A method for predicting and warning of cavity deformation and ground subsidence of a salt cavern gas storage

Abstract

The present application belongs to the technical field of safety evaluation and analysis in the construction and operation process of underground salt cavern gas storage, and specifically relates to a method for predicting and warning the deformation of a salt cavern gas storage cavity and ground subsidence, comprising the following steps: S1: carrying out a creep parameter inversion test on the site of the gas storage to obtain the actual rock mechanics parameters of the salt cavern gas storage cavity engineering; S2: using the rock mechanics parameters obtained in step S1 to construct a ground subsidence prediction model, and applying the model to predict ground subsidence; S3: determining a ground subsidence warning threshold and, based on the threshold and the ground subsidence prediction in S2, carrying out safety warning for the salt cavern gas storage cavity. The mechanics parameters obtained by the present application are closer to the actual rock mechanics parameters of the engineering, so as to ensure that the actual rock mechanics properties of the salt layer in the engineering are accurately reflected, so that the prediction model established based on the mechanics parameters is more reliable, and thus the ground subsidence prediction and warning are more accurate.

Description

Technical Field

[0001] This invention relates to a method for predicting and warning of deformation of the cavity and ground subsidence in a salt cavern gas storage facility, belonging to the technical field of safety evaluation and analysis during the construction and operation of underground salt cavern gas storage facilities. Background Technology

[0002] Natural gas is an important component of my country's energy system, and its consumption will continue to increase. To ensure a stable supply of natural gas, various gas storage methods have emerged, among which underground salt cavern gas storage is one of the main methods of natural gas energy storage and an important part of my country's basic gas storage facilities.

[0003] Underground salt cavern gas storage facilities are typically located in areas with thick salt rock layers. Salt rock has low porosity and permeability and exhibits good creep characteristics, making it an excellent surrounding rock medium for gas storage facilities. However, due to its excellent creep characteristics, creep will occur even under relatively small deviatoric stresses, causing the salt rock around the cavity to flow inwards. This leads to contraction and deformation of the cavity, resulting in surface subsidence. When the subsidence is significant, or even when the surface collapses, it can trigger serious accidents. Therefore, the prediction and early warning of cavity deformation and surface subsidence in gas storage facilities are of great guiding significance for the stable operation of gas storage facilities and the safety assessment of the storage area.

[0004] Currently, in order to promptly grasp the relevant safety issues in the construction and operation of gas storage facilities, salt cavity sonar detection technology is mainly used to detect the cavity morphology. By comparing the sonar measurement results over a certain time interval, the morphological changes of the cavity can be obtained. Traditional leveling or emerging technologies such as InSAR, GPS, and PSI are used to monitor the ground subsidence of the gas storage facility. In addition, three-dimensional numerical simulation based on geological data of the storage area, cavity data, and rock mechanics parameters is used to predict the deformation of the cavity under the current operating pressure to guide actual engineering and determine the operating pressure limit of the gas storage facility.

[0005] Predictions of deformation of salt cavern gas storage chambers and ground subsidence are generally obtained through numerical simulation. Numerical simulation consists of two parts: modeling and calculation. Whether the calculation results of numerical simulation are accurate and can be used to guide actual engineering depends on the establishment of the numerical model, the research and selection of calculation methods, and the appropriateness of the selection of calculation parameters.

[0006] Most existing numerical simulation modeling schemes can only reflect the approximate shape of salt caverns, and there is still a large gap between them and the actual shape of the caverns.

[0007] In existing numerical simulation schemes, regardless of whether ABAQUS, Adagio, or FLAC are used... 3DNumerical calculation software requires the use of the mechanical parameters of salt rocks. Currently, these parameters are generally obtained through laboratory measurements. However, given the characteristics of multi-layered salt rock strata in my country, the mechanical parameters obtained from laboratory tests may not accurately reflect the rock mechanical properties at the actual engineering salt layer. In the theoretical prediction of surface subsidence in salt cavern gas storage, the influence function method is usually used. Its principle is simple and its applicability is strong. However, in practice, the research on the key parameter (volume transfer coefficient) is not in-depth, and its value is currently determined by empirical values.

[0008] On the other hand, the research on setting the ground subsidence threshold is one of the key parts of risk analysis for salt cavern gas storage. It can be directly applied to practical engineering guidance and is of great significance to ensuring the construction and operation safety of salt cavern gas storage. However, the criteria for the early warning threshold of ground subsidence for salt cavern gas storage are still unclear.

[0009] Furthermore, due to the mutual influence of the multiple cavities, existing technologies struggle to accurately calculate the ground subsidence of underground salt cavern gas storage facilities.

