Salt cavern gas storage real-time monitoring and early warning method and system based on optical fiber sensing

Abstract

The invention relates to the technical field of salt-cavern gas storage monitoring, in particular to a salt-cavern gas storage real-time monitoring and early warning method and system based on optical fiber sensing, and the method comprises the following steps: constructing a three-dimensional model of a salt-cavern gas storage, and then determining monitoring nodes; laying distributed sensing optical fibers along the inner wall of a cavity of the salt cavern gas storage according to the layout of the monitoring nodes so as to obtain temperature data and strain data in real time; according to the three-dimensional model, the temperature data and the strain data, a pressure field of the salt cavern gas storage is inversed based on a finite element method, and pressure data in the salt cavern are obtained; dTS-Raman composite optical fibers are vertically hung in the salt cavern gas storage to obtain gas-halogen interface height data; and a salt cavern gas storage environment monitoring and early warning system is constructed, and early warning is given out when the early warning condition is met. According to the invention, long-distance online monitoring and early warning of the salt-cavern gas storage can be realized, multi-parameter fusion analysis of the salt-cavern gas storage can be carried out, the accuracy of monitoring and early warning can be improved, and the cost of monitoring and early warning can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of salt cavern gas storage monitoring, and in particular to a real-time monitoring and early warning method and system for salt cavern gas storage based on optical fiber sensing. Background Art

[0002] As an important natural gas storage facility, salt cavern gas storage plays a key role in my country's energy strategy. However, due to its special structural characteristics and operating conditions, there are many potential safety hazards in the well site of salt cavern gas storage, including complex equipment layout, widely distributed leakage sources and high probability of micro-leakage events. In order to effectively monitor and prevent micro-leakage in the well site and improve the safety and operating efficiency of the gas storage, it is particularly important to accurately monitor the temperature, strain, pressure and interface position of the salt cavern gas storage.

[0003] However, traditional salt rock gas storage monitoring technology has the following defects: (1) Sensor limitations: Electronic sensors are easily affected by the high humidity, high pressure and strong corrosion environment in salt rock storage, and have short lifespans, high maintenance costs and difficulties in maintenance; (2) Static deployment blind spots: Due to the complex structure of deep salt cavern gas storage, fixed sensor networks cannot dynamically track and judge gas-halogen interface migration, cavity shrinkage rate and local leakage; (3) Insufficient multi-parameter coordination: Discrete sensors are difficult to synchronously obtain multi-dimensional data such as pressure, temperature and strain, and the monitoring data is single; (4) Response lag: Manual inspections and offline analysis cannot meet the needs of real-time online monitoring and early warning, increasing the risk of gas storage 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 the advantages of distributed measurement, strong anti-interference ability, and high real-time performance, which can provide a more effective means for monitoring salt cavern gas storage. However, there is no mature method to comprehensively and systematically apply fiber optic sensing technology to real-time monitoring and early warning of salt cavern gas storage, and it is still in the exploratory stage. Summary of the invention

[0005] In view of the defects in the prior art, the present invention provides a real-time monitoring and early warning method and system for salt cavern gas storage based on optical fiber sensing.

[0006] In order to achieve the above-mentioned purpose, in the first aspect, the present invention provides a real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing, the method comprising the following steps: constructing a three-dimensional model of the salt cavern gas storage, and determining monitoring nodes on the inner wall of the cavity of the salt cavern gas storage according to the three-dimensional model; laying distributed sensing optical fibers along the inner wall of the cavity of the salt cavern gas storage according to the layout of the monitoring nodes, so as to obtain the temperature data and strain data inside the salt cavern in real time; inverting the pressure field of the salt cavern gas storage based on the finite element method according to the three-dimensional model, the temperature data and the strain data, and obtaining the pressure data inside the salt cavern; vertically suspending DTS-Raman composite optical fiber inside the salt cavern gas storage, and obtaining the gas-halogen interface height data according to the temperature gradient and the Raman scattering intensity mutation point; constructing a salt cavern gas storage environment monitoring and early warning system, and then 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. The present invention can realize long-distance online monitoring and early warning of the salt cavern gas storage, and can perform multi-parameter fusion analysis of the salt cavern gas storage, improve the accuracy of monitoring and early warning, and reduce the cost of monitoring and early warning.

