Method for testing influence of hydrogen and anode dissolution coupling on stress corrosion fracture of oil well pipe

Abstract

The invention belongs to the technical field of oil well pipe stress corrosion performance detection, and particularly relates to a method for testing the influence of hydrogen and anode dissolution coupling on oil well pipe stress corrosion fracture, which comprises the following steps: respectively carrying out slow strain rate tensile tests in a hydrogen sulfide environment and a nitrogen environment to determine the damage degree of the hydrogen sulfide environment to the mechanical properties of an oil well pipe; carrying out potentiodynamic polarization curve testing on the oil well pipe by adopting slow-rate scanning and fast-rate scanning respectively, wherein the space between corrosion potentials Vs-Vf is the potential interval of the hydrogen and anode dissolution coupling effect; respectively carrying out constant potential slow stretching test on the oil well pipe in an acid environment; according to the damage degree of the hydrogen sulfide environment to the mechanical property of the oil well pipe, the influence degree of the coupling effect of anode dissolution and hydrogen induced cracking in the hydrogen sulfide environment to the stress corrosion fracture of the oil well pipe is determined by combining the damage degrees of the anode dissolution mechanism and the hydrogen induced cracking mechanism to the mechanical property of the oil well pipe. The device has the advantages of simplicity in operation and accurate measurement result.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of stress corrosion performance detection of oil well pipes, and particularly relates to a test method for the influence of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well pipes. BACKGROUND

[0002] Stress corrosion cracking (SCC) refers to a phenomenon that a metal material under the action of tensile stress produces lagging cracking or lagging fracture in some specific medium due to the synergistic effect of the corrosion medium and the stress, and is one of the most common and most harmful corrosion failure forms. In recent years, with the exploration and development of super-deep, super-high temperature, super-high corrosion harsh environment oil and gas wells, the working conditions of oil and gas wells generally have the characteristics of "high temperature, high pressure, high CO2, high H2S, high Cl - , high salinity", and these complex and harsh working conditions combined with special operation processes lead to stress corrosion failure of sulfur-resistant oil well pipes, which seriously affects the normal production and operation of oil and gas fields.

[0003] In the well conditions containing hydrogen sulfide gas, the sulfur-resistant oil well pipe needs to withstand the combined action of tension and corrosion and other factors, and finally hydrogen sulfide stress corrosion cracking occurs, and its mechanism mainly includes anodic dissolution type, hydrogen-induced cracking type, and mixed type of anodic dissolution and hydrogen-induced cracking synergistic effect, that is, the fracture of the oil well pipe is usually the result of the corrosion alone, hydrogen or the coupling of the two. At present, constant strain method, constant load method and slow strain rate tensile method (SSRT) are commonly used to study the hydrogen sulfide stress corrosion resistance of oil well pipes. Among them, the evaluation sample of the constant strain method and the constant load method can only give the information of failure and non-failure, and cannot quantitatively evaluate the sulfur stress corrosion resistance, and cannot provide stress corrosion sensitivity data, which needs to be combined with other experimental methods, prolonging the test period or requiring the purchase of new equipment, and the cost is high.

[0004] At present, the stress corrosion sensitivity is generally used to evaluate the degree of hydrogen sulfide stress corrosion cracking of oil well pipes, and the stress corrosion sensitivity of oil well pipes is composed of three parts, one is caused by anodic dissolution, the second is caused by hydrogen entering the sample, and the third is caused by the coupling of hydrogen and anodic dissolution. Under normal circumstances, the slow strain rate tensile test is used in the test to obtain the hydrogen sulfide stress corrosion sensitivity of the oil well pipe, and the test result is the sum of the stress corrosion sensitivity of the above three parts, and the actual contribution degree of a certain part cannot be obtained. Especially in the hydrogen sulfide environment, the stress corrosion fracture of the oil well pipe is not only controlled by hydrogen and anodic dissolution, but also by the coupling of the two, that is, the contribution rate of hydrogen and anodic dissolution coupling to the stress corrosion fracture of the oil well pipe.

