Intelligent monitoring methods and systems for the entire lifecycle of liquefied natural gas storage facilities

Abstract

This application provides a method and system for full-cycle intelligent monitoring of liquefied natural gas (LNG) storage facilities. The method includes: installing distributed fiber optic temperature sensors in the surrounding rock of the storage cavern to monitor the ambient temperature; installing displacement sensors around the storage cavern to monitor convergence displacement; installing servo level gauges inside the storage cavern for level monitoring and alarm functions; installing multi-point averaging thermometers inside the storage cavern to measure the medium temperature; setting multi-level thresholds based on the ambient temperature, convergence displacement, level monitoring, and medium temperature; assessing the risk of freezing zone control, storage stability, and LNG leakage based on the multi-level thresholds and generating assessment results; implementing corresponding prevention and control measures based on the assessment results; and uploading the assessment results to a ground control room via fiber optic cable, and implementing corresponding prevention and control measures based on the assessment results, thereby achieving full lifecycle monitoring.

Description

Technical Field

[0001] This application relates to the technical field of cryogenic liquefied natural gas (LNG) storage facilities, specifically to a method and system for full-cycle intelligent monitoring of LNG storage facilities. Background Technology

[0002] Existing gas storage facilities primarily utilize depleted oil and gas reservoirs and salt caverns, but their site selection is severely limited by geological conditions, resulting in poor site suitability and slow construction progress. Rapidly advancing gas storage projects is crucial to addressing the pressure gap in the natural gas pipeline network and ensuring natural gas supply. In particular, the supply capacity of liquefied natural gas (LNG) is insufficient, and there is an urgent need to reduce the construction costs of new LNG storage facilities.

[0003] With the continuous growth of global natural gas utilization and the development of storage tank construction technology, the trend towards larger liquefied natural gas (LNG) storage tanks is becoming increasingly apparent. The construction technology for single-tank capacity tanks of 27 × 10⁴ cubic meters is mature, and the largest underground storage tanks have reached a capacity of 25 × 10⁴ cubic meters. Cryogenic underground LNG storage, as a new technology, can achieve single-tank capacities of up to one million cubic meters. Compared to above-ground and underground storage tanks, cryogenic underground LNG storage tanks are safer, more environmentally friendly, and require less land. As storage capacity increases, their economic advantages become more pronounced: the investment for above-ground LNG storage is approximately 10 yuan / cubic meter; for gas reservoir-type storage, it is approximately 8 yuan / cubic meter; and for underground LNG storage, the investment is expected to decrease to 6 yuan / cubic meter.

[0004] With the increasing number of liquefied natural gas (LNG) receiving terminals being built, available port resources are becoming increasingly limited. Low-temperature underground LNG storage facilities utilize abandoned mine resources, especially in inland areas where mines are widely distributed, offering a wide range of site selection options and promising development prospects. However, existing technologies in this area are still largely unexplored.

[0005] Currently, underground cryogenic liquefied natural gas (LNG) storage facilities are still in their initial stages, lacking mature construction cases and core technologies. In particular, the safety monitoring systems and control methods for the risks associated with cryogenic LNG storage, such as cryosphere control, storage stability, and LNG leakage, are not yet fully understood. Therefore, there is an urgent need to develop a comprehensive intelligent monitoring and safety risk control solution for the entire lifecycle of cryogenic LNG storage facilities. This would provide suitable construction and safety control solutions to address challenges such as concentrated gas consumption and the difficulties in building storage facilities. Summary of the Invention

[0006] This application proposes a method and system for full-cycle intelligent monitoring of liquefied natural gas storage facilities to address the shortcomings of the aforementioned prior art.

[0007] According to a first aspect of the embodiments of this application, a method for full-cycle intelligent monitoring of a liquefied natural gas (LNG) storage facility is provided, comprising:

[0008] Distributed fiber optic temperature sensors are installed in the surrounding rock of the storage cavern to monitor the ambient temperature of the temperature field, and displacement sensors are installed around the storage cavern to monitor the convergence displacement.

[0009] A servo level gauge is installed inside the storage cavern for level monitoring and alarm functions, and a multi-point averaging thermometer is installed inside the storage cavern for measuring the temperature of the medium.

[0010] Multiple threshold levels are set based on the ambient temperature, the convergence displacement, the liquid level monitoring, and the medium temperature;

[0011] The risk assessment of freezing zone control, storage stability, and liquefied natural gas leakage is based on the multi-level thresholds, and assessment results are generated. Corresponding prevention and control measures are then implemented based on the assessment results.

[0012] The assessment results are uploaded to the ground control room via optical fiber, and corresponding prevention and control measures are implemented based on the assessment results to achieve full life cycle monitoring.

[0013] In some embodiments, the step of installing distributed fiber optic temperature sensors in the surrounding rock of the storage cavern and monitoring the ambient temperature of the temperature field, and installing displacement sensors around the storage cavern and monitoring convergence displacement, includes:

[0014] The process involves drilling holes in the surrounding rock of the storage cavern and continuously arranging distributed optical fiber temperature sensors at multiple locations along the drilling depth along the cavern wall at preset intervals, thereby monitoring the ambient temperature of the temperature field based on the distributed optical fiber temperature sensors.

[0015] The displacement sensors are arranged at the interface between the lining layer and the surrounding rock of the storage cavern and in the surrounding rock at different depths, and the convergence displacement is monitored based on the displacement sensors.

[0016] In some embodiments, the step of installing a servo level gauge inside the storage cavern for level monitoring and alarm functions, and installing a multi-point averaging thermometer inside the storage cavern for measuring the medium temperature, includes:

[0017] Pressure transmitters and temperature transmitters are installed on the pipelines leading to and from liquefied natural gas.

[0018] The servo level gauge is installed on the operating platform at the top of the cavern inside the storage cavern. The servo level gauge is connected to the high and low level alarm system to monitor the liquid level and trigger the alarm.

[0019] The multi-point average thermometer is installed vertically along the cave wall inside the storage cave to measure the temperature of the medium.

[0020] In some implementations, the multi-level thresholds include temperature thresholds, and assessing the freeze zone control risk based on the multi-level thresholds includes:

[0021] When the ambient temperature is no more than ±150% below the temperature threshold, the risk of freezing zone is assessed as normal.

[0022] When the temperature at any single point in the ambient temperature is lower than the temperature threshold by more than ±150%, the risk of the freezing zone is assessed as a warning state.

[0023] When any number of individual points in the ambient temperature are lower than the temperature threshold by more than ±150%, the freezing zone risk is assessed as a dangerous state.

[0024] In some implementations, the multi-level thresholds include daily displacement fluctuation thresholds, and the assessment of the storage stability risk based on the multi-level thresholds includes:

[0025] When the daily fluctuation of the convergence displacement does not exceed 2 mm, the stability risk of the storage facility is assessed as normal.

[0026] When the daily fluctuation of the convergence displacement exceeds 2 mm but does not exceed 5 mm, the stability risk of the storage facility is assessed as an early warning state.

[0027] When the daily fluctuation of the convergence displacement exceeds 5 mm, the stability risk of the storage facility is assessed as dangerous.

[0028] In some implementations, the multi-level threshold includes a level-corrected liquid level threshold, and assessing the risk of liquefied natural gas leakage based on the multi-level threshold includes:

[0029] Evaporation loss is calculated based on the medium temperature, and the current liquid level value is obtained based on the evaporation loss and the liquid level monitoring results.

[0030] When the current liquid level is lower than the corrected liquid level threshold by more than ±1% but not more than ±3%, or the temperature deviation is not more than 3°C, the risk of liquefied natural gas leakage is assessed as normal.

[0031] When the current liquid level is lower than the corrected liquid level threshold by more than ±3% but not more than ±5%, or the temperature deviation exceeds 3°C but not more than 10°C, the risk of liquefied natural gas leakage is assessed as an early warning state.