[0007] Optionally, the constructing of a three-dimensional model of the salt cavern gas storage reservoir, and determining monitoring nodes on the inner wall of the cavity of the salt cavern gas storage reservoir according to the three-dimensional model comprises the following steps: Conduct geological surveys of the salt cavern gas storage reservoir’s location and use lidar to scan the salt cavern gas storage reservoir cavity; According to the scanning results and geological survey results, combined with the cavity design data of the salt cavern gas storage reservoir, the three-dimensional model of the salt cavern gas storage reservoir is established; According to the three-dimensional model, monitoring nodes are selected on the inner wall of the cavity of the salt cavern gas storage reservoir by comprehensively considering the geological conditions, operation requirements and cavity geometry of the salt cavern gas storage reservoir.

[0008] Optionally, the method 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 obtain temperature data and strain data inside the salt cavern in real time includes the following steps: According to the layout of the monitoring nodes, manually setting the initial optical fiber laying path; Using an ant colony algorithm to optimize the initial optical fiber laying path to obtain an optimal optical fiber laying path; According to the optimal optical fiber laying path, distributed sensing optical fiber is laid along the inner wall of the salt cavern gas storage cavity to obtain temperature data and strain data inside the salt cavern in real time.

[0009] Optionally, inverting the pressure field of the salt cavern gas storage based on the finite element method according to the three-dimensional model, the temperature data and the strain data to obtain the pressure data inside the salt cavern comprises the following steps: performing finite element discretization on the salt cavern according to the three-dimensional model, and applying temperature boundary conditions according to the temperature data; Generate a temperature field and a strain field of the salt cavern gas storage based on the temperature data and the strain data based on a spatial interpolation method; Conduct parameter coupling analysis on salt cavern gas storage and then build a coupling model; 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.

[0010] Optionally, the step of continuously updating the pressure field based on the temperature field and the coupling model to invert the strain field, and then obtaining the pressure data inside the salt cavern comprises the following steps: Initialize the pressure field; According to the temperature field and the pressure field, a coupling model is used to obtain a simulated strain field, and then strain inversion data of the monitoring node is determined according to the simulated strain field; Setting an optimization objective function with the goal of minimizing the strain inversion data and the strain data; The gradient of the optimization objective function 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, and finally the pressure data is obtained.

[0011] Optionally, the coupling model satisfies the following relationship: in, is the thermal strain tensor, is the thermal expansion coefficient of rock salt, I is the unit tensor, T is the temperature field, is the reference temperature field, is the effective stress tensor, P is the pressure field, is the thermal stress coefficient, is the mechanical strain tensor, G is the shear modulus, For time, is the creep time constant, is Poisson's ratio, E is the elastic modulus of salt rock, for traces, is the total strain tensor.

[0012] Optionally, the optimization objective function satisfies the following relationship: in, is the difference value, N is the number of monitoring nodes, is the strain inversion value of the nth monitoring node obtained by the coupling model under the pressure field P and the temperature field T, is the strain data of the nth monitoring node, is the regularization parameter.

[0013] Optionally, the construction of a salt cavern gas storage environment monitoring and early warning system, and then issuing an early warning when the temperature data, the strain data, the pressure data and the gas-halogen interface height data meet early warning conditions, comprises the following steps: Determine whether there is a local temperature drop in the salt cavern gas storage according to the temperature data, and issue a temperature warning when there is a local temperature drop in the salt cavern gas storage; Determine the cavity shrinkage rate of the salt cavern gas storage according to the strain data, and issue a strain warning when the cavity shrinkage rate is greater than a shrinkage rate threshold value each month; Acquire a maximum daily pressure fluctuation in the salt cavern gas storage according to the pressure data, and issue a pressure warning when the maximum daily pressure fluctuation is greater than a pressure fluctuation threshold; The daily migration amount of the gas-halogen interface is determined according to the gas-halogen interface height data, and a gas-halogen interface migration warning is issued when the daily migration amount of the gas-halogen interface is greater than a migration amount threshold.

[0014] Optionally, determining the cavity shrinkage rate of the salt cavern gas storage according to the strain data, and issuing a strain warning when the cavity shrinkage rate is greater than a shrinkage rate threshold each month comprises the following steps: According to 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 shrinkage rate of the cavity is greater than a shrinkage rate threshold.

[0015] In a second aspect, the present invention provides a real-time monitoring and early warning system for a salt cavern gas storage reservoir based on optical fiber sensing, wherein the real-time monitoring and early warning system for a salt cavern gas storage reservoir based on optical fiber sensing comprises: a data acquisition device, a data output device, a processor and a storage device, wherein the storage device comprises a computer-readable storage medium, wherein a computer program is stored in the computer-readable storage medium, wherein the computer program comprises program instructions, and when the program instructions are executed by the processor, the processor implements the real-time monitoring and early warning method for a salt cavern gas storage reservoir based on optical fiber sensing provided by the present invention.

