A goaf mineralization storage and coalbed gas displacement system and method

Abstract

The application discloses a goaf mineralization sealing and coalbed gas displacement system and method, relates to the field of energy development and low-carbon technology, and is applied to a goaf. The goaf mineralization sealing and coalbed gas displacement system comprises a grouting pipeline assembly arranged along the side of the goaf, a plurality of grouting pipeline units, and a plurality of grouting pipeline units arranged at intervals along the longitudinal direction of the goaf and configured to inject filling slurry into the goaf; an air injection pipeline assembly arranged close to the goaf and extending into the goaf and configured to inject CO2 and heat generated by mineralization reaction of the filling slurry into the goaf; and a coalbed gas extraction assembly comprising a pump body and an extraction pipe assembly connected to the pump body, wherein the extraction pipe assembly extends into the goaf and is configured to extract coalbed gas in the goaf.

Description

Technical Field

[0001] This invention relates to the fields of energy development and low-carbon technology, and in particular to a system and method for mineralization and sequestration of goaf and displacement of coalbed methane. Background Technology

[0002] Coalbed methane, also known as coal seam methane or coalbed gas, is both an important unconventional energy source and a major hazard source of coal mine gas disasters. Due to mining disturbances and overburden destruction, numerous fractures and delamination spaces form within the goaf and adjacent coal seams. The remaining coal continuously desorbs and releases coalbed methane, leaving a large amount of residual coalbed methane in the goaf. Compared to the coal seam itself, coalbed methane in the goaf is characterized by complex occurrence states, uneven gas distribution, and diverse migration paths. Therefore, efficient and safe extraction methods are urgently needed. Summary of the Invention

[0003] This solution addresses the problems and needs raised above by proposing a system and method for mineralization preservation and coalbed methane displacement in goaf areas. The system achieves the aforementioned technical objectives and brings about several other technical benefits due to the adoption of the following technical features.

[0004] One object of the present invention is to provide a goaf mineralization preservation and coalbed methane displacement system, applicable to goaf areas, comprising:

[0005] The grouting pipeline assembly is arranged along the side wall of the goaf and includes multiple grouting pipeline units. The multiple grouting pipeline units are spaced apart along the longitudinal direction of the goaf and are configured to inject filling grout into the goaf.

[0006] The gas injection pipeline assembly is located near the goaf and extends into the goaf, and is configured to inject CO2 into the goaf to react with the filling slurry to generate heat through a mineralization reaction.

[0007] A coalbed methane extraction assembly includes a pump body and an extraction pipe assembly connected thereto, the extraction pipe assembly extending into the goaf and configured for extracting coalbed methane within the goaf.

[0008] In addition, the goaf mineralization preservation and coalbed methane displacement system according to the present invention may also have the following technical features:

[0009] In one example of the present invention, the grouting pipeline units are arranged at intervals in the longitudinal direction and extend laterally into the goaf, and the length of the grouting pipeline units in the lateral direction increases sequentially from top to bottom along the longitudinal direction.

[0010] In one example of the present invention, the gas injection pipeline assembly includes an outer tube and an inner tube disposed within the outer tube, wherein a high-strength thermally conductive fiber bundle is filled between the inner tube and the outer tube, wherein the inner tube is used to transport CO2 gas, and the thermal conductivity λ of the high-strength thermally conductive fiber bundle is ≥50W / (m·K).

[0011] In one example of the present invention, the gas injection pipeline assembly includes a main pipe extending in a transverse direction and a plurality of branch pipes connected thereto, wherein the plurality of branch pipes are arranged at intervals along the transverse direction of the goaf, and wherein the branch pipes extend in the longitudinal direction to a position of 40%-50% of the height of the goaf.

[0012] In one example of the present invention, the extraction pipe assembly includes: a main extraction pipe and a plurality of extraction branch pipes connected thereto, the plurality of extraction branch pipes being arranged at intervals along the transverse direction of the goaf, and the plurality of extraction branch pipes and the plurality of branch pipe sections being arranged alternately in the transverse direction.

[0013] Another objective of this invention is to provide a method for mineralization preservation and coalbed methane displacement in a goaf mineralization preservation and coalbed methane displacement system as described above, comprising the following steps:

[0014] S10: Prepare a filling slurry including high-calcium fly ash, steel slag powder, cement, coal gangue and composite additives; inject the prepared filling slurry into the goaf through the grouting pipeline assembly, and stop the first stage of grouting when the height reaches 60%-70% of the height of the goaf to form a mineralized reaction layer.

