Communication well salt cavern old cavity hydrogen storage reservoir hydrogen injection and production and brine discharge linkage cavity building and capacity expansion method

Abstract

The invention provides a connected well salt cavern old cavity hydrogen storage reservoir hydrogen injection and production and brine discharge linkage cavity construction and capacity expansion method. The method comprises the following steps that 1, evaluation and connectivity analysis of a connected well old cavity of a target salt cavern are conducted; secondly, a new well is built on the upper portion of the communication channel; step 3, hydrogen injection and production and brine discharge linkage capacity expansion and cavity construction: designing a hydrogen injection and production and brine discharge linkage operation scheme, pushing brine discharge and cavity expansion through a hydrogen injection and production process, adopting a periodic hydrogen injection and production mode in the hydrogen injection and production and brine discharge linkage process, and adjusting the hydrogen injection and production period according to the dissolution condition of the salt cavern and the brine discharge amount, the volume of the salt cavity of the cavity building well reaches the required capacity of the hydrogen storage reservoir; 4, monitoring and safety control are conducted on the hydrogen injection and production and brine discharge linkage capacity expansion and cavity construction process; and 5, verifying and adjusting the storage capacity.

Description

Technical Field

[0001] The invention relates to the field of hydrogen storage technology, in particular to a brine-exhausting linked cavity-making and capacity expansion method suitable for a hydrogen injection and production process of an old cavity hydrogen storage reservoir in a connected well salt cavern, belonging 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 the application of hydrogen energy. 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 mainly used for natural gas and compressed air storage. Unlike natural gas and compressed air, hydrogen has the characteristics of low density, high activity, high diffusivity, low viscosity and strong permeability, and the storage conditions of hydrogen are relatively harsh. Therefore, when the old salt cavern gas storage is used as a resource for the construction of salt cavern hydrogen storage, it is necessary to more accurately control the shape and volume of the cavity to ensure safe and efficient hydrogen storage.

[0004] At present, the 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. The two old water injection wells 13 and brine drainage wells 19 are drilled into the target salt rock layer in sequence and built by 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). Most of the gas storage cavities built by this water-soluble cavity method are dumbbell-shaped. Figure 1 Since my country's salt rock layers contain a large amount of insoluble or sparingly soluble impurities, a sediment zone 11 is likely to appear in the horizontal connecting channel. The main components of the solid particles in the sediment zone are calcium sulfate, calcium carbonate, magnesium hydroxide, and sparingly soluble or slightly soluble silicates. There are pores between the solid particles and they are filled with brine.

[0005] When the dumbbell-shaped old salt cavern gas storage is used as a salt cavern hydrogen storage, the high-pressure hydrogen will cause uneven stress distribution in the cavity during the cyclic storage and release process, especially in the middle large-span connecting channel, which increases the risk of collapse or deformation of the upper roof. At the same time, the upper salt mine of the middle large-span connecting channel is not dissolved, resulting in idle waste of salt mine resources and reducing the available gas storage space. In addition, this irregular shape of the cavity makes the injection and extraction of hydrogen more complicated, increasing the difficulty of monitoring and maintenance during the cyclic injection and extraction process. Due to the creep characteristics of salt rock, during the operation of the salt cavern hydrogen storage, with the injection and extraction of hydrogen, the pressure in the hydrogen storage will change greatly, and the salt cavern volume contraction and other problems are prone to occur. Therefore, when constructing a salt cavern hydrogen storage, especially when the old cavity of the salt cavern in the connecting well is expanded to store hydrogen, it is usually faced with how to quickly and safely expand the cavity capacity, improve the hydrogen storage efficiency and accelerate the commissioning of the hydrogen storage.

[0006] At present, there is relatively little research on the methods of injecting and producing hydrogen, draining brine, and expanding the capacity of caverns in connected well salt caverns. The 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 cavity expansion by linking hydrogen injection and production and brine removal in an old cavity hydrogen storage reservoir of a connected well, aiming to reasonably regulate the hydrogen injection and production and brine removal processes, utilize the connectivity in the salt caverns and the solubility characteristics of salt rock, and simultaneously remove brine to expand the cavity during the hydrogen injection and production 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 production operation as soon as possible. The technical scheme 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 hydrogen, producing hydrogen and removing brine, 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 passage of the old hydrogen injection and production well and the brine drainage well. The vertical wells enter the connecting passage as new cavity making wells. The two old connecting wells are used as hydrogen injection and production wells and brine drainage wells respectively.

