Intelligent evaluation method for effective packing length of cement sheath of gas storage

Abstract

The invention discloses an intelligent evaluation method for the effective packing length of a cement sheath of a gas storage, and is characterized in that the intelligent evaluation method for the effective packing length of the cement sheath based on indoor experimental data driving is provided; according to the method, the actual well bore structure, the operation condition and the cement paste system of a gas storage site are combined, and the cement sheath gas breakthrough pressure under different cementation lengths, alternating temperatures and alternating pressures is tested by adopting a stepping method; a cement sheath gas breakthrough pressure prediction model is established by adopting a global optimization algorithm based on a test result, and cement sheath gas breakthrough pressure prediction under different working conditions is realized; a BP neural network-based cement sheath effective packing length intelligent prediction system is established to predict the effective packing length of the cement sheath under different operating years, so that whether the cement sheath of the gas storage meets the packing requirement or not is evaluated by combining the well cementation quality logging result of the well cementation gas storage. Therefore, the intelligent evaluation method for the effective packing length of the cement sheath of the gas storage is formed.

Description

Technical Field

[0001] This patent relates to the field of oil and natural gas drilling and production engineering technology, specifically an intelligent evaluation method for the effective sealing length of the cement sheath of a gas storage reservoir. Background Art

[0002] As a crucial gas storage facility, underground gas storage plays a vital role in peak-shaving and is a crucial component of the natural gas supply chain. However, due to its cyclical nature, underground gas storage (UGS) undergoes alternating loads on the wellbore, which can easily lead to failure of the wellbore seal and, consequently, failure of the gas storage facility. The cement sheath, the weakest component of the wellbore barrier, is susceptible to damage, destruction, and cementation failure under alternating loads, resulting in microgaps at the casing-cement sheath interface and microcracks in the cement sheath itself. These microgaps and cracks create pathways for underground gas to escape, leading to containment failure.

[0003] Currently, to ensure the effective isolation capability of the cement sheath during gas storage well operation, the SY / T 7648-2021 standard for gas storage well cementing technology stipulates that the continuous high-quality section (i.e., the section with good cementing quality) from the reservoir top to the caprock should be no less than 25 meters, and the cumulative high-quality section should be no less than 50 meters. Clearly, this standard, SY / T 7648-2021, applies uniform requirements to all gas storage wells, ignoring the crucial factor of adapting to local conditions. For example, some gas storage wells, due to relatively good operating conditions, do not need to meet the requirements for a continuous high-quality cement sheath section of 25 meters and a cumulative high-quality section of 50 meters. Alternatively, some wells, even if they meet the requirements for a continuous high-quality cement sheath section of 25 meters and a cumulative high-quality section of 50 meters, may fail to meet these requirements due to poor operating conditions. Therefore, an intelligent evaluation method for the effective isolation length of the cement sheath under different gas storage operating conditions is urgently needed to ensure the long-term and safe operation of the gas storage. Patent CN118390991A proposes a theoretically derived method for designing the effective sealing length of cement sheaths in natural gas wells. However, the underlying data used is derived from cement stone specimen testing and fails to account for the combined effects of failures in the integrity of the cement sheath itself and its interface. Therefore, only a cement sheath effective isolation length calculation model, established based on sealing performance testing results of a full-scale, physical "casing-cement sheath-casing / formation" assembly, can scientifically calculate and evaluate the effective isolation length of the cement sheath.

[0004] To this end, the present invention overcomes the shortcomings of the existing technology and provides an intelligent evaluation method for the effective isolation length of the cement sheath of a gas storage reservoir. This method can calculate the required effective isolation length of the cement sheath based on the injection and production design of the gas storage reservoir and the injection and production years, providing theoretical support for the long-term safe operation of the gas storage reservoir. Summary of the Invention

[0005] The purpose of the present invention is to provide an intelligent evaluation method for the effective isolation length of the cement sheath of a gas storage reservoir, which provides a reference and basis for the evaluation and decision-making of the cementing quality of the gas storage reservoir. The method is simple and feasible, and can quickly and quantitatively obtain the effective isolation length of the cement sheath under different gas storage injection and production conditions.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for intelligently evaluating the effective isolation length of a cement sheath in a gas storage reservoir mainly comprises the following steps:

[0008] Step 1: Determine the typical operating conditions of the gas storage reservoir: (1) Obtain the typical wellbore structure of the gas storage reservoir well cap layer; (2) Obtain the typical injection and production conditions of the gas storage well, including the upper limit temperature T of the wellbore during the injection and production period. max , lower limit temperature T min , upper limit pressure P max and lower limit pressure P min ;(3) Obtain typical cement slurry system for gas storage wells;

[0009] Step 2: Carry out cement sheath gas sealing performance test under different cementing lengths: (1) Based on the cement slurry system of gas storage wells and actual maintenance conditions, establish and prepare full-scale "casing-cement sheath-casing / formation" combinations with different cement sheath bonding lengths under typical wellbore structures; (2) Use the step method to test the gas sealing performance of the full-scale "casing-cement sheath-casing / formation" combination under different cement sheath bonding lengths, and define the cement sheath gas breakthrough pressure P corresponding to the injection end annulus pressure when gas leaks from the cement sheath annulus injection end to the other end of the cement sheath annulus g ;

[0010] Step 3: Conduct gas sealing performance test of cement ring under alternating temperature: (1) Based on the cement slurry system of gas storage well and actual curing conditions, establish and prepare full-scale "casing-cement ring-casing / formation" combination with different cement ring bonding lengths under typical wellbore structure; (2) Conduct alternating temperature test of full-scale "casing-cement ring-casing / formation" combination with different cement ring bonding lengths, where the alternating temperature test range is within the lower limit temperature of the wellbore T min To the upper limit temperature T max The alternating times range from 0 to 50 times; (3) The step method is used to test the gas sealing performance of the full-scale "casing-cement sheath-casing / formation" assembly at different alternating temperatures and different cement sheath bonding lengths, and the corresponding cement sheath gas breakthrough pressure P is obtained. g ;

[0011] Step 4: Conduct cement sheath gas sealing performance test under alternating pressure: (1) Based on the gas storage well cement slurry system and actual maintenance conditions, establish and prepare full-scale "casing-cement sheath-casing / formation" combinations with different cement sheath bonding lengths under typical wellbore structures; (2) Conduct alternating pressure tests on full-scale "casing-cement sheath-casing / formation" combinations with different cement sheath bonding lengths, where the alternating pressure test range is within the wellbore lower limit pressure P min To upper limit pressure P max The alternating times range from 0 to 50 times; (3) the gas sealing performance of the full-scale "casing-cement sheath-casing / formation" assembly at different cement sheath bonding lengths after alternating pressure was tested by the step method, and the corresponding cement sheath gas breakthrough pressure was obtained;

[0012] Step 5: Establish a cement sheath gas breakthrough pressure prediction model based on the global optimization algorithm: (1) Establish a cement sheath breakthrough pressure fitting function, where the fitting variables include cement sheath isolation length x1, inner casing outer diameter x2, outer casing outer diameter x3, wellbore upper limit temperature x4, wellbore lower limit temperature x5, wellbore upper limit pressure x6, wellbore lower limit pressure x7, and operating years x8; (2) Establish a cement sheath breakthrough pressure P g and the optimal fitting expression of the above 8 fitting variables; (3) using the experimental results of steps 2, 3, and 4 as basic data, a general global optimization algorithm is used to fit the parameters required for the cement sheath breakthrough pressure function; (4) based on the fitted parameters, a cement sheath gas breakthrough pressure prediction model is formed;

[0013] Step 6: Establish a database required for intelligent prediction: (1) Based on the established cement sheath gas breakthrough pressure prediction model, calculate the cement sheath gas breakthrough pressure under typical wellbore structures, typical operating conditions, and different cementation lengths of the gas storage reservoir, and enter the corresponding parameters and results into the database;

