A method for expanding the capacity of an old cavity hydrogen storage reservoir in a connected well salt cavern by injecting hydrogen, producing hydrogen and removing brine

Abstract

The present invention provides a method for cavity expansion of a hydrogen storage reservoir in a connected well salt cavern old cavity by hydrogen injection and production and brine discharge linkage, comprising the following steps: step 1, evaluation and connectivity analysis of the connected well old cavity of the target salt cavern; step 2, construction of a new well on the upper part of the connected channel; step 3, cavity expansion by hydrogen injection and production linkage and brine discharge: designing a hydrogen injection and production linkage operation scheme, promoting brine discharge and cavity expansion through the hydrogen injection and production process, adopting a periodic hydrogen injection and production mode during the hydrogen injection and production linkage process, adjusting the hydrogen injection and production cycle according to the dissolution condition of the salt cavern and the brine discharge amount, until the salt cavity volume of the cavity production well reaches the required hydrogen storage reservoir capacity; step 4, monitoring and safety control of the cavity expansion process by hydrogen injection and production linkage and brine discharge; step 5, storage capacity verification and adjustment.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen storage technology, in particular to a brine-exhausting, cavity-building and capacity expansion method suitable for hydrogen injection and production processes in connected well salt cavern old cavity hydrogen storage reservoirs. The invention belongs to the field of underground hydrogen energy storage technology, in particular to the resource utilization technology of abandoned old cavity salt cavern hydrogen storage reservoirs. Background Art

[0002] As a clean and efficient energy carrier, hydrogen energy has broad application prospects. With the continuous development of the hydrogen energy industry, hydrogen storage has become an important support for promoting hydrogen energy applications. Salt cavern hydrogen storage has become an ideal choice for underground hydrogen storage due to its large storage capacity, strong stability, and low storage cost.

[0003] Traditional salt cavern gas storage technology is primarily used for storing natural gas and compressed air. Unlike these gases, hydrogen has low density, high reactivity, high diffusivity, low viscosity, and strong permeability, and its storage conditions are relatively demanding. Therefore, when reusing existing salt cavern gas storage for the expansion of salt cavern hydrogen storage, more precise control of the cavity shape and volume is required to ensure safe and efficient hydrogen storage.

[0004] At present, traditional connected well salt cavern gas storage usually has two wells, one of which is mainly used for water injection and the other is mainly used for brine drainage. Two old water injection wells 13 and brine drainage wells 19 are drilled into the target salt rock layer in sequence and built through the water-soluble cavity method. Among them, the horizontal distance between the two old water injection wells and the brine drainage wells is usually 500m to 1000m (called the connecting channel). The gas storage cavity built by this water-soluble cavity method is mostly dumbbell-shaped. Figure 1 Since my country's salt rock layers contain a large amount of insoluble or poorly soluble impurities, sediment areas 11 are easily formed in the horizontal connecting channels. The main components of the solid particles in the sediment area are calcium sulfate, calcium carbonate, magnesium hydroxide, and poorly soluble or slightly soluble silicates. There are pores between the solid particles and they are filled with brine.

[0005] When repurposing dumbbell-shaped old salt cavern gas storage as salt cavern hydrogen storage, the high-pressure hydrogen cyclic storage and release process results in uneven stress distribution within the cavern, particularly in the central, long-span connecting channel. This increases the risk of collapse or deformation of the upper roof. Furthermore, the salt deposits above the central, long-span connecting channel remain undissolved, resulting in idle salt resources and reduced available gas storage space. Furthermore, the irregular shape of the cavern complicates hydrogen injection and extraction, increasing the difficulty of monitoring and maintenance during the cyclic injection and extraction process. Due to the creep properties of salt rock, the pressure within the salt cavern fluctuates significantly during operation as hydrogen is injected and withdrawn, making the cavern volume shrinkage a common problem. Therefore, when constructing salt cavern hydrogen storage, especially when expanding the old cavern cavity of a connecting well, challenges arise in how to quickly and safely expand the cavern capacity, improve hydrogen storage efficiency, and accelerate the storage's commissioning.

[0006] Currently, there is relatively little research on methods for injecting and producing hydrogen, removing brine, and expanding the capacity of caverns connected to well-salt cavern hydrogen storage facilities. Existing methods are difficult to meet the needs of efficient, safe, and large-scale hydrogen storage. Summary of the Invention

[0007] The present invention provides a method for expanding the capacity of a hydrogen storage reservoir in an old cavity of a connected well by injecting and producing hydrogen and removing brine in a linked manner. The method aims to rationally regulate the hydrogen injection and removal and brine removal processes, utilize the connectivity within the salt caverns and the solubility characteristics of the salt rock, and simultaneously remove brine to expand the capacity and create the cavity during the hydrogen injection and removal process. On the premise of ensuring the safety and stability of the hydrogen storage reservoir, by optimizing the operating procedures and technical means, the capacity of the hydrogen storage reservoir can be further expanded, the hydrogen storage efficiency and operating speed can be improved, and the salt cavern hydrogen storage reservoir can be put into hydrogen injection and removal operation as soon as possible. The technical solution of the present invention is as follows:

