Waste coal mine gas storage capacity parameter design method

Abstract

The invention discloses an abandoned coal mine gas storage capacity parameter design method. The method comprises the following steps: (1) calculating the total effective gas storage space volume of an abandoned coal mine gas storage; (2) calculating the adsorption volume of the coal seam to the natural gas; (3) setting safety operation upper limit pressure and lower limit pressure of the abandoned coal mine gas storage; (4) calculating the total storage capacity of the abandoned coal mine gas storage under the upper limit pressure based on the results of the steps (1), (2) and (3); (5) based on the results of the steps (1), (2) and (3), calculating the cushion gas amount of the abandoned coal mine gas storage under the lower limit pressure; and (6) calculating the working gas quantity of the gas storage according to the total storage capacity obtained in the step (4) and the cushion gas quantity obtained in the step (5). The invention provides a technical scheme for the design of the storage capacity of the gas storage rebuilt by the waste coal mine, and is beneficial to solving the problems of insufficient natural gas storage space and waste mine resource utilization.

Description

Technical Field

[0001] This invention relates to the field of underground natural gas storage technology, and more specifically to a method for designing storage capacity parameters for a gas storage facility in an abandoned coal mine. Background Technology

[0002] Many coal mines have closed due to the end of their life cycle, overcapacity, or failure to meet safety and environmental standards. This change not only signifies a large-scale cleanup of outdated and inefficient mining facilities, but also highlights the huge potential space resources, providing possibilities for the reuse and transformation of underground space.

[0003] Therefore, converting abandoned coal mines into natural gas storage facilities is a win-win solution, addressing both the resource utilization of abandoned mines and the demand for natural gas storage facility construction. Under current technological conditions, natural gas storage in abandoned coal mines primarily relies on utilizing the vast space created by room-and-pillar mining and the adsorption capacity of the coal seam itself. In abandoned coal mines with well-preserved roofs and ample underground space, the mining shafts (vertical or inclined) are sealed, and the problem of accumulated water in the goaf is addressed. Finally, a certain number of injection and production wells and monitoring wells are drilled above the goaf, and well control measures are implemented to construct a natural gas storage facility. The design of storage capacity parameters is fundamental to the conversion of abandoned coal mines into natural gas storage facilities and is a crucial indicator of whether an abandoned coal mine is suitable for such conversion. Due to the unique characteristics of the underground space in abandoned coal mines, the storage capacity design requires separate calculations for different storage spaces, such as development roadways, preparation roadways, and mining roadways. Furthermore, the adsorption of natural gas by coal pillars and groundwater must be considered. Currently, China still lacks a scientific and comprehensive method for designing storage capacity parameters for converting abandoned coal mines into gas storage facilities. Summary of the Invention

[0004] The purpose of this invention is to provide a method for designing storage capacity parameters of gas storage facilities in abandoned coal mines, providing a technical solution for the storage capacity design of gas storage facilities converted from abandoned coal mines, which is beneficial to solving the problems of insufficient natural gas storage space and resource utilization in abandoned mines.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for designing storage capacity parameters for a gas storage facility in an abandoned coal mine includes the following steps:

[0007] (1) Calculate the total effective gas storage space volume of the abandoned coal mine gas storage facility;

[0008] (2) Calculate the adsorption volume of natural gas in the coal seam;

[0009] (3) Set the upper and lower pressure limits for safe operation of gas storage facilities in abandoned coal mines;

[0010] (4) Based on the results of steps (1), (2), and (3), calculate the total storage capacity of the abandoned coal mine gas storage facility under the upper limit pressure.

[0011] (5) Based on the results of steps (1), (2), and (3), calculate the cushion gas volume of the abandoned coal mine gas storage tank under the lower limit pressure.

[0012] (6) Calculate the working gas volume of the gas storage tank based on the total storage capacity obtained in step (4) and the cushion gas volume obtained in step (5).

[0013] The abandoned coal mine gas storage facilities are converted from room-and-pillar or room-type mining operations. Their underground gas storage spaces are mainly divided into two types: newly developed mine roadways and old mining area spaces. Mine roadways, due to their relatively good support conditions, usually have a long service life and can be converted into gas storage spaces with basic processing. For mining areas that have fallen into disrepair, as long as the sealing is properly addressed, they can also be transformed into effective gas storage facilities.

