A method for locating natural gas leak sources at salt cavern gas storage well sites

Abstract

This invention discloses a method for locating natural gas leak sources in salt cavern gas storage well sites, comprising the following steps: 1) Deployment of point-type laser methane detectors within key monitoring areas. 2) Monitoring of unknown areas outside the key monitoring areas. 3) Leak source inversion and location: When the concentration value of leaked natural gas in a salt cavern gas storage well site, as monitored by the point-type laser methane detector, reaches a predetermined threshold, the leak source needs to be located promptly. The specific process is as follows: Step 1) Establishing a leak diffusion model; Step 2) Establishing an objective function F; Step 3) Locating the leak point. The leak source location method of this invention has high accuracy and cost-effectiveness, can efficiently obtain concentration interpolation with smaller errors, and solves the problem of insufficient full-coverage monitoring of salt cavern gas storage well sites.

Description

Technical Field

[0001] This invention relates to the field of safety monitoring technology for salt cavern gas storage well sites, and in particular to a method for locating natural gas leakage sources at salt cavern gas storage well sites. Background Technology

[0002] Salt cavern gas storage facilities, serving as underground reservoirs for natural gas, are the optimal geological formations for underground storage and supply regulation of natural gas. With continuous natural gas injection and production, and seasonal peak shaving, minor leaks are inevitable at salt cavern gas storage well sites. Natural gas leaks not only cause direct economic losses to the country but also pose significant safety hazards due to their flammability and explosiveness, severely compromising the safe operation of salt cavern gas injection and production wells. Therefore, developing effective methods to monitor and / or locate leak sources is essential.

[0003] Currently, the general methods for monitoring and locating natural gas leaks at salt cavern gas storage well sites are as follows: Figure 1 As shown, some methods employ array-type multi-point sensor deployment, utilizing the effective monitoring range of point-type laser methane detectors to cover the entire well site area, thus achieving well site coverage monitoring. Other methods deploy methane detectors within the effective range of process equipment and pipelines in the well site area. However, these methods suffer from several drawbacks. First, they involve installing numerous devices, resulting in inefficient use of the effective monitoring range and increased wiring and maintenance costs. Second, the selection of monitoring points is too subjective, compromising monitoring accuracy.

[0004] In addition, current monitoring and location technologies include: 1) Hardware-based methods, which have the advantages of low cost and high accuracy. However, the improvement in gas monitoring accuracy has not increased the efficiency of leak location. Furthermore, the number and cost of deploying and installing hardware devices pose another major challenge to leak detection. At the same time, hardware monitoring devices cannot cover the entire salt cavern gas storage well site, making it impossible to avoid missing the location of leak sources in unmonitored areas within the well site. 2) Software-based methods, which mainly rely on mathematical models and monitoring systems, result in relatively high costs for system development and measurement instruments. Software-based monitoring and location have real-time monitoring capabilities, but the main work of leak monitoring still relies on inspection personnel. For example, the accurate location of leak sources and leak handling mainly depend on the experience of the staff and heavy mechanical labor. The uncertainty of monitoring equipment (due to the inability to provide full coverage and the existence of unmonitored areas) and the instability of human intervention (relying on the experience of the staff) bring many difficulties to the monitoring and location of leaks in gas storage well sites.

[0005] With the development of intelligence and data, it is particularly important to integrate the advantages of hardware systems and mathematical models to locate leak points in a timely and accurate manner using more intelligent and efficient methods, thereby achieving well site leak risk management and the goal of "reducing costs and increasing efficiency." Based on this, our research group has conducted further research and development, building upon our previous research results (some results can be found in CN116105932A). Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a high-precision and cost-effective method for locating natural gas leakage sources in salt cavern gas storage well sites. This method utilizes an improved interpolation method to solve the problem of incomplete monitoring of salt cavern gas storage well sites. Then, using concentration monitoring values ​​and concentration interpolation values ​​as parameters, the leakage source is located by inversion based on a gas leakage diffusion model.

