Calculation method for checking metal loss and mechanical strength of production string of offshore oil and gas well

Abstract

According to the calculation method for checking the metal loss and the mechanical strength of the offshore oil and gas well production pipe column, the metal loss of the full-well-section production pipe column is calculated based on the coupling effect of the corrosion rate and the abrasion loss, and the mechanical strength of the full-well-section production pipe column is checked and calculated. Establishing a metal loss prediction model suitable for the offshore oil and gas well production string, and calculating a first type metal loss-corrosion rate of the production string; and the loss-abrasion loss of the second type of metal of the production pipe column is calculated through parameters such as oil and gas well inclinometry data, drilling parameters, drill bit sizes and drill rod sizes. The method has the beneficial effects that the metal loss of the pipe column under the influence of the corrosion rate and the abrasion loss is considered at the same time, and the mechanical strength of the pipe column is checked. The metal loss including corrosion and abrasion conditions of an offshore oil and gas well production pipe column is calculated, the pipe column result residual mechanical strength is checked, the residual bearing capacity and integrity of a shaft production pipe column are evaluated, and the safety and reliability of the oil and gas well production pipe column in a complex environment are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of calculating metal loss and mechanical strength check of production strings in offshore oil and gas wells, and more specifically to a calculation method for metal loss and mechanical strength check of production strings in offshore oil and gas wells. Background Art

[0002] In the field of wellbore integrity, there is currently no integrated calculation method for corrosion rate - wear amount - residual strength of production strings in oil and gas wells. The algorithms of current international mainstream tools, such as Deward, NORSOK, ECE, etc., can only calculate corrosion alone, cannot calculate the mechanical strength after corrosion, and do not consider the impact of wear on the structural mechanical strength; the LANDMARK tool can only calculate the wear amount of the production string alone, cannot calculate corrosion and the residual mechanical strength after corrosion, and cannot calculate the residual mechanical strength under the superposition of corrosion and wear. Due to the complex downhole conditions, the actual metal loss will have the situation of superposition of corrosion and wear. Therefore, the above algorithms have certain limitations in mechanical strength check. Summary of the Invention

[0003] The present invention overcomes the deficiencies in the prior art and provides a calculation method for metal loss and mechanical strength check of production strings in offshore oil and gas wells.

[0004] The object of the present invention is achieved by the following technical solutions.

[0005] A calculation method for metal loss and mechanical strength check of production strings in offshore oil and gas wells, the specific steps include:

[0006] S1. Collect basic information data for calculating metal loss and mechanical strength of production strings in offshore oil and gas wells;

[0007] S2. Calculate and obtain the wellbore temperature, wellbore pressure, carbon dioxide partial pressure, well fluid partial pressure, and hydrogen ion activity coefficient of formation water at a specified vertical depth point of the production string according to the data collected in S1;

[0008] S3. Calculate the short - term first - type metal loss rate and long - term first - type metal loss rate at a specified well depth point of the production string through the parameters obtained in S2;

[0009] S4. Calculate and obtain the first - type metal loss - corrosion rate at a specified well depth point through the short - term first - type metal loss rate, long - term first - type metal loss rate, and service life of the production string;

[0010] S5. Calculate and obtain the second - type metal loss - wear amount of the production string at a specified well depth point through well deviation data and drilling parameters;

[0011] S6. Superpose and calculate the first - type metal loss - corrosion rate and the second - type metal loss - wear amount to obtain the total metal loss at the specified well depth point;

[0012] S7. Conduct a mechanical strength check at the specified well depth point and calculate the residual mechanical strength at the specified well depth point;

[0013] S8. Repeat S2 to S7 to complete the calculation of the remaining collapse strength, residual mechanical strength, and residual mechanical strength safety factor at the specified well depth points from 1 to n;

[0014] S9. End the calculation and output the calculation results.

[0015] The basic information collected in S1 includes tubing string geometric data, metal material properties, service life, acid gas components and partial pressures, gas relative density, oil properties, content of corrosive ions in water, temperature, pressure, and daily oil, gas, and water production.