[0014] Furthermore, in step (1), the total effective gas storage space volume includes the gas storage space volume of the mine roadways and the space volume of the old goaf area and its overlying rock fracture zone. The formula for calculating the total effective gas storage space volume is:

[0015]

[0016] Among them, V t L is the volume of the gas storage space. i S is the length of the i-th alleyway; i V represents the cross-sectional area of ​​the i-th tunnel; n represents the number of tunnels; k represents the residual space in the overlying fracture zone; and V c This represents the volume of coal extracted.

[0017] Furthermore, the value of k is k = 1 - q, where q is the surface subsidence coefficient.

[0018] Furthermore, in step (2), the adsorption volume is calculated based on the Langmuir adsorption isotherm model, and the calculation formula is as follows:

[0019]

[0020] In the formula: V A q represents the volume of natural gas adsorbed by the coal seam in the gas storage facility under the upper pressure condition. max V is the maximum adsorption capacity per unit mass of adsorbent; K is the Langmuir constant; P is the pressure of the gas storage tank; M is the mass of the coal seam from which natural gas is adsorbed; V m This represents the molar volume of natural gas under standard conditions.

[0021] Furthermore, in step (3), the upper limit pressure P of the abandoned coal mine gas storage facility... max The hydrostatic pressure should not exceed the depth of the mine shaft.

[0022] Furthermore, in step (3), the lower limit pressure P of the abandoned coal mine gas storage tank... min The setting is based on ensuring that the top slab of the storage tank does not suffer tensile failure, and its calculation formula is as follows:

[0023] P min ≥v(σ1+σ2)-|σ ut |

[0024] Where, σ ut σ represents the uniaxial tensile strength of the rock; v represents the Poisson's ratio of the rock; σ1 and σ2 represent the two principal stresses, respectively.

[0025] Furthermore, in step (4), the formula for calculating the storage capacity of the abandoned coal mine gas storage facility is as follows:

[0026]

[0027] Among them, V e P represents the total storage capacity of the gas storage facility. max V is the upper limit pressure of the gas storage facility; t T represents the volume of the gas storage space. cav Temperature of the gas storage facility; T s Standard temperature; Z is the natural gas compressibility factor of the storage space; P s Standard pressure, MPa; q max V represents the maximum adsorption capacity per unit mass of adsorbent; K is the Langmuir constant; M is the mass of the coal seam from which natural gas is adsorbed; V m This represents the molar volume of natural gas under standard conditions.

[0028] Furthermore, in step (5), the formula for calculating the cushion gas volume of the abandoned coal mine gas storage tank is as follows:

[0029]

[0030] Among them, V c P represents the cushion gas volume of the gas storage facility. min V is the lower limit pressure of the gas storage facility; t T represents the volume of the gas storage space. cav Temperature of the gas storage facility; T s Standard temperature; Z is the natural gas compressibility factor of the storage space; P s The standard pressure; q min V represents the maximum adsorption capacity per unit mass of adsorbent at the lower limit pressure; K is the Langmuir constant, reflecting the strength of the adsorption force; M is the mass of the coal seam adsorbing natural gas; V mThis represents the molar volume of natural gas under standard conditions.

[0031] Furthermore, in step (6), the working gas volume of the abandoned coal mine gas storage tank is the difference between the storage capacity and the cushion gas volume, calculated as follows:

[0032]

[0033] Beneficial effects: The storage capacity parameter design method for abandoned coal mine gas storage facilities of the present invention, based on the characteristics of abandoned coal mines and the adsorption characteristics of coal on natural gas, analyzes the gas storage capacity and injection and production capacity of abandoned coal mine gas storage facilities, establishes a scientific and complete storage capacity design technical approach for the reconstruction of abandoned coal mine gas storage facilities, can provide technical reference for related research in this direction, and is conducive to solving the problems of insufficient natural gas storage space and resource utilization of abandoned mines. Attached Figure Description

[0034] Figure 1 This is a flowchart of the storage capacity parameter design for this invention. Detailed Implementation

[0035] The invention will now be further explained with reference to the accompanying drawings.

[0036] The abandoned coal mine gas storage facility involved in this invention is located in a coal mine with room-type mining operations. The underground gas storage space is mainly divided into two types: newly developed mine roadways and old mining area spaces. Mine roadways, due to their relatively good support, usually have a long service life and can be converted into gas storage spaces with basic processing. For mining areas that have fallen into disrepair, as long as the sealing is properly addressed, they can also be transformed into effective gas storage facilities.