[0007] To achieve the above objectives, the present invention provides a method for locating natural gas leakage sources at salt cavern gas storage well sites, comprising the following steps:

[0008] I. Deployment of point-type laser methane detectors in key monitoring areas

[0009] Step 1) Determining the key monitoring areas of the salt cavern gas storage well site operation area;

[0010] Step 2) Based on the key monitoring areas of the salt cavern gas storage well site obtained in Step 1), deploy point-type laser methane detectors.

[0011] II. Monitoring of Unknown Areas Outside Key Monitoring Areas

[0012] By deploying point-type laser methane detectors within the key monitoring area, the real-time methane concentration values ​​in the areas where each detector is located and the gas leakage status within the coverage area of ​​each detector are obtained. Based on the real-time methane concentration values ​​and their location distribution, gas leakage detection is performed in unknown areas outside the key monitoring area, and concentration interpolation calculations are performed for other grid nodes. The specific steps are as follows:

[0013] Step 1) The point-type laser methane detectors are deployed on the same horizontal plane, z i =1.5m, to simplify calculations, the coordinate information and concentration values ​​of each point-type laser methane detector are expressed as: C(x i y i ), i = 1, 2, 3, ..., n, where n is the number of point-type laser methane detectors; x i y i Let C(x) be the coordinates of the i-th point laser methane detector; i y i Let x be the coordinates of the i-th point laser methane detector. iy i Concentration value at location.

[0014] Step 2) Combine the Kriging interpolation method and the modified Shebeder interpolation method to calculate the concentration interpolation.

[0015] III. Leakage Source Inversion and Localization

[0016] When the concentration of leaked natural gas at a salt cavern gas storage well site reaches a predetermined threshold as monitored by a point-type laser methane detector, the leak source must be located promptly. The specific process is as follows:

[0017] Step 1) Establish a leakage diffusion model;

[0018] Step 2) Establish the objective function F;

[0019] Step 3) Locating the leak point: The problem of finding the location and concentration of the leak source is transformed into a mathematical problem of minimizing the difference between the monitored value of the gas leak concentration and the calculated value of the leak diffusion theory; when the minimum value is obtained, it is the leak inversion location result, and then the leak intensity and the location of the leak source are obtained by inversion.

[0020] Preferably, the determination of the key monitoring area in the salt cavern gas storage well site operation area is as follows:

[0021] First, from a qualitative perspective, key monitoring areas are determined: the equipment layout of salt cavern gas storage well sites is complex. Based on the leakage probability, the potential leakage sources are mainly the wellhead, valve group, gas injection and production pipeline, compressor unit, container, and pump body. The wellhead area, valve group area, gas injection and production pipeline area, compressor unit area, container area, and pump body area are designated as key monitoring areas.

[0022] Secondly, from a quantitative perspective, key monitoring areas are determined: based on the leakage frequency and storage accident frequency of the International Oil and Gas Producers Association and the hydrocarbon leakage statistical frequency of DNV GL, the frequency distribution F under different leakage orifice diameters is calculated. y The calculation formula is as follows:

[0023]

[0024] In the formula, The leakage frequencies for apertures x1 and x2 can be found by referring to a table. -1 ; y represents the leakage probability of an unknown leakage orifice, with a value range of y∈(x1, x2); where a -1 It is a unit of measurement, indicating one year.

[0025] Combining the qualitative and quantitative approaches to identifying key monitoring areas, the key monitoring areas for the salt cavern gas storage well site operation area are determined to be the areas where the wellhead, valve group, compressor unit, pump body, container, and injection / production pipeline are located, with the probability of leakage decreasing in that order.

[0026] Preferably, point-type laser methane detectors are deployed in the key monitoring areas of the salt cavern gas storage well site obtained in step 1), specifically as follows: point-type laser methane detectors are deployed in the wellhead area, valve group area, compressor group area, pump body area, container area, and injection and production pipeline area, respectively, and the deployment meets the following criteria: (1) the point-type laser methane detectors are installed at the location with the highest leakage probability in each area, (2) the point-type laser methane detectors are erected at the same horizontal height of 1.5m, (3) the point-type laser methane detectors are located on the upwind side of the minimum frequency wind direction at the location with the highest leakage probability in each area, and the deployment location is no more than 2m away from the potential leakage source, (4) the installation spacing of each point-type laser methane detector is 10-15m, (5) each point-type laser methane detector is staggered from the ground pipelines to facilitate equipment deployment and pipeline maintenance, (6) the distance between each point-type laser methane detector is as equal as possible so that the time difference of data transmission can be controlled within a certain range.

