Method for simulating bridge plug corrosion in variable-temperature and variable-pressure environment through multi-field coupling model

Abstract

The invention belongs to the field of optimal design of soluble bridge plugs, and particularly relates to a method for simulating bridge plug corrosion in a variable-temperature and variable-pressure environment through a multi-field coupling model. The method comprises the following steps: S1, designing each part of the bridge plug; s2, establishing a stress corrosion model of the bridge plug; s3, establishing a high-temperature corrosion model of the bridge plug; s4, evaluating the corrosion rate of the bridge plug; s5, predicting the stress corrosion failure time of the bridge plug; and S6, carrying out secondary optimization and analysis on the bridge plug structure. According to the invention, the setting time of the bridge plug can be predicted and materials can be optimized according to engineering requirements under the condition of variable-temperature variable-pressure corrosion. According to the method, bridge plug performance evaluation and optimization links are designed, construction of a bridge plug alloy material corrosion model in a high-temperature and high-pressure corrosion environment is completed, and reproduction of a corrosion mechanism is achieved through a multi-field coupling corrosion model. Calculating the corrosion rate of the bridge plug and the failure time of the bridge plug caused by stress corrosion, predicting the setting failure of the bridge plug caused by the stress corrosion, and optimizing the structure of the bridge plug part.

Description

Technical Field

[0001] The invention relates to the field of soluble bridge plug design, and in particular to a method for simulating bridge plug corrosion in a variable temperature and pressure environment using a multi-field coupling model. Background Art

[0002] Reservoir fracturing technology is an important technology for transforming reservoirs to increase oil and gas production, and is often used in the development of tight gas reservoirs in oil and gas fields. As a temporary plugging tool for staged sealing of horizontal wells, bridge plugs play a vital role in the temporary plugging stage of staged fracturing technology. However, traditional drillable composite bridge plugs face problems such as easy damage to casing after achieving the sealing effect. Therefore, bridge plugs made of soluble alloy components are mostly used for sealing in engineering. In engineering, there are many studies on the solubility of alloy components, but most of them ignore the relationship between electrochemical corrosion and mechanical properties. Under actual engineering conditions, bridge plugs need to meet a certain period of effective sealing. After meeting the effective sealing time, the bridge plug will cause yield failure due to the weakening of strength caused by corrosion.

[0003] The existing solution to the problems of uncertainty and inaccurate analysis of the mechanical properties and corrosion properties of bridge plugs made of soluble magnesium-aluminum alloys is to compare finite element simulation results with test results to improve accuracy. However, after the results are compared, the yield failure of the bridge plug cannot be optimized accordingly in combination with engineering needs, which to a certain extent restricts the development of soluble bridge plugs. It is necessary to improve the development technology in terms of size design, numerical simulation, and structural re-optimization. Summary of the invention

[0004] In view of the above problems, the present invention creatively provides a method for simulating bridge plug corrosion in a variable temperature and pressure environment by using a multi-field coupling model, taking into account the influence of temperature and stress changes in the formation on the electrochemical corrosion rate of the bridge plug, and analyzing the effective sealing time of the bridge plug for corrosion resistance by constructing a bridge plug corrosion model in a high temperature and stress corrosion environment. This set of analysis processes can cope with the research and development of bridge plugs that meet most engineering needs, and has a rigorous sealing failure prediction scheme and a reproducible bridge plug structure optimization process.

[0005] The present application discloses a method for simulating bridge plug corrosion in a variable temperature and pressure environment using a multi-field coupling model, which is characterized by comprising the following steps:

[0006] S1. Design of various components of bridge plug;

[0007] S2. Establish a stress corrosion model for bridge plugs;

[0008] S3, establishing a high temperature corrosion model of the bridge plug;

[0009] S4. Evaluate the corrosion rate of bridge plugs;

[0010] S5. Predict the stress corrosion failure time of bridge plugs;

[0011] S6. Secondary optimization and analysis of bridge plug structure.

