Self-sealing compressed air energy storage guide deep ultra thick coal seam mining method

Abstract

The application discloses a deep and super-thick coal seam mining method guided by a self-sealing compressed air energy storage library, which is characterized in that: the mining process is constrained by the gas storage demand conditions of a compressed air energy storage power station in advance, and the adaptive room-and-pillar mining parameters are designed according to the energy storage parameters and the coal seam geological conditions; the undamaged room-and-pillar tunneling is used to form an uncaving goaf, and the original low-permeability sealing structure of the roof and floor is reserved; the low-permeability paste is prepared from coal-based solid waste to cast a partition wall, so that the roof support and the gas storage unit are separated; after the partition wall meets the standard, the support coal pillars are recovered in the partitioned intervals, and the gas storage space is released; the self-sealing cavity is constructed on the basis of the original coal rock, and the closure is completed by matching the gate wall and the sealing coating; and after the gas pressure drop and the tracer gas method are used for the air tightness detection, the compressed air energy storage system is connected. The application solves the defects of the traditional goaf reconstruction, such as broken surrounding rock, high sealing cost and low space utilization rate, realizes the synchronous construction of coal mining and gas storage, and the utilization rate of the gas storage space is more than 90%. The underground mine can consume the mine solid waste, and has the advantages of safety, economy and low carbon.

Description

Technical Field

[0001] This invention relates to the field of integrated technology of deep coal mining and underground compressed air energy storage, and in particular to a method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system. Background Technology

[0002] Driven by the "dual carbon" goals, compressed air energy storage (CAES), as a core technology for large-scale, long-term energy storage, is entering a window of opportunity for large-scale development. National energy policies continue to promote the construction of megawatt-level CAES power plants. However, the large-scale deployment of CAES power plants faces a key bottleneck—the constraint of underground gas storage resources. Currently, both domestically and internationally, CAES gas storage facilities are mainly constructed using layered salt caverns or salt domes. Although my country has abundant salt rock resources, their distribution is highly concentrated in specific salt mining areas and does not completely overlap with the western regions rich in wind and solar resources, leading to an increasingly prominent spatial mismatch between "storage resources" and "source-grid resources." Finding large-scale, low-cost, and widely distributed underground gas storage solutions beyond salt caverns has become an urgent issue for the development of the CAES industry.

[0003] my country possesses abundant underground space resources from closed / abandoned mines. These massive underground spaces, once converted and utilized as CAES (Cabinetized Energy Storage) gas storage facilities, will become crucial strategic reserves supporting my country's new energy storage system. Simultaneously, my country has a wide distribution of deep, thick coal seams. As mining depths increase, the goaf areas left after the extraction of these deep, thick coal seams become even more substantial, representing a "rich mine of underground space" awaiting systematic development.

[0004] The current mainstream technical approach for utilizing abandoned mine goafs for compressed air energy storage (CAES) generally adopts a post-construction modification model: "coal mining – abandonment – ​​goaf redevelopment – ​​gas storage construction." Under this model, the goaf space is a product of conventional caving mining processes. Its inherent irregularities, high degree of surrounding rock fragmentation, poor permeability, and low space utilization rate lead to the following significant technical and economic obstacles when directly converting it into a CAES gas storage facility: 1. The surrounding rock structure is broken and the stability is insufficient: the complete collapse process causes the roof to collapse periodically, and a large amount of broken rock mass accumulates in the goaf. The original fissures in the surrounding rock are greatly expanded. Under the cyclic gas storage pressure load of 4~10MPa, instability and cracking of the surrounding rock are likely to occur, and the safety risk of long-term service is extremely high. 2. Poor air tightness and high cost of sealing modification: After mining disturbance, the permeability of coal and rock mass increases by several orders of magnitude, making direct gas storage impossible. It is necessary to lay flexible gas storage bags, multi-layer lining composite sealing systems, steel plate rigid pipes and other artificial sealing structures, which greatly increases the investment and operation and maintenance costs of sealing projects. 3. The utilization rate of underground space is extremely low: the coefficient of collapse of the rock mass is 1.3~1.5, the broken body occupies a large amount of mined-out space, and the space occupied by the reserved safety coal pillar and sealing structure is also occupied. The utilization rate of the effective gas storage space of the existing renovation plan is only 20%~40%, and the economic efficiency per unit gas storage capacity is poor. 4. Disconnection between the timing and space of coal mining and energy storage projects: Coal mining and gas storage renovation are carried out in separate phases, requiring secondary site entry for development, support, and sealing operations, resulting in serious duplication of investment in the project; 5. The technical approach has inherent limitations: The key limitation of existing CAES research in abandoned mines is that "taking the goaf / abandoned roadway as the target for transformation" has become the default technical premise. Only the sealing materials and gas storage structure are optimized, but the problems of surrounding rock fracture and high permeability are not avoided from the source of coal mining process, and the shortcomings of sealing and space utilization cannot be eradicated.

[0005] The original, intact coal and shale roofs and floors naturally possess extremely low permeability (shale permeability as low as 10). -21 m 2 10% of raw coal permeability -19 ~10 -18 m 2 This meets the sealing threshold of the compressed air storage tank (maximum permeability of the surrounding rock is 1×10⁻⁶). - 14 m 2 It possesses natural self-sealing potential; the core defect of existing technologies lies in the destruction of the original low-permeability and intact structure of coal and rock during the coal mining process. If the demand for gas storage space is pre-constrained by the coal mining process, and the original integrity of the roof, floor, and coal wall is preserved throughout the mining process, the self-sealing of the gas storage space can be achieved by relying on the natural low-permeability characteristics of coal and rock, thus fundamentally solving the pain points of sealing, stability, and space utilization in existing technologies.