[0015] S20: CO2 is injected into the goaf through the gas injection pipeline assembly. The CO2 is induced to enter the filling slurry through pulse pressurization. It reacts with the active components in the filling slurry to produce heat. The kinetic energy of the gas molecules increases dramatically after heating, and the density decreases, generating an upward thermal buoyancy. With the assistance of the heat-conducting fiber bundles embedded in the gas injection pipeline assembly, the heat energy of the lower filling slurry is transferred upward, and thermal convection is generated inside the goaf.

[0016] S30: The pump body of the coalbed methane extraction component is turned on, a negative pressure environment is formed in the goaf, and the coalbed methane in the goaf is extracted.

[0017] S40: Monitor the gas concentration C at the extraction pipe in real time. When C>15%, maintain extraction. When C<10% and CO2 concentration C1>5%, start the circulation reinjection. Repeat steps S20 and S30.

[0018] S50: When the extraction port C < 5% and C1 > 30%, stop extraction, close the extraction pipe group and the gas injection pipeline assembly, open the high-level side grouting pipeline assembly to carry out the second stage of grouting, until the top is reached.

[0019] In one example of the present invention, in step S20, the CO2 injection method is segmented pulsed stepped pressurization injection, which varies according to three stages: penetration, diffusion, and displacement, with the injection pressure P... in The expression is:

[0020]

[0021] In the formula, P1 is the initial osmotic pressure; P2 is the peak displacement pressure, P2= ; The boost rate is set to 0.01-0.05 MPa / min; t1 is the pulse angular velocity, ranging from 0.02 to 0.2 rad / s; t2 is the duration of the infiltration stage, which depends on the initial setting time of the slurry and ranges from 5 to 30 min; t3 is the end time of the pressurization and diffusion stage, ranging from 10 to 60 min.

[0022] In one example of the present invention, in step S20, the expression for the instantaneous exothermic power Q(t) of the mineralization reaction is:

[0023]

[0024] In the formula, k is the apparent reaction rate constant of the slurry; A r For effective reaction specific surface area; Let t be the partial pressure of CO2 at the reaction interface at time t, and n be the pressure coefficient.

[0025] In one example of the present invention, in step S30, the extraction negative pressure P of the coalbed methane extraction assembly... v Based on the residual space V in the goaf g Adjust the extraction negative pressure P in accordance with the real-time temperature T. v The expression is:

[0026]

[0027] In the formula, P0 is the initial negative pressure for extraction; V is the pressure sensitivity coefficient to temperature; T0 is the temperature of the goaf before grouting; V g This refers to the volume of the remaining space in the goaf after the first stage of grouting.

[0028] In one example of the present invention, in step S50, the side grouting pipeline assembly is opened to carry out the second stage of grouting until the top is reached. Specifically, the filling slurry injected by opening the high side grouting pipeline assembly is a modified expanding slurry. Based on the original material ratio, 0.5%-1.0% of aluminum powder gas generator and 2.0%-4.0% of MgO expanding agent are added. The expansion stress generated by the expanding slurry ensures the top of the filling body.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention can simultaneously control surface subsidence, seal CO2 underground, and displace coalbed methane by injecting grout and introducing CO2 into the goaf. It significantly improves the stability of CO2 sealing, realizes efficient and safe extraction of coalbed methane in the goaf, and reduces the risk of gas accumulation in the goaf.

[0031] 2. The filling slurry of the present invention uses sodium citrate retarder, sodium sulfate early strength agent and triethanolamine reaction promoter as composite additives, which can delay early hydration, activate later activity and coordinate the mineralization and hydration reaction pathways, effectively prolong the time for CO2 to participate in the reaction, improve the mineralization reaction efficiency, and at the same time ensure the mechanical properties of the filling body.

[0032] 3. After grouting, the present invention uses segmented pulsed stepped pressurized injection to react with the active components in the filling material to achieve CO2 sequestration. Furthermore, the heat generated by the exothermic reaction of the mineralization reaction increases the kinetic energy of the gas molecules, reduces their density, and generates an upward thermal buoyancy, thereby improving the displacement and recovery efficiency of coalbed methane.

[0033] 4. In the second stage of grouting, the present invention incorporates aluminum powder gas generator and MgO expansion agent to accelerate the formation of a continuous filling structure and densely fill the goaf, thereby improving the overall stability and load-bearing capacity of the filling body.