[0012] Furthermore, the step S1 of designing the components of the bridge plug includes:

[0013] (1) Complete the determination of the dimensional parameters of each component of the bridge plug tool, design the structure and draw drawings of each component;

[0014] (2) According to the specific engineering and technical requirements, the dimensional parameters are refined, and the modeling of the bridge plug's seating mechanism, anti-rebound mechanism, sealing mechanism, anchoring mechanism, and release mechanism is completed in combination with the strength of the selected material and the electrochemical performance parameters measured experimentally, thus completing the construction and assembly of the models of the various components of the soluble bridge plug.

[0015] Furthermore, the step S2 establishes a stress corrosion model of the bridge plug, including:

[0016] (1) The pressure distribution in the formation is volume force, which is evenly distributed in the component domain and the formation domain, simulating the high-pressure environment of the formation;

[0017] (2) Establish a stress corrosion model for bridge plug materials, set the mechanical and electrochemical dynamic change parameters of the bridge plug, and establish the relationship between mechanics and electrochemistry.

[0018] Furthermore, the step S3 establishes a high temperature corrosion model of the bridge plug, including:

[0019] (1) Establish a dynamic coupling model of temperature and corrosion environment. The change of temperature will change the electrochemical corrosion reaction rate by changing the migration and free rate of particles in the galvanic cell and the dissolution rate of the alloy surface film;

[0020] (2) For the corrosion environment under the influence of temperature, a dynamically balanced temperature field is established, and the temperature is distributed non-uniformly in the domain as a dynamic quantity to keep the heat input outside the reaction domain consistent with the heat output inside the domain, thereby ensuring the consistency of the reaction heat of the corrosion simulation.

[0021] Furthermore, the step S4 of evaluating the bridge plug corrosion rate includes:

[0022] (1) A dynamic coupling model of temperature and corrosion environment is established. Temperature changes change the electrochemical corrosion reaction rate by changing the particle migration and free rate in the galvanic cell formed by the bridge plug and the formation seepage, as well as the dissolution rate of the alloy surface film;

[0023] (2) For the corrosion environment under the influence of temperature, a dynamic temperature field is established, and the temperature is distributed non-uniformly in the domain as a dynamic quantity to keep the heat input outside the reaction domain consistent with the heat output inside the domain, thereby ensuring the consistency of the reaction heat of the corrosion simulation.

[0024] Furthermore, the step S5 predicts the bridge plug stress corrosion failure time, including:

[0025] (1) The corrosion potential and corrosion current density of magnesium-aluminum alloy can be obtained from the polarization curve of the reaction interface obtained from the bridge plug corrosion output;

[0026] (2) Based on the output of the ion concentration change diagram in the electrolyte, it is possible to obtain how the corrosion rate changes with the electrolyte concentration during the bridge plug corrosion process. Combined with the stress corrosion cloud map, the time when the bridge plug fails due to stress corrosion can be predicted.

[0027] Furthermore, the secondary optimization and analysis of the bridge plug structure in step S6 includes:

[0028] (1) Based on the stress cloud map, reaction interface polarization curve map, and current density distribution map obtained by multi-field coupling simulation, the weak position of bridge plug corrosion failure is optimized in combination with engineering requirements;

[0029] (2) In order to extend the setting time, the components in the bridge plug are selectively treated with corrosion-resistant coating, and the corrosion process is simulated cyclically. The results before and after optimization are compared and the rationality of the optimized structure is evaluated.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention can realize the design of soluble bridge plugs and optimize weak points, evaluate the strength reduction of bridge plugs caused by corrosion, and predict the stress corrosion yield failure of bridge plugs, so as to facilitate the implementation of bridge plug design optimization schemes according to specific engineering needs;

[0032] (2) The present invention simplifies the high temperature stress corrosion process of the bridge plug, and defines the optimized re-simulation process, and can evaluate the optimization by comparing the simulation result diagrams before and after optimization;

[0033] (3) The present invention depicts the corrosion-resistant coating on the surface of the bridge plug, so that the bridge plug can meet different engineering requirements, and constructs a suitable electrochemical corrosion environment in combination with different formation conditions to achieve more accurate simulation, so that the bridge plug design can ultimately meet engineering requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the implementation process of the present invention;