[0006] Compressed air storage facilities (CAES) place stringent requirements on the sealing performance of the surrounding rock. Salt caverns are the preferred medium for CAES storage facilities precisely because of their extremely low permeability (approximately 10⁻⁶). -20 m 2 (On a scale of magnitude), it possesses good rheological properties and self-healing ability. An important fact revealed in this study is that the porosity and permeability of primary structured coal are stable and consistent under the same confining pressure, with extremely low inherent permeability. The permeability of mudstone and shale can be as low as 10... -21 m 2Coal is a recognized natural gas sealing medium. However, after mining disturbance, the structural integrity of the coal and rock mass is destroyed, and the permeability increases by orders of magnitude. Experimental results show that the permeability of tectonically disturbed coal is about 100 times or even higher than that of the original structural coal, and the development of microscopic fractures and pores is greatly increased. This explains why goaf areas must rely on artificial sealing—the root cause is not that the coal and rock themselves lack sealing performance, but that the "mining" process destroys its original low-permeability structure. This scientific understanding constitutes the core theoretical basis of this invention: if the construction of gas storage function can be brought forward to the coal mining process design stage, and the original integrity of the coal and rock mass can be actively preserved during the mining process, then the extremely low permeability characteristics of the coal and rock can be fully utilized to achieve "self-sealing," fundamentally avoiding the sealing problem of post-mining modification. Summary of the Invention

[0007] To address the prominent issues in existing technologies, such as incomplete goaf structure, poor sealing performance, low space utilization, high retrofit costs, and reliance on artificial sealing layers, this invention provides a deep, extra-thick coal seam mining method guided by a self-sealing compressed gas storage system. This method pre-constrains the geometry, mechanics, and sealing requirements of the compressed gas storage space throughout the entire coal mining process, simultaneously completing the integrated construction of coal recovery and the self-sealing gas storage cavity. It leverages the natural self-sealing of the storage space based on the original, intact coal and rock, significantly improving the utilization rate of the storage space, reducing the investment in sealing engineering, and achieving integrated and coordinated construction of coal mining and underground energy storage.

[0008] To achieve the above objectives, the present invention provides the following solution: A method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system, the method comprising the following steps: S1. Coal mining process design constrained by energy storage targets: Based on the gas storage requirements parameters of the compressed gas energy storage power station, and according to the geological conditions of deep thick coal seams, the room span and coal pillar width are designed in accordance with the roadway surrounding rock stability theory and combined with computer numerical simulation or physical similarity simulation test, and the gas storage-adaptive coal mining process parameters are determined. S2. Room-and-pillar mining to form a non-collapsed goaf: Based on the mining process parameters determined in step S1, non-destructive room-and-pillar mechanized tunneling is adopted to preserve the original, intact, low-permeability structure of the coal seam roof and floor and the coal wall throughout the process, forming an independent room-type goaf without roof collapse. S3. Construction of coal-based solid waste partition walls and roof support: Using coal-based solid waste as the main aggregate, adding cementitious materials and functional additives, low-permeability and high-strength paste materials are prepared. Continuous partition walls are poured on both sides of each goaf cavity, and the permanent roof support and gas storage unit space division are completed simultaneously. S4. Recycling of abandoned coal pillars in room-and-pillar mining: Once the solidification strength of the partition wall and the roof deformation monitoring indicators meet the safety threshold, the supporting coal pillars reserved for room-and-pillar mining are recycled in an intermittent manner, from far to near, and in a zoned manner, to release effective gas storage space. S5. Formation of self-sealing gas storage space and isolation of gate wall: After the coal pillar is recovered, the original complete roof and floor plate, boundary coal pillar and partition wall are used as the main sealing boundary of gas storage. A sealing gate wall is constructed at the roadway connection, and a sealing and reinforcing coating is sprayed to form a complete self-sealing gas storage cavity. S6. Air tightness testing and energy storage system access: The air tightness of the self-sealing gas storage cavity is completed by using the pressure drop method and tracer gas method. Injection and production wells are constructed and equipped with ground compression, power generation and heat exchange equipment to form a complete compressed gas energy storage power station.

[0009] Furthermore, in S1, the gas storage requirements parameters proposed by the compressed gas energy storage power station for the gas storage space include gas storage pressure P, gas storage capacity V, operating pressure range, and circulation frequency. The geological conditions of deep, thick coal seams include: coal seam thickness H, lithology and mechanical parameters of the roof and floor, geostress state, and coal and rock permeability; the deep, thick coal seams adapted in step S1 meet the following geological conditions: burial depth ≥ 500m, coal seam thickness ≥ 5m, and roof and floor permeability ≤ 10. -18 m 2 The rock strata are intact and free from geological structural damage. The design parameters for gas storage-adaptive coal mining processes include: Determination of the retention ratio and extraction rate: Under the premise of meeting the parameters of room span and coal mine width, the initial value of the retention ratio is set at 1.5~3.0, corresponding to an initial extraction rate of 60%~75%; Mining sequence design: adopt skip mining or retreating interval mining to control the initial pressure step distance of the roof.

[0010] Furthermore, in S2, non-destructive room-and-pillar mechanized tunneling is employed, and the specific operation is as follows: The cutting height of the tunneling machine is strictly limited to the inside of the coal seam. A 50-100mm protective coal skin is reserved in the top and bottom plates, and cutting the rock strata in the top and bottom plates is prohibited. After the single-room mining is completed, the integrity of the top and bottom plates is tested by ultrasonic testing. The core wave velocity attenuation is ≤5% and the increase in the permeability of the bottom plate is not more than one order of magnitude to be considered qualified. Clean the loose coal from the bottom plate until the residual thickness is ≤20mm; When revealing areas with abnormal geological fracturing, increase the density of anchor bolt support and construct locally reinforced partition walls in advance, or designate them as non-gas storage and extraction areas.