[0010] As my country's gas storage infrastructure is in a phase of rapid development, safety issues during its construction and operation deserve greater attention. Therefore, there is an urgent need for a complete and accurate method for predicting and providing early warning of gas storage cavity deformation and ground subsidence, which can be used for on-site guidance to ensure the safe construction and operation of gas storage facilities. Summary of the Invention

[0011] The purpose of this invention is to provide a method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence, in order to solve the problem that the current salt rock mechanical parameters are generally obtained by laboratory measurement, but given the characteristics of multi-layered salt rock strata in my country, the creep parameters obtained by laboratory tests may not accurately reflect the rock mechanical properties at the actual engineering salt layer.

[0012] To achieve the above objectives, the present invention provides a method for predicting and warning of deformation of a salt cavern gas storage cavity and ground subsidence, comprising the following steps:

[0013] S1: Conduct on-site creep parameter inversion tests of the gas storage facility to obtain the actual rock mechanics parameters of the salt cavern gas storage cavity engineering;

[0014] S2: Construct a ground settlement prediction model using the rock mechanics parameters obtained in step S1, and apply the model to predict ground settlement.

[0015] S3: Determine the ground subsidence early warning threshold and conduct safety early warning for the salt cavern gas storage cavity based on the threshold and the ground subsidence prediction in S2.

[0016] This invention obtains the actual rock mechanical parameters of the gas storage facility by conducting on-site creep parameter inversion tests. The obtained mechanical parameters are closer to the actual rock mechanical parameters of the project, ensuring that they accurately reflect the rock mechanical properties at the salt layer in the actual project. This makes the prediction model based on these mechanical parameters more reliable, and thus more accurate in predicting and warning of land subsidence.

[0017] Furthermore, in step S1, rock mechanical parameters consistent with engineering realities are obtained by conducting on-site creep parameter inversion tests at the gas storage facility, including:

[0018] S11: Conduct a well closure and pressurization field test: Select a cavity that has been completed and has undergone sonar testing after the cavity construction is completed, measure the data of wellhead pressure change over time, and plot the curve of wellhead pressure change over time.

[0019] S12: Calculate the change in cavity volume during the well closure pressurization test, i.e., the actual cavity volume shrinkage rate;

[0020] S13: Perform simulation calculations on the numerical model of the test cavity to obtain the cavity shrinkage rate during the well closure pressurization test;

[0021] S14: Compare the actual cavity shrinkage rate in S12 with the cavity shrinkage rate that occurred during the well closure pressurization test in S13, and select the combination value of creep parameters that is closest to the two as the rock mechanics parameters for subsequent numerical simulation analysis.

[0022] This invention provides a preferred scheme for calculating the actual cavity shrinkage rate and the cavity shrinkage rate that occurs during the well closure pressurization test. This preferred scheme can ensure that reliable actual cavity shrinkage rates and cavity shrinkage rates that occur during the well closure pressurization test are obtained. Thus, by comparison, rock mechanics parameters that can better reflect the rock properties in actual engineering can be determined.

[0023] Furthermore, when measuring the data on the change of wellhead pressure over time, a pressure gauge capable of remote data transmission is installed at the wellhead to achieve wellhead pressure data acquisition and remote transmission.

[0024] A pressure gauge capable of remote data transmission is installed at the wellhead to remotely transmit the collected pressure data from the inlet to the data processing terminal.

[0025] Further, in step S2, constructing the ground subsidence prediction model includes:

[0026] S21: Select the cavity of a salt cavern gas storage facility that has been put into operation, has undergone sonar cavity measurement, and has injection and production pressure data since the sonar cavity measurement. Combine the sonar cavity measurement data of the cavity with geological data to establish a three-dimensional numerical simulation analysis geological model, set boundary conditions, and adopt the actual rock mechanics parameters obtained by conducting on-site creep parameter inversion tests of the gas storage facility in S1. The monitoring objects are set as cavity volume change and displacement of ground settlement monitoring points in the upper strata of the cavity.

[0027] S22: Numerical calculation code for organizing the injection and production pressure data of the cavity, expanding the existing injection and production operation data cyclically to several years, performing numerical simulation, and obtaining the cavity volume change and monitoring data of the ground subsidence monitoring point of the upper stratum of the cavity.

[0028] S23: Organize the data obtained in step S22 to obtain the ground settlement curves of the cavity under different volume shrinkage rates;

[0029] S24: Calculate the corresponding volume transfer coefficient based on the ground settlement curves with multiple different volume shrinkage rates in S23, and obtain the variation curve of the volume transfer coefficient under different volume shrinkage rates.

[0030] S25: Apply the above volume transfer coefficients to the ground settlement prediction model to obtain a settlement model for calculating the ground settlement of other cavities under the corresponding volume shrinkage rate.

[0031] This invention provides a scheme for constructing a ground subsidence prediction model based on the system transfer coefficient obtained by theoretical derivation. Compared with the existing schemes that rely solely on experience to determine the system transfer coefficient, this scheme has higher reliability.