[0035] Figure 2This is the modeling and assembly diagram of the entire bridge plug component;

[0036] Figure 3 Schematic diagram of stress corrosion mechanism of bridge plug;

[0037] Figure 4 This is a schematic diagram of the temperature conduction in the domain when simulating the setting of the bridge plug;

[0038] Figure 5 This is a schematic diagram of the calculation process of the multi-field coupling model of bridge plug corrosion;

[0039] Figure 6 Schematic diagram for evaluating electrode corrosion rate;

[0040] Figure 7 Schematic diagram of the damage domain in the bridge plug corrosion area. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Reference Figure 1 The present invention proposes a deep shale gas horizontal well anti-pressure channeling and casing change and full-fracture support fracturing technology, which mainly includes the following 6 steps:

[0043] S1. Design of various components of bridge plug;

[0044] S2. Establish a stress corrosion model for bridge plugs;

[0045] S3, establishing a high temperature corrosion model of the bridge plug;

[0046] S4. Evaluate the corrosion rate of bridge plugs;

[0047] S5. Predict the stress corrosion failure time of bridge plugs;

[0048] S6. Secondary optimization and analysis of bridge plug structure.

[0049] Specifically, step S1 includes:

[0050] According to the needs of the working conditions, the selection of soluble bridge plug materials is completed, the graphic size parameters are determined, the size parameters of each component of the bridge plug tool are determined, the structure is designed and the drawings of each component are drawn. The modeling of the bridge plug's setting mechanism, anti-rebound mechanism, sealing mechanism, anchoring mechanism and release mechanism are completed; the constructed bridge plug component models are assembled as a whole in the modeling software, and the mechanical, electrochemical and thermodynamic related material property parameters of the selected materials are entered to complete the construction, assembly and definition of material properties of the soluble bridge plug full component model.

[0051] Specifically, step S2 includes:

[0052] The high-pressure environment in the domain is kept close to the real formation, and the pressure is evenly distributed in the bridge plug component domain and the formation domain as a volume force. Therefore, the stress is also based on the requirements of the longer-term corrosion-resistant sealing project, and the contact layer between the magnesium-aluminum alloy electrode and the electrolyte is constructed. According to the mechanical and electrochemical parameters of the contact layer, the electrochemical corrosion reaction of the alloy of the soluble magnesium-aluminum alloy bridge plug in the sealing environment of the formation changes with temperature and pressure.

[0053] The small deformation plasticity model is used to define the elastic-plastic stress in the corrosion domain and define the hardening function σ yh :

[0054]

[0055] Among them, σ exp is the stress-strain curve of the analyzed magnesium-aluminum alloy sample; ε p is the plastic strain of the soluble magnesium-aluminum alloy; σ e is the von Mises stress; E is the Young's modulus; K is the ionization proportionality constant described in step S2; α is the linear thermal expansion coefficient; T and T 0 are the real-time temperature and initial temperature in the domain respectively; σ ys is the yield strength of magnesium-aluminum alloy.

[0056] Soluble rubber material is a non-metallic component of the bridge plug and is not suitable for small deformation plasticity models. Its macromolecular network structure enables it to withstand large strain nonlinear elastic deformation. From a microscopic level, it can be seen that rubber materials are composed of sparsely cross-linked long-chain molecules.

[0057] Therefore, the elastic strain energy function W can be obtained from the change of configuration entropy. s as follows:

[0058]

[0059] Among them, μ and α are constants and can be adjusted according to engineering needs to fit the data at hand; Main elongation; J e1is the elastic volume ratio, dimensionless; Q is the diffusion activation energy of the electrolyte, kJ / mol; T 0 Normal temperature is 298.15K; T k is the actual temperature, K; R is the gas constant 8.314 J / mol·K.