[0014] Step 7: Based on the BP neural network, a machine learning model for predicting the effective sealing length of the cement sheath is established: (1) Randomly initialize the weights and biases of the neural network; (2) Based on the data obtained in step 6, pass the input data through each layer of the network and apply the activation function to calculate the output of each neuron; (3) Compare the output of the network with the target value and calculate the error; (4) Based on the error, starting from the output layer, calculate the contribution of each neuron to the error and update the weights and biases; (5) Repeat steps (2) to (4) and continuously adjust the weights and biases through multiple iterations until the predetermined number of training times is reached or the error converges; (6) Use the trained network to predict new inputs;

[0015] Step 8: Establish an intelligent prediction system for the effective isolation length of cement sheath based on step 7: After the error of the machine learning model in step 7 is within 5%, the wellbore structure, the cementing quality logging results after cementing, and the upper limit temperature T of the wellbore during operation are calculated. max , lower limit temperature T min , upper limit pressure P max and lower limit pressure P min The operating years are input into the machine learning model to establish an intelligent prediction system for the effective sealing length of the cement sheath;

[0016] Step 9: Drawing of cement sheath gas breakthrough pressure prediction chart: (1) Based on the wellbore structure design, injection and production conditions, and injection and production years of the on-site gas storage reservoir, parameters are obtained, including cement sheath isolation length x1, inner casing outer diameter x2, outer casing outer diameter x3, wellbore upper limit temperature x4, wellbore lower limit temperature x5, wellbore upper limit pressure x6, wellbore lower limit pressure x7, and operating years x8; (2) Using the cement sheath effective isolation length intelligent prediction system established in step 8, calculate the cement sheath gas breakthrough pressure P corresponding to different isolation lengths x1 g , and plot the isolation length x1 and cement sheath gas breakthrough pressure P g 's plate.

[0017] Step 10: Calculation of effective sealing length of cement ring: (1) Combined with the sealing pressure P required by the on-site gas storage d Considering the safety factor a, the minimum gas breakthrough pressure of the cement sheath required for the safe operation of the gas storage is calculated as P gm =a*P d (2) According to the drawn cement sheath gas breakthrough pressure prediction chart, find the lowest cement sheath gas breakthrough pressure P gm The corresponding cement sheath packer length x 1m , x 1m The minimum continuous high-quality length of the cement sheath required, 2x 1m The minimum cumulative high-quality length of the cement sheath required;

[0018] Step 11: Determine whether the cementing quality of the cemented gas storage meets the requirements for cement sheath isolation: (1) Determine the range and length of the high-quality cement sheath section from the reservoir top to the caprock based on the cementing quality logging curve; (2) If the length of the continuous high-quality cement sheath section is greater than the minimum effective isolation length x 1m , the cementing quality meets the requirements; if the continuous high-quality section of the cement sheath is lower than the minimum effective isolation length of the cement sheath x 1m , but the cumulative high-quality section in the barrier is the minimum effective sealing length of the cement sheath x 1m If the value of the cementing material is less than 2 times of the value of the cementing material, the cementing quality can still be considered to meet the requirements; (3) If both (1) and (2) are not met, the cementing quality does not meet the requirements.

[0019] Step 12: Optimize operating conditions to meet long-term isolation requirements: For gas storage wells whose cementing quality evaluation results do not meet the 50-year isolation requirements of the gas storage, the corresponding minimum effective isolation length of the cement sheath can be recalculated by reducing operating conditions and operating years until the minimum effective isolation length of the cement sheath meets the current cementing quality requirements.

[0020] The present invention has the following advantages:

[0021] Based on the indoor measured cement sheath gas breakthrough pressures under different isolation lengths, typical wellbore structures, and typical operating conditions, the present invention adopts a universal global optimization algorithm to fit a cement sheath gas breakthrough pressure prediction model, thereby providing basic data for the intelligent prediction of the effective isolation length of the cement sheath. Furthermore, the BP neural network is combined to establish an intelligent prediction of the effective isolation length of the cement sheath, thereby realizing the intelligent evaluation of the minimum effective isolation length of the cement sheath, and providing a practical and feasible method and technology for the design and evaluation of oil and gas well cementing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the technical roadmap of the present invention.

[0023] Figure 2 is the gas breakthrough pressure of cement sheath at different bonding lengths.

[0024] Figure 3 It is the gas breakthrough pressure of 500mm long cement sheath under alternating temperature.

