Method for predicting corrosion of carbon steel in high-temperature and high-pressure supercritical CO2-H2S-Cl <-> environment

Abstract

The invention provides a corrosion prediction method for carbon steel in a high-temperature and high-pressure supercritical CO2-H2S-Cl <-> environment. The corrosion prediction method comprises the following steps: firstly, establishing a solubility model of supercritical CO2-H2S; establishing a hydrochemical model on the basis of the solubility model; establishing an electrochemical corrosion thermodynamic model; establishing an electrochemical corrosion kinetic model; through the model, the corrosion rate and the polarization curve of the carbon steel in the high-temperature and high-pressure supercritical CO2-H2S-Cl <-> environment are obtained. According to the method, the influence rule of the environmental condition change on the water phase chemical characteristics can be easily found, and guidance is provided for corrosion allowance design and operation maintenance of oil and gas pipes.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion protection in oil and gas fields, and specifically relates to a method for predicting the corrosion of carbon steel in a high-temperature, high-pressure, supercritical CO 2 -H 2 S-Cl - environment. Background Art

[0002] Currently, for the corrosion prediction of carbon steel in a CO 2 and H 2 S environment, some scholars have established some models, including empirical models, semi-empirical models and mechanism models. Among them, the empirical models and semi-empirical models are obtained by fitting laboratory data and are only applicable to specific environments. When the corrosion environment becomes more complex, they become no longer applicable. The mechanism model is based on corrosion thermodynamics and kinetics theories and has stronger extrapolation ability. However, the current CO 2 -H 2 S corrosion prediction mechanism model can only be applied to a low-pressure CO 2 and H 2 S environment. This is because Henry's law is used in the hydrochemical calculation, and when this method is applied to a high-pressure and supercritical CO 2 -H 2 S environment, the solubility of CO 2 and H 2 S in water will be seriously overestimated, resulting in the corrosion rate prediction result being too conservative and causing unnecessary economic investment. Therefore, for the problem of predicting the corrosion of carbon steel in a supercritical CO 2 -H 2 S environment, it is necessary to use the gas state equation, gas equilibrium constant and gas mixing principle applicable to the high-pressure system to replace Henry's law in order to calculate the solubility of supercritical CO 2 and H 2 S in water more accurately, so that the corrosion prediction result is closer to the actual situation. Summary of the Invention

[0003] The object of the present invention is to provide a method for predicting the corrosion of carbon steel in a high-temperature, high-pressure, supercritical CO 2 -H 2 S-Cl - environment. The model established by this method can be used to predict the corrosion rate and polarization curve of carbon steel in a supercritical CO 2 -H 2 S-Cl - environment.

[0004] The present invention is achieved through the following technical solutions:

[0005] High-temperature, high-pressure, supercritical CO2 -H 2 S-Cl - A method for predicting the corrosion of carbon steel in an environment, comprising the following steps:

[0006] S1. First, establish a solubility model of supercritical CO 2 -H 2 S, and the specific process is as follows: Based on the theory that the chemical potentials of substances in the gas-liquid two phases are equal at equilibrium, construct a multi-solubility mathematical equation for supercritical CO 2 -H 2 S-H 2 O. Then, use the Soave-Redlich-Kwong (SRK) equation of state and its mixing rules to calculate the fugacity coefficients of each substance, so as to determine the solubility of CO 2 and H 2 S in the aqueous phase. The solubility model mainly includes the following formula:

[0007]

[0008]

[0009] In the formula, 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, and the subscript i represents CO 2 , H 2 S and H 2 O 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 partial molar volume of pure component i between pressures P 0 -P, cm 3 ·mol -1 ; represents the mole fraction of H 2 O in the gas phase; and represent the mole fractions of CO 2 and H 2 S in water respectively; 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 .