[0008] A method for expanding the capacity of an old cavity hydrogen storage reservoir in a connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner, comprising the following steps:

[0009] Step 1: Evaluation and connectivity analysis of the target salt cavern's connected wells and old cavities

[0010] Step 2: Build a new well on the upper part of the connecting channel. The method is as follows:

[0011] Drill two or more vertical wells on the upper part of the old cavity connecting channel of the old hydrogen injection and production well and the brine drainage well. The vertical wells enter the connecting channel as new cavity wells, and the two old connecting wells are used as hydrogen injection and production wells and brine drainage wells respectively;

[0012] Arrange the tubing string according to cavity creation requirements;

[0013] A water injection casing, a brine drainage casing, and a cavity creation casing are installed in the vertical well, with the water injection flow rate and the brine drainage flow rate being regulated by the water injection control valve and the brine drainage control valve, respectively. An oil and gas cushion protection fluid is injected through the oil injection casing, with the injection flow rate regulated by the oil and gas injection control valve to prevent excessive upward dissolution of the salt rock. A filter device and a flow control valve are installed on the brine drainage casing, thereby forming a cavity creation well on the basis of the vertical well.

[0014] Step 3: Hydrogen injection and production are linked with brine discharge to expand the cavern: A hydrogen injection and production linkage operation plan is designed to promote brine discharge and cavern expansion through the hydrogen injection and production process. During the hydrogen injection and production linkage process, a periodic hydrogen injection and production mode is adopted. The hydrogen injection and production cycle is adjusted according to the dissolution of the salt cavern and the amount of brine discharged, until the salt cavern volume of the cavern reaches the required hydrogen storage capacity.

[0015] Step 4: Monitoring and safety control of the process of expanding and creating the cavity by linking hydrogen injection and production with brine removal;

[0016] Step 5: Storage capacity verification and adjustment.

[0017] Furthermore, the method of step one is: to conduct geological survey and evaluation of the old cavity of the connected wells of the target salt cavern, and obtain the basic geological characteristic data of the gas storage reservoir in the old cavity of the connected wells, including the thickness of the salt layer, pore structure, distribution of soluble salt layers, and physical and mechanical properties of the salt rock; to evaluate the fluidity and connectivity of hydrogen in the old cavity of the salt cavern and the solubility of the salt rock, and to determine whether the old cavity of the connected wells is suitable for expansion operation, and the expected capacity of the cavity after expansion.

[0018] Furthermore, in step 2, during the drilling process of the vertical well, the connecting channel is not drilled directly, but water injection and fracturing are performed at an appropriate distance above the connecting channel. After the fracturing enters the connecting channel, fresh water or brine is continued to be injected for a period of time to prevent the bare hole section of the brine drainage well from shrinking, collapsing or being blocked.

[0019] Furthermore, in step 3, each hydrogen injection and production cycle includes:

[0020] Inject hydrogen, drain brine and create cavities: The hydrogen injection pressure is adjusted by the hydrogen injection and production control valve, and hydrogen is injected into the salt cavity through the hydrogen injection and production casing to displace brine from top to bottom. The brine flows into the brine drainage well through the connecting channel and is discharged. At the beginning of gas injection, a high-pressure pump is used to pump fresh water or brine from the cavity creation well into the cavity to dissolve the salt rock and create cavities. The brine formed by the cavity creation is discharged through the brine drainage well. When injecting hydrogen and pumping fresh water or brine, it is necessary to prevent brine from flowing back into the hydrogen injection and production well. As the hydrogen injection process proceeds, hydrogen The interface between hydrogen and brine gradually moves downward. The timing to stop pumping fresh water or fresh brine is determined according to the position of the interface between hydrogen and brine in the hydrogen injection and production wells, and the injection control valve of the cavity making well is closed. When hydrogen is injected to a certain extent, the interface between hydrogen and brine moves downward further. The timing to close the brine discharge control valve of the brine discharge well is determined according to the position of the interface between hydrogen and brine in the salt cavity of the hydrogen injection and production wells. After continuing to inject hydrogen to the design pressure, stop hydrogen injection, maintain the design hydrogen injection pressure and close the hydrogen injection and production wells, and the entire hydrogen injection cycle ends.

