High temperature high pressure supercritical co2-h2s-ci - Method for predicting corrosion of carbon steel in an environment

Abstract

The application provides a high-temperature high-pressure supercritical CO2-H2S-Cl ‑ The application provides a method for predicting corrosion of carbon steel in an environment, which comprises the following steps: firstly, a solubility model of supercritical CO2-H2S is established; secondly, a water chemistry model is established based on the solubility model; thirdly, an electrochemical corrosion thermodynamic model is established; fourthly, an electrochemical corrosion kinetic model is established; and finally, corrosion rate and polarization curves of the carbon steel in a high-temperature high-pressure supercritical CO2-H2S-Cl ‑ environment are obtained through the above models. The application is helpful to find out the influence law of environmental condition change on water phase chemical characteristics, and provides guidance for corrosion allowance design and operation and maintenance of oil and gas pipe materials.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field corrosion protection technology, specifically relating to a high-temperature, high-pressure supercritical CO2-H2S-Cl - Corrosion prediction method for carbon steel in the environment. Background Technology

[0002] Currently, several models have been established for predicting the corrosion of carbon steel in CO2 and H2S environments, including empirical models, semi-empirical models, and mechanistic models. Empirical and semi-empirical models are derived from laboratory data and are only applicable to specific environments; they become inapplicable when the corrosion environment becomes more complex. Mechanistic models, based on corrosion thermodynamics and kinetics, have stronger extrapolation capabilities. However, current CO2-H2S corrosion prediction mechanistic models are only applicable to low-pressure CO2 and H2S environments. This is because they use Henry's Law in water chemistry calculations. Applying this method to high-pressure and supercritical CO2-H2S environments significantly overestimates the solubility of CO2 and H2S in water, leading to overly conservative corrosion rate predictions and unnecessary economic investment. Therefore, for predicting the corrosion of carbon steel in supercritical CO2-H2S environments, it is necessary to replace Henry's Law with gas state equations, gas equilibrium constants, and gas mixing principles applicable to high-pressure systems. This would allow for more accurate calculations of the solubility of supercritical CO2 and H2S in water, resulting in corrosion predictions that are closer to reality. Summary of the Invention

[0003] The purpose of this invention is to provide a high-temperature, high-pressure supercritical CO2-H2S-Cl - A method for predicting the corrosion of carbon steel in the environment; the model established by this method can be used to predict supercritical CO2-H2S-Cl. - Corrosion rate and polarization curve of carbon steel in the environment.

[0004] This invention is achieved through the following technical solution:

[0005] High temperature and high pressure supercritical CO2-H2S-Cl - A method for predicting the corrosion of carbon steel in an environment includes the following steps:

[0006] S1. First, a solubility model for supercritical CO2-H2S is established. The specific process is as follows: Based on the theory that substances in equilibrium have equal chemical potential in both gas and liquid phases, a mathematical equation for the solubility of multiple substances in supercritical CO2-H2S-H2O is constructed. Then, the Soave-Redlich-Kwong (SRK) equation of state and its mixing principle are used to calculate the fugacity coefficients of each substance, thereby determining the solubility of CO2 and H2S in the aqueous phase under different environmental conditions. The solubility model mainly includes the following formulas:

[0007]

[0008]

[0009] In the formula, K i f is the true equilibrium constant. i It is the fugacity of the gas, a i This represents the activity of the liquid phase component, with the subscript i representing CO2, H2S, and H2O respectively; P is the system pressure, in MPa; P 0 It is the standard pressure, 0.1 MPa; T is the temperature, K; R is the ideal gas constant; It is pure component i under pressure P 0 The average partial molar volume between -P, cm 3 ·mol -1 ; This represents the mole fraction of H2O in the gas phase. and These represent the mole fractions of CO2 and H2S in water, respectively. y is the fugacity coefficient of component i; i It is the mole fraction of component i in the gas phase; a and b represent the intermolecular attraction and repulsion, respectively; a ij V is the gravitational parameter between component i and component j; V is the molar volume, cm. 3 ·mol -1 .