[0032] When the current liquid level is lower than the corrected liquid level threshold by more than ±5% or the temperature deviation exceeds 10°C, the risk of liquefied natural gas leakage is assessed as a dangerous state.

[0033] In some embodiments, the method further includes:

[0034] A vibrating wire osmotic pressure sensor is buried around the rock mass near the cryosphere of the storage cavern to monitor the osmotic pressure.

[0035] Multiple threshold levels are set based on the ambient temperature, the convergence displacement, the liquid level monitoring, the medium temperature, and the osmotic pressure.

[0036] In some implementations, the multi-level thresholds include a pressure threshold, and the assessment of the freeze zone control risk based on the multi-level thresholds further includes:

[0037] The surrounding rock seepage pressure risk is assessed based on the aforementioned multi-level thresholds, wherein...

[0038] When the permeability pressure is lower than the pressure threshold by no more than ±20%, the permeability pressure risk of the surrounding rock is assessed as a safe state.

[0039] When the permeability pressure is lower than the pressure threshold by more than ±20% but not more than ±50%, the risk of permeability pressure in the surrounding rock is assessed as an early warning state.

[0040] When the osmotic pressure is lower than the pressure threshold by more than ±50% and is accompanied by abnormal temperature, the osmotic pressure risk of the surrounding rock is assessed as a dangerous state.

[0041] According to a second aspect of this application, a full-cycle intelligent monitoring system for a liquefied natural gas storage facility is provided, comprising:

[0042] The cavern perimeter monitoring module is used to install distributed fiber optic temperature sensors in the surrounding rock of the storage cavern and monitor the ambient temperature of the temperature field, and to install displacement sensors around the storage cavern and monitor convergence displacement.

[0043] The cavern interior monitoring module is used to install a servo level gauge inside the cavern of the storage tank for level monitoring and alarm, and to install a multi-point averaging thermometer inside the cavern of the storage tank for measuring the temperature of the medium.

[0044] A multi-level threshold building module is used to set multi-level thresholds based on the ambient temperature, the convergence displacement, the liquid level monitoring, and the medium temperature.

[0045] The risk assessment module is used to assess the risks of freezing zone control, storage stability, and liquefied natural gas leakage based on the multi-level thresholds, generate assessment results, and implement corresponding prevention and control measures based on the assessment results.

[0046] The lifecycle monitoring module is used to upload the assessment results to the ground control room via optical fiber and to implement corresponding prevention and control measures based on the assessment results, thereby realizing full lifecycle monitoring.

[0047] In some embodiments, the cavern perimeter monitoring module is also used to bury vibrating wire osmotic pressure sensors around the rock mass near the cryosphere of the storage cavern, and monitor osmotic pressure based on the vibrating wire osmotic pressure sensors;

[0048] The multi-level threshold building module is also used to set multi-level thresholds based on the ambient temperature, the convergence displacement, the liquid level monitoring, the medium temperature, and the osmotic pressure.

[0049] The beneficial effects of the full-cycle intelligent monitoring method and system for liquefied natural gas storage facilities according to the embodiments of this application include at least the following:

[0050] This application's embodiments achieve precise identification of cryosphere formation and evolution trends by real-time tracking of surrounding rock temperature field changes, preventing the risk of rock mass freezing and cracking due to temperature runaway; synchronously monitor convergence displacement (cavity wall shrinkage deformation towards the interior of the cavity) to promptly detect low-temperature shrinkage deformation of the rock mass, ensuring the long-term stability of the storage structure; implement real-time high and low liquid level alarms through servo level gauges to prevent leakage accidents caused by liquefied natural gas overflow or desiccation; measure medium temperature with multi-point averaging thermometers to assess its state changes, providing direct evidence for leakage risk; achieve risk classification identification and improve response accuracy by defining a three-level system of normal range, early warning threshold, and danger threshold; comprehensively set multiple parameters to avoid misjudgment of single-point data and enhance the reliability of risk assessment; dynamically assess cryosphere risk and storage stability risk, and promptly implement grouting or structural reinforcement; combine leakage risk assessment with medium temperature and liquid level deviation to trigger valve control or isolation measures, effectively curbing the expansion of accidents; use fiber optic transmission to ensure data real-time performance and anti-interference, supporting remote monitoring from the ground control room; and automatically execute prevention and control measures based on assessment results to achieve intelligent management of the storage facility throughout its entire lifecycle from construction to operation. Attached Figure Description

[0051] Figure 1 This is a flowchart illustrating the full-cycle intelligent monitoring method for liquefied natural gas storage facilities according to an embodiment of this application.

[0052] Figure 2 This is a schematic diagram of the structure of the cryogenic liquefied natural gas storage rock mass under frozen and cracked conditions according to an embodiment of this application;

[0053] Figure 3 This is a schematic diagram of the structure of the monitoring section of the cryogenic liquefied natural gas storage facility according to an embodiment of this application;

[0054] Figure 4 This is a schematic diagram of the structure of monitoring section B or section C of the cryogenic liquefied natural gas storage facility according to an embodiment of this application;

[0055] Figure 5 This is a schematic diagram of the structure of monitoring section A in a cryogenic liquefied natural gas storage facility, as described in an embodiment of this application.

[0056] Figure 6 This is a distribution diagram of surface resistance thermometers in a cryogenic liquefied natural gas storage facility according to an embodiment of this application.

[0057] Figure 7 This is a schematic diagram of the structure of the pressure transmitter, temperature transmitter, and orifice flow meter for a cryogenic liquefied natural gas storage facility according to an embodiment of this application.

[0058] Figure 8 This is a schematic diagram of the full-cycle intelligent monitoring system for liquefied natural gas storage facilities, as described in an embodiment of this application. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0060] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed embodiments of the present application, but merely to illustrate selected embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are within the scope of protection of the embodiments of the present application.

[0061] It can be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0062] In the description of the embodiments of this application, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0063] This application discloses a method for full-cycle intelligent monitoring of liquefied natural gas (LNG) storage facilities, which is executed by a full-cycle intelligent monitoring system for LNG storage facilities. (See attached document.) Figure 1 As shown, the method includes steps 110-150.

[0064] Step 110: Install distributed fiber optic temperature sensors in the surrounding rock of the storage cavern and monitor the ambient temperature of the temperature field; install displacement sensors around the storage cavern and monitor the convergence displacement.

[0065] In some embodiments, the step of setting distributed optical fiber temperature sensors in the surrounding rock of the storage cavern and monitoring the ambient temperature of the temperature field includes: drilling holes in the surrounding rock of the storage cavern and continuously arranging distributed optical fiber temperature sensors at multiple locations along the drilling depth of the cavern wall at preset intervals, and monitoring the ambient temperature of the temperature field based on the distributed optical fiber temperature sensors.

[0066] For example, to detect the temperature at different locations in the surrounding rock of a cryogenic liquefied natural gas (LNG) storage facility and understand the spatiotemporal evolution of the cryosphere, distributed fiber optic temperature sensors are installed at different locations in the surrounding rock around the cavern. Fiber optic temperature sensors are also installed between the concrete lining and the insulation layer. Utilizing the optical fiber itself as the sensing element, the temperature distribution within the fiber's length is measured, offering advantages such as low cost, long measurement distance, accurate temperature readings, and high resolution. First, based on a finite element multi-field coupled numerical model, the approximate location of the 0°C isotherm of the cryosphere under the coupled conditions of the temperature field, force field, and seepage field is simulated and calculated. Then, the distributed fiber optic temperature sensors around the cavern are arranged accordingly. Taking this embodiment as an example, numerical simulation is performed using simulation software (such as COMSOL Multiphysics). The calculation shows that the 0°C isotherm of the cryogenic LNG storage facility is within approximately 4 meters around the cavern. Considering a safety margin of 1 meter, the temperature sensors are arranged within a 5-meter radius around the cavern.