[0011] Furthermore, in S3, the characteristics of the low-permeability, high-strength paste material are as follows: Coal-based solid waste accounts for ≥80% of the total solid waste, and cement consumption is ≤13%. 28-day compressive strength: ≥10 MPa; Permeability: ≤1×10 -14 m 2 ; Pumpability: slump 180~220 mm; Curing time is controllable: initial setting 2~4 h, final setting 8~12 h; Expansion rate: 0.01%~0.05%; The leaching toxicity test meets the relevant requirements of GB 5085.3, ensuring that the material itself is free from secondary pollution.

[0012] Furthermore, in S3, the partition walls are arranged in a strip pattern, specifically according to the following requirements: The density and thickness of the partition walls are determined through theoretical calculations of mine pressure and optimization through computer numerical simulation or physical similarity simulation tests. The following requirements must be met: the partition walls themselves must be strong and safe under confining pressure and air pressure; the spacing between the partition walls must not exceed the critical span of the roof strata; and the number of partition walls must be matched with the amount of solid waste to be disposed of. Partition wall arrangement: arranged along the dip of the mining area, located on both sides of each room, with a thickness of 8.0~12.0 m and a height level with the mining height. The strength of the partition wall is set according to the stress distribution characteristics inside the wall. The construction process for the partition wall is as follows: Variable-height steel formwork is installed in each coal mining room to form a closed wall space. The paste material is pumped into the formwork, poured in layers, and vibrated to compact it. After pouring, it is kept moist and cured. The curing time is determined according to the material ratio and ambient temperature. The strength development of the partition wall is monitored. Only after it meets the standard can the next step be carried out. Before pouring the partition wall, the coal wall in contact with it is roughened and an interface agent is applied.

[0013] Furthermore, in S4, the recovery of room-pillar type residual coal pillars specifically includes: The process involves interval recovery, progressing from far to near, and advancing in zones. The horizontal partition walls serve as boundaries, and coal pillars are recovered in sequence. Once a zone is completed and passes inspection, the process moves to the next zone. Within the same zone, coal pillars farther from the main transport roadway are recovered first, and the process gradually moves towards the shaft entrance. Within the same gas storage unit, only one coal pillar is recovered at a time, and adjacent coal pillars are kept supported to avoid large-scale depressurization. According to the layout design of the gas storage chamber, a cantilever tunneling machine is used to cut the coal pillar layer by layer. The recovered coal is transported out through the underground transportation system and included in the total coal recovery volume. During the recycling process, monitoring needs to be strengthened, and the recycling speed and process parameters should be controlled according to the detection results. The physical parameters to be monitored include: gas, the amount of movement of the top and bottom plates, and the lateral displacement of the partition walls.

[0014] Furthermore, in S5, the construction process of the gate wall is as follows: at the connection channel between the gas storage space and the external roadway and the bottom of the injection and production well, a concrete gate wall is constructed to achieve the closed isolation of the gas storage space. The materials, parameters and construction operation process are the same as those for the construction of the partition wall, and the embedding depth in the surrounding rock is ≥0.5 m, forming a wedge-shaped engagement with the surrounding rock; injection and production pipelines and monitoring cable sleeves are pre-embedded in the gate wall. Spray-applied sealing and reinforcing coating: A 2-5 mm thick polymer cement-based sealing coating is applied to the entire surface of the gas storage space using a high-pressure airless spraying process. The coating's permeability coefficient is ≤1×10⁻⁶. -14 m 2 The bond strength with the coal body is ≥1.0 MPa.

[0015] Furthermore, in S6, the air tightness is tested unit by unit using the pressure drop method and the tracer method. The specific requirements are as follows: Pressure drop method: Nitrogen or compressed air is filled into the gas storage cavity to the design pressure, the valve is closed, and the pressure change is monitored within 24~72 hours. The pressure drop rate is ≤0.5% / d to be qualified; Tracer gas method: A trace amount of tracer gas is added to the filling medium, and a detection point is set in the downwind shaft to detect the leakage concentration. The leakage rate is ≤0.1% / d to be qualified.

[0016] Furthermore, in S6, an injection-production well with a diameter of 0.3~0.8 m is constructed above the gas storage cavity. The casing is sealed with the surrounding rock using cementing technology. An injection-production gas valve group, a safety valve, and an emergency shut-off valve are installed at the wellhead. A compressor unit, an expansion generator unit, and a heat exchange system are constructed on the surface and connected to the underground gas storage space through pipelines to form a complete compressed gas energy storage power station.

[0017] According to specific embodiments of the present invention, the deep, extra-thick coal seam mining method guided by a self-sealing compressed gas storage system changes the existing passive goaf energy storage model of "mining coal first, then modifying" by incorporating the space requirements for compressed gas storage as a constraint target into the coal mining process design. Through proactive adjustment and functional construction of the coal mining process, a gas storage space with natural sealing capabilities and high space utilization is simultaneously constructed while recovering coal resources, fundamentally avoiding the mechanical instability, sealing difficulties, and space waste problems caused by the fractured and highly permeable goaf. The following technical effects are specifically disclosed: (1) Solve the problem of insufficient structural stability of the goaf: The goaf structure is formed by room-and-pillar mining and a partition wall support system with predetermined strength is constructed using coal-based solid waste to replace the broken accumulation formed by all caving mining processes, so that the gas storage boundary can obtain controllable and predictable mechanical bearing capacity and meet the requirements for long-term safe service under circulating gas pressure load.