[0010] S2. Based on the solubility model, establish a water chemistry model. The specific process is as follows: Calculate the solubility of CO2 and H2S in aqueous solution according to the solubility model. Furthermore, consider the salt concentration (i.e., Cl-). - The effect of salt concentration on solution non-ideality was investigated. The influence of salt concentration on the solubility of CO2 and H2S was characterized by introducing the Pitzer activity model. Then, based on the dissociation equilibrium of CO2 and H2S, the principle of electrolyte electroneutrality, and the Debye-Hückel extended equation, the concentrations of relevant substances in the salt solution were calculated. Through this process, a supercritical CO2-H2S-Cl solution was established. - The water chemistry model of the environment mainly includes the following formulas:

[0011]

[0012] a i =γ i *C i (18)

[0013] lnγ i =Σc2λ i_c C c +Σa2λ i_aC a +Σ c Σ a ζ i_c_a C c C a (19)

[0014]

[0015]

[0016] In the formula, K hy K represents the thermodynamic equilibrium constant for the CO2 hydration reaction. ca K bi , K w Representing H2CO3 and HCO3 respectively - H2S, HS - Thermodynamic equilibrium constant of the dissociation equilibrium reaction with H2O; a i The activity level of species i; γ i The activity coefficient representing species i; C i The concentration of species i; λ i_c The binary interaction parameter representing species i and cation c in solution; λ i_c The binary interaction parameter representing species i and anion a in solution; ζ i_c_a The ternary interaction parameters between species i and cations c and anions a in the solution; A and B are characteristic constants of the solution; I is the ionic strength of the solution; z i The charge number of substance i; r i The ionic radius of substance i is pm; ∈0 is the vacuum permittivity; ∈ is the relative permittivity of the solution; F is the Faraday constant; T k K represents temperature; R represents the gas constant.

[0017] S3. Establish an electrochemical corrosion thermodynamic model. The specific process is as follows: Based on the hydrochemical model established in step S2, obtain the equilibrium concentrations of various species in the salt solution. Use the Nernst equation to calculate the equilibrium potentials of the anodic and cathodic reactions that may occur during the electrochemical corrosion of carbon steel. Then, compare the equilibrium potentials of each electrode reaction with the corrosion potentials obtained from experimental tests to determine the electrode reaction processes occurring on the carbon steel surface. Supercritical CO2-H2S-Cl - The electrochemical corrosion thermodynamic model in the environment mainly includes the following formulas:

[0018]

[0019]

[0020] In the formula, and These are the equilibrium electrode potentials for reactions (26)-(31), respectively. The standard equilibrium electrode potential of reaction i is represented by F; F represents the Faraday constant; n represents the charge number of reaction i; ΔG represents the Gibbs free energy. and These represent the Gibbs free energies of the reactants and products, respectively.

[0021] S4. Establish an electrochemical corrosion kinetic model. The specific process is as follows: Based on the corrosion thermodynamic model established in step S3, determine the electrode reaction processes occurring on the steel surface. Then, apply the electrochemical activation polarization kinetic equation and the mass transfer control equation to determine the electron transfer control current density and the diffusion control limiting diffusion current density, thereby calculating the current density of each electrode reaction. Based on the mixed potential theory, couple the electrode reactions to determine the corrosion potential and corrosion current density of carbon steel, and then establish a supercritical CO2-H2S-Cl... - The electrochemical corrosion kinetics model for carbon steel in an environment, including the following main formulas:

[0022] l = -0.00005T 2 +0.03015T-4.144 (42)

[0023]

[0024]

[0025] i Fe =i c (46)

[0026]

[0027] In the formula Represents the anodic current density in a CO2 environment; i 0，Fe E represents the exchange current density at the anode in a CO2 environment; E represents the electrode potential; E rev The equilibrium potential of the electrode; Represents the anodic current density in an H2S environment; The standard exchange current density of the anode in the H2S environment represents the reaction current density; ΔH is the reaction current density; T ref For reference temperature, 293K; b a The Tafel slope is the anode slope. For HS - Ion coverage on the steel surface; K2 is the adsorption constant; i Fe The anodic current density in an environment where CO2 and H2S coexist; i c，ii represents the current density of the cathode reaction i; r，i Let i be the charge transfer current density of cathode reaction i; L，i The limiting diffusion current density of cathode reaction i; i 0，i b is the exchange current density of cathode reaction i; c The cathode Tafel slope; i 0，ref D is the standard exchange current density for the cathode reaction. i Let be the diffusion constant of substance i; F be the Faraday constant; l be the thickness of the diffusion layer; μ be the diffusion constant of substance i. ref ρ is the reference viscosity of water; μ is the viscosity of water. i is the forward reaction constant for the CO2 hydration reaction; c V is the cathode current density; corr Represents corrosion rate, mm / y; M Fe ρ represents the molar mass of Fe; Fe This represents the density of Fe.