[0067] See attached document Figure 3 -Appendix Figure 5 As shown, before constructing the concrete lining layer of the tunnel, three sections are arranged inside the tunnel, corresponding to sections A, B, and C respectively. Four monitoring boreholes are set in four directions for each section. Eight monitoring sensors are installed in each borehole at locations 1 meter, 2 meters, 3 meters, 4 meters, and 5 meters from the tunnel wall, between the tank wall and the insulation layer and the lining layer, between the lining layer and the surrounding rock, and at depths of 5 meters. The borehole diameter is 110 mm, and the borehole depth is 5.2 meters. Distributed fiber optic temperature sensors are continuously arranged horizontally along the borehole wall to detect temperature changes throughout the borehole and transmit the data to a server for temperature change analysis via a data acquisition instrument. Simultaneously, fiber optic temperature sensors are installed between the concrete lining and the insulation layer to detect temperature changes outside the insulation layer and to monitor the sealing effect of the stainless steel membrane. This step is based on surface resistance thermometers installed in abandoned tunnels. The execution conditions also include temperature sensors, pressure sensors, displacement sensors, liquid nitrogen (-162℃), an insulation layer (200 mm thick), and a concrete lining (350 mm thick), with a measurement interval of 1 meter.

[0068] In some embodiments, setting displacement sensors around the storage cavern and monitoring convergence displacement includes: arranging the displacement sensors at the interface between the lining layer and the surrounding rock of the storage cavern and in the surrounding rock at different depths, and monitoring the convergence displacement based on the displacement sensors.

[0069] For example, to detect the convergent displacement of the walls of a medium-sized cavern under ultra-low temperature conditions, convergence meters are installed around the cavern. These meters can detect the deformation development of the surrounding rock and support, and the data is transmitted to a server via a data acquisition instrument for displacement change analysis. For instance, to facilitate construction, equipment installation, and subsequent data evaluation, the displacement sensors are installed in locations similar to temperature sensors. Before the construction of the concrete lining layer in the cavern, three cross-sections are arranged inside the cavern, with four monitoring boreholes in four directions on each cross-section. These boreholes can be placed, for example, between the cavern wall, the insulation layer and the lining layer, and between the lining layer and the surrounding rock, as well as at 1 meter, 2 meters, 3 meters, 4 meters, and 5 meters on the cavern wall, with eight displacement sensors installed at each location. The borehole diameter is 110 mm, and the borehole depth is 5.2 meters.

[0070] This application's embodiments involve installing distributed fiber optic temperature sensors at different locations in the surrounding rock around a cryogenic liquefied natural gas (LNG) storage facility to detect temperature variations. To detect changes in osmotic pressure within the rock near the radial depths of the cavern, vibrating wire pressure sensors are embedded around the cavern. Furthermore, to detect the convergence displacement of the cavern wall under cryogenic conditions, displacement sensors are installed around the cavern. The number, location, and burial depth of each sensor can be optimized and adjusted according to the geological conditions and underground engineering layout during actual application.

[0071] Step 120: Install a servo level gauge inside the storage cavern and perform level monitoring and alarm functions; install a multi-point average thermometer inside the storage cavern and measure the medium temperature.

[0072] In some embodiments, the step of installing a servo level gauge inside the storage cavern and performing level monitoring and alarm functions includes: installing the servo level gauge on the operating platform at the top of the cavern inside the storage cavern, connecting the servo level gauge to a high and low level alarm system, and performing the level monitoring and alarm functions.

[0073] In some embodiments, installing a multi-point average thermometer inside the storage cavern and measuring the medium temperature includes: installing the multi-point average thermometer vertically along the cavern wall inside the storage cavern and measuring the medium temperature.

[0074] For example, at least one servo level gauge should be installed inside the tunnel to detect the liquid level and output high and low level alarm signals. A multi-point averaging thermometer should also be installed inside the tunnel, with one thermometer placed every 30 centimeters to measure the temperature of the medium at different heights within the tunnel. For instance, an operating platform, at least 1.5 meters high, can be installed on the top side of the tunnel, with one servo level gauge installed on the top platform to detect the liquid level and output high and low level alarm signals. A ball valve should be installed between the process connection interface (e.g., a 6' CLASS150 RF interface) and the servo level gauge to allow for calibration or maintenance of the level gauge.

[0075] See attached document Figure 6 As shown, a multi-point averaging thermometer is installed in the cavern to measure the temperature of the medium at different heights within the cavern. The temperature measurement instrument on the inner wall of the cavern's membrane steel plate is a surface resistance thermometer, with one thermometer installed every 30 cm. The resistance wire is connected to the transmitter via a flange at the cavern roof. (Refer to Appendix) Figure 7 As shown, one pressure transmitter is installed in each of the liquefied natural gas (LNG) inlet pipeline (inlet pipe) and LNG outlet pipeline (production pipe) in the cavern. These transmitters are used to detect the pressure of the cryogenic LNG in the pipelines and output high and low pressure alarm signals. The pressure transmitters can be installed remotely, maintaining a certain distance from the pressure tapping point to ensure that the installation location of the transmitter can reach ambient temperature.

[0076] In some implementations, the step further includes installing pressure transmitters and temperature transmitters on the inlet and outlet liquefied natural gas pipelines.

[0077] For example, see Appendix Figure 7 As shown, temperature transmitters are installed in the cryogenic liquefied natural gas (LNG) inlet and outlet pipes (inlet and outlet pipes). These transmitters utilize platinum resistance thermometers or integrated platinum resistance thermometers, with the sensing element being a platinum resistance thermometer (e.g., Pt100, or RTD for short). The temperature transmitters can be installed remotely as separate units. For measuring cryogenic media like LNG, this application uses a differential pressure flowmeter, saving the cost of orifice plate flowmeters. The orifice plate flowmeter used in this embodiment is economical, as gas phase flow monitoring does not require a high range ratio. Furthermore, compared to orifice plate flowmeters, classic Venturi flowmeters offer advantages such as high measurement accuracy, low head loss, short straight pipe installation requirements, low maintenance workload (measuring elements are essentially maintenance-free), and no need to replace the measuring element. Specially manufactured classic Venturi flowmeters can achieve a range ratio of 10:1. For applications with significant flow variations in cryogenic LNG pipelines, this embodiment uses a classic Venturi flowmeter for flow measurement.

[0078] Step 130: Set multiple threshold levels based on the ambient temperature, the convergence displacement, the liquid level monitoring, and the medium temperature.

[0079] The embodiments of this application improve the accuracy of the evaluation results by comprehensively implementing multi-level thresholds.

[0080] Step 140: Assess the risks of freezing zone control, storage stability, and liquefied natural gas leakage based on the multi-level thresholds, generate assessment results, and implement corresponding prevention and control measures based on the assessment results.

[0081] A significant characteristic of underground cryogenic liquefied natural gas (LNG) storage facilities is that the surrounding rock mass is subjected to extremely low temperatures. Rock contraction generates high tensile forces, and joints and fissures, as initial defects in the rock, will further open or expand under these conditions. This leads to long-term stability issues caused by the freezing of the rock mass, which can be categorized into three main risks: cryosphere control risk, storage stability risk, and LNG leakage risk. (See attached document) Figure 2 As shown, the tensile stress caused by temperature drops can also lead to new fractures, affecting the long-term stability of the surrounding rock of underground cryogenic liquefied natural gas (LNG) caverns. This also exacerbates leakage of the storage medium along these fracture surfaces and causes more evaporation losses, reducing the cavern's airtightness and potentially leading to underground storage failure. Specifically, cryosphere control risk can be understood as the risk of controlling the temperature field or cryosphere, i.e., by deploying temperature sensors within a certain range around the cryogenic LNG cavern to monitor changes in the temperature field and assess the risk of the cryosphere; storage stability risk can be understood as the stability risk of the cryogenic LNG storage facility, i.e., by monitoring data such as displacement caused by rock shrinkage, joint and fissure opening, and assessing the stability of rock damage and support structures caused by low temperatures; LNG leakage risk can be understood as the leakage risk of cryogenic LNG, i.e., by monitoring the liquid level inside the cavern, as well as the storage temperature and pressure in the cavern and inlet / outlet pipelines, and calculating based on evaporation losses, assessing the leakage risk of cryogenic LNG inside the cavern and inlet / outlet pipelines.