[0018] (2) Solve the fundamental problem of poor sealing performance of gas storage space: break away from the existing technical path of "laying artificial sealing layer on broken high permeability medium", and by preserving the integrity and extremely low permeability of the original coal seam and the top and bottom rock layers, make the main boundary of the gas storage space composed of original coal and rock with natural sealing function, thereby greatly reducing or even eliminating the dependence on complex artificial sealing system and realizing "self-sealing".

[0019] (3) Solve the problem of low utilization rate of underground space: By actively constructing gas storage space structure that has not collapsed during the coal mining process, and by orderly recycling the coal pillars after the solidification of coal-based solid waste partition walls, the space originally occupied by the coal pillars is released as an effective gas storage volume. At the same time, the original coal and rock self-sealing does not require additional sealing layer to occupy space, so that the utilization rate of effective gas storage space is increased to more than 90%, and the gas storage capacity per unit goaf volume is increased by 2 to 4 times, significantly improving the economic efficiency of gas storage.

[0020] (4) Solve the problem of the disconnect between coal mining and energy storage in time and space: Integrate the spatial geometric constraints and mechanical requirements of compressed gas energy storage into the entire process of coal mining process design, so that the coal mining process has the dual functions of "resource recovery" and "storage construction", realize "one mine for two uses", avoid the repeated investment caused by the secondary entry and transformation after mining, and adapt to the engineering characteristics of deep thick coal seams with high stress, strong rheology and severe mining impact, and meet the system requirements of large-scale commercial energy storage. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is an overall flowchart of the deep, ultra-thick coal seam mining method guided by the self-sealing compressed air energy storage of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The self-sealing compressed gas energy storage method for deep, extra-thick coal seam mining provided by this invention pre-constrains the geometry, mechanics, and sealing requirements of the compressed gas energy storage space throughout the entire coal mining process. It simultaneously completes the integrated construction of coal mining and the self-sealing gas storage cavity, relying on the original intact coal and rock to achieve natural self-sealing of the gas storage space, significantly improving the utilization rate of the gas storage space, reducing the investment in sealing engineering, and realizing the integrated and coordinated construction of coal mining and underground energy storage.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, the core idea of ​​the deep, extra-thick coal seam mining method guided by the self-sealed compressed gas storage system provided by this invention is to pre-constrain the coal mining process design with the demand target for compressed gas storage space. Through a combination of room-and-pillar mining, coal-based solid waste partition wall support, and coal pillar recovery processes, a self-sealed gas storage space with the primary boundary of the primary coal and rock is actively constructed during the coal mining process, without relying on complex artificial sealing. The overall technical solution includes the following key steps: S1: Coal mining process design constrained by energy storage targets (1) Applicable coal seam conditions This invention is particularly applicable to deep, thick coal seams, provided that the coal seams meet the following geological conditions: 1) Deep burial depth: Coal seams are generally buried at depths greater than 500 m. Deep coal seams have high in-situ stress (usually vertical stress > 12.5 MPa), dense surrounding rock, poorly developed primary fractures, and extremely low permeability (usually < 10). -17 m 2 This facilitates self-sealing.

[0027] 2) Large thickness: The coal seam thickness is generally greater than 5.0 m (typically 6~10 m). Sufficient mining height can provide ample vertical space for the gas storage chamber, enabling the gas storage unit to have a larger single-chamber volume, reducing the number of partition walls and improving space utilization.

[0028] 3) Good integrity: The original structure of the coal seam and its roof and floor strata is intact, without large faults, folds or collapse columns or other geological structural damage. The roof is generally medium to hard strata, the floor is stable, and joints and fissures within the coal seam are not well developed, ensuring that the roof can remain stable and not collapse under the support of coal pillars after mining, and providing a reliable foundation for subsequent partition wall support and coal pillar recovery.

[0029] 4) Low permeability of the top and bottom plates: The immediate top and bottom plates are mainly composed of low-permeability rock layers such as mudstone, sandy mudstone, and shale, with permeability ≤10. -18 m 2 Together with the coal seam, it forms a complete natural sealed boundary.

[0030] (2) Gas storage parameter design 1) Based on the gas storage power station's requirements for gas storage space, propose the gas storage requirements parameters, such as gas storage pressure P (MPa) and gas storage capacity V (m³). 3 ), working pressure range, cycle frequency, etc.; 2) Based on the principle of ensuring structural stability and uniform gas flow, and according to the geological conditions of deep thick coal seams, such as coal seam thickness H, lithology and mechanical parameters of the roof and floor, geostress state, coal and rock permeability, the room span that meets the requirements of preventing roof cracking and the coal pillar width that meets the requirements of long-term stability are designed according to the theory of roadway (tunnel) surrounding rock stability supplemented by computer numerical simulation or physical similarity simulation test.

[0031] (3) Design of coal mining process parameters 1) Determination of the retention ratio and extraction rate: Under the premise of meeting the aforementioned room span and coal mine width parameters, and in accordance with the requirement that the initial extraction rate should not be too low to ensure coal recovery efficiency, and at the same time reserve sufficient coal pillars to maintain roof stability before the partition wall solidifies, the initial value of the retention ratio is set to 1.5~3.0, corresponding to an initial extraction rate of 60%~75%.

[0032] 2) Mining sequence design: Adopt "skip mining" or "retreat mining" interval mining to avoid simultaneous exposure of large areas of goaf and control the initial pressure step distance of the roof. The mining sequence should be coordinated with the partition wall construction organization to ensure that the partition wall can be constructed in a timely manner after the mining of a room is completed.