[0034] 5. The method of the present invention has simple process steps, strong operability, no need to make major modifications to the existing mine infrastructure, and has good engineering applicability and promotion value.

[0035] The preferred embodiments of the invention will be described in more detail below with reference to the accompanying drawings, so as to facilitate an understanding of the features and advantages of the invention. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments of the present invention will be briefly described below. The drawings are merely illustrative of some embodiments of the present invention and are not intended to limit the scope of the present invention to all embodiments.

[0037] Figure 1 This is a schematic diagram of the structure of the goaf mineralization preservation and coalbed methane displacement system according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of the gas injection pipeline assembly according to an embodiment of the present invention;

[0039] Figure 3 This is a flowchart of a goaf mineralization and coalbed methane displacement method according to an embodiment of the present invention.

[0040] List of reference numerals in the attached diagram:

[0041] 300g of filling slurry;

[0042] 200 mined-out area;

[0043] Mineralization preservation and coalbed methane displacement system 100;

[0044] Grouting pipeline assembly 10;

[0045] Grouting pipeline unit 11;

[0046] Gas injection piping assembly 20;

[0047] Outer tube 21;

[0048] Inner tube 22;

[0049] Thermally conductive fiber bundle 23;

[0050] Main pipe section 24;

[0051] Branch pipe section 25;

[0052] Coalbed methane extraction assembly 30;

[0053] Pump body 31;

[0054] Extraction tube assembly 32;

[0055] Sampling Supervisor 321;

[0056] 322 sampling points are under management.

[0057] Lateral direction X;

[0058] The vertical direction is Y. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0060] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0061] According to a first aspect of the present invention, a goaf mineralization preservation and coalbed methane displacement system 100 is provided, such as Figure 1 As shown, it is applied to goaf 200, including:

[0062] Grouting pipeline assembly 10 is arranged along the side wall of goaf 200 and includes multiple grouting pipeline units 11. The multiple grouting pipeline units 11 are arranged at intervals along the longitudinal direction Y of goaf 200 and configured to inject filling grout 300 into goaf 200.

[0063] The gas injection pipeline assembly 20 is located near the goaf 200 and extends into the goaf 200, and is configured to inject CO2 into the goaf 200 to generate heat through a mineralization reaction with the filling slurry 300.

[0064] The coalbed methane extraction assembly 30 includes a pump body 31 and an extraction pipe assembly 32 connected thereto, the extraction pipe assembly 32 extending to the goaf 200 and configured for extracting coalbed methane within the goaf 200.

[0065] The mineralization and coalbed methane displacement method of this system is as follows: A filling slurry 300, comprising high-calcium fly ash, steel slag powder, cement, coal gangue, and composite additives, is prepared. The prepared slurry is injected into the goaf 200 through the grouting pipeline assembly 10. The first stage of grouting is stopped when the slurry reaches 60%-70% of the goaf height, forming a mineralization reaction layer. CO2 is injected into the goaf 200 through the gas injection pipeline assembly 20. Pulsed pressurization induces the CO2 to enter the filling slurry 300, where it reacts with the active components in the slurry in a mineralization reaction, releasing heat. The heated gas molecules experience a dramatic increase in kinetic energy and a decrease in density, generating upward thermal buoyancy. With the assistance of pre-embedded heat-conducting fiber bundles, the heat energy of the lower slurry is transferred upwards, and thermal convection is generated inside the goaf 200. The extraction pump of the coalbed methane extraction component 30 is turned on, and a negative pressure environment is formed in the goaf 200, and the coalbed methane in the goaf 200 is extracted. The gas concentration C at the extraction pipe opening is monitored in real time. When C>15%, extraction is maintained. When C<10% and CO2 concentration C1>5%, circulation reinjection is started, and circulation steps S20 and S30 are repeated. When C<5% and C1>30 at the extraction port, extraction is stopped, the extraction pipe group and gas injection pipeline component 20 are closed, and the high-level side grouting pipeline component 10 is opened to continue grouting until the roof is connected.

[0066] This system can simultaneously control surface subsidence, seal CO2 underground, and displace coalbed methane by injecting grout and introducing CO2 into the goaf 200. It significantly improves the stability of CO2 sealing, realizes efficient and safe extraction of coalbed methane in the goaf 200, and reduces the risk of gas accumulation in the goaf 200.