[0016] The calculation formulas for each data at the specified vertical depth point in S2 are as follows:

[0017] Wellbore temperature = surface temperature + vertical depth * geothermal gradient + 273.15;

[0018] Wellbore pressure = surface casing pressure + vertical depth * formation pressure gradient;

[0019] Carbon dioxide partial pressure = wellbore pressure * carbon dioxide content;

[0020] Well fluid partial pressure = wellbore pressure * number of moles of corrosive gas / total number of moles of well fluid;

[0021] Hydrogen ion activity coefficient: pHCO2 = 3.71 + 0.00417 * wellbore temperature (°C) - 0.5 * lg (carbon dioxide partial pressure);

[0022] The calculation formulas for each data at the specified well depth point in S3 and S4 are as follows:

[0023] The calculation formula for the short - term first - type metal loss rate is

[0024] CR (mm / a) = 10 ^ (a + b / wellbore temperature (K) + c * lg (carbon dioxide partial pressure) + d * (7 - hydrogen ion activity coefficient));

[0025] where a is the short - term corrosion coefficient, b is the wellbore temperature coefficient, c is the carbon dioxide partial pressure coefficient, and d is the acidity coefficient;

[0026] The long - term first - type metal loss rate CR year The calculation formula is CR year (mm / a) = CR / E;

[0027] The first type of metal loss - corrosion rate is CR year *Service life

[0028] The calculation formula for the second type of metal loss - wear amount at the specified well depth point in S5 is:

[0029] The second type of metal loss - wear amount = wear efficiency E / Brinell hardness E * sliding friction coefficient H * lateral force F * sliding distance L

[0030] The calculation formula for the total metal loss at the specified well depth point in S6 is:

[0031] Total metal loss = the first type of metal loss - corrosion rate + the second type of metal loss - wear amount

[0032] The specific steps of S7 are as follows:

[0033] S71. Calculate the yield strength S of the pipe at the specified well depth point

[0034] The yield strength S of the pipe = the yield strength of the pipe body / 0.0007854 / (outer diameter of the casing * outer diameter of the casing - inner diameter of the casing * inner diameter of the casing)

[0035] S72. Obtain the process parameters A, process parameter B, process parameter C, process parameter F, and process parameter G at the specified well depth point through the yield strength S of the pipe

[0036] Process parameter A = 2.8762 + 0.000154885 * S + 0.00000044806 * S 2 - 0.0000000001621 * S 3 ;

[0037] Process parameter B = 0.026233 + 0.0000734 * S

[0038] Process parameter C = 4.4741 * S - 0.0002205 * S 2 + 0.00000011285 * S 3 - 465.93

[0039] The process parameter F = (323700 * ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)) * ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)) * ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A))) / (yield strength of the pipe * (((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)) - (process parameter B / process parameter A)) * (1 - ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A))) * (1 - ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A))));

[0040] The process parameter G = process parameter F * (process parameter B / process parameter A);

[0041] S73. Calculate the diameter - thickness ratios μ, μ 1、、 μ2 and μ3;

[0042] μ = outer diameter of the casing / (designed wall thickness - total metal loss);

[0043] μ1 = SQRT(((process parameter A - 2) * (process parameter A - 2) + 8 * (process parameter B + 0.0068947 * process parameter C / S) + (process parameter A - 2)) / (2 * (process parameter B + 0.0068947 * process parameter C / S)));

[0044] μ2 = (S * (process parameter A - process parameter F)) / (0.0068947 * process parameter C + S * (process parameter B - process parameter G));

[0045] μ3 = (2 + process parameter B / process parameter A) / (3 * process parameter B / process parameter A);

[0046] S74. Compare the diameter - thickness ratios μ, μ 1、、 μ2 and μ3, and obtain the collapse strength W at the specified well depth point as follows,

[0047] When μ ≤ μ1, W YIELD = 2 * S * ((μ - 1) / μ 2 ;

[0048] When μ1 < μ ≤ μ2, W PLASTIC = (process parameter A / μ - process parameter B) * S - 0.0068947 * process parameter C;

[0049] When μ1 < μ ≤ μ3, W TRANSITIONAL = S * (process parameter F / μ - process parameter G);

[0050] When μ > μ3, W ELASTIC = 323710000 / ((μ) * (μ - 1) 2 / 1000);

[0051] S74. Calculate the residual mechanical strength and the safety factor of the residual mechanical strength at the specified well depth point;

[0052] Residual mechanical strength = 0.875 * (2 * S * (design wall thickness of the pipe - total metal loss) / outer diameter of the casing or tubing);

[0053] Safety factor of the residual mechanical strength = residual mechanical strength / production pressure.