[0025] Figure 4 It is the gas breakthrough pressure of 750mm long cement sheath under alternating temperature.

[0026] Figure 5 It is the gas breakthrough pressure of 500mm long cement sheath under alternating pressure.

[0027] Figure 6 It is the gas breakthrough pressure of 750mm long cement sheath under alternating pressure.

[0028] Figure 7 This is the relationship between the isolation length and the cement sheath gas breakthrough pressure under different isolation years. DETAILED DESCRIPTION

[0029] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0030] Step 1: Determine the typical working conditions of the gas storage reservoir: (1) The typical wellbore structure of the well cap layer section of a gas storage reservoir in Northwest my country is a Φ139.7mm production casing-Φ177.8mm technical casing structure; (2) The upper limit temperature of the wellbore during the injection and production period of the gas storage well in this block is 120℃, and the lower limit temperature is 70℃; the upper limit pressure is 40MPa, and the lower limit pressure is 13MPa; (3) The cement slurry system of the gas storage well in this block is a tough cement slurry system;

[0031] Step 2: Carry out the gas sealing performance test of the cement sheath under the typical wellbore structure of the gas storage well: (1) Based on the cement slurry system of the gas storage well and the actual curing conditions, establish and prepare the "Φ139.7mm production casing-cement sheath-Φ177.8mm technical casing" combination with cement sheath bonding lengths of 500mm, 750mm, 2000mm, 3000mm, 4000mm and 5000mm; (2) Use the step method to test the gas sealing performance of the "Φ139.7mm production casing-cement sheath-Φ177.8mm technical casing" combination with different cement sheath bonding lengths, and obtain the cement sheath gas breakthrough pressure P under different bonding lengths. g , as attached Figure 2 As shown;

[0032] Step 3: Carry out gas sealing performance test of cement ring under alternating temperature: (1) Establish and prepare 10 groups of "Φ139.7mm production casing-cement ring-Φ177.8mm technical casing" combinations with cement ring bonding lengths of 500mm and 750mm; (2) Carry out alternating temperature test of "Φ139.7mm production casing-cement ring-Φ177.8mm technical casing" combinations with cement ring bonding lengths of 500mm and 750mm in the range of 70℃ to 120℃, with the alternating times of 10, 20, 30, and 40 respectively. 40 times and 50 times; (3) Carry out alternating temperature tests on the combination of "Φ139.7mm production casing-cement ring-Φ177.8mm technical casing" with cement ring bonding lengths of 500mm and 750mm in the range of 90℃ to 120℃, with the alternating times being 10 times, 20 times, 30 times, 40 times and 50 times respectively; (4) Use the step method to test the gas sealing performance of the combination of "Φ139.7mm production casing-cement ring-Φ177.8mm technical casing" after different alternating temperatures, and obtain the corresponding cement ring gas breakthrough pressure P g , 500mm long cement sheath gas breakthrough pressure test results are as attached Figure 3 As shown in the attached figure, the gas breakthrough pressure test results of 750mm long cement sheath are as follows: Figure 4 As shown;

[0033] Step 4: Carry out gas sealing performance test of cement sheath under alternating internal pressure: (1) Establish and prepare 10 groups of "Φ139.7mm production casing-cement sheath-Φ177.8mm technical casing" assemblies with cement sheath bonding lengths of 500mm and 750mm; (2) Carry out alternating internal pressure test of "Φ139.7mm production casing-cement sheath-Φ177.8mm technical casing" assemblies with cement sheath bonding lengths of 500mm and 750mm in the range of 13MPa to 20MPa, with the alternating times being 10, 20, 30, and 40 times respectively. 40 and 50 times; (3) Carry out alternating internal pressure tests on the "Φ139.7mm production casing-cement ring-Φ177.8mm technical casing" combination with cement ring bonding lengths of 500mm and 750mm in the range of 13MPa to 40MPa, with the alternating times being 10, 20, 30, 40 and 50 times respectively; (4) Use the step method to test the gas sealing performance of the "Φ139.7mm production casing-cement ring-Φ177.8mm technical casing" combination after different alternating internal pressures, and obtain the corresponding cement ring gas breakthrough pressure P g , 500mm long cement sheath gas breakthrough pressure test results are as attached Figure 5 As shown in the attached figure, the gas breakthrough pressure test results of 750mm long cement sheath are as follows: Figure 6 As shown;