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

[0013] A water injection casing, a brine drainage casing and a cavity-making casing are installed in the vertical well, wherein the water injection flow rate and the brine drainage flow rate are adjusted by the water injection control valve and the brine drainage control valve respectively; an oil and gas cushion layer protection liquid is injected through the oil injection casing, and the injection flow rate of the oil and gas cushion layer protection liquid is adjusted by the oil injection control valve to prevent excessive upward dissolution of salt rock; a filtering device and a flow control valve are set on the brine drainage casing, thereby forming a cavity-making well on the basis of the vertical well;

[0014] Step 3: Hydrogen injection and production and brine discharge linkage to expand the cavity: Design a hydrogen injection and production linkage operation plan, promote brine discharge and cavity expansion through hydrogen injection and production process, and adopt a periodic hydrogen injection and production mode in the process of hydrogen injection and production linkage, and adjust the hydrogen injection and production cycle according to the dissolution of the salt cavern and the amount of brine discharged, until the salt cavity volume of the cavity well reaches the required hydrogen storage capacity;

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

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

[0017] Furthermore, the method of step one is: to conduct geological survey and evaluation on the connected well old cavity of the target salt cavern, and obtain the basic geological characteristic data of the connected well old cavity gas storage, including the thickness of the salt layer, pore structure, distribution of soluble salt layer, and physical and mechanical properties of salt rock; to evaluate the fluidity and connectivity of hydrogen in the old cavity of the salt cavern and the solubility of salt rock, to determine whether the connected well old cavity 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 continuously 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 to 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 well, and the water 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 well. After hydrogen is injected to the design pressure, the hydrogen injection is stopped, the design hydrogen injection pressure is maintained, and the hydrogen injection and production well is closed, 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 water 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 to dissolve the salt rock to form brine. 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 upwards. 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 making well is closed at this time; after hydrogen production continues to reach a certain level, the interface between hydrogen and brine further moves upwards. 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 making 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 to gradually reach the maximum capacity on the basis of ensuring the stability of the salt cavern; in the linkage process of 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 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 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 stage of capacity expansion, the water injection pressure and hydrogen injection and production pressure are controlled in the range of 5-8MPa, and the hydrogen injection and production flow rate is controlled in the range of 0.5-1m 3 / min range to avoid excessive (too low) salt rock pressure causing damage to the cavity structure; as the capacity expansion proceeds, in the middle stage of capacity expansion, the hydrogen injection and production pressure is appropriately increased, and 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 capacity expansion, when the capacity of the salt cavern is expanded to the expected target, the hydrogen injection flow rate and 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 expansion of the salt cavern, 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.

[0025] Furthermore, in step four, the pressure sensor, temperature sensor and flow sensor installed at the wellhead are used to monitor the hydrogen pressure change, temperature change 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, 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 cavity creation process of hydrogen injection and production and brine discharge linkage expansion.

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

[0027] 1 The present invention combines the process of hydrogen injection and production with the process of brine discharge. By precisely controlling the flow rates of hydrogen injection and brine discharge, the connectivity in the salt cavern and the solubility of the salt rock are fully utilized, the process of volume expansion and cavity creation 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 arrangement, and can also reduce problems such as pipeline blockage in the brine treatment process. Through reasonable control and adjustment, the cavity creation speed is accelerated, and the risks caused 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 cavity expansion structure for connecting well salt cavern hydrogen storage reservoir to inject hydrogen, produce brine and discharge brine

[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 filtering 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 is described below in conjunction with 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 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 with 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, so as to achieve the effect of producing hydrogen and dissolving salt rock. The specific steps are as follows:

[0034] 1. Old cavity assessment and connectivity analysis:

[0035] Before expanding the cavern, we first conduct a comprehensive geological survey and assessment of the old caverns in the connected wells of the target salt caverns. We use advanced geological exploration technologies such as seismic exploration and geological drilling to obtain the basic geological characteristic data of the hydrogen storage reservoir in the old caverns 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 (such as strength and permeability). We use methods such as downhole gas composition analysis, flow path of injected hydrogen, and pressure monitoring to evaluate the fluidity and connectivity of hydrogen in the old caverns and the solubility of salt rock, and determine whether the old caverns of the connected wells are suitable for expansion operations, as well as the expected capacity of the cavity after expansion.

