Method for evaluating stability of multi-shaft horizontal salt cavern hydrogen storage

Abstract

The invention relates to a method for evaluating the stability of a multi-shaft horizontal salt cavern hydrogen storage reservoir. The method comprises the following steps: evaluating geological conditions; s2, analyzing morphological parameters of the three-dimensional cavity of the salt-cavern hydrogen storage; determining a stability evaluation index of the salt-cavern hydrogen storage; establishing a three-dimensional geomechanical model and performing simulation calculation; evaluating the influence of long-term operation of the salt-cavern hydrogen storage; carrying out field real-time monitoring and risk early warning; and stability evaluation index calibration: calibrating the stability evaluation indexes by combining the on-site real-time monitoring result of the hydrogen storage library in actual operation, and determining the stability of the multi-shaft horizontal salt cavern hydrogen storage library.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen energy storage by resource utilization of salt caverns, and particularly to a stability evaluation technology for a multi-shaft horizontal salt cavern hydrogen storage reservoir under cyclic injection and production. Background Technique

[0002] With the transformation of the global energy structure, hydrogen energy, as an important part of clean energy, its storage and utilization technologies have become research hotspots. Salt cavern hydrogen storage has advantages such as good geological stability, tightness, and low construction cost, and is regarded as an ideal hydrogen storage method. However, due to the influence of factors such as the special large-span cavity roof structure (which is extremely prone to unbalanced deformation, damage, and even cracking, and is likely to become a gas leakage channel), complex geological conditions (including interlayers and faults), diverse cavity shapes, operating pressure fluctuations, temperature changes, hydrogen migration effects, and the interaction between hydrogen and surrounding rocks in a multi-shaft horizontal salt cavern hydrogen storage reservoir, it will face more complex geomechanical problems and potential hydrogen leakage risks, making stability evaluation a key challenge.

[0003] A salt cavern hydrogen storage reservoir is a technology that utilizes the solubility of salt rock in a natural salt layer to form a hydrogen storage space by artificial water injection. Among them, the double-well convection leaching method has a faster water dissolution cavity formation speed and can be used to build larger salt cavern cavities. However, the horizontal cavity shape formed by the double-well convection leaching method is usually dumbbell-shaped (see Figure 2), which has a large difference from the designed form and cannot effectively utilize the layered salt rock space in the given area. The basic process of solution mining for a multi-shaft horizontal salt cavern hydrogen storage reservoir is generally as follows: Drill new wells on the basis of the cavity formed by the double-well convection leaching method. The well spacing is usually 250m to 500m, that is, drill two new vertical wells 12 respectively at the middle connection of the double wells 13 in the target salt layer to connect the target salt layer with the ground. Connect the bottom cavities at the middle connection of the two vertical wells through the single-well convection method. There is sediment 11 at the bottom containing a small amount of insoluble impurities accumulated during the solution mining of the salt cavern. Arrange the pipe string according to the cavity formation requirements. Install the injection-production casing 5 and the cavity formation casing 14 in the two vertical wells respectively. The injection flow rate is adjusted by the injection control valve 8. Inject the oil (gas) cushion protection liquid through the oil injection casing 7. The injection flow rate of the oil (gas) cushion protection liquid is adjusted by the oil (gas) injection control valve 10 to prevent the salt cavern at the well end from developing excessively upward, so as to ensure that the roof form of the salt cavern cavity at the well end is stable and the thickness of the roof protection layer reaches the preset thickness. Then inject fresh water or unsaturated brine through the two newly built vertical wells, and discharge the brine through the old well brine discharge casing 6 on both sides of the high-concentration brine. Adjust the brine flow rate through the brine discharge control valve 9. Continuously and alternately adjust the positions of the injection water pipes 5 of the two newly built vertical wells, step by step raise the height of the cavity formation casing 14 and the oil cushion 4, and supplement the amount of the oil (gas) cushion protection liquid. Inject water into the cavity through the two middle new wells 12, and discharge the brine from the side wells on both sides for annular cavity formation. In such a cyclic manner, a new cavity will be formed under the new vertical wells, and finally a cavity shape that meets the requirements will be obtained (see Figure 3 ). This method can form a cavity with a larger volume in the given layered salt mine space, making the utilization efficiency of the salt mine formation higher, increasing the storage capacity of the hydrogen storage reservoir. However, compared with the double-well dumbbell-shaped cavity, the safety and stability of the multi-shaft horizontal cavity formed after the new wells are built need to be further explored.

[0004] Hydrogen storage reservoirs are mainly applied in seasonal peak shaving, daily consumption and industrial fields. The injection-production cycle is variable and the physical, chemical and biological reactions are complex, and the disaster risk is high during operation. At present, the salt cavern hydrogen storage technology is still in the development stage. The existing evaluation methods mostly focus on single-factor analysis, lacking a comprehensive evaluation of geological conditions, salt cavern structures, operation parameters and monitoring data, and it is difficult to comprehensively reflect the stability of the hydrogen storage reservoir. There is an urgent need for a stability evaluation method for multi-shaft horizontal salt cavern hydrogen storage reservoirs to ensure the safety during cyclic injection-production of large-capacity multi-shaft horizontal cavities, avoid safety hazards such as leakage and rupture caused by the instability of the hydrogen storage reservoir, and provide theoretical guidance and technical support for practical applications. Summary of the Invention

[0005] The present invention provides a method for evaluating the stability of a multi-shaft horizontal salt cavern hydrogen storage reservoir, which comprehensively considers the salt cavern geological conditions, cavity structure, collection of hydrogen storage characteristic parameters, and the influence of long-term operation. Through a multi-step and multi-level analysis process, a comprehensive and accurate evaluation of the stability of the hydrogen storage reservoir is achieved, providing a scientific basis for the safe and efficient operation of hydrogen energy storage facilities. The technical solution is as follows:

[0006] A method for evaluating the stability of a multi-shaft horizontal salt cavern hydrogen storage reservoir, comprising the following steps:

[0007] S1, Geological condition assessment;

[0008] S2, Analysis of the three-dimensional cavity shape parameters of the salt cavern hydrogen storage reservoir, including: measuring the three-dimensional cavity shape of the hydrogen storage reservoir with vertical and inclined wells, and obtaining the horizontal cavity shape parameters from the measurement results of the three-dimensional cavity shape, including: the burial depth of the salt cavern top, the burial depth of the salt cavern bottom, the height of the salt cavern, the maximum diameter of the salt cavern cross-section, and the length of the horizontal cavity. The three-dimensional coordinate values of each point of the cavity are given by the measurement results, and the three-dimensional structure contour of the salt cavern is drawn;

[0009] S3, Determination of the stability evaluation indexes of the salt cavern hydrogen storage reservoir, including:

[0010] S31, Since salt rock exhibits typical brittle and plastic failure characteristics under cyclic internal pressure, select the expansion safety factor, equivalent strain, maximum deformation of key points on the cavity wall, cavity top and cavity bottom, volume shrinkage rate, and plastic zone volume as the stability evaluation indexes of the salt cavern hydrogen storage reservoir;

[0011] S32, When the volume of the salt cavern hydrogen storage reservoir is under cyclic creep load, the completion string at the top of the salt cavern is at risk of axial tensile failure. Take the axial strain of the completion string as the stability evaluation index of the salt cavern hydrogen storage reservoir;

[0012] S33, When the salt cavern hydrogen storage reservoir shows seal failure, it is manifested as the seepage range exceeding the limit and hydrogen permeating into the overlying formation. Select the hydrogen penetration safety factor and hydrogen seepage range as the stability evaluation indexes of the salt cavern hydrogen storage reservoir;

[0013] S34, According to the requirements of the safety critical value in the cavity design specification of the salt cavern gas storage reservoir, combined with the formation structure, physical and mechanical parameters of salt rock, the measurement results of the three-dimensional cavity shape of the target salt cavern hydrogen storage reservoir, and the operation parameters of the salt cavern hydrogen storage reservoir in the specific construction area where the target salt cavern hydrogen storage reservoir is located, determine the safety critical values corresponding to the stability evaluation indexes of the salt cavern hydrogen storage reservoir determined in S31, S32, and S33. Each stability evaluation index of the salt cavern hydrogen storage reservoir should be lower than the critical safety value, and adjust and optimize the parameters affecting the stability of the hydrogen storage reservoir according to the evaluation results;

[0014] S4, Establishment and simulation calculation of the three-dimensional geomechanical model, including:

[0015] S41. Based on the formation structure where the salt cavern hydrogen storage reservoir is located, the physical and mechanical parameters of the salt rock, and the detected three-dimensional shape and size of the salt cavern hydrogen storage reservoir, establish a three-dimensional geomechanical model; divide the established three-dimensional geomechanical model into grids, and then check the independence of the grid size, the convergence of the calculation results, and the grid quality to ensure the reliability of the calculation results;

[0016] S42. According to the established three-dimensional geomechanical model and the set boundary conditions, analyze the cyclic internal pressure of the cavity, that is, the force exerted by the hydrogen gas in the cavity on the cavity wall during the stable operation of the salt cavern hydrogen storage reservoir, the cycle period, that is, the time required for the salt cavern hydrogen storage reservoir to complete one cycle in the four stages of gas injection and pressurization, high-pressure operation, gas production and depressurization, and low-pressure operation, the maximum and minimum gas production rates, that is, the maximum and minimum rates of increase and decrease of the hydrogen gas pressure in the cavity during the emergency gas production and gas injection of the salt cavern hydrogen storage reservoir, the pillar width, that is, the salt body within the minimum width range between the cavity walls of two salt cavern hydrogen storage reservoirs, the influence of different shaft spacings and roof spans, that is, the length of the salt body retained at the top of the salt cavern after the salt layer is dissolved, and the cavity shape, cavity size, and cavity burial depth parameters on the stability of the salt cavern hydrogen storage reservoir, analyze the changes in the stress field and seepage field during the hydrogen injection and production processes of the hydrogen storage reservoir under different conditions, the distribution of the plastic zone, the seepage pressure, and the surrounding rock deformation index, and predict potential unstable areas;

[0017] S43. According to the stability evaluation indexes of the salt cavern hydrogen storage reservoir established in S3, obtain the values of each evaluation index and draw the corresponding cloud diagrams, evaluate the stability of the multi-shaft horizontal salt cavern hydrogen storage reservoir according to the critical safety values of the evaluation indexes, and optimize and adjust the parameters affecting the stability of the hydrogen storage reservoir based on the evaluation results;

[0018] S5. Evaluation of the long-term operation impact of the salt cavern hydrogen storage reservoir

[0019] S6. On-site real-time monitoring and risk warning: Install monitoring equipment at key positions of the hydrogen storage reservoir, and use sensors to real-time monitor geological deformation, hydrogen gas pressure and temperature, and hydrogen gas leakage parameters; establish a risk warning system;

[0020] S7. Calibration of stability evaluation indexes: Calibrate the above stability evaluation indexes in combination with the on-site real-time monitoring results of the actually operating hydrogen storage reservoir to determine the stability of the multi-shaft horizontal salt cavern hydrogen storage reservoir.

[0021] Furthermore, S1 includes:

[0022] S11, Acquisition of in-situ stress in salt mine formations: Conduct geological surveys on the target formations of the hydrogen storage reservoir to understand the lithology, thickness, and burial depth parameters of the formations, design a suitable small-scale hydraulic fracturing test plan, drill one or more wells in the target formations to the target formations for hydrogen storage construction, and conduct small-scale hydraulic fracturing tests to obtain the minimum horizontal stress, maximum horizontal stress, vertical in-situ stress, and stress gradient parameters of the salt rock formations;

[0023] S12, acquisition of salt mine stratigraphic structural parameters: using 3D seismic exploration technology to obtain stratigraphic structural parameters of the hydrogen storage construction area, including: sedimentary rhythm of the salt-bearing layer where the cavity is located, fault structure distribution, salt rock distribution characteristics, salt layer top and bottom plate characteristics, and interlayer distribution characteristics;

[0024] S13, acquisition of physical and mechanical parameters of salt rock: core sampling is carried out in the near-field drilling data well outside the hydrogen storage reservoir, and the formation core of the data well in the expanded hydrogen storage reservoir area is obtained for testing.

[0025] Furthermore, in S13, the coring range was from the surface to 100m below the bottom of the salt rock layer, and core samples of the overlying rock layer, salt rock layer and underlying stratum were obtained. The cores of the data well were processed into standard samples required by different test types. The tests carried out included: density test, uniaxial compressive strength test, tensile strength test, internal friction angle test, cohesion test, steady-state creep rate test, breakthrough pressure test, permeability test and porosity test; all the above tests were carried out on the salt rock samples; all the above tests except the breakthrough pressure test were carried out on the mudstone and interlayer samples after being immersed in saturated brine to obtain the basic physical and mechanical parameters of the sediment.

[0026] Furthermore, in S2, by continuously adjusting the horizontal measurement distance on the vertical plane and the measurement inclination angle on the horizontal plane at different depths and different inclination angles, the three-dimensional coordinate values ​​of each point on the irregular contour surface of the top, bottom and local cantilevered and finger-like protrusions on the cavity wall of the entire cavity are determined.