[0067] The filling slurry 300 of this system uses sodium citrate retarder, sodium sulfate early strength agent and triethanolamine reaction promoter as composite additives, which can delay early hydration, activate later activity and coordinate the mineralization and hydration reaction pathways, effectively prolong the time for CO2 to participate in the reaction, improve the mineralization reaction efficiency, and at the same time ensure the mechanical properties of the filling body.

[0068] After grouting, the system injects gas through segmented pulsed stepped pressurization, which reacts with the active components in the filling material to form a mineralization reaction. This not only achieves CO2 sequestration, but also utilizes the heat generated by the mineralization reaction to increase the kinetic energy of gas molecules, reduce their density, and generate upward thermal buoyancy, thereby promoting the displacement and recovery efficiency of coalbed methane.

[0069] The system incorporates aluminum powder gas generator and MgO expansion agent during the second stage of grouting, which accelerates the formation of a continuous filling structure and densely fills the goaf area 200, thereby improving the overall stability and load-bearing capacity of the filling body.

[0070] The system method has simple process steps, is highly operable, does not require major modifications to existing mine infrastructure, and has good engineering applicability and promotion value.

[0071] In one example of the present invention, the grouting pipeline units 11 are arranged at intervals in the longitudinal direction Y and extend into the transverse direction X inside the goaf, and the length of the grouting pipeline units 11 in the transverse direction X increases sequentially from top to bottom along the longitudinal direction Y.

[0072] For example, the grouting pipeline unit 11 is arranged at a spacing of 20-30m and extends into the goaf 200, and the length of the grouting pipeline unit 11 in the transverse direction X increases from top to bottom along the longitudinal direction Y.

[0073] In one example of the present invention, such as Figure 2 As shown, the gas injection pipeline assembly 20 includes an outer pipe 21 and an inner pipe 22 disposed within the outer pipe 21, and a high-strength thermally conductive fiber bundle 23 is filled between the inner pipe 22 and the outer pipe 21. The inner pipe 22 is used to transport CO2 gas, and the thermal conductivity λ of the high-strength thermally conductive fiber bundle 23 is ≥50W / (m·K).

[0074] In one example of the present invention, the gas injection pipeline assembly 20 includes a main pipe extending along the transverse direction X and a plurality of branch pipes 25 connected thereto, and the plurality of branch pipes 25 are arranged at intervals along the transverse direction X of the goaf 200, wherein the branch pipes 25 extend in the longitudinal direction Y to a position of 40%-50% of the height of the goaf 200.

[0075] In one example of the present invention, the extraction pipe assembly 32 includes: an extraction main pipe 321 and a plurality of extraction branch pipes 322 connected thereto, the plurality of extraction branch pipes 322 being arranged at intervals along the transverse direction X of the goaf 200, and the plurality of extraction branch pipes 322 and the plurality of branch pipe sections 25 being arranged alternately in the transverse direction X.

[0076] According to a second aspect of the present invention, a method for mineralization preservation and coalbed methane displacement in a goaf 200 mineralization preservation and coalbed methane displacement system 100 as described above is provided. Figure 3 As shown, it includes the following steps:

[0077] S10: Prepare filling slurry 300, which includes high-calcium fly ash, steel slag powder, cement, coal gangue and composite additives, at the ground mixing plant; inject the prepared filling slurry 300 into the goaf 200 through the grouting pipeline assembly 10, and stop the first stage of grouting when the height reaches 60%-70% of the height of the goaf 200 to form a mineralized reaction layer;

[0078] S20: CO2 is injected into the goaf 200 through the gas injection pipeline assembly 20. The CO2 is induced to enter the filling slurry 300 through pulse pressurization. It reacts with the active components in the filling slurry 300 to produce heat through mineralization. The kinetic energy of the gas molecules increases dramatically after heating, and the density decreases, generating an upward thermal buoyancy. With the assistance of the heat-conducting fiber bundles 23 embedded in the gas injection pipeline assembly 20, the heat energy of the lower filling slurry 300 is transferred upward, and thermal convection is generated inside the goaf 200.

[0079] S30: The pump body 31 of the coalbed methane extraction component 30 is turned on, a negative pressure environment is formed in the goaf 200, and the coalbed methane in the goaf 200 is extracted.

