GB/T 47376-2026Full life cycle corrosion evaluation method for oil and gas well tubing strings (English PDF)

7.1 Class I Environmental Corrosion Test

7.1.1 Test Procedure The tubing or casing samples were subjected to corrosion tests sequentially in three test media. fresh acid, residual acid, and formation water. The placement of the samples in each medium... The order of extraction is shown in Table 2, and the experimental procedure diagram is shown in Figure 2. Table

2.Sequence of placing and removing samples in three test media environments Serial Number Medium Test Specimen After Test, Remove Specimen and Add New Specimen

7.1.2 Fresh Acid Environment Corrosion Test

7.1.2.1 Inject fresh acid solution into the high-temperature and high-pressure reactor without deoxygenation, and test the acid concentration or pH value of the solution.

7.1.2.2 Fix the samples from groups A, B, and C (3 parallel samples per group) as specified in Table 2 onto the annular sample holder of the high-temperature autoclave. The length of the sample should be parallel to the autoclave wall, and there should be a minimum distance of

3.0 mm between samples. Confirm sample installation. After completion, seal the high-temperature and high-pressure autoclave.

7.1.2.3 The heating rate of the high-temperature and high-pressure reactor should be controlled at 3°C/min~6°C/min. After reaching the predetermined test temperature, N2 is injected, and the pressure is increased to the pre-pressurized level. The total pressure of the test should be determined, and the specific time should be determined based on the actual working conditions on site or through consultation. The test cycle should preferably be 4 hours.

7.1.2.4 After the test, cool the high-temperature autoclave to room temperature, and take out the Group A samples in the order specified in Table 2 for use in tubing or casing. Analysis of the results of the fresh acid corrosion test.

7.1.2.5 Clean the samples from groups B and C with residual acid solution, blow them dry, and then place them in a drying oven under vacuum or inert gas protection. Store in a cool, dry place to prevent oxidation and contamination from contact with air.

7.1.2.6 Take a portion of the solution from the high-temperature autoclave and test the acid concentration or pH value of the solution.

7.1.2.7 Drain the residual liquid from the high-temperature and high-pressure reactor and thoroughly clean the reactor body.

7.1.3 Residual Acid Environmental Corrosion Test

7.1.3.1 Add the group D samples in the order shown in Table 2, and then fix them together with the group B and group C samples in the annular sample holder of the high-temperature and high-pressure reactor. Next, the residual acid environmental corrosion test was carried out. A pre-deoxygenated residual acid solution was injected into the high-temperature and high-pressure reactor, and the pH value of the solution was tested.

7.1.3.2 Introduce N2 into the high-temperature and high-pressure reactor at a flow rate of not less than 100 mL/min for deoxygenation, and the deoxygenation time shall not be less than 2 hours.

7.1.3.3 Heat to the predetermined temperature at the heating rate specified in 7.1.2.3, and inject CO2 and [other gases] according to the partial pressure of corrosive gases in the formation. H2S, N2 injected to the total test pressure, test cycle is the time of on-site residual acid backflow operation.

7.1.3.4 After the test, cool the high-temperature autoclave to room temperature, and take out the samples from groups B and D in the order shown in Table

2.The samples from group B are then used... Analysis of the results of the continuous corrosion test of oil tubing and casing with fresh acid and residual acid; Group D samples were used for oil tubing or casing after the residual acid corrosion test. Results analysis.

7.1.3.5 The C group samples were washed with formation aqueous solution, dried, and then stored in a drying oven under vacuum or inert gas protection. Avoid oxidation and contamination due to contact with air.

7.1.3.6 Test the pH value of the solution after the experiment.

7.1.4 Formation water environment corrosion test

7.1.4.1 Add the E group samples in the order shown in Table 2, and then fix them together with the C group samples on the annular sample holder of the high-temperature and high-pressure reactor. Further formation water environment corrosion tests were conducted by injecting pre-deoxygenated formation water solution into a high-temperature and high-pressure reactor and testing the pH value of the solution.