[0033] S2: Room-and-pillar mining creates a non-collapsed goaf. (1) Room-and-pillar mining is carried out according to the design parameters. The core requirement of this step is to achieve non-destructive mining of the roof and floor, that is, to avoid causing obvious cracks or structural damage to the roof and floor strata during the mining process, ensuring that their original low permeability characteristics and integrity are fully preserved, and providing a reliable natural boundary for subsequent self-sealing gas storage. Generally, tunneling machines are used for fully mechanized mining, and the cutting height is strictly controlled within the range of coal seam thickness. A 50-100mm protective coal skin is reserved for the roof and floor, and cutting the roof or floor rock is strictly prohibited.

[0034] (2) Inspection and protection of roof and floor integrity. After each room is mined, ultrasonic testing is used to inspect the exposed roof, floor and coal wall. There are no fresh cutting marks or visible cracks on the surface of the roof rock strata, and the longitudinal wave velocity of the ultrasonic wave decreases by ≤5% compared with the original core. The surface of the floor rock strata is flat, without pressure pits or shear cracks, and the permeability of the floor increases by no more than one order of magnitude compared with the original value. There are no peeling or opening cracks at the junction of the coal wall and the roof and floor, and the bonding is good.

[0035] (3) Goaf clearing. After mining is completed, the loose coal on the floor should be cleared manually in conjunction with a small loader. It is strictly forbidden to use heavy scraper conveyors or steel buckets to directly scrape the floor. After clearing, the floor should expose a fresh and flat rock surface, and the thickness of the loose coal residue should be ≤20 mm, so as to provide a clean base surface for the construction of the partition wall and subsequent sealing.

[0036] (4) If geological anomalies such as faults, fracture zones, or collapse columns are exposed, one of the following measures should be taken: adjust the mining plan to avoid the anomaly area; or increase the anchor bolt support in the anomaly area and construct a local reinforced partition wall in advance. If the anomaly area is large and cannot be avoided, the area shall be designated as a non-gas storage area, and only coal shall be recovered without participating in subsequent gas storage functions.

[0037] S3: Construction of partition walls and roof support for coal-based solid waste This step is one of the core components of this invention, combining four functions: permanent roof support, gas storage space partitioning, sealing assistance, and underground disposal of bulk solid waste. Its core innovation lies in using coal-based solid waste as the main material to construct the partition wall, transforming mine solid waste from an environmental burden into a functional engineering material, and realizing "treating waste with waste and turning waste into treasure".

[0038] (1) Partition wall materials The partition wall material uses coal-based solid waste (including coal gangue, fly ash, gasification slag, desulfurization gypsum, etc.) as the main aggregate, and adds cementitious materials (cement, slag, etc.), admixtures, and functional additives (such as expanding agents and water-reducing agents) to prepare a paste material with the following characteristics: 1) Coal-based solid waste accounts for ≥80% of the total solid waste, and cement usage is ≤13%, forming a low-carbon, low-cost, and high-solid-waste utilization paste filling material system; 2) 28-day compressive strength: ≥10 MPa (can be adjusted according to the control requirements of the overlying strata and the gas storage pressure); 3) Permeability: ≤1×10 -14 m 2 (Meets the minimum requirements for gas storage sealing); 4) Pumpability: Slump 180~220 mm; 5) Curing time is controllable: initial setting 2~4 h, final setting 8~12 h; 6) It has a certain degree of micro-expansion (expansion rate 0.01%~0.05%), which is beneficial for close adhesion to the coal wall; 7) The leaching toxicity test meets the relevant requirements of GB 5085.3 to ensure that the material itself is not subject to secondary pollution.

[0039] (2) Layout of partition walls Based on the needs of the gas storage unit division, the mining area should be rationally set up and the room-and-column working face should be deployed, with the partition walls arranged in a strip pattern. To maximize the disposal of solid waste, the partition wall layout should take into account both structural function and disposal volume, and should be arranged according to the following requirements: 1) The density and thickness of the partition walls are determined through numerical simulation optimization and must meet the following requirements: ① The partition walls themselves are strong and safe under confining pressure and gas pressure; ② The spacing between the partition walls (i.e. the span of the final gas storage chamber) does not exceed the critical span of the top rock layer; ③ The number of partition walls is matched with the amount of solid waste to be disposed of.

[0040] 2) Partition wall arrangement: The partition walls are arranged along the dip of the mining area, located on both sides of each room, with a thickness of 8.0~12.0 m and a height level with the mining height. This serves both to control the roof and effectively dispose of coal-based solid waste. To balance the amount of solid waste disposed of and material costs, the strength of the partition walls can be set according to the stress distribution characteristics inside the walls.

[0041] 3) The density and thickness of the partition walls are determined through numerical simulation optimization and must meet the following requirements: ① The partition walls themselves are strong and safe under confining pressure and gas pressure; ② The spacing between the partition walls (i.e., the span of the final gas storage chamber) does not exceed the critical span of the top stratum; ③ The number of partition walls is matched with the amount of solid waste to be disposed of.

[0042] (3) Partition wall construction process Variable-height steel formwork is installed in each coal mining room to form enclosed wall spaces. The paste material is pumped into the formwork, poured in layers, and compacted with vibration. After pouring, moisture curing is carried out; the curing time is determined based on the material ratio and ambient temperature, generally ranging from 7 to 28 days. The strength development of the partition wall needs to be monitored; the next step can only proceed after it meets the standards.

[0043] (4) Sealing enhancement at the coal-rock interface Before pouring the partition wall, the coal wall in contact with it is roughened (e.g., by high-pressure water jet erosion or mechanical roughening) and an interface agent (cement-based penetrating crystalline material or polymer emulsion) is applied to improve bonding strength and impermeability. The micro-expansion characteristics of the partition wall material help to generate lateral compaction stress on the coal wall after curing, sealing the micro-gaps at the interface.