[0080] S40: Monitor the gas concentration C at the extraction pipe in real time. When C>15%, maintain extraction. When C<10% and CO2 concentration C1>5%, start the circulation reinjection. Repeat steps S20 and S30.

[0081] S50: When the extraction port C < 5% and C1 > 30%, stop extraction, close the extraction pipe group and the gas injection pipeline assembly 20, open the high-level side grouting pipeline assembly 10 to carry out the second stage of grouting, until the top is reached.

[0082] This method, by injecting grout and introducing CO2 into the goaf 200, can simultaneously achieve the goals of controlling surface subsidence, sealing CO2 underground, and displacing coalbed methane. It significantly improves the stability of CO2 sealing, realizes efficient and safe extraction of coalbed methane within the goaf 200, and reduces the risk of gas accumulation in the goaf 200.

[0083] The filling slurry 300 of this method uses sodium citrate retarder, sodium sulfate early strength agent and triethanolamine reaction promoter as composite additives, which can delay early hydration, activate later activity and coordinate the mineralization and hydration reaction pathways, effectively prolong the time for CO2 to participate in the reaction, improve the mineralization reaction efficiency, and at the same time ensure the mechanical properties of the filling body.

[0084] This method involves injecting gas through segmented pulsed stepped pressurization after grouting, which causes a mineralization reaction with the active components in the filling material. This not only achieves CO2 sequestration but also utilizes the heat generated by the mineralization reaction to increase the kinetic energy of gas molecules, reduce their density, and generate upward thermal buoyancy, thereby promoting the displacement and recovery efficiency of coalbed methane.

[0085] This method incorporates aluminum powder gas generator and MgO expansion agent during the second stage of grouting, which accelerates the formation of a continuous filling structure and densely fills the goaf area 200, thereby improving the overall stability and load-bearing capacity of the filling body.

[0086] This method has simple process steps, is highly operable, does not require major modifications to existing mine infrastructure, and has good engineering applicability and promotion value.

[0087] For example, multiple goaf areas 200 are set at intervals along the longitudinal direction Y and extend in the transverse direction X. After the construction of one goaf area 200 is completed, the construction of the next goaf area 200 is carried out.

[0088] In one example of the present invention, in step S10, the composite additive includes: sodium citrate retarder, sodium sulfate early strength agent and triethanolamine reaction promoter, and the mass ratio of the three is 1-2:1-3:0.5-1.

[0089] In one example of the present invention, in step S20, the CO2 injection method is segmented pulsed stepped pressurization injection, which varies according to three stages: penetration, diffusion, and displacement, with the injection pressure P... in The expression is:

[0090]

[0091] In the formula, P1 is the initial osmotic pressure, Pa; P2 is the peak displacement pressure, Pa, P2= ; The boost rate is set to 0.01-0.05 MPa / min; t1 is the pulse angular velocity, ranging from 0.02 to 0.2 rad / s; t2 is the duration of the infiltration stage, which depends on the initial setting time of the slurry and ranges from 5 to 30 min; t3 is the end time of the pressurization and diffusion stage, ranging from 10 to 60 min.

[0092] In one example of the present invention, in step S20, the expression for the instantaneous exothermic power Q(t) of the mineralization reaction is:

[0093]

[0094] In the formula, Q(t) is the instantaneous exothermic power, W; k is the apparent reaction rate constant of the slurry, W·m -2 ·Pa -n It can be measured by TG-DSC test; A r For an effective reaction surface area, m 2 It can be determined by mercury porosimetry and nitrogen adsorption method; Let t be the partial pressure of CO2 at the reaction interface at time t, in Pa, and n be the pressure coefficient, taken as 0.5.

[0095] In one example of the present invention, in step S30, the extraction negative pressure P of the coalbed methane extraction assembly 30 is... v According to the residual space V in the goaf area g Adjust the extraction negative pressure P in accordance with the real-time temperature T. v The expression is:

[0096]

[0097] In the formula, P0 is the initial negative pressure for extraction, in Pa; The pressure sensitivity coefficient to temperature is typically taken as 0.15~0.25; T0 is the temperature of the goaf 200°C before grouting; V g This represents the volume of the 200 m³ remaining space in the goaf after the first stage of grouting. 3 The expression is: V g =V t -V f V t For a total volume of 200 in the goaf, V f 300 cubic meters of filling slurry was injected.

[0098] Preferably, the coalbed methane extraction assembly 30 is opened in the following order during the extraction process: from bottom to top, and the extraction pipes 322 are opened sequentially from the center to the edge.