[0021] Water injection for hydrogen production and cavity creation: When hydrogen is produced in the hydrogen storage reservoir, the brine drainage well is closed, and the injection pressure is adjusted by the water injection control valve. Fresh water or brine is injected into the salt cavity through the water injection casing, and brine is formed after dissolving the salt rock. The brine gradually displaces hydrogen from top to bottom, and the hydrogen in the hydrogen storage reservoir flows into the hydrogen injection and production well through the connecting channel to be produced; at the same time as the water injection begins, the hydrogen injection and production control valve is opened, and a high-pressure pump is used to pump fresh water or brine from the cavity creation well into the salt cavity to dissolve the salt rock and create a cavity; when injecting hydrogen and pumping fresh water or brine, it is necessary to prevent the brine from being discharged. to the hydrogen injection and production well; as the hydrogen production process proceeds, the interface between hydrogen and brine gradually moves upward. When the interface between hydrogen and brine is below the hydrogen injection and production casing of the hydrogen injection and production well, hydrogen is produced from the hydrogen injection and production casing of the hydrogen injection and production well, and the water injection control valve of the cavity well is closed at this time; after continuing to produce hydrogen to a certain extent, the interface between hydrogen and brine further moves upward. When the interface between hydrogen and brine is above the hydrogen injection and production casing of the gas injection and production well, hydrogen is produced from the cavity casing of the hydrogen injection and production well. When hydrogen production stops, the hydrogen injection and production well and the hydrogen injection and production control valve are closed, and the entire hydrogen production cycle ends.

[0022] Furthermore, in each hydrogen injection and production cycle, the hydrogen injection and production flow rate and pressure should be gradually increased, and gradually reach the maximum capacity on the basis of ensuring the stability of the salt cavern; a dynamic adjustment method is adopted in the linkage process of hydrogen injection and production and brine discharge, and the ratio of hydrogen injection and production to brine discharge is adjusted according to real-time monitoring data to ensure the balance between the two; in the process of mutual replacement of brine and hydrogen in the above-mentioned salt cavern hydrogen storage reservoir, the operating pressure fluctuation of the hydrogen storage reservoir is controlled within ±3% to improve the geological stability of the hydrogen storage reservoir, and the brine discharge volume is matched with the hydrogen injection flow rate to achieve stable capacity expansion.

[0023] Furthermore, in each hydrogen injection and production cycle of step 3, the injection and production hydrogen flow rate and pressure should be gradually increased. The method of gradually reaching the maximum capacity on the basis of ensuring the stability of the salt cavern is as follows: in the initial expansion stage, the injection pressure and the injection and production hydrogen pressure are controlled in the range of 5-8 MPa, and the injection and production hydrogen flow rate is controlled in the range of 0.5-1 m 3 / min range to avoid excessive (too low) salt rock pressure causing damage to the cavity structure; as the expansion proceeds, in the middle stage of expansion, the hydrogen injection and production pressure is appropriately increased, and at the same time, the flow rate of hydrogen or water injection is gradually increased to accelerate the expansion of the cavity and the brine discharge process; in the later stage of expansion, when the capacity of the salt cavern is expanded to the expected target, the hydrogen injection flow rate and hydrogen injection pressure gradually reach the maximum value to ensure that the volume of the hydrogen storage reservoir fully meets the design requirements.

[0024] Furthermore, during the salt cavern expansion process, the brine discharge flow rate is initially controlled at a low level to avoid uneven expansion of the cavity caused by rapid brine discharge and to prevent excessive dissolution of salt rock; as the cavity gradually expands, the brine discharge flow rate gradually increases to accelerate brine discharge.

[0025] Furthermore, in step four, the pressure sensor, temperature sensor and flow sensor installed at the wellhead are used to monitor the hydrogen pressure changes, temperature changes and fresh water injection and brine discharge flow changes in the hydrogen storage tank respectively to ensure that the hydrogen injection pressure is within the set range and to prevent gas leakage or structural damage caused by excessive temperature; the structural deformation of the salt cavern is monitored by the stress displacement sensor to realize the monitoring and safety control of the hydrogen injection and brine discharge linkage expansion and cavity creation process.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention combines the hydrogen injection and production process with the brine drainage process. By precisely controlling the hydrogen injection and brine drainage flow rates, the connectivity within the salt cavern and the solubility of the salt rock are fully utilized, the expansion and cavity creation process is optimized, and the expansion speed and the capacity of the hydrogen storage reservoir can be significantly improved, while shortening the time it takes for the salt cavern hydrogen storage reservoir to be put into use.

[0028] 2 The present invention can improve the efficiency of hydrogen injection and brine removal through reasonable well selection and layout, and can also reduce problems such as pipeline blockage during brine treatment. Through reasonable control and adjustment, the cavity creation speed is accelerated, and the risks brought by single method operation can be reduced, reducing development costs and ensuring that the salt cavern hydrogen storage can be put into use efficiently and safely. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the dumbbell-shaped connected well salt cavern gas storage and hydrogen storage structure.