[0028] S5. Using the above model, the predicted conditions for carbon steel under high temperature and high pressure supercritical CO2-H2S-Cl are obtained. - Corrosion rate and polarization curve in the environment.

[0029] The beneficial effects of the present invention include, but are not limited to:

[0030] (1) The hydrochemical model established by this method can accurately calculate the species types, species equilibrium concentrations and pH in salt solutions, which helps to explore the influence of environmental conditions on the chemical properties of water phase.

[0031] (2) This method can be used to predict high-temperature and high-pressure supercritical CO2-H2S-Cl - The corrosion rate of carbon steel in the environment provides guidance for the design and operation and maintenance of corrosion allowances for oil and gas pipelines, reducing economic costs.

[0032] (3) This method can also predict high-temperature and high-pressure supercritical CO2-H2S-Cl - The polarization curves of carbon steel in the environment can be obtained, and the electrochemical corrosion mechanism of carbon steel under different environmental conditions can be explored by decomposing the polarization curves and adjusting the kinetic parameters. This helps to take more reasonable corrosion protection measures for specific environments. Attached Figure Description

[0033] Figure 1 This is a flowchart of the calculation process of the method in this application.

[0034] Figure 2 This is a comparison between the measured polarization curves and model predictions of carbon steel in Example 1 of this application.

[0035] Figure 3This is a comparison between the measured polarization curves and model predictions of carbon steel in Example 2 of this application.

[0036] Figure 4 This is a comparison between the measured polarization curves and model predictions of carbon steel in Example 3 of this application.

[0037] Figure 5 This is a comparison between the measured polarization curves and model predictions of carbon steel in Example 4 of this application. Detailed Implementation

[0038] The specific technical solutions of the present invention will be described with reference to the embodiments.

[0039] Example 1

[0040] The specific experimental conditions involved in this embodiment are 80℃, 8MPa CO2, 3.5% NaCl solution, and 80SS carbon steel as the experimental material. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, as follows... Figure 1 As shown, this will be achieved through the following steps (Note: all potentials mentioned below are relative to the Ag / AgCl (0.1M KCl) reference electrode):

[0041] S1. Based on the hydrochemical model, the concentrations of CO2 and related species, as well as the pH value of the solution, were calculated under the above environmental conditions. The results show that in this environment, the concentration of CO2 in the salt solution is 0.7615 mol / L, the concentration of H2CO3 is 0.001969 mol / L, and the concentration of HCO3... - The concentration was 0.00056 mol / L, CO3 2- The concentration was 5.156 × 10⁻⁶. -11 mol / L, the corresponding solution pH value is 3.255.

[0042] S2, in supercritical CO2-Cl - The anodic reaction occurring on the carbon steel surface in the environment is the oxidation of Fe, and the cathodic reaction may be H. + H2CO3, HCO3 - The reduction of H₂O. Therefore, based on the electrochemical corrosion thermodynamic model, the equilibrium potential of the above electrode reactions in this environment was calculated. The results show that H₂O… + The equilibrium potential for reduction is -0.508V, while the equilibrium potential for the reduction of H2CO3 is -0.618V. - The equilibrium potential for reduction is -0.449V, the equilibrium potential for H2O reduction is -0.356V, and the equilibrium potential for Fe oxidation is -0.86V.

[0043] S3. Supercritical CO2-Cl2 reaction is carried out in a high-temperature and high-pressure reactor using a three-electrode system. -In-situ electrochemical testing in the environment yielded the corrosion potential and polarization curves of 80SS carbon steel. The test results showed that the corrosion potential of the carbon steel in this environment was -0.710V. Clearly, the corrosion potential is lower than that of H... + H2CO3, HCO3 - The equilibrium potential for H2O reduction is higher than that for Fe oxidation, which means that, thermodynamically speaking, the above electrode reactions can all occur during the corrosion process.

