors that directly affect CO2 concentration and adsorption collected from each part of the target coal seam. The target coal seam is divided into three treatment levels: high, medium, and low. The number of casings installed is proportional to the level. The casings are equipped with several segmented gas injection holes, and the lengths of the segmented gas injection holes are all different.

[0057] Step 5, High-Temperature CO2 Injection and Fracturing Enhancement: High-temperature CO2 is injected into predetermined sections of the horizontal well using a high-pressure pump. The injection pressure needs to be adjusted according to the reservoir pressure and permeability. Fracturing enhancement technology is employed to control the diffusion range and speed of high-temperature CO2 in the coal seam by adjusting the injection pressure and injection rate. Before high-temperature CO2 injection, a positive injection isolation slug operation is required, i.e., cryogenic diesel oil or other cryogenically resistant media that do not damage the reservoir are injected positively from the wellhead or pump outlet pipeline. During CO2 injection, the filling volume is controlled, and the working pressure and temperature of the storage tank are monitored.

[0058] The controlled fracture energy enhancement technology process involves calculating the downhole fracture closure pressure based on low-pressure testing, well pressure drop, and a matrix adsorption-desorption-seepage model. This determines the well-drainage-backflow time and develops a dynamic adjustment plan for the production pressure differential, ultimately forming a CO2 displacement and storage energy enhancement and production improvement technology. Specifically, it first involves collecting coal seam geological parameters and monitoring and recording the pressure and flow rate during high-temperature CO2 injection. The collected data is then preprocessed to establish a matrix adsorption-desorption-seepage model.

[0059] The small-pressure test and well-sealing pressure drop are as follows: First, a local high-temperature CO2 injection test is conducted in the coal seam, the pressure response is observed and recorded, the small-pressure test data is analyzed, and the pressure sensitivity and fracture development of the coal seam are evaluated. At the same time, after the high-temperature CO2 injection, a well-sealing operation is performed, that is, the injection is stopped and the wellhead is kept closed for a period of time. The pressure changes during the well-sealing period are monitored, the pressure drop trend and rate are analyzed, and the closure pressure and permeability changes of the downhole fractures are calculated through the well-sealing pressure drop data.

[0060] The data obtained from the low-pressure test and the pressure drop analysis of the sealed well were compared with the matrix adsorption-desorption-seepage model to correct the model parameters. Using the corrected model and the pressure drop data of the sealed well, the closure pressure of the downhole fracture was calculated, and the impact of the fracture closure pressure on CO2 storage and coalbed methane extraction was evaluated. Based on the fracture closure pressure and the coalbed methane extraction requirements, the sealed well time and flowback time were determined. Finally, the pressure changes during the production process were analyzed, and a plan for dynamically adjusting the production pressure differential was formulated.

[0061] The high-temperature CO2 injection process involves first connecting the high-temperature CO2 output device to the pressurization device, then using the pressurization device to inject the high-temperature CO2 at high pressure into the casing of the target coal seam, and using the casing to guide the high-temperature CO2. The metering device measures the injected high-temperature CO2 in real time and provides a basis for adjusting the various parameters of the high-temperature CO2. Finally, the collection device separates and collects the gas and CO2 separately.

[0062] With the injection of CO2, the gas changes are measured in real time. The specific formula is as follows:

[0063]

[0064] In the formula, C pr ρ represents the CO2r adsorbate content. ra Let ρ be the density of CO2r under standard conditions. c Let α be the density of the coal. r b is the limiting adsorption capacity of CO2r. r p is the CO2 adsorption equilibrium constant. r The CO2r equilibrium partial pressure is represented by the subscripts r = 1 and 2, which respectively indicate the variables corresponding to gas and injected CO2.

[0065] Step 6, Gas Recovery and CO2 Sequestration: After high-temperature CO2 injection, the natural desorption and diffusion of coalbed methane, as well as the competitive adsorption of high-temperature CO2, are used to improve the gas recovery rate. Furthermore, the high-temperature CO2 can be adsorbed by the coal seam and stored in the reservoir, thus achieving geological sequestration of high-temperature CO2.

[0066] Step 7, CO2 and gas separation: After gas extraction, the gas extracted from the coal seam is collected through the coalbed methane extraction system, and dust, particulate matter and moisture impurities are removed. Then, CO2 and gas are selectively separated using an adsorbent. During separation, the temperature and pressure are adjusted to achieve full separation of CO2 and gas. The separated CO2 is enriched and compressed according to the technical means in Step 2 for subsequent reuse, while the gas is stored.