[0060] The following is a full Lagrangian formula that describes the stress distribution for large deformation simulations:

[0061]

[0062] Among them, S is the second-order Piola-Kirchhoff stress tensor, which is used to describe the tensor of stress distribution inside the inhomogeneous continuous medium; ε is the Green-Lagrange strain. The multi-field coupling model of the hyperelastic material can simulate the large deformation of the rubber during setting.

[0063] Specifically, step S3 includes:

[0064] For the corrosion environment under the influence of temperature, a dynamically balanced temperature field is established, and the temperature is distributed in the domain as a dynamic variable to make it more realistic. The input and output of the heat flux are set to be consistent to ensure the consistency of the reaction heat of the corrosion simulation. The temperature change is reflected by the dynamic heat release of the oxidation reaction of the magnesium-aluminum alloy. If the temperature in the domain gradually increases due to the heat release of the alloy anodic oxidation reaction, the temperature change will also lead to changes in the corrosion reaction. The main reasons are as follows:

[0065] (i) The metal potential of alloy electrochemical corrosion shifts with temperature;

[0066] (ii) Temperature changes the rate of ion diffusion and the rate of reaction.

[0067] A dynamic coupled bridge plug corrosion model is constructed to simulate the dynamic high temperature and corrosion environment of the formation. The change in temperature will change the electrochemical corrosion reaction rate by changing the migration and free rate of particles in the galvanic cell and the dissolution rate of the alloy surface film. Temperature, chloride ion concentration and microstructure will affect the corrosion mechanism of magnesium-aluminum soluble alloys. The corrosion product film on the surface of the sample is denser at low temperatures; corrosion products are difficult to precipitate on the alloy surface at high temperatures; chloride ions affect the formation of corrosion product films on the one hand, and on the other hand, chloride ions can accelerate the pitting process on the alloy surface. In addition, changes in temperature will lead to changes in the corrosion potential of the alloy. As the temperature rises, the corrosion potential shifts negatively and the corrosion rate increases.

[0068] In order to obtain the alloy ionization rate, first obtain the ionization / hydrolysis proportional constant K

[0069]

[0070] Where K 0is the reaction constant at room temperature; T 0 is room temperature 294.15K; R is the gas constant (8.314 J / mol·K); Q is the diffusion activation energy of the electrolyte.

[0071] Solubility limit K of alloy dissolution sp It can be obtained from the Gibbs free energy change ΔG(T) of ions and alloys:

[0072]

[0073] Where ΔG(T) is the change in Gibbs free energy, kJ / mol; ΔS(T) is the change in entropy, J / K; ΔC p (T) is the variation of heat capacity among species.

[0074] Specifically, step S4 includes:

[0075] As shown in the figure, the corrosion potential and corrosion current density of the magnesium-aluminum alloy soluble bridge plug can be obtained according to the output of the bridge plug corrosion in the finite element software. The corrosion model is as follows:

[0076] The anode Tafel expression simulates the oxidation reaction of magnesium-aluminum alloy as follows:

[0077]

[0078] Among them, i 0,a is the anode exchange current density, A / m 2 ; A a is the anode Tafel slope, V; η a is the overpotential of the anode reaction, V.

[0079] The equilibrium potential of the anodic reaction is given by:

[0080]

[0081] Where E eq0,a is the standard equilibrium potential of the anode reaction, V; ΔP m is the overpressure that causes elastic deformation, Pa; V m is the molar volume of steel, m 3 / mol; z is the charge number of the metal; F is the Faraday constant (96485.34C / mol); T is the ambient temperature, K; R is the ideal gas constant; v is the direction-dependent factor; α is the coefficient, 1.67×10 15 m -2 ; N 0 is the initial dislocation density, m -2 .

[0082] The cathode Tafel expression simulates the reduction reaction of magnesium-aluminum alloy as follows

[0083]

[0084] Among them, i 0,c is the cathode exchange current density, A / m 2 ; A c is the Tafel slope, V; η c is the overpotential of the anode reaction, V; E eq0,c is the standard equilibrium potential of the cathode reaction, V.