[0010] S2. Based on the solubility model, establish a hydrochemical model. The specific process is as follows: Calculate the solubility of CO 2 and H 2 S in the aqueous solution according to the solubility model. Further, consider the influence of the salt concentration (i.e., the Cl - content) on the non-ideality of the solution. Characterize the influence law of the salt concentration on the solubility of CO 2 and H 2 S by introducing the Pitzer activity model. Then, according to the dissociation equilibrium process of CO 2 and H 2 S, the electroneutrality principle of the electrolyte, and the Debye-Hückel extended equation, solve the concentrations of the relevant substances in the salt solution. After the above process, a hydrochemical model of the supercritical CO 2 -H 2 S-Cl - environment is established, which mainly includes the following formulas:

[0011]

[0012] a i =γ i *C i (18)

[0013] lnγ i =Σc 2 λ i_c C c +Σa 2 λ i_a C a +Σ c Σ a ζ i_c_a C c C a (19)

[0014]

[0015]

[0016] In the formula, K hy represents the thermodynamic equilibrium constant of the CO 2 hydration reaction; K ca , K bi , K w respectively represent the thermodynamic equilibrium constants of the dissociation equilibrium reactions of H 2 CO 3 , HCO 3 - , H 2 S, HS - and H 2 O; ai represents the activity of species i; γ i represents the activity coefficient of species i; C i represents the concentration of species i; λ i_c represents the binary interaction parameter between species i and cation c in the solution; λ i_c represents the binary interaction parameter between species i and anion a in the solution; ζ i_c_a represents the ternary interaction parameter between species i and cation c and anion a in the solution; A and B are characteristic constants of the solution; I is the ionic strength of the solution; z i represents the charge number of substance i; r i represents the ionic radius of substance i, pm; ∈ 0 is the vacuum permittivity; ∈ is the relative permittivity of the solution; F is the Faraday constant; T k represents the temperature, K; R represents the gas constant.

[0017] S3. Establish an electrochemical corrosion thermodynamics 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, and use the Nernst equation to calculate the equilibrium potentials of the anodic reaction and cathodic reaction that may occur during the electrochemical corrosion of carbon steel. Then compare the equilibrium potentials of each electrode reaction with the corrosion potential obtained from experimental tests to judge the electrode reaction process occurring on the surface of carbon steel. Supercritical CO 2 -H 2 S-Cl - The electrochemical corrosion thermodynamics model in the environment mainly includes the following formulas:

[0018]

[0019]

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

[0021] S4. Establish an electrochemical corrosion kinetics model. The specific process is as follows: Based on the corrosion thermodynamics model established in step S3, determine the electrode reaction process occurring on the steel surface. Then, apply the electrochemical activation polarization kinetics equation and the mass transfer control equation to determine the electron transfer control current density and the limiting diffusion current density under diffusion control respectively, so as to calculate the current density of each electrode reaction. According to the mixed potential theory, couple each electrode reaction to determine the corrosion potential and corrosion current density of carbon steel, and then establish the electrochemical corrosion kinetics model of carbon steel in the supercritical CO 2 -H 2 S-Cl - environment. The main formulas included are as follows:

[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 the CO 2 environment; i 0，Fe represents the exchange current density of the anode in the CO 2 environment; E represents the electrode potential; E rev represents the equilibrium potential of the electrode; represents the anodic current density in the H 2 S environment; represents the standard exchange current density of the anode in the H 2 S environment; ΔH is the reaction enthalpy; T ref is the reference temperature, 293K; b a is the anodic Tafel slope; is the coverage rate of HS - ions on the steel surface; K 2 is the adsorption constant; i Fe is the anodic current density in the coexistence environment of CO 2 and H 2 S; i c，i is the current density of the cathode reaction i; i r，i is the charge transfer current density of the cathode reaction i; i L，iis the limiting diffusion current density of the cathodic reaction i; i 0，i is the exchange current density of the cathodic reaction i; b c is the cathodic Tafel slope; i 0，ref is the standard exchange current density of the cathodic reaction; D i is the diffusion constant of substance i; F is the Faraday constant; l is the diffusion layer thickness; μ ref is the reference viscosity of water; μ is the viscosity of water; is CO 2 is the forward reaction constant of the CO hydration reaction; i c is the cathodic current density; V corr represents the corrosion rate, mm / y; M Fe represents the molar mass of Fe; ρ Fe represents the density of Fe.

[0028] S5. Through the above model, the corrosion rate and polarization curve of carbon steel in high-temperature, high-pressure, supercritical CO 2 -H 2 S-Cl - environment are obtained.