[0034] Step 5: Establish a cement sheath gas breakthrough pressure prediction model based on the global optimization algorithm: (1) Establish a cement sheath breakthrough pressure fitting function, where the fitting variables include cement sheath bonding length x1, wellbore upper limit temperature x2, wellbore upper limit pressure x3, and operating years x4; (2) Establish a cement sheath breakthrough pressure P g The optimal fitting expression of the above 8 fitting variables is y=a+b*x1*x2+c*x1*x3+d*x1*x4+e*x2*x4+f*x3*x4+g*x1; (3) The experimental results tested in steps 2, 3 and 4 are used as basic data, and the parameters required for fitting the cement sheath breakthrough pressure function using the general global optimization algorithm are a=0.028, b=-0.0067, c=-0.00029, d = -0.00018, e = -0.00031, f = -0.00042, g = 0.4062; (4) Based on the fitting parameters, the cement sheath gas breakthrough pressure prediction model is y = 0.028-0.0067x1*x2-0.00029x1*x3-0.00018*x1*x4-0.00031*x2*x4-0.00042*x3*x4+0.4062*x1;

[0035] Step 6: Establish the database required for intelligent prediction: (1) Based on the established cement sheath gas breakthrough pressure prediction model, calculate the cement sheath gas breakthrough pressure under the wellbore structure of "Φ139.7mm production casing-Φ177.8mm technical casing" of the gas storage reservoir, different operating conditions, and different cementing lengths, and enter the corresponding parameters and results into the database;

[0036] Step 7: Based on the BP neural network, a machine learning model for predicting the effective sealing length of the cement sheath is established: (1) Randomly initialize the weights and biases of the neural network; (2) Based on the data obtained in step 6, pass the input data through each layer of the network and apply the activation function to calculate the output of each neuron; (3) Compare the output of the network with the target value and calculate the error; (4) Based on the error, starting from the output layer, calculate the contribution of each neuron to the error and update the weights and biases; (5) Repeat steps (2) to (4) and continuously adjust the weights and biases through multiple iterations until the predetermined number of training times is reached or the error converges; (6) Use the trained network to predict new inputs;

[0037] Step 8: Establish an intelligent prediction system for the effective isolation length of cement sheath based on step 7: After the error of the machine learning model in step 7 is within 5%, the wellbore structure, the cementing quality logging results after cementing, and the upper limit temperature T of the wellbore during operation are calculated. max , lower limit temperature T min , upper limit pressure P max and lower limit pressure P min The operating years are input into the machine learning model to establish an intelligent prediction system for the effective sealing length of the cement sheath;

[0038] Step 9: Draw a prediction chart for cement sheath gas breakthrough pressure: (1) Based on the wellbore structure design, injection and production conditions, and injection and production years of the on-site gas storage reservoir, obtain parameters including cement sheath isolation length x1, wellbore upper limit temperature x2, wellbore upper limit pressure x3, and operating years x4; (2) Using the cement sheath effective isolation length intelligent prediction system established in step 8, calculate the cement sheath gas breakthrough pressure P corresponding to different isolation lengths x1 g , and plot the isolation length x1 and cement sheath gas breakthrough pressure P g The plate, as attached Figure 7 shown.

[0039] Step 10: Determine the effective sealing length of the cement sheath: (1) The sealing pressure required for the gas storage is 24 MPa. Considering the safety factor of 1.25, the minimum gas breakthrough pressure of the cement sheath required for the safe operation of the gas storage is calculated to be 30 MPa; (2) According to the cement sheath gas breakthrough pressure prediction chart drawn, the cement sheath sealing length corresponding to the minimum gas breakthrough pressure of 30 MPa after the gas storage well has been operated for 50 years is found to be 22.1 m. Therefore, the minimum continuous high-quality section length required for the gas storage is 22.1 m, and the cumulative high-quality section length is 44.2 m.