[0030] Figure 2 Schematic diagram of the cavity expansion structure for connecting the well salt cavern hydrogen storage reservoir with hydrogen injection and production and brine discharge

[0031] Among them, 1 is mudstone, 2 is salt rock, 3 is interlayer, 4 is oil and gas cushion, 5 is water injection casing, 6 is brine drainage casing, 7 is oil injection casing, 8 is water injection control valve, 9 is brine drainage control valve, 10 is oil and gas injection control valve, 11 is sediment area, 12 is cavity well, 13 is old hydrogen injection and production well, 14 is cavity casing, 15 is hydrogen injection and production casing, 16 is hydrogen injection and production well, 17 is hydrogen and brine interface, 18 is hydrogen injection and production control valve, 19 is brine drainage well, 20 is filter device, 21 is pressure sensor, 22 is temperature sensor, 23 is flow sensor, and 24 is stress displacement sensor. DETAILED DESCRIPTION

[0032] The present invention will be described below with reference to the accompanying drawings and embodiments.

[0033] In order to improve the working efficiency and availability of salt cavern hydrogen storage, the present invention proposes a method for cavity expansion by linking hydrogen injection and production with brine discharge. By injecting fresh water to dissolve salt rock while injecting and producing hydrogen, the connectivity of salt caverns and the solubility characteristics of salt rock are utilized to increase the capacity of salt cavern hydrogen storage. That is, when injecting hydrogen: inject hydrogen into the hydrogen injection and production well, and the hydrogen forms a certain pressure in the cavity. At the same time, inject fresh water or brine into the water injection well. The hydrogen forming a certain pressure in the cavity helps the diffusion of salt-dissolving media such as fresh water or brine in the salt cavern, and accelerates the dissolution of salt rock. When producing hydrogen: inject fresh water or brine into the water injection well, and at the same time open the hydrogen injection and production well, and displace hydrogen under the pressure of fresh water or brine, thereby achieving the purpose of producing hydrogen and dissolving salt rock. The specific steps are as follows:

[0034] 1. Laoqiang assessment and connectivity analysis:

[0035] Before expansion and cavitation, a comprehensive geological survey and assessment of the target salt cavern's connected wells and old cavities is first conducted. Advanced geological exploration techniques, such as seismic exploration and geological drilling, are used to obtain basic geological characteristics of the connected wells' old cavities, including salt layer thickness, pore structure, distribution of soluble salt layers, and the physical and mechanical properties of the salt rock (such as strength and permeability). Downhole gas composition analysis, the flow path of injected hydrogen, and pressure monitoring are used to assess the fluidity and connectivity of hydrogen within the old salt caverns, as well as the solubility of the salt rock. This allows for a determination of the suitability of the connected wells' old cavities for expansion, as well as the expected capacity of the expanded cavity.

[0036] 2. Build a new well on the upper part of the connecting channel:

[0037] Based on the construction standards of hydrogen storage reservoirs, two vertical wells are drilled on the upper part of the old cavity connecting channel of the old hydrogen injection and production well 13 and the brine drainage well 19 (the well spacing is usually 250m to 500m). The two vertical wells enter the connecting channel as the new cavity well 12, and the two old connecting wells are used as the hydrogen injection and production well 16 and the brine drainage well 19 respectively. Figure 2As shown in the figure, the tubing strings are arranged according to the cavity creation requirements. Water injection casing 5, brine drainage casing 6, and cavity creation casing 14 are installed in two vertical wells, respectively. The water injection and brine drainage rates are regulated by water injection control valve 8 and brine drainage control valve 9, respectively. A protective fluid for the oil and gas cushion is injected through the oil injection casing 7. The thickness of the oil and gas cushion is typically 1 to 10 meters, preferably 2 to 5 meters. The primary purpose of injecting the protective fluid is to isolate the oil and gas cushion from the salt rock, preventing dissolution and corrosion. The injection rate of the protective fluid is regulated by the oil and gas control valve 10 to prevent excessive upward dissolution of the salt rock, ensuring a stable roof morphology at the wellhead salt cavern and that the thickness of the roof protective layer reaches the preset value. The protective fluid for the oil and gas cushion can be of various types and compositions, including crude oil or synthetic oil: these liquids effectively isolate the oil and gas cushion from the salt rock, preventing gas leakage or salt rock dissolution; and organic solvents: certain organic solvents, such as alkanes and cycloalkanes, can also be used in the protective fluid.

[0038] The brine discharge pipe 6 is made of a new, corrosion-resistant, and anti-clogging material (such as a special ceramic-coated steel pipe). A filter 20 is installed on the brine discharge pipe 6 to prevent salt crystallization or other impurities from clogging the pipe. A flow control valve 9 is also installed on the brine discharge pipe to precisely adjust the brine discharge flow rate according to the required flow rate.

[0039] The interconnected well salt cavern hydrogen storage reservoir referred to here refers to a salt cavern that has undergone renovation of its old cavity. Its sealing and stability have been verified, meeting the gas injection and production standards for hydrogen storage. When the cavity well is drilled above the connecting channel between two interconnected wells, it is not advisable to drill directly into the connecting channel. Instead, water injection and fracturing should be performed 10 to 50 meters above the connecting channel (preferably 25 to 35 meters). After fracturing into the connecting channel, continue injecting fresh water or brine for 15 days to prevent shrinkage, collapse, and blockage of the open hole section of the brine drainage well 19.

