An experimental method suitable for corrosion simulation evaluation of metal pipe string materials

Abstract

The present invention belongs to the technical field of oil and gas extraction, and relates to an experimental method suitable for corrosion simulation evaluation of metal pipe column materials. The test piece is connected to the upper and lower layers of the test piece fixture, and a liquid medium is injected into the alloy kettle cavity until the liquid medium completely immerses the lower test piece; the prepared supercritical CO2 and water mixture is respectively injected into the upper gas phase space and the lower liquid phase space in the alloy kettle cavity, and monitored, and the environment in the alloy kettle cavity is adjusted according to the monitoring results; after the experiment, the test piece is taken out for characterization testing to explore the corrosion mechanism. It solves the problem that the existing evaluation method is limited by the simulation conditions and does not carry out targeted classification research, and cannot accurately evaluate the relationship between the corrosion test results and the corrosion mechanism under different simulation conditions. The present invention meets the experimental needs of accurate evaluation of the safety performance of pipe column materials under supercritical CO2 conditions, in-depth research on the corrosion failure mechanism of pipe column materials, and reliable evaluation of the application effect of pipe column anti-corrosion measures.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploitation, and in particular relates to an experimental method suitable for simulating and evaluating corrosion of metal pipe column materials. Background Art

[0002] By utilizing the high density, low viscosity, strong diffusion and strong solubility characteristics of supercritical CO2 fluid, CO2 displacement is carried out in low-porosity, low-permeability and heterogeneous reservoirs, which can further improve the recovery rate compared with water injection. In the actual CO2 oil recovery process test, liquid CO2 is injected into the wellbore by a booster pump. As the formation temperature rises, the CO2 fluid reaches a supercritical state in a certain section of the wellbore. After being injected into the reservoir, it forms a miscible phase with the crude oil in the rock pores, and effectively displaces the oil by reducing the density and interfacial tension. However, in order to control the mobility ratio, increase the sweep coefficient of supercritical CO2, and delay the time to see gas, WAG water-gas alternation (i.e., water segment plug and Gas segment plugs are injected alternately). This process directly causes supercritical CO2 to contact and dissolve with the retained water in the formation to form a corrosion electrolytic cell, which produces electrochemical corrosion behavior on the metal pipe column. At the same time, because CO2 reaches the supercritical state, its solubility in the water phase, ion diffusion rate, and electrochemical reaction rate all increase with increasing pressure. Therefore, the critical CO2 / H2O system is more serious than the low partial pressure CO2 acid corrosion on metal pipes, causing metal pipe column corrosion perforation, stress corrosion cracking and other failure behaviors, which are easy to cause engineering associated problems such as gas channeling, directly affect safe production, and restrict the promotion and implementation of CO2 oil recovery technology. Therefore, in-depth research on the corrosion mechanism of pipe columns in different phases of CO2 / H2O environment has important engineering guidance significance for the formulation of anti-corrosion measures in the subsequent construction process.

[0003] During the CO2 flooding experiment, the CO2 fluid is not in a single phase, and the working conditions are complex and changeable: ① In the downhole working conditions, CO2, crude oil, and formation water form a mixed system of CO2 / H2O / crude oil under the action of miscibility and dissolution. The CO2 / H2O system itself is corrosive. At the same time, crude oil in some blocks is also corrosive due to the presence of sulfides or low acidity. Therefore, the CO2 / H2O / crude oil mixed system increases the complexity of its corrosion behavior on metal pipes; ② In the CO2 / H2O system, the solubility of CO2 in water changes dynamically with the ambient temperature and pressure. At the same time, the water content of the water phase in supercritical CO2 will also change, which results in different degrees of corrosion.

[0004] Harsh and complex wellbore conditions have put forward higher requirements for corrosion simulation experimental equipment and corrosion experimental methods. There are many studies on the corrosion behavior of CO2 acidic gas fields at home and abroad, and a large number of research results have been formed. However, there are fewer studies on the corrosion problems associated with the development of CO2 oil recovery technology in recent years, and there are even fewer applicable metal pipe string corrosion evaluation methods. The existing methods mostly use high-temperature and high-pressure autoclaves for weight loss simulation, which has the following problems:

[0005] (1) The corrosion behavior of metal pipe column materials in the simulated CO2 gas environment or the liquid environment of high-ore formation water has been simulated, and similar corrosion evaluation experiments of metal materials have been carried out in the high-temperature and high-pressure autoclave chamber to simulate a single-phase environmental medium. However, because the corrosion environment that the metal pipe column material is exposed to during CO2 oil recovery or CO2 fracturing is not a single-phase state, but a mixed system, the existing experimental equipment and experimental methods are not designed according to the actual working conditions, resulting in limited evaluation capabilities;