[0037] like Figure 1 As shown, the present invention provides a method for designing storage capacity parameters for a gas storage facility in an abandoned coal mine, comprising the following steps:

[0038] (1) Calculate the total effective gas storage space volume of the abandoned coal mine gas storage facility;

[0039] The volume of gas storage space in mine roadways is calculated using the following formula:

[0040]

[0041] Where V1 is the volume of the gas storage space in the mine roadway, in m³. 3 L i S represents the length of the i-th tunnel, in meters (m). i Let be the cross-sectional area of ​​the i-th tunnel, in meters. 2 n represents the number of lanes.

[0042] The spatial volume of the old goaf area and its overlying fracture zone in the mining area is calculated using the following formula:

[0043] V2=k·V c

[0044] Where V2 represents the spatial volume of the old goaf area and its overlying fracture zone, in m³. 3 ;k represents the residual space in the overlying fracture zone, which is related to the mining method and the lithology of the overlying strata. For a typical mining area, a surface subsidence coefficient q is set, then k = 1 - q; V c The volume of coal extracted is expressed in cubic meters (m³). 3 .

[0045] The volume expression for the underground space of an abandoned coal mine is:

[0046] V t =V1+V2

[0047] Right now

[0048] (2) Calculate the adsorption volume of natural gas in the coal seam;

[0049] The adsorption and desorption of natural gas by coal is a crucial factor affecting the storage capacity of gas storage facilities in abandoned coal mines. Based on the Langmuir adsorption isotherm model, the adsorption is assumed to be a monolayer, with only one gas molecule adsorbed at each adsorption site. The adsorption capacity is obtained through Langmuir isotherms and then converted into volume. The volume of natural gas adsorbed in the coal seam is calculated using the following formula:

[0050]

[0051] Among them, V A q represents the volume of natural gas adsorbed by the coal seam in the gas storage facility under the upper pressure condition. max The maximum adsorption capacity per unit mass of adsorbent, expressed in cm³. 3 / g; K is the Langmuir constant, reflecting the strength of the adsorption force; P is the pressure of the gas storage tank, in MPa; M is the mass of the coal seam adsorbing natural gas, in g; V m The molar volume of natural gas under standard conditions is approximately 0.0224 m³. 3 / mol.

[0052] (3) Set the upper and lower pressure limits for safe operation of gas storage facilities in abandoned coal mines;

[0053] When setting the maximum operating pressure of a gas storage facility, the integrity of the facility must be ensured. High pressure can cause the development of fissures in the surrounding rock, similar to the principle of hydraulic fracturing in geostress measurements. Based on the magnitude of the geostress, the ultimate pressure is calculated, and then multiplied by a proportionality coefficient to determine the maximum gas storage pressure. The maximum gas storage pressure of an abandoned coal mine gas storage facility should not exceed the hydrostatic pressure at its burial depth.

[0054] Setting the lower limit operating pressure for the storage facility must ensure that the roof does not experience tensile failure. Based on the maximum elongation strain theory, the operating pressure is approximately equal to the minimum principal stress of the surrounding rock. The lower limit pressure P of an abandoned coal mine gas storage facility... min The calculation formula is as follows:

[0055] P min ≥v(σ1+σ2)-|σ ut |

[0056] Where, σ ut σ represents the uniaxial tensile strength of the rock; v represents the Poisson's ratio of the rock; σ1 and σ2 represent the two maximum principal stresses, respectively.

[0057] (4) Calculate the total storage capacity of the abandoned coal mine gas storage facility under the upper limit pressure;

[0058] Calculating the storage capacity of a gas storage facility in an abandoned coal mine requires considering both the volume of natural gas stored in the storage space under the upper pressure limit and the volume of natural gas adsorbed in the coal seam within the storage facility under the same pressure limit. The calculation model for the storage capacity of a gas storage facility in an abandoned coal mine is as follows:

[0059]

[0060] Among them, V e This refers to the total storage capacity of the gas storage facility, measured in meters (m). 3 ;P max V represents the upper limit pressure of the gas storage facility, in MPa. t This refers to the volume of the gas storage space, in meters (m). 3 ;T cav Temperature of the gas storage facility, K; T s Standard temperature (K); Z is the natural gas compressibility factor of the storage space; P s Standard pressure, unit is MPa; q max V represents the maximum adsorption capacity per unit mass of adsorbent, in mol; K is the Langmuir constant, reflecting the strength of the adsorption force; M is the mass of the coal seam adsorbing natural gas, in g; V m The molar volume of natural gas under standard conditions is approximately 0.0224 m³. 3 / mol.

