Real-time monitoring and early warning method and system for salt cavern gas storage based on optical fiber sensing

Abstract

The present application relates to salt cavern gas storage monitoring technical field, especially in based on optical fiber sensing's salt cavern gas storage real time monitoring early warning method and system, the method includes the following steps: the three-dimensional model of salt cavern gas storage is built, and then the monitoring node is determined; according to the layout of monitoring node along the cavity inner wall of salt cavern gas storage lays distributed sensing optical fiber, to obtain temperature data and strain data in real time;According to three-dimensional model, temperature data and strain data, based on finite element method inversion salt cavern gas storage pressure field, obtains the pressure data in the salt cavern; DTS-Raman compound optical fiber is vertically hung in the salt cavern gas storage to obtain gas halogen interface height data;The salt cavern gas storage environment monitoring early warning system is built, and when meeting the early warning condition, early warning is sent out.The present application can realize long distance on-line monitoring and early warning to salt cavern gas storage, and can carry out the multi-parameter fusion analysis of salt cavern gas storage, improve the accuracy of monitoring and early warning, and can reduce the cost of monitoring and early warning.

Description

Technical Field

[0001] This invention relates to the field of salt cavern gas storage monitoring technology, and in particular to a real-time monitoring and early warning method and system for salt cavern gas storage based on fiber optic sensing. Background Technology

[0002] Salt cavern gas storage facilities play a crucial role in my country's energy strategy as important natural gas storage facilities. However, due to their unique structural characteristics and operating conditions, salt cavern gas storage well sites present numerous potential safety hazards, including complex equipment layouts, widely distributed leakage sources, and a high probability of micro-leakage events. To effectively monitor and prevent micro-leakage at well sites and improve the safety and operational efficiency of gas storage facilities, accurate monitoring of temperature, strain, pressure, and interface locations within salt cavern gas storage facilities is particularly important.

[0003] However, traditional monitoring technology for salt cavern gas storage facilities has the following drawbacks: (1) Sensor limitations: Electronic sensors are susceptible to the high humidity, high pressure, and strong corrosion environment inside the salt cavern gas storage facility, resulting in short lifespan, high maintenance costs, and difficult maintenance; (2) Static deployment blind spots: Due to the complex structure of deep salt cavern gas storage facilities, fixed sensor networks cannot dynamically track and judge the migration of the gas-halogen interface, the cavity shrinkage rate, and local leakage; (3) Insufficient multi-parameter coordination: Discrete sensors are difficult to acquire multi-dimensional data such as pressure, temperature, and strain simultaneously, resulting in single monitoring data; (4) Response lag: Manual inspection and offline analysis cannot meet the real-time online monitoring and early warning requirements, increasing the risk of gas storage facility leakage or severe cavity deformation.

[0004] With the continuous development of fiber optic sensing technology, it has shown great application potential in the field of engineering monitoring. Fiber optic sensing technology has advantages such as distributed measurement, strong anti-interference capability, and high real-time performance, providing a more effective means for monitoring salt cavern gas storage facilities. However, there is currently no mature method for comprehensively and systematically applying fiber optic sensing technology to real-time monitoring and early warning of salt cavern gas storage facilities; it is still in the exploratory stage. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and system for real-time monitoring and early warning of salt cavern gas storage facilities based on fiber optic sensing.

[0006] To achieve the above objectives, in a first aspect, this invention provides a real-time monitoring and early warning method for salt cavern gas storage facilities based on fiber optic sensing. The method includes the following steps: constructing a three-dimensional model of the salt cavern gas storage facility; determining monitoring nodes on the inner wall of the cavity of the salt cavern gas storage facility based on the three-dimensional model; laying distributed sensing optical fibers along the inner wall of the cavity of the salt cavern gas storage facility according to the layout of the monitoring nodes to acquire temperature and strain data inside the salt cavern in real time; obtaining pressure data inside the salt cavern by inverting the pressure field of the salt cavern gas storage facility based on the three-dimensional model, the temperature data, and the strain data using the finite element method; vertically suspending a DTS-Raman composite optical fiber inside the salt cavern gas storage facility and acquiring the gas-halogen interface height data based on the abrupt change points of the temperature gradient and Raman scattering intensity; constructing an environmental monitoring and early warning system for the salt cavern gas storage facility, and issuing an early warning when the temperature data, the strain data, the pressure data, and the gas-halogen interface height data meet the early warning conditions. This invention enables long-distance online monitoring and early warning of salt cavern gas storage facilities, and can perform multi-parameter fusion analysis of salt cavern gas storage facilities, improving the accuracy of monitoring and early warning, and reducing the cost of monitoring and early warning.

[0007] Optionally, constructing a three-dimensional model of the salt cavern gas storage facility and determining monitoring nodes on the inner wall of the cavity of the salt cavern gas storage facility based on the three-dimensional model includes the following steps:

[0008] Geological surveys were conducted on the location of the salt cavern gas storage facility, and lidar was used to scan the cavity of the salt cavern gas storage facility.