[0006] (2) During the construction of CO2 flooding or CO2 fracturing. CO2 will undergo a phase change as the formation temperature and pressure increase, especially after reaching the supercritical state, it will dissolve a portion of the liquid. At the same time, as the pressure and temperature change, the solubility will also change, which directly causes different effects on corrosion. Therefore, the corrosion macroscopic characteristics and action mechanisms of metal materials in different sections of the same operating wellbore are quite different. The existing experimental equipment and experimental methods have not carried out targeted classification research due to the limited simulation conditions;

[0007] (3) In order to study the effect of supercritical CO2 / H2O system on corrosion, it is necessary to study the corrosion effect of supercritical CO2 / H2O system (H2O-rich phase and CO2-rich phase) on metal materials separately. The existing experimental equipment and experimental methods cannot measure the solubility of supercritical CO2 in H2O and the solubility change of supercritical CO2 in H2O in real time, resulting in the inability to accurately evaluate the corrosion test results and the influence of corrosion mechanism under different working conditions. Summary of the invention

[0008] The experimental method for corrosion simulation evaluation of metal pipe column materials provided by the present invention aims to overcome the above-mentioned technical problems so as to meet various experimental requirements such as accurate evaluation of the safety performance of pipe column materials under supercritical CO2 conditions, in-depth research on the corrosion failure mechanism of pipe column materials, and reliable evaluation of the application effect of pipe column anti-corrosion measures.

[0009] To this end, the present invention provides an experimental method suitable for simulating and evaluating corrosion of metal pipe materials, comprising the following steps:

[0010] 1) preparing a test piece, a test piece fixture and a liquid medium; the test piece fixture adopts a double-layer concentric circle fixture, the double-layer concentric circle fixture comprises an upper fixture and a lower fixture, the upper fixture is connected to the lower fixture, the test piece is connected to the upper fixture and the lower fixture, and the test piece fixture is located in the alloy kettle cavity; injecting the liquid medium into the alloy kettle cavity until the liquid medium completely immerses the test piece in the lower fixture;

[0011] 2) Check the air tightness of the alloy kettle cavity and discharge all the O2 in the alloy kettle cavity;

[0012] 3) preparing a mixture of supercritical CO2 and water;

[0013] 4) Injecting the prepared supercritical CO2 and water mixture into the upper gas phase space and the lower liquid phase space in the alloy kettle cavity respectively, and monitoring the gas phase medium in the upper gas phase space and the liquid phase medium in the lower liquid phase space in the alloy kettle cavity, and adjusting the environment in the alloy kettle cavity according to the monitoring results;

[0014] 5) After the experiment, the test piece was taken out for characterization test. The corrosion mechanism was analyzed and explored by combining the characterization test results with the above monitoring results.

[0015] The test piece is a metal test piece of the same material as the on-site production oil and gas well pipe string to be simulated and evaluated. Multiple groups of parallel test pieces are connected to the upper fixture and the lower fixture, and the number of parallel test pieces in each group is more than 3.

[0016] The heights of the upper clamp and the lower clamp can be adjusted up and down.

[0017] The step 2) checks the air tightness of the alloy kettle cavity and discharges all the O2 in the alloy kettle cavity. The specific steps are: inject N2 into the alloy kettle cavity, increase the pressure in the alloy kettle cavity to a set pressure and then stabilize it, and after confirming that there is no pressure reduction or air leakage, discharge all the O2 in the alloy kettle cavity.

[0018] The step 3) prepares a mixture of supercritical CO2 and water, and the specific steps are: heating and pressurizing the CO2 gas to a supercritical phase, and mixing the supercritical CO2 with water to obtain a mixture of supercritical CO2 and water; the water is deionized water or mineralized formation water.

[0019] The step 4) monitors the gaseous medium in the upper gas phase space in the alloy kettle cavity, and the specific steps are: the gaseous medium in the upper gas phase space in the alloy kettle cavity is collected by a fidelity sampler (18) and transported to a supercritical fluid chromatography analysis, and the solubility of water in supercritical CO2 is measured by the supercritical fluid chromatography analysis.

[0020] The step 4) monitors the liquid medium in the lower liquid space in the alloy kettle cavity, and the specific steps are: injecting the liquid medium in the lower liquid space in the alloy kettle cavity into the titration cell, measuring the CO3 in the solution in the titration cell. 2- or HCO3 - concentration.