[0016] The present invention has at least the following beneficial effects: 1. Fiber optic sensing technology has the advantages of anti-electromagnetic interference, corrosion resistance, long-distance transmission, high sensitivity and high resolution. Therefore, this method based on fiber optic sensing technology can achieve long-term and accurate measurement of the temperature, strain, pressure and gas-halogen interface of salt cavern gas storage.

[0017] 2. This method uses the ant colony algorithm to optimize the initial optical fiber laying path to obtain the optimal optical fiber laying path, which reduces the optical fiber laying length and thus reduces the monitoring cost of the salt cavern gas storage.

[0018] 3. Distributed fiber optic sensing technology can realize multi-point monitoring on one optical fiber and measure the temperature and strain at multiple locations at the same time, which greatly reduces the number of sensors and wiring complexity, improves the efficiency and reliability of monitoring, and further reduces the monitoring cost of salt cavern gas storage.

[0019] 4. This method first uses distributed sensing optical fiber to measure the temperature strain of the salt cavern gas storage reservoir, and then inverts the pressure field in the salt cavern gas storage reservoir based on the finite element method. This solves the problem that a single optical fiber is difficult to simultaneously and accurately measure the temperature, strain and pressure in the salt cavern gas storage reservoir. It is beneficial to further reduce the monitoring cost of the salt cavern gas storage reservoir and provide a new idea for the monitoring of the salt cavern gas storage reservoir.

[0020] 5. This method constructs a salt cavern gas storage environment monitoring and early warning system, and can issue an early warning when the temperature, strain, pressure and the height of the gas-halogen interface meet the early warning conditions, so that relevant personnel can take timely response measures.

[0021] 6. A real-time monitoring and early warning system for salt cavern gas storage that is compatible with the real-time monitoring and early warning method for salt cavern gas storage is provided, thereby improving the practicability of the real-time monitoring and early warning method for salt cavern gas storage and facilitating the promotion of the real-time monitoring and early warning method for salt cavern gas storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a flow chart of a method for real-time monitoring and early warning of a salt cavern gas storage based on optical fiber sensing according to an embodiment of the present invention; Figure 2 It is a schematic diagram of the framework of a real-time monitoring and early warning system for salt cavern gas storage based on optical fiber sensing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0025] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or subcombination. In addition, it should be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale.

[0026] It should be noted in advance that, in an optional embodiment, except for independent explanations, the same symbols or letters appearing in all formulas have the same meanings and values.

[0027] In an alternative embodiment, see Figure 1 The present invention provides a real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing, the method comprising the following steps: S1. construct a three-dimensional model of a salt cavern gas storage reservoir, and determine monitoring nodes on the inner wall of the cavity of the salt cavern gas storage reservoir according to the three-dimensional model.

[0028] Wherein, step S1 specifically includes the following steps: S11. Conduct geological surveys on the location of the salt cavern gas storage reservoir and use laser radar to scan the cavity of the salt cavern gas storage reservoir.

[0029] Specifically, in this embodiment, the geological survey is to fully understand the geological conditions of the area where the salt cavern gas storage is located, and to provide basic data for the subsequent cavity design, three-dimensional modeling, and selection of monitoring nodes. Through geological survey, the stability of underground rock formations, the thickness and purity of salt layers, whether there are faults, fissures and other unfavorable geological structures, and the distribution of groundwater can be evaluated. LiDAR scanning is to obtain the precise geometric shape and spatial position information of the salt cavern gas storage cavity. Through geological survey and LiDAR scanning, the geological conditions of the salt cavern gas storage and the three-dimensional point cloud data of the cavity can be obtained, providing a data basis for the subsequent construction of accurate and reliable three-dimensional modeling.

[0030] More specifically, holes are drilled at a certain interval and depth in the area where the salt cavern gas storage is located to obtain underground core samples, and the physical and mechanical properties of the salt layer, such as density, porosity, permeability, etc., as well as the stratigraphic sequence and thickness changes of the rock layer, are determined through analysis of the core samples; seismic exploration, electrical exploration, magnetic exploration and other methods are used to detect the underground geological structure of the location where the salt cavern gas storage is located; the water level, water quality, recharge and discharge conditions of the groundwater at the location of the salt cavern gas storage are understood through hydrogeological surveys; a three-dimensional laser scanner is used at the wellhead of the salt cavern gas storage to perform a full-scale scan of the cavity to obtain the three-dimensional coordinate information of each point on the inner wall of the cavity. After the scan is completed, the acquired point cloud data needs to be pre-processed by denoising and registration to improve the accuracy and integrity of the data.