[0005] In order to accurately and quickly evaluate the hydrogen sulfide stress corrosion resistance of oil well pipe, the contribution rate of hydrogen alone and the contribution rate of anodic dissolution are respectively calculated accurately, and then the influence degree of anodic dissolution and hydrogen coupling on stress corrosion cracking of the oil well pipe is calculated. SUMMARY

[0006] To overcome the shortcomings of the prior art, the purpose of the present application is to provide a test method for the influence of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well pipe, accurately evaluate the hydrogen sulfide stress corrosion resistance of oil well pipe, and calculate the contribution rate of anodic dissolution and hydrogen induced cracking coupling on stress corrosion cracking in a hydrogen sulfide environment.

[0007] To achieve the above purpose, the present application realizes the following technical solutions:

[0008] A test method for the influence of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well pipe, comprising:

[0009] 1) Slow strain rate tensile test is carried out in a hydrogen sulfide environment and a nitrogen environment respectively, stress-strain curves of the oil well pipe samples in the two environments are obtained, the damage degree of the hydrogen sulfide environment on the mechanical properties of the oil well pipe is determined, and a stress corrosion sensitivity factor is obtained;

[0010] 2) Dynamic potential polarization curve test is carried out on the oil well pipe by using slow rate scanning and fast rate scanning respectively, the potential range of the stress corrosion sensitivity area is determined, the maximum value V s of the corrosion potential is the starting potential of anodic dissolution alone, the minimum value V f of the corrosion potential is the starting potential of hydrogen induced cracking alone, and the potential interval between the corrosion potential V s and V f is the potential interval of hydrogen induced cracking and anodic dissolution coupling;

[0011] 3) Constant potential slow tensile test is carried out on the oil well pipe in the hydrogen sulfide environment at the starting potential of anodic dissolution alone and the starting potential of hydrogen induced cracking alone respectively, test results and stress-strain curves are obtained, the damage degrees of anodic dissolution and hydrogen induced cracking on the mechanical properties of the oil well pipe are determined respectively, and corresponding stress corrosion sensitivity factors are obtained;

[0012] 4) According to the damage degree of the hydrogen sulfide environment on the mechanical properties of the oil well pipe, combined with the damage degrees of anodic dissolution and hydrogen induced cracking on the mechanical properties of the oil well pipe, the influence degree of hydrogen and anodic dissolution coupling on stress corrosion cracking of the oil well pipe in the hydrogen sulfide environment is determined.

[0013] The damage degree of the hydrogen sulfide environment on the mechanical property of the oil well pipe is determined by taking the tensile property parameter in the nitrogen environment as a benchmark, and combining the tensile property parameter in the hydrogen sulfide environment, so as to determine the stress corrosion cracking sensitivity of the oil well pipe sample in the hydrogen sulfide environment;

[0014] Wherein, the cross-sectional shrinkage rate of the sample is calculated based on the cross-sectional area of the oil well pipe sample before and after stretching:

[0015] Ψ = (S0-S1) / S0*100% (1)

[0016] In formula (1), Ψ is the cross-sectional shrinkage rate of the sample; S0 and S1 are the cross-sectional areas of the sample before and after fracture, respectively;

[0017] Based on the cross-sectional shrinkage rate of the sample in the nitrogen environment and the hydrogen sulfide environment, the stress corrosion sensitivity factor of the sample in the hydrogen sulfide environment is calculated , that is, is the influence of anodic dissolution, hydrogen induced cracking and coupling effect of the two on the stress corrosion cracking of the sample in the hydrogen sulfide environment:

[0018]

[0019] In formula (2), Ψ a and Ψ b are the cross-sectional shrinkage rates of the sample in the nitrogen and hydrogen sulfide environments, respectively.

[0020] In the process of the dynamic potential polarization curve test, the test solution is 5% NaCl solution, a three-electrode system is used, the reference electrode is saturated calomel electrode, the fast rate scanning speed is 1000-1200 mV / min, and the slow rate scanning speed is 5-10 mV / min.

[0021] In the slow strain rate tensile test, the sample is first preloaded at a fast rate to 80% of the yield strength value of the oil well pipe sample, and then started at a strain rate of 5*10 -6 mm / s, and the strain rate of the fast preloading is 1*10 -4 mm / s.

[0022] The constant potential slow tensile test is a slow strain rate tensile test under a constant potential, the sample is first preloaded at a fast rate to 80% of the yield strength value of the oil well pipe sample, and then started at a strain rate of 5*10 -6 mm / s, and the strain rate of the fast preloading is 1*10 -4 mm / s.