[0032] Furthermore, when determining the ground subsidence warning threshold, the ground subsidence warning threshold is determined based on the permissible deformation of the salt cavern cavity of 15-20%.

[0033] Based on the analysis of the risk of cavity shrinkage: when the cavity volume shrinkage rate reaches 20%, it will cause serious risk consequences, such as severe deformation and damage to the cavity, impairment of its main functions, and a relatively dangerous state. When the cavity volume shrinkage rate reaches 30%, it will cause catastrophic consequences. Therefore, from a conservative perspective, the cavity volume shrinkage rate should not exceed 20%. This invention, combined with specific engineering conditions, provides an optional range of 15-20% permissible deformation to ensure the rationality of the determined warning threshold.

[0034] Furthermore, when determining the ground subsidence early warning threshold, the surface subsidence of each cavity is calculated separately, and then a correction coefficient is added to the surface subsidence of each cavity for linear superposition to obtain the overall surface subsidence.

[0035] This invention considers the mutual influence effect between cavities, thereby deriving a more realistic ground subsidence early warning threshold.

[0036] Furthermore, determining the ground subsidence early warning threshold includes:

[0037] S31: Select a specific salt cavern gas storage area;

[0038] S32: Collect sonar test data and geological data for all cavities within the salt cavern gas storage area;

[0039] S33: Verify the obtained volume transfer coefficient, influence angle, and ground settlement theoretical prediction model using step S24, and calculate the ground settlement caused by each cavity when the cavity shrinks to the set value;

[0040] S34: Identify the cavities that will cause mutual influence among the cavities, add a correction coefficient to the surface subsidence of each cavity and perform linear superposition to obtain the overall surface subsidence prediction data;

[0041] S35: Based on the above overall ground subsidence prediction data, find the location with the maximum cumulative ground subsidence value in the selected area, and then set an early warning threshold in combination with the permissible deformation of the selected salt cavern gas storage area.

[0042] S36: Provide safety warnings based on the warning thresholds in S35 and the predicted ground subsidence in S2.

[0043] This invention provides a preferred scheme for ground subsidence early warning based on the permissible deformation of salt cavern cavities and considering the mutual influence between cavities.

[0044] Furthermore, in step S35, when finding the location with the maximum cumulative ground settlement value in the selected area based on the overall ground settlement prediction data, the following method is used: a corresponding ground settlement cloud map is generated based on the overall ground settlement prediction data, and the location with the maximum cumulative ground settlement value in the selected area is found based on the ground settlement cloud map.

[0045] Ground subsidence cloud maps can intuitively and vividly reflect ground subsidence prediction data, making it easier to accurately and quickly identify the location of the maximum cumulative ground subsidence value. Attached Figure Description

[0046] Figure 1 This is a flowchart of the method of the present invention;

[0047] Figure 2 This is a schematic diagram of the cavity creep contraction mechanism in this invention;

[0048] Figure 3 This is a schematic diagram of the surface subsidence of the spherical cavity in this invention;

[0049] Figure 4 This is a flowchart of the process for obtaining rock mechanical parameters according to the present invention;

[0050] Figure 5 This is a flowchart of the present invention for calculating the ground settlement curves of the cavity under different volume shrinkage rates;

[0051] Figure 6 This is a flowchart of the ground subsidence prediction model established in this invention;

[0052] Figure 7 This is a flowchart illustrating the process of determining the early warning threshold for ground subsidence according to the present invention;

[0053] Figure 8 This is a graph showing the change of wellhead pressure over time according to the present invention;

[0054] Figure 9 This is a schematic diagram of the three-dimensional model of the cavity created using modeling software in this invention;

[0055] Figure 10 This is a schematic diagram of the numerical calculation model established by the present invention based on the geological data of the cavity;

[0056] Figure 11 This is a comparison chart of the cavity shrinkage rate during the well closure pressurization test and the actual cavity shrinkage rate;

[0057] Figure 12 This is a schematic diagram of the geological body model constructed in this invention;

[0058] Figure 13 This is a graph showing the change in cavity volume shrinkage rate over time, based on the numerical simulation results of this invention.

[0059] Figure 14 This is a graph showing the change of the volume transfer coefficient of the present invention with the cavity volume shrinkage rate;

[0060] Figure 15 This is a comparison graph of the theoretical model and numerical simulation curves of the present invention when the cavity shrinks by 20%.

[0061] Figure 16 This is a map showing the distribution of the internal cavities of the Jintan salt cavern gas storage area;

[0062] Figure 17 This is a ground settlement cloud map of the cavity in this invention at a volume shrinkage rate of 20%. Detailed Implementation

[0063] To more clearly illustrate the technical approach, implementation strategy, and advantages of this invention, the following analysis and explanation of the invention will be conducted in conjunction with the accompanying drawings. However, the implementation method of this invention is not limited to this.