[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 (the well spacing is usually 250m to 500m) 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 two vertical wells enter the connecting channel as the new cavity making 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. Arrange the pipe string according to the cavity making requirements, install water injection casing 5 and brine drainage casing 6 and cavity making casing 14 in two vertical wells respectively, wherein the water injection flow rate and brine drainage flow rate are adjusted by water injection control valve 8 and brine drainage control valve 9 respectively. Inject the oil and gas cushion layer protection liquid through the oil injection casing 7. Usually, the thickness of the oil and gas cushion layer is 1 to 10m, preferably 2m to 5m. The main purpose of injecting the oil and gas cushion layer protection liquid is to isolate the contact between the oil and gas cushion layer and the salt rock to prevent dissolution and corrosion. The injection flow rate of the oil and gas cushion layer protection liquid is adjusted by the oil injection gas control valve 10 to prevent the salt rock from dissolving upward excessively, so as to ensure that the well end salt cave forms a stable roof morphology and the thickness of the roof protection layer reaches the preset thickness. The oil and gas cushion layer protection liquid can have various types and components, for example, crude oil or synthetic oil: this type of liquid can effectively isolate the oil and gas cushion layer from the salt rock to prevent gas leakage or salt rock dissolution; organic solvent: some organic solvents such as alkanes, cycloalkanes, etc. can also be used in the protection liquid.

[0038] The brine discharge casing 6 is made of new corrosion-resistant and anti-clogging materials (such as special ceramic coated steel pipes, etc.), and a filter device 20 is set on the brine discharge casing 6 to prevent salt crystallization or other impurities from clogging the pipeline. At the same time, a flow control valve 9 is installed on the brine discharge pipeline to accurately adjust the brine discharge flow according to the brine discharge flow demand.

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

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

[0041] After the construction of the two new wells for cavity creation is completed, the key to designing a reasonable linkage operation plan for hydrogen injection and production and brine discharge is to coordinate hydrogen injection, production and brine discharge to gradually dissolve the salt rock and expand the volume of the salt cavern, while avoiding excessive hydrogen injection and production that may lead to cavity instability. The core of cavity expansion is to promote brine discharge and cavity expansion through the process of hydrogen injection and production. Under the premise of ensuring good connectivity of the salt cavern, hydrogen is injected to increase the gas pressure inside the salt cavern through the expansion of the gas, dissolve the surrounding salt rock, and gradually expand the cavity volume.

[0042] Inject hydrogen, drain brine and create a cavity: 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 to displace 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 to create a cavity. 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, which is about 0.1-1MPa (preferably 0.2-0.4MPa). The purpose is to prevent brine from flowing back into the hydrogen injection and production well and ensure the smooth progress of hydrogen injection and brine drainage. As the hydrogen injection process proceeds, the interface 17 of hydrogen and brine gradually moves downward. When the hydrogen-water interface in the hydrogen injection and production well is located 10 to 20 m (preferably 14 to 16 m) above the sediment channel, stop pumping fresh water or fresh brine, and close the water injection control valve 8 of the cavity making well. When hydrogen injection continues to a certain extent, the interface of hydrogen and brine moves further downward. When the gas-liquid interface in the salt cavity of the hydrogen injection and production well is located 5 m above the sediment area, close the brine discharge control valve 9 of the brine discharge well, continue to inject hydrogen to the design pressure, and then stop injecting hydrogen, maintain the design hydrogen injection pressure and close the hydrogen injection and production well, and the entire hydrogen injection cycle ends.