[0021] Step 5) After the experiment, the steps for taking out the test piece are as follows: after the experiment, the temperature in the alloy kettle cavity is lowered to room temperature, the mixed gas in the alloy kettle cavity is discharged, and the test piece is taken out when the pressure in the alloy kettle cavity drops to normal pressure.

[0022] Step 5) Characterization test includes: observing the macroscopic morphology of the corrosion of the test piece; analyzing the phase composition of the corrosion product by XRD; observing the microscopic morphology of the corrosion product by SEM and qualitatively analyzing the composition of the corrosion product by EDS scanning; cleaning and removing the corrosion product film, weighing and calculating the weight difference, and calculating the weight loss uniform corrosion rate; measuring the maximum pitting depth of the substrate surface of the test piece and calculating the pitting rate.

[0023] The test piece fixture rotates during the experiment, and the rotation speed is determined according to the flow rate in the actual working condition.

[0024] Beneficial effects of the present invention:

[0025] The experimental method for simulating and evaluating the corrosion of metal pipe column materials provided by the present invention comprises a double-layer concentric circle clamp for testing piece, the double-layer concentric circle clamp comprises an upper clamp and a lower clamp, the lower of the upper clamp is connected to the lower clamp, the testing piece is connected to the upper clamp and the lower clamp, and the testing piece is located in the alloy kettle cavity; the upper clamp and the lower clamp are synchronously and dynamically rotated; a liquid medium is injected into the alloy kettle cavity until the liquid medium completely immerses the testing piece of the lower clamp; the testing piece is selected as a metal testing piece of the same material as the on-site production oil and gas well pipe column to be simulated and evaluated, the liquid medium injected into the alloy kettle cavity is selected from the produced water collected on-site or the simulated water prepared according to the mineralization degree of the produced water, a mixture of supercritical CO2 and water is prepared, and the prepared liquid medium is injected into the alloy kettle cavity A mixture of supercritical CO2 and water is injected into the upper gas phase space and the lower liquid phase space in the alloy kettle cavity respectively, so that the environment in the alloy kettle cavity satisfies that the test piece in the upper fixture contacts the gas phase-dominated corrosive medium formed by supercritical CO2 dissolving a certain amount of mineralized formation water, and the test piece in the lower fixture contacts the liquid phase-dominated corrosive medium formed by mineralized formation water dissolving a certain concentration of supercritical CO2. In this way, a supercritical CO2 / H2O mixed system (CO2-rich phase and H2O-rich phase) of the corrosive medium is formed; the gas phase medium in the upper gas phase space and the liquid phase medium in the lower liquid phase space in the alloy kettle cavity are monitored, and the environment in the alloy kettle cavity is adjusted according to the monitoring results; after the experiment, the test piece is taken out for characterization test to explore the corrosion mechanism. This method overcomes the problem that the existing alloy kettle cavity can only simulate a single phase environment medium to carry out corrosion evaluation experiments on metal materials, and realizes a mixed system that simultaneously simulates the corrosion behavior of the CO2 gas phase environment on the metal pipe column material and the corrosion behavior of the high-ore formation water liquid phase environment on the metal pipe column material; the gas phase medium in the upper gas phase space and the liquid phase medium in the lower liquid phase space in the alloy kettle cavity are monitored, and the environment in the alloy kettle cavity is adjusted according to the monitoring results to achieve accurate simulation of different corrosion conditions. It is used to simulate the corrosion behavior of the metal pipe column material in the supercritical CO2 / H2O system after CO2 reaches the supercritical phase during CO2 oil recovery and CO2 fracturing construction, and meets various experimental needs such as accurate evaluation of the safety performance of the pipe column material under supercritical CO2 conditions, in-depth research on the corrosion failure mechanism of the pipe column material, and reliable evaluation of the application effect of the pipe column anti-corrosion measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described in detail below with reference to the accompanying drawings.

[0027] Figure 1 It is a schematic diagram of the structure of an experimental device suitable for simulating and evaluating the corrosion of metal pipe materials;

[0028] Figure 2 This is the 8MPa macro corrosion morphology in Example 3;

[0029] Figure 3 This is the 10MPa macro corrosion morphology diagram in Example 4;

[0030] Figure 4 It is the microscopic morphology comparison (SEM) of 8MPa and 10MPa liquid phase corrosion products in Example 4;

[0031] Figure 5 This is a comparison of the substrate microstructures after 8MPa and 10MPa vapor phase etching in Example 4 (SEM).