[0064] Example 1

[0065] S1: Obtain the actual rock mechanics parameters for the gas storage facility by conducting inversion tests on in-situ creep parameters.

[0066] S11: Conduct a well closure and pressurization field test: Select a cavity where cavity construction has been completed and sonar testing has been conducted after cavity construction.

[0067] Measure the data on wellhead pressure changes over time and plot the curve of wellhead pressure changes over time;

[0068] S12: Calculate the change in cavity volume during the well closure pressurization test, i.e., the actual cavity volume shrinkage rate.

[0069] Linear fitting was performed on the curve of wellhead pressure change over time to obtain the wellhead pressure change rate, i.e., pressure growth rate dp / dt. Based on the wellhead pressure change and the location of the cavity, the original rock stress p0 at the depth of the salt cavity and the brine pressure p inside the cavity were calculated. i Combined with equation (3), the A value corresponding to different n values ​​is calculated. A and n are creep parameters. Based on the original rock stress p0 at the depth of the salt cavity and the brine pressure p in the cavity, the A value is calculated. i By combining equations (1) and (3), the change in the volume of the cavity during the well-closure pressurization test can be calculated, i.e., the actual volume shrinkage rate of the cavity.

[0070] S13: Simulate the test cavity using a numerical model to obtain the cavity contraction rate during the well closure and pressurization test.

[0071] Simulates the cavity deformation from the start of the sonar cavity measurement test to the start of the well closure pressurization test;

[0072] Calculate the cavity shrinkage rate during the well closure pressurization test under different combinations of creep parameters A and n obtained in S12.

[0073] S14: Compare the actual cavity shrinkage rate in S12 with the cavity shrinkage rate that occurred during the well closure pressurization test in S13, and select the combination value of creep parameters A and n that is closest to the two as the rock mechanics parameters for subsequent numerical simulation analysis.

[0074] Among them, the cavity creep contraction mechanism (see Figure 2 In this case, the entire cavity is considered to be subjected to confining pressure p0-p i Given a brine body with a bulk modulus of K, the brine body is subjected to a confining pressure p0-p i Volumetric strain ε per unit time v for:

[0075]

[0076] Formula for volume shrinkage rate of an infinite internal cavity:

[0077]

[0078] In the formula, V is the original volume of the salt cavity. This represents the volumetric shrinkage of the salt cavity per unit time, where A and n are creep parameters, p0 is the original rock stress at the depth of the salt cavity, and p i The pressure of the brine inside the cavity;

[0079] Since the increase in pressure within the cavity is mainly due to confining pressure creep contraction, the volume shrinkage rate equals the volume strain of the brine, i.e.:

[0080]

[0081] in, This is due to the increasing pressure.

[0082] S2: Construct a ground subsidence prediction model and apply the model to predict ground subsidence.

[0083] S3: Determine the ground subsidence early warning threshold and conduct safety early warning for the salt cavern gas storage cavity based on the threshold and the ground subsidence prediction in S2.

[0084] Example 2

[0085] A method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence, comprising:

[0086] S1: Conduct inversion tests of creep parameters at the gas storage facility to obtain rock mechanics parameters that are more consistent with engineering realities. See [link / reference]. Figure 4 :

[0087] S11: Conduct a well closure and pressurization field test: Select a cavity that has been completed and has undergone sonar testing after cavity construction. The cavity is filled with saturated brine and will not experience volume changes due to salt rock dissolution. Install a pressure gauge with remote data transmission capability at the wellhead and then close the wellhead valve. The pressure inside the cavity will gradually increase due to the creep of the surrounding rock. Set the pressure data transmission interval to 2 hours and record the changes in wellhead pressure value daily. Compile the wellhead pressure gauge monitoring data for about 2 months and plot the curve of wellhead pressure change over time.

[0088] S12: Calculate the change in cavity volume during the well closure pressurization test, i.e., the actual cavity volume shrinkage rate;

[0089] Linear fitting was performed on the curve of wellhead pressure change over time to obtain the wellhead pressure change rate, i.e., the pressure growth rate dp / dt in equation (3). Based on the wellhead pressure change and the location of the cavity, the original rock stress p0 and the brine pressure p at the depth of the salt cavity were calculated. i Combined with equation (3), the A value corresponding to n values ​​of 1.5-4.0 is calculated (A and n are creep parameters), and different combinations of creep parameters are obtained. Based on the original rock stress p0 and the brine pressure p at the depth of the salt cavity, the values ​​are calculated. i By combining equations (1) and (3), the change in the volume of the cavity during the well-closure pressurization test can be calculated, i.e., the actual volume shrinkage rate of the cavity.

[0090] S13: Numerical simulation software is used to simulate and calculate the numerical model of the test cavity.