[0043] Water injection for hydrogen extraction and cavity making: When extracting hydrogen from the hydrogen storage reservoir, first close the brine discharge well 19, adjust the water injection pressure through the water injection control valve 8, and inject fresh water or brine into the salt cavity through the water injection casing 5. Fresh water or brine dissolves salt rock to form brine, and brine gradually displaces hydrogen from top to bottom. The hydrogen in the hydrogen storage reservoir flows into the hydrogen injection and extraction well 16 through the connecting channel to be extracted. At the same time as the water injection begins, open the hydrogen injection and extraction control valve 18, and use a high-pressure pump to pump fresh water or brine (NaCl content is 20g / L) from the cavity making well 12 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 ensure that the hydrogen extraction pressure in the hydrogen storage salt cavity is slightly less than the pressure of pumping fresh water or brine, which is about 0.1-1MPa (preferably 0.2-0.4MPa). The purpose is to prevent brine from being discharged into the hydrogen injection and extraction well 16, and to ensure that the water injection, salt dissolution, and hydrogen extraction process proceed smoothly. 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 making 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 making 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 flow rates 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 the 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 (8-12MPa), and the hydrogen (water) injection flow rate (1-2m 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 (3-5m 3 / min) and the hydrogen injection pressure gradually reach the maximum value (12-15MPa) to ensure that the volume of the hydrogen storage reservoir fully meets the design requirements. In the hydrogen injection stage, the role of hydrogen is mainly to gradually expand the cavity and promote the discharge of brine dissolved in salt rock to ensure the stability of the salt cavern cavity; in the hydrogen extraction stage, the injection of fresh water is mainly to expand the cavity volume to promote the extraction of hydrogen and the expansion of the cavity.

[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 kept low in the early stage, usually 0.5-1m 3 / min, in order to avoid uneven expansion of the cavity caused by excessive brine discharge and 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] Since it takes a long time to drain the brine and create a cavity during the hydrogen injection and production process, the above steps are repeated after the next hydrogen injection and production cycle begins, and the cycle continues until the volume of the salt cavity in the cavity-making well reaches the required hydrogen storage capacity. During the entire hydrogen injection and production brine drainage and cavity-making process, the water injection pressure of the cavity-making well changes dynamically with the change of the operating pressure of the hydrogen injection and production well 16, and the fresh water or brine injected during the entire time period can only dissolve the salt rock in the salt cave of the cavity-making well, and will not affect the stability of the hydrogen injection and production well 16 and the connecting channel.

[0047] In the process of linkage between hydrogen injection and brine discharge, a dynamic adjustment method is adopted to adjust the ratio of hydrogen injection and 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 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. The brine discharge volume should match the hydrogen injection flow rate to achieve stable capacity expansion.

[0048] 4. Monitoring and safety control:

[0049] In the process of hydrogen injection, brine drainage and cavity expansion, in order to ensure the safety and stability of the entire expansion and cavity making process, it is necessary to monitor the hydrogen injection pressure, the temperature inside the cavity, and the fresh water injection and brine discharge flow rates through a real-time monitoring system. The pressure sensor 21, temperature sensor 22 and flow sensor 23 installed at the wellhead monitor the hydrogen pressure changes, temperature changes, fresh water injection and brine discharge flow changes in the hydrogen storage reservoir to ensure that the hydrogen injection pressure is within the set range, while preventing gas leakage or structural damage caused by excessive temperature. If the pressure in the salt cavern is found to be too high during the hydrogen injection process, the hydrogen injection rate is appropriately reduced. On the contrary, if the pressure is too low and affects the dissolution rate, the hydrogen injection rate and the water injection and drainage volume need to be increased; if the pressure in the salt cavern is found to be too low during the hydrogen production process, the hydrogen production rate is appropriately reduced. On the contrary, if the pressure is too high and affects the dissolution rate, the hydrogen production rate and water injection flow rate are increased. It is also necessary to focus on monitoring the structural deformation of the salt cavern through the stress displacement sensor 24 to avoid collapse or cracks caused by excessively fast or uneven expansion, and to ensure the stability of the cavity. The monitoring system should have an early warning function, which can detect potential abnormal conditions (such as excessive pressure, uneven brine discharge, etc.) in time, 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 cavity making is completed, the hydrogen storage capacity of the salt cavern needs to be verified to evaluate the maximum amount of hydrogen that can be injected and produced, the effective gas storage volume, and the gas injection and production efficiency. The capacity of the salt cavern is measured through pressure recovery experiments, gas analysis, and other means to evaluate the expansion effect. According to the storage capacity test results, the operating parameters of hydrogen injection and production and brine removal are optimized to further improve the gas injection and production efficiency and safety of the hydrogen storage. Through the above multiple tests and optimization of operating parameters, it is ensured that the hydrogen storage after the salt cavern expansion meets the hydrogen storage demand so that it can be put into actual hydrogen injection and production operations.