[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 types of various species, the equilibrium concentrations of species, and pH, etc. in the salt solution, which helps to explore the influence law of environmental condition changes on the chemical characteristics of the aqueous phase.

[0031] (2) This method can be used to predict the corrosion rate of carbon steel in high-temperature, high-pressure, supercritical CO 2 -H 2 S-Cl - environment, provide guidance for the corrosion allowance design and operation and maintenance of oil and gas pipeline materials, and reduce economic investment.

[0032] (3) This method can also predict the polarization curve of carbon steel in high-temperature, high-pressure, supercritical CO 2 -H 2 S-Cl - environment, and can explore the electrochemical corrosion mechanism of carbon steel under different environmental conditions by decomposing the polarization curve and adjusting the kinetic parameters, which helps to take more reasonable corrosion protection measures for specific environments. Brief Description of the Drawings

[0033] Figure 1 is the flow chart of the calculation process of the method of this application.

[0034] Figure 2 is the comparison between the measured polarization curve of carbon steel in Example 1 of this application and the model prediction result.

[0035] Figure 3 Comparison between the measured polarization curve of carbon steel in Example 2 of this application and the model prediction results.

[0036] Figure 4 Comparison between the measured polarization curve of carbon steel in Example 3 of this application and the model prediction results.

[0037] Figure 5 Comparison between the measured polarization curve of carbon steel in Example 4 of this application and the model prediction results. Detailed implementation manners

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

[0039] Example 1

[0040] The specific experimental conditions involved in this example are 80°C and 8 MPa CO 2 , the solution is 3.5% NaCl, and the experimental material is 80SS carbon steel. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, as Figure 1 shown, the following steps will be taken to achieve it (note: the potentials involved hereinafter are all relative to the Ag / AgCl (0.1 M KCl) reference electrode):

[0041] S1. Calculate the concentrations of CO 2 and related species and the pH value of the solution under the above environmental conditions according to the water chemistry model. The results show that in this environment, the concentration of CO 2 in the salt solution is 0.7615 mol / L, the concentration of H 2 CO 3 is 0.001969 mol / L, the concentration of HCO 3 - is 0.00056 mol / L, the concentration of CO 3 2- is 5.156×10 -11 mol / L, and the corresponding solution pH value is 3.255.

[0042] S2. The anodic reaction occurring on the surface of carbon steel in the supercritical CO 2 -Cl - environment is the oxidation of Fe, and the cathodic reaction may be the reduction of H + , H 2 CO 3 , HCO 3 - and H 2 O. Therefore, according to the electrochemical corrosion thermodynamics model, the equilibrium potentials of the above electrode reactions in this environment were calculated. The results show that the equilibrium potential of H + reduction is -0.508 V, H2 CO 3 The reduction equilibrium potential is -0.618 V, HCO 3 - The reduction equilibrium potential is -0.449 V, H 2 The reduction equilibrium potential of O is -0.356 V, and the oxidation equilibrium potential of Fe is -0.86 V.

[0043] S3. In a high-temperature and high-pressure autoclave, an in-situ electrochemical test was carried out in a supercritical CO 2 -Cl - environment, and the corrosion potential and polarization curve of 80SS carbon steel were obtained. The test results show that the corrosion potential of carbon steel in this environment is -0.710 V. Obviously, the corrosion potentials are all lower than those of H + , H 2 CO 3 , HCO 3 - and H 2 O reduction equilibrium potential and higher than the oxidation equilibrium potential of Fe, which means that thermodynamically, the above electrode reactions can all occur during the corrosion process.

[0044] S4. According to the anodic and cathodic reactions on the surface of carbon steel determined in step S3, a corresponding electrochemical corrosion kinetics model was established. Then, the polarization curve in this environment was calculated according to the corrosion kinetics model and compared with the measured value, as Figure 2 shown. Obviously, the predicted polarization curve is in good agreement with the measured value. Furthermore, the corrosion rate of carbon steel was calculated to be 19.03 mm / y, and the measured value was 19.75 ± 1.21 mm / y. It can be seen that the two are very close, and the error is only 3.6%.