[0040] Step 11: Determine whether the cementing quality of the cemented gas storage reservoir meets the cement sheath isolation requirements: (1) According to the cementing quality logging curve, the cementing quality results of the reservoir section and the cap rock section are divided into poor, medium and excellent. As shown in the following table, the maximum length of the continuous high-quality cement sheath section from the reservoir top to the cap rock section of the gas storage reservoir is 18m, and the cumulative high-quality section is 47m; (2) According to the calculation results and the cementing quality logging results, although the maximum length of the continuous high-quality cement sheath section of the gas storage reservoir cap rock section is 18m, which is lower than the minimum continuous high-quality section length of 22.1m required by the calculation, the cumulative high-quality cement sheath section of the gas storage reservoir cap rock section is 47.0m, which exceeds the cumulative high-quality section length of 44.2m required by the calculation of the gas storage reservoir, so the gas storage well still meets the cementing quality requirements.

[0041] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. An intelligent evaluation method for the effective isolation length of cement sheath in a gas storage facility, characterized in that: The method mainly comprises the following steps: Step 1: Determine the typical operating conditions of the gas storage reservoir: (1) Obtain the typical wellbore structure of the gas storage reservoir well cap layer; (2) Obtain the typical injection and production conditions of the gas storage well, including the upper limit temperature T of the wellbore during the injection and production period. max , lower limit temperature T min , upper limit pressure P max and lower limit pressure P min ;(3) Obtain typical cement slurry system for gas storage wells; Step 2: Carry out cement sheath gas sealing performance test under different cementing lengths: (1) Based on the cement slurry system of gas storage wells and actual maintenance conditions, establish and prepare full-scale "casing-cement sheath-casing / formation" combinations with different cement sheath bonding lengths under typical wellbore structures; (2) Use the step method to test the gas sealing performance of the full-scale "casing-cement sheath-casing / formation" combination under different cement sheath bonding lengths, and define the cement sheath gas breakthrough pressure P corresponding to the injection end annulus pressure when gas leaks from the cement sheath annulus injection end to the other end of the cement sheath annulus g ; Step 3: Conduct gas sealing performance test of cement ring under alternating temperature: (1) Based on the cement slurry system of gas storage well and actual curing conditions, establish and prepare full-scale "casing-cement ring-casing / formation" combination with different cement ring bonding lengths under typical wellbore structure; (2) Conduct alternating temperature test of full-scale "casing-cement ring-casing / formation" combination with different cement ring bonding lengths, where the alternating temperature test range is within the lower limit temperature of the wellbore T min To the upper limit temperature T max The alternating times range from 0 to 50 times; (3) The step method is used to test the gas sealing performance of the full-scale "casing-cement sheath-casing / formation" assembly at different alternating temperatures and different cement sheath bonding lengths, and the corresponding cement sheath gas breakthrough pressure P is obtained. g ; Step 4: Conduct cement sheath gas sealing performance test under alternating pressure: (1) Based on the gas storage well cement slurry system and actual maintenance conditions, establish and prepare full-scale "casing-cement sheath-casing / formation" combinations with different cement sheath bonding lengths under typical wellbore structures; (2) Conduct alternating pressure tests on full-scale "casing-cement sheath-casing / formation" combinations with different cement sheath bonding lengths, where the alternating pressure test range is within the wellbore lower limit pressure P min To upper limit pressure P max The alternating times range from 0 to 50 times; (3) the gas sealing performance of the full-scale "casing-cement sheath-casing / formation" assembly at different cement sheath bonding lengths after alternating pressure is tested by the step method, and the corresponding cement sheath gas breakthrough pressure is obtained; Step 5: Establish a cement sheath gas breakthrough pressure prediction model based on the global optimization algorithm: (1) Establish a cement sheath breakthrough pressure fitting function, where the fitting variables include cement sheath isolation length x1, inner casing outer diameter x2, outer casing outer diameter x3, wellbore upper limit temperature x4, wellbore lower limit temperature x5, wellbore upper limit pressure x6, wellbore lower limit pressure x7, and operating years x8; (2) Establish a cement sheath breakthrough pressure P g and the optimal fitting expression of the above 8 fitting variables; (3) using the experimental results of steps 2, 3, and 4 as