[0031] S12. According to the scanning results and geological survey results, combined with the cavity design data of the salt cavern gas storage reservoir, the three-dimensional model of the salt cavern gas storage reservoir is established.

[0032] Specifically, in this embodiment, the cavity three-dimensional point cloud data obtained by laser radar scanning is integrated with the geological survey results, and the cavity design data such as the size, shape, and layout of the salt cavern gas storage cavity are combined to establish the three-dimensional model of the salt cavern gas storage reservoir, ensuring that the three-dimensional model can accurately reflect the design intent and actual geological conditions. The specific process of constructing the three-dimensional model of the salt cavern gas storage reservoir can refer to the existing technical means, which will not be described in detail here.

[0033] S13. According to the three-dimensional model, the geological conditions, operation requirements and the geometric shape of the cavity of the salt cavern gas storage are comprehensively considered, and monitoring nodes are selected on the inner wall of the cavity of the salt cavern gas storage.

[0034] Specifically, in this embodiment, monitoring nodes are manually set on the three-dimensional model, and the monitoring nodes should be as dense as possible to facilitate the subsequent construction of temperature fields and strain fields. In areas with unstable geological conditions, such as areas with developed faults and fissures, the density of monitoring nodes should be appropriately increased to timely detect the deformation and displacement of rock formations. Considering operational needs, in order to monitor changes in temperature, strain, pressure and other data in salt cavern gas storage, monitoring nodes should be set at different heights and positions of the cavity. Considering the geometry of the cavity, monitoring nodes should be set in corners, interfaces and other places of the cavity where strain concentration is likely to occur, to monitor changes in temperature, strain, pressure and other data.

[0035] More specifically, except for areas with unstable geological conditions and areas prone to strain concentration in the salt cavern gas storage, the distribution of monitoring nodes should be as uniform as possible so that temperature and strain data at various locations in the salt cavern gas storage can be collected as much as possible in the future.

[0036] S2. According to the layout of the monitoring nodes, distributed sensing optical fibers are laid along the inner wall of the salt cavern gas storage cavity to obtain the temperature data and strain data inside the salt cavern in real time.

[0037] Wherein, step S2 specifically includes the following steps: S21. Manually set an initial optical fiber laying path according to the layout of the monitoring nodes.

[0038] Specifically, in this embodiment, the initial optical fiber 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.

[0039] S22. Use an ant colony algorithm to optimize the initial optical fiber laying path to obtain an optimal optical fiber laying path.

[0040] Specifically, in this embodiment, the parameter settings are initialized first, the number of ants is set to 1.5 times the number of monitoring nodes, the pheromone volatility coefficient is set to 0.3, the pheromone importance is set to 1, the heuristic information importance is set to 2, and the pheromone concentration is initialized according to the initial fiber optic laying path, wherein the initial value of the long path pheromone concentration should be lower than the initial value of the short path pheromone concentration. After the initialization parameter settings, the ant colony algorithm can be used to optimize the initial fiber optic laying path with the goal of minimizing the fiber optic laying path length, and the optimal fiber optic laying path can be obtained, thereby reducing the length of the sensing fiber required for monitoring the salt cavern gas storage reservoir and reducing the monitoring cost of the salt cavern gas storage reservoir.

[0041] Furthermore, after the ant colony algorithm outputs the optimal fiber optic laying path, relevant technical personnel can also optimize it according to their own experience and the actual situation of the salt cavern to improve the rationality of the optimal fiber optic laying path.

[0042] S23. According to the optimal optical fiber laying path, distributed sensing optical fiber is laid along the inner wall of the cavity of the salt cavern gas storage reservoir to obtain temperature data and strain data inside the salt cavern in real time.

[0043] Specifically, in this embodiment, a Brillouin optical time domain reflectometry (BOTDR) system is used to simultaneously measure the temperature data and strain data of each monitoring node inside the salt cavern, thereby reducing the monitoring cost and improving the dynamic monitoring capability of the operating status of the salt cavern gas storage.

[0044] Furthermore, after obtaining the optimal optical fiber laying path, the distributed sensing optical fiber of the BOTDR system is laid along the inner wall of the cavity of the salt cavern gas storage reservoir according to the optimal optical fiber laying path.

[0045] More specifically, in order to improve the spatial resolution of the BOTDR system, iXblue's MXER-LN series intensity modulator was used, a distributed feedback (DFB) laser was used as the light source, and the wavelength of the light source was selected to be 1550nm.