[0027] Furthermore, in S31, the deformation is the displacement of each node of the cavity unit, the volume of the plastic zone is the total volume of the surrounding rock unit that undergoes tensile and shear failure, the hydrogen seepage range is the maximum range of pore pressure change in the salt cavern surrounding rock caused by hydrogen injection and production, and the maximum deformation of the key points of the cavity wall, cavity top and cavity bottom, the volume of the plastic zone, and the hydrogen seepage range are obtained from the numerical simulation results;

[0028] The expansion safety factor is used to predict the expansion failure of salt rock. The expansion of salt rock is mainly affected by the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor. Its expression is:

[0029]

[0030] Among them, SF is the dilation safety factor, I1 is the first invariant of the stress tensor, and J2 is the second invariant of the deviatoric stress tensor. Their expressions are as follows:

[0031] I1 = σ1 + σ2 + σ3

[0032]

[0033] Among them, σ1, σ2, and σ3 are the first, second, and third principal stresses respectively;

[0034] According to the calculation result of the dilation safety factor SF, estimate the safety critical value of local damage, failure, or collapse of the salt cavern.

[0035] The equivalent strain mentioned above refers to the damage caused by the salt rock under three-dimensional in-situ stress and plastic deformation. The damage of the salt rock around the salt cavern is evaluated through the equivalent strain, which characterizes the plastic creep safety of the cavity. The equivalent strain is used to define and measure the damage of the salt rock through the change of modulus before and after damage. Its expression is as follows:

[0036]

[0037] Among them, ε' is the equivalent strain, and J2' is the second invariant of the deviatoric strain tensor;

[0038]

[0039] Among them, where ε x 、ε y 、ε z 、ε xy 、ε yz 、ε xz are strain components in different directions;

[0040] The volume shrinkage rate mentioned above refers to the ratio of the reduction in the total volume of the cavity after a certain operation time to the initial volume. Its expression is as follows:

[0041]

[0042] Among them, V S is the volume shrinkage rate, V1 is the initial volume of the salt cavern, V2 is the volume of the salt cavern after a certain operation time. According to the design life of the salt cavern hydrogen storage reservoir, estimate the critical safety value of the volume shrinkage rate.

[0043] Further, in S4, the established three-dimensional geomechanical model is as follows: it is in the shape of a cuboid, and the side lengths of the cuboid are not less than 5 times the maximum diameter in each side direction of the cavity of the salt cavern gas storage reservoir; the salt rock layer is located in the middle of the model and the salt rock layer is watertight, and the hydrogen storage cavity is located in the middle of the salt rock layer; a designed cyclic internal pressure acts on the surface of the cavity wall of the salt cavern; it is assumed that the three-dimensional salt cavern hydrogen storage reservoir model is under the initial in-situ stress state of triaxial equal pressure, and the average gravity of the overlying rock formation is applied to the top surface of the model; horizontal constraints are applied to the four vertical surfaces of the model to restrict the model from undergoing horizontal deformation; a fixed constraint is applied to the bottom surface of the model to restrict the model from undergoing horizontal and vertical deformation.

[0044] Further, in S43, the method for optimizing and adjusting the parameters affecting the stability of the hydrogen storage reservoir according to the evaluation results is as follows:

[0045] (1) If the evaluation result shows that the hydrogen storage reservoir is in a stable state and there is a safety margin, continue to operate normally and appropriately optimize the hydrogen storage and extraction operations to improve efficiency, including appropriately increasing the hydrogen injection rate;

[0046] (2) If the evaluation result shows that the stability of the hydrogen storage reservoir is in a critical state, it is necessary to take timely measures for adjustment, including reducing the hydrogen pressure, adjusting the operating temperature of the hydrogen storage reservoir, and strengthening the monitoring frequency of the hydrogen storage reservoir, and closely monitoring its stability changes;

[0047] (3) If the evaluation result shows that there is a risk of instability in the hydrogen storage reservoir, immediately stop the hydrogen injection or extraction operation, inspect the hydrogen storage reservoir, analyze the reasons for the instability, and take corresponding improvement measures until the stability is restored to the safe range and then put it back into operation.

[0048] Further, S5 includes,

[0049] (1) Salt cavern stability assessment: Analyze the stability of the salt cavern during long-term operation, including the creep characteristics of the salt rock, the change of geological stress, and the influence of possible geological disasters on the stability of the salt cavern;

[0050] (2) Hydrogen leakage risk and monitoring: Evaluate the hydrogen leakage risk in the salt cavern, including the possible reasons for leakage, the leakage amount, and the impact of leakage on the environment and safety;

[0051] (3) Maintenance and operation costs: Consider the maintenance and operation costs of the salt cavern hydrogen storage facility, including the costs of regular inspection, maintenance, repair, and replacement of damaged components, and evaluate the impact of different operation strategies including storage cycle, injection / production rate on the costs;

[0052] (4) Regulatory compliance and environmental protection assessment;

[0053] (5) Long-term operation benefit analysis.

[0054] Furthermore, S6 includes:

[0055] S61, geological stability monitoring: Monitor the stability of the geological structure around the salt cavern, including the displacement of surrounding rocks and the expansion of cracks, to evaluate the geological safety risks of the hydrogen storage facility in the salt cavern;

[0056] S62, monitoring of hydrogen pressure and temperature under cyclic injection and production: Install pressure and temperature sensors at different positions in the hydrogen storage reservoir to obtain real-time pressure and temperature data of hydrogen during injection and production; When the pressure or temperature inside the hydrogen storage facility exceeds the preset safety range, trigger an alarm;

[0057] S63, hydrogen leakage monitoring: Install sensors in and around the salt cavern to detect the hydrogen concentration in real time, discover and handle potential leakage risks in a timely manner; Identify possible leakage paths through tracer gases; When the hydrogen leakage concentration reaches or exceeds the preset threshold, trigger an alarm;

[0058] S64, monitoring of the interaction between hydrogen and the salt cavern: By regularly collecting gas samples near the salt cavern wall, detect whether there are products of chemical reactions between hydrogen and microorganisms in the salt rock, and analyze the chemical reaction situation between hydrogen and the salt cavern wall.

[0059] Furthermore, the method of S7 is: Monitor the multi-shaft horizontal salt cavern hydrogen storage reservoir to obtain the volume shrinkage rate and cavity wall deformation results of the salt cavern hydrogen storage reservoir; Measure the ground settlement amount of the salt cavern hydrogen storage reservoir to obtain its ground settlement amount; Use the helium mass spectrometry leak detection method to monitor the sealing performance of the casing shoe and the cavity sandwich position of the salt cavern hydrogen storage reservoir; Use the above on-site monitoring results to adjust the critical safety value of the stability evaluation index in real time to ensure that the evaluation index for the stability of the multi-shaft horizontal salt cavern hydrogen storage reservoir is scientific and reliable.