[0032] Explanation of the reference numerals: 1. N2 gas source; 2. Fluid replenishment tank; 3. Injection pump; 4. CO2 gas source; 5. Temperature control device; 6. Constant flow metering plunger pump; 7. Mixing device; 8. Temperature and liquid level control device; 9. Heating temperature control device; 10. Agitator; 11. Alloy kettle chamber; 12. Test piece fixture; 13. Upper fixture; 14. Lower fixture; 15. Bottom tube; 16. Observation window; 17. Pressure sensor; 18. Fidelity sampler; 19. Supercritical fluid chromatograph; 20. PC control device; 21. Liquid storage tank; 22. Titration cell; 23. Potential indicator electrode; 24. Automatic titration device. DETAILED DESCRIPTION

[0033] Embodiment 1:

[0034] like Figure 1 As shown, an experimental method suitable for simulating and evaluating corrosion of metal pipe materials includes the following steps:

[0035] 1) preparing a test piece, a test piece fixture 12 and a liquid medium; the test piece fixture adopts a double-layer concentric circle fixture, the double-layer concentric circle fixture comprises an upper fixture 13 and a lower fixture 14, the upper fixture 13 is connected to the lower fixture 14, the test piece is connected to both the upper fixture 13 and the lower fixture 14, and the test piece is located in the alloy kettle cavity 11; injecting the liquid medium into the alloy kettle cavity 11 until the liquid medium completely immerses the test piece in the lower fixture 14;

[0036] 2) Check the air tightness of the alloy kettle cavity 11 and discharge all the O2 in the alloy kettle cavity 11;

[0037] 3) preparing a mixture of supercritical CO2 and water;

[0038] 4) Injecting the prepared supercritical CO2 and water mixture into the upper gas phase space and the lower liquid phase space in the alloy kettle cavity 11 respectively, and monitoring the gas phase medium in the upper gas phase space and the liquid phase medium in the lower liquid phase space in the alloy kettle cavity 11, and adjusting the environment in the alloy kettle cavity 11 according to the monitoring results;

[0039] 5) After the experiment, the test piece was taken out for characterization test. The corrosion mechanism was analyzed and explored by combining the characterization test results with the above monitoring results.

[0040] The test piece fixture adopts a double-layer concentric circle fixture, and liquid medium is injected into the alloy kettle cavity 11 until the liquid medium completely immerses the test piece of the lower fixture 14; the structure is simple, so that the test piece of the upper fixture 13 is in contact with a corrosion simulation environment dominated by a gas phase medium, and the lower layer of the test piece of the lower fixture 14 is in contact with a corrosion simulation environment dominated by a liquid phase medium, and the liquid phase medium is selected from the formation produced water collected on site or the simulated water prepared according to the mineralization of the formation produced water; compared with the prior art that only a single phase environmental medium can be simulated in the alloy kettle cavity 11 (simulating the corrosion behavior of the CO2 gas phase environment on the metal pipe column material or the corrosion behavior of the liquid phase environment of high-ore formation water on the metal pipe column material) to carry out corrosion evaluation of the metal material, the experiment of the present invention realizes a mixed system that simultaneously simulates the corrosion behavior of the CO2 gas phase environment on the metal pipe column material and the corrosion behavior of the liquid phase environment of high-ore formation water on the metal pipe column material.

[0041] Furthermore, the test piece is a metal test piece made of the same material as the on-site production oil and gas well pipe string to be simulated and evaluated, and multiple groups of parallel test pieces are connected to the upper fixture 13 and the lower fixture 14, and the number of parallel test pieces in each group is more than 3.

[0042] Set up multiple groups of parallel test pieces, with each group containing more than 3 pieces, to prevent accidental errors and improve the accuracy of the experiment.

[0043] In actual operation, the test piece is weighed with an analytical balance to an accuracy of 0.1 mg, and the length, width, height, opening diameter and other dimensions of the test piece are measured with a vernier caliper to an accuracy of 0.02 mm; and the surface area of ​​the test piece is calculated according to the formula: S = 2 (lw + lh + wh) - 1 / 2πd 2 +πdh (where l / w / h are the length / width / height of the test piece, respectively, and d is the aperture of the hole on the surface of the test piece); use petroleum ether and ethanol solution to degrease and dehydrate the surface of the test piece, respectively, blow dry with cold air and set aside; improve the accuracy of the experiment.

[0044] Furthermore, the multiple groups of parallel test pieces on the upper fixture 13 and the lower fixture 14 are circumferentially evenly spaced, thereby improving the stability of the device during the experimental rotation process.