[0046] In other optional embodiments, different types of optical fibers may be used to measure the temperature data and strain data of each monitoring node respectively.

[0047] S3. Invert the pressure field of the salt cavern gas storage based on the finite element method according to the three-dimensional model, the temperature data and the strain data to obtain the pressure data inside the salt cavern.

[0048] Wherein, step S3 specifically includes the following steps: S31. Perform finite element discretization on the salt cavern according to the three-dimensional model, and apply temperature boundary conditions according to the temperature data.

[0049] Specifically, in this embodiment, unstructured tetrahedral meshes are used in Abaqus to divide the three-dimensional model of the salt cavern gas storage reservoir, ensuring that the mesh density is higher in areas with unstable geological conditions and areas prone to strain concentration. According to the temperature data, the temperature of the mesh nodes on the boundary is obtained by interpolation. Considering that this step is a prior art method, only a brief description is given here.

[0050] S32. Generate a temperature field and a strain field of the salt cavern gas storage based on the temperature data and the strain data using a spatial interpolation method.

[0051] According to the measured temperature data and strain data, the temperature field and strain field are generated by ordinary Kriging interpolation method. In other optional embodiments, the measured temperature data 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 will consume a lot of computing resources.

[0052] S33. Carry out parameter coupling analysis on salt cavern gas storage and then construct a coupling model.

[0053] Specifically, in this embodiment, temperature changes directly cause salt rock to expand or contract, change the volume of salt caverns, and break the original mechanical balance; pore pressure changes trigger mechanical strain through the effective stress principle; salt rock deformation changes the pore structure, affecting gas permeability and storage space; the creep characteristics of salt rock cause strain to continue to evolve over time, changing the strain field; strain field changes may further induce thermal-mechanical feedback; at the same time, pore pressure adjustments will affect the fluid flow state, forming a closed-loop coupling. Through the above analysis, it can be seen that temperature and pressure drive strain by changing the energy state of salt rock, and strain reacts to the fluid flow and heat conduction process by changing the microstructure of the material, forming a self-organized nonlinear system. This coupling continues to evolve throughout the life cycle of the gas storage reservoir and is the root cause of safety risks in the long-term operation of salt cavern gas storage reservoirs.

[0054] In addition, the following further considerations are made: 1. In the long-term analysis of salt cavern gas storage, other stresses such as tectonic stress and fluid viscosity are usually secondary to pore pressure and thermal stress. This is because tectonic stress changes slowly on a geological time scale, and fluid viscosity is usually small in the operation of a gas storage, so the total stress at the monitoring node is considered to be dominated by pore pressure and thermal stress.

[0055] 2. Salt cavern strain 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 elastic theory, the strains caused by different physical fields can be linearly superimposed. Therefore, the sum of the mechanical strain and thermal strain of salt rock is taken as the total strain.

[0056] According to the above analysis, the following coupling model can be constructed: in, is the 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; For the reference temperature field, it can be obtained by calculating the historical average temperature of each monitoring node; is the effective stress tensor; P is the pressure field, which is obtained through iterative updating; is the thermal stress coefficient, which is calculated from the thermal expansion coefficient and elastic modulus, that is, ; is the mechanical strain tensor; G is the shear modulus, which is calculated from the elastic modulus and Poisson's ratio, that is, ; For time; is the creep time constant, obtained by creep experiments in the laboratory; is Poisson's ratio, obtained through triaxial compression test; E is the elastic modulus of salt rock, obtained through uniaxial compression test; for traces; is the total strain tensor.

[0057] 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.

[0058] Wherein, step S34 specifically includes the following steps: S341. Initialize the pressure field.

[0059] Specifically, in this embodiment, when the inversion starts, the initial pressure field is set according to the wellhead pressure of the salt cavern gas storage and in combination with pressure monitoring cases of other salt cavern gas storages.

[0060] S342: According to the temperature field and the pressure field, a coupling model is used to obtain a simulated strain field, and then strain inversion data of the monitoring node is determined according to the simulated strain field.

[0061] Specifically, in this embodiment, the temperature field and the initial pressure field are brought into the coupling model to calculate the simulated strain field under the corresponding temperature field and pressure field, and then the strain on the monitoring node can be obtained directly or by linear interpolation according to the position of the monitoring node, that is, the strain inversion data.

[0062] S343, setting an optimization objective function with the goal of minimizing the strain inversion data and the strain data.