basic data, a general global optimization algorithm is used to fit the parameters required for the cement sheath breakthrough pressure function; (4) based on the fitted parameters, a cement sheath gas breakthrough pressure prediction model is formed; Step 6: Establish a database required for intelligent prediction: (1) Based on the established cement sheath gas breakthrough pressure prediction model, calculate the cement sheath gas breakthrough pressure under typical wellbore structures, typical operating conditions, and different cementing lengths of the gas storage reservoir, and enter the corresponding parameters and results into the database; (2) Obtain the corresponding on-site gas storage reservoir well cap layer cementing quality evaluation results and enter them into the database; Step 7: Based on the BP neural network, a machine learning model for predicting the effective sealing length of the cement sheath is established: (1) Randomly initialize the weights and biases of the neural network; (2) Based on the data obtained in step 6, pass the input data through each layer of the network and apply the activation function to calculate the output of each neuron; (3) Compare the output of the network with the target value and calculate the error; (4) Based on the error, starting from the output layer, calculate the contribution of each neuron to the error and update the weights and biases; (5) Repeat steps (2) to (4) and continuously adjust the weights and biases through multiple iterations until the predetermined number of training times is reached or the error converges; (6) Use the trained network to predict new inputs; Step 8: Establish an intelligent prediction system for the effective isolation length of cement sheath based on step 7: After the error of the machine learning model in step 7 is within 5%, the wellbore structure, the cementing quality logging results after cementing, and the upper limit temperature T of the wellbore during operation are calculated. max , lower limit temperature T min , upper limit pressure P max and lower limit pressure P min The operating years are input into the machine learning model to establish an intelligent prediction system for the effective sealing length of the cement sheath; Step 9: Drawing of cement sheath gas breakthrough pressure prediction chart: (1) Based on the wellbore structure design, injection and production conditions, and injection and production years of the on-site gas storage reservoir, parameters are obtained, including cement sheath isolation length x1, inner casing outer diameter x2, outer casing outer diameter x3, wellbore upper limit temperature x4, wellbore lower limit temperature x5, wellbore upper limit pressure x6, wellbore lower limit pressure x7, and operating years x8; (2) Using the cement sheath effective isolation length intelligent prediction system established in step 8, calculate the cement sheath gas breakthrough pressure P corresponding to different isolation lengths x1 g , and plot the isolation length x1 and cement sheath gas breakthrough pressure P g 's plate. Step 10: Calculation of effective sealing length of cement ring: (1) Combined with the sealing pressure P required by the on-site gas storage d Considering the safety factor a, the minimum gas breakthrough pressure of the cement sheath required for the safe operation of the gas storage is calculated as P gm =a*P d (2) According to the drawn cement sheath gas breakthrough pressure prediction chart, find the lowest cement sheath gas breakthrough pressure P gm The corresponding cement sheath packer length x 1m , x 1m The minimum continuous high-quality length of the cement sheath required, 2x 1m The minimum cumulative high-quality length of the cement sheath required; Step 11: Determine whether the cementing quality of the cemented gas storage meets the requirements for cement sheath isolation: (1) Determine the range and length of the high-quality cement sheath section from the reservoir top to the caprock based on the cementing quality logging curve; (2) If the length of the continuous high-quality cement sheath section is greater than the minimum effective isolation length x 1m , the cementing quality meets the requirements; if the continuous high-quality section of the cement sheath is lower than the minimum effective isolation length of the cement sheath x 1m , but the cumulative high-quality section in the barrier is the minimum effective sealing length of the cement sheath x 1m If the value of the cementing material is less than 2 times of the value of the cementing material, the cementing quality can still be considered to meet the requirements; (3) If both (1) and (2) are not met, the cementing quality does not meet the requirements. Step 12: Optimize operating conditions to meet long-term isolation requirements: For gas storage wells whose cementing quality evaluation results do not meet the 50-year isolation requirements of the gas storage, the corresponding minimum effective isolation length of the cement sheath can be recalculated by reducing operating conditions and operating years until the minimum effective isolation length of the cement sheath meets the current cementing quality requirements.

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