[0091] Simulates the cavity deformation from the start of the sonar cavity measurement test to the start of the well closure pressurization test;

[0092] The cavity deformation during the field test was simulated by inverting creep parameters to reflect the change in cavity pressure over time. The creep parameter combination value was changed. Based on the creep parameter n value obtained from the indoor test, which is generally taken as 3.5, 11 specific values ​​of n were selected from 3.0 to 4.0. The cavity shrinkage rate during the well closure pressurization test was calculated under the corresponding 11 different creep parameter combination values ​​(n, A).

[0093] S14: Compare the actual cavity shrinkage rate with the cavity shrinkage rate that occurred during the well closure pressurization test in S13, and select the creep parameter A and n combination value that is closest to the two as the rock mechanics parameter for subsequent numerical simulation analysis.

[0094] The schematic diagram of the cavity creep contraction mechanism is shown below. Figure 2 As shown, the entire cavity is considered to be subjected to confining pressure p0-p i Given a brine body with a bulk modulus of K, the brine body is subjected to a confining pressure p0-p i Volumetric strain ε per unit time v for:

[0095]

[0096] Formula for volume shrinkage rate of an infinite internal cavity:

[0097]

[0098] In the formula, V is the original volume of the salt cavity. This represents the volumetric shrinkage of the salt cavity per unit time, where A and n are material parameters, p0 is the original rock stress at the depth of the salt cavity, and p i The pressure of the brine inside the cavity;

[0099] Since the increase in pressure within the cavity is mainly due to confining pressure creep contraction, the volume shrinkage rate equals the volume strain of the brine, i.e.:

[0100]

[0101] in, This is due to the increasing pressure.

[0102] S2: Deformation prediction of the selected cavity was performed using three-dimensional numerical simulation software. A salt cavern gas storage facility already in operation was selected, and its ground settlement curves under different volumetric shrinkage rates were calculated. (See...) Figure 5 :

[0103] S21: Select a cavity of a salt cavern gas storage facility that has been put into operation, requiring that it has undergone sonar cavity testing and has injection and production pressure data since the sonar cavity testing. Combining the sonar cavity testing data and geological data, establish a three-dimensional numerical simulation analysis geological model using a power law creep constitutive model, set boundary conditions, adopt the salt rock creep parameters selected in S14, and set the monitoring objects as cavity volume change and displacement of ground settlement monitoring points in the upper strata of the cavity.

[0104] S22: Write numerical calculation code for cavity injection and production operation pressure data, expand the existing injection and production operation data cyclically to 30 years, perform numerical simulation, and save the cavity volume change and the monitoring data of the ground subsidence monitoring point above the cavity during the numerical simulation process.

[0105] S23: Organize the data obtained in step S22 to obtain the ground settlement curves of the cavity under different volume shrinkage rates;

[0106] See Figure 6 S24: Determine the influence range R0 of ground settlement based on the ground settlement curves in S23 when the volume shrinkage rate is 5%, 10%, 15%, 20%, and 25%;

[0107] The magnitude of the influence angle γ is calculated based on the influence range R0 and the depth f of the cavity;

[0108] S25: Then calculate the volume of the ground subsidence basin;

[0109] S26: The volume transfer coefficient is calculated by α=Vs(t) / Vc(t), and the variation curve of the volume transfer coefficient under different volume shrinkage rates is obtained, that is, the medium parameter system transfer coefficient α of the ground settlement prediction model (4) under different volume shrinkage rates is obtained.

[0110] S27: Substitute the above parameters into (4) to establish a ground settlement prediction model. Based on this ground settlement model, the ground settlement of other cavities under the corresponding volume shrinkage rate can be simplified.

[0111] A schematic diagram of surface subsidence of the spherical cavity is shown below. Figure 3 As shown, the expression for the ground subsidence prediction model of salt cavern gas storage is:

[0112]

[0113] In the formula, α is the volume transfer coefficient, which is calculated as α=Vs(t) / Vc(t), where Vs(t) is the ground settlement volume, Vc(t) is the cavity shrinkage volume, γ is the influence angle, f is the depth of the cavity center, and R0 is the influence range of ground settlement.

[0114] Salt cavern gas storage facilities typically exist in the form of a group of chambers. When calculating the surface movement and deformation of this group, by studying the ground settlement curves of individual chambers and the group of chambers, it was found that when calculating the overall ground settlement of a salt cavern gas storage facility, the mutual influence effect of the chambers can be ignored first, and the surface settlement of each chamber can be calculated separately. Then, a correction factor is added to the surface settlement of each chamber, and the results are linearly superimposed to obtain the formula for calculating the overall surface settlement:

[0115]

[0116] In the formula, k is the surface subsidence correction coefficient of the cavity group, which can be estimated by formula (6). It is recommended that the value range be 1.0-1.2, and n is the number of cavities.