[0009] Based on the scanning results and geological survey results, combined with the cavity design data of the salt cavern gas storage, the three-dimensional model of the salt cavern gas storage was established.

[0010] Based on the aforementioned three-dimensional model, and taking into account the geological conditions, operational requirements, and geometry of the salt cavern gas storage facility, monitoring nodes are selected on the inner wall of the cavity.

[0011] Optionally, the step of laying distributed sensing optical fibers along the inner wall of the salt cavern gas storage cavity according to the layout of the monitoring nodes to acquire temperature and strain data inside the salt cavern in real time includes the following steps:

[0012] Based on the layout of the monitoring nodes, the initial fiber optic laying path is manually set;

[0013] The initial fiber optic laying path was optimized using the ant colony algorithm to obtain the optimal fiber optic laying path.

[0014] Based on the optimal fiber optic laying path, distributed sensing fibers are laid along the inner wall of the salt cavern gas storage chamber to acquire temperature and strain data inside the salt cavern in real time.

[0015] Optionally, the step of obtaining the pressure data inside the salt cavern by inverting the pressure field of the salt cavern gas storage tank based on the three-dimensional model, the temperature data, and the strain data using the finite element method includes the following steps:

[0016] The salt cavern is discretized using the finite element method based on the three-dimensional model, and temperature boundary conditions are applied based on the temperature data.

[0017] Based on the temperature data and the strain data, the temperature field and strain field of the salt cavern gas storage are generated using spatial interpolation.

[0018] Parametric coupling analysis was performed on the salt cavern gas storage, and then a coupled model was constructed.

[0019] Based on the temperature field and the coupling model, the pressure field is continuously updated to invert the strain field, thereby obtaining the pressure data inside the salt cavern.

[0020] Optionally, the step of continuously updating the pressure field based on the temperature field and the coupling model to invert the strain field and thus obtain the pressure data inside the salt cavern includes the following steps:

[0021] Initialize the pressure field;

[0022] Based on the temperature field and the pressure field, a coupled model is used to obtain a simulated strain field, and then the strain inversion data of the monitoring node is determined based on the simulated strain field.

[0023] The objective function is set to minimize the difference between the strain inversion data and the strain data.

[0024] The gradient of the optimization objective function with respect to the pressure field is calculated, and then the pressure field is iteratively updated using the gradient descent method until the constraint conditions are met, finally obtaining the pressure data.

[0025] Optionally, the coupling model satisfies the following relationship:

[0026]

[0027] in, For thermal strain tensor, Let I be the coefficient of thermal expansion of the salt rock, I be the unit tensor, and T be the temperature field. For reference temperature field, Let P be the effective stress tensor and P be the pressure field. The coefficient of thermal stress, G is the mechanical strain tensor, and G is the shear modulus. For time, The creep time constant is Where E is Poisson's ratio and E is the elastic modulus of salt rock. for traces, Let be the total strain tensor.

[0028] Optionally, the optimization objective function satisfies the following relationship:

[0029]

[0030] in, The difference value is N, where N is the number of monitoring nodes. This refers to the strain inversion value of the nth monitoring node obtained through the coupling model under pressure field P and temperature field T. For the strain data of the nth monitoring node, This is the regularization parameter.

[0031] Optionally, the construction of the environmental monitoring and early warning system for the salt cavern gas storage facility, and the issuance of an early warning when the temperature data, strain data, pressure data, and gas-halogen interface height data meet the early warning conditions, includes the following steps:

[0032] Based on the temperature data, determine whether there is a sudden drop in local temperature in the salt cavern gas storage, and issue a temperature warning when there is a sudden drop in local temperature in the salt cavern gas storage.

[0033] The cavity contraction rate of the salt cavern gas storage is determined based on the strain data, and a strain warning is issued when the cavity contraction rate exceeds the contraction rate threshold each month.

[0034] The maximum daily pressure fluctuation in the salt cavern gas storage is obtained based on the pressure data, and a pressure warning is issued when the maximum daily pressure fluctuation exceeds the pressure fluctuation threshold.

[0035] The daily migration amount of the brine interface is determined based on the brine interface height data, and a brine interface migration warning is issued when the daily migration amount of the brine interface exceeds the migration amount threshold.

[0036] Optionally, the step of determining the cavity contraction rate of the salt cavern gas storage based on the strain data and issuing a strain warning when the cavity contraction rate exceeds a monthly contraction rate threshold includes the following steps:

[0037] Based on the strain data of each monitoring node, the cavity shrinkage rate of the salt cavern gas storage is estimated using the equivalent average strain method.

[0038] A strain warning is issued when the monthly cavity shrinkage rate exceeds the shrinkage rate threshold.