[0023] According to stress-strain curves and test results of nitrogen environment, hydrogen sulfide environment and constant potential slow tensile test, damage degrees of hydrogen induced cracking and anodic dissolution in hydrogen sulfide environment on mechanical properties of the oil well pipe sample are determined, and specific calculation methods are as follows:

[0024]

[0025] In formula (3), is a stress corrosion sensitivity factor of the sample in the hydrogen sulfide environment; is a stress corrosion sensitivity factor of the sample under the anodic dissolution single action starting potential; is a stress corrosion sensitivity factor of the sample under the hydrogen induced cracking single action starting potential; a=V f / V s ;C c is an influence degree of the coupling action of the anodic dissolution and hydrogen in the hydrogen sulfide environment on the hydrogen sulfide stress corrosion cracking of the oil well pipe sample;

[0026] The dynamic potential polarization curve test, the slow strain rate tensile test and the constant potential slow tensile test all adopt the test solution after oxygen removal by high-purity nitrogen.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] The present application combines the electrochemical workstation and the slow strain rate tensile equipment, determines the potential range of the stress corrosion sensitivity area through the fast and slow scanning dynamic potential polarization curve, tests the hydrogen sulfide stress corrosion cracking sensitivity factors of the anodic dissolution and the hydrogen induced cracking through the slow strain rate tensile test under the constant potential, further calculates the contribution rate of the coupling action of the two on the stress corrosion cracking of the oil well pipe, provides a theoretical basis for improving the SSC resistance of the oil well pipe, and the method is simple in operation and accurate in measurement result. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of sizes before and after the slow tensile sample.

[0030] Figure 2 is a fast and slow scanning dynamic potential polarization curve diagram of the oil well pipe sample in 5% NaCl solution.

[0031] Figure 3 is a stress-strain curve diagram of the oil well pipe sample under the nitrogen environment, the hydrogen sulfide environment, the hydrogen induced cracking potential and the anodic dissolution potential. DETAILED DESCRIPTION

[0032] The present application will be described in detail below in combination with the drawings of the specification, but it should be pointed out that the implementation of the present application is not limited to the following embodiments.

[0033] A test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well pipe, comprising:

[0034] 1) Using a CORTEST type slow strain rate tensile testing machine, slow strain rate tensile (SSRT) experiments are carried out on oil well pipe samples in a hydrogen sulfide environment and a nitrogen environment, respectively, and the size of the tensile sample is shown in Figure 1 . Before the test, the sample is polished with 1000 # grit sandpaper, then cleaned with acetone and anhydrous ethanol, and dried with cold air before use. After installing the sample, a 200 kgf load is applied to eliminate the gap of the reduction gear, clamp, etc., and the sample is preloaded at a strain rate of 1 x 10 -4 mm / s to 80% of the yield strength value of the oil well pipe sample, with a load of 2000 ± 10 kgf, and after stabilization, slow tensile test is carried out at a strain rate of 5 x 10 -6 mm / s until the sample is pulled apart, and the stress-strain curve and mechanical property parameters of the sample in the two environments are recorded, and the cross-sectional shrinkage rate of the oil well pipe sample in the hydrogen sulfide environment and the nitrogen environment is calculated according to formula (1), with values of 7.06% and 72.76%, respectively, and the stress corrosion sensitivity factor of the oil well pipe sample in the hydrogen sulfide environment is calculated according to formula (2) , which is 90.30%, and this sensitivity factor is the total effect of anodic dissolution (AD), cathodic reaction hydrogen permeation (i.e. hydrogen embrittlement, HE), and their coupling effect on the stress corrosion cracking (SSC) of the sample in the hydrogen sulfide environment, which is the total stress corrosion cracking sensitivity in the hydrogen sulfide environment, and characterizes the stress corrosion cracking sensitivity of the sample in the hydrogen sulfide environment.

[0035] 2) In a 5% NaCl solution, fast and slow potential polarization curve tests are carried out on the oil well pipe sample using an electrochemical workstation, as shown in Figure 2 , the V s value is determined to be -681 mV (relative to a saturated calomel electrode, the same below), and the V f value is determined to be -730 mV, and the potential -730 mV ~ -681 mV is the mixed action region of anodic dissolution and hydrogen embrittlement.