[0117] Correction factor calculation formula:

[0118]

[0119] In the formula, k d It is the surface settlement correction factor for the radial distance between the two cavities within 1000m. r / r* is the ratio of the surface settlement of the two cavities to the surface settlement of the two single cavities linearly superimposed. r* is the unit length, l is the distance between the centers of the cavities, and d is the diameter of the cavity.

[0120] S3: As Figure 7 Based on the regional overall ground subsidence prediction data considering the mutual influence of the gas caverns and the permissible deformation of the salt cavern gas storage cavity, the ground subsidence early warning threshold is determined:

[0121] S31: Select a salt cavern gas storage area and create a map showing the location distribution of the cavity groups within that area.

[0122] S32: Collect sonar test data and geological data (deep, size, geological conditions, etc. of each cavity) for all cavities in the salt cavern gas storage area;

[0123] S33: The volume transfer coefficient, influence angle and ground settlement theoretical prediction model obtained by step S24 are verified, i.e., equation (4), and a simplified calculation of ground settlement prediction is performed for all cavities in the area to obtain the ground settlement amount caused by each cavity when the cavity is allowed to deform.

[0124] S34: Based on the cavity group location distribution map in S31, identify the cavities that will have mutual influence effects, and group the cavities with mutual influence effects together (generally, when the location of two cavities exceeds the influence range R0 of ground settlement, no cavity group effect will occur).

[0125] S35: The ground settlement of the cavity divided together is calculated using Equation (5), where the correction coefficient is 1.2, and the ground settlement in the salt cavern gas storage area is superimposed to obtain the overall ground settlement prediction data of the area.

[0126] S36: Based on the overall ground subsidence prediction data of the salt cavern gas storage area obtained in step S35, make the corresponding ground subsidence cloud map.

[0127] S37: Based on the above ground subsidence cloud map, find the location with the maximum cumulative ground subsidence value in the selected area. Then, combine the analysis and research on the early warning threshold of the cavity permissible deformation in the selected salt cavern gas storage area. Based on the scholars' analysis of the cavity shrinkage risk: when the cavity volume shrinkage rate reaches 20%, it will cause serious risk consequences, severe deformation and damage to the cavity, damage to its main functions, and a relatively dangerous state. When the cavity volume shrinkage rate reaches 30%, it will cause catastrophic consequences. Therefore, from a conservative point of view, the cavity volume shrinkage rate should not exceed 20%.

[0128] Example 3

[0129] A method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence, which is based on Example 2 with the following adjustments:

[0130] When measuring the data on the change of wellhead pressure over time, the pressure data transmission interval is set to 1-3 hours, preferably 1 hour, 1.5 hours, 2.5 hours, or 3 hours.

[0131] Record the changes in wellhead pressure value daily and compile the wellhead pressure gauge pressure monitoring data for a period of 1-4 months. The preferred method is to compile data for 1 month, 2 months, 3 months or 4 months.

[0132] The creep parameter n in S13 can be selected from multiple different values ​​between 3.0 and 4.0, among which n is preferably 8, 9, 10, 11, or 12, and the specific preferred values ​​include 3.0, 3.5, and 4.0;

[0133] The preferred surface subsidence correction factor for the cavity group is 1.0 or 1.2;

[0134] The permissible deformation of the salt cavern cavity is preferably 15% or 20%.

[0135] Example 4

[0136] A method for predicting and warning of deformation and ground subsidence in a salt cavern gas storage chamber is disclosed. This method is based on Example 1 (i.e., all steps in Example 1 can be applied to this example), specifically illustrating Example 1. For instance, the salt layer section tested ranges from 937.2m to 1093.0m, with a thickness of 155.8m. This includes six mudstone layers greater than or close to 1.0m thick: 977.1-978.0m, 1029.0-1030.1m, 1037.6-1038.5m, 1074.3-1075.6m, 1081.6-1083.3m, and 1087.6-1091.8m. The chamber depth ranges from -1029m to 1062m. The curves showing the change in wellhead pressure over time during the experiment are shown below. Figure 8 As shown, the curve, after fitting calculation, has a slope of 0.00105 MPa / hour, which is the volumetric strain per unit time according to Equation 2.

[0137] Based on the depth range of the cavity from -1029m to -1062m, the average original rock stress P0 is taken as 24.05MPa. According to the wellhead pressure and brine depth, the pressure variation range inside the cavity is calculated to be 14.62MPa-15.01MPa (wellhead pressure is 2.27MPa, brine pressure is 12.35MPa-12.74MPa). The brine pressure Pi in the cavity core is taken as 14.81MPa. According to the cavity temperature, the volumetric modulus K of the brine at 50 degrees is taken as 3.56GPa in the calculation. Substituting the above parameters into Equation 3, different combinations of A and n values ​​can be calculated, as shown in Table 1.