[0039] Secondly, the present invention provides a real-time monitoring and early warning system for salt cavern gas storage based on optical fiber sensing. The real-time monitoring and early warning system for salt cavern gas storage based on optical fiber sensing includes: a data acquisition device, a data output device, a processor, and a storage device. The storage device includes a computer-readable storage medium storing a computer program. The computer program includes program instructions, which, when executed by the processor, cause the processor to implement the real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing provided by the present invention.

[0040] The present invention has at least the following beneficial effects:

[0041] 1. Fiber optic sensing technology has advantages such as resistance to electromagnetic interference, corrosion resistance, long-distance transmission, high sensitivity and high resolution. Therefore, this method based on fiber optic sensing technology can realize long-term accurate measurement of temperature, strain, pressure and gas-halogen interface in salt cavern gas storage.

[0042] 2. This method uses the ant colony algorithm to optimize the initial fiber optic laying path to obtain the optimal fiber optic laying path, which reduces the fiber optic laying length and thus reduces the monitoring cost of the salt cavern gas storage facility.

[0043] 3. Distributed fiber optic sensing technology can achieve multi-point monitoring on a single fiber, simultaneously measuring temperature and strain at multiple locations. This greatly reduces the number of sensors and wiring complexity, improves monitoring efficiency and reliability, and further reduces the monitoring cost of salt cavern gas storage facilities.

[0044] 4. This method first uses distributed sensing optical fibers to measure the temperature and strain of a salt cavern gas storage facility, and then uses the finite element method to invert the pressure field in the salt cavern gas storage facility. This solves the problem that a single optical fiber cannot simultaneously and accurately measure the temperature, strain, and pressure in a salt cavern gas storage facility, which is conducive to further reducing the monitoring cost of salt cavern gas storage facilities and provides a new approach to the monitoring of salt cavern gas storage facilities.

[0045] 5. This method establishes an environmental monitoring and early warning system for salt cavern gas storage facilities, which can issue early warnings when the temperature, strain, pressure, and the height of the gas-halogen interface meet the early warning conditions, facilitating timely response by relevant personnel.

[0046] 6. A real-time monitoring and early warning system for salt cavern gas storage facilities was provided, which is compatible with the real-time monitoring and early warning method for salt cavern gas storage facilities. This improves the practicality of the real-time monitoring and early warning method for salt cavern gas storage facilities and facilitates its promotion. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart illustrating the real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing, according to an embodiment of the present invention.

[0049] Figure 2 This is a schematic diagram of the framework of a real-time monitoring and early warning system for salt cavern gas storage based on fiber optic sensing, according to an embodiment of the present invention. Detailed Implementation

[0050] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, software, or methods have not been specifically described to avoid obscuring the invention.

[0051] Throughout this specification, references to "an embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale.

[0052] It should be noted in advance that, in one alternative embodiment, except for independent descriptions, the same symbols or letters appearing in all formulas have the same meaning and value.

[0053] In one optional embodiment, please refer to Figure 1 This invention provides a real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing, the method comprising the following steps:

[0054] S1. Construct a three-dimensional model of the salt cavern gas storage facility, and determine monitoring nodes on the inner wall of the cavity of the salt cavern gas storage facility based on the three-dimensional model.

[0055] Step S1 specifically includes the following steps:

[0056] S11. Conduct geological surveys of the location of the salt cavern gas storage facility, and simultaneously use lidar to scan the cavity of the salt cavern gas storage facility.

[0057] Specifically, in this embodiment, geological surveying is conducted to comprehensively understand the geological conditions of the area where the salt cavern gas storage is located, providing fundamental data for subsequent cavity design, 3D modeling, and the selection of monitoring nodes. Geological surveying allows for the assessment of the stability of underground rock strata, the thickness and purity of the salt layer, the presence of faults, fissures, and other adverse geological structures, as well as the distribution of groundwater. LiDAR scanning is used to obtain the precise geometric shape and spatial location information of the salt cavern gas storage cavity. Through geological surveying and LiDAR scanning, the geological conditions of the salt cavern gas storage and the 3D point cloud data of the cavity can be obtained, providing a data foundation for the subsequent construction of accurate and reliable 3D modeling.

[0058] More specifically, boreholes are drilled at specific intervals and depths in the area where the salt cavern gas storage is located to obtain underground core samples. The physical and mechanical properties of the salt layer, such as density, porosity, and permeability, as well as the sequence and thickness variations of the rock layers, are determined through analysis of the core samples. Seismic exploration, electrical exploration, and magnetic exploration methods are used to detect the underground geological structure of the salt cavern gas storage location. Hydrogeological surveys are conducted to understand the groundwater level, water quality, recharge, and discharge conditions at the location of the salt cavern gas storage. A 3D laser scanner is used at the wellhead of the salt cavern gas storage to perform a 3D scan of the cavity, obtaining the 3D coordinate information of various points on the inner wall of the cavity. After scanning, the obtained point cloud data needs to undergo preprocessing operations such as noise reduction and registration to improve the accuracy and completeness of the data.