[0040] 3. Hydrogen injection and production and brine removal linked to expand the cavity:

[0041] After the construction of the two new cavern formation wells mentioned above is completed, the key to designing a rationally coordinated hydrogen injection and brine drainage operation plan is to coordinate hydrogen injection, production, and brine drainage to gradually dissolve the salt rock and expand the cavern volume, while avoiding excessive hydrogen injection and production that could lead to cavern instability. The core of cavern expansion is to promote brine drainage and cavern expansion through hydrogen injection and production. While ensuring good connectivity of the salt cavern, hydrogen is injected. The expansion effect of the gas increases the gas pressure inside the salt cavern, dissolving the surrounding salt rock and gradually expanding the cavern volume.

[0042] Injecting hydrogen and draining brine to create cavities: The hydrogen injection pressure is adjusted by the hydrogen injection and production control valve 18, and hydrogen is injected into the salt cavity through the hydrogen injection and production casing 15, displacing brine from top to bottom. The brine flows into the brine drainage well 19 through the connecting channel and is discharged. At the beginning of gas injection, a high-pressure pump is used to pump fresh water or brine (NaCl content is 20g / L) from the cavity creation well 12 into the cavity to dissolve the salt rock and create cavities. The brine formed by the cavity creation is discharged through the brine drainage well 19. When injecting hydrogen and pumping fresh water or brine, it is necessary to ensure that the gas injection pressure in the hydrogen storage salt cavity is slightly greater than the pressure of pumping fresh water or brine, about 0.1-1MPa (preferably 0.2-0.4MPa), in order to prevent brine from flowing back into the hydrogen injection and production well and ensure smooth hydrogen injection and brine drainage. As the hydrogen injection process progresses, the hydrogen-brine interface 17 gradually moves downward. When the hydrogen-water interface in the hydrogen injection and production well is 10-20 m (preferably 14-16 m) above the sediment channel, the pumping of fresh water or fresh brine is stopped, and the water injection control valve 8 of the cavity well is closed. After hydrogen injection continues to a certain level, the hydrogen-brine interface moves further downward. When the gas-liquid interface in the salt cavity of the hydrogen injection and production well is 5 m above the sediment area, the brine discharge control valve 9 of the brine discharge well is closed. After continuing to inject hydrogen to the design pressure, hydrogen injection is stopped, the design hydrogen injection pressure is maintained, and the hydrogen injection and production well is closed, completing the entire hydrogen injection cycle.

[0043] Water injection for hydrogen production and cavity formation: When producing hydrogen from the hydrogen storage reservoir, the brine drainage well 19 is first closed. The injection pressure is adjusted using the water injection control valve 8. Fresh water or brine is then injected into the salt cavity through the water injection casing 5. The fresh water or brine dissolves the salt rock to form brine, which gradually displaces hydrogen from top to bottom. The hydrogen in the hydrogen storage reservoir flows through the connecting channel into the hydrogen injection and production well 16 for production. At the same time as water injection begins, the hydrogen injection and production control valve 18 is opened, and a high-pressure pump is used to pump fresh water or brine (with a NaCl content of 20 g / L) from the cavity formation well 12 into the salt cavity to dissolve the salt rock and form a cavity. During hydrogen injection and pumping of fresh water or brine, the hydrogen production pressure in the hydrogen storage salt cavity must be slightly lower than the pressure of the fresh water or brine being pumped, approximately 0.1 to 1 MPa (preferably 0.2 to 0.4 MPa). This prevents brine from being discharged into the hydrogen injection and production well 16, ensuring smooth water injection, salt dissolution, and hydrogen production. As the hydrogen production process proceeds, the interface 17 of hydrogen and brine gradually moves upward. When the interface of hydrogen and brine is below the opening of the hydrogen injection and production casing 15 of the hydrogen injection and production well 16, hydrogen is produced from the hydrogen injection and production casing of the hydrogen injection and production well 16, and the water injection control valve 8 of the cavity well is closed at this time; when hydrogen production continues to reach a certain level, the interface of hydrogen and brine will further move upward. When the interface of hydrogen and brine is above the opening of the hydrogen injection and production casing of the gas injection and production well, hydrogen is only produced from the cavity casing 14 of the hydrogen injection and production well 16. When the produced hydrogen accounts for 25% to 30% of the volume capacity of the hydrogen storage cavity, the hydrogen injection and production well 16 and the hydrogen injection and production control valve 18 are closed, hydrogen production is stopped, and the entire hydrogen production cycle ends.