[0044] S4: Recovery of abandoned coal pillars in room-pillar type Once the strength of the partition wall reaches the design value (usually more than 75% of the 28-day strength) and the roof stability monitoring data meets the requirements, the reserved coal pillars are recovered.

[0045] (1) Recycling order The recovery process adopts an intermittent, step-by-step, and zoned approach, with transverse partitions serving as boundaries. Coal pillars are recovered sequentially in each zone, and only after a zone is completed and deemed satisfactory can the next zone be moved on. Within the same zone, coal pillars farther from the main transport roadway are recovered first, gradually advancing towards the shaft entrance. Within the same gas storage unit, only one coal pillar is recovered at a time, with adjacent pillars maintained in support to avoid large-scale depressurization.

[0046] (2) Coal pillar recovery process Based on the layout design of the gas storage chamber, cantilever tunneling machines are used to cut the coal pillars layer by layer as needed. The recovered coal is transported out via the underground transportation system and included in the total coal recovery volume. The coal pillar recovery rate can typically reach 70% to 95%, depending on the coal pillar size, surrounding rock conditions, and recovery process.

[0047] (3) Monitoring should be strengthened during the recovery process, and the recovery speed and process parameters should be controlled according to the detection results. The physical parameters that must be monitored are: 1) Gas monitoring: Gas may be present in deep coal seams. Ventilation and gas detection should be strengthened during the recovery process to ensure safety; 2) Monitoring of roof and floor displacement: Install multi-point displacement gauges or laser rangefinders to monitor roof deformation in real time. Once the warning value is exceeded (usually the maximum allowable subsidence designed), the operation should be stopped immediately; 3) Monitoring of partition wall lateral displacement: Install pressure boxes or strain gauges at key parts of the partition wall to monitor the stress state of the partition wall and prevent the partition wall from becoming unstable due to coal pillar recovery.

[0048] S5: Self-sealing gas storage space formation and barrier wall separation After the coal pillar is recovered, a closed gas storage space is formed, which is jointly enclosed by the original roof strata, the original floor strata, the fresh coal wall and the artificial gate wall.

[0049] (1) Analysis of self-sealing mechanism Most of the gas storage space's boundaries (typically including the roof, floor, and extra-wide coal pillars, accounting for over 80% of the total surface area) are undisturbed primary coal and rock strata with extremely low permeability (coal: 10). -19 ~10 -18 m 2 Mudstone and shale: 10 -21 ~10 -18 m 2 This meets the sealing requirements of compressed air storage facilities (the internationally recognized maximum allowable permeability of the surrounding rock is approximately 1×10⁻⁶). -14 m 2 Specifically: 1) Roof and floor: Complete sedimentary rock layers, with a thickness much greater than the depth affected by gas seepage (generally <1 m), and no large-scale through-cracks, enabling reliable sealing; 2) Coal wall: Boundary coal pillars form an original composite structure with the roof and floor, exhibiting extremely low permeability under original stress conditions; 3) Internal partition walls: Artificial partition walls installed for coal pillar recovery have permeability controlled to ≤1×10⁻⁶. -14m 2 It can meet the sealing requirements and is an intermediate structure between adjacent storage tanks. The spaces on both sides are in approximately the same gas storage pressure environment. Under the condition of a small osmotic pressure difference, there will be no leakage and it will not affect the overall sealing performance. (2) Construction of the outlet gate wall partition At the connection points between the gas storage space and the external roadways and the bottom of the injection and production wells, an ultra-thick concrete barrier wall is constructed to achieve a closed enclosure of the gas storage space. The materials, parameters, and construction procedures are the same as for manual barriers, and the barrier wall is embedded in the surrounding rock to a depth of ≥0.5 m, forming a wedge-shaped interlock with the surrounding rock. Injection and production pipelines and monitoring cable conduits are pre-embedded within the barrier wall.

[0050] (3) Complete sealing of the gas storage space The gas storage space is coated with a 2-5 mm thick polymer cement-based sealing coating using a full-surface high-pressure airless spraying process. The coating's permeability coefficient is ≤1×10⁻⁶. -14 m 2 The bonding strength with the coal body is ≥1.0 MPa. The spraying can seal the micro-cracks generated by pressure relief and reduce surface seepage. This forms a complete airtight sealed space composed of a self-sealing gas storage boundary (original coal and rock and internal partition wall), an outlet gate wall, and local reinforcement spraying.

[0051] S6: Air tightness testing and energy storage system access (1) Air tightness test The air tightness was tested unit by unit using the pressure drop method and the tracer method respectively. The specific requirements were as follows: 1) Pressure drop method: Nitrogen or compressed air was filled into the gas storage unit to the design pressure, the valve was closed, and the pressure change was monitored within 24~72 hours. The pressure drop rate ≤0.5% / d was considered qualified; 2) Tracer gas method: A trace amount of tracer gas (such as SF6) was added to the filling medium, and a detection point was set up in the downwind shaft to detect the leakage concentration. The leakage rate ≤0.1% / d was considered qualified.

[0052] (2) Access to compressed gas energy storage system Injection and production wells (0.3-0.8 m in diameter) are constructed above the gas storage unit. Cementing technology is used to seal the casing between it and the surrounding rock. Injection and production valve assemblies, safety valves, and emergency shut-off valves are installed at the wellhead. Compressor units, expansion generator units, and heat exchange systems are constructed on the surface and connected to the downhole gas storage space through pipelines to form a complete compressed gas energy storage power station.