[0054] According to the remaining collapse resistance, residual mechanical strength, and safety factor of the residual mechanical strength obtained at the corresponding specified well depth point in S8, plot the curves of the remaining collapse resistance varying with the well depth, the residual mechanical strength varying with the well depth, and the safety factor of the residual mechanical strength varying with the well depth.

[0055] The beneficial effects of the present invention are as follows: This solution simultaneously considers the metal loss of the pipe string under the influence of the corrosion rate and wear amount, and checks its mechanical strength. By calculating the metal loss of the production pipe string in offshore oil and gas wells, including corrosion and wear conditions, the residual mechanical strength of the pipe string result is checked to evaluate the remaining load-bearing capacity and integrity of the wellbore production pipe string, aiming to ensure the safety and reliability of the production pipe string in offshore oil and gas wells under complex environments. Brief Description of the Drawings

[0056] Figure 1 is the flowchart of the calculation method for metal loss and mechanical strength check of the production pipe string in offshore oil and gas wells of the present invention;

[0057] Figure 2 is the result diagram of the remaining collapse resistance in the embodiment;

[0058] Figure 3 is the result diagram of the residual mechanical strength in the embodiment;

[0059] Figure 4 is the result diagram of the safety factor of the residual mechanical strength in the embodiment. Detailed Embodiment

[0060] Embodiment

[0061] As Figure 1 shown, the calculation method for metal loss and mechanical strength check of the production pipe string in offshore oil and gas wells specifically includes the following steps:

[0062] S1. Collect the basic information data for calculating the metal loss and mechanical strength of the production string in offshore oil and gas wells. The basic information collected in S1 includes string geometry data, metal material properties, service life, acidic gas components and partial pressures, gas relative density, oil properties, content of corrosive ions in water, temperature, pressure, and daily oil, gas, and water production.

[0063] S2. Calculate and obtain the wellbore temperature, wellbore pressure, bubble point partial pressure, carbon dioxide partial pressure, well stream partial pressure, and hydrogen ion activity coefficient of formation water at the specified vertical depth point of the string based on the data collected in S1.

[0064] The calculation formulas for each data at the specified vertical depth point in S2 are as follows:

[0065] Wellbore temperature = surface temperature + vertical depth * geothermal gradient + 273.15;

[0066] Wellbore pressure = surface casing pressure + vertical depth * formation pressure gradient;

[0067] Carbon dioxide partial pressure = wellbore pressure * carbon dioxide content;

[0068] Well stream partial pressure = wellbore pressure * moles of corrosive gas / total moles of well stream;

[0069] Hydrogen ion activity coefficient: pHCO2 = 3.71 + 0.00417 * wellbore temperature (°C) - 0.5 * lg(carbon dioxide partial pressure);

[0070] S3. Calculate the short-term first-class metal loss rate and long-term first-class metal loss rate at the specified well depth point of the production string using the parameters obtained in S2.

[0071] The calculation formula for the short-term first-class metal loss rate is CR (mm / a) = 10^(a + b / wellbore temperature (K) + c * lg(carbon dioxide partial pressure) + d * (7 - hydrogen ion activity coefficient));

[0072] Among them, the values of the short-term corrosion coefficient a, wellbore temperature coefficient b, carbon dioxide partial pressure coefficient c, and acidity coefficient d are shown in the following table.

[0073] Table 1 Values of coefficients a, b, c, and d

[0074] Coefficient value table a b c d Carbon steel -7.545 -3359.5 -2.4622 5.9977 1Cr -7.0579 -3217.8 -2.2736 5.66 3Cr -9.0949 -3872.8 -2.8146 6.9479 9Cr -6.4943 -3787.5 -2.2258 5.5489 13Cr -4.9262 -3255 -1.4069 4.3171

[0075] The long-term first-class metal loss rate CR year is calculated by the formula CR year (mm / a) = CR / E;

[0076] The first-class metal loss amount is CR year * service life.