[0082] In one exemplary embodiment, based on monitoring data from thermometers, piezometers, displacement gauges, servo level gauges, etc., normal state, early warning thresholds, and danger thresholds are set respectively to assess risks such as freezing zone, surrounding rock permeability pressure, storage stability, and cryogenic liquefied natural gas leakage, and corresponding measures are taken to prevent and control these risks.

[0083] In some implementations, the multi-level thresholds include a temperature threshold, a daily displacement fluctuation threshold, and a corrected liquid level threshold.

[0084] In some implementations, assessing the freezing zone control risk based on the multi-level thresholds includes: assessing the freezing zone risk as normal when the ambient temperature is no more than ±150% below the temperature threshold; assessing the freezing zone risk as a warning state when any single point of the ambient temperature is more than ±150% below the temperature threshold; and assessing the freezing zone risk as a dangerous state when multiple single points of the ambient temperature are more than ±150% below the temperature threshold.

[0085] For example, a total of eight monitoring sensors are used to monitor and assess the risk of temperature field or cryosphere by embedding them in the tank wall, between the insulation layer and the lining layer, between the lining layer and the surrounding rock, and at depths of 1 meter, 2 meters, 3 meters, 4 meters, and 5 meters in the tunnel wall. Under normal conditions, the temperature monitored by each sensor is below the temperature threshold, which is understood as a preset temperature design value, obtained through multi-field coupling simulation. Monitoring is conducted once a week. For warning thresholds, such as when the temperature of a sensor drops abnormally to below 150% of the design value, it may be due to insulation failure or liquefied natural gas leakage; monitoring for these thresholds is conducted four times a day. For danger thresholds, such as when the temperature of multiple sensors continues to rise, especially when the outermost temperature sensor drops below 150% of the design value, it indicates that the cryosphere is expanding and the project's energy consumption will increase; monitoring for these thresholds is conducted in real time. The remedial measures include: if the temperature field or cryosphere monitoring range exceeds the preset value, the project's cold energy consumption and storage benefits can be calculated based on the actual monitored cryosphere range. If it is still within an acceptable range, the cryosphere design scheme can be optimized and adjusted, and the storage scheme of the cryogenic liquefied natural gas storage facility can be adjusted accordingly. If it is not within an acceptable range, it is recommended to take measures such as consolidation grouting to reduce permeability and improve the quality of the surrounding rock to reduce the cryosphere range.

[0086] In some implementations, assessing the storage stability risk based on the multi-level thresholds includes: assessing the storage stability risk as normal when the daily fluctuation of the convergence displacement does not exceed 2 mm; assessing the storage stability risk as a warning state when the daily fluctuation of the convergence displacement exceeds 2 mm but does not exceed 5 mm; and assessing the storage stability risk as a dangerous state when the daily fluctuation of the convergence displacement exceeds 5 mm.

[0087] In some embodiments, assessing the liquefied natural gas (LNG) leakage risk based on the multi-level thresholds includes: calculating evaporation loss based on the medium temperature, and obtaining the current liquid level value based on the evaporation loss and the results of the liquid level monitoring; when the current liquid level value is lower than the corrected liquid level threshold by more than ±1% but not more than ±3% or the temperature deviation is not more than 3°C, the LNG leakage risk is assessed as a normal state; when the current liquid level value is lower than the corrected liquid level threshold by more than ±3% but not more than ±5% or the temperature deviation is more than 3°C but not more than 10°C, the LNG leakage risk is assessed as a warning state; when the current liquid level value is lower than the corrected liquid level threshold by more than ±5% or the temperature deviation is more than 10°C, the LNG leakage risk is assessed as a dangerous state.

[0088] As a preferred embodiment, the calculation of evaporation loss based on medium temperature is specifically achieved through the following empirical formula:

[0089] BOR=k×(T medium -T setpoint )×P / V;

[0090] Where BOR is the instantaneous evaporation loss rate, T medium T is the average temperature of the medium measured by a multi-point averaging thermometer. setpoint The standard storage temperature for liquefied natural gas is -162℃, P is the pressure inside the cavern measured by a pressure transmitter, V is the volume of liquefied natural gas corresponding to the current liquid level, and k is a correction factor related to the thermodynamic characteristics of the storage facility.

[0091] As a preferred embodiment, obtaining the current liquid level value based on evaporation loss and liquid level monitoring can be performed according to the following steps: the original liquid level value read by the servo level gauge is L. raw Based on the BOR value mentioned above, calculate the evaporation loss ΔV within a unit time Δt: ΔV = BOR × V × Δt; convert the evaporation loss ΔV into the corresponding liquid level drop ΔL; finally, use the current liquid level value L for risk assessment. current =L raw +ΔL, this value has deducted the effect of natural evaporation and can more realistically reflect the liquid level change caused by potential leakage.

[0092] For example, six displacement sensors are installed between the lining layer and the surrounding rock, and at depths of 1 meter, 2 meters, 3 meters, 4 meters, and 5 meters on the tunnel wall to monitor and assess the stability risk of the surrounding rock. A normal state could be defined as a daily fluctuation in convergent displacement of no more than 2 millimeters, monitored weekly. A warning threshold could be defined as a daily fluctuation in convergent displacement greater than 2 millimeters but not exceeding 5 millimeters, triggering enhanced monitoring four times a week. Combined with historical monitoring data, localized reinforcement of the surrounding rock and support structure can be implemented. A danger threshold could be defined as a daily fluctuation in convergent displacement greater than 5 millimeters, monitored in real time. This state might be due to excessively low surrounding rock temperature leading to unexpected joint and fissure expansion, resulting in excessive damage to the surrounding rock and affecting the structural stability of the tunnel. The measures to be taken in this step may include, for example, immediately stopping construction and taking measures such as structural reinforcement and consolidation grouting; during operation, reducing the amount of cryogenic liquefied natural gas stored in the cavern, reducing the groundwater seepage around the cavern, and taking grouting reinforcement measures for the surrounding rock to improve the overall stability of the cryogenic liquefied natural gas storage facility.

[0093] In one exemplary embodiment, the leakage risk of cryogenic liquefied natural gas (LNG) can be assessed by monitoring the liquid level inside the cavern, as well as the storage temperature and pressure in the cavern and inlet / outlet pipelines, and calculating based on evaporation losses. Specifically, the LNG level inside the cavern is monitored using a servo level gauge, the storage temperature of the LNG is monitored using a cavern wall thermometer, and the delivery pressure of the LNG is monitored using a pressure transmitter. After deducting evaporation losses, the leakage risk of cryogenic LNG is assessed by comparing the results with the theoretical liquid level value. In this context, "normal state" can be understood as the servo level gauge monitoring data being between high and low liquid levels, with the corrected liquid level value within ±1% of the liquid level value after deducting evaporation loss (e.g., the measured daily evaporation loss rate BOR in this embodiment is 1‰), the cave wall thermometer monitoring data being within ±3℃ of the preset temperature value (e.g., the measured data in this embodiment is -100℃), and the liquefied natural gas delivery pressure and cave storage pressure monitored by the pressure regulator being within ±5% of the preset pressure value (e.g., 3MPa in this embodiment), with a monitoring frequency of once a week. The warning threshold can be understood as the servo level gauge monitoring data being higher than the high liquid level or lower than the low liquid level, with the corrected liquid level value being less than 3% of the liquid level value after deducting evaporation loss, and the cave wall thermometer... If the monitored data exceeds the preset temperature value by 3°C to 10°C, or if the liquefied natural gas (LNG) delivery pressure and the underground storage pressure monitored by the pressure regulator are 5% to 10% lower than the preset pressure value, enhanced monitoring will be triggered. This monitoring will be conducted four times a week, and historical monitoring data will be used to assess the risk of localized leaks. The danger threshold can be understood as follows: if the servo level gauge reading is below the low level, the corrected level value is less than 5% of the level value after deducting evaporation losses, the underground wall thermometer reading exceeds the preset temperature value by more than 10°C, or the LNG delivery pressure and the underground storage pressure monitored by the pressure regulator are 10% or more lower than the preset pressure value, enhanced monitoring will be triggered. This monitoring will be conducted four times a week, and historical monitoring data will be used to assess the risk of large-scale leaks. The handling measures in this step may include, for example, immediately closing the emergency shut-off valve of the storage facility through the central control system if a cryogenic LNG leak has occurred after assessment, stopping the LNG inlet and outlet operations, and closing the upstream and downstream valves of the leak point to reduce the leakage. The approach should be "rapid shut-off, effective isolation, scientific leak sealing, and strict prevention of secondary disasters." Risks will be minimized through technical means (such as grouting reinforcement, seepage prevention and reduction, and gas monitoring) and organizational management (such as tiered response and multi-departmental collaboration). The specific measures in this application can be dynamically adjusted according to the scale of the leak, prioritizing personnel safety and environmental protection.