[0099] In one example of the present invention, in step S50, the high-level side grouting pipeline assembly 10 is opened to carry out the second stage of grouting until the top is reached. Specifically, the filling slurry 300 injected by opening the high-level side grouting pipeline assembly 10 is a modified expanding slurry. Based on the original material ratio, 0.5%-1.0% of aluminum powder gas generator and 2.0%-4.0% of MgO expanding agent are added. The expansion stress generated by the expanding slurry ensures the top of the filling body.

[0100] Specific examples:

[0101] Taking mining area 2 of a certain mine as an example, the mining area level is -300m, and the volume of the goaf 200 is 100,000 m³. 3 .

[0102] Step S10: Prepare a filling slurry 300 at a ground mixing plant. The filling material comprises 30%-40% high-calcium fly ash, 15%-25% steel slag powder, 10%-20% ordinary Portland cement, 20%-30% coal gangue, and 0.5%-1.5% composite additives by mass, with a water-cement ratio of 0.6. The composite additives include sodium citrate retarder, sodium sulfate early-strength agent, and triethanolamine reaction accelerator, with a preferred mass ratio of 1-2:1-3:0.5-1. Grouting pipeline units 11 are arranged every 20-30m along the sidewall of the goaf 200. Simultaneously, a gas injection pipeline assembly 20 is arranged along the top of the goaf 200 through ground boreholes through the rock strata, with extraction branch pipes 322 and branch pipe sections 25 arranged alternately. The prepared grout is injected into the goaf 200 through the grouting pipeline assembly 10, with the grouting flow rate controlled at 20-40 m³ / h. 3 / h, when the injection height reaches 60%-70% of the height of the goaf 200, the first stage of grouting is stopped, and a slurry layer is formed in the lower part of the goaf 200. This slurry layer serves as the main mineralization reaction layer for subsequent CO2 injection.

[0103] Step S20: CO2 is injected into the goaf 200 through the gas injection pipeline assembly 20. The CO2 injection proceeds through three stages: "infiltration-diffusion-displacement". In the first stage, the CO2 injection pressure is controlled at 0.2-0.5 MPa, and the duration is 5-10 min. In the second stage, the injection pressure is gradually increased, with the pressurization rate controlled at 0.01-0.05 MPa / min, so that the injection pressure is steadily increased from the initial pressure to 0.8-1.5 MPa. This stage lasts for 10-60 min. In the third stage, the injection pressure is controlled at 1.2-2.0 MPa. After CO2 is injected, it reacts with the active components in the filling slurry 300 to produce a mineralization reaction and release heat. The kinetic energy of the gas molecules increases dramatically after heating, and the density decreases, generating an upward thermal buoyancy. With the assistance of the pre-embedded thermally conductive fiber bundles 23, the heat energy of the lower slurry is transferred upward, and thermal convection is generated inside the goaf 200.

[0104] Step S30: The pump 31 of the coalbed methane extraction pipeline is activated, creating a negative pressure environment within the goaf 200. The coalbed methane extraction assembly 30 is activated sequentially from bottom to top, from the center of the goaf 200 towards the edges, prioritizing the extraction of coalbed methane enriched in the lower and middle parts of the goaf 200, and then gradually expanding to the upper and edge areas. Initially, the negative pressure for coalbed methane extraction is controlled within the range of 5-10 kPa. As the mineralization reaction continues and the internal temperature of the goaf 200 increases, the negative pressure is gradually increased to 10-20 kPa.

[0105] Step S40: Using an online gas monitoring device installed at the coalbed methane extraction pipe inlet, the gas concentration C and CO2 concentration C1 in the extracted gas are monitored in real time. When the gas concentration C at the extraction pipe inlet is >15%, extraction operations continue. When C <10% and CO2 concentration C1 >5%, some extraction branches 322 are reduced or intermittently closed, while the gas injection pipeline assembly 20 is reopened to reinject CO2 into the goaf 200. The reinjection pressure is controlled at 0.5-1.2 MPa, and the reinjection time is controlled at 10-30 minutes.

[0106] Step S50: When the extraction port C < 5% and C1 > 30%, stop extraction, seal the coalbed methane extraction assembly 30 and the gas injection pipeline assembly 20, open the high-level side grouting pipeline unit 11 and inject modified expansion slurry. Add 0.5%-1.0% aluminum powder gas generator and 2.0%-4.0% MgO expansion agent based on the original material ratio, and use the expansion stress generated by the expansion slurry to ensure that the filling body is in contact with the top.