[0067] Step 8, Monitoring and Evaluation: Using seismic, logging and inter-well tracer monitoring technologies, the injection effect of high-temperature CO2, gas recovery and CO2 sequestration status are monitored and evaluated in real time. Based on the monitoring results, the injection strategy and recovery plan are adjusted to ensure the continuous optimization of gas recovery rate and CO2 sequestration rate.

[0068] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0069] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas, characterized in that: Includes the following steps: Step 1, Power Plant Flue Gas: The hot flue gas generated by the gas power plant is collected through the flue gas collection system, and the flue gas is pretreated by dust removal, desulfurization and denitrification; at the same time, the residual heat energy in the flue gas is recovered through the waste heat boiler or heat exchanger, and the residual heat energy is used to maintain the working temperature of the adsorption bed or converted into the power energy to drive the compressor. Step 2, High-temperature CO2 enrichment and compression: Solid adsorbent is attached to the adsorption bed, and then the pretreated flue gas is introduced. The temperature and pressure are adjusted to separate the CO2 in the flue gas to achieve enrichment. The enriched CO2 is injected into the compressor for compression to obtain the high-temperature CO2 required for subsequent injection. Step 3, Reservoir Evaluation and Site Selection: Geological, geophysical and geochemical evaluations are conducted on the target coalbed methane reservoir to determine reservoir parameters. Gas occurrence patterns are obtained through calculations. Based on the evaluation and gas occurrence patterns, blocks with simple geological structures, good roof and floor sealing, large coal seam thickness and high gas content are selected as sites for high-temperature CO2 injection. Step 4, Horizontal Well Design and Construction: Based on the reservoir evaluation results and geological conditions, design the trajectory, length, and segmentation scheme of the horizontal well. After segmentation, obtain the factors that directly affect CO2 enrichment and adsorption based on reservoir parameters and using the grey theory correlation method. Classify the coal seam according to the factors that directly affect CO2 enrichment and adsorption, and install casing according to the classification. Determine the sealing position based on the casing installation and determine the injection value of high-temperature CO2. Step 5, High-temperature CO2 injection and controlled fracture energy enhancement: High-temperature CO2 is injected into the predetermined section of the horizontal well through a high-pressure pump. The injection pressure needs to be adjusted according to the reservoir pressure and permeability. Furthermore, controlled fracture energy enhancement technology is adopted to control the diffusion range and speed of high-temperature CO2 in the coal seam by adjusting the injection pressure and injection rate. The process of controlled fracture energy enhancement technology involves calculating the downhole fracture closure pressure based on low-pressure testing, well pressure drop, and matrix adsorption-desorption-seepage model, determining the well-drainage-flow-back time, and formulating a dynamic adjustment plan for production pressure difference, thereby forming CO2 displacement and storage energy enhancement and production improvement technology. Step 6, Gas Recovery and CO2 Sequestration: After high-temperature CO2 injection, the natural desorption and diffusion of coalbed methane, as well as the competitive adsorption of high-temperature CO2, are used to improve the gas recovery rate. In addition, high-temperature CO2 can be adsorbed by the coal seam and stored in the reservoir, thus realizing the geological sequestration of high-temperature CO2. Step 7, CO2 and gas separation: After gas extraction, the gas extracted from the coal seam is collected through the coalbed methane extraction system, and dust, particulate matter and moisture impurities are removed. Then, CO2 and gas are selectively separated using an adsorbent. During separation, the temperature and pressure are adjusted to achieve full separation of CO2 and gas. The separated CO2 is enriched and compressed according to the technical means in Step 2 for subsequent reuse, while the gas is stored. Step 8, Monitoring and Evaluation: Using seismic, logging and inter-well tracer monitoring technologies, the injection effect of high-temperature CO2, gas recovery and CO2 sequestration status are monitored and evaluated in real time. Based on the monitoring results, the injection strategy and recovery plan are adjusted to ensure the continuous optimization of gas recovery rate and CO2 sequestration rate.

2. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 1, characterized in that: In step three, the process of obtaining the gas occurrence law is as follows: first, the gas content in the coal seam is measured; then, the pore structure and fracture development of the coal seam are analyzed to determine the gas occurrence state; and combined with the influencing factors of gas migration in the coal seam, the gas migration law is obtained; finally, the gas occurrence law is obtained by combining gas monitoring and data analysis in mine production practice.

3. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 2, characterized in that: In step five, before high-temperature CO2 injection, a positive injection isolation slug operation is required, which involves injecting low-temperature diesel or other low-temperature resistant media that do not damage the reservoir from the wellhead or pump outlet pipeline. During high-temperature CO2 injection, the filling volume is controlled, and the working pressure and temperature of the storage tank are monitored.

4. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 3, characterized in that: In step five, the controlled fracture energy enhancement technology process specifically involves first, based on the collected coal seam geological parameters and monitoring and recording the pressure and flow rate during the high-temperature CO2 injection process, and then preprocessing the collected data to establish a matrix adsorption-desorption-seepage model. The small-pressure test and well-sealing pressure drop are as follows: First, a local high-temperature CO2 injection test is conducted in the coal seam, the pressure response is observed and recorded, the small-pressure test data is analyzed, and the pressure sensitivity and fracture development of the coal seam are evaluated. At the same time, after the high-temperature CO2 injection, a well-sealing operation is performed, that is, the injection is stopped and the wellhead is kept closed for a period of time. The pressure changes during the well-sealing period are monitored, the pressure drop trend and rate are analyzed, and the closure pressure and permeability changes of the downhole fractures are calculated through the well-sealing pressure drop data. The data obtained from the low-pressure test and the pressure drop analysis of the sealed well were compared with the matrix adsorption-desorption-seepage model to correct the model parameters. Using the corrected model and the pressure drop data of the sealed well, the closure pressure of the downhole fracture was calculated, and the impact of the fracture closure pressure on CO2 storage and coalbed methane extraction was evaluated. Based on the fracture closure pressure and the coalbed methane extraction requirements, the sealed well time and flowback time were determined. Finally, the pressure changes during the production process were analyzed, and a plan for dynamically adjusting the production pressure differential was formulated.

5. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 4, characterized in that: In step four, the collected reservoir parameter information includes coal thickness, Protodyakonov coefficient of coal body, moisture, ash content, porosity, permeability, gas content, gas pressure, gas saturation, Langmuir pressure constant, and Langmuir volume constant.

6. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 5, characterized in that: In step four, the specific process of the grey theory correlation method is as follows: First, determine the reference sequence and the comparison sequence, perform dimensionless processing on the reference sequence and the comparison sequence to eliminate the difference in dimensions, calculate the grey correlation coefficient ξ between the reference sequence and the comparison sequence, then calculate the correlation degree ri, and finally rank the correlation order to obtain the factors that directly affect CO2 concentration and adsorption.

7. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 6, characterized in that: In step four, after obtaining the factors directly affecting CO2 concentration and adsorption, a further confidence assessment of these factors is required. The specific formula is as follows: [X-t 0th (n-1)S*n -0.5 ,X+t 0th (n-1)S*n -0.5 ] In the formula, X is the mean of the successful sample of the influencing factors, and t 0th (n-1) is the upper quantile of the t-distribution with n-1 degrees of freedom about 0.5α, Xt 0th (n-1)S*n -0.5 , X+t 0th (n-1)S*n -0.5 These are the lower and upper confidence limits, respectively.

8. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 7, characterized in that: In step four, the coal seam grading process is as follows: First, the coal seam is divided into segments based on the parameter values ​​of factors that directly affect CO2 concentration and adsorption collected from each part of the target coal seam. The target coal seam is divided into three treatment levels: high, medium, and low. The number of casings installed is proportional to the level. The casings are equipped with several segmented gas injection holes, and the lengths of the segmented gas injection holes are all different.

9. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 8, characterized in that: In step five, the high-temperature CO2 injection process involves first connecting the high-temperature CO2 output device to the pressurization device, then using the pressurization device to inject the high-temperature CO2 at high pressure into the casing within the target coal seam, and using the casing to guide the high-temperature CO2. The metering device measures the injected high-temperature CO2 in real time and provides a basis for adjusting the various parameters of the high-temperature CO2. Finally, the collection device separates and collects the gas and CO2 separately.

10. The zero-carbon method for enhancing coal seam gas recovery and CO2 sequestration using residual heat of flue gas according to claim 9, characterized in that: In step five, as high-temperature CO2 is injected, the gas change is measured in real time. The specific formula is as follows: In the formula, C pr ρ represents the CO2r adsorbate content. ra Let ρ be the density of CO2r under standard conditions. c Let α be the density of the coal. r b is the limiting adsorption capacity of CO2r. r p is the CO2 adsorption equilibrium constant. r The CO2r equilibrium partial pressure is represented by the subscripts r = 1 and 2, which respectively indicate the variables corresponding to gas and injected CO2.

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