[0045] It can be determined therefrom that in the embodiment of the present invention, the corrosion rate of carbon steel, the predicted value and the measured value of the polarization curve are in good agreement, indicating that this method can be used for the corrosion prediction of carbon steel in the above environment.

[0046] Example 2

[0047] The specific experimental conditions involved in this example are 80 °C, 8 MPa CO 2 , 0.004 MPa H 2 S, the solution is 3.5% NaCl, and the experimental material is 80SS carbon steel. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, the following steps will be implemented (note: the potentials involved hereinafter are all relative to the Ag / AgCl (0.1 M KCl) reference electrode):

[0048] S1. Calculate CO under the above environmental conditions according to the hydrochemical model 2, H 2 The concentrations of S and related species, as well as the pH value of the solution. The results show that in this environment, the concentration of CO 2 in the salt solution is 0.7610 mol / L, and the concentration of H 2 CO 3 is 0.001968 mol / L, the concentration of HCO 3 - is 0.00056 mol / L, the concentration of CO 3 2- is 5.151×10 -11 mol / L, the concentration of H 2 S is 0.00098 mol / L, and the concentration of HS - is 5.307×10 -7 mol / L. The corresponding pH value of the solution is 3.255.

[0049] S2. The anodic reaction occurring on the surface of carbon steel in the supercritical CO 2 -H 2 S-Cl - environment is the oxidation of Fe, and the cathodic reaction may be the reduction of H + , H 2 CO 3 , HCO 3 - , H 2 S and H 2 O. Therefore, according to the electrochemical corrosion thermodynamics model, the equilibrium potentials of the above electrode reactions in this environment were calculated. The results show that the equilibrium potential of H + reduction is -0.508 V, the equilibrium potential of H 2 CO 3 reduction is -0.618 V, the equilibrium potential of HCO 3 - reduction is -0.449 V, the equilibrium potential of H 2 S reduction is -0.465 V, the equilibrium potential of H 2 O reduction is -0.356 V, and the equilibrium potential of Fe oxidation is -0.86 V.

[0050] S3. In a high-temperature and high-pressure autoclave, an in-situ electrochemical test was carried out in the supercritical CO 2 -H 2 S-Cl - environment, and the corrosion potential and polarization curve of 80SS carbon steel were obtained. The test results show that the corrosion potential of carbon steel in this environment is -0.739 V. Obviously, the corrosion potential is lower than that of H + , H 2 CO 3 , HCO3 - , H 2 S and H 2 The equilibrium potential of S and H O reduction is higher than that of Fe oxidation, which means that thermodynamically, the above electrode reactions can all occur during the corrosion process.

[0051] S4. According to the anodic and cathodic reactions on the carbon steel surface determined in step S3, establish the corresponding electrochemical corrosion kinetics model. Then, calculate the polarization curve in this environment according to the corrosion kinetics model and compare it with the measured value, as Figure 3 shown. Obviously, the predicted polarization curve is in good agreement with the measured value. Further, the corrosion rate of carbon steel was calculated to be 5.68 mm / y, and the measured value was 5.58 ± 0.48 mm / y. It can be seen that the two are very close, with an error of only 1.8%.

[0052] It can be determined therefrom that in the embodiment of the present invention, the corrosion rate of carbon steel, the predicted value and the measured value of the polarization curve are in good agreement, indicating that this method can be used for the corrosion prediction of carbon steel in the above environment.

[0053] Example 3

[0054] The specific experimental conditions involved in this example are 80°C, 8 MPa CO 2 , 0.016 MPa H 2 S, the solution is 3.5% NaCl, and the experimental material is 80SS carbon steel. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, it will be achieved through the following steps (note: the potentials involved hereinafter are all relative to the Ag / AgCl (0.1 M KCl) reference electrode):

[0055] S1. According to the water chemistry model, calculate the concentrations of CO 2 , H 2 S and related species and the pH value of the solution. The results show that in this environment, the concentration of CO 2 in the salt solution is 0.7596 mol / L, the concentration of H 2 CO 3 is 0.001965 mol / L, the concentration of HCO 3 - is 0.00055 mol / L, the concentration of CO 3 2- is 5.137×10 -11 mol / L, the concentration of H 2 S is 0.0039 mol / L, and the concentration of HS - is 2.118×10 -6 mol / L, and the corresponding solution pH value is 3.255.