[0044] S4. Based on the anode and cathode reactions on the carbon steel surface determined in step S3, a corresponding electrochemical corrosion kinetic model was established. Then, the polarization curve in this environment was calculated based on the corrosion kinetic model and compared with the measured values, such as... Figure 2 As shown, the predicted polarization curves are in excellent agreement with the measured values. Furthermore, the corrosion rate of carbon steel was calculated to be 19.03 mm / y, while the measured value was 19.75 ± 1.21 mm / y. The two values ​​are very close, with an error of only 3.6%.

[0045] Therefore, it can be determined that in the embodiments described in this invention, the corrosion rate and polarization curve prediction values ​​of carbon steel are in good agreement with the measured values, indicating that the method can be used for corrosion prediction of carbon steel in the above-mentioned environment.

[0046] Example 2

[0047] The specific experimental conditions involved in this embodiment are 80℃, 8MPa CO2, 0.004MPa H2S, 3.5% NaCl solution, and 80SS carbon steel as the experimental material. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, the following steps will be taken (Note: all potentials mentioned below are relative to an Ag / AgCl (0.1M KCl) reference electrode):

[0048] S1. Based on the hydrochemical model, the concentrations of CO2, H2S, and related species, as well as the pH value of the solution, were calculated under the above environmental conditions. The results show that in this environment, the concentration of CO2 in the salt solution is 0.7610 mol / L, the concentration of H2CO3 is 0.001968 mol / L, and the concentration of HCO3... - The concentration was 0.00056 mol / L, CO3 2- The concentration was 5.151 × 10⁻⁶. -11 The concentration of H2S is 0.00098 mol / L, and the concentration of HS is... - The concentration was 5.307 × 10⁻⁶. -7 mol / L, the corresponding solution pH value is 3.255.

[0049] S2, in supercritical CO2-H2S-Cl -The anodic reaction occurring on the carbon steel surface in the environment is the oxidation of Fe, and the cathodic reaction may be H. + H2CO3, HCO3 - The reduction of H2S and H2O. Therefore, based on the electrochemical corrosion thermodynamic model, the equilibrium potential of the above electrode reactions in this environment was calculated. The results show that H + The equilibrium potential for reduction is -0.508V, while the equilibrium potential for the reduction of H2CO3 is -0.618V. - The equilibrium potential for reduction is -0.449V, the equilibrium potential for H2S reduction is -0.465V, the equilibrium potential for H2O reduction is -0.356V, and the equilibrium potential for Fe oxidation is -0.86V.

[0050] S3. In a high-temperature, high-pressure reactor, a three-electrode system is used to conduct supercritical CO2-H2S-Cl... - In-situ electrochemical tests in the environment yielded the corrosion potential and polarization curves of 80SS carbon steel. The results showed that the corrosion potential of the carbon steel in this environment was -0.739V. Clearly, the corrosion potential is lower than that of H... + H2CO3, HCO3 - The equilibrium potentials for the reduction of H2S and H2O are higher than the equilibrium potential for the oxidation of Fe, which means that, thermodynamically speaking, the above electrode reactions can all occur during the corrosion process.

[0051] S4. Based on the anode and cathode reactions on the carbon steel surface determined in step S3, a corresponding electrochemical corrosion kinetic model was established. Then, the polarization curve in this environment was calculated based on the corrosion kinetic model and compared with the measured values, such as... Figure 3 As shown, the predicted polarization curves are in excellent agreement with the measured values. Furthermore, the corrosion rate of carbon steel was calculated to be 5.68 mm / y, while the measured value was 5.58 ± 0.48 mm / y. The two values ​​are very close, with an error of only 1.8%.

[0052] Therefore, it can be determined that in the embodiments described in this invention, the corrosion rate and polarization curve prediction values ​​of carbon steel are in good agreement with the measured values, indicating that the method can be used for corrosion prediction of carbon steel in the above-mentioned environment.

[0053] Example 3

[0054] The specific experimental conditions involved in this embodiment are 80℃, 8MPa CO2, 0.016MPa H2S, 3.5% NaCl solution, and 80SS carbon steel as the experimental material. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, the following steps will be taken (Note: all potentials mentioned below are relative to an Ag / AgCl (0.1M KCl) reference electrode):

[0055] S1. Based on the hydrochemical model, the concentrations of CO2, H2S, and related species, as well as the pH value of the solution, were calculated under the above environmental conditions. The results show that in this environment, the concentration of CO2 in the salt solution is 0.7596 mol / L, the concentration of H2CO3 is 0.001965 mol / L, and the concentration of HCO3... - The concentration is 0.00055 mol / L, CO3 2- The concentration was 5.137 × 10⁻⁶. -11 The concentration of H2S is 0.0039 mol / L, and the concentration of HS is... - The concentration was 2.118 × 10⁻⁶. -6 mol / L, the corresponding solution pH value is 3.255.