[0027] Preferably, the concentration interpolation is obtained by combining Kriging interpolation and the modified Shebeder interpolation method, specifically in the following manner:

[0028] 2-1. The concentration interpolation is calculated using the Kriging interpolation method. The calculation formula is as follows:

[0029]

[0030] In the formula, C * (x j y j The value is the concentration interpolation obtained by Kriging interpolation, and its coordinate is x. j y j The concentration at the j-th unknown region point; λ i Let be the weight of the i-th point-type laser methane detector relative to the unknown region. 2-2. The concentration interpolation is calculated using the improved Shepard interpolation method. The calculation formula is:

[0031]

[0032]

[0033] Wherein, C″(x j y j This is an improved concentration distribution interpolation obtained using the Schieber interpolation method; w is the weighted derivative, d is the distance between the unknown monitoring point and the known monitoring point, and p is the power of the distance d, p = dk , 0≤k≤2, preferably k=2; δ is the smoothing factor; n is the number of monitoring points; Q i For quadratic surface functions,

[0034] Q i =c i1 (xx i ) 2 +c i2 (xx i (yy) i )+c i3 (yy i ) 2 +c i4 (xx i )+c i5 (yy i )+C(x i y i ), and the coordinates x of the i-th point laser methane detector. i y i Location and concentration value C(x) i y i (related to) c in the formula i1 c i2 c i3 c i4 c i5 It is to solve for the quadratic surface function and its coordinates x. i y i Location-related correction factors, in calculating gas leak concentration, c i1 c i2 c i3 c i4 c i5 All values ​​are set to 1; 2-3, the concentration interpolation result C*(x) calculated by Kriging interpolation in 2-1 is used. i y i The results of concentration interpolation C″(x) calculated by the improved Shebert interpolation method in 2-2 are as follows: j y j Substituting into the following formula, the concentration interpolation is calculated:

[0035]

[0036] In the formula, Q(x) j y j ) represents the concentration interpolation, m is the number of interpolation points, m is greater than n, and the specific value is determined according to the required accuracy; n is the number of monitoring points.

[0037] Preferably, establishing the leakage diffusion model specifically involves using a Gaussian plume model as the calculation model for leakage diffusion.

[0038]

[0039] In the formula, Z(x) t y t , z t ) represents the coordinate position (x) t y t , z t The concentration value is calculated from the data; Q0 is the concentration value at the leakage source. The ambient wind speed is in m / s; σ y σ z The diffusion coefficients for the y and z axes are respectively, given by x0 and x... t And determined by atmospheric stability; z t =1.5m.

[0040] Preferably, the objective function F is established as follows:

[0041]

[0042] Where, T(x) t y t , z t )∈{C(x i y i , z i ),Q(x j y j , z j )};t=1,2,3,……,n+m;

[0043] In the formula, Z(x) t y t , z t ), C(x) i y i , z i ), Q(x) j y j , z j The data are calculated concentration values, actual monitored concentration values, and concentration interpolation data, respectively; n is the number of monitoring points; and m is the number of interpolation points.

[0044] Preferably, the location of the leak point is specifically as follows: The concentration value obtained by the point-type laser methane detector and the concentration interpolation of the corresponding unknown area are used as sample points. The sample points are then processed using the firefly algorithm to obtain the point with the brightest fluorescein, i.e., the leak source C(x0, y0, z0). The firefly algorithm is specifically as follows:

[0045] First, the attractiveness of fireflies is calculated, as follows.