[0056] S2. In the supercritical CO 2 -H 2 S-Cl - environment, the anodic reaction occurring on the surface of carbon steel is the oxidation of Fe, and the cathodic reaction may be the reduction of H + , H 2 CO 3 , HCO 3 - , H 2 S and H 2 O. Therefore, according to the electrochemical corrosion thermodynamics model, the equilibrium potentials of the above electrode reactions in this environment were calculated. The results show that the equilibrium potential of H + reduction is -0.508 V, the equilibrium potential of H 2 CO 3 reduction is -0.617 V, the equilibrium potential of HCO 3 - reduction is -0.449 V, the equilibrium potential of H 2 S reduction is -0.465 V, the equilibrium potential of H 2 O reduction is -0.356 V, and the equilibrium potential of Fe oxidation is -0.86 V.

[0057] S3. In a high-temperature and high-pressure reactor, an in-situ electrochemical test was carried out in the supercritical CO 2 -H 2 S-Cl - environment, and the corrosion potential and polarization curve of 80SS carbon steel were obtained. The test results show that the corrosion potential of carbon steel in this environment is -0.739 V. Obviously, the corrosion potential is lower than that of H + , H 2 CO 3 , HCO 3 - , H 2 S and H 2 O reduction equilibrium potential and higher than the equilibrium potential of Fe oxidation, which means that thermodynamically, the above electrode reactions can all occur during the corrosion process.

[0058] S4. According to the anodic and cathodic reactions determined on the surface of carbon steel in step S3, the corresponding electrochemical corrosion kinetics model was established. Then, the polarization curve in this environment was calculated according to the corrosion kinetics model and compared with the measured value, as Figure 4 shown. Obviously, the predicted polarization curve is in good agreement with the measured value. Further, the corrosion rate of carbon steel was calculated to be 6.92 mm / y, and the measured value is 7.15 ± 0.47 mm / y. It can be seen that the two are very close, and the error is only 3.2%.

[0059] It can be determined therefrom that, in the embodiments of the present invention, the corrosion rate of carbon steel, the predicted and measured values of the polarization curve are in good agreement, indicating that this method can be used for the corrosion prediction of carbon steel in the above environment.

[0060] Example 4

[0061] The specific experimental conditions involved in this example are 80 °C, 8 MPa CO 2 , 0.4 MPa H 2 S, the solution is 3.5% NaCl, and the experimental material is 80SS carbon steel. To predict the corrosion rate and polarization curve of 80SS carbon steel in the above environment, the following steps will be implemented (note: the potentials involved hereinafter are all relative to the Ag / AgCl (0.1 M KCl) reference electrode):

[0062] S1. Calculate the concentrations of CO 2 , H 2 S and related species, as well as the pH value of the solution according to the water chemistry model. The results show that in this environment, the concentration of CO 2 in the salt solution is 0.7192 mol / L, the concentration of H 2 CO 3 is 0.001860 mol / L, the concentration of HCO 3 - is 0.00052 mol / L, the concentration of CO 3 2- is 4.707×10 -11 mol / L, the concentration of H 2 S is 0.0923 mol / L, the concentration of HS - is 4.916×10 -5 mol / L, and the corresponding solution pH value is 3.248.

[0063] S2. The anodic reaction occurring on the surface of carbon steel in the supercritical CO 2 -H 2 S-Cl - environment is the oxidation of Fe, and the cathodic reaction may be the reduction of H + , H 2 CO 3 , HCO 3 - , H 2 S and H 2 O. Therefore, according to the electrochemical corrosion thermodynamics model, the equilibrium potentials of the above electrode reactions in this environment were calculated. The results show that the equilibrium potential of H + reduction is -0.508 V, and the equilibrium potential of H 2 CO 3The reduced equilibrium potential is -0.617V, HCO 3 - The reduced equilibrium potential is -0.449V, H 2 The reduced equilibrium potential of S is -0.465V, H 2 The reduced equilibrium potential of O is -0.356V, and the oxidized equilibrium potential of Fe is -0.86V.