[0077] Among them, the value of the coefficient E is shown in the following table.

[0078] Table 2 Table of the value of coefficient E

[0079] Coefficient value table E Carbon steel 0.5611 1Cr 0.2648 3Cr 0.1955 9Cr 0.1955 13Cr 0.1955

[0080] S4. Calculate the first type of metal loss-corrosion rate at a specified well depth point through the short-term first type of metal loss rate, long-term first type of metal loss rate, and service life of the production string.

[0081] S5. Calculate the second type of metal loss-wear amount of the production string at a specified well depth point through well deviation data and drilling parameters.

[0082] The calculation formula for the second type of metal loss-wear amount in S5 is:

[0083] The second type of metal loss-wear amount = wear efficiency E / Brinell hardness E * sliding friction coefficient H * lateral force F * sliding distance L.

[0084] S6. Perform superposition calculation on the first type of metal loss amount and the second type of metal loss amount to obtain the total metal loss amount at a specified well depth point.

[0085] The calculation formula for the total metal loss amount in S6 is:

[0086] The total metal loss amount = the first type of metal loss-corrosion rate + the second type of metal loss-wear amount.

[0087] S7. Conduct mechanical strength check at a specified well depth point and calculate the residual mechanical strength at the specified well depth point.

[0088] The specific steps of S7 are as follows:

[0089] S71. Calculate the yield strength S of the pipe at a specified well depth point;

[0090] The yield strength S of the pipe = the yield strength of the pipe body / 0.0007854 / (outer diameter of the casing * outer diameter of the casing - inner diameter of the casing * inner diameter of the casing);

[0091] S72. Obtain process parameters A, B, C, F, and G at a specified well depth point through the yield strength S of the pipe;

[0092] Process parameter A = 2.8762 + 0.000154885 * S + 0.00000044806 * S 2 -0.0000000001621 * S 3 ;

[0093] Process parameter B = 0.026233 + 0.0000734 * S;

[0094] Process parameter C = 4.4741*S - 0.0002205*S 2 + 0.00000011285*S 3 - 465.93;

[0095] Process parameter F = (323700*(((3*Process parameter B / Process parameter A) / (2 + Process parameter B / Process parameter A))*((3*Process parameter B / Process parameter A) / (2 + Process parameter B / Process parameter A))*((3*Process parameter B / Process parameter A) / (2 + Process parameter B / Process parameter A)))) / (Yield strength of the pipe*(((3*Process parameter B / Process parameter A) / (2 + Process parameter B / Process parameter A)) - (Process parameter B / Process parameter A))*(1 - ((3*Process parameter B / Process parameter A) / (2 + Process parameter B / Process parameter A)))*(1 - ((3*Process parameter B / Process parameter A) / (2 + Process parameter B / Process parameter A)))));

[0096] Process parameter G = Process parameter F*(Process parameter B / Process parameter A);

[0097] S73. Calculate the diameter - to - thickness ratios μ, μ1, μ2, and μ3 at the specified well depth points;

[0098] μ = Outer diameter of the casing / total metal loss));

[0099] μ1 = SQRT(((Process parameter A - 2)*(Process parameter A - 2)+8*(Process parameter B + 0.0068947*Process parameter C / S)+(Process parameter A - 2)) / (2*(Process parameter B + 0.0068947*Process parameter C / S)));

[0100] μ2 = (S*(Process parameter A - Process parameter F)) / (0.0068947*Process parameter C+S*(Process parameter B - Process parameter G));

[0101] μ3 = (2 + Process parameter B / Process parameter A) / (3*Process parameter B / Process parameter A);

[0102] S74. Compare the diameter - to - thickness ratios μ, μ 1、、 μ2, and μ3, and obtain the collapse strength W at the specified well depth points as follows,

[0103] When μ ≤ μ1, W YIELD = 2*S*((μ - 1) / μ 2 ;

[0104] When μ1 < μ ≤ μ2, W PLASTIC= (Process Parameter A / μ - Process Parameter B) * S - 0.0068947 * Process Parameter C;

[0105] When μ1 < μ ≤ μ3, W TRANSITIONAL = S * (Process Parameter F / μ - Process Parameter G);

[0106] When μ > μ3, W ELASTIC = 323710000 / ((μ) * (μ - 1) 2 / 1000;

[0107] S74. Calculate the residual mechanical strength and the safety factor of the residual mechanical strength at the specified well depth point;

[0108] Residual mechanical strength = 0.875 * (2 * S * (wall thickness design - total metal loss) / outside diameter of the casing or tubing);

[0109] Safety factor of residual mechanical strength = Residual mechanical strength / production pressure.