[0107] The mineralization and coalbed methane displacement method of this system can effectively control rock strata movement and optimize stress distribution in the mining area through filling. It can also efficiently solidify CO2 through chemical mineralization reaction and simultaneously displace and recover coalbed methane, thus achieving efficient and safe extraction of coalbed methane.

[0108] The foregoing description, with reference to preferred embodiments, details an exemplary implementation of the present invention’s proposed system 100 for mineralization preservation and coalbed methane displacement in a goaf 200. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the concept of the present invention, and various combinations can be made to the various technical features and structures proposed in the present invention without exceeding the protection scope of the present invention, which is determined by the appended claims.

Claims

1. A method for mineralization preservation and coalbed methane displacement in goaf areas, characterized in that, Includes the following steps: S10: Prepare a filling slurry (300) including high-calcium fly ash, steel slag powder, cement, coal gangue and composite additives; inject the prepared filling slurry (300) into the goaf (200) through the grouting pipeline assembly (10), and stop the first stage of grouting when the height reaches 60%-70% of the height of the goaf (200) to form a mineralization reaction layer; S20: CO2 is injected into the goaf (200) through the gas injection pipeline assembly (20). The CO2 is induced to enter the filling slurry (300) through pulse pressurization. It reacts with the active components in the filling slurry (300) to produce heat. The kinetic energy of the gas molecules increases dramatically after heating, and the density decreases, generating an upward thermal buoyancy. With the assistance of the heat-conducting fiber bundle (23) pre-embedded in the gas injection pipeline assembly (20), the heat energy of the lower filling slurry (300) is transferred upward, and thermal convection is generated inside the goaf (200). The CO2 injection method is a segmented pulsed stepped pressurization injection, which changes according to three stages: penetration, diffusion, and displacement, with the injection pressure varying accordingly. P in The expression is: In the formula, P 1 Initial osmotic pressure; P 2 For peak displacement pressure, P 2 = ; The boost rate is set to 0.01-0.05 MPa / min; The pulse angular velocity is taken as 0.02-0.2 rad / s; t 1 The duration of the penetration stage depends on the initial setting time of the slurry and ranges from 5 to 30 minutes. t 2 This is the end time of the pressurization-diffusion stage, ranging from 10 to 60 minutes. Among them, the instantaneous exothermic power of the mineralization reaction is Q(t) The expression is: In the formula, k is the apparent reaction rate constant of the slurry; A r For effective reaction specific surface area; Let t be the partial pressure of CO2 at the reaction interface. n Pressure coefficient; S30: The pump body (31) of the coalbed methane extraction assembly (30) is activated, creating a negative pressure environment in the goaf (200), and the coalbed methane in the goaf (200) is extracted; wherein, the extraction negative pressure of the coalbed methane extraction assembly (30) is... P v Based on the remaining space in the goaf (200) V g Adjust the extraction negative pressure in accordance with the real-time temperature T. P v The expression is: In the formula, P 0 Initial negative pressure for extraction; This is the pressure sensitivity coefficient to temperature; T 0 Temperature of the goaf (200°C) before grouting; V g The volume of the remaining space in the goaf (200) after the first stage of grouting; S40: Real-time monitoring of gas concentration at the extraction pipe inlet. C ,when C When >15%, continue sampling; when C <10% and CO2 concentration C 1 If the value exceeds 5%, initiate the cyclic injection, repeating steps S20 and S30. S50: When the extraction port C <5% and C 1 When the grouting rate is >30%, stop the extraction, close the extraction pipe group and the gas injection pipeline assembly (20), open the side grouting pipeline assembly (10) to carry out the second stage of grouting, and continue until the top is reached.

2. The method for mineralization preservation and coalbed methane displacement in goaf areas according to claim 1, characterized in that, In step S50, the side grouting pipeline assembly (10) is opened to carry out the second stage of grouting until the top is reached. Specifically, the filling slurry (300) injected by opening the high side grouting pipeline assembly (10) is a modified expanding slurry. Based on the original material ratio, 0.5%-1.0% of aluminum powder gas generator and 2.0%-4.0% of MgO expanding agent are added to ensure the top of the filling body by utilizing the expansion stress generated by the expanding slurry.

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