[0060] The beneficial effects of the above technical solutions are as follows: The technical solutions provided by the present invention are applicable to the stability evaluation method of multi-shaft horizontal salt cavern hydrogen storage reservoirs. The evaluation process and steps are simple, the evaluation indexes are clear, and the operability is strong. It can realize the quantitative evaluation of the stability of multi-shaft horizontal salt cavern hydrogen storage reservoirs, optimize the multi-shaft spacing and the span of the horizontal cavity roof, improve the stability of multi-shaft horizontal salt cavern hydrogen storage reservoirs, and at the same time give reasonable measures according to the stability evaluation results to prevent the possible operation instability and damage of the gas storage reservoir. Brief Description of the Drawings

[0061] Figure 1 It is a flow schematic diagram of a stability evaluation method for a multi-shaft horizontal salt cavern hydrogen storage reservoir.

[0062] Figure 2 It is a structural schematic diagram of a double-well dumbbell-shaped horizontal salt cavern hydrogen storage reservoir.

[0063] Figure 3Schematic diagram of a multi - shaft horizontal salt - cavern hydrogen storage reservoir

[0064] Figure 4 It is a sectional view of a multi - shaft horizontal salt - cavern hydrogen storage reservoir model.

[0065] Among them, 1 is mudstone, 2 is salt rock, 3 is interlayer, 4 is oil - gas cushion layer, 5 is injection - production casing, 6 is brine - discharging casing, 7 is oil - injection casing, 8 is water - injection control valve, 9 is brine - discharging control valve, 10 is oil - (gas) - injection control valve, 11 is sediment area, 12 is newly - built well, 13 is old well, 14 is cavity - forming casing. Specific implementation manners

[0066] First, the basic scheme of the present invention will be further described.

[0067] 1. Geological condition assessment

[0068] (1) Acquisition of in - situ stress in salt - mine strata

[0069] First, conduct a detailed geological survey on the target strata of the hydrogen storage reservoir to understand parameters such as the lithology, thickness, and burial depth of the strata, and design a suitable small - scale hydraulic fracturing test scheme. Drill one or more wells in the target strata to the target layer for building the hydrogen storage reservoir, and carry out small - scale hydraulic fracturing tests to obtain parameters such as the minimum horizontal stress, maximum horizontal stress, vertical in - situ stress, and stress gradient of the salt - rock strata. Among them, for the same well, no less than 3 horizons are selected at different depths for in - situ stress tests, and no less than 5 crack opening and closing tests are required for each horizon.

[0070] (2) Collection of salt - mine strata structure parameters

[0071] Adopt high - precision three - dimensional seismic exploration technology to obtain the strata structure parameters of the hydrogen storage reservoir construction area, including: sedimentary rhythm of the salt - bearing layer where the cavity is located, distribution of fault structures, distribution characteristics of salt rock, characteristics of the top and bottom plates of the salt layer, and distribution characteristics of interlayers. Among them, the distribution characteristics of salt rock include: thickness of the salt layer, grade of the salt layer, and physical and chemical properties.

[0072] (3) Collection of physical and mechanical parameters of salt rock

[0073] Core samples were taken from the near-field drill data wells outside the hydrogen storage cavern to obtain the formation cores of the drill data wells in the expanded hydrogen storage area for testing. The coring range was from the ground surface to 100 m below the bottom surface of the salt formation, and core samples of the overlying rock formation, salt formation, and underlying strata were obtained. According to the requirements in the "Standard for Test Methods of Engineering Rock Masses" (GBT 50266-2013), the cores of the data wells were processed into standard specimens required for different test types. The test contents carried out included: density test, uniaxial compressive strength test, tensile strength test, internal friction angle test, cohesion test, steady-state creep rate test, breakthrough pressure test, permeability test, and porosity test. In order to ensure the reliability of the experimental results, 3 to 5 specimens were used for the rock mechanics experimental tests under the same conditions; among them, all the above tests were carried out on salt rock; for mudstone and interlayer specimens, all the above tests except the breakthrough pressure test were carried out after soaking and saturating them with brine to obtain the basic physical and mechanical parameters of the sediment.

[0074] 2. Analysis of Three-Dimensional Cavity Shape Parameters of Salt Cavern Hydrogen Storage Cavern

[0075] A sonar instrument was used to measure the three-dimensional cavity shape of the hydrogen storage cavern with vertical and inclined wells to obtain the three-dimensional shape and volume of the hydrogen storage cavern. The sonar probe was placed in the salt cavity, and acoustic wave pulses were emitted towards the salt mine solution cavity wall. After detecting the echo signal, it was transmitted back to the ground computer system. By continuously adjusting the horizontal measurement distance on the vertical plane at different depths and different inclination angles and the measurement inclination angle on the horizontal plane, the three-dimensional coordinate values of each point on the irregular contour surfaces of the top, bottom, and local overhanging and finger-like protrusions on the cavity wall of the entire cavity were determined. The horizontal cavity shape parameters obtained from the above measurement results included: the burial depth of the salt cavern top, the burial depth of the salt cavern bottom, the height of the salt cavern, the maximum diameter of the salt cavern cross-section, and the length of the horizontal cavity. Based on the three-dimensional coordinate values of each point of the cavity given by the measurement results, a sonar ranging imaging analysis software was used to accurately draw the three-dimensional structure contour of the salt cavern, providing basic data for subsequent analysis.

[0076] 3. Determination of Stability Evaluation Indexes for Salt Cavern Hydrogen Storage Cavern

[0077] Due to the typical brittle and plastic failure characteristics of salt rock under cyclic internal pressure, the expansion safety factor, equivalent strain, maximum deformation of key points such as the cavity wall and the cavity top, volume shrinkage rate, plastic zone volume, etc. are selected as the stability evaluation indicators for the salt cavern hydrogen storage reservoir; under the action of cyclic creep load, the volume of the salt cavern hydrogen storage reservoir, and the completion string at the top of the salt cavern mainly undergoes axial tensile failure. The axial strain of the completion string is used as the stability evaluation indicator; the sealing failure of the salt cavern hydrogen storage reservoir is mainly manifested as the seepage range exceeding the limit and hydrogen gas penetrating into the overlying formation. The hydrogen penetration safety factor and the hydrogen seepage range are selected as the stability evaluation indicators; according to the requirements of the safety critical values in the "Design Specification for Salt Cavern Gas Storage Reservoir Cavities" (Q / SY01416-2020), combined with the formation structure, physical and mechanical parameters of salt rock, three-dimensional shape parameters of the salt cavern hydrogen storage reservoir, and operating parameters of the salt cavern hydrogen storage reservoir in the specific construction area where the target salt cavern hydrogen storage reservoir is located, the safety critical values corresponding to the above indicators are determined, and all the above indicators should be lower than the critical safety value. Adjust and optimize the parameters affecting the stability of the hydrogen storage reservoir according to the evaluation results.