[0064] S3. In a high-temperature and high-pressure autoclave, an in-situ electrochemical test was carried out in a supercritical CO 2 -H 2 S-Cl - environment, and the corrosion potential and polarization curve of 80SS carbon steel were obtained. The test results show that the corrosion potential of carbon steel in this environment is -0.766V. Obviously, the corrosion potential is lower than that of H + , H 2 CO 3 , HCO 3 - , H 2 S, and H 2 O reduction equilibrium potential, and higher than the oxidized equilibrium potential of Fe, which means that thermodynamically, the above electrode reactions can all occur during the corrosion process.

[0065] S4. According to the anodic and cathodic reactions on the surface of carbon steel determined in step S3, a corresponding electrochemical corrosion kinetics model was established. Then, the polarization curve in this environment was calculated according to the corrosion kinetics model and compared with the measured value, as Figure 5 shown. Obviously, the predicted polarization curve is in good agreement with the measured value. Furthermore, the corrosion rate of carbon steel was calculated to be 4.38 mm / y, and the measured value was 4.61 ± 0.47 mm / y. It can be seen that the two are very close, and the error is only 5.0%.

[0066] It can be determined therefrom that in the embodiment of the present invention, the corrosion rate of carbon steel, the predicted and measured values of the polarization curve are in good agreement, indicating that this method can be used for predicting the corrosion of carbon steel in the above environment.

[0067] Through the above 4 examples, it can be determined that this method can be used to predict the corrosion rate and polarization curve of carbon steel in a high-temperature and high-pressure supercritical CO 2 -H 2 S-Cl - environment. In addition, by comparing 4 groups of examples, the influence law of H 2 S change on the aqueous phase chemical characteristics of the supercritical CO 2 -H 2 S-Cl - environment can be determined.

Claims

1. High temperature and high pressure supercritical CO2-H2S-Cl - A method for predicting corrosion of carbon steel in an environment, characterized in that: The following steps are involved: S1. First, establish the solubility model of supercritical CO2-H2S; S2. Establish a water chemistry model based on the solubility model; S3. Establishing the electrochemical corrosion thermodynamic model; S4. Establish an electrochemical corrosion kinetic model; S5. Through the above model, the carbon steel was obtained in the high temperature and high pressure supercritical CO2-H2S-Cl - Corrosion rate and polarization curve in environment.

2. The high temperature and high pressure supercritical CO2-H2S-Cl according to claim 1 - A method for predicting corrosion of carbon steel in an environment, characterized in that: The specific process of S1 is as follows: Based on the theory of equal chemical potential of equilibrium substances in gas and liquid phases, a mathematical equation of supercritical CO2-H2S-H2O multi-mutual solubility is constructed; then the Soave-Redlich-Kwong state equation and its mixing principle are used to calculate the fugacity coefficient of each substance, thereby determining the solubility of CO2 and H2S in the aqueous phase under different environmental conditions.

3. The high temperature and high pressure supercritical CO2-H2S-Cl according to claim 2 - A method for predicting corrosion of carbon steel in an environment, characterized in that: The solubility model contains the following equation: In the formula, K i is the true equilibrium constant, f i is the fugacity of the gas, a i is the activity of the liquid component, the subscript i represents CO2, H2S and H2O respectively; P is the system pressure, MPa; P 0 is the standard pressure, 0.1MPa; T is the temperature, K; R is the ideal gas constant; is the pure component i at pressure P 0 Average partial molar volume between -P, cm 3 ·mol -1 ; represents the mole fraction of H2O in the gas phase; and Represent the mole fractions of CO2 and H2S in water respectively; 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 attraction and repulsion between molecules, 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 and high pressure supercritical CO2-H2S-Cl according to claim 1 - A method for predicting corrosion of carbon steel in an environment, characterized in that: The specific process of S2 is as follows: The solubility of CO2 and H2S in aqueous solution was calculated based on the solubility model, and the Pitzer activity model was introduced to characterize the influence of salt concentration on the solubility of CO2 and H2S. Then, based on the dissociation equilibrium process of CO2 and H2S, the principle of electrolyte neutrality and the Debye-Huckel extended equation, the concentration of related substances in the salt solution was solved, and the supercritical CO2-H2S-Cl - Water chemistry model of the environment.

