Method for testing the effect of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well pipe

Abstract

This invention belongs to the field of stress corrosion performance testing technology for oil well pipes, and particularly relates to a testing method for the influence of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well pipes. Slow strain rate tensile tests are conducted in hydrogen sulfide and nitrogen environments respectively to determine the degree of damage to the mechanical properties of the oil well pipe caused by the hydrogen sulfide environment. Potentiodynamic polarization curves of the oil well pipe are tested using slow and fast rate scans respectively, and the corrosion potential V is determined. s ~V f The potential range between hydrogen and anodic dissolution coupling effects is defined. Constant potential slow tensile tests are performed on the oil well tubing under acidic conditions. Based on the degree of damage to the mechanical properties of the oil well tubing caused by the hydrogen sulfide environment, combined with the degree of damage to the mechanical properties of the oil well tubing caused by the anodic dissolution mechanism and the hydrogen-induced cracking mechanism, the influence of the coupling effect of anodic dissolution and hydrogen-induced cracking on the stress corrosion fracture of the oil well tubing in the hydrogen sulfide environment is determined. The advantages are: simple operation and accurate measurement results.

Description

Technical Field

[0001] This invention belongs to the field of oil well pipe stress corrosion performance testing technology, and particularly relates to a test method for the effect of hydrogen and anodic dissolution coupling on oil well pipe stress corrosion fracture. Background Technology

[0002] Stress corrosion cracking (SCC) refers to the phenomenon where metallic materials subjected to tensile stress in certain media experience delayed cracking or delayed fracture due to the synergistic effect of the corrosive medium and stress. It is one of the most common and most damaging forms of corrosion failure. In recent years, with the exploration and development of oil and gas wells in ultra-deep, ultra-high temperature, and ultra-high corrosive environments, the operating conditions of oil and gas wells generally exhibit characteristics such as "high temperature, high pressure, high CO2, high H2S, and high Cl-". - The characteristics of "high mineralization" and these complex and harsh working conditions, coupled with special operating 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 well conditions containing hydrogen sulfide gas, sulfur-resistant oil well tubing needs to withstand the combined effects of tensile stress and corrosion, ultimately leading to hydrogen sulfide stress corrosion cracking (HSC). The mechanisms mainly include anodic dissolution, hydrogen-induced cracking, and a mixed type resulting from the synergistic effect of anodic dissolution and hydrogen-induced cracking. In other words, oil well tubing fracture is usually the result of corrosion alone, hydrogen, or a coupling effect of both. Currently, 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 tubing. However, the constant strain method and constant load method can only provide information on failure and non-failure of the specimens, and cannot quantitatively evaluate the sulfur sulfide stress corrosion resistance or provide stress corrosion sensitivity data. These methods require combination with other experimental techniques, extending the testing cycle or requiring the purchase of new equipment, resulting in high costs.

[0004] Currently, stress corrosion susceptibility is generally used to assess the degree of hydrogen sulfide stress corrosion cracking (HSCCC) in oil well tubing. The HSCCC of oil well tubing consists of three parts: anodic dissolution, hydrogen entering the sample, and the coupling effect of hydrogen and anodic dissolution. Typically, slow strain rate tensile tests are used to obtain the HSCCC of oil well tubing. The test results represent the sum of the three components and do not accurately reflect the actual contribution of any single component. Especially in hydrogen sulfide environments, the HSCCC of oil well tubing is controlled not only by hydrogen and anodic dissolution but also by their coupling effect, i.e., the contribution rate of the hydrogen-anodic dissolution coupling to the HSCCC of oil well tubing.

[0005] To accurately and quickly evaluate the hydrogen sulfide stress corrosion resistance of oil well tubing, it is necessary to accurately calculate the contribution rate of hydrogen acting alone and the contribution rate of anodic dissolution, and then calculate the degree of influence of anodic dissolution and hydrogen coupling on the stress corrosion fracture of oil well tubing. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a test method for the influence of hydrogen and anodic dissolution coupling on stress corrosion fracture of oil well pipes, accurately evaluate the hydrogen sulfide stress corrosion resistance of oil well pipes, and calculate the contribution rate of the coupling effect of anodic dissolution and hydrogen-induced cracking in the hydrogen sulfide environment to stress corrosion fracture.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A test method for the effect of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well tubing includes:

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] Ψ=(S0-S1) / S0×100% (1)

[0016] 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.

[0017] 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.

[0018]

[0019] 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.

[0020] During the potentiodynamic polarization curve test, the test solution was a 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.

[0021] 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.

[0022] 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.

[0023] 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:

[0024]

[0025] 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.

[0026] 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.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention combines an electrochemical workstation and a slow strain rate tensile testing device. By using fast and slow sweep potential polarization curves, the potential range of the stress corrosion susceptibility region is determined. Through slow strain rate tensile tests at a constant potential, the susceptibility factors for hydrogen sulfide stress corrosion fracture (SSC) caused by anodic dissolution and hydrogen-induced cracking are measured separately. Furthermore, the contribution rate of the coupling effect between these two factors to the stress corrosion fracture of oil well tubing is calculated, providing a theoretical basis for improving the SSC resistance of oil well tubing. The method of this invention is simple to operate and yields accurate measurement results. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the dimensions of the slow-tensioned specimen before and after.