7.1.4.2 Introduce N2 into the high-temperature and high-pressure reactor to remove oxygen. The deoxygenation shall meet the requirements of 7.1.3.2.

7.1.4.3 Heat to the predetermined temperature at the heating rate specified in 7.1.2.3, and inject CO2 and [other gases] according to the partial pressure of corrosive gases in the formation. H2S, inject N2 to increase the pressure to the expected total test pressure, and the test time should be 7 days to 90 days.

7.1.4.4 After the test, cool the high-temperature autoclave to room temperature, and take out the oil pipe samples from groups C and E in the order shown in Table

2.Group C samples... Samples from group E are used for analyzing the results of continuous corrosion tests on tubing or casing subjected to fresh acid-residual acid-formation water. Analysis of the results of the corrosion test of the pipe through the formation water.

7.1.4.5 Test the pH value of the solution after the experiment.

7.2 Class II Environmental Corrosion Test

7.2.1 Inject pre-deoxygenated annular protective solution into the high-temperature and high-pressure reactor and test the pH value of the solution.

7.2.2 Introduce N2 into the high-temperature and high-pressure reactor to remove oxygen. The deoxygenation shall meet the requirements of 7.1.3.2.

7.2.3 Heat to the predetermined temperature at the heating rate specified in 7.1.2.3, inject N2, and pressurize to the expected total test pressure. The test time should be [time to be specified]. 7d~90d.

7.2.4 After the test, the high-temperature and high-pressure reactor was cooled to room temperature, and the samples were taken out for corrosion test result analysis.

7.2.5 Test the pH value of the solution after the experiment.

7.3 Class III Environmental Corrosion Test

7.3.1 Inject pre-deoxygenated formation simulation solution into the high-temperature and high-pressure reactor, test the pH value of the solution, and the sample installation shall meet the requirements of 7.1.2.2.

7.3.2 Introduce N2 into the high-temperature and high-pressure reactor to remove oxygen. The deoxygenation shall meet the requirements of 7.1.3.2.

7.3.3 Heat to the predetermined temperature at the heating rate specified in 7.1.2.3, ultimately reaching the operating temperature of the outer wall of the casing at different depths, and then inject. N2, pressurize to the total test pressure, and the test time should be 7 days to 90 days.

7.3.4 Test the pH value of the solution after the experiment.

7.4 Sample Post-treatment

7.4.1 After the test, the sample was rinsed with deionized water, dehydrated with anhydrous ethanol, and dried with cold air.

7.4.2 Remove corrosion products from the sample surface in accordance with GB/T 16545.

7.4.3 The sample after removing corrosion products was degreased with anhydrous ethanol and acetone, dried with cold air, and then weighed. The arithmetic mean of three consecutive weighings was taken. The average value is accurate to

0.1 mg. After weighing, the sample should be stored in a dry oven under vacuum or inert gas protection to avoid damage from contact with air. Oxidative pollution.

9.1 Evaluation of Class I Environmental Corrosion Test Results

9.1.1 The evaluation index of corrosion rate of carbon steel pipes in fresh acid (with added corrosion inhibitor) environment is shown in Table 3.

9.1.2 The evaluation indexes for the corrosion rate of carbon steel pipes in residual acid environment are shown in Table 4.

9.1.3 The evaluation indexes for corrosion rate in formation water are shown in Table 5.

9.2 Evaluation of Class II Environmental Corrosion Test Results The uniform corrosion rate in the annular protective fluid should not exceed

0.076 mm/a, and the maximum pitting rate should be less than

0.13 mm/a.

9.3 Evaluation of the results of the Class III environmental corrosion test The corrosion rate evaluation indexes in the formation simulation fluid are shown in Table 5.

10 Test Report The test report should include at least the following.

a) This document number;

b) Sample information;

c) Test conditions;

d) Raw experimental data, see Appendix B;

e) Test results.