[0063] Specifically, in this embodiment, the optimization objective function satisfies the following relationship: in, is the difference value, N is the number of monitoring nodes, is the strain inversion value of the nth monitoring node obtained by the coupling model under the pressure field P and temperature field T, is the strain data of the nth monitoring node, is the regularization parameter and . is a regularization term, and L2 regularization is used to suppress local violent fluctuations.

[0064] S344, calculating the gradient of the optimization objective function with respect to the pressure field, and then using the gradient descent method to iteratively update the pressure field until the constraint conditions are met, and finally obtaining the pressure data.

[0065] Specifically, in this embodiment, the adjoint method is used to calculate the gradient of the optimization objective function to the pressure field, and then the gradient descent method is used to iteratively update the pressure field to minimize the optimization objective function, that is: in, is the pressure field obtained by the k+1th update, is the pressure field obtained by the kth update, is the learning rate and , To optimize the gradient of the objective function with respect to the pressure field.

[0066] Furthermore, in general, when When , it is considered that the pressure field satisfies the constraint condition, and the pressure field at this time is taken as the real pressure field in the salt cavern gas storage reservoir, and then the pressure value on the monitoring node can be obtained directly or by linear interpolation according to the position of the monitoring node.

[0067] S4. Vertically suspend the DTS-Raman composite optical fiber inside the salt cavern gas storage reservoir to obtain the gas-halogen interface height data based on the temperature gradient and the Raman scattering intensity mutation point.

[0068] Specifically, in this embodiment, a DTS-Raman composite optical fiber is vertically suspended inside the salt cavern gas storage reservoir, and then the gas-halogen interface height data is acquired based on the DTS system and OTDR technology. When the DTS-Raman composite optical fiber is vertically suspended, optical fibers at different heights will produce significant temperature gradients after active heating due to the difference in specific heat capacity of the medium in which they are located, and the sudden change in heat exchange efficiency at the gas-halogen interface leads to a temperature gradient inflection point. The DTS system utilizes the Raman scattering effect in the optical fiber, measures the intensity ratio of Stokes and anti-Stokes scattered light, and demodulates the temperature signal in combination with the dual-channel dual-wavelength comparison method to achieve continuous temperature distribution monitoring along the optical fiber. At the same time, the Raman scattering intensity changes significantly at the gas-halogen interface due to the sudden change in material composition. The scattering intensity mutation point is identified through the time-space domain filtering algorithm, and cross-validated with the temperature gradient inflection point to improve positioning reliability. The OTDR technology measures the transmission time difference of the laser pulse in the optical fiber, and calculates the position of the scattering point in combination with the refractive index of the optical fiber to achieve accurate positioning of the gas-halogen interface height.

[0069] S5. Construct a salt cavern gas storage environment monitoring and early warning system, and then issue an early warning when the temperature data, the strain data, the pressure data and the gas-halogen interface height data meet early warning conditions.

[0070] This embodiment constructs a salt cavern gas storage environment monitoring and early warning system to issue an early warning when the temperature, strain, pressure and gas-halogen interface height meet the early warning conditions, so that relevant personnel can take timely response measures. Step S5 specifically includes the following steps: S51. Determine whether there is a local temperature drop in the salt cavern gas storage according to the temperature data, and issue a temperature warning when there is a local temperature drop in the salt cavern gas storage.

[0071] Specifically, in this embodiment, according to 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 local temperature drop in the salt cavern gas storage, and gas leakage is suspected.

[0072] S52: determining the cavity shrinkage rate of the salt cavern gas storage according to the strain data, and issuing a strain warning when the cavity shrinkage rate is greater than a shrinkage rate threshold value each month.

[0073] Wherein, step S52 specifically includes the following steps: S521. Estimate the cavity shrinkage rate of the salt cavern gas storage using the equivalent average strain method according to the strain data of each monitoring node.

[0074] Specifically, in this embodiment, since the monitoring nodes are distributed as evenly as possible when setting the monitoring nodes in step S13, the equivalent average strain method can be used to estimate the cavity shrinkage rate of the salt cavern gas storage. The cavity shrinkage rate specifically satisfies the following relationship: in, represents the cavity shrinkage rate, is the volume change of the salt cavern gas storage at the end of the month, is the volume of the salt cavern gas storage at the beginning of the month, , and is the strain components of the strain data of the nth monitoring node in three orthogonal directions.

[0075] Furthermore, in other optional embodiments, the cavity shrinkage rate may be calculated by using a direct integration method based on the strain field and an indirect prediction method based on the salt rock creep model.

[0076] S522. When the monthly shrinkage rate of the cavity is greater than a shrinkage rate threshold, a strain warning is issued.