[0044] In the above-mentioned process of hydrogen injection and production and brine drainage linkage, the injection and production of hydrogen need to select appropriate injection and production pressures and flows according to the structural characteristics and pressure-bearing capacity of the salt cavern. A periodic hydrogen injection and production mode is adopted, and the hydrogen injection and production cycle is adjusted according to the dissolution of the salt cavern and the amount of brine discharged. In each cycle, the hydrogen injection and production flow rate and pressure should be gradually increased, and the maximum capacity should be gradually reached on the basis of ensuring the stability of the salt cavern. That is, usually in the initial stage of expansion, the water injection pressure and hydrogen injection and production pressure (usually 5-8MPa) and hydrogen injection and production flow rate (0.5-1m 3 / min) should be kept at a low level to avoid excessive (too low) salt rock pressure causing damage to the cavity structure; as the expansion progresses, in the middle of the expansion, the injection and production hydrogen pressure can be appropriately increased (8 to 12 MPa), and the hydrogen (water) injection flow rate (1 to 2 m 3 / min) can be gradually increased to accelerate the expansion of the cavity and the brine discharge process; in the later stage of expansion, when the capacity of the salt cavern is expanded to the expected target, the hydrogen injection flow rate (3 to 5m 3 The hydrogen injection rate (at 12-15 MPa / min) and the hydrogen injection pressure gradually reach their maximum values ​​(12-15 MPa) to ensure that the hydrogen storage reservoir's volume fully meets the design requirements. During the hydrogen injection phase, the hydrogen's primary function is to gradually expand the cavern and promote the discharge of brine dissolved in the salt rock, ensuring the stability of the salt cavern. During the hydrogen extraction phase, fresh water injection primarily expands the cavern volume, facilitating hydrogen extraction and cavity expansion.

[0045] The design of brine discharge rate should be closely coordinated with the hydrogen injection and production process. With the increase of hydrogen injection and production and the discharge of brine, the volume of salt caverns gradually expands, and the capacity of hydrogen storage is effectively increased. In the process of salt cavern expansion, the brine discharge flow rate usually needs to be controlled at a low level in the early stage, usually 0.5 to 1m 3 / min, in order to avoid uneven expansion of the cavity caused by excessive discharge of brine and to prevent excessive dissolution of salt rock. As the cavity gradually expands, the brine discharge flow rate can be gradually increased to 3-5m 3 / min, accelerating brine discharge.

[0046] Because the hydrogen injection and production process requires a long period of time to remove brine and create a cavity, the above steps are repeated after the next hydrogen injection and production cycle begins, and this cycle continues until the salt cavity volume of the cavity well reaches the required hydrogen storage capacity. Throughout the entire hydrogen injection and production process, the injection pressure of the cavity well changes dynamically with the operating pressure of the hydrogen injection and production well 16. During this entire period, the fresh water or brine injected can only dissolve the salt rock in the salt cavern of the cavity well, and will not affect the stability of the hydrogen injection and production well 16 and the connecting channel.

[0047] A dynamic adjustment method is used in the linkage process between hydrogen injection and production and brine discharge, adjusting the ratio of hydrogen injection and production to brine discharge based on real-time monitoring data to ensure a balance between the two. During the exchange of brine and hydrogen in the salt cavern hydrogen storage, the operating pressure fluctuation of the hydrogen storage is controlled within ±3% to improve the geological stability of the hydrogen storage. The brine discharge volume should be matched with the hydrogen injection flow rate to achieve stable capacity expansion.

[0048] 4. Monitoring and safety control:

[0049] During the hydrogen injection, brine extraction, and cavern expansion process, to ensure safety and stability, a real-time monitoring system monitors parameters such as hydrogen injection pressure, internal cavern temperature, and freshwater injection and brine discharge flow rates. Pressure sensors 21, temperature sensors 22, and flow sensors 23 installed at the wellhead monitor changes in hydrogen pressure and temperature, freshwater injection, and brine discharge within the hydrogen storage reservoir, respectively, to ensure the injection pressure is within the set range while preventing excessive temperatures from causing gas leakage or structural damage. If the pressure within the salt cavern is found to be too high during hydrogen injection, the injection rate is appropriately reduced. Conversely, if the pressure is too low, affecting the dissolution rate, the injection rate and water flow rate are increased. If the pressure within the salt cavern is found to be too low during hydrogen extraction, the extraction rate is appropriately reduced. Conversely, if the pressure is too high, affecting the dissolution rate, the extraction rate and water flow rate are increased. Stress-displacement sensors 24 are also used to monitor structural deformation of the salt cavern to prevent collapse or cracks caused by rapid or uneven expansion, thereby ensuring cavern stability. The monitoring system should have an early warning function, which can detect potential abnormal conditions (such as excessive pressure, uneven brine discharge, etc.) in a timely manner, and automatically adjust operating parameters, or start a safe shutdown procedure to avoid safety accidents.

[0050] 5. Storage capacity verification and adjustment:

[0051] After the expansion and cavitation are complete, the salt cavern's hydrogen storage capacity needs to be verified, assessing the maximum injectable hydrogen volume, effective gas storage volume, and gas injection and production efficiency. Pressure recovery tests and gas analysis are used to measure the salt cavern's capacity and evaluate the expansion's effectiveness. Based on the storage capacity test results, the operating parameters for hydrogen injection and production, as well as brine removal, are optimized to further improve the efficiency and safety of the hydrogen storage. Through these multiple tests and optimization of operating parameters, the expanded salt cavern ensures that the hydrogen storage meets hydrogen storage requirements, allowing for actual hydrogen injection and production operations.