[0078] Among them, the deformation amount is the vector sum of the displacements of each node of the cavity unit in the x, y, and z directions. The maximum deformation amount within 30 years of the design life of the salt cavern hydrogen storage reservoir is less than 10% of the maximum diameter of the salt cavern. The plastic zone volume is the total volume of the surrounding rock units that have undergone tensile and shear failures. To ensure the stability of the cavity injection and production operation process, tensile and shear stress failures are absolutely not allowed in the salt cavern. The hydrogen seepage range (the maximum range of pore pressure change in the salt cavern surrounding rock caused by injecting and producing hydrogen) can be obtained from the numerical simulation results, and the expansion safety factor is used to predict the expansion failure of salt rock. The expansion of salt rock is mainly affected by the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor. Its expression is:

[0079]

[0080] Among them, SF is the expansion safety factor, I1 is the first invariant of the stress tensor, J2 is the second invariant of the deviatoric stress tensor, and its expression is:

[0081] I1 = σ1 + σ2 + σ3

[0082]

[0083] Among them, σ1, σ2, and σ3 are the first, second, and third principal stresses respectively. Generally, it is considered that when SF < 1.5 for the salt cavern surrounding rock, it indicates local damage; when SF < 1.0, it indicates failure; when SF < 0.6, it indicates collapse.

[0084] Underground salt cavern hydrogen storage will be damaged due to three-dimensional in-situ stress and plastic deformation. The damage of the salt rock around the salt cavern is evaluated by the equivalent strain, which characterizes the plastic creep safety of the cavity. The equivalent strain is mainly used to define and measure the damage of salt rock by the change of modulus before and after damage, and its expression is:

[0085]

[0086] Among them, ε' is the equivalent strain, and J2' is the second invariant of the deviatoric strain tensor.

[0087]

[0088] Among them, ε x 、ε y 、ε z 、ε xy 、ε yz 、ε xz are the strain components in different directions.

[0089] The volume shrinkage rate refers to the ratio of the reduction in the total volume of the cavity after a certain operation time to the initial volume, and its expression is:

[0090]

[0091] Among them, V S is the volume shrinkage rate, V1 is the initial volume of the salt cavern, and V2 is the volume of the salt cavern after a certain operation time. The designed service life of the salt cavern hydrogen storage is 30 years, and it is usually considered that the volume shrinkage rate should not exceed 30%.

[0092] 4. Establishment of three-dimensional geomechanical model and simulation calculation

[0093] According to the above-mentioned stratum structure, physical and mechanical parameters of salt rock, and the three-dimensional shape and size of the salt cavern hydrogen storage detected by sonar at the location of the salt cavern hydrogen storage, a three-dimensional geomechanical model is established. The model is a cuboid, and the side lengths of the cuboid should not be less than 5 times the maximum diameter in each side direction of the cavity of the salt cavern gas storage. The salt rock layer is located in the middle of the model and the salt rock layer has water tightness, and the hydrogen storage cavity is located in the middle of the salt rock layer; a designed cyclic internal pressure acts on the surface of the cavity wall of the salt cavern; it is assumed that the three-dimensional salt cavern hydrogen storage model is under the initial in-situ stress of triaxial equal pressure, and the average gravity of the overlying rock layer is applied to the top surface of the model; horizontal constraints are applied to the four vertical surfaces of the model to limit the horizontal deformation of the model; a fixed constraint is applied to the bottom surface of the model to limit the horizontal and vertical deformation of the model. The established three-dimensional geomechanical model is meshed, and then the independence of the mesh size, the convergence of the calculation results, and the mesh quality are checked to ensure the reliability of the calculation results.

[0094] According to the three-dimensional geomechanical model established above and the set boundary conditions, analyze the influence of parameters such as the cyclic internal pressure of the cavity (the force of hydrogen gas in the cavity on the cavity wall during the stable operation of the salt cavern hydrogen storage library), the cycle period (the time required for the salt cavern hydrogen storage library to complete one cycle through four stages: gas injection and pressurization, high-pressure operation, gas production and depressurization, and low-pressure operation), the maximum and minimum gas production rates (the maximum and minimum rates of increase and decrease of hydrogen gas pressure in the cavity during emergency gas production and gas injection of the salt cavern hydrogen storage library), the pillar width (the salt body within the minimum width range between the cavity walls of two salt cavern hydrogen storage libraries), different shaft spacings (the distance between the centers of different wells), and the size of the roof span (the length of the salt body remaining at the top of the salt cavern after the salt layer is dissolved), as well as the cavity shape, cavity size, cavity burial depth, etc. on the stability of the salt cavern hydrogen storage library. Analyze the changes in the stress field, seepage field, plastic zone distribution, seepage pressure, and surrounding rock deformation during the hydrogen injection and production processes of the hydrogen storage library under different conditions, and predict potential unstable areas.

[0095] According to the above calculation formulas of evaluation indexes, obtain the corresponding numerical values and draw the corresponding contour maps. Evaluate the stability of the multi-shaft horizontal salt cavern hydrogen storage library according to the critical safety values of the evaluation indexes, and optimize and adjust the parameters affecting the stability of the hydrogen storage library based on the evaluation results.

[0096] (1) If the evaluation result shows that the hydrogen storage library is in a stable state and has a large safety margin, it can continue to operate normally, and appropriately optimize the hydrogen storage and extraction operations to improve efficiency. For example, under stable conditions, the hydrogen injection speed can be appropriately increased.

[0097] (2) If the evaluation result shows that the stability of the hydrogen storage library is in a critical state, measures need to be taken in a timely manner for adjustment. Such as reducing the hydrogen pressure, adjusting the operating temperature of the hydrogen storage library, etc., and at the same time strengthening the monitoring frequency of the hydrogen storage library and closely observing its stability changes.

[0098] (3) If the evaluation result shows that the hydrogen storage library has a large unstable risk, the hydrogen injection or extraction operation should be stopped immediately, the hydrogen storage library should be comprehensively inspected, the reasons for instability should be analyzed, and corresponding improvement measures should be taken until the stability is restored to the safe range and then put into operation again.

[0099] 5. Evaluation of the long-term operation impact of the salt cavern hydrogen storage library

[0100] (1) Salt cavern stability evaluation: Analyze the stability of the salt cavern during long-term operation, including the creep characteristics of salt rock, the changes in geological stress, and the influence of possible geological disasters (such as earthquakes, ground subsidence, etc.) on the stability of the salt cavern.

[0101] (2) Hydrogen leakage risk and monitoring: Evaluate the hydrogen leakage risk in the salt cavern, including the possible causes of leakage, leakage volume, and the impact of leakage on the environment and safety. Meanwhile, develop an appropriate monitoring plan to detect and handle hydrogen leakage incidents in a timely manner.

[0102] (3) Maintenance and operation costs: Consider the maintenance and operation costs of the salt cavern hydrogen storage facility, including the costs of regular inspections, maintenance, repairs, and replacement of damaged components. Meanwhile, evaluate the impact of different operation strategies (such as storage cycle, injection / production rate, etc.) on costs.