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

[0053] Improving hydrogen storage capacity: By combining the brine discharge 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] Enhance hydrogen storage efficiency: While expanding capacity, precise control of hydrogen injection and brine removal processes can ensure that hydrogen storage efficiency is maximized, avoiding unnecessary energy consumption and waste of resources.

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

[0056] Saving development costs: The present invention utilizes the existing salt caverns for capacity expansion, thus 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 passage of the old hydrogen injection and production well and the brine drainage well. The vertical wells enter the connecting passage as new cavity making wells. The two old connecting wells are used as hydrogen injection and production wells and brine drainage wells respectively. Arrange the pipe string according to the cavity creation requirements; A water injection casing, a brine drainage casing and a cavity-making casing are installed in the vertical well, wherein the water injection flow rate and the brine drainage flow rate are adjusted by the water injection control valve and the brine drainage control valve respectively; an oil and gas cushion layer protection liquid is injected through the oil injection casing, and the injection flow rate of the oil and gas cushion layer protection liquid is adjusted by the oil injection control valve to prevent excessive upward dissolution of salt rock; a filtering device and a flow control valve are set on the brine drainage casing, thereby forming a cavity-making well on the basis of the vertical well; Step 3: Hydrogen injection and production and brine discharge linkage to expand the cavity: Design a hydrogen injection and production linkage operation plan, promote brine discharge and cavity expansion through hydrogen injection and production process, and adopt a periodic hydrogen injection and production mode in the process of hydrogen injection and production linkage, and adjust the hydrogen injection and production cycle according to the dissolution of the salt cavern and the amount of brine discharged, until the salt cavity volume of the cavity well reaches the required hydrogen storage capacity; Step 4: Monitoring and safety control of the process of expanding the cavity by hydrogen injection and production and brine removal; Step 5: Storage capacity verification and adjustment.

2. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting hydrogen and producing brine in a linked manner according to claim 1, characterized in that: The method of step one is: to conduct geological survey and evaluation on the old cavity of the connected wells of the target salt cavern, and 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 salt rock; to evaluate the fluidity and connectivity of hydrogen in the old cavity of the salt cavern and the solubility of salt rock, to determine whether the old cavity of the connected well is suitable for capacity expansion operation, and the expected capacity of the cavity after expansion.

3. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting hydrogen and producing brine in a linked manner according to claim 1, 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 continuously 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 hydrogen and producing brine in a linked manner according to claim 1, characterized in that: In step 3, each hydrogen injection and production cycle includes: Inject hydrogen to 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 well, and the water 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 well. After hydrogen is injected to the design pressure, the hydrogen injection is stopped, the design hydrogen injection pressure is maintained, and the hydrogen injection and production well is closed, 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 water 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 to dissolve the salt rock to form brine. 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 upwards. 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 making well is closed at this time; after hydrogen production continues to reach a certain level, the interface between hydrogen and brine further moves upwards. 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 making 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.

5. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting hydrogen and producing brine in a linked manner according to claim 1, characterized in that: In each hydrogen injection and production cycle, the hydrogen injection and production flow rate and pressure should be gradually increased to gradually reach the maximum capacity on the basis of ensuring the stability of the salt cavern; in the linkage process of 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.

6. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting hydrogen and producing 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 stage of capacity expansion, the water injection pressure and hydrogen injection and production pressure are controlled in the range of 5-8MPa, 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 capacity expansion proceeds, in the middle stage of capacity expansion, the hydrogen injection and production pressure is appropriately increased, and 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 capacity expansion, when the capacity of the salt cavern is expanded to the expected target, the hydrogen injection flow rate and injection pressure gradually reach the maximum value to ensure that the volume of the hydrogen storage reservoir fully meets the design requirements.

7. 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.

8. The method for expanding the capacity of the old cavity hydrogen storage reservoir of the connected well salt cavern by injecting hydrogen and producing brine in a linked manner according to claim 1, characterized in that: In step 4, the pressure sensor, temperature sensor and flow sensor installed at the wellhead are used to monitor the changes in hydrogen pressure, temperature, fresh water injection and brine discharge flow 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 stress displacement sensor is used to monitor the structural deformation of the salt cavern, so as to realize the monitoring and safety control of the cavity creation process of hydrogen injection and production and brine discharge linkage expansion.

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