[0061] (5) Calculate the cushion gas volume of the abandoned coal mine gas storage tank under the lower limit pressure;

[0062] The cushion gas volume in a gas storage facility refers to the volume of natural gas remaining in the storage facility under the lower pressure condition. The calculation model for the cushion gas volume of a gas storage facility in an abandoned coal mine is as follows:

[0063]

[0064] In the formula: V cThe gas volume of the gas storage facility is expressed in cubic meters (m³). 3 ;P min V represents the lower limit pressure of the gas storage facility, in MPa. t This refers to the volume of the gas storage space, in meters (m). 3 ;T cav Temperature of the gas storage facility, in Kelvin (K); T s Standard temperature, in Kelvin; Z is the natural gas compressibility factor of the storage space; P s Standard pressure, unit is MPa; q min V represents the maximum adsorption capacity per unit mass of adsorbent at the lower limit pressure, expressed in mol; K is the Langmuir constant, reflecting the strength of the adsorption force; M is the mass of the coal seam adsorbing natural gas, expressed in g; V m The molar volume of natural gas under standard conditions is approximately 0.0224 m³. 3 / mol.

[0065] (6) Calculate the working gas volume of the gas storage tank;

[0066] The working gas volume of a gas storage facility refers to the difference between the storage capacity and the cushion gas volume. The calculation model for the working gas volume of a gas storage facility in an abandoned coal mine is as follows:

[0067]

[0068] The present invention will be further described below with reference to embodiments. A better understanding of the present invention can be achieved through the following embodiments.

[0069] Example

[0070] The mining method used in this mine is the room-and-pillar method. The average coal seam thickness is 4.34m, and the average overburden depth reaches 340m. This coal seam has a simple geological structure and good stability. Its immediate roof is a 6.2m thick layer of argillaceous sandstone, overlain by a 27m thick layer of hard feldspathic sandstone. These rock layers have strong compressive, tensile, and shear resistance, and are classified as a Class II medium-risk roof according to caving classification. The overburden is a 5.35m thick layer of mudstone, with good spatial continuity and low water content and permeability, and almost no fractures. The coal seam is generally gentle, exhibiting an almost horizontal monocline structure, without obvious large folds or faults, and has a simple geological structure.

[0071] like Figure 1 As shown, this invention provides a method for designing storage capacity parameters for a gas storage facility in an abandoned coal mine. Based on the characteristics of abandoned coal mines and the adsorption properties of coal for natural gas, the method analyzes the gas storage capacity and injection / production capacity of the gas storage facility. Through effective storage volume calculation, operating pressure design, and storage capacity technical index design, the storage capacity parameters are finally determined. Specifically, the method includes the following steps:

[0072] S1, Calculation of underground gas storage space

[0073] The goaf areas of the three mining panels were selected for conversion into gas storage facilities. The first panel has a planar area of ​​approximately 390,000 m². 2 The average mining height is 3.3m, and the extraction rate of this mining method is 51.03%; the planar area of ​​the second panel is approximately 534,500 m². 2 The average mining height is 3 meters, and the extraction rate of the room-type mining method is 50.81%; the planar area of ​​the three-panel area is approximately 364,300 square meters. 2 The average mining height is 3m, and the extraction rate of the room-type mining is 50.42%. Without considering rock collapse expansion and other effects, the underground space of the three panels is calculated:

[0074] V t =S×H×P

[0075] In the formula: V t The underground space volume of the gas storage facility converted from the mine is expressed in m³. 3 S represents the planar area of ​​the panel, in meters. 2 H represents the average mining height; P represents the extraction rate of room-type mining.

[0076] Calculations show that the underground space volume of the first area is 656,800 m³. 3 The underground space volume of the second phase area is 814,700 m³. 3 The underground space volume of the three districts is 551,000 m³. 3 The total gas storage capacity is 2,022,500 m³. 3 .

[0077] S2, Gas storage facility operating pressure design

[0078] Based on the mine's burial depth of 340m, hydrostatic pressure of 2.5MPa, and constant ground temperature of approximately 20℃, the maximum gas storage pressure is designed to be 80% of the mine's hydrostatic pressure, with an upper limit pressure of 2.0MPa. The minimum operating pressure of the gas storage facility should be greater than the minimum principal stress of the surrounding rock, with a lower limit pressure of 0.5MPa. The designed operating pressure for the gas storage facility is 0.5MPa-2.0MPa.