[0094] In some embodiments, the method further includes: burying a vibrating wire osmotic pressure sensor around the rock mass near the cryosphere of the storage cavern, and monitoring the osmotic pressure based on the vibrating wire osmotic pressure sensor; and setting multiple threshold levels based on the ambient temperature, the convergence displacement, the liquid level monitoring, the medium temperature, and the osmotic pressure.

[0095] For example, to detect changes in osmotic pressure within the rock near the deep radial cryosphere of a tunnel, vibrating wire piezometers are embedded in the rock mass at the 4-meter location of the cryosphere, calculated numerically on both sides of the tunnel. Corresponding piezometers are also embedded within a 5-meter radius on the side at the same horizontal position. The data is transmitted to a server via a data acquisition device for pressure change analysis. A vibrating wire piezometer is a measuring device that can be permanently embedded in concrete or rock mass and can simultaneously measure the temperature at the embedment point, providing timely feedback on the cryosphere's diffusion location. To facilitate construction, equipment installation, and subsequent data evaluation, the vibrating wire piezometers are embedded in locations similar to temperature sensors. Three cross-sections are arranged within the tunnel, with four monitoring boreholes in four directions on each cross-section. Each borehole contains six monitoring sensors at points between the lining layer and the surrounding rock, and at depths of 1, 2, 3, 4, and 5 meters on the tunnel wall. The borehole diameter is 110 mm, and the borehole depth is 5.2 meters.

[0096] In some implementations, the multi-level threshold also includes a pressure threshold.

[0097] In some embodiments, assessing the freezing zone control risk based on the multi-level thresholds further includes: assessing the surrounding rock seepage pressure risk based on the multi-level thresholds, wherein when the seepage pressure is lower than the pressure threshold by no more than ±20%, the surrounding rock seepage pressure risk is assessed as a safe state; when the seepage pressure is lower than the pressure threshold by more than ±20% but no more than ±50%, the surrounding rock seepage pressure risk is assessed as a warning state; and when the seepage pressure is lower than the pressure threshold by more than ±50% and is accompanied by temperature anomalies, the surrounding rock seepage pressure risk is assessed as a dangerous state. Here, the temperature anomaly in this application is a key correlation indicator triggering the dangerous threshold, specifically referring to an abnormal change in monitored temperature data that significantly deviates from normal expectations at the same time as a sudden drop in surrounding rock seepage pressure. The specific judgment criteria include surrounding rock temperature anomalies and medium temperature anomalies. Surrounding rock temperature anomalies refer to data anomalies monitored by distributed fiber optic temperature sensors buried in the surrounding rock around the cavern. When the temperature of the surrounding rock corresponding to the area of ​​sudden pressure drop also decreases significantly and synchronously (for example, the temperature at the monitoring point is lower than 150% of the design temperature value at that point determined by the multi-field coupled numerical model), it can be determined as an accompanying temperature anomaly. This situation indicates that the insulation layer may have failed or liquefied natural gas (LNG) leakage has occurred, causing the low temperature to be directly conducted to the surrounding rock, triggering rapid freezing of groundwater and a sudden drop in seepage pressure. An abnormal temperature in the medium refers to an abnormal increase in the temperature of the LNG medium monitored by multi-point average thermometers installed inside the storage facility. When the pressure drops suddenly, if the average temperature of the LNG inside the tunnel is significantly higher than its standard storage temperature (-162℃), for example, if the temperature deviation continues to exceed 10℃, it is also determined as an accompanying temperature anomaly. This situation is usually caused by LNG leakage leading to a reduction in heat absorption during partial vaporization of the low-temperature liquid, or by external heat intrusion, which is important evidence of leakage risk. The aforementioned correlation judgment mechanism of "sudden pressure drop accompanied by temperature anomaly" greatly improves the accuracy of hazardous state identification, effectively avoids misjudgments caused by fluctuations in a single pressure parameter, and ensures the accuracy and reliability of the response to prevention and control measures.

[0098] The storage facility constructed in this application embodiment can be a storage tank excavated from stable rock. A stainless steel membrane is used as the first airtight barrier for the tank body, and frozen groundwater (cryosphere) is used as the second airtight barrier. An insulation layer, a waterproof layer, and a concrete lining are respectively set between the two barriers to achieve the function of low-temperature, airtight storage of liquefied natural gas.

[0099] For example, six pressure sensors are used to monitor and assess the risk of surrounding rock seepage pressure by embedding them in the tank wall, between the insulation layer and the lining layer, between the lining layer and the surrounding rock, and at depths of 1 meter, 2 meters, 3 meters, 4 meters, and 5 meters on the tunnel wall. The normal state can be understood as the seepage pressure being consistent with the historical baseline without significant fluctuations, and this is monitored weekly. The warning threshold can be understood as a sudden drop or continuous decrease in pressure (e.g., a decrease exceeding 20% ​​of the historical baseline), possibly caused by insulation failure or liquefied natural gas leakage leading to groundwater freezing, and this is monitored four times daily. The danger threshold can be understood as a sudden drop in pressure (e.g., a decrease exceeding 50% of the historical baseline), possibly indicating that the freezing zone has expanded, and this is monitored in real time. This embodiment of the application can perform correlation analysis based on the surrounding rock seepage pressure monitoring data and the monitoring data from the temperature sensors. A sudden drop in pressure accompanied by a decrease in temperature may indicate insulation failure or a liquefied natural gas leak inside the tunnel. The steps include: if the insulation fails, the insulation layer can be repaired; if there is a liquefied natural gas leak, the leaked liquefied natural gas needs to be removed, the frost-damaged surrounding rock and concrete lining layer in the leak area needs to be reinforced, and the adjacent surrounding rock needs to be grouted to reinforce and repair the rock mass damage.

[0100] This application embodiment monitors temperature field changes and assesses the risk of freezing zone by deploying temperature sensors within a certain range around the cryogenic liquefied natural gas (LNG) cavern. The stability risk of the cryogenic LNG storage is assessed by monitoring data such as displacement caused by rock shrinkage, joint and fissure opening, etc., to evaluate rock damage and support structure stability due to low temperatures. The leakage risk of cryogenic LNG is assessed by monitoring the liquid level inside the cavern, as well as the storage temperature and pressure in the cavern and inlet / outlet pipelines, and calculating based on evaporation losses. Temperature sensors around the cavern monitor and assess the risk of temperature field or freezing zone, seepage pressure sensors around the cavern monitor and assess the risk of surrounding rock seepage pressure, and displacement sensors around the cavern monitor and assess the risk of surrounding rock stability. Servo level gauges inside the cavern monitor the LNG level, cavern wall thermometers monitor the LNG storage temperature, and pressure transmitters monitor the LNG delivery pressure. After deducting evaporation losses, the results are compared with theoretical liquid level values ​​to assess the leakage risk of cryogenic LNG. Various risk monitoring systems are set with normal ranges, early warning thresholds, and danger thresholds to assess risks such as freezing zone, surrounding rock seepage pressure, storage stability, and cryogenic liquefied natural gas leakage, and corresponding measures are taken to control these risks.