[0059] S12. Based on the scanning results and geological survey results, and combined with the cavity design data of the salt cavern gas storage, establish the three-dimensional model of the salt cavern gas storage.

[0060] Specifically, in this embodiment, the three-dimensional point cloud data of the cavity obtained by lidar scanning is integrated with the geological survey results. Combined with the cavity design data such as the size, shape, and layout of the salt cavern gas storage cavity, a three-dimensional model of the salt cavern gas storage is established to ensure that the three-dimensional model accurately reflects the design intent and actual geological conditions. The specific process of constructing the three-dimensional model of the salt cavern gas storage can refer to existing technical methods and will not be described in detail here.

[0061] S13. Based on the three-dimensional model, taking into account the geological conditions, operational requirements, and geometry of the salt cavern gas storage, a monitoring node is selected on the inner wall of the salt cavern gas storage cavity.

[0062] Specifically, in this embodiment, monitoring nodes are manually set on the 3D model. These nodes should be as dense as possible to facilitate the subsequent construction of temperature and strain fields. In areas with unstable geological conditions, such as zones with developed faults and fissures, the density of monitoring nodes should be appropriately increased to promptly detect deformation and displacement of rock strata. Considering operational needs, monitoring nodes should be set at different heights and locations within the salt cavern gas storage facility to monitor changes in temperature, strain, and pressure. Considering the geometry of the cavity, monitoring nodes should be set in areas prone to strain concentration, such as corners and interfaces, to monitor changes in temperature, strain, and pressure.

[0063] More specifically, in addition to areas with unstable geological conditions and areas prone to strain concentration in salt cavern gas storage, the distribution of monitoring nodes should be as uniform as possible so that temperature and strain data can be collected from various locations within the salt cavern gas storage.

[0064] S2. Based on the layout of the monitoring nodes, distributed sensing optical fibers are laid along the inner wall of the salt cavern gas storage chamber to acquire temperature and strain data inside the salt cavern in real time.

[0065] Step S2 specifically includes the following steps:

[0066] S21. Based on the layout of the monitoring nodes, manually set the initial fiber optic laying path.

[0067] Specifically, in this embodiment, the initial fiber optic laying path is manually set according to the layout of the monitoring nodes, and it is necessary to ensure that each monitoring node can be covered.

[0068] S22. Optimize the initial fiber optic laying path using the ant colony algorithm to obtain the optimal fiber optic laying path.

[0069] Specifically, in this embodiment, the parameters are first initialized: the number of ants is set to 1.5 times the number of monitoring nodes, the pheromone evaporation coefficient is set to 0.3, the pheromone importance is set to 1, and the heuristic pheromone importance is set to 2. The pheromone concentration is then initialized based on the initial fiber optic laying path, with the initial value of the pheromone concentration for long paths being lower than that for short paths. After initializing the parameters, the ant colony algorithm is used to optimize the initial fiber optic laying path with the goal of minimizing the fiber optic laying path length, obtaining the optimal fiber optic laying path. This reduces the length of the sensing fiber required for monitoring the salt cavern gas storage facility, thereby lowering the monitoring cost of the salt cavern gas storage facility.

[0070] Furthermore, after the ant colony algorithm outputs the optimal fiber optic laying path, relevant technical personnel can further optimize it based on their own experience and the actual conditions of the salt cave to improve the rationality of the optimal fiber optic laying path.

[0071] S23. Based on the optimal fiber optic laying path, a distributed sensing fiber optic cable is laid along the inner wall of the salt cavern gas storage chamber to obtain temperature and strain data inside the salt cavern in real time.

[0072] Specifically, in this embodiment, a Brillouin optical time domain reflectance (BOTDR) system is used to simultaneously measure the temperature and strain data of each monitoring node inside the salt cavern, thereby reducing monitoring costs and improving the dynamic monitoring capability of the salt cavern gas storage facility's operating status.

[0073] Furthermore, after obtaining the optimal fiber optic laying path, the distributed sensing fiber optic cable of the BOTDR system is laid along the inner wall of the cavity of the salt cavern gas storage facility according to the optimal fiber optic laying path.

[0074] More specifically, in order to improve the spatial resolution of the BOTDR system, iXblue's MXER-LN series intensity modulator is used, and a distributed feedback (DFB) laser is used as the light source with a wavelength of 1550nm.

[0075] In other alternative embodiments, different types of optical fibers may be used to measure the temperature and strain data of each monitoring node separately.

[0076] S3. Based on the three-dimensional model, the temperature data, and the strain data, the pressure field of the salt cavern gas storage tank is inverted using the finite element method to obtain the pressure data inside the salt cavern.