[0046]

[0047] In the formula, β0 is the maximum attraction; γ is the light intensity attraction factor; (x a y a z a ) and (x b y b z b (a) and (b) represent the coordinates of firefly a and firefly b, respectively, in meters; a and b here represent two fireflies. ab The spatial distance between firefly a and firefly b is calculated using the Euler distance formula, which is:

[0048] Next, based on the calculation of firefly attraction, the firefly positions are updated, as expressed by:

[0049]

[0050] In the formula, s t For step t; ε t s(t) represents the random coefficients at step t, which follow a uniform distribution; s(t) represents the update step size; x a t y a t z a t and Let x, y, z be the x, y, z coordinates of firefly a at step t and at step t+1, respectively; x b t y b t z b t Let x, y, z be the x, y, z coordinates of firefly a in step t;

[0051] During the location update process, two main methods are used to determine whether the calculation results have converged: 1) If the firefly at the new location is brighter than the one at the previous location, the iterative calculation continues; otherwise, it stops. 2) If the maximum number of iterations is reached, the brightest location is found based on the firefly cluster, which is the optimal solution. The expression for calculating the firefly brightness value is:

[0052]

[0053] In the formula, I0 is the initial brightness of the firefly.

[0054] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0055] 1. In this invention, the point-type laser methane detector is deployed at a specific location within the key monitoring area. Considering the leakage probability, deployment distance, and deployment density, it can monitor and determine the gas concentration at that location in real time, with a detection accuracy of up to 1 ppm. It is usually small in size, lightweight, and easy to install and deploy. It is relatively inexpensive (market price 3000 yuan / unit) and has high accuracy, making it cost-effective.

[0056] 2. In this invention, the point-type laser methane detector provides accurate concentration data, offering advantages in cost-effectiveness and accuracy compared to point-type infrared detectors and linear laser methane detectors. In actual construction, deploying six point-type laser methane detectors in key monitoring areas results in a cost far below 20,000 yuan.

[0057] 3. This invention establishes a probability distribution based on qualitative empirical analysis and quantitative mathematical models, and combines this with the key monitoring areas of the salt cavern gas storage well site to make the monitoring points more accurate. Furthermore, the effective monitoring areas do not overlap and make full use of the effective monitoring area of ​​the methane detector.

[0058] 4. This invention's data gridding multi-point deployment method based on interpolation eliminates the need for deployment in every corner of the salt cavern gas storage well site. Deployment is only required at the points with the highest leakage probability in the established key monitoring areas of the well site, reducing equipment and deployment costs. The data interpolation method can also fill in missing leakage gas concentration values ​​in blank areas, offering truly high cost-effectiveness compared to high-density deployment monitoring, achieving the goal of "cost reduction and efficiency improvement." By comprehensively utilizing concentration interpolation to monitor unknown areas, known concentration values ​​are treated as discrete points. The concentration values ​​in unknown areas can be inferred through the relationships between these discrete points. For example, concentration interpolation can be obtained by simultaneously calculating using Kriging interpolation and a modified Shepard interpolation method. An example of the results using the data gridding method based on interpolation is attached. Figure 2 The dots represent interpolation points, the red dots represent known monitoring points, and the red dashed area represents the effective monitoring area.

[0059] 5. Sufficient sample points are required for leak source inversion and localization. Point-type laser methane detectors provide concentration values ​​at monitoring points and corresponding concentration interpolations for unknown areas, providing accurate and abundant sample data for leak source inversion and localization. The accuracy and efficiency of different interpolation methods are compared in the appendix. Figure 3 As shown, the present invention can obtain concentration interpolation more efficiently and with smaller data errors. Attached Figure Description

[0060] Figure 1 Schematic diagram of traditional array-style multi-point deployment

[0061] Figure 2 Example of interpolation for gas leakage concentration at salt cavern gas storage well sites

[0062] Figure 3 A comparison chart of calculation time and data error for different interpolation methods.

[0063] Figure 4 This is a flowchart of the method for locating natural gas leakage sources at salt cavern gas storage well sites according to the present invention.

[0064] Figure 5 This is a flowchart of the calculation process for leak source inversion and localization in this invention.

[0065] Figure 6 This is a schematic diagram of the salt cavern gas storage well site layout scheme of the present invention.