[0045] Furthermore, the heights of the upper fixture 13 and the lower fixture 14 can be adjusted up and down. By adjusting the heights of the upper fixture 13 and the lower fixture 14 up and down, the liquid medium is injected into the alloy kettle chamber 11 until the liquid medium completely immerses the test piece of the lower fixture 14, and the alloy kettle chamber 11 is divided into two upper and lower space areas. The test piece of the upper fixture 13 is in contact with a corrosion simulation environment dominated by a gas phase medium, and the test piece of the lower fixture 14 is in contact with a corrosion simulation environment dominated by a liquid phase medium.

[0046] Furthermore, as described above, both the upper clamp 13 and the lower clamp 14 are provided with slots, so that the test piece can be conveniently installed and fixed on the upper clamp 13 and the lower clamp 14, and the installation and disassembly are convenient and easy to operate.

[0047] Furthermore, the test piece fixture 12 is made of a tetrafluoroethylene insulating material; the test piece fixture 12 made of a tetrafluoroethylene insulating material has excellent chemical stability, corrosion resistance, high lubricity and non-stickiness, electrical insulation and good anti-aging resistance. The tetrafluoroethylene insulating material includes polytetrafluoroethylene material.

[0048] Furthermore, liquid medium is injected into the alloy kettle chamber 11 until the liquid medium completely immerses the test piece of the lower fixture 14; the liquid level should be at least 2 cm higher than the test piece of the lower fixture 14, while being able to contact the test piece of the upper fixture 13. This method simulates the actual working conditions more accurately.

[0049] Furthermore, the step 2) checks the air tightness of the alloy kettle cavity 11 and discharges all the O2 in the alloy kettle cavity 11, and specifically includes the following steps: injecting N2 into the alloy kettle cavity 11, increasing the pressure in the alloy kettle cavity 11 to a set pressure and stabilizing it, and discharging all the O2 in the alloy kettle cavity 11 after confirming that there is no decompression and gas leakage. This avoids the influence of O2 on the experimental results and improves the accuracy of the experiment.

[0050] Furthermore, the step 3) prepares a mixture of supercritical CO2 and water, specifically comprising the steps of: heating and pressurizing the CO2 gas to a supercritical phase, and mixing the supercritical CO2 with water to obtain a mixture of supercritical CO2 and water; the water is deionized water or formation water with mineralization. The preparation method is simple and can be dynamically adjusted at any time as needed, including the adjustment of temperature, pressure, injection volume, etc.

[0051] Furthermore, in the step 4), the gaseous medium in the upper gas phase space in the alloy kettle cavity 11 is monitored, and the specific steps are: the gaseous medium in the upper gas phase space in the alloy kettle cavity 11 is collected by the fidelity sampler 18 and transported to the supercritical fluid chromatography analysis 19, and the solubility of water in supercritical CO2 is measured by the supercritical fluid chromatography analysis 19.

[0052] The step 4) monitors the liquid medium in the lower liquid space in the alloy kettle chamber 11, and the specific steps are: injecting the liquid medium in the lower liquid space in the alloy kettle chamber 11 into the titration cell 22, measuring the CO3 in the solution in the titration cell. 2- or HCO3 - concentration.

[0053] The purpose of monitoring is to facilitate the adjustment of the corrosion environment in the alloy reactor chamber 11, so that the established corrosion environment is maintained in a relatively stable state, ensuring that the corrosion experiment has a certain reproducibility; real-time detection of the dynamic changes of parameters in the corrosion environment that affect the corrosion results, for in-depth exploration of the corrosion mechanism.

[0054] The monitoring contents include: (a) the solubility of formation water in supercritical CO2 in the upper gas phase environment in the alloy kettle chamber 11 changes with pressure; (b) the solubility of formation water in supercritical CO2 in the lower liquid phase environment in the alloy kettle chamber 11 changes with pressure; (c) the dynamic changes of the corrosive medium in which the test piece is located.

[0055] Further, after the experiment is completed in step 5), the step of taking out the test piece is as follows: after the experiment is completed, the temperature in the alloy kettle chamber 11 is lowered to room temperature, the mixed gas in the alloy kettle chamber 11 is discharged, and the test piece is taken out when the pressure in the alloy kettle chamber 11 drops to normal pressure. The pressure in the alloy kettle chamber 11 needs to be reduced slowly at a certain speed to improve the safety of the operation.

[0056] Furthermore, step 5) characterization testing includes: observing the macroscopic morphology of corrosion of the test piece; analyzing the phase composition of the corrosion product by XRD; observing the microscopic morphology of the corrosion product by SEM and qualitatively analyzing the composition of the corrosion product by EDS scanning; cleaning and removing the corrosion product film, weighing and calculating the weight difference, and calculating the weight loss uniform corrosion rate; measuring the maximum pitting depth on the surface of the test piece substrate and calculating the pitting rate.