[0138] Based on the formula for the volume shrinkage rate of an infinite internal cavity and its derivation formulas (Equations 1 and 3), the actual cavity volume shrinkage rate during the test can be obtained as 0.0467%.

[0139] Table 1. Correspondence between different values ​​of A and n obtained from the calculation.

[0140]

[0141]

[0142] A three-dimensional model of the cavity is created using modeling software, such as Figure 9 As shown, a numerical calculation model is established based on the geological data of the cavity, such as... Figure 10As shown, considering the changes in cavity pressure during the test, and using 11 different creep parameters (Tables 3.0-4.0 above) for simulation calculations, the calculation results were compared with the actual cavity shrinkage rate. Figure 11 As shown, when n is 3.6, the corresponding value of A is 1.344 × 10⁻⁶. -5 MPa -n a -1 .

[0143] Figure 12 The image shows the constructed geological model, modeled according to lithological sections such as clay, mudstone, basalt, and salt rock layers from the surface profile. The gas storage facility is located within the salt rock layer, which is modeled using a power-law creep constitutive model. The mechanical parameters used in the calculation model are shown in Table 2.

[0144] Table 2. Stratigraphic Lithology and Mechanical Properties in the Calculation Model

[0145]

[0146] Based on the creep parameters obtained in step S1 and the injection-production operating pressure, a three-dimensional numerical calculation software was used for simulation. The numerical simulation results show the curve of cavity volume shrinkage rate changing with time, as follows: Figure 13 As shown.

[0147] Based on the numerical simulation results of step S2, the ground settlement curves at cavity shrinkage rates of 5%, 10%, 15%, 20%, and 25% were analyzed and calculated to plot the curve of volume transfer coefficient as a function of cavity volume shrinkage rate. Figure 14 Taking the surface subsidence corresponding to a cavity volume shrinkage rate of 20% as an example, the volume transfer coefficient and influence angle γ of the surface movement deformation when the cavity volume shrinkage rate is 20% are calculated, and the influence range R0 is calculated. Substituting the parameters obtained above into equation (4), the ground subsidence prediction model with a cavity volume shrinkage rate of 20% can be obtained. Applying this model can simplify the calculation of other ground subsidence situations with a cavity volume shrinkage rate of 20%. Figure 15 The figure shows the surface settlement curve corresponding to a 20% shrinkage of the cavity. The largest settlement occurs at the center point of the surface, at 17.5 mm, roughly in an S-shape. The surface settlement gradually decreases with increasing distance from the center point and slowly approaches zero, similar to a normal distribution curve. Using Equation 4, the volume transfer coefficient for surface movement deformation within a 20% cavity shrinkage rate is calculated. Taking 0.75 and an influence angle of 34°, the influence range is 1522 m. Substituting these parameters into the theoretical model of the influence function, a comparison between the theoretical model and the numerical simulation curves is obtained. Figure 15 As shown.

[0148] The selected gas storage calculation area (Jintan Salt Cavern Gas Storage Area) is shown below. The cavity distribution within this area is as follows: Figure 16As shown, using the theoretical prediction parameters and model of ground settlement obtained in step S3, the ground settlement of the cavities in the region at a volume shrinkage rate of 20% is calculated. Considering the mutual influence of surface settlement of the cavity group, the k value is taken as 1.2. The ground settlement values ​​of this region are calculated by current superposition, and a ground settlement cloud map of the cavities at a volume shrinkage rate of 20% is produced, as shown. Figure 17 As shown.

[0149] When the cavity volume shrinkage rate of the cavity group is 20%, the maximum surface subsidence in the Jintan salt cavern gas storage area is 213.65 mm. Considering a certain safety factor and the actual operating conditions of the Jintan gas storage facility, the annual cavity volume shrinkage rate should not exceed 1.5%, and the cumulative shrinkage rate should not exceed 20%. Based on the permissible cavity volume shrinkage, the early warning threshold for surface movement and deformation in the salt cavern gas storage area can be determined as follows:

[0150] (1) Starting from the first year after the salt cavity is put into operation, the changes in surface subsidence at the monitoring points shall be observed regularly every year. The annual volume shrinkage rate of the cavity shall not exceed 1.5%, and the surface subsidence shall not exceed 15 mm / year.

[0151] (2) Starting from the first year after the salt cavity is put into operation, calculate the change in the cumulative value of surface subsidence at the monitoring point. The cumulative value of surface subsidence should not exceed 200mm.