[0066] Figure 7 A graph showing the relationship between the number of sample points and the accuracy of the leak inversion location calculation results. Detailed Implementation

[0067] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0068] See Figure 4 , 5 This invention provides a method for locating a natural gas leak source at a salt cavern gas storage well site, comprising the following steps:

[0069] I. Deployment of point-type laser methane detectors in key monitoring areas

[0070] Step 1) Determination of key monitoring areas in the salt cavern gas storage well site operation area:

[0071] First, from a qualitative perspective, key monitoring areas are determined: the equipment layout of salt cavern gas storage well sites is complex. Based on the leakage probability, the potential leakage sources are mainly the wellhead, valve group, gas injection and production pipeline, compressor unit, container, and pump body. The wellhead area, valve group area, gas injection and production pipeline area, compressor unit area, container area, and pump body area are designated as key monitoring areas.

[0072] Secondly, from a quantitative perspective, key monitoring areas are determined: based on the leakage frequency and storage accident frequency of the International Oil and Gas Producers Association and the hydrocarbon leakage statistical frequency of DNV GL, the frequency distribution F under different leakage orifice diameters is calculated. y The calculation formula is as follows:

[0073]

[0074] In the formula, The leakage frequencies for apertures x1 and x2 can be found by referring to a table. -1 ; y represents the leakage probability of an unknown leakage orifice, with a value range of y∈(x1, x2); where a -1 It is a unit, representing one year;

[0075] Combining the qualitative and quantitative approaches to identifying key monitoring areas, the key monitoring areas for the salt cavern gas storage well site operation area are determined to be the areas where the wellhead, valve group, compressor unit, pump body, container, and injection / production pipeline are located, with the probability of leakage decreasing in that order.

[0076] Step 2) Based on the key monitoring areas of the salt cavern gas storage well site obtained in Step 1), deploy point-type laser methane detectors:

[0077] As attached Figure 6 As shown, point-type laser methane detectors are installed in the wellhead area, valve group area, compressor group area, pump body area, container area, and gas injection and production pipeline area, respectively, and the installation meets the following criteria: (1) The point-type laser methane detectors are installed at the location with the highest leakage probability in each area; (2) The point-type laser methane detectors are installed at the same horizontal height of 1.5m; (3) The point-type laser methane detectors are located on the upwind side of the minimum frequency wind direction at the location with the highest leakage probability in each area, and the installation location is no more than 2m away from the potential leakage source; (4) The installation spacing between each point-type laser methane detector is 10-15m; (5) Each point-type laser methane detector is staggered from the ground pipeline to facilitate equipment installation and pipeline maintenance; (6) The distance between each point-type laser methane detector is as equal as possible so that the time difference of data transmission can be controlled within a certain range.

[0078] II. Monitoring of Unknown Areas Outside Key Monitoring Areas

[0079] By deploying point-type laser methane detectors within the key monitoring area, the real-time methane concentration values ​​in the areas where each detector is located and the gas leakage status within the coverage area of ​​each detector are obtained. Based on the real-time methane concentration values ​​and their location distribution, gas leakage detection is performed in unknown areas outside the key monitoring area, and concentration interpolation calculations are performed for other grid nodes. The specific steps are as follows:

[0080] Step 1) The point-type laser methane detectors are deployed on the same horizontal plane, z i =1.5m, to simplify calculations, the coordinate information and concentration values ​​of each point-type laser methane detector are expressed as: C(x i y i ), i = 1, 2, 3, ..., n, where n is the number of point-type laser methane detectors; x i y i Let C(x) be the coordinates of the i-th point laser methane detector; i y i Let x be the coordinates of the i-th point laser methane detector. i y i Concentration value at location.

[0081] Step 2) Combine Kriging interpolation and the modified Shebeder interpolation to calculate the concentration interpolation. The specific method is as follows:

[0082] 2-1. The concentration interpolation is calculated using the Kriging interpolation method. The calculation formula is as follows:

[0083]

[0084] In the formula, C * (x j y j The value is the concentration interpolation obtained by Kriging interpolation, and its coordinate is x. j y j The concentration at the j-th unknown region point; λ i The weight of the i-th point-type laser methane detector relative to the unknown region; 2-2, the concentration interpolation is calculated using the improved Shepard interpolation method, and the calculation formula is:

[0085]

[0086]

[0087] Wherein, C″(x j y j This is an improved concentration distribution interpolation obtained using the Schieber interpolation method; w is the weighted derivative, d is the distance between the unknown monitoring point and the known monitoring point, and p is the power of the distance d, p = d k , 0≤k≤2, preferably k=2; δ is the smoothing factor; n is the number of monitoring points; Q i For quadratic surface functions,