[0057] The corrosion product film is removed by cleaning, weighed and the weight difference is calculated, and the weight loss uniform corrosion rate is calculated by the formula: v 均匀 =(8.76×10 4 ×Δm) / (S·ρ·t) (where Δm is the weight loss difference, S is the surface area of ​​the test piece, ρ is the metal material density, and t is the experimental period);

[0058] The calculation formula for calculating the pitting rate is: 点蚀 =(8.76×10 3 ×h) / t (where h is the maximum pitting depth and t is the experimental period).

[0059] Furthermore, the test piece fixture 12 rotates during the experiment, and the rotation speed is determined according to the flow rate in the actual working condition. The experimental cycle of the corrosion evaluation or corrosion inhibitor evaluation is set according to the experimental plan, and the general experiment is 72h or 168h. The rotation speed of the stirring shaft is calculated according to the flow rate in the actual working condition, and the general experiment is in the range of 100r / min to 300r / min. It is required that the key parameters affecting the corrosion test results such as the rotation speed, temperature, and pressure during the corrosion test should be kept constant to maintain the relative stability of the system, which is conducive to the reproduction of the experimental results.

[0060] Embodiment 2:

[0061] On the basis of Example 1, Figure 1 As shown, an experimental method suitable for corrosion simulation evaluation of metal pipe column materials of the present invention adopts the following experimental device for experiment, which includes N2 gas source 1, liquid replenishment tank 2, injection pump 3, CO2 gas source 4, temperature control device 5, constant flow metering plunger pump 6, mixing device 7, temperature and liquid level control device 8, heating temperature control device 9, stirrer 10, alloy kettle chamber 11, test piece fixture 12, bottom probe tube 15, pressure sensor 17, fidelity sampler 18, supercritical fluid chromatograph 19, PC control device 20, storage The liquid tank 21, the titration cell 22, the potential indicating electrode 23 and the automatic titration device 24; the liquid replenishing tank 2 is connected to the inlet of the mixing device 7 through the injection pump 3, the CO2 gas source 4, the temperature control device 5, and the constant flow metering plunger pump 6 are connected to the inlet of the mixing device 7 in sequence, and the outlet of the mixing device 7 and the outlet of the N2 gas source 1 are connected through a pipeline and then connected to the upper gas phase space in the alloy kettle chamber 11 through one way, and the other way is connected to the lower liquid phase space through the bottom probe 15. The sensing end of the temperature and liquid level control device 8 is located inside the alloy kettle chamber 11, and the pressure sensor 1 7 is connected to the upper side of the alloy kettle chamber 11 and the sensing end of the pressure sensor 17 is located in the upper gas phase space of the alloy kettle chamber 11, the heating temperature control device 9 is connected to the side of the alloy kettle chamber 11, the test piece fixture 12 includes an upper fixture 13 and a lower fixture 14, the lower side of the upper fixture 13 is connected to the lower fixture 14, the upper fixture 13 is connected to the stirrer 10, the upper fixture 13 and the lower fixture 14 are both installed with a connected test piece, the gas phase outlet of the alloy kettle chamber 11 is connected to the supercritical fluid chromatograph 19 through the fidelity sampler 18, the alloy kettle chamber 11 1 is connected to a liquid storage tank 21 and a titration cell 22 in sequence, one end of a potential indicating electrode 23 and one end of an automatic titration device 24 are connected to the titration cell 22, the other end of the potential indicating electrode 23, the other end of the automatic titration device 24, a supercritical fluid chromatograph 19, an alloy kettle chamber 11, and a heating temperature control device 9 are all electrically connected to a PC control device 20; a transparent observation window 16 is provided in front of the alloy kettle chamber 11; the liquid phase outlet of the alloy kettle chamber 11 is provided at the bottom of the alloy kettle chamber 11, so as to facilitate the liquid phase medium to flow into the liquid storage tank 21.