5. The high temperature and high pressure supercritical CO2-H2S-Cl according to claim 4 - A method for predicting corrosion of carbon steel in an environment, characterized in that: The water chemistry model contains the following equations: a i =c i *C i (18) lnγ i =∑ c 2 min i_c C c +∑ a a2l i_a C a +∑ c ∑ a g i_c_a C c C a (19) In the formula, K hy represents the thermodynamic equilibrium constant of CO2 hydration reaction; K ca , K bi , K w Represent H2CO3, HCO3 - , H2S, HS - The thermodynamic equilibrium constant for the dissociation equilibrium reaction with H2O; a i represents the activity of species i; γ i represents the activity coefficient of species i; C i represents the concentration of species i; λ i_c represents the binary interaction parameter between species i and cation c in solution; λ i_c represents the binary interaction parameter between species i and anion a in solution; ζ i_c_a represents the ternary interaction parameter between species i and cation c and anion a in solution; A and B are characteristic constants of the solution; I is the ionic strength of the solution; z i represents the charge number of substance i; r i represents the ionic radius of substance i, pm; ∈0 is the dielectric constant of vacuum; ∈ is the relative dielectric constant of the solution; F is the Faraday constant; T k represents temperature, K; R represents the gas constant.

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

7. The high temperature and high pressure supercritical CO2-H2S-Cl according to claim 6 - A method for predicting corrosion of carbon steel in an environment, characterized in that: The electrochemical corrosion thermodynamic model contains the following formula: In the formula, and are the equilibrium electrode potentials of reactions (26)-(31), respectively; represents the standard equilibrium electrode potential of reaction i; F represents the Faraday constant; n represents the charge number of reaction i; ΔG represents the Gibbs free energy; and represent the Gibbs free energy of reactants and products, respectively.

8. The high temperature and high pressure supercritical CO2-H2S-Cl according to claim 1 - A method for predicting corrosion of carbon steel in an environment, characterized in that: 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 kinetic equation and the mass transfer control equation are applied to respectively determine the electron transfer control current density and the diffusion control limiting diffusion current density, thereby calculating the current density of each electrode reaction; according to the mixed potential theory, each electrode reaction is coupled to determine the corrosion potential and corrosion current density of carbon steel, and then establish the supercritical CO2-H2S-Cl - Kinetic model of electrochemical corrosion of carbon steel in an environment.

9. The high temperature and high pressure supercritical CO2-H2S-Cl according to claim 8 - A method for predicting corrosion of carbon steel in an environment, characterized in that: The electrochemical corrosion kinetic model is as follows: l=-0.00005T 2 +0.03015T-4.144 (42) i Fe =i c (46) In the formula represents the anode current density in CO2 environment; i 0，Fe represents the exchange current density of the anode in the CO2 environment; E represents the electrode potential; E rev represents the equilibrium potential of the electrode; represents the anode current density in H2S environment; represents the standard exchange current density of the anode in H2S environment; ΔH is the reaction temperature; T ref is the reference temperature, 293K; b a is the anodic Tafel slope; For HS - The coverage of ions on the steel surface; K2 is the adsorption constant; i Fe is the anode current density in the coexistence environment of CO2 and H2S; i c，i is the current density of cathode reaction i; i r，i is the charge transfer current density of cathode reaction i; i L，i is the limiting diffusion current density of cathode reaction i; i 0，i is the exchange current density of cathode reaction i; b c is the cathode Tafel slope; i 0，ref is the standard exchange current density of the cathode reaction; D i is the diffusion constant of substance i; F is the Faraday constant; l is the thickness of the diffusion layer; μ ref is the reference viscosity of water; μ is the viscosity of water; is the forward reaction constant of CO2 hydration reaction; i c is the cathode current density; V corr Represents the corrosion rate, mm / y; M Fe represents the molar mass of Fe; ρ Fe Represents the density of Fe.

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