[0077] Step S3 specifically includes the following steps:

[0078] S31. The salt cavern is discretized using the finite element method based on the three-dimensional model, and temperature boundary conditions are applied based on the temperature data.

[0079] Specifically, in this embodiment, an unstructured tetrahedral mesh is used in Abaqus to divide the 3D model of the salt cavern gas storage, ensuring a higher mesh density in areas with unstable geological conditions and areas prone to strain concentration. Based on temperature data, the temperature of the mesh nodes at the boundary is obtained through interpolation. Considering that this step is a prior art method, it will only be briefly described here.

[0080] S32. Based on the temperature data and the strain data, generate the temperature field and strain field of the salt cavern gas storage tank using spatial interpolation.

[0081] Based on the measured temperature and strain data, the temperature and strain fields are generated using ordinary kriging interpolation. In other alternative embodiments, the measured temperature and strain data can also be used as boundary conditions, combined with finite element analysis to invert the full-field temperature and strain, but this would consume a large amount of computational resources.

[0082] S33. Perform parameter coupling analysis on the salt cavern gas storage facility, and then construct a coupling model.

[0083] Specifically, in this embodiment, temperature changes directly induce expansion or contraction of the salt rock, altering the volume of the salt cavern and disrupting the original mechanical equilibrium; changes in pore pressure trigger mechanical strain through the effective stress principle; salt rock deformation alters the pore structure, affecting gas permeability and storage space; the creep characteristics of the salt rock cause strain to evolve continuously over time, changing the strain field; changes in the strain field may further induce thermal-mechanical feedback; simultaneously, adjustments in pore pressure affect the fluid flow state, forming a closed-loop coupling. As the above analysis shows, temperature and pressure drive strain by changing the energy state of the salt rock, while strain, by altering the material's microstructure, reacts to the fluid flow and heat conduction processes, forming a self-organized nonlinear system. This coupling evolves continuously throughout the entire lifecycle of the gas storage facility and is the root cause of safety risks in the long-term operation of salt cavern gas storage facilities.

[0084] In addition, the following considerations were made:

[0085] 1. In long-term analysis of salt cavern gas storage facilities, tectonic stress, fluid viscosity, and other stresses are generally secondary to pore pressure and thermal stress. This is because tectonic stress changes slowly on geological timescales, while fluid viscosity is typically small during the operation of the gas storage facility. Therefore, the total stress at the monitoring nodes is considered to be dominated by pore pressure and thermal stress.

[0086] 2. The strain in salt caverns is usually no more than 0.5%. In order to simplify the calculation and improve real-time performance, it is assumed that the effects of mechanical field and temperature field on strain are independent of each other. According to the linear elasticity theory, the strains caused by different physical fields can be linearly superimposed. Therefore, the sum of mechanical strain and thermal strain of salt rock is taken as the total strain.

[0087] Based on the above analysis, the following coupling model can be constructed:

[0088]

[0089] in, For thermal strain tensor; is the thermal expansion coefficient of salt rock, obtained through laboratory thermal expansion experiments; I is the unit tensor; T is the temperature field. The reference temperature field can be obtained by calculating the historical average temperature of each monitoring node; P represents the effective stress tensor; P is the pressure field, obtained through iterative updates. The thermal stress coefficient is calculated from the coefficient of thermal expansion and the modulus of elasticity, i.e. ; G is the mechanical strain tensor; G is the shear modulus, calculated from the elastic modulus and Poisson's ratio, i.e. ; For time; The creep time constant is obtained through creep experiments in the laboratory. E is Poisson's ratio, obtained through triaxial compression experiments; E is the elastic modulus of salt rock, obtained through uniaxial compression experiments. for traces; Let be the total strain tensor.

[0090] S34. Based on the temperature field and the coupling model, the pressure field is continuously updated to invert the strain field, thereby obtaining the pressure data inside the salt cavern.

[0091] Specifically, step S34 includes the following steps:

[0092] S341. Initialize the pressure field.

[0093] Specifically, in this embodiment, at the start of the inversion, an initial pressure field is set based on the wellhead pressure of the salt cavern gas storage facility and in conjunction with pressure monitoring cases of other salt cavern gas storage facilities.

[0094] S342. Based on the temperature field and the pressure field, a coupled model is used to obtain a simulated strain field, and then the strain inversion data of the monitoring node is determined based on the simulated strain field.

[0095] Specifically, in this embodiment, by substituting the temperature field and the initial pressure field into the coupled model, the simulated strain field under the corresponding temperature and pressure fields can be calculated. Then, the strain on the monitoring node can be obtained directly or through linear interpolation based on the location of the monitoring node, i.e. strain inversion data.

[0096] S343. Set an optimization objective function with the goal of minimizing the strain inversion data and the strain data.