[0036] 3) Constant potential slow tensile tests are carried out on the oil well pipe at V s and V f potentials, respectively, to obtain test results and stress-strain curves, determine the damage degree of anodic dissolution mechanism and hydrogen induced cracking mechanism on the mechanical properties of the oil well pipe, and obtain the corresponding stress corrosion sensitivity factor. The specific method is as follows:

[0037] a In the constant potential slow tensile test, the corrosion medium is a 5% NaCl solution, a high temperature and high pressure reference electrode is used, the cathode hydrogen charging potential is set to -730 mV, and the sample is preloaded at a strain rate of 1 x 10-4 The strain rate was rapidly preloaded to 80% of the yield strength of the oil well pipe specimen at a strain rate of mm / s, with a load of 2000±10 kgf, and then subjected to 5×10 -6 The test was conducted at a strain rate of mm / s until the specimen broke, and the stress-strain curves and mechanical property parameters were recorded. The cracking potential V induced by nitrogen and hydrogen was compared. f Based on the slow tensile test results and mechanical property parameters, the cross-sectional reduction rate of the sample under cathodic hydrogen charging was calculated to be 18.05% according to equation (1). Based on the cross-sectional reduction rate of the sample in the nitrogen environment and equation (2), the degree of damage to the mechanical properties of the oil well pipe sample caused by hydrogen embrittlement under cathodic hydrogen charging in the hydrogen sulfide environment was calculated, i.e., the stress corrosion sensitivity factor. .

[0038] b. In step a above, change the setting of the cathode hydrogen charging potential to the setting of the anolyte dissolution potential to -681mV, and repeat step a. Compare the nitrogen environment and the anolyte dissolution potential V. s Based on the slow tensile test results and mechanical property parameters, the cross-sectional reduction rate of the sample at the anodic dissolution potential was calculated to be 56.19% according to equation (1). Based on the cross-sectional reduction rate of the sample in the nitrogen environment and equation (2), the degree of damage to the mechanical properties of the oil well pipe sample caused by anodic dissolution in the hydrogen sulfide environment, i.e., the stress corrosion susceptibility factor, can be calculated. .

[0039] Specifically, the influence of the coupling effect between hydrogen and anodic dissolution in the hydrogen sulfide environment on the hydrogen sulfide stress corrosion fracture of the oil well pipe sample is calculated using equation (3). c It is 2.42%.

[0040] Therefore, it can be seen that the stress corrosion cracking process of oil well pipe in the hydrogen sulfide environment is jointly controlled by anodic dissolution and hydrogen. The contribution rate of the coupling effect of the two to the stress corrosion cracking of hydrogen sulfide is only 2.42%, and the coupling effect accounts for a small proportion in the hydrogen sulfide environment.

[0041] In the above embodiments, the well tubing is a Cr and Mo-containing 110S sulfur-resistant well tubing, and the hydrogen sulfide environment is a 5% NaCl solution (pH=3) with hydrogen sulfide introduced into it. The slow tensile test specimens used in steps a and b are parallel specimens processed from the same seamless tube.

[0042] The test data under other hydrogen sulfide environments are as follows:

[0043]

[0044] hydrogen sulfide environment 110S oil well tubing exhibits a significant tendency for hydrogen-induced cracking, with pH value and stress corrosion susceptibility factors in hydrogen sulfide environments being relevant. The hydrogen coupled effect and the anodic dissolution effect on the hydrogen sulfide stress corrosion cracking increase with the increase of the pH value.

[0045] The application simulates the actual service environment of the anti-sulfur oil well pipe, firstly calculates a stress corrosion cracking sensitivity factor, then further analyzes the stress corrosion performance of the oil well pipe, analyzes the stress corrosion mechanism, provides a theoretical basis for improving the anti-SSCC performance of the oil well pipe. Finally, the stress corrosion performance and service life of the anti-sulfur oil well pipe under the actual service environment are predicted, and the safety and stability of the oil and gas field exploitation process are realized.