[0085] The exchange current density of the cathode reaction is calculated by

[0086]

[0087] where i 0,c,ref is the reference exchange current density of the cathode reaction without external stress strain, A / m 2 .

[0088] According to the output of the chloride ion concentration change diagram in the electrolyte, the changing trend of the corrosion rate with the change of electrolyte concentration during the bridge plug corrosion process can be obtained, and the chloride ion concentration in the electrolyte in the pitting pit can be extracted through the simulation software.

[0089] Calculate the corrosion rate of magnesium-aluminum alloy. The calculation of the corrosion rate of the oxidation reaction of the alloy as an anode involves the current density and ambient temperature of the contact surface. The calculation model is as follows:

[0090]

[0091] Among them, R corr is the corrosion rate, mm / a; M m is the metal molecular weight, mol; z m is the effective valence of the metal; F is the Faraday constant, 96485.34C / mol; integration domain is the contact interface between the anode and the electrolyte; i a is the metal corrosion current density, A / m 2 ; K 0 is the reaction constant at room temperature, dimensionless; T is the ambient temperature, °C; T 0 is room temperature, 25°C; R is the gas constant, 8.314 J / mol·K; Q is the diffusion activation energy of the electrolyte, kJ / mol.

[0092] Obviously aThe domain will change with the electrochemical corrosion reaction. Specifically, as the corrosion reaction occurs, the alloy's contact area with the electrolyte increases due to pitting. The migration of the metal corrosion phase interface will change the surface potential and current density distribution, and then change its corrosion rate. The change in corrosion rate will directly determine the corrosion expansion of the metal interface. Therefore, the migration of the corrosion phase interface is the key to the accuracy of the corrosion model construction. Therefore, it is necessary to consider the simulation of the migration of the phase interface position. The interface evolution can be described by the following formula:

[0093]

[0094] in, is the position vector; i a is the anode Tafel reaction expression; is the anode-electrolyte contact interface at time t.

[0095] Under the condition of applied anode current or potential, taking into account the difference effect Δ, the difference in cathode reaction rate under different polarization conditions is as follows:

[0096] Δ=|I 0 |-|I H |

[0097] When Δ>0, it is a positive difference effect, that is, the self-corrosion rate of the polarized state of the anode metal is relatively small compared to the unpolarized state; when Δ<0, it is a negative difference effect, and the corrosion current density of magnesium metal increases with the increase of polarization potential or current under the condition of applied anode current or potential. 0 and I H Represents the initial polarization curve (initially the anode and cathode are equal) and the polarization curve of the cathode hydrogen evolution reaction.

[0098] Specifically, step S5 includes:

[0099] The parameters of the multi-field coupling simulation are set according to the working conditions of the sealing environment. The mechanical-thermodynamic-electrochemical multi-field coupling is conducive to simulating the sealing under a state close to the real state. The heat released by the oxidation reaction of the magnesium-aluminum alloy also causes the electrolyte in the domain to heat up. It is possible to explore the weakening of the effective compressive strength of the alloy with the intensity of corrosion under the condition of corrosion reaction heat-induced heating promoting corrosion, as well as the complex changes of the effective sealing time of the bridge plug after adding the corrosion-resistant coating.

[0100] The Nernst-Planck mass transfer equation is used to describe the sum of the net flux of ion diffusion, electromigration, convection and homogeneous reaction in the electrochemical analysis process. Diffusion refers to the movement of substances under the action of concentration gradient; electromigration refers to the movement of charged particles under the action of potential gradient; convection refers to the relative displacement between different parts of the fluid; homogeneous reaction means that all reactions are in the same phase and there is no phase interface. Therefore, the following formula is obtained:

[0101]

[0102] Among them, c i is the ion concentration, mol / m 3 ; is the solution flow velocity vector; D i is the diffusion coefficient, m 2 / s;m i is the electromigration coefficient; z is the metal charge; F is the Faraday constant, 96485.34C / mol; R i is the net flux.