[0097] Specifically, in this embodiment, the objective function satisfies the following relationship:

[0098]

[0099] in, Here, N represents the difference value, and N is the number of monitoring nodes. This represents the strain inversion value of the nth monitoring node obtained through a coupled model under pressure field P and temperature field T. For the strain data of the nth monitoring node, The regularization parameter and . For regularization, L2 regularization is used to suppress local drastic fluctuations.

[0100] S344. Calculate the gradient of the optimization objective function with respect to the pressure field, and then use the gradient descent method to iteratively update the pressure field until the constraint conditions are met, and finally obtain the pressure data.

[0101] Specifically, in this embodiment, the adjoint method is used to calculate the gradient of the objective function with respect to the pressure field, and then the gradient descent method is used to iteratively update the pressure field to minimize the objective function, that is:

[0102]

[0103] in, The pressure field obtained from the (k+1)th update. The pressure field obtained in the k-th update, For learning rate and , To optimize the gradient of the objective function with respect to the pressure field.

[0104] Furthermore, generally speaking, when If the pressure field satisfies the constraint conditions, then the pressure field at this time is taken as the real pressure field in the salt cavern gas storage. Then, the pressure value at the monitoring node can be obtained directly or through linear interpolation based on the location of the monitoring node.

[0105] S4. DTS-Raman composite optical fiber is vertically suspended inside the salt cavern gas storage facility, and the height data of the gas-halogen interface is obtained based on the temperature gradient and the abrupt change point of Raman scattering intensity.

[0106] Specifically, in this embodiment, a DTS-Raman composite optical fiber is vertically suspended inside the salt cavern gas storage facility, and the height data of the gas-halogen interface is acquired based on the DTS system and OTDR technology. When the DTS-Raman composite optical fiber is vertically suspended, significant temperature gradients are generated at different heights of the fiber due to differences in the specific heat capacity of the medium they are in, after active heating. The abrupt change in heat exchange efficiency at the gas-halogen interface leads to an inflection point in the temperature gradient. The DTS system utilizes the Raman scattering effect in the optical fiber, measuring the intensity ratio of Stokes and anti-Stokes scattered light, and demodulating the temperature signal using a dual-channel, dual-wavelength comparison method to achieve continuous temperature distribution monitoring along the optical fiber. Simultaneously, the Raman scattering intensity changes significantly at the gas-halogen interface due to abrupt changes in material composition. A spatiotemporal filtering algorithm is used to identify the abrupt change in scattering intensity, and cross-validation with the temperature gradient inflection point improves positioning reliability. OTDR technology measures the propagation time difference of laser pulses in the optical fiber and calculates the scattering point position based on the fiber refractive index, achieving precise positioning of the gas-halogen interface height.

[0107] S5. Construct an environmental monitoring and early warning system for salt cavern gas storage, and then issue an early warning when the temperature data, strain data, pressure data, and gas-halogen interface height data meet the early warning conditions.

[0108] This embodiment constructs an environmental monitoring and early warning system for salt cavern gas storage facilities. When temperature, strain, pressure, and the height of the gas-halogen interface meet the warning conditions, an early warning is issued, facilitating timely response by relevant personnel. Step S5 specifically includes the following steps:

[0109] S51. Determine whether there is a sudden drop in local temperature in the salt cavern gas storage based on the temperature data, and issue a temperature warning when there is a sudden drop in local temperature in the salt cavern gas storage.

[0110] Specifically, in this embodiment, based on the temperature data of each monitoring node, if the temperature change of a certain monitoring node within a unit time is not less than 5°C, it is considered that there is a sudden drop in local temperature in the salt cavern gas storage, which is suspected to be a gas leak.

[0111] S52. Determine the cavity contraction rate of the salt cavern gas storage tank based on the strain data, and issue a strain warning when the cavity contraction rate exceeds the contraction rate threshold each month.

[0112] Specifically, step S52 includes the following steps:

[0113] S521. Based on the strain data of each monitoring node, the cavity contraction rate of the salt cavern gas storage is estimated using the equivalent average strain method.

[0114] Specifically, in this embodiment, since step S13 ensures the monitoring nodes are distributed as evenly as possible when setting them up, the equivalent average strain method can be used to estimate the cavity contraction rate of the salt cavern gas storage tank. The cavity contraction rate specifically satisfies the following relationship:

[0115]

[0116] in, Indicates the cavity shrinkage rate. This represents the month-end change in the volume of the gas storage cavity in the salt cavern. This represents the initial volume of the cavity in the salt cavern gas storage facility. , and Let be the strain components of the strain data of the nth monitoring node in three orthogonal directions.

[0117] Furthermore, in other alternative embodiments, the cavity shrinkage rate can also be calculated using a direct integration method based on the strain field and an indirect prediction method based on a salt rock creep model.

[0118] S522. Issue a strain warning when the monthly cavity shrinkage rate exceeds the shrinkage rate threshold.

[0119] Specifically, in this embodiment, the shrinkage rate threshold is 5%.