[0103] (4) Regulatory compliance and environmental assessment: Ensure that the salt cavern hydrogen storage facility complies with relevant regulations and standards, including environmental protection regulations, safety regulations, etc. Meanwhile, evaluate the potential impact of the facility on the environment and develop corresponding environmental protection measures to reduce negative impacts.

[0104] (5) Long-term operation benefit analysis: Conduct a long-term operation benefit analysis, including the return on investment of the salt cavern hydrogen storage facility, operation cost savings, and contributions to energy supply, etc. Meanwhile, consider the impact of future changes in the energy market and technological progress on the operation benefits of the facility.

[0105] 6. On-site real-time monitoring and risk warning

[0106] Install monitoring equipment at key positions in the hydrogen storage depot, and use high-precision sensors to real-time monitor key parameters such as geological deformation, hydrogen pressure and temperature, and hydrogen leakage. Establish a risk warning system, and issue warning signals in a timely manner according to the monitoring data to provide decision-making support for emergency response.

[0107] (1) Geological stability monitoring: Monitor the stability of the geological structure around the salt cavern, including rock formation displacement, crack propagation, etc., to evaluate the geological safety risk of the salt cavern hydrogen storage facility.

[0108] (2) Monitoring of hydrogen pressure and temperature under cyclic injection and production: Since the change of hydrogen temperature will affect its density and volume, and further affect the pressure distribution and stress state in the salt cavern. At the same time, the change of hydrogen pressure will generate different degrees of stress on the salt cavern wall. Install high-precision pressure and temperature sensors at different positions in the hydrogen storage depot to obtain real-time pressure and temperature data of hydrogen during injection and production processes. When the pressure or temperature inside the hydrogen storage facility exceeds the preset safety range, trigger a warning.

[0109] (3) Hydrogen leakage monitoring: Install sensors in and around the salt cavern to real-time detect hydrogen concentration, discover and handle potential leakage risks in a timely manner. Meanwhile, through technologies such as tracer gases (helium, sulfur hexafluoride, etc.), identify possible leakage paths. When the hydrogen leakage concentration reaches or exceeds the preset threshold, trigger a warning.

[0110] (4) Monitoring the interaction between hydrogen and the salt cavern: Since the chemical reaction between hydrogen and microorganisms in the salt cavern may change the physical and chemical properties of the salt rock, thus affecting the stability of the salt cavern. By regularly collecting gas samples near the salt cavern wall, detecting whether there are products of the chemical reaction between hydrogen and the salt rock, and analyzing the chemical reaction situation between hydrogen and the salt cavern wall.

[0111] 7. Calibration of stability evaluation indicators

[0112] Calibrate the above stability evaluation indicators based on the on-site real-time monitoring results of the actual operating hydrogen storage cavern to determine the stability of the multi-shaft horizontal salt cavern hydrogen storage cavern. Use high-precision cavity measurement equipment to monitor the multi-shaft horizontal salt cavern hydrogen storage cavern (monitoring once every 5 years) to obtain results such as the volume shrinkage rate and cavity wall deformation of the salt cavern hydrogen storage cavern; use GPS and level to measure the ground settlement of the salt cavern hydrogen storage cavern (monitoring once a year) to obtain its ground settlement; use helium mass spectrometry leak detection method to monitor the sealing performance at positions such as the casing shoe and cavity interlayer of the salt cavern hydrogen storage cavern; use the above on-site monitoring results to adjust the critical safety values of the stability evaluation indicators in real time to ensure that the evaluation indicators proposed for the stability of the multi-shaft horizontal salt cavern hydrogen storage cavern are scientific and reliable.

[0113] 8. Comprehensive evaluation and measure suggestions

[0114] (1) Adopt mathematical methods such as the analytic hierarchy process and fuzzy comprehensive evaluation method, and establish a stability evaluation model coupled with multiple factors based on geological conditions, salt cavern structure, operating parameters and monitoring data to quantitatively evaluate the stability of the hydrogen storage cavern. According to the comprehensive evaluation results, formulate a suitable selection strategy for the horizontal multi-shaft salt cavern hydrogen storage technology, considering the possibility of technology update and replacement, as well as flexibility and scalability in long-term operation.

[0115] (2) According to the evaluation results, identify the risks and challenges that the salt cavern hydrogen storage may face in long-term operation, such as geological disasters, hydrogen leakage, etc. According to the evaluation results, propose targeted stability enhancement measures and emergency plans to ensure the safe and efficient operation of the hydrogen storage cavern.

[0116] The present invention will be described below in conjunction with embodiments.

[0117] The three-dimensional geomechanical cavity model consists of three parts (such as Figure 3As shown in the figure, the center of the combination of the three parts is taken as the origin of the cavity model. The model is a cuboid with dimensions of 1320m×728m×1000m. The total height of the salt cavern cavity is 78m, the maximum radius is 120m, the upper part is an arc-shaped dome with a height of 26m, the lower part is a hemisphere with a radius of 52m, and the middle part is a rectangle with a thickness of 2m and a length of 60m. There are three layers of salt rock formations (2) with a total thickness of 124m, which are 50m, 24m, and 50m from top to bottom in sequence; there are two layers of interlayers (3) with a thickness of 2m each; the upper and lower cover layers are two mudstone formations (1) with a thickness of 300m each; the thickness of the top and bottom plates of the cavity is 25m each. The mechanical parameters of the salt layer are shown in Table 1.

[0118] Table 1 Basic mechanical parameters of different rock formations

[0119]

[0120] Taking the depth from the upper surface of the model to the ground surface as 800m and the average geological stress gradient as 0.023MPa / m, the equivalent load on the upper surface is obtained as 18.4MPa, which is simplified to a vertical uniformly distributed load perpendicular to the upper surface of the model. The surrounding surfaces of the model are simplified to vertical simply supported constraints without normal movement, and the bottom surface (1528m) of the model is simplified to a fixed constraint without normal and horizontal movement. The burial depth of the top of the salt rock hydrogen storage cavity is 1125m. Assuming that the cavity is filled with saturated brine after cavity formation, a uniform internal pressure of 13.5MPa on the cavity wall surface is set for the calculation of cavity stability. During the actual cyclic injection and production of hydrogen, the internal gas pressure in the cavity is simplified to a uniform load perpendicular to the inner surface of the cavity, and the maximum upper limit and minimum lower limit pressures are taken as 0.8σ z and 0.35σ z , that is, 18.0MPa and 8.0MPa. Considering different injection and production pressures, cycle periods, maximum and minimum injection and production rates based on the upper and lower pressure limits, results such as the dilatancy safety factor, equivalent strain, deformation, volume shrinkage rate, and plastic zone volume around the cavity are obtained, and a comprehensive long-term operation stability evaluation of the hydrogen storage reservoir is carried out (the evaluation and parameter optimization are carried out according to the above description and will not be elaborated here).