[0088] Q i =c i1 (xx i ) 2 +c i2 (xx i (yy) i )+c i3 (yy i ) 2 +c i4 (xx i )+c i5 (yy i )+C(x i y i ),

[0089] The coordinates x of the i-th point laser methane detector i y i Location and concentration value C(x) i y i (related to) c in the formulai1 c i2 c i3 c i4 c i5 It is to solve for the quadratic surface function and its coordinates x. i y i Location-related correction factors, in calculating gas leak concentration, c i1 c i2 c i3 c i4 c i5 All values ​​are set to 1; 2-3, the concentration interpolation result C*(x) calculated by Kriging interpolation in 2-1 is used. i y i The results of concentration interpolation C″(x) calculated by the improved Shebert interpolation method in 2-2 are as follows: j y j Substituting into the following formula, the concentration interpolation is calculated:

[0090]

[0091] In the formula, Q(x) j y j ) represents the concentration interpolation, m is the number of interpolation points, m is greater than n, and the specific value is determined according to the required accuracy; n is the number of monitoring points.

[0092] III. Leakage Source Inversion and Localization

[0093] When the concentration of leaked natural gas at a salt cavern gas storage well site reaches a predetermined threshold as monitored by a point-type laser methane detector, the leak source must be located promptly. The specific process is as follows:

[0094] Step 1) Establish a leakage diffusion model: Use the Gaussian plume model as the calculation model for leakage diffusion.

[0095]

[0096] In the formula, Z(x) t y t , z t ) represents the coordinate position (x) t y t , z t The concentration value is calculated from the data; Q0 is the concentration value at the leakage source. The ambient wind speed is in m / s; σ y σ z The diffusion coefficients for the y and z axes are respectively, given by x0 and x... t And determined by atmospheric stability; z t =1.5m.

[0097] Step 2) Establish the objective function F, specifically:

[0098]

[0099] Where, T(x) t y t , z t )∈{C(x i y i , z i ),Q(x j y j , z j )};t=1,2,3,……,n+m;

[0100] In the formula, Z(x) t y t , z t ), C(x) i , t i , z i ), Q(x) j y j , z j The data are calculated concentration values, actual monitored concentration values, and concentration interpolation data, respectively; n is the number of monitoring points; and m is the number of interpolation points.

[0101] Step 3) Locating the leak source: The concentration values ​​obtained by the point laser methane detector and the concentration interpolation of the unknown area corresponding to the point laser methane detector are used as sample points. The sample points are processed based on the firefly algorithm to obtain the point with the brightest fluorescein, which is the leak source C(x0, y0, z0).

[0102] The firefly algorithm is as follows:

[0103] First, the attractiveness of fireflies is calculated, as follows.

[0104]

[0105] In the formula, β0 is the maximum attraction; γ is the light intensity attraction factor; (x a y a z a ) and (x b y b z b (a) and (b) represent the coordinates of firefly a and firefly b, respectively, in meters; a and b here represent two fireflies. ab The spatial distance between firefly a and firefly b is calculated using the Euler distance formula, which is:

[0106] Next, based on the calculation of firefly attraction, the firefly positions are updated, as expressed by:

[0107]

[0108] In the formula, s t For step t; ε t s(t) represents the random coefficients at step t, which follow a uniform distribution; s(t) represents the update step size; x a t y a t z a t and Let x, y, z be the x, y, z coordinates of firefly a at step t and at step t+1, respectively; x b t y b t z b t Let x, y, z be the x, y, z coordinates of firefly a in step t;

[0109] During the location update process, two main methods are used to determine whether the calculation results have converged: 1) If the firefly at the new location is brighter than the one at the previous location, the iterative calculation continues; otherwise, it stops. 2) If the maximum number of iterations is reached, the brightest location is found based on the firefly cluster, which is the optimal solution. The expression for calculating the firefly brightness value is:

[0110]

[0111] In the formula, I0 is the initial brightness of the firefly.