[0056] S2, in supercritical CO2-H2S-Cl - The anodic reaction occurring on the carbon steel surface in the environment is the oxidation of Fe, and the cathodic reaction may be H. + H2CO3, HCO3 - The reduction of H2S and H2O. Therefore, based on the electrochemical corrosion thermodynamic model, the equilibrium potential of the above electrode reactions in this environment was calculated. The results show that H + The equilibrium potential for reduction is -0.508V, and the equilibrium potential for the reduction of H2CO3 is -0.617V. - The equilibrium potential for reduction is -0.449V, the equilibrium potential for H2S reduction is -0.465V, the equilibrium potential for H2O reduction is -0.356V, and the equilibrium potential for Fe oxidation is -0.86V.

[0057] S3. In a high-temperature, high-pressure reactor, a three-electrode system is used to conduct supercritical CO2-H2S-Cl... - In-situ electrochemical tests in the environment yielded the corrosion potential and polarization curves of 80SS carbon steel. The results showed that the corrosion potential of the carbon steel in this environment was -0.739V. Clearly, the corrosion potential is lower than that of H... + H2CO3, HCO3 - The equilibrium potentials for the reduction of H2S and H2O are higher than the equilibrium potential for the oxidation of Fe, which means that, thermodynamically speaking, the above electrode reactions can all occur during the corrosion process.

[0058] S4. Based on the anode and cathode reactions on the carbon steel surface determined in step S3, a corresponding electrochemical corrosion kinetic model was established. Then, the polarization curve in this environment was calculated based on the corrosion kinetic model and compared with the measured values, such as... Figure 4As shown, the predicted polarization curves are in excellent agreement with the measured values. Furthermore, the corrosion rate of carbon steel was calculated to be 6.92 mm / y, while the measured value was 7.15 ± 0.47 mm / y. The two values ​​are very close, with an error of only 3.2%.

[0059] Therefore, it can be determined that in the embodiments described in this invention, the corrosion rate and polarization curve prediction values ​​of carbon steel are in good agreement with the measured values, indicating that the method can be used for corrosion prediction of carbon steel in the above-mentioned environment.

[0060] Example 4

[0061] The specific experimental conditions involved in this embodiment are 80℃, 8MPa CO2, 0.4MPa H2S, 3.5% NaCl solution, and 80SS carbon steel as the experimental material. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, the following steps will be taken (Note: all potentials mentioned below are relative to an Ag / AgCl (0.1M KCl) reference electrode):

[0062] S1. Based on the hydrochemical model, the concentrations of CO2, H2S, and related species, as well as the pH value of the solution, were calculated under the above environmental conditions. The results show that in this environment, the concentration of CO2 in the salt solution is 0.7192 mol / L, the concentration of H2CO3 is 0.001860 mol / L, and the concentration of HCO3... - The concentration was 0.00052 mol / L, CO3 2- The concentration was 4.707 × 10⁻⁶. -11 The concentration of H2S is 0.0923 mol / L, and the concentration of HS is... - The concentration was 4.916 × 10⁻⁶. -5 mol / L, the corresponding solution pH value is 3.248.

[0063] S2, in supercritical CO2-H2S-Cl - The anodic reaction occurring on the carbon steel surface in the environment is the oxidation of Fe, and the cathodic reaction may be H. + H2CO3, HCO3 - The reduction of H2S and H2O. Therefore, based on the electrochemical corrosion thermodynamic model, the equilibrium potential of the above electrode reactions in this environment was calculated. The results show that H + The equilibrium potential for reduction is -0.508V, and the equilibrium potential for the reduction of H2CO3 is -0.617V. - The equilibrium potential for reduction is -0.449V, the equilibrium potential for H2S reduction is -0.465V, the equilibrium potential for H2O reduction is -0.356V, and the equilibrium potential for Fe oxidation is -0.86V.