Claims

1. A method for predicting and warning of deformation of a salt cavern gas storage cavity and ground subsidence, characterized in that, The steps include the following: S1: Conduct inversion tests of creep parameters at the gas storage site to obtain rock mechanical parameters that conform to the actual engineering of the salt cavern gas storage cavity, including the following steps: S11: Conduct a well closure and pressurization field test: Select a cavity that has been completed and has undergone sonar testing after the cavity construction is completed, measure the data of wellhead pressure change over time, and plot the curve of wellhead pressure change over time. S12: Linearly fit the curve of wellhead pressure change over time to obtain the wellhead pressure change rate. Based on the wellhead pressure change and the location of the cavity, calculate the original rock stress p0 at the depth of the salt cavity and the brine pressure p within the cavity. i Combined with formula Calculate the combined values ​​of different creep parameters A and n, where K is the bulk modulus of the brine and t is time, and then calculate the change in the volume of the cavity during the well-closure pressurization test, i.e. the actual volume shrinkage rate of the cavity. S13: Simulate and calculate the numerical model of the test cavity to obtain the cavity shrinkage rate during the well-closure pressurization test under each combination of values; S14: Compare the actual cavity shrinkage rate in S12 with the cavity shrinkage rate that occurred during the well closure pressurization test in S13, and select the combination value of creep parameters that is closest to the two as the rock mechanics parameters for subsequent numerical simulation analysis. S2: Construct a ground settlement prediction model using the rock mechanics parameters obtained in step S1, and apply the model to predict ground settlement. S3: Determine the ground subsidence early warning threshold and conduct safety early warning for the salt cavern gas storage cavity based on the threshold and the ground subsidence prediction in S2.

2. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 1, characterized in that, When simulating the numerical model of the test cavity, the cavity deformation is simulated from the start of the sonar cavity test to the start of the well closure and pressurization test.

3. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 1, characterized in that, When measuring the change of wellhead pressure over time, a pressure gauge capable of remote data transmission is installed at the wellhead to achieve wellhead pressure data acquisition and remote transmission.

4. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 1, characterized in that, In step S2, constructing the ground subsidence prediction model includes: S21: Select the cavity of a salt cavern gas storage facility that has been put into operation, has undergone sonar cavity measurement, and has injection and production pressure data since the sonar cavity measurement. Combine the sonar cavity measurement data of the cavity with geological data to establish a three-dimensional numerical simulation analysis geological model, set boundary conditions, and adopt the actual rock mechanics parameters obtained by conducting on-site creep parameter inversion tests of the gas storage facility in S1. The monitoring objects are set as cavity volume change and displacement of ground settlement monitoring points in the upper strata of the cavity. S22: Numerical calculation code for organizing the injection and production pressure data of the cavity, expanding the existing injection and production operation data cyclically to several years, performing numerical simulation, and obtaining the cavity volume change and monitoring data of the ground subsidence monitoring point of the upper stratum of the cavity. S23: Organize the data obtained in step S22 to obtain the ground settlement curves of the cavity under different volume shrinkage rates; S24: Calculate the corresponding volume transfer coefficient based on the ground settlement curves at multiple different volume shrinkage rates in S23, and obtain the variation curve of the volume transfer coefficient under different volume shrinkage rates. S25: Apply the above volume transfer coefficients to the ground settlement prediction model to obtain a settlement model for calculating the ground settlement of other cavities under the corresponding volume shrinkage rate.

5. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 1, characterized in that, When determining the ground subsidence warning threshold, the ground subsidence warning threshold is determined based on the permissible deformation of the salt cavern cavity of 15-20%.

6. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 1, characterized in that, When determining the ground subsidence early warning threshold, the surface subsidence of each cavity is calculated separately, and then a correction coefficient is added to the surface subsidence of each cavity for linear superposition to obtain the overall surface subsidence.

7. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 4, characterized in that, Determining the ground subsidence early warning threshold includes: S31: Select a specific salt cavern gas storage area; S32: Collect sonar test data and geological data for all cavities within the salt cavern gas storage area; S33: Verify the obtained volume transfer coefficient, influence angle, and ground settlement theoretical prediction model using step S24, and calculate the ground settlement caused by each cavity when the cavity shrinks to the set value; S34: Identify the cavities that will cause mutual influence among the cavities, add a correction coefficient to the surface settlement of each cavity and perform linear superposition to obtain the overall ground settlement prediction data; S35: Based on the above overall ground subsidence prediction data, find the location with the maximum cumulative ground subsidence value in the selected area, and then set an early warning threshold in combination with the permissible deformation of the selected salt cavern gas storage area. S36: Provide safety warnings based on the warning thresholds in S35 and the predicted ground subsidence in S2.

8. The method for predicting and warning of deformation of salt cavern gas storage chambers and ground subsidence according to claim 7, characterized in that, In step S35, when finding the location with the maximum cumulative ground settlement value in the selected area based on the overall ground settlement prediction data, the following method is used: a corresponding ground settlement cloud map is generated based on the overall ground settlement prediction data, and the location with the maximum cumulative ground settlement value in the selected area is found based on the ground settlement cloud map.

Images