[0062] The liquid level can be determined and adjusted through the transparent observation window, or the liquid level control device in the chamber can automatically determine, identify and control the liquid level;

[0063] Check the air tightness of the alloy kettle chamber 11 and exhaust all the O2 in the alloy kettle chamber 11. The specific steps are as follows: only open the valve of the N2 gas source 1 and the corresponding inlet of the alloy kettle chamber 11, increase the pressure in the alloy kettle chamber 11 to 1MPa by adjusting the N2 gas source valve, and stabilize it for 10 minutes to ensure that there is no decompression and gas leakage, then open the exhaust valve of the device to completely exhaust the O2 retained in the alloy kettle chamber 11 into the air;

[0064] A supercritical CO2 and water mixture is prepared by: introducing the CO2 in the CO2 gas source 4 into the temperature control device 5 for heating by controlling the valve, and the heated CO2 is pressurized by the constant flow metering plunger pump 6 and then injected into the mixing device 7; the liquid in the liquid replenishment tank 2 is injected into the mixing device 7 by the injection pump 3, and the mixing device 7 mixes the injected CO2 and the liquid; until the desired supercritical CO2 and water mixture is reached; during the experiment, the supercritical CO2 and water mixture can be adjusted at any time according to the situation, including the temperature, pressure, and injection amount; this experiment requires the CO2 temperature to be 80°C, and the pressure to be 8MPa and 10MPa. Studies have confirmed that the supercritical phase can be reached after the critical point when the CO2 pressure is greater than 7.3MPa and the temperature is greater than 31.3°C. During implementation, the pressure and temperature can be adjusted according to the specific experimental requirements to meet the supercritical phase requirements. After the supercritical CO2 in the mixing device 7 contacts the liquid in the replenishment tank 2 (ordinary deionized water or formation water with a certain degree of mineralization) and forms a mixed system, it is injected into the upper gas phase space and the lower liquid phase space in the alloy kettle chamber 11 through different pipelines, so that the environment in the alloy kettle chamber 11 satisfies that the test piece in the upper clamp 13 contacts the corrosive medium mainly in the gas phase formed by supercritical CO2 dissolving a certain amount of formation water with a certain degree of mineralization, and the test piece in the lower clamp 14 contacts the corrosive medium mainly in the liquid phase formed by formation water with a certain concentration of supercritical CO2 dissolving. In this way, a corrosive medium of a supercritical CO2 / H2O mixed system (CO2-rich phase and H2O-rich phase) is formed.

[0065] The gas phase medium in the upper gas phase space in the alloy kettle chamber 11 is monitored. The specific method is as follows: the fidelity sampler 18 synchronously collects the CO2 fluid mixed with formation water in the upper gas phase space of the alloy kettle chamber 11, and connects to the supercritical fluid chromatography analysis 19 to measure the solubility of formation water in supercritical CO2, and can adjust the environment in the alloy kettle chamber 11 according to the change of data feedback value;

[0066] The liquid medium in the lower liquid phase space in the alloy kettle chamber 11 is monitored by opening the drain port at the bottom of the alloy kettle chamber 11, and a certain volume of liquid is pumped from the liquid storage tank 21 to the titration cell 22 through a peristaltic pump or other automatic sampling device, and the PC control device 20 controls the potential indicator electrode 23 and the automatic titration device 24 to measure the CO3 in the solution in the titration cell 22. 2- or HCO3 - concentration and other parameters; realize the dissolution of CO2 in the corrosive medium in the high temperature and high pressure reactor chamber, and the conversion of CO2 into CO3 2- / HCO3 - Concentration detection.

[0067] The change of liquid level height is judged and adjusted through the observation window or automatically judged and identified through the liquid level control device. When the liquid level drops, the front valve is opened to add liquid to the kettle chamber; when the liquid level rises, the liquid is discharged through the bottom drain port to lower the liquid level and maintain the relative stability of the system.

[0068] Embodiment 3:

[0069] An experimental method suitable for simulating and evaluating corrosion of metal pipe materials comprises the following steps:

[0070] 750 mL of high-mineralization formation produced fluid was injected into the 2.5 L alloy reactor chamber 11 as the corrosive medium. The N80 material test pieces (size: 50 mm × 10 mm × 3 mm) that are the same as the wellbore string were selected, and the pretreated test pieces were installed in the double-layer concentric circle fixtures made of polytetrafluoroethylene materials, so that the lower fixture test pieces were completely immersed in the high-mineralization formation produced water (the experimental mineralization was 1.0 × 10 5 mg / L), the upper fixture specimen is placed in a supercritical CO2 fluid dissolved with a small amount of formation water, the stirring shaft drives the specimen to rotate axially (speed 100r / min), and the corrosion conditions of the supercritical CO2 / H2O systems (CO2-rich phase and H2O-rich phase) are simulated in the alloy reactor chamber 11 at the same time.