[0052] The technical effects of the present invention are mainly manifested as follows:

[0053] Improve hydrogen storage capacity: By combining the brine drainage and hydrogen injection process with cavity expansion technology, the hydrogen storage space of the salt cavern can be effectively increased, thereby improving the overall capacity of the salt cavern hydrogen storage reservoir.

[0054] Enhanced hydrogen storage efficiency: While expanding capacity, precise control of hydrogen injection and brine removal processes can ensure maximum hydrogen storage efficiency and avoid unnecessary energy consumption and resource waste.

[0055] Ensure safety: By real-time monitoring of salt cavern pressure, temperature and other data, the injection and production process can be adjusted in a timely manner to ensure the long-term stable operation of the hydrogen storage reservoir and avoid salt rock damage or gas leakage.

[0056] Saving development costs: The present invention utilizes the existing salt caverns for expansion, avoiding the high development costs required for building new salt caverns, and has good economy and operability.

Claims

1. A method for expanding the capacity of an old cavity hydrogen storage reservoir in a connected well salt cavern by injecting hydrogen and producing brine, comprising the following steps: Step 1: Evaluation and connectivity analysis of the target salt cavern's connected wells and old cavities Step 2: Build a new well on the upper part of the connecting channel. The method is as follows: Drill two or more vertical wells on the upper part of the old cavity connecting channel of the old hydrogen injection and production well and the brine drainage well. The vertical wells enter the connecting channel as new cavity wells, and the two old connecting wells are used as hydrogen injection and production wells and brine drainage wells respectively; Arrange the tubing string according to cavity creation requirements; A water injection casing, a brine drainage casing, and a cavity creation casing are installed in the vertical well, with the water injection flow rate and the brine drainage flow rate being regulated by the water injection control valve and the brine drainage control valve, respectively. An oil and gas cushion protection fluid is injected through the oil injection casing, with the injection flow rate regulated by the oil and gas injection control valve to prevent excessive upward dissolution of the salt rock. A filter device and a flow control valve are installed on the brine drainage casing, thereby forming a cavity creation well on the basis of the vertical well. Step 3: Hydrogen injection and production are linked with brine discharge to expand the cavity: A hydrogen injection and production linkage operation plan is designed to promote brine discharge and cavity expansion through the hydrogen injection and production process. During the hydrogen injection and production linkage process, a periodic hydrogen injection and production mode is adopted. The hydrogen injection and production cycle is adjusted according to the dissolution of the salt cavern and the amount of brine discharged until the salt cavern volume of the cavity well reaches the required hydrogen storage capacity. Each hydrogen injection and production cycle includes: Inject hydrogen, drain brine and create cavities: The hydrogen injection pressure is adjusted by the hydrogen injection and production control valve, and hydrogen is injected into the salt cavity through the hydrogen injection and production casing to displace brine from top to bottom. The brine flows into the brine drainage well through the connecting channel and is discharged. At the beginning of gas injection, a high-pressure pump is used to pump fresh water or brine from the cavity creation well into the cavity to dissolve the salt rock and create cavities. The brine formed by the cavity creation is discharged through the brine drainage well. When injecting hydrogen and pumping fresh water or brine, it is necessary to prevent brine from flowing back into the hydrogen injection and production well. As the hydrogen injection process proceeds, hydrogen The interface between hydrogen and brine gradually moves downward. The timing to stop pumping fresh water or fresh brine is determined according to the position of the interface between hydrogen and brine in the hydrogen injection and production wells, and the injection control valve of the cavity making well is closed. When hydrogen is injected to a certain extent, the interface between hydrogen and brine moves downward further. The timing to close the brine discharge control valve of the brine discharge well is determined according to the position of the interface between hydrogen and brine in the salt cavity of the hydrogen injection and production wells. After continuing to inject hydrogen to the design pressure, stop hydrogen injection, maintain the design hydrogen injection pressure and close the hydrogen injection and production wells, and the entire hydrogen injection cycle ends. Water injection for hydrogen production and cavity creation: When hydrogen is produced in the hydrogen storage reservoir, the brine drainage well is closed, and the injection pressure is adjusted by the water injection control valve. Fresh water or brine is injected into the salt cavity through the water injection casing, and brine is formed after dissolving the salt rock. The brine gradually displaces hydrogen from top to bottom, and the hydrogen in the hydrogen storage reservoir flows into the hydrogen injection and production well through the connecting channel to be produced; at the same time as the water injection begins, the hydrogen injection and production control valve is opened, and a high-pressure pump is used to pump fresh water or brine from the cavity creation well into the salt cavity to dissolve the salt rock and create a cavity; when injecting hydrogen and pumping fresh water or brine, it is necessary to prevent the brine from being discharged. to the hydrogen injection and production well; as the hydrogen production process proceeds, the interface between hydrogen and brine gradually moves upward. When the interface between hydrogen and brine is below the hydrogen injection and production casing of the hydrogen injection and production well, hydrogen is produced from the hydrogen injection and production casing of the hydrogen injection and production well, and the water injection control valve of the cavity well is closed at this time; after hydrogen production continues to reach a certain level, the interface between hydrogen and brine further moves upward. When the interface between hydrogen and brine is above the hydrogen injection and production casing of the gas injection and production well, hydrogen is produced from the cavity casing of the hydrogen injection and production well. When hydrogen production stops, the hydrogen injection and production well and the hydrogen injection and production control valve are closed, and the entire hydrogen production cycle ends; Step 4: Monitoring and safety control of the process of expanding and creating the cavity by linking hydrogen injection and production with brine removal; Step 5: Storage capacity verification and adjustment.