Claims

1. A method for evaluating the stability of a multi - vertical - shaft horizontal salt - cavern hydrogen storage reservoir, comprising the following steps: S1, Geological condition assessment; S2, Three-dimensional cavity shape parameter analysis of the salt cavern hydrogen storage reservoir, including: Perform three - dimensional cavity shape measurement on the hydrogen storage reservoir with vertical and inclined wells. The horizontal cavity shape parameters obtained from the measurement results of the three - dimensional cavity shape measurement include: the buried depth of the salt - cavern top, the buried depth of the salt - cavern bottom, the height of the salt - cavern, the maximum diameter of the salt - cavern cross - section, and the length of the horizontal cavity. The three - dimensional coordinate values of each point of the cavity given by the measurement results are used to draw the three - dimensional structure contour of the salt - cavern; S3, Determination of the stability evaluation indexes of the salt - cavern hydrogen storage reservoir, including: S31, Since salt rock exhibits typical brittle and plastic failure characteristics under cyclic internal pressure, select the dilation safety factor, equivalent strain, maximum deformation of key points on the cavity wall, top and bottom of the cavity, volume shrinkage rate, and plastic zone volume as the stability evaluation indexes of the salt - cavern hydrogen storage reservoir; S32, Under cyclic creep load, the completion string located at the top of the salt - cavern has a risk of axial tensile failure. Take the axial strain of the completion string as the stability evaluation index of the salt - cavern hydrogen storage reservoir; S33, The sealing failure of the salt - cavern hydrogen storage reservoir is manifested as the seepage range exceeding the limit value and hydrogen gas penetrating into the overlying formation. Select the hydrogen penetration safety factor and hydrogen seepage range as the stability evaluation indexes of the salt - cavern hydrogen storage reservoir; S34, According to the requirements of the safety critical values in the cavity design specifications of the salt - cavern gas storage reservoir, combined with the formation structure, physical and mechanical parameters of salt rock, the measurement results of the three - dimensional cavity shape of the target salt - cavern hydrogen storage reservoir, and the operation parameters of the salt - cavern hydrogen storage reservoir, determine the safety critical values corresponding to the stability evaluation indexes of the salt - cavern hydrogen storage reservoir determined in S31, S32, and S33. All the stability evaluation indexes of the salt - cavern hydrogen storage reservoir should be lower than the critical safety value. Adjust and optimize the parameters affecting the stability of the hydrogen storage reservoir according to the evaluation results; S4, Establishment and simulation calculation of the three - dimensional geomechanical model, including: S41, According to the formation structure, physical and mechanical parameters of salt rock, and the detected three - dimensional shape and size of the salt - cavern hydrogen storage reservoir, establish a three - dimensional geomechanical model; perform mesh division on the established three - dimensional geomechanical model, and then check the independence of the mesh size, the convergence of the calculation results, and the mesh quality to ensure the reliability of the calculation results; S42. According to the established three-dimensional geomechanical model and the set boundary conditions, analyze the cyclic internal pressure of the cavity, i.e., the force exerted by the hydrogen gas in the cavity on the cavity wall during the stable operation of the salt cavern hydrogen storage reservoir; the cycle period, i.e., the time required for the salt cavern hydrogen storage reservoir to complete one cycle during the four stages of gas injection and pressurization, high-pressure operation, gas production and depressurization, and low-pressure operation; the maximum and minimum gas production rates, i.e., the maximum and minimum rates of increase and decrease of the hydrogen gas pressure in the cavity during emergency gas production and gas injection in the salt cavern hydrogen storage reservoir; the pillar width, i.e., the salt body within the minimum width range between the cavity walls of two salt cavern hydrogen storage reservoirs; the sizes of different shaft spacings and roof spans, i.e., the length of the salt body retained at the top of the salt cavern after the salt layer is dissolved; and the influence of the cavity shape, cavity size, and cavity burial depth parameters on the stability of the salt cavern hydrogen storage reservoir. Analyze the changes in the stress field, seepage field, plastic zone distribution, seepage pressure, and surrounding rock deformation index during the hydrogen injection and production processes of the hydrogen storage reservoir under different conditions, and predict potential unstable regions. S43. According to the stability evaluation indicators of the salt cavern hydrogen storage reservoir established in S3, obtain the values of each evaluation indicator and draw the corresponding nephograms. Evaluate the stability of the multi-shaft horizontal salt cavern hydrogen storage reservoir according to the critical safety values of the evaluation indicators, and optimize and adjust the parameters affecting the stability of the hydrogen storage reservoir based on the evaluation results. S5. Evaluation of the long-term operation impact of the salt cavern hydrogen storage reservoir. S6. On-site real-time monitoring and risk warning: Install monitoring equipment at key positions of the hydrogen storage reservoir, and use sensors to real-time monitor geological deformation, hydrogen gas pressure and temperature, and hydrogen gas leakage parameters. Establish a risk warning system. S7. Calibration of stability evaluation indicators: Calibrate the above stability evaluation indicators in combination with the on-site real-time monitoring results of the actually operating hydrogen storage reservoir to determine the stability of the multi-shaft horizontal salt cavern hydrogen storage reservoir.

2. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, wherein S1 includes: S11. Obtaining the in-situ stress of the salt mine formation: Conduct a geological survey on the target formation of the hydrogen storage reservoir to understand the lithology, thickness, and burial depth parameters of the formation. Design a suitable small-scale hydraulic fracturing test plan, drill one or more wells in the target formation to the target layer for building the hydrogen storage reservoir, and carry out a small-scale hydraulic fracturing test to obtain the minimum horizontal stress, maximum horizontal stress, vertical in-situ stress, and stress gradient parameters of the salt rock formation. S12. Collecting the structural parameters of the salt mine formation: Use three-dimensional seismic exploration technology to obtain the structural parameters of the formation in the construction area of the hydrogen storage reservoir, including: the sedimentary rhythm of the salt-bearing layer where the cavity is located, the distribution of fault structures, the distribution characteristics of salt rock, the characteristics of the top and bottom plates of the salt layer, and the distribution characteristics of interlayers. S13. Collecting the physical and mechanical parameters of salt rock: Conduct core sampling on the drill data wells near the hydrogen storage reservoir to obtain the formation cores of the data wells in the expanded hydrogen storage reservoir area for testing.

3. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, characterized in that In S13, the coring range is from the ground surface to 100 m below the bottom surface of the salt rock layer, and core samples of the overlying rock layer, salt rock layer, and underlying strata are obtained. The cores of the data well are processed into standard samples required for different test types, and the test contents carried out include: density test, uniaxial compressive strength test, tensile strength test, internal friction angle test, cohesion test, steady-state creep rate test, breakthrough pressure test, permeability test, and porosity test; all the above tests are performed on the salt rock samples; for the mudstone and interlayer samples, all the above tests except the breakthrough pressure test are carried out after soaking and saturating them with brine to obtain the basic physical and mechanical parameters of the sediment.

4. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, characterized in that, In S2, by continuously adjusting the horizontal measurement distance on the vertical plane and the measurement inclination angle on the horizontal plane at different depths and different inclination angles, the three-dimensional coordinate values of each point on the irregular contour surfaces of the top, bottom, and local overhanging and finger-like protruding parts on the cavity wall of the entire cavity are determined.

5. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, wherein, In S31, the deformation amount is the displacement of each node of the cavity element, the plastic zone volume is the total volume of the surrounding rock element that undergoes tensile and shear failures, and the hydrogen seepage range is the maximum range of the pore pressure change in the salt cavern surrounding rock caused by hydrogen injection and production. The maximum deformation amount, plastic zone volume, and hydrogen seepage range of the key points on the cavity wall, cavity top, and cavity bottom are obtained from the numerical simulation results; The swelling safety factor is used to predict the swelling failure of salt rock. The swelling of salt rock is mainly affected by the first invariant of the stress tensor and the second invariant of the deviatoric stress tensor, and its expression is: where SF is the swelling safety factor, I1 is the first invariant of the stress tensor, and J2 is the second invariant of the deviatoric stress tensor, and its expression is: I1 = σ1 + σ2 + σ3 where σ1, σ2, and σ3 are the first, second, and third principal stresses, respectively; According to the calculation result of the swelling safety factor SF, estimate the safety critical value of local damage, failure, or collapse of the salt cavern. The equivalent strain refers to the failure of salt rock caused by three-dimensional in-situ stress and plastic deformation. The equivalent strain is used to evaluate the failure of the salt rock around the salt cavern and characterize the plastic creep safety of the cavity; the equivalent strain is used to define and measure the damage of salt rock through the change of modulus before and after damage, and its expression is: where ε' is the equivalent strain and J2 ' is the second invariant of the deviatoric strain tensor; Among them, where ε x , ε y , ε z , ε xy , ε yz , ε xz are strain components in different directions; The volume shrinkage rate refers to the ratio of the reduction amount of the total volume of the cavity after a certain operation time to the initial volume, and its expression is: Among them, V S is the volume shrinkage rate, V1 is the initial volume of the salt cavern, and V2 is the volume of the salt cavern after a certain operation time. According to the design life of the salt cavern hydrogen storage reservoir, the critical safety value of the volume shrinkage rate is estimated.

6. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, wherein In S4, the established three-dimensional geomechanical model is: in the shape of a cuboid, and the side lengths of the cuboid are not less than 5 times the maximum diameter in each side direction of the salt cavern gas storage cavity; the salt rock layer is located in the middle of the model and the salt rock layer has water tightness, and the hydrogen storage cavity is located in the middle of the salt rock layer; the designed cyclic internal pressure acts on the surface of the salt cavern cavity wall. It is assumed that the three-dimensional salt cavern hydrogen storage reservoir model is under the initial in-situ stress state of triaxial equal pressure, and the average gravity of the overlying rock layer is applied to the top surface of the model; horizontal constraints are applied to the four vertical surfaces of the model to restrict the horizontal deformation of the model; a fixed constraint is applied to the bottom surface of the model to restrict the horizontal and vertical deformation of the model.

7. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, characterized in that, In S43, the method for optimizing and adjusting the parameters affecting the stability of the hydrogen storage reservoir according to the evaluation results is as follows: (1) If the evaluation result shows that the hydrogen storage reservoir is in a stable state and there is a safety margin, continue normal operation and appropriately optimize the hydrogen storage and extraction operations to improve efficiency, including appropriately increasing the hydrogen injection rate; (2) If the evaluation result shows that the stability of the hydrogen storage reservoir is in a critical state, timely measures need to be taken for adjustment, including reducing the hydrogen pressure, adjusting the operating temperature of the hydrogen storage reservoir, and strengthening the monitoring frequency of the hydrogen storage reservoir to closely monitor its stability changes; (3) If the evaluation result shows that there is a risk of instability in the hydrogen storage reservoir, immediately stop the hydrogen injection or extraction operation, inspect the hydrogen storage reservoir, analyze the reasons for instability, and take corresponding improvement measures until the stability is restored to the safe range before resuming operation.

8. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, characterized in that S5 includes, (1) Salt cavern stability assessment: Analyze the stability of the salt cavern during long-term operation, including the creep characteristics of the salt rock, changes in geological stress, and the impact of possible geological disasters on the stability of the salt cavern; (2) Hydrogen leakage risk and monitoring: Evaluate the hydrogen leakage risk in the salt cavern, including the possible reasons for leakage, leakage volume, and the impact of leakage on the environment and safety; (3) Maintenance and operation costs: Consider the maintenance and operation costs of the salt cavern hydrogen storage facility, including the costs of regular inspections, maintenance, repairs, and replacement of damaged components, and evaluate the impact of different operation strategies, including storage cycle, injection / production rate, on costs; (4) Regulatory compliance and environmental protection assessment; (5) Long-term operation benefit analysis.

9. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, wherein S6 Include: S61, Geological stability monitoring: Monitor the stability of the geological structure around the salt cavern, including the displacement of the surrounding rock and crack expansion, to evaluate the geological safety risk of the salt cavern hydrogen storage facility; S62, Hydrogen pressure and temperature monitoring under cyclic injection and production: Install pressure and temperature sensors at different positions in the hydrogen storage reservoir to obtain real-time pressure and temperature data of hydrogen during injection and production; when the pressure or temperature inside the hydrogen storage facility exceeds the preset safety range, trigger an alarm; S63, Hydrogen leakage monitoring: Install sensors in and around the salt cavern to detect the hydrogen concentration in real time, promptly discover and handle potential leakage risks; identify possible leakage paths through tracer gases; when the hydrogen leakage concentration reaches or exceeds the preset threshold, trigger an alarm; S64, Monitoring of the interaction between hydrogen and the salt cavern: By regularly collecting gas samples near the salt cavern wall, detect whether there are products of chemical reactions between hydrogen and microorganisms in the salt rock, and analyze the chemical reaction situation between hydrogen and the salt cavern wall.

10. The stability evaluation method of the multi-shaft horizontal salt cavern hydrogen storage library according to claim 1, wherein The method of S7 is: Monitor the multi-shaft horizontal salt cavern hydrogen storage reservoir to obtain the volume shrinkage rate and cavity wall deformation results of the salt cavern hydrogen storage reservoir; measure the ground settlement amount of the salt cavern hydrogen storage reservoir to obtain its ground settlement amount; use the helium mass spectrometry leak detection method to monitor the sealing performance of the casing shoe and cavity sandwich position of the salt cavern hydrogen storage reservoir; Use the above on-site monitoring results to adjust the critical safety values of the stability evaluation indicators in real time to ensure that the evaluation indicators for the stability of the multi-shaft horizontal salt cavern hydrogen storage reservoir are scientific and reliable.

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