[0079] S3, Calculation of natural gas storage volume in gas storage space

[0080] The gas storage facility has an upper pressure limit of 2.0 MPa and a temperature of 293.15 K. Referring to the natural gas compressibility factor quick reference table, the compressibility factor of natural gas at 20℃ and 2.0 MPa is 0.956. The storage capacity is 2,022,500 m³. 3 The volume of natural gas stored in underground gas storage spaces under standard conditions is calculated as follows:

[0081]

[0082] In the formula: V S The storage space contains the volume of natural gas under standard conditions, in cubic meters (m³). 3 ;P max V represents the upper limit pressure of the gas storage facility, in MPa. t This refers to the volume of the gas storage space, in meters (m). 3 Z represents the natural gas compressibility factor for the gas storage space; T cav Temperature of the gas storage facility, in Kelvin (K); T s Standard state temperature, 273.15 K; P s The standard pressure is 0.101325 MPa.

[0083] Calculations show that at 20℃ and 2.0MPa pressure, the underground space of the gas storage facility can store approximately 38.93 million cubic meters of gas. 3 Natural gas (under standard conditions, i.e., 0°C and 1 atmosphere).

[0084] S4, Calculation of the volume of natural gas adsorbed in the coal seam.

[0085] According to the adsorption and desorption tests of natural gas by coal, the maximum adsorption capacity of coal is 8.3 cm³. 3 / g, with a maximum adsorption capacity of 4cm³ at 2.0MPa. 3 / g, the porosity of the coal sample is 0.014, and the Langmuir constant is 0.447 (MPa). -1 The coal sample mass capable of absorbing natural gas in this mining area is approximately 2.55 million tons. The volume of natural gas absorbed in the coal seam is calculated as follows:

[0086]

[0087] In the formula: V A q represents the volume of natural gas adsorbed by the coal seam in the gas storage facility under the upper pressure condition. max The maximum adsorption capacity per unit mass of adsorbent, expressed in cm³. 3 / g; K is the Langmuir constant, reflecting the strength of the adsorption force; P is the pressure of the gas storage tank, in MPa; M is the mass of the coal seam adsorbing natural gas, in g; V m The molar volume of natural gas under standard conditions is approximately 0.0224 m³. 3 / mol.

[0088] Calculations show that the volume of natural gas adsorbed in the coal seams of this mining area is approximately 10.2 million m³. 3 .

[0089] S5, Storage Capacity Technical Specifications Design

[0090] (1) Calculation of total storage capacity of gas storage facility

[0091] The total storage capacity of the gas storage facility should be calculated by adding the volume of natural gas in the storage space under standard conditions, plus the volume of natural gas adsorbed in the coal seam and the volume of natural gas adsorbed in the mine water, all under the upper limit pressure (2.0 MPa). Since the amount of natural gas adsorbed by the mine water is extremely small, this part is ignored for ease of calculation. The total storage capacity of the gas storage facility is then calculated as follows:

[0092] V e =V S +V A

[0093] Calculations show that the total storage capacity of the gas storage facility is 49.13 million m³. 3 .

[0094] (2) Calculation of cushion gas volume in gas storage

[0095] The cushion gas volume of the gas storage facility is the volume of natural gas stored in the facility under standard conditions at the lower limit pressure. The operating pressure range of this gas storage facility is 0.5 MPa-2.0 MPa, with the lower limit pressure being 0.5 MPa. The cushion gas volume of the gas storage facility is calculated as follows:

[0096]

[0097] In the formula: V c The gas volume of the gas storage facility is expressed in cubic meters (m³). 3 ;P min V represents the lower limit pressure of the gas storage facility, in MPa. t This refers to the volume of the gas storage space, in meters (m). 3 ;T cav Temperature of the gas storage facility, K; T s Standard temperature, in Kelvin; Z is the natural gas compressibility factor of the storage space; P s Standard pressure, unit is MPa; q min V represents the maximum adsorption capacity per unit mass of adsorbent at the lower limit pressure, expressed in mol; K is the Langmuir constant, reflecting the strength of the adsorption force; M is the mass of the coal seam adsorbing natural gas, expressed in g; V m The molar volume of natural gas under standard conditions is approximately 0.0224 m³. 3 / mol.

[0098] Calculations show that the underground space of this mine can store approximately 9.3 million cubic meters of gas at a pressure of 0.5 MPa. 3 The natural gas (standard state) adsorbed on the coal sample had a volume of 118,500 m³. 3 The gas storage facility has a cushion gas volume of 9.41 million m³. 3 .