[0077] Specifically, in this embodiment, the shrinkage rate threshold is 5%.

[0078] S53. Acquire a maximum daily pressure fluctuation in the salt cavern gas storage according to the pressure data, and issue a pressure warning when the maximum daily pressure fluctuation is greater than a pressure fluctuation threshold.

[0079] Specifically, in this embodiment, the pressure fluctuation of each monitoring node is calculated in real time according to the following relationship: Among them, r is the pressure fluctuation of the monitoring node, P is the real-time pressure of the monitoring node on the day, is the initial pressure of the monitoring node on that day.

[0080] Furthermore, the pressure fluctuation threshold is specifically 0.1.

[0081] S54, determining the daily migration amount of the gas-halogen interface according to the gas-halogen interface height data, and issuing a gas-halogen interface migration warning when the daily migration amount of the gas-halogen interface is greater than a migration amount threshold.

[0082] Specifically, in this embodiment, the daily migration amount of the gas-halogen interface is the change in the height of the gas-halogen interface within 24 hours.

[0083] Furthermore, the migration amount threshold is specifically 1m.

[0084] It should be noted that, in some cases, the actions described in the specification can be performed in a different order and still achieve the desired results. In this embodiment, the order of steps given is only to make the embodiment appear clearer and easier to explain, rather than to limit it.

[0085] In an alternative embodiment, see Figure 1 In order to improve the practicality of the method, the present invention also 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 1, a data output device 2, a processor 3 and a storage 4. The storage 4 includes a computer-readable storage medium. The computer-readable storage medium stores a computer program. The computer program includes program instructions. When the program instructions are executed by the processor 3, the processor 3 implements the contents described in steps S1 to S5.

[0086] Specifically, in this embodiment, the data acquisition device 1 includes various optical fibers used in this method.

[0087] In summary, this embodiment has at least the following beneficial effects: 1. Fiber optic sensing technology has the advantages of anti-electromagnetic interference, corrosion resistance, long-distance transmission, high sensitivity and high resolution. Therefore, this method based on fiber optic sensing technology can achieve long-term and accurate measurement of the temperature, strain, pressure and gas-halogen interface of salt cavern gas storage.

[0088] 2. This method uses the ant colony algorithm to optimize the initial optical fiber laying path to obtain the optimal optical fiber laying path, which reduces the optical fiber laying length and thus reduces the monitoring cost of the salt cavern gas storage.

[0089] 3. Distributed fiber optic sensing technology can realize multi-point monitoring on one optical fiber and measure the temperature and strain at multiple locations at the same time, which greatly reduces the number of sensors and wiring complexity, improves the efficiency and reliability of monitoring, and further reduces the monitoring cost of salt cavern gas storage.

[0090] 4. This method first uses distributed sensing optical fiber to measure the temperature strain of the salt cavern gas storage reservoir, and then inverts the pressure field in the salt cavern gas storage reservoir based on the finite element method. This solves the problem that a single optical fiber is difficult to simultaneously and accurately measure the temperature, strain and pressure in the salt cavern gas storage reservoir. It is beneficial to further reduce the monitoring cost of the salt cavern gas storage reservoir and provide a new idea for the monitoring of the salt cavern gas storage reservoir.

[0091] 5. This method constructs a salt cavern gas storage environment monitoring and early warning system, and can issue an early warning when the temperature, strain, pressure and gas-halogen interface height meet the early warning conditions, so that relevant personnel can take timely response measures.

[0092] 6. A real-time monitoring and early warning system for salt cavern gas storage that is compatible with the real-time monitoring and early warning method for salt cavern gas storage is provided, thereby improving the practicability of the real-time monitoring and early warning method for salt cavern gas storage and facilitating the promotion of the real-time monitoring and early warning method for salt cavern gas storage.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in 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 optical fiber sensing, characterized in that: The steps include: Constructing a three-dimensional model of the salt cavern gas storage reservoir, and determining monitoring nodes on the inner wall of the cavity of the salt cavern gas storage reservoir according to the three-dimensional model; According to the layout of the monitoring nodes, distributed sensing optical fibers are laid along the inner wall of the salt cavern gas storage cavity to obtain temperature data and strain data inside the salt cavern in real time; According to the three-dimensional model, the temperature data and the strain data, the pressure field of the salt cavern gas storage is inverted based on the finite element method to obtain the pressure data inside the salt cavern; A DTS-Raman composite optical fiber is vertically suspended inside the salt cavern gas storage reservoir to obtain the gas-halogen interface height data based on the temperature gradient and Raman scattering intensity mutation point; A salt cavern gas storage environment monitoring and early warning system is constructed, and an early warning is issued when the temperature data, the strain data, the pressure data and the gas-halogen interface height data meet the early warning conditions.