[0064] S3. In a high-temperature, high-pressure reactor, a three-electrode system is used to conduct supercritical CO2-H2S-Cl... - In-situ electrochemical tests were conducted in the environment to obtain the corrosion potential and polarization curves of 80SS carbon steel. The test results showed that the corrosion potential of the carbon steel in this environment was -0.766V. Clearly, the corrosion potential is lower than that of H... + H2CO3, HCO3 - The equilibrium potentials for the reduction of H2S and H2O are higher than the equilibrium potential for the oxidation of Fe, which means that, thermodynamically speaking, the above electrode reactions can all occur during the corrosion process.

[0065] S4. Based on the anode and cathode reactions on the carbon steel surface determined in step S3, a corresponding electrochemical corrosion kinetic model was established. Then, the polarization curve in this environment was calculated based on the corrosion kinetic model and compared with the measured values, such as... Figure 5 As shown, the predicted polarization curves are in excellent agreement with the measured values. Furthermore, the corrosion rate of carbon steel was calculated to be 4.38 mm / y, while the measured value was 4.61 ± 0.47 mm / y. The two values ​​are very close, with an error of only 5.0%.

[0066] Therefore, it can be determined that in the embodiments described in this invention, the corrosion rate and polarization curve prediction values ​​of carbon steel are in good agreement with the measured values, indicating that the method can be used for corrosion prediction of carbon steel in the above-mentioned environment.

[0067] Based on the above four examples, it can be determined that this method can be used to predict high-temperature and high-pressure supercritical CO2-H2S-Cl - The corrosion rate and polarization curves of carbon steel in the environment were studied. Furthermore, by comparing four sets of examples, the effect of H2S variation on the supercritical CO2-H2S-Cl... - The influence of aqueous phase chemical properties on the environment.

Claims

1. High temperature high pressure supercritical CO2-H2S-Cl - A method for predicting corrosion of carbon steel in an environment, characterized by The method comprises the following steps: S1, first, a solubility model of supercritical CO2-H2S is established; S2, on the basis of the solubility model, a water chemistry model is established; S3, an electrochemical corrosion thermodynamic model is established; S4, an electrochemical corrosion kinetic model is established; The specific process of S4 is as follows: based on the corrosion thermodynamic model established in step S3, the electrode reaction process occurring on the steel surface is determined; then the electrochemical activation polarization kinetics equation and the mass transfer control equation are applied to determine the electron transfer control current density and the diffusion control limit diffusion current density respectively, so as to calculate the current density of each electrode reaction; according to the mixed potential theory, the electrode reactions are coupled to determine the corrosion potential and the corrosion current density of the carbon steel, and then the electrochemical corrosion kinetics model of the carbon steel in the supercritical CO2-H2S-Cl - environment is established. The electrochemical corrosion kinetic model is shown in the following formula: ； ； ； ； ； ； ； ； ； ； ； ； ； ； wherein represents the anodic current density in a CO2 environment; represents the exchange current density of the anode in a CO2 environment; E represents the electrode potential; E rev represents the equilibrium potential of the electrode; represents the anodic current density in a H2S environment; represents the standard exchange current density of the anode in a H2S environment; is the reaction enthalpy; T ref is the reference temperature, 293 K; b a is the anodic Tafel slope; is the HS - coverage of the ion on the steel surface; is the adsorption constant; is the anodic current density in a CO2 and H2S coexisting environment; is the current density of the cathodic reaction i; is the charge transfer current density of the cathodic reaction i; is the limiting diffusion current density of the cathodic reaction i; is the exchange current density of the cathodic reaction i; b c is the cathode Tafel slope; is the standard exchange current density of the cathodic reaction; is the diffusion constant of the species i; F is the Faraday constant; and l is the diffusion layer thickness; is the reference viscosity of water; is the viscosity of water; is the forward reaction constant of the CO2 hydration reaction; is the cathodic current density; V corr represents the corrosion rate, mm / y; M Fe represents the molar mass of Fe; p Fe represents the density of Fe; S5、Through the above model, the corrosion rate and polarization curve of carbon steel in high-temperature and high-pressure supercritical CO2-H2S-Cl - environment.