[0030] Figure 2 This is a fast and slow sweep potential polarization curve of an oil well tubing sample in a 5% NaCl solution.

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

[0032] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0033] Test methods for the influence of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well tubing include:

[0034] 1) Using a CORTEST slow strain rate tensile testing machine (USA), slow strain rate tensile (SSRT) tests were conducted on oil well pipe specimens in hydrogen sulfide and nitrogen atmospheres, respectively. Specimen dimensions are shown in [reference needed]. Figure 1 Before the test, the sample was soaked in 1000... # After sanding to a bright finish, clean with acetone and anhydrous ethanol respectively, and dry with cold air. After installing the sample, apply a 200 kgf load to eliminate clearances in the reduction gears, clamps, etc., initially according to 1×10... -4 The strain rate was rapidly preloaded to 80% of the yield strength of the well pipe specimen at a strain rate of mm / s, with a load of 2000±10 kgf. After stabilization, the strain was increased by 5×10 mm / s. -6 Slow tensile tests were conducted at a strain rate of mm / s until the specimen broke. The stress-strain curves and mechanical property parameters of the specimens in the two environments were recorded. The reduction of area of ​​the oil well pipe specimens in the hydrogen sulfide environment and the nitrogen environment were calculated according to Equation (1), and the values ​​were 7.06% and 72.76%, respectively. The stress corrosion susceptibility factor of the oil well pipe specimens in the hydrogen sulfide environment was calculated according to Equation (2). The sensitivity factor is 90.30%. This sensitivity factor is the total effect of anodic dissolution (AD), cathodic reaction hydrogen permeation (i.e. hydrogen embrittlement, HE) in the hydrogen sulfide environment, and the coupling effect of the two on the hydrogen sulfide stress corrosion cracking (SSC) of the sample. It is the total stress corrosion cracking sensitivity in the hydrogen sulfide environment, which characterizes the stress corrosion cracking sensitivity of the sample in the hydrogen sulfide environment.

[0035] 2) In a 5% NaCl solution, the oil well tubing sample was tested using a fast and slow sweep potentiodynamic polarization curve test with an electrochemical workstation, such as... Figure 2 As shown, determine V s The value is -681mV (relative to a saturated calomel electrode, the same below), determine V f The value is -730mV, while the potential range of -730mV to -681mV is the region of mixed effects of anodic dissolution and hydrogen embrittlement.

[0036] 3) In V s Potential and V f Constant potential slow tensile tests were performed on the oil well tubing to obtain experimental results and stress-strain curves. The extent of damage to the mechanical properties of the oil well tubing caused by anodic dissolution and hydrogen-induced cracking mechanisms was determined, and the corresponding stress corrosion susceptibility factors were obtained. The specific methods are as follows:

[0037] In the constant potential slow tensile test, the corrosive medium was a 5% NaCl solution, a high temperature and high pressure reference electrode was used, and the cathode hydrogen charging potential was set to -730mV. Initially, a 1×10⁻⁶ ohmmeter was used.-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. Inversely proportional to the pH value, the influence of anodic dissolution and hydrogen coupling on hydrogen sulfide stress corrosion cracking increases.

[0045] This invention simulates the actual service environment of sulfur-resistant oil well pipes. First, it calculates the stress corrosion cracking susceptibility factor, then further analyzes the stress corrosion performance of the oil well pipes, elucidating the mechanism of stress corrosion and providing a theoretical basis for improving the SSCC resistance of oil well pipes. Finally, it predicts the stress corrosion performance and service life of sulfur-resistant oil well pipes under actual service conditions, achieving safe and stable oil and gas field extraction.

Claims

1. A method of testing the effect of hydrogen and anodic dissolution coupling on stress corrosion cracking of oil well pipe, 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) Slow rate scanning and fast rate scanning are respectively used for the oil well pipe to test the dynamic potential polarization curve, to determine the potential range of stress corrosion sensitivity area, the maximum value of corrosion potential V s is the anodic dissolution single action starting potential, the minimum value of corrosion potential V f is the hydrogen induced cracking single action starting potential, the corrosion potential V s f between them is the potential interval of hydrogen induced cracking and anodic dissolution coupling​ 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 formula (2), Ψ a and Ψ b are the cross-sectional shrinkages of the test piece 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 is first preloaded to 80% of the yield strength value of the oil well pipe sample, and then starts at a strain rate of 5x10 -6 mm / s. The strain rate of the preloading is 1x10 -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 stretching test is a slow strain rate tensile test under a constant potential, and is first preloaded to 80% of the yield strength value of the oil well pipe sample, and then starts at a strain rate of 5x10 -6 mm / s, and the strain rate of the preloading is 1x10 -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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