[0120] S53. Obtain the maximum daily pressure fluctuation in the salt cavern gas storage based on the pressure data, and issue a pressure warning when the maximum daily pressure fluctuation exceeds the pressure fluctuation threshold.

[0121] Specifically, in this embodiment, the pressure fluctuations at each monitoring node are calculated in real time according to the following formula:

[0122]

[0123] Where r represents the pressure fluctuation of the monitoring node, and P represents the real-time pressure of the monitoring node on that day. To monitor the initial pressure of the node on that day.

[0124] Furthermore, the pressure fluctuation threshold is specifically 0.1.

[0125] S54. Determine the daily migration amount of the gas-brine interface based on the gas-brine interface height data, and issue a gas-brine interface migration warning when the daily migration amount of the gas-brine interface is greater than the migration amount threshold.

[0126] Specifically, in this embodiment, the daily migration of the gas-brine interface is the change in the height of the gas-brine interface over 24 hours.

[0127] Furthermore, the migration threshold is specifically 1m.

[0128] It should be noted that in some cases, the actions described in the specification can be performed in different orders and still achieve the desired results. In this embodiment, the order of steps is given only to make the embodiment clearer and easier to explain, and not to limit it.

[0129] In one optional embodiment, please refer to Figure 1 To improve the practicality of this method, the present invention also provides a real-time monitoring and early warning system for salt cavern gas storage based on fiber optic sensing. The real-time monitoring and early warning system for salt cavern gas storage based on fiber optic sensing includes: a data acquisition device 1, a data output device 2, a processor 3, and a storage device 4. The storage device 4 includes a computer-readable storage medium storing a computer program. The computer program includes program instructions, which, when executed by the processor 3, cause the processor 3 to perform the contents described in steps S1 to S5.

[0130] Specifically, in this embodiment, the data acquisition device 1 includes various optical fibers used in this method.

[0131] In summary, this embodiment has at least the following beneficial effects:

[0132] 1. Fiber optic sensing technology has advantages such as resistance to electromagnetic interference, corrosion resistance, long-distance transmission, high sensitivity and high resolution. Therefore, this method based on fiber optic sensing technology can realize long-term accurate measurement of temperature, strain, pressure and gas-halogen interface in salt cavern gas storage.

[0133] 2. This method uses the ant colony algorithm to optimize the initial fiber optic laying path to obtain the optimal fiber optic laying path, which reduces the fiber optic laying length and thus reduces the monitoring cost of the salt cavern gas storage facility.

[0134] 3. Distributed fiber optic sensing technology can achieve multi-point monitoring on a single fiber, simultaneously measuring temperature and strain at multiple locations. This greatly reduces the number of sensors and wiring complexity, improves monitoring efficiency and reliability, and further reduces the monitoring cost of salt cavern gas storage facilities.

[0135] 4. This method first uses distributed sensing optical fibers to measure the temperature and strain of a salt cavern gas storage facility, and then uses the finite element method to invert the pressure field in the salt cavern gas storage facility. This solves the problem that a single optical fiber cannot simultaneously and accurately measure the temperature, strain, and pressure in a salt cavern gas storage facility, which is conducive to further reducing the monitoring cost of salt cavern gas storage facilities and provides a new approach to the monitoring of salt cavern gas storage facilities.

[0136] 5. This method establishes an environmental monitoring and early warning system for salt cavern gas storage facilities, which can issue early warnings when temperature, strain, pressure, and gas-halogen interface height meet the early warning conditions, facilitating timely response measures by relevant personnel.

[0137] 6. A real-time monitoring and early warning system for salt cavern gas storage facilities was provided, which is compatible with the real-time monitoring and early warning method for salt cavern gas storage facilities. This improves the practicality of the real-time monitoring and early warning method for salt cavern gas storage facilities and facilitates its promotion.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing, characterized in that, Includes the following steps: A three-dimensional model of the salt cavern gas storage facility is constructed, and monitoring nodes are determined on the inner wall of the cavity of the salt cavern gas storage facility based on the three-dimensional model. Based on the layout of the monitoring nodes, distributed sensing optical fibers are laid along the inner wall of the salt cavern gas storage cavity to acquire temperature and strain data inside the salt cavern in real time. Based on the three-dimensional model, the temperature data, and the strain data, the pressure field of the salt cavern gas storage tank is inverted using the finite element method to obtain the pressure data inside the salt cavern. DTS-Raman composite optical fiber is vertically suspended inside the salt cavern gas storage facility, and the height data of the gas-halogen interface is obtained based on the temperature gradient and the abrupt change point of Raman scattering intensity. Based on the temperature data, determine whether there is a sudden drop in local temperature in the salt cavern gas storage, and issue a temperature warning when there is a sudden drop in local temperature in the salt cavern gas storage; The cavity contraction rate of the salt cavern gas storage is determined based on the strain data, and a strain warning is issued when the cavity contraction rate exceeds the contraction rate threshold each month. The maximum daily pressure fluctuation in the salt cavern gas storage is obtained based on the pressure data, and a pressure warning is issued when the maximum daily pressure fluctuation exceeds the pressure fluctuation threshold. The daily migration amount of the brine interface is determined based on the brine interface height data, and a brine interface migration warning is issued when the daily migration amount of the brine interface exceeds the migration amount threshold.

2. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 1, characterized in that, The construction of a three-dimensional model of the salt cavern gas storage facility, and the determination of monitoring nodes on the inner wall of the cavity of the salt cavern gas storage facility based on the three-dimensional model, includes the following steps: Geological surveys were conducted on the location of the salt cavern gas storage facility, and lidar was used to scan the cavity of the salt cavern gas storage facility. Based on the scanning results and geological survey results, combined with the cavity design data of the salt cavern gas storage, the three-dimensional model of the salt cavern gas storage was established. Based on the aforementioned three-dimensional model, and taking into account the geological conditions, operational requirements, and geometry of the salt cavern gas storage facility, monitoring nodes are selected on the inner wall of the cavity.

3. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 1, characterized in that, The step of laying distributed sensing optical fibers along the inner wall of the salt cavern gas storage cavity, based on the layout of the monitoring nodes, to acquire real-time temperature and strain data inside the salt cavern includes the following steps: Based on the layout of the monitoring nodes, the initial fiber optic laying path is manually set; The initial fiber optic laying path was optimized using the ant colony algorithm to obtain the optimal fiber optic laying path. Based on the optimal fiber optic laying path, distributed sensing fibers are laid along the inner wall of the salt cavern gas storage chamber to acquire temperature and strain data inside the salt cavern in real time.

4. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 1, characterized in that, The step of obtaining the pressure data inside the salt cavern by inverting the pressure field of the salt cavern gas storage tank based on the three-dimensional model, the temperature data, and the strain data using the finite element method includes the following steps: The salt cavern is discretized using the finite element method based on the three-dimensional model, and temperature boundary conditions are applied based on the temperature data. Based on the temperature data and the strain data, the temperature field and strain field of the salt cavern gas storage are generated using spatial interpolation. Parametric coupling analysis was performed on the salt cavern gas storage, and then a coupled model was constructed. Based on the temperature field and the coupling model, the pressure field is continuously updated to invert the strain field, thereby obtaining the pressure data inside the salt cavern.

5. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 4, characterized in that, The process of continuously updating the pressure field based on the temperature field and the coupling model to invert the strain field and obtain the pressure data inside the salt cavern includes the following steps: Initialize the pressure field; Based on the temperature field and the pressure field, a coupled model is used to obtain a simulated strain field, and then the strain inversion data of the monitoring node is determined based on the simulated strain field. The objective function is set to minimize the difference between the strain inversion data and the strain data. The gradient of the optimization objective function with respect to the pressure field is calculated, and then the pressure field is iteratively updated using the gradient descent method until the constraint conditions are met, finally obtaining the pressure data.

6. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 5, characterized in that, The coupling model satisfies the following relationship: in, For thermal strain tensor, Let I be the coefficient of thermal expansion of the salt rock, I be the unit tensor, and T be the temperature field. For reference temperature field, Let P be the effective stress tensor and P be the pressure field. The coefficient of thermal stress, G is the mechanical strain tensor, and G is the shear modulus. For time, The creep time constant is Where is Poisson's ratio, and E is the elastic modulus of salt rock. for traces, Let be the total strain tensor.

7. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 5, characterized in that, The optimization objective function satisfies the following relationship: in, The difference value is N, where N is the number of monitoring nodes. This refers to the strain inversion value of the nth monitoring node obtained through the coupling model under pressure field P and temperature field T. For the strain data of the nth monitoring node, This is the regularization parameter.

8. The real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing according to claim 1, characterized in that, The step of determining the cavity contraction rate of the salt cavern gas storage based on the strain data and issuing a strain warning when the cavity contraction rate exceeds a monthly threshold includes the following steps: Based on the strain data of each monitoring node, the cavity shrinkage rate of the salt cavern gas storage is estimated using the equivalent average strain method. A strain warning is issued when the monthly cavity shrinkage rate exceeds the shrinkage rate threshold.

9. A real-time monitoring and early warning system for salt cavern gas storage based on fiber optic sensing, characterized in that, The real-time monitoring and early warning system for salt cavern gas storage based on fiber optic sensing includes: a data acquisition device, a data output device, a processor, and a storage device. The storage device includes a computer-readable storage medium storing a computer program. The computer program includes program instructions, which, when executed by the processor, cause the processor to implement the real-time monitoring and early warning method for salt cavern gas storage based on fiber optic sensing as described in any one of claims 1-8.

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