2. The high temperature high pressure supercritical CO2-H2S-Cl - A method for predicting corrosion of carbon steel in an environment, characterized by The specific process of S1 is as follows: based on the theory that the chemical potentials of substances in equilibrium state are equal in gas-liquid two phases, a supercritical CO2-H2S-H2O multi-phase solubility mathematical equation is constructed; then, the fugacity coefficients of substances are calculated by using the Soave-Redlich-Kwong state equation and the mixing principle, so as to determine the solubility of CO2 and H2S in water phase under different environmental conditions.

3. The high temperature high pressure supercritical CO2-H2S-Cl of claim 2. - A method for predicting corrosion of carbon steel in an environment, characterized by The solubility model comprises the following formula: ； ； ； ； ； ； ； ； ； ； ； where K i is the true equilibrium constant, f i is the fugacity of the gas, a i is the activity of the liquid phase component, subscript i represents CO2, H2S and H2O, respectively; P is the system pressure, MPa; P 0 is the standard pressure, 0.1 MPa; T is the temperature, K; R is the ideal gas constant; is the average molar volume of pure component i between pressures P 0 and P 3 ; ∙ is the molar fraction of H2O in the gas phase; -1 ; ; and ; and represent the molar fraction of CO2 and H2S in water, respectively; φ i is the fugacity coefficient of component i; y i is the mole fraction of component i in the gas phase; a and b represent the intermolecular attraction and repulsion, respectively; a ij is the attraction parameter between component i and component j; V is the molar volume, cm 3 • mol -1 .

4. The high temperature high pressure supercritical CO2-H2S-Cl of claim 1 - A method for predicting corrosion of carbon steel in an environment, characterized by The specific process of S2 is as follows: The solubility of CO2 and H2S in aqueous solution was calculated according to the solubility model, the Pitzer activity model was introduced to characterize the influence of salt concentration on the solubility of CO2 and H2S, then according to the dissociation equilibrium process of CO2 and H2S, the principle of electrolyte electroneutrality and the Debye-Huckel extension equation, the concentration of related substances in salt solution was solved, and the supercritical CO2-H2S-Cl - environmental water chemistry model.

5. The high temperature high pressure supercritical CO2-H2S-Cl of claim 4 - A method for predicting corrosion of carbon steel in an environment, characterized by The water chemistry model comprises the following formula: ； ； ； ； ； ； ； ； ； ； ； ； ； ； In the formula, Thermodynamic equilibrium constant representing the CO2 hydration reaction; , , , , Representing H2CO3 and HCO3 respectively - H2S, HS - Thermodynamic equilibrium constant of the dissociation equilibrium reaction with H2O; a i The activity level of species i; γ i The activity coefficient representing species i; C i The concentration of species i; λ i_c The binary interaction parameter representing species i and cation c in solution; λ i_a The binary interaction parameter representing species i and anion a in solution; ζ i_c_a The ternary interaction parameters between species i and cations c and anions a in the solution; A and B are characteristic constants of the solution; I is the ion strength of the solution; z i charge number of the species i; r i ionic radius of the species i, pm; e0is the vacuum permittivity; e is the relative permittivity of the solution; F is the Faraday constant; T represents the temperature, K; R represents the gas constant.

6. The high temperature high pressure supercritical CO2-H2S-Cl of claim 1 - A method for predicting corrosion of carbon steel in an environment, characterized by The specific process of S3 is as follows: based on the water chemical model established in step S2, the equilibrium concentrations of various species in the salt solution are obtained, and the equilibrium potentials of the anodic reaction and the cathodic reaction that may occur in the electrochemical corrosion process of carbon steel are calculated by using the Nernst equation; then the equilibrium potentials of each electrode reaction are compared with the corrosion potential obtained by experimental test, and the electrode reaction process occurring on the surface of carbon steel is judged; the supercritical CO2-H2S-Cl - Electrochemical corrosion thermodynamic model in environment.

7. The high temperature high pressure supercritical CO2-H2S-Cl of claim 6 - A method for predicting corrosion of carbon steel in an environment, characterized by The electrochemical corrosion thermodynamic model comprises the following formula: ； ； ； ； ； ； ； ； wherein , , , , and are the equilibrium electrode potentials of the reactions, respectively; represents the standard equilibrium electrode potential of reaction i; F represents Faraday's constant; n represents the number of charges of reaction i; G represents Gibbs free energy; and G represents Gibbs free energy of reactants and products, respectively.

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