[0101] Step 150: The assessment results are uploaded to the ground control room via optical fiber, and corresponding prevention and control measures are implemented based on the assessment results to achieve full life cycle monitoring.

[0102] In some implementations, this application embodiment sets up a data acquisition instrument in the tunnel to collect sensor data such as distributed fiber optic temperature sensors, piezometers, and convergence meters in the cavern; and sets up a programmable logic controller (PLC) to collect data from equipment such as pressure transmitters, temperature transmitters, and flow meters. All of the above signals are converted into optical signals and uploaded to the ground control room through optical fiber for intelligent monitoring and control throughout the entire life cycle.

[0103] The automatic control system of this application transmits relevant data such as temperature, displacement, seepage pressure, and liquid level from various detection instruments installed near the underground cavern to the ground control room, as shown in the attached diagram. Figure 8 As shown, data is stored and processed within a high-performance server, and then displayed on a large screen in the control room. By transmitting data such as temperature, displacement, seepage pressure, and liquid level from various monitoring instruments located near the underground cavern to the ground control room, where the data is stored and processed on a high-performance server and then displayed on a large screen in the control room, intelligent monitoring and safety risk prevention throughout the entire lifecycle of the cryogenic liquefied natural gas storage facility are achieved.

[0104] This application's embodiments achieve real-time tracking of surrounding rock temperature field changes, accurately identifying the formation and evolution trends of the cryosphere and preventing the risk of rock mass freezing and cracking due to temperature runaway; synchronously monitoring convergence displacement (cavity wall shrinkage deformation towards the interior) to promptly detect low-temperature shrinkage deformation of the rock mass and ensure the long-term stability of the storage structure; real-time high and low liquid level alarms are achieved through servo level gauges; multi-point averaging thermometers measure the medium temperature and assess its state changes, providing direct evidence for leakage risk; a three-level system of normal range, warning threshold, and danger threshold is defined to achieve risk classification and identification, improving response accuracy; comprehensive setting of multiple parameters avoids misjudgment of single-point data, enhancing the reliability of risk assessment; dynamic assessment of cryosphere risk and storage stability risk enables timely grouting or structural reinforcement; leakage risk assessment, combined with medium temperature and liquid level deviation, triggers valve control or isolation measures to effectively curb the escalation of accidents; fiber optic transmission ensures data real-time performance and anti-interference capabilities, supporting remote monitoring from the ground control room; and automatic execution of prevention and control measures based on assessment results enables intelligent management of the storage facility throughout its entire lifecycle from construction to operation.

[0105] This application also discloses a full-cycle intelligent monitoring system for liquefied natural gas (LNG) storage facilities. (See attached document.) Figure 8 As shown, the system includes: a cavern perimeter monitoring module 810, a cavern interior monitoring module 820, a multi-level threshold construction module 830, a risk assessment module 840, and a life cycle monitoring module 850.

[0106] The cavern perimeter monitoring module 810 is used to install distributed fiber optic temperature sensors in the surrounding rock of the storage cavern and monitor the ambient temperature of the temperature field, and to install displacement sensors around the storage cavern and monitor convergence displacement.

[0107] The cavern interior monitoring module 820 is used to install a servo level gauge inside the cavern of the storage tank for level monitoring and alarm, and to install a multi-point averaging thermometer inside the cavern of the storage tank for measuring the temperature of the medium.

[0108] The multi-level threshold building module 830 is used to set multi-level thresholds based on the ambient temperature, the convergence displacement, the liquid level monitoring, and the medium temperature.

[0109] The risk assessment module 840 is used to assess the risks of freezing zone control, storage stability, and liquefied natural gas leakage based on the multi-level thresholds, generate assessment results, and implement corresponding prevention and control measures based on the assessment results.

[0110] The life cycle monitoring module 850 is used to upload the assessment results to the ground control room via optical fiber and to implement corresponding prevention and control measures based on the assessment results, thereby realizing full life cycle monitoring.

[0111] In some embodiments, the cavern perimeter monitoring module 820 is also used to bury a vibrating wire osmotic pressure sensor around the rock mass near the cryosphere of the storage cavern, and to monitor the osmotic pressure based on the vibrating wire osmotic pressure sensor.

[0112] In some implementations, the multi-level threshold building module 830 is also used to set multi-level thresholds based on the ambient temperature, the convergence displacement, the liquid level monitoring, the medium temperature, and the osmotic pressure.

[0113] In one exemplary embodiment, this application example includes a data acquisition device installed in the tunnel to collect data from distributed fiber optic temperature sensors, piezometers, convergence meters, and other sensors within the cavern; and a programmable logic controller (PLC) to collect data from pressure transmitters, temperature transmitters, flow meters, and other equipment. All signals are converted into optical signals and transmitted via fiber optic cable to the ground control room for intelligent monitoring and control throughout the entire lifecycle. The control system of the cavern PLC is responsible for real-time monitoring of cavern pressure, temperature, liquid level, and other data, while simultaneously controlling the flow rate within the injection and production pipelines and the operating status of various equipment such as the unloading pressurization skid, thereby achieving automatic control of injection and production in the cryogenic liquefied natural gas storage facility and automatic adjustment of cavern pressure.

[0114] This application also discloses an intelligent monitoring system, which collects data (temperature, displacement, seepage pressure, liquid level) from sensors (temperature, displacement, seepage pressure, liquid level) preset near a cryogenic liquefied natural gas storage facility through a data acquisition module, constructs a data communication network, and transmits the raw data to an intelligent control system and a visualization terminal; stores and processes the raw data in a high-performance server, and finally visualizes the processed data and displays it on a data display platform.

[0115] This application also discloses an intelligent control system, which monitors the gas pressure, temperature, and liquid level of the test cavern in real time; the flow rate in the inlet and outlet pipelines and the working status of each piece of equipment; the pressure of the unloading pressurization skid and the radiation tower and the volume of released liquefied natural gas; thereby realizing automatic control of the inlet and outlet of the cryogenic liquefied natural gas cavern and automatic adjustment of the cavern pressure.

[0116] In some implementations, the intelligent control system monitors data such as temperature, seepage pressure, and displacement around the cryogenic liquefied natural gas (LNG) storage facility to determine the degree of rock frost damage and the extent of the cryosphere, assess the structural stability of the storage facility, and regulate cryosphere evolution. It automatically adjusts the operating power of the submersible pump in the production pipeline and the booster skid in the injection pipeline based on the LNG level and flow velocity data in the LNG cavern storage facility. By monitoring the pressure of the radiating tower and the volume of LNG released, the system can further analyze the LNG consumption of the cryogenic LNG storage facility in real time on a data display platform. By determining whether the gas pressure and LNG level data in the cavern reach preset thresholds, it automatically controls the evaporation gas pipe (see attached diagram). Figure 7 The pipeline valves of the BOG pipe are switched on and off, and a portion of the liquefied natural gas is automatically discharged, compressed and cooled into liquefied natural gas and stored in the storage tank. The storage tank is judged to have reached the storage threshold by the gas pressure and liquid level data of the storage tank, and the excess liquefied natural gas in the evaporation gas pipe is directly discharged into the external environment through the venting tower.

[0117] In some implementations, the hardware of the intelligent data monitoring and display platform includes data acquisition hardware, data transmission hardware, data storage and processing hardware, data display hardware, and auxiliary hardware. Specifically, data acquisition hardware includes sensors (temperature, osmotic pressure, liquid level, flow rate, displacement), data acquisition cards, etc.; data transmission hardware includes routers and switches, network interface cards, etc.; data storage and processing hardware includes servers, direct-attached storage (DAS), network-attached storage (NAS), storage area networks (SAN), etc.; data display hardware includes displays, printing devices, etc.; and auxiliary hardware includes overload protectors, short-circuit protectors, keyboards, mice, touchscreens, and power supply units (PSUs), etc.