Claims

1. A test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well tubing, characterized in that, include: 1) Slow strain rate tensile tests were conducted in hydrogen sulfide and nitrogen environments to obtain stress-strain curves of oil well pipe samples in the two environments, determine the degree of damage to the mechanical properties of oil well pipe caused by hydrogen sulfide environment, and obtain stress corrosion susceptibility factor. 2) The potentiodynamic polarization curves of the oil well tubing were tested using both slow-rate and fast-rate scanning methods to determine the potential range of the stress corrosion sensitive region and the maximum corrosion potential V. s The minimum corrosion potential V is the initial potential of anodic dissolution acting alone. f The corrosion potential V is the initiation potential for hydrogen-induced cracking alone. s ~V f The potential range between these two points represents the coupling effect between hydrogen-induced cracking and anodic dissolution. During the potentiodynamic polarization curve test, the test solution was 5% NaCl solution, a three-electrode system was used, the reference electrode was a saturated calomel electrode, the fast rate scan rate was 1000~1200mV / min, and the slow rate scan rate was 5~10mV / min. 3) At the starting potential of anodic dissolution and the starting potential of hydrogen-induced cracking, constant potential slow tensile tests were conducted on the oil well pipe under hydrogen sulfide environment. The test results and stress-strain curves were obtained to determine the degree of damage to the mechanical properties of the oil well pipe caused by anodic dissolution and hydrogen-induced cracking, and to obtain the corresponding stress corrosion susceptibility factor. 4) Based on the degree of damage to the mechanical properties of oil well tubing caused by hydrogen sulfide environment, and combined with the degree of damage to the mechanical properties of oil well tubing caused by anodic dissolution and hydrogen-induced cracking, determine the degree of influence of the coupling effect of hydrogen and anodic dissolution in hydrogen sulfide environment on the stress corrosion fracture of oil well tubing. Based on the stress-strain curves and test results from nitrogen environment, hydrogen sulfide environment, and constant potential slow tensile testing, the degree of damage to the mechanical properties of oil well tubing samples caused by hydrogen-induced cracking and anodic dissolution in the hydrogen sulfide environment was determined. The specific calculation method is as follows: ； In equation (3), The stress corrosion susceptibility factor of the sample in a hydrogen sulfide environment; The stress corrosion susceptibility factor for the sample at the starting potential of anodic dissolution alone; The stress corrosion susceptibility factor of the sample at the hydrogen-induced cracking initiation potential alone; a=V f / V s C c The influence of the coupling effect of anodic dissolution and hydrogen in a hydrogen sulfide environment on the hydrogen sulfide stress corrosion fracture of oil well pipe samples is considered.

2. The test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well tubing according to claim 1, characterized in that, The degree of damage to the mechanical properties of oil well pipe in the hydrogen sulfide environment is determined by using the tensile properties in the nitrogen environment as a benchmark and combining them with the tensile properties in the hydrogen sulfide environment to determine the stress corrosion fracture susceptibility of the oil well pipe sample in the hydrogen sulfide environment. The area reduction ratio Ψ of the well tubing sample is calculated based on the cross-sectional area of ​​the sample before and after tensioning. Ψ=(S0-S1) / S0×100% (1); In equation (1), Ψ is the reduction of area of ​​the specimen; S0 and S1 are the cross-sectional areas of the gauge section before and after the specimen fractures, respectively. Based on the reduction of area of ​​the sample in nitrogen and hydrogen sulfide environments, the stress corrosion susceptibility factor of the sample in hydrogen sulfide environment was calculated. ,Right now The effects of anodic dissolution, hydrogen-induced cracking, and their coupling in a hydrogen sulfide environment on stress corrosion cracking of the samples are investigated. ； In equation (2), Ψ a and Ψ b The values ​​represent the reduction of area of ​​the sample in nitrogen and hydrogen sulfide environments, respectively.

3. The test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well tubing according to claim 1, characterized in that, The slow strain rate tensile test involves first rapidly preloading the oil well pipe specimen to 80% of its yield strength, then applying a 5×10⁻⁶ strain rate tensile load. -6 The strain rate starts at 1 mm / s, and the strain rate for rapid preloading is 1 × 10⁻⁶ mm / s. -4 mm / s.

4. The test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well tubing according to claim 1, characterized in that, The constant potential slow tensile test is a slow strain rate tensile test under a constant potential. First, the sample is rapidly preloaded to 80% of its yield strength, then subjected to a strain rate of 5 × 10⁻⁶. -6 The strain rate starts at 1 mm / s, and the strain rate for rapid preloading is 1 × 10⁻⁶ mm / s. -4 mm / s.

5. The test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well tubing according to claim 1, characterized in that, The potentiodynamic polarization curve test, slow strain rate tensile test, and constant potential slow tensile test all use a test solution after deoxygenation with high-purity nitrogen.

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