2. The real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing according to claim 1 is characterized in that: The three-dimensional model of the salt cavern gas storage is constructed, and the monitoring nodes are determined on the inner wall of the cavity of the salt cavern gas storage according to the three-dimensional model, including the following steps: Conduct geological surveys of the salt cavern gas storage reservoir’s location and use lidar to scan the salt cavern gas storage reservoir cavity; According to the scanning results and geological survey results, combined with the cavity design data of the salt cavern gas storage reservoir, the three-dimensional model of the salt cavern gas storage reservoir is established; According to the three-dimensional model, monitoring nodes are selected on the inner wall of the cavity of the salt cavern gas storage reservoir by comprehensively considering the geological conditions, operation requirements and cavity geometry of the salt cavern gas storage reservoir.

3. The real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing according to claim 1 is characterized in that: According to the layout of the monitoring nodes, the distributed sensing optical fiber is laid along the inner wall of the cavity of the salt cavern gas storage reservoir to obtain the temperature data and strain data inside the salt cavern in real time, which includes the following steps: According to the layout of the monitoring nodes, manually setting the initial optical fiber laying path; Using an ant colony algorithm to optimize the initial optical fiber laying path to obtain an optimal optical fiber laying path; According to the optimal optical fiber laying path, distributed sensing optical fiber is laid along the inner wall of the salt cavern gas storage cavity to obtain temperature data 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 optical fiber sensing according to claim 1 is characterized in that: The inversion of the pressure field of the salt cavern gas storage based on the finite element method according to the three-dimensional model, the temperature data and the strain data to obtain the pressure data inside the salt cavern comprises the following steps: performing finite element discretization on the salt cavern according to the three-dimensional model, and applying temperature boundary conditions according to the temperature data; Generate a temperature field and a strain field of the salt cavern gas storage based on the temperature data and the strain data based on a spatial interpolation method; Conduct parameter coupling analysis on salt cavern gas storage and then construct a coupling model; 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 optical fiber sensing according to claim 4 is characterized in that: The step of continuously updating the pressure field based on the temperature field and the coupling model to invert the strain field and thereby obtain the pressure data inside the salt cavern comprises the following steps: Initialize the pressure field; According to the temperature field and the pressure field, a coupling model is used to obtain a simulated strain field, and then strain inversion data of the monitoring node is determined according to the simulated strain field; Setting an optimization objective function with the goal of minimizing the strain inversion data and the strain data; The gradient of the optimization objective function 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, and finally the pressure data is obtained.

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

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

8. The real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing according to claim 1 is characterized in that: The construction of the salt cavern gas storage environment monitoring and early warning system, and then 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, comprises the following steps: Determine whether there is a local temperature drop in the salt cavern gas storage according to the temperature data, and issue a temperature warning when there is a local temperature drop in the salt cavern gas storage; Determine the cavity shrinkage rate of the salt cavern gas storage according to the strain data, and issue a strain warning when the cavity shrinkage rate is greater than a shrinkage rate threshold value each month; Acquire a maximum daily pressure fluctuation in the salt cavern gas storage according to the pressure data, and issue a pressure warning when the maximum daily pressure fluctuation is greater than a pressure fluctuation threshold; The daily migration amount of the gas-halogen interface is determined according to the gas-halogen interface height data, and a gas-halogen interface migration warning is issued when the daily migration amount of the gas-halogen interface is greater than a migration amount threshold.

9. The real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing according to claim 8 is characterized in that: The method of determining the cavity shrinkage rate of the salt cavern gas storage according to the strain data and issuing a strain warning when the cavity shrinkage rate is greater than a shrinkage rate threshold each month comprises the following steps: According to 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 shrinkage rate of the cavity is greater than a shrinkage rate threshold.

10. A real-time monitoring and early warning system for salt cavern gas storage based on optical fiber sensing, characterized in that: The real-time monitoring and early warning system for salt cavern gas storage based on optical fiber sensing comprises: a data acquisition device, a data output device, a processor and a storage device, wherein the storage device comprises a computer-readable storage medium, wherein a computer program is stored in the computer-readable storage medium, and wherein the computer program comprises program instructions, and when the program instructions are executed by the processor, the processor implements the real-time monitoring and early warning method for salt cavern gas storage based on optical fiber sensing as described in any one of claims 1 to 9.

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