[0118] This application addresses the current situation where there are no precedents for converting abandoned mine shafts into cryogenic liquefied natural gas (LNG) storage facilities, and existing storage technologies mainly focus on surface membrane tanks, salt cavern gas storage facilities, and depleted gas reservoir gas storage facilities. Surface membrane tanks are costly and small in scale, while salt cavern gas storage facilities and depleted gas reservoir gas storage facilities are greatly limited by geological structure, geographical resources, and location, making it difficult to meet the needs of large-scale underground gas storage facilities in severely gas-deficient areas. This application promotes the healthy development of cryogenic LNG storage facilities, has significant advantages in terms of both time and spatial scale, and is the best approach for long-term, large-scale gas storage, which is of great significance. This application's embodiments address the problems of small scale, high cost, and significant limitations imposed by geological conditions and geographical location in existing gas storage and cryogenic liquefied natural gas (LNG) storage methods. It solves the challenges of intelligent monitoring and safety control of LNG leakage risks. Through a complete system solution, from temperature, pressure, and displacement sensors in the surrounding rock of the cryogenic LNG storage facility, to servo level gauges, multi-point thermometers inside the cavern, and pressure and temperature transmitters for cryogenic LNG inlet and outlet pipelines, to the functional design of monitoring threshold settings and risk management measures for various monitoring data, and the structural design of important auxiliary systems such as monitoring data acquisition, data transmission, and the prevention and control platform architecture, all construction requirements can be met by selecting underground spaces with moderate strength and high stability. It exhibits extremely high tolerance for geological conditions and has a wide range of applications. In this embodiment of the application, distributed fiber optic temperature sensors, vibrating wire pressure sensors, and displacement sensors are installed around the cryogenic liquefied natural gas (LNG) storage facility. Servo level gauges and multi-point averaging thermometers are installed inside the cryogenic LNG storage facility. Pressure transmitters and temperature transmitters are installed on the cryogenic LNG inlet and outlet pipelines. A safety control platform is constructed in the ground control room. Together, they form a full life cycle intelligent monitoring system and safety risk control method for cryogenic LNG storage facilities. This solves the problem of intelligent monitoring and safety control of LNG leakage risks. The device parameters can be appropriately adjusted according to actual working conditions, and there is a large optimization space.

[0119] In some embodiments, the present application can be applied not only to liquefied natural gas (LNG) storage but also to cryogenic liquefied petroleum gas (LPG) storage, which is of significant value for natural gas reserves, comprehensive utilization of underground space, and energy structure transformation. The embodiments of the present application have advantages such as large scale, strong targeting, high reliability, convenient operation, low cost, and wide applicability. They can be quickly applied to the construction of underground space for comprehensive utilization, such as LNG and LPG storage facilities, effectively reducing the storage cost of cryogenic LNG, improving the economic benefits of storage construction, and thus promoting the healthy development of the gas storage and underground space utilization industry chain.

[0120] This application addresses the current situation where there are no precedents for the construction of underground cryogenic liquefied natural gas (LNG) storage facilities, and existing storage technologies mainly focus on surface membrane tanks, salt cavern gas storage facilities, and depleted gas reservoir gas storage facilities. Surface membrane tanks are costly and small in scale, while salt cavern gas storage facilities and depleted gas reservoir gas storage facilities are significantly limited by geological structure, geographical resources, and location, making it difficult to meet the needs of large-scale underground gas storage construction in severely gas-deficient areas. This application proposes a dynamic evolution and control system for the frozen zone of fractured surrounding rock in cryogenic LNG storage facilities. This system has significant advantages in terms of both time and spatial scales, representing the optimal approach for long-term, large-scale gas storage and is of great significance. This invention addresses the limitations of existing gas storage and cryogenic liquefied natural gas (LNG) storage methods, such as small scale, high cost, and constraints related to geological conditions and geographical location. It effectively solves the sealing and stability problems of cryogenic LNG storage facilities, which are difficult to control effectively due to the 0°C isotherm. A dynamic evolution and control system for the frozen zone of fractured surrounding rock in cryogenic LNG storage facilities has been invented. The system provides a complete solution, encompassing functional design of various individual components, from site selection, working pressure and temperature settings, insulation layer calculations, and frozen zone control systems, to crucial auxiliary designs such as efficiency testing and construction procedures for the groundwater control system. Only the appropriate strength needs to be selected. Medium- and high-stability underground spaces can meet all construction requirements, exhibiting extremely high tolerance for geological conditions and a wide range of applications. This application's embodiment optimizes key parameters such as in-cavity storage pressure, liquefied natural gas storage temperature, and contact surface temperature, shortening the 0°C isotherm range to reduce cold energy consumption and improve storage efficiency. By setting up a groundwater control system and dividing the freezing zone into six steps, it achieves precise control of the dynamic evolution of the freezing zone, effectively solving the sealing and stability problems of low-temperature liquefied natural gas storage facilities caused by the difficulty in effectively controlling the 0°C isotherm. The device parameters can be appropriately adjusted according to actual working conditions, offering significant optimization potential. The embodiments described herein can be used not only for liquefied natural gas (LNG) storage but also for cryogenic liquefied petroleum gas (LPG) storage. They are of great value for the comprehensive utilization of underground space for natural gas storage and energy structure transformation. The embodiments described herein utilize a variety of underground structures, individual units, and materials, and have the advantages of large scale, strong targeting, high reliability, convenient operation, low cost, and wide applicability. They can be quickly used in the construction of underground space for comprehensive utilization of LNG and LPG storage facilities, effectively reducing the storage cost of cryogenic LNG, improving the economic benefits of storage construction, and thus promoting the healthy development of the gas storage and underground space comprehensive utilization industry chain.

[0121] This application also discloses an electronic device that integrates the above-mentioned control system for the frozen zone of fractured surrounding rock in underground natural gas storage, for implementing the above-mentioned control method for the frozen zone of fractured surrounding rock in underground natural gas storage.

[0122] This application has the advantages of high relevance, high reliability, convenient operation, low cost, and wide applicability. It solves the problems of small scale, high cost, and geographical limitations of existing liquefied natural gas (LNG) storage facilities. It has invented a complete system solution, from the functional design of different individual units such as the site selection of cryogenic LNG storage facilities, working pressure and temperature setting, insulation layer calculation, and freezing zone control system, to important auxiliary designs such as the efficiency test and construction steps of the groundwater control system. It only requires the selection of underground space with moderate strength and high stability to meet all construction requirements. It has extremely high tolerance for geological conditions and a wide range of applications. This application provides a complete set of technologies and solutions for the dynamic evolution and regulation of the frozen zone in fractured surrounding rock of cryogenic liquefied natural gas (LNG) storage facilities. This promotes the long-term, large-scale storage of natural gas and LNG and ensures energy security. Based on the construction principles of cryogenic LNG storage facilities and the functional requirements of the frozen zone in cryogenic liquid storage, this application provides a complete system solution from the perspective of engineering practice. It covers the functional design of different individual units, such as the site selection of cryogenic LNG storage facilities, working pressure and temperature settings, insulation layer calculation, and frozen zone control system, as well as important auxiliary designs such as the efficiency test and construction steps of the groundwater control system. All construction requirements can be met by selecting underground spaces with moderate strength and high stability. It has a very high tolerance for geological conditions and is applicable to various scenarios with different engineering geology, hydrogeology, and underground engineering layouts. By integrating various underground units, structures, and devices, this method provides a large-scale, highly targeted, highly reliable, easy-to-operate, low-cost, and widely applicable approach for the dynamic evolution and regulation of the frozen zone in fractured surrounding rock of cryogenic liquefied natural gas (LNG) storage facilities. It can be rapidly applied to various natural gas storage and LNG industry chain construction projects, effectively reducing the storage costs of natural gas and LNG, improving economic efficiency, and thus promoting the healthy development of the gas storage and abandoned underground space utilization industry chain.