[0103] The continuous phase field parameter φ is introduced as a function of phase boundary evolution, φ = 1 represents the solid electrode domain; φ = 0 represents the liquid electrolyte domain; 0 < φ < 1 ​​represents the corrosion phase transition evolution domain between the electrode and electrolyte phases. Therefore, there is a free energy functional as follows:

[0104]

[0105] Among them, f e-chem is the electrochemical field density function; f grad is the gradient function; f mech is the mechanical field function; c i is the concentration of metal ions, mol / L; u is the solid phase displacement field;

[0106] The role of mechanical field in electrochemical corrosion can be summarized as corrosion leading to phase interface migration, so there is an evolution of interface mobility, and the interface mobility is similar to the mechanical field and can be expressed as follows:

[0107]

[0108] Among them, L and L 0 is the kinetic coefficient used to characterize the mobility of the phase interface under the applied load and unapplied load conditions; i and i 0 is the anode current density under stress and the anode current density without stress, A / m 2 ; ε p is the effective plastic strain; ε y is the yield strain; σ h is the static pressure of the electrolyte liquid phase, MPa; V m is the molar volume of the metal, L / mol; R is the ideal gas constant; T is the ambient temperature, ℃.

[0109] After establishing the relationship between mechanics, thermodynamics and electrochemistry, it is necessary to set constraints. The governing equation for the evolution of the phase field over time is as follows:

[0110]

[0111] in, is the isotropic gradient energy coefficient.

[0112] The governing equations for the time-dependent changes in the concentrations of magnesium and aluminum ions in the electrolyte domain are as follows:

[0113]

[0114] in, is the metal ion concentration in the liquid electrolyte, mol / L; is the metal ion concentration in the solid electrode, mol / L; is the content of metal ions in the solid phase, mol / L.

[0115] By measuring the change of the bridge plug corrosion rate at each stage of the setting process in the aforementioned step S4, the speed of the bridge plug corrosion is obtained, so that the time for the bridge plug to be completely corroded and dissolved can be evaluated. In the context of actual setting, the bridge plug will yield and fail due to the effect of stress after being corroded to a certain extent. Therefore, on the basis of evaluating the time for the bridge plug to be completely dissolved, the strength of the alloy weakened due to electrochemical corrosion is considered. When the overall compressive strength is weakened until it is less than the applied load, it can be considered that the alloy component has yielded and failed. Therefore, it is of great significance to establish a correlation model between compressive strength and corrosion.

[0116] Stress corrosion is particularly evident in tensile stress, but even when alloy components are under compression, they are still affected by stress corrosion. Therefore, the relationship between corrosion electrochemical properties and compressive strength is constructed as follows:

[0117]

[0118] Among them, R corr is the corrosion rate described in the aforementioned step S4, mm / a; m 0 and m are the initial mass of the alloy material and the weight after reaction to time t, kg; ρ is the density of the magnesium-aluminum alloy, kg / m 3 .

[0119] When the compressive strength at a certain point in the domain decreases to below the pressure range due to corrosion, it can be considered that the alloy has yielded, thus establishing the relationship between electrochemical corrosion performance and compressive strength. Combined with the evaluation of bridge plug corrosion rate described in S4, the failure time of bridge plug components caused by stress corrosion can be accurately predicted. Figure 7 As shown, it is a polarization curve diagram of the faster boundary of the corrosion reaction at the pressure-bearing joint between components. It characterizes the functional relationship between the driving force potential of the corrosion galvanic cell reaction and the reaction rate current. It can be used to evaluate the electrochemical properties of materials and help evaluate the corrosion performance and corrosion rate of materials.

[0120] Specifically, step S6 includes:

[0121] Based on the design requirements for the corrosion performance of bridge plugs, combined with the calculation results of the multi-physics field bridge plug corrosion simulation model, the local and overall optimization of the bridge plug is carried out in a targeted manner to meet the design requirements, and the simulation analysis diagram of the optimized bridge plug is obtained by repeating the above steps S1 to S5. Figure 4 The stress cloud diagram shown is Figure 5 The exothermic diagram of the reaction in the domain shown, such as Figure 6 The current density diagram shown in Figure 7 The finite element simulation results including the polarization curve diagram shown are analyzed to optimize the bridge plug structure and process in a targeted manner until they meet the engineering requirements.