[0112] In this embodiment, six point-type laser methane detectors (as shown in the attached diagram) are deployed in six key monitoring areas. Figure 6 As shown in the figure, a total of 6 concentration values ​​are provided, and 6 corresponding concentration interpolations are calculated. These 6 concentration values ​​and 6 concentration interpolations provide a total of 12 sample points. Based on these 12 samples, the calculation accuracy for leak source inversion and localization is shown in the appendix. Figure 7 .

[0113] The embodiments described above in conjunction with the accompanying drawings are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for locating a natural gas leak source at a salt cavern gas storage well site, comprising the following steps: (I) Deployment of point-type laser methane detectors in key monitoring areas; Step 1) Determining the key monitoring areas of the salt cavern gas storage well site operation area; Step 2) Based on the key monitoring areas of the salt cavern gas storage well site obtained in Step 1), deploy point-type laser methane detectors; (ii) Monitoring of unknown areas outside key monitoring areas; By deploying point-type laser methane detectors within the key monitoring area, the real-time methane concentration values ​​in the areas where each detector is located and the gas leakage status within the coverage area of ​​each detector are obtained. Based on the real-time methane concentration values ​​and their location distribution, gas leakage detection is performed in unknown areas outside the key monitoring area, and concentration interpolation calculations are performed for other grid nodes. The specific steps are as follows: Step 1) The point-type laser methane detectors are deployed on the same horizontal plane. To simplify calculations, the coordinates and concentration values ​​of each point-type laser methane detector are expressed as follows: , 2, 3, ... , The number of point-type laser methane detectors; , For the first Coordinates of the platform-type laser methane detector; For the first Coordinates of the platform-type laser methane detector , Concentration value at location; Step 2) Combine the Kriging interpolation method and the modified Shebeder interpolation method to calculate the concentration interpolation; (III) Leakage source inversion and localization; When the concentration of leaked natural gas at a salt cavern gas storage well site reaches a predetermined threshold as monitored by a point-type laser methane detector, the leak source must be located promptly. The specific process is as follows: Step 1) Establish a leakage diffusion model; Step 2) Establish the objective function F for the probability distribution of gas leakage concentration difference, specifically: ； in, ; ; In the formula, These are the calculated concentration value, the actual monitored concentration value, and the concentration interpolation data, respectively. Number of monitoring points; The number of interpolation points; Step 3) Locating the leak point: The problem of solving the location and concentration of the leak source is transformed into a mathematical problem of minimizing the difference between the monitored value of the gas leak concentration and the calculated value of the leak diffusion model; when the minimum value is obtained, it is the leak inversion location result, and then the leak intensity and the location of the leak source are obtained by inversion.

2. The method for locating a natural gas leak source at a salt cavern gas storage well site according to claim 1, characterized in that, The determination of key monitoring areas in the salt cavern gas storage well site operation area is as follows: First, from a qualitative perspective, key monitoring areas are determined: the equipment layout of salt cavern gas storage well sites is complex. Based on the leakage probability, potential leakage sources are wellheads, valve groups, gas injection and production pipelines, compressor units, containers, and pumps. The key monitoring areas are the wellhead area, valve group area, gas injection and production pipeline area, compressor unit area, container area, and pump area. Secondly, from a quantitative perspective, key monitoring areas are determined: based on the leakage frequency and storage accident frequency of the International Oil and Gas Producers Association and the hydrocarbon leakage statistical frequency of DNV GL, the frequency distribution under different leakage orifice diameters is calculated. The calculation formula is as follows: ； In the formula, , aperture , The leakage frequency; This represents the leakage probability for an unknown leakage orifice diameter, and its value ranges from [value missing]. ; Combining the qualitative and quantitative approaches to identifying key monitoring areas, the key monitoring areas for the salt cavern gas storage well site operation area are determined to be the areas where the wellhead, valve group, compressor unit, pump body, container, and injection / production pipeline are located.