[0110] S8. Repeat S2 to S7 to complete the mechanical strength check and the calculation of the residual mechanical strength for well depth points 1 to n at the specified well depth;

[0111] S9. When the calculation is completed, output the calculation results.

[0112] Based on the remaining collapse resistance, residual mechanical strength, and safety factor of the residual mechanical strength obtained at the corresponding specified well depth points in S8, plot the curves of the remaining collapse resistance varying with the well depth, the residual mechanical strength varying with the well depth, and the safety factor of the residual mechanical strength varying with the well depth.

[0113] Taking the production string of a certain offshore oil and gas well as an example, as Figures 2 to 4 shown, the calculation results of this solution are as shown in the figure.

[0114] The above has described the embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as used to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A calculation method for checking metal loss and mechanical strength of production strings in offshore oil and gas wells, characterized in that, The specific steps are as follows: S1. Collect the basic information data for calculating the metal loss and mechanical strength of the production string in offshore oil and gas wells; S2. Calculate and obtain the wellbore temperature, wellbore pressure, carbon dioxide partial pressure, well fluid partial pressure, and hydrogen ion activity coefficient of formation water at the specified vertical depth point of the string based on the data collected in S1; S3. Calculate the short-term first-class metal loss rate and long-term first-class metal loss rate at the specified well depth point of the production string using the parameters obtained in S2; S4. Calculate the first-class metal loss-corrosion rate at the specified well depth point through the short-term first-class metal loss rate, long-term first-class metal loss rate, and service life of the production string; S5. Calculate the second-class metal loss-wear amount of the production string at the specified well depth point through the well deviation data and drilling parameters; S6. Perform superposition calculation on the first-class metal loss-corrosion rate and the second-class metal loss-wear amount to obtain the total metal loss at the specified well depth point; S7. Conduct mechanical strength check at the specified well depth point and calculate the residual mechanical strength at the specified well depth point; S8. Repeat S2 to S7 to complete the calculation of the remaining collapse strength, residual mechanical strength, and residual mechanical strength safety factor from the specified well depth point 1 to the specified well depth point n; S9. After the calculation is completed, output the calculation results.

2. The calculation method for checking metal loss and mechanical strength of the production string of an offshore oil and gas well according to claim 1, characterized in that: The basic information collected in S1 includes string geometric data, metal material properties, service life, acidic gas components and partial pressures, gas relative density, oil properties, content of corrosive ions in water, temperature and pressure, and daily oil, gas, and water production.

3. The calculation method for checking metal loss and mechanical strength of a production string in an offshore oil and gas well according to claim 1, wherein The calculation formulas for each data at the specified vertical depth point in S2 are as follows: Wellbore temperature = surface temperature + vertical depth * geothermal gradient + 273.15; Wellbore pressure = surface casing pressure + vertical depth * formation pressure gradient; Carbon dioxide partial pressure = wellbore pressure * carbon dioxide content; Well fluid partial pressure = wellbore pressure * number of moles of corrosive gas / total number of moles of well fluid; Hydrogen ion activity coefficient: pHCO2 = 3.71 + 0.00417 * wellbore temperature (°C) - 0.5 * lg (carbon dioxide partial pressure).