2. The method for expanding the capacity of the hydrogen storage reservoir in the old cavity of the connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner according to claim 1 is characterized in that: The method for step one is: conduct geological survey and assessment of the old cavity of the connected wells in the target salt cavern to obtain the basic geological characteristic data of the hydrogen storage reservoir in the old cavity of the connected wells, including the thickness of the salt layer, pore structure, distribution of soluble salt layers, and physical and mechanical properties of the salt rock; evaluate the hydrogen fluidity and connectivity in the old cavity of the salt cavern and the solubility of the salt rock to determine whether the old cavity of the connected well is suitable for expansion operation and the expected capacity of the cavity after expansion.

3. The method for expanding the capacity of the hydrogen storage reservoir in the old cavity of the connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner according to claim 1 is characterized in that: Step 2: During the drilling process of the vertical well, instead of drilling directly into the connecting channel, water injection and fracturing are performed at an appropriate distance above the connecting channel. After the fracturing enters the connecting channel, fresh water or brine is continued to be injected for a period of time to prevent the bare hole section of the brine drainage well from shrinking, collapsing or being blocked.

4. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner according to claim 1 is characterized in that: In each hydrogen injection and production cycle, the hydrogen injection and production flow rate and pressure should be gradually increased, and gradually reach the maximum capacity on the basis of ensuring the stability of the salt cavern; in the process of linkage between hydrogen injection and production and brine discharge, a dynamic adjustment method is adopted to adjust the ratio of hydrogen injection and production to brine discharge according to real-time monitoring data to ensure the balance between the two; in the process of mutual replacement of brine and hydrogen in the salt cavern hydrogen storage reservoir, the operating pressure fluctuation of the hydrogen storage reservoir is controlled within ±3% to improve the geological stability of the hydrogen storage reservoir, and the brine discharge volume is matched with the hydrogen injection flow rate to achieve stable capacity expansion.

5. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner according to claim 1, characterized in that: In each hydrogen injection and production cycle of step 3, the hydrogen injection and production flow rate and pressure should be gradually increased. The method of gradually reaching the maximum capacity on the basis of ensuring the stability of the salt cavern is as follows: in the initial expansion stage, the water injection pressure and hydrogen injection and production pressure are controlled in the range of 5-8 MPa, and the hydrogen injection and production flow rate is controlled in the range of 0.5-1m 3 / min range to avoid damage to the cavity structure caused by excessive or insufficient salt rock pressure; as the expansion proceeds, in the middle stage of expansion, the hydrogen injection and production pressure is appropriately increased, and at the same time, the flow rate of hydrogen or water injection is gradually increased to accelerate the expansion of the cavity and the brine discharge process; in the later stage of expansion, when the capacity of the salt cavern is expanded to the expected target, the hydrogen injection flow rate and hydrogen injection pressure gradually reach the maximum value to ensure that the volume of the hydrogen storage reservoir fully meets the design requirements.

6. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner according to claim 1, characterized in that: During the salt cavern expansion process, the brine discharge flow rate is controlled at a low level in the early stage to avoid uneven expansion of the cavity caused by excessive brine discharge and to prevent excessive dissolution of salt rock; as the cavity gradually expands, the brine discharge flow rate gradually increases to accelerate brine discharge.

7. The method for expanding the capacity of the hydrogen storage reservoir in the old cavity of the connected well salt cavern by injecting and producing hydrogen and removing brine in a linked manner according to claim 1, characterized in that: In step four, the pressure sensor, temperature sensor and flow sensor installed at the wellhead are used to monitor the hydrogen pressure changes, temperature changes, fresh water injection, and brine discharge flow changes in the hydrogen storage tank, respectively, to ensure that the hydrogen injection pressure is within the set range and to prevent gas leakage or structural damage caused by excessive temperature; the structural deformation of the salt cavern is monitored by the stress displacement sensor, so as to realize the monitoring and safety control of the expansion and cavity creation process of the linkage between hydrogen injection and production and brine discharge.

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