[0123] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims

1. A full-cycle intelligent monitoring method of a liquefied natural gas storage, characterized in that, The application relates to a method for monitoring a liquefied natural gas (LNG) storage cavern, which comprises the following steps. Drilling a hole in the surrounding rock of the storage cavern, and arranging distributed optical fiber temperature sensors at multiple positions of the hole wall along the hole depth at a preset interval, so as to monitor the ambient temperature of a temperature field based on the distributed optical fiber temperature sensors; arranging displacement sensors at the interface between the lining layer of the storage cavern and the surrounding rock and in the surrounding rock at different depths, so as to monitor the convergence displacement based on the displacement sensors; burying a vibrating string type seepage pressure sensor around the rock mass near the permafrost zone of the storage cavern, so as to monitor the seepage pressure based on the vibrating string type seepage pressure sensor; arranging a servo liquid level meter in the storage cavern and monitoring and alarming the liquid level, and arranging a multi-point average thermometer in the storage cavern and measuring the medium temperature; setting multi-level thresholds based on the ambient temperature, the convergence displacement, the liquid level monitoring, the medium temperature and the seepage pressure, wherein the multi-level thresholds comprise a temperature threshold, a displacement daily fluctuation threshold, a corrected liquid level threshold and a pressure threshold; calculating the evaporation loss based on the medium temperature, and obtaining a current liquid level value based on the evaporation loss and the result of the liquid level monitoring; evaluating the permafrost control risk, the storage stability risk, the liquefied natural gas leakage risk and the surrounding rock seepage pressure risk based on the multi-level thresholds and generating an evaluation result, and executing corresponding prevention and control measures based on the evaluation result, wherein the evaluation of the permafrost control risk, the storage stability risk, the liquefied natural gas leakage risk and the surrounding rock seepage pressure risk based on the multi-level thresholds comprises: when the ambient temperature is less than 150% of the temperature threshold, evaluating that the permafrost control risk is in a normal state; when the single-day fluctuation of the convergence displacement is not more than 2 mm, evaluating that the storage stability risk is in a normal state; when the current liquid level value is less than 1% to 3% of the corrected liquid level threshold or the temperature deviation is not more than 3 DEG C, evaluating that the liquefied natural gas leakage risk is in a normal state; and when the seepage pressure is less than 20% of the pressure threshold, evaluating that the surrounding rock seepage pressure risk is in a safe state; uploading the evaluation result to a ground control room through an optical fiber, and executing corresponding prevention and control measures based on the evaluation result, so as to realize whole life cycle monitoring.

2. The method of claim 1, wherein, The arrangement of the servo liquid level meter in the storage cavern and the monitoring and alarming of the liquid level, and the arrangement of the multi-point average thermometer in the storage cavern and the measurement of the medium temperature comprise the following steps. arranging pressure transmitters and temperature transmitters on the liquefied natural gas inlet and outlet pipelines; arranging the servo liquid level meter on a cavern top operation platform in the storage cavern, connecting the servo liquid level meter with a high and low liquid level alarm system, and monitoring and alarming the liquid level; arranging the multi-point average thermometer along the vertical direction of the hole wall in the storage cavern and measuring the medium temperature.

3. The method of claim 1, wherein, The evaluation of the permafrost control risk based on the multi-level thresholds further comprises the following steps. when any single-point temperature of the ambient temperature is more than 150% of the temperature threshold, evaluating that the permafrost control risk is in a pre-warning state. When the extent to which any multiple single-point temperatures of the ambient temperature are below the temperature threshold value exceeds 150%, the frozen circle control risk is evaluated as a dangerous state.

4. The method of claim 1, wherein, The evaluation of the reservoir stability risk based on the multiple-level threshold values further includes: When the single-day fluctuation of the convergence displacement exceeds 2 millimeters and does not exceed 5 millimeters, the reservoir stability risk is evaluated as a pre-warning state; When the single-day fluctuation of the convergence displacement exceeds 5 millimeters, the reservoir stability risk is evaluated as a dangerous state.

5. The method of claim 1, wherein, The evaluation of the liquefied natural gas leakage risk based on the multiple-level threshold values further includes: When the extent to which the current liquid level value is below the corrected liquid level threshold value exceeds 3% and does not exceed 5% or the temperature deviation exceeds 3°C and does not exceed 10°C, the liquefied natural gas leakage risk is evaluated as a pre-warning state; When the extent to which the current liquid level value is below the corrected liquid level threshold value exceeds 5% or the temperature deviation exceeds 10°C, the liquefied natural gas leakage risk is evaluated as a dangerous state.

6. The method of claim 1, wherein, The evaluation of the frozen circle control risk based on the multiple-level threshold values further includes: When the extent to which the osmotic pressure is below the pressure threshold value exceeds 20% and does not exceed 50%, the surrounding rock osmotic pressure risk is evaluated as a pre-warning state; When the extent to which the osmotic pressure is below the pressure threshold value exceeds 50% and is accompanied by temperature abnormalities, the surrounding rock osmotic pressure risk is evaluated as a dangerous state.

7. A full-cycle intelligent monitoring system for a liquefied natural gas storage, characterized in that, The method includes: a cavern periphery monitoring module for drilling in the periphery surrounding rock of a reservoir cavern, and continuously arranging distributed optical fiber temperature sensors at multiple places of the cavern wall along the drilling depth at a preset interval, monitoring the ambient temperature of the temperature field based on the distributed optical fiber temperature sensors; arranging displacement sensors at the interface between the lining layer of the reservoir cavern and the surrounding rock and in the surrounding rock at different depths, monitoring the convergence displacement based on the displacement sensors; burying a vibrating string osmotic pressure sensor around the rock mass near the frozen circle of the reservoir cavern, monitoring the osmotic pressure based on the vibrating string osmotic pressure sensor; a cavern interior monitoring module for setting a servo liquid level meter in the interior of the reservoir cavern and performing liquid level monitoring and alarming, and setting a multi-point average thermometer in the interior of the reservoir cavern and performing medium temperature measurement; a multiple-level threshold value building module for setting multiple-level threshold values based on the ambient temperature, the convergence displacement, the liquid level monitoring, the medium temperature, and the osmotic pressure, the multiple-level threshold values including a temperature threshold value, a displacement daily fluctuation threshold value, a corrected liquid level threshold value, and a pressure threshold value; calculating evaporation loss based on the medium temperature, and obtaining a current liquid level value based on the evaporation loss and the result of the liquid level monitoring; The risk assessment module is configured to evaluate the frozen circle control risk, the reservoir stability risk, the liquefied natural gas leakage risk and the surrounding rock permeation pressure risk based on the multi-level threshold and generate an evaluation result, and execute corresponding prevention and control measures based on the evaluation result. The evaluation of the frozen circle control risk, the reservoir stability risk, the liquefied natural gas leakage risk and the surrounding rock permeation pressure risk based on the multi-level threshold includes: when the ambient temperature is less than the temperature threshold by not more than 150%, the frozen circle control risk is evaluated as normal; when the single-day fluctuation of the convergence displacement is not more than 2 mm, the reservoir stability risk is evaluated as normal; when the current liquid level value is less than the corrected liquid level threshold by more than 1% and not more than 3% or the temperature deviation is not more than 3℃, the liquefied natural gas leakage risk is evaluated as normal; and when the permeation pressure is less than the pressure threshold by not more than 20%, the surrounding rock permeation pressure risk is evaluated as safe. The life cycle monitoring module is configured to upload the evaluation result to a ground control room through an optical fiber and execute corresponding prevention and control measures based on the evaluation result, so as to realize whole life cycle monitoring.

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