[0099] (3) Calculation of working gas volume for gas storage

[0100] The working gas volume of the gas storage facility is the difference between the storage capacity and the cushion gas volume. Calculations show that the working gas volume of the gas storage facility is approximately 29,812,500 m³. 3 .

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for designing storage capacity parameters of a gas storage facility in an abandoned coal mine, characterized in that: Includes the following steps: (1) Calculate the total effective gas storage space volume of the abandoned coal mine gas storage facility; (2) Calculate the adsorption volume of natural gas in the coal seam; (3) Set the upper and lower pressure limits for safe operation of gas storage facilities in abandoned coal mines; (4) Based on the results of steps (1), (2), and (3), calculate the total storage capacity of the abandoned coal mine gas storage facility under the upper limit pressure. (5) Based on the results of steps (1), (2), and (3), calculate the cushion gas volume of the abandoned coal mine gas storage tank under the lower limit pressure; (6) Calculate the working gas volume of the gas storage tank based on the total storage capacity obtained in step (4) and the cushion gas volume obtained in step (5).

2. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: The abandoned coal mine gas storage facility was converted from a coal mine with room-and-pillar mining or room-and-column mining.

3. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (1), the total effective gas storage volume includes the gas storage volume of the mine roadways and the volume of the old goaf area and its overlying fracture zone. The formula for calculating the total effective gas storage volume is: Among them, V t L is the volume of the gas storage space. i S is the length of the i-th alleyway; i V represents the cross-sectional area of ​​the i-th tunnel; n represents the number of tunnels; k represents the residual space in the overlying fracture zone; and V c This represents the volume of coal extracted.

4. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 3, characterized in that: The value of k is k = 1 - q, where q is the surface subsidence coefficient.

5. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (2), the adsorption volume is calculated based on the Langmuir adsorption isotherm model, and the calculation formula is as follows: In the formula: V A q represents the volume of natural gas adsorbed by the coal seam in the gas storage facility under the upper pressure condition. max V is the maximum adsorption capacity per unit mass of adsorbent; K is the Langmuir constant; P is the pressure of the gas storage tank; M is the mass of the coal seam from which natural gas is adsorbed; V m This represents the molar volume of natural gas under standard conditions.

6. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (3), the upper limit pressure P of the abandoned coal mine gas storage tank max The hydrostatic pressure should not exceed the depth of the mine shaft.

7. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (3), the lower limit pressure P of the abandoned coal mine gas storage tank min The setting is based on ensuring that the top slab of the storage tank does not suffer tensile failure, and its calculation formula is as follows: P min ≥v(σ1+σ2)-|σ ut | Where, σ ut σ represents the uniaxial tensile strength of the rock; v represents the Poisson's ratio of the rock; σ1 and σ2 represent the two principal stresses, respectively.

8. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (4), the formula for calculating the storage capacity of the abandoned coal mine gas storage facility is as follows: Among them, V e P represents the total storage capacity of the gas storage facility. max V is the upper limit pressure of the gas storage facility; t T represents the volume of the gas storage space. cav Temperature of the gas storage facility; T s Standard temperature; Z is the natural gas compressibility factor of the storage space; P s Standard pressure, MPa; q max V represents the maximum adsorption capacity per unit mass of adsorbent; K is the Langmuir constant; M is the mass of the coal seam from which natural gas is adsorbed; V m This represents the molar volume of natural gas under standard conditions.

9. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (5), the formula for calculating the cushion gas volume of the abandoned coal mine gas storage tank is as follows: Among them, V c P represents the cushion gas volume of the gas storage facility. min V is the lower limit pressure of the gas storage facility; t T represents the volume of the gas storage space. cav Temperature of the gas storage facility; T s Standard temperature; Z is the natural gas compressibility factor of the storage space; P s The standard pressure; q min V represents the maximum adsorption capacity per unit mass of adsorbent at the lower limit pressure; K is the Langmuir constant, reflecting the strength of the adsorption force; M is the mass of the coal seam adsorbing natural gas; V m This represents the molar volume of natural gas under standard conditions.

10. The method for designing storage capacity parameters of an abandoned coal mine gas storage facility according to claim 1, characterized in that: In step (6), the working gas volume of the abandoned coal mine gas storage facility is the difference between the storage capacity and the cushion gas volume, calculated as follows:

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