[0053] The steps described above in this invention are not simply an aggregation of independent methods, but rather involve an organic synergistic relationship and temporal constraints: Step 1 (energy storage target constraint design) determines the geometric parameters of Step 2 (room and pillar coal mining), which in turn affects the morphology of Step 3 (partition wall arrangement) and the feasibility of Step 4 (coal pillar recovery). The strength development progress of Step 3 (partition wall construction) determines the initiation timing of Step 4 (coal pillar recovery). The successful implementation of Step 4 (coal pillar recovery) depends on the protection of the roof integrity by Step 2 (coal mining) and the permanent support of the roof by Step 3 (partition wall). The realization of Step 5 (self-sealing) depends on the protection of the integrity of the original coal and rock by Steps 1-4, and the guarantee of the sealing performance of the partition wall material in Step 3. This closed-loop design of "target guidance - process control - function realization" distinguishes this invention from the loose combination scheme of "mining coal first and then modifying" in the prior art, forming a complete and indivisible technical system.

[0054] The comparison between the present invention and the prior art is shown in Table 1: Table 1

[0055] As shown in Table 1, compared to the existing "mining first, then modifying" goaf post-storage energy storage scheme, this invention pre-constrains the gas storage space requirements of compressed gas energy storage throughout the entire coal mining process, revolutionizing the underlying development logic and achieving integrated simultaneous construction of coal mining and gas storage, eliminating the need for repetitive secondary modification projects. It employs non-destructive room-and-pillar mining combined with permanent support from coal-based solid waste partition walls, preserving the original, intact structure of the roof, floor, and coal walls throughout the process, forming a complete, uncollapsed gas storage cavity. This fundamentally solves the safety problems of fractured surrounding rock and structural instability under high-pressure circulating conditions in traditional collapsed goaf areas. Over 80% of the gas storage cavity boundary is composed of original low-permeability coal and rock, achieving self-sealing based on the natural low permeability of the rock mass, requiring only a small amount of gate walls and thin coating reinforcement, significantly reducing the material, construction, and maintenance costs of artificial sealing systems. Through room-and-pillar mining combined with partition wall compliance and subsequent zoned and intermittent recovery of supporting coal pillars, This method eliminates the space encroachment problem caused by collapsed rock masses, increasing the effective utilization rate of gas storage space from 20%~40% in traditional schemes to over 90%, and increasing the gas storage capacity per unit volume by 2~4 times. At the same time, the coal pillar recovery rate can reach 70%~95%, taking into account the efficient recovery of coal resources. The partition wall uses coal gangue, fly ash and other coal-based solid waste as the main raw materials, with solid waste accounting for no less than 80%, which can dispose of large quantities of mine solid waste in situ underground, reducing the cost of surface environmental remediation. It has four functions: roof support, cavity separation, gas sealing and solid waste disposal. The whole process forms a closed-loop and controllable complete construction sequence, with clear quantification of various parameters and acceptance standards. It is suitable for deep and extra-thick coal seams with a burial depth of over 500m, a thickness of over 5m, and low permeability of the roof and floor. The energy storage project's economics, engineering safety, green and low-carbon benefits and adaptability for large-scale promotion are significantly better than existing technologies.

[0056] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system, characterized in that, Includes the following steps: S1. Coal mining process design constrained by energy storage targets: Based on the gas storage requirements parameters of the compressed gas energy storage power station, and according to the geological conditions of deep thick coal seams, the room span and coal pillar width are designed in accordance with the roadway surrounding rock stability theory and combined with computer numerical simulation or physical similarity simulation test, and the gas storage-adaptive coal mining process parameters are determined. S2. Room-and-pillar mining to form a non-collapsed goaf: Based on the mining process parameters determined in step S1, non-destructive room-and-pillar mechanized tunneling is adopted to preserve the original, intact, low-permeability structure of the coal seam roof and floor and the coal wall throughout the process, forming an independent room-type goaf without roof collapse. S3. Construction of coal-based solid waste partition walls and roof support: Using coal-based solid waste as the main aggregate, adding cementitious materials and functional additives, low-permeability and high-strength paste materials are prepared. Continuous partition walls are poured on both sides of each goaf cavity, and the permanent roof support and gas storage unit space division are completed simultaneously. S4. Recycling of abandoned coal pillars in room-and-pillar mining: Once the solidification strength of the partition wall and the roof deformation monitoring indicators meet the safety threshold, the supporting coal pillars reserved for room-and-pillar mining are recycled in an intermittent manner, from far to near, and in a zoned manner, to release effective gas storage space. S5. Formation of self-sealing gas storage space and isolation of gate wall: After the coal pillar is recovered, the original complete roof and floor plate, boundary coal pillar and partition wall are used as the main sealing boundary of gas storage. A sealing gate wall is constructed at the roadway connection, and a sealing and reinforcing coating is sprayed to form a complete self-sealing gas storage cavity. S6. Air tightness testing and energy storage system access: The air tightness of the self-sealing gas storage cavity is completed by using the pressure drop method and tracer gas method. Injection and production wells are constructed and equipped with ground compression, power generation and heat exchange equipment to form a complete compressed gas energy storage power station.

2. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S1, the gas storage requirements parameters proposed by the compressed gas energy storage power station for the gas storage space include gas storage pressure P, gas storage capacity V, operating pressure range, and circulation frequency. The geological conditions of deep, thick coal seams include: coal seam thickness H, lithology and mechanical parameters of the roof and floor, geostress state, and coal and rock permeability; the deep, thick coal seams adapted in step S1 meet the following geological conditions: burial depth ≥ 500m, coal seam thickness ≥ 5m, and roof and floor permeability ≤ 10. -18 m 2 The rock strata are intact and free from geological structural damage. The design parameters for gas storage-adaptive coal mining processes include: Determination of the retention ratio and extraction rate: Under the premise of meeting the parameters of room span and coal mine width, the initial value of the retention ratio is set at 1.5~3.0, corresponding to an initial extraction rate of 60%~75%; Mining sequence design: adopt skip mining or retreating interval mining to control the initial pressure step distance of the roof.

3. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S2, non-destructive room-and-pillar mechanized tunneling is employed, and the specific operation is as follows: The cutting height of the tunneling machine is strictly limited to the inside of the coal seam. A 50-100mm protective coal skin is reserved in the top and bottom plates, and cutting the rock strata in the top and bottom plates is prohibited. After the single-room mining is completed, the integrity of the top and bottom plates is tested by ultrasonic testing. The core wave velocity attenuation is ≤5% and the increase in the permeability of the bottom plate is not more than one order of magnitude to be considered qualified. Clean the loose coal from the bottom plate until the residual thickness is ≤20mm; When revealing areas with abnormal geological fracturing, increase the density of anchor bolt support and construct locally reinforced partition walls in advance, or designate them as non-gas storage and extraction areas.

4. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, The characteristics of the low-permeability, high-strength paste material in S3 are as follows: Coal-based solid waste accounts for ≥80% of the total solid waste, and cement consumption is ≤13%. 28-day compressive strength: ≥10 MPa; Permeability: ≤1×10 -14 m 2 ; Pumpability: slump 180~220 mm; Curing time is controllable: initial setting 2~4 h, final setting 8~12 h; Expansion rate: 0.01%~0.05%; The leaching toxicity test meets the relevant requirements of GB 5085.3, ensuring that the material itself is free from secondary pollution.

5. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S3, the partition walls are arranged in a strip pattern, specifically according to the following requirements: The density and thickness of the partition walls are determined through theoretical calculations of mine pressure and optimization through computer numerical simulation or physical similarity simulation tests. The following requirements must be met: the partition walls themselves must be strong and safe under confining pressure and air pressure; the spacing between the partition walls must not exceed the critical span of the roof strata; and the number of partition walls must be matched with the amount of solid waste to be disposed of. Partition wall arrangement: arranged along the dip of the mining area, located on both sides of each room, with a thickness of 8.0~12.0 m and a height level with the mining height. The strength of the partition wall is set according to the stress distribution characteristics inside the wall. The construction process for the partition wall is as follows: Variable-height steel formwork is installed in each coal mining room to form a closed wall space. The paste material is pumped into the formwork, poured in layers, and vibrated to compact it. After pouring, it is kept moist and cured. The curing time is determined according to the material ratio and ambient temperature. The strength development of the partition wall is monitored. Only after it meets the standard can the next step be carried out. Before pouring the partition wall, the coal wall in contact with it is roughened and an interface agent is applied.

6. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S4, the recovery of room-pillar type residual coal pillars specifically includes: The process involves interval recovery, progressing from far to near, and advancing in zones. The horizontal partition walls serve as boundaries, and coal pillars are recovered in sequence. Once a zone is completed and passes inspection, the process moves to the next zone. Within the same zone, coal pillars farther from the main transport roadway are recovered first, and the process gradually moves towards the shaft entrance. Within the same gas storage unit, only one coal pillar is recovered at a time, and adjacent coal pillars are kept supported to avoid large-scale depressurization. According to the layout design of the gas storage chamber, a cantilever tunneling machine is used to cut the coal pillar layer by layer. The recovered coal is transported out through the underground transportation system and included in the total coal recovery volume. During the recycling process, monitoring needs to be strengthened, and the recycling speed and process parameters should be controlled according to the detection results. The physical parameters to be monitored include: gas, the amount of movement of the top and bottom plates, and the lateral displacement of the partition walls.

7. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S5, the construction process of the gate wall is as follows: at the connection channel between the gas storage space and the external roadway and the bottom of the injection and production well, a concrete gate wall is constructed to realize the closed isolation of the gas storage space. The materials, parameters and construction operation process are the same as those for the construction of the partition wall, and the embedding depth in the surrounding rock is ≥0.5 m, forming a wedge-shaped engagement with the surrounding rock; injection and production pipelines and monitoring cable sleeves are pre-embedded in the gate wall. Spray-applied sealing and reinforcing coating: A 2-5 mm thick polymer cement-based sealing coating is applied to the entire surface of the gas storage space using a high-pressure airless spraying process. The coating's permeability coefficient is ≤1×10⁻⁶. -14 m 2 The bond strength with the coal body is ≥1.0 MPa.

8. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S6, the air tightness is tested unit by unit using the pressure drop method and the tracer method. The specific requirements are as follows: Pressure drop method: Nitrogen or compressed air is filled into the gas storage cavity to the design pressure, the valve is closed, and the pressure change is monitored within 24~72 hours. The pressure drop rate is ≤0.5% / d to be qualified; Tracer gas method: A trace amount of tracer gas is added to the filling medium, and a detection point is set in the downwind shaft to detect the leakage concentration. The leakage rate is ≤0.1% / d to be qualified.

9. The method for mining deep, extra-thick coal seams guided by a self-sealing compressed air energy storage system according to claim 1, characterized in that, In S6, injection-production wells with a diameter of 0.3 to 0.8 m are constructed above the gas storage cavity. The casing is sealed to the surrounding rock using cementing technology. Injection-production gas valve groups, safety valves, and emergency shut-off valves are installed at the wellhead. Compressor units, expansion generator units, and heat exchange systems are constructed on the surface and connected to the underground gas storage space through pipelines to form a complete compressed gas energy storage power station.

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