4. The calculation method for checking metal loss and mechanical strength of a production string in an offshore oil and gas well according to claim 1, characterized in that The calculation formulas for each data at the specified well depth point in S3 and S4 are as follows: The calculation formula for the short-term first-class metal loss rate is CR (mm / a) = 10 ^ (a + b / wellbore temperature (K) + c * lg (carbon dioxide partial pressure) + d * (7 - hydrogen ion activity coefficient)); where a is the short-term corrosion coefficient, b is the wellbore temperature coefficient, c is the carbon dioxide partial pressure coefficient, and d is the acidity coefficient; Long-term first type of metal loss rate CR year The calculation formula for CR year (mm / a) = CR / E; The first type of metal loss - the corrosion rate is CR year *Service life.

5. The calculation method for checking metal loss and mechanical strength of the production string of an offshore oil and gas well according to claim 1, characterized in that, The calculation formula for the second-class metal loss-wear amount at the specified well depth point in S5 is: Second-class metal loss-wear amount = wear efficiency E / Brinell hardness E * sliding friction coefficient H * lateral force F * sliding distance L.

6. The calculation method for checking metal loss and mechanical strength of a production string in an offshore oil and gas well according to claim 1, wherein The calculation formula for the total metal loss at the specified well depth point in S6 is: Total metal loss = first-class metal loss-corrosion rate + second-class metal loss-wear amount.

7. The calculation method for checking metal loss and mechanical strength of the production string of an offshore oil and gas well according to claim 1, characterized in that The specific steps of S7 are as follows: S71. Calculate the yield strength S of the pipe material at the specified well depth point; Yield strength S of the pipe material = body yield strength / 0.0007854 / (casing outer diameter * casing outer diameter - casing inner diameter * casing inner diameter); S72. Obtain process parameters A, B, C, F, and G at a specified well depth point based on the yield strength S of the pipe; Process parameter A = 2.8762 + 0.000154885*S + 0.00000044806*S 2 -0.0000000001621*S 3 ; Process parameter B = 0.026233 + 0.0000734 * S; Process parameter C = 4.4741*S - 0.0002205*S 2 + 0.00000011285*S 3 - 465.93; Process parameter F = (323700 * ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)) * ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)) * ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A))) / (yield strength of the pipe * (((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)) - (process parameter B / process parameter A)) * (1 - ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A))) * (1 - ((3 * process parameter B / process parameter A) / (2 + process parameter B / process parameter A)))); Process parameter G = process parameter F * (process parameter B / process parameter A); S73. Calculate the diameter-to-thickness ratios μ, μ 1、、 μ2 and μ3; μ = outer diameter of the casing / (designed wall thickness of the pipe - total metal loss); μ1 = SQRT(((process parameter A - 2) * (process parameter A - 2) + 8 * (process parameter B + 0.0068947 * process parameter C / S) + (process parameter A - 2)) / (2 * (process parameter B + 0.0068947 * process parameter C / S))); μ2 = (S * (process parameter A - process parameter F)) / (0.0068947 * process parameter C + S * (process parameter B - process parameter G)); μ3 = (2 + process parameter B / process parameter A) / (3 * process parameter B / process parameter A); S74. Compare the diameter-to-thickness ratios μ, μ 1、、 μ2 and μ3, and obtain the collapse strength W at a specified well depth point as follows: When μ ≤ μ1, W YIELD = 2 * S * ((μ - 1) / μ 2 ; When μ1 < μ ≤ μ2, W PLASTIC = (Process parameter A / μ - Process parameter B) * S - 0.0068947 * Process parameter C; When μ1 < μ ≤ μ3, W TRANSITIONAL = S * (process parameter F / μ - process parameter G); When μ > μ3, W ELASTIC = 323710000 / ((μ) * (μ - 1) 2 / 1000; S74. Calculate the residual mechanical strength and the safety factor of the residual mechanical strength at the specified well depth point; Residual mechanical strength = 0.875 * (2 * S * (designed wall thickness of the pipe - total metal loss) / outer diameter of the casing); Safety factor of the residual mechanical strength = residual mechanical strength / production pressure; 8. The calculation method for checking metal loss and mechanical strength of the production string of an offshore oil and gas well according to claim 1, characterized in that: Based on the remaining collapse strength, residual mechanical strength, and safety factor of the residual mechanical strength obtained at the corresponding specified well depth point in S8, plot the curves of the remaining collapse strength varying with well depth, the residual mechanical strength varying with well depth, and the safety factor of the residual mechanical strength varying with well depth.

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