[0122] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the technical contents to make slight changes or modifications. Without departing from the scope of the technical solution of the present invention, the technical contents disclosed above can be used to make slight changes or modifications to equivalent embodiments of equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model, characterized in that: It has the following features: S1. Design of various components of bridge plug; S2. Establish a stress corrosion model for bridge plugs; S3, establishing a high temperature corrosion model of the bridge plug; S4. Evaluate the corrosion rate of bridge plugs; S5. Predict the stress corrosion failure time of bridge plugs; S6. Secondary optimization and analysis of bridge plug structure.

2. The method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model according to claim 1, characterized in that: The step S1 comprises: (1) Complete the determination of the dimensional parameters of each component of the bridge plug tool, design the structure and draw drawings of each component; (2) According to the specific engineering and technical requirements, the dimensional parameters are refined, and the modeling of the bridge plug's seating mechanism, anti-rebound mechanism, sealing mechanism, anchoring mechanism, and release mechanism is completed in combination with the strength of the selected material and the electrochemical performance parameters measured experimentally, thus completing the construction and assembly of the models of the various components of the soluble bridge plug.

3. The method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model according to claim 1, characterized in that: The step S2 comprises: (1) The distribution of pressure in the formation is volume force, which is evenly distributed in the component domain and the formation domain, simulating the high-pressure environment of the formation; (2) Establish a stress corrosion model for bridge plug materials, set the mechanical and electrochemical dynamic change parameters of the bridge plug, and establish the relationship between mechanics and electrochemistry.

4. The method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model according to claim 1, characterized in that: The step S3 comprises: (1) Establish a dynamic coupling model of temperature and corrosion environment. The change of temperature will change the migration and free rate of particles in the galvanic cell and the dissolution rate of the alloy surface film, thereby changing the electrochemical corrosion reaction rate; (2) For the corrosion environment under the influence of temperature, a dynamically balanced temperature field is established, and the temperature is distributed non-uniformly in the domain as a dynamic quantity to keep the heat input outside the reaction domain consistent with the heat output inside the domain, thereby ensuring the consistency of the reaction heat of the corrosion simulation.

5. The method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model according to claim 1, characterized in that: The step S4 comprises: (1) A dynamic coupling model of temperature and corrosion environment is established. Temperature changes change the electrochemical corrosion reaction rate by changing the particle migration and free rate in the galvanic cell formed by the bridge plug and the formation seepage, as well as the dissolution rate of the alloy surface film; (2) For the corrosion environment under the influence of temperature, a dynamic temperature field is established, and the temperature is distributed non-uniformly in the domain as a dynamic quantity to keep the heat input outside the reaction domain consistent with the heat output inside the domain, thereby ensuring the consistency of the reaction heat of the corrosion simulation.

6. The method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model according to claim 1, characterized in that: Described step S5 comprises: (1) The corrosion potential and corrosion current density of magnesium-aluminum alloy can be obtained from the polarization curve of the reaction interface obtained from the bridge plug corrosion output; (2) Based on the output of the ion concentration change diagram in the electrolyte, it is possible to obtain how the corrosion rate changes with the electrolyte concentration during the bridge plug corrosion process. Combined with the stress corrosion cloud map, the time when the bridge plug fails due to stress corrosion can be predicted.

7. The method for simulating bridge plug corrosion under variable temperature and pressure environment using a multi-field coupling model according to claim 1, characterized in that: The step S6 comprises: (1) Based on the stress cloud map, reaction interface polarization curve map, and current density distribution map obtained by multi-field coupling simulation, the weak position of bridge plug corrosion failure is optimized in combination with engineering requirements; (2) In order to extend the setting time, the components in the bridge plug are selectively treated with corrosion-resistant coating, and the corrosion process is simulated cyclically. The results before and after optimization are compared and the rationality of the optimized structure is evaluated.

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