3. The method for locating a natural gas leak source at a salt cavern gas storage well site according to claim 2, characterized in that, According to step 1), point-type laser methane detectors are deployed in the key monitoring areas of the salt cavern gas storage well site, as follows: point-type laser methane detectors are deployed in the wellhead area, valve group area, compressor group area, pump body area, container area, and injection and production pipeline area, with one point-type laser methane detector deployed in each area, for a total of 6 detectors. The deployment meets the following criteria: (1) the point-type laser methane detectors are installed at the location with the highest leakage probability in each area, and (2) the point-type laser methane detectors are installed at the same horizontal height. (3) The point laser methane detector is located on the upwind side of the minimum frequency wind direction at the location with the highest leakage probability in each zone, and the installation location is no more than 2m away from the potential leakage source. (4) The installation spacing of each point laser methane detector is 10~15m. (5) Each point laser methane detector should be staggered from the ground pipeline to facilitate equipment installation and pipeline maintenance. (6) The distance between each point laser methane detector is equal to achieve the control of the time difference of data transmission within a certain range.

4. The method for locating a natural gas leak source at a salt cavern gas storage well site according to claim 1, characterized in that, The concentration interpolation is calculated by combining Kriging interpolation and the modified Shebeder interpolation method, specifically as follows: 2-1. The concentration interpolation is calculated using the Kriging interpolation method. The calculation formula is as follows: ； In the formula, The concentration interpolation obtained by Kriging interpolation is represented by the following coordinates: The Concentration at unknown points in the region; For the first Weight of the platform-type laser methane detector relative to the unknown region; 2-2. The concentration interpolation is calculated using the modified Shebert interpolation method. The calculation formula is as follows: ； ； in, To improve the concentration distribution interpolation obtained by the Shebert interpolation method; For the weighted derivative, The distance between unknown monitoring points and known monitoring points. Distance The power of, , 0≤k≤2; It is a smoothing factor; Number of monitoring points; For quadratic surface functions, ， With the Coordinates of the platform-type laser methane detector , Location and concentration value The equation relates to the solution of the quadratic surface function and its coordinates. , Location-related correction factors in calculating gas leak concentrations. All values ​​are set to 1; 2-3. The results of concentration interpolation calculated by Kriging interpolation in 2-1. The results of concentration interpolation calculated using the improved Shebert interpolation method in section 2-2 Substituting into the following formula, the concentration interpolation is calculated: ； In the formula, For concentration interpolation, The number of interpolation points. Greater than The specific value is determined based on the required precision; This represents the number of monitoring points.

5. The method for locating a natural gas leak source at a salt cavern gas storage well site according to claim 1, characterized in that, The establishment of the leakage diffusion model specifically involves using a Gaussian plume model as the calculation model for leakage diffusion. ； In the formula, Coordinate position ( The concentration value obtained from the calculation on ) The concentration value at the leak source; For external wind speed, ; They are respectively , The diffusion coefficient of the shaft is determined by... And determined by atmospheric stability; .

6. The method for locating a natural gas leak source at a salt cavern gas storage well site according to claim 1, characterized in that, The specific method for locating the leak point is as follows: The concentration value obtained by the point-type laser methane detector and the concentration interpolation value of the corresponding unknown area are used as sample points. The sample points are then processed using the firefly algorithm to obtain the point with the brightest fluorescein, which is the leak source. The firefly algorithm is as follows: First, the attractiveness of fireflies is calculated, as follows. ； In the formula, To maximize attraction; The light intensity attractor factor; )and( ( ) are fireflies With fireflies The location coordinates, in meters; and In this context, it represents two fireflies; Fireflies With fireflies The spatial distance between them is calculated using the Euler distance formula, which is: ; Next, based on the calculation of firefly attraction, the firefly positions are updated, as expressed by: ； In the formula, For the first Locate the fireflies; For the first uniformly distributed Step random coefficients; To update the step size; and The first Fireflies x, y, z coordinates and the first Find the x, y, and z coordinates of firefly a; For the first Fireflies The x, y, and z coordinates; The first Step sample points The x, y, and z coordinates; During the location update process, two methods are used to determine whether the calculation results have converged: 1) If the brightness of the firefly at the new location is brighter than that of the former, the iterative calculation continues; otherwise, it stops. 2) If the maximum number of iterations is reached, the brightest location is found based on the firefly cluster, which is the optimal solution. The expression for calculating the brightness value of a firefly is: ； In the formula, This represents the initial brightness of the firefly.

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