[0071] After sealing the alloy kettle chamber 11, N2 is first introduced to remove oxygen, and then the temperature is raised to 80°C. The high-purity CO2 at the front end is heated to 80°C and pressurized to 8MPa. After the temperature and pressure are stabilized, the supercritical state is reached, and the mixture is mixed with the formation water in the replenishment tank and introduced into the upper gas phase space and the lower liquid phase space of the alloy kettle chamber 11 as the corrosion medium. The pressure of the alloy kettle chamber 11 is controlled to be constant at 8MPa, and the temperature is controlled to be constant at 80°C. A high-temperature and high-pressure dynamic corrosion weight loss simulation experiment with a cycle of 168h is carried out. During the experiment, supercritical fluid chromatography and potentiometric titration methods are used to monitor the solubility of formation water in supercritical CO2 and the solubility of formation water in supercritical CO2.

[0072] After the experiment, when the temperature in the kettle chamber drops to room temperature, slowly open the valve to exhaust the mixed gas in the kettle chamber at a low airflow rate until the pressure in the kettle chamber drops to normal pressure (0MPa), open the kettle cover, and remove the corroded test piece. ① Observe the macroscopic morphology of the corrosion of the test piece; ② Perform XRD analysis of the inorganic components of the corrosion product; ③ SEM observation of the microscopic morphology of the corrosion product, EDS scanning qualitative analysis of the composition of the corrosion product; ④ Clean and remove the corrosion product film, weigh and calculate the weight difference, calculate the weight loss uniform corrosion rate, and the calculation formula is: v 均匀 =(8.76×10 4 ×Δm) / (S·ρ·t) (where Δm is the weight loss difference, S is the surface area of ​​the test piece, ρ is the metal material density, and t is the experimental period); ⑥ If there is obvious pitting on the substrate surface, measure the maximum pitting depth and calculate the pitting rate. The calculation formula is: v 点蚀 =(8.76×10 3 ×h) / t (where h is the maximum pitting depth and t is the experimental period). By analyzing the experimental data and characterization results, the corrosion mechanism is explored. (See Table 1 and Figure 2 )

[0073] Table 1 Corrosion evaluation test data (8MPa, 80℃)

[0074]

[0075] Example 4

[0076] Except that the CO2 pressure was increased to 10 MPa, other conditions were the same as those in Example 3, and the experimental results were compared with the experimental results at 8 MPa. (See Table 2-4, Figure 3-5 )

[0077] Table 2 Corrosion evaluation test data (10MPa, 80℃)

[0078]

[0079] Table 3 Solubility of formation water in supercritical CO2 at different pressures

[0080] Temperature(℃) Pressure(MPa) <![CDATA[Supercritical CO2 density (g / L)]]> <![CDATA[Mole fraction of formation water (10 -3 )]]> 80 8 111 5.35 80 10 270 5.87

[0081] Table 4 Local pitting rates of corrosion test pieces in the gas phase at different pressures

[0082] Temperature(℃) Pressure(MPa) Maximum pitting depth (μm) Pitting rate (mm / a) 80 8 32 1.686 80 10 147 7.665

[0083] Under the same temperature conditions, as the pressure increases, the density of the supercritical CO2 fluid increases. At the same time, the solubility of formation water in the supercritical CO2 fluid increases, the corrosion electrochemical mass transfer process is faster, and the active dissolution of the carbon steel material is accelerated, causing the local corrosion of the specimen matrix corresponding to 10MPa to be more serious than that of 8MPa.

[0084] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "inner", etc. indicating orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention.

[0085] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. An experimental method suitable for simulating and evaluating corrosion of metal pipe materials, characterized in that: The steps include: 1) preparing a test piece, a test piece fixture (12) and a liquid medium; the test piece fixture adopts a double-layer concentric circle fixture, the double-layer concentric circle fixture comprises an upper fixture (13) and a lower fixture (14), the upper fixture (13) is connected to the lower fixture (14), the test piece is connected to both the upper fixture (13) and the lower fixture (14), and the test piece is located in the alloy kettle chamber (11); the liquid medium is injected into the alloy kettle chamber (11) until the liquid medium completely immerses the test piece in the lower fixture (14); 2) Checking the air tightness of the alloy kettle cavity (11) and exhausting all the O2 in the alloy kettle cavity (11); 3) preparing a mixture of supercritical CO2 and water; 4) The prepared mixture of supercritical CO2 and water is respectively injected into the upper gas phase space and the lower liquid phase space in the alloy kettle cavity (11), and the gas phase medium in the upper gas phase space and the liquid phase medium in the lower liquid phase space in the alloy kettle cavity (11) are monitored, and the environment in the alloy kettle cavity (11) is adjusted according to the monitoring results; the gas phase medium in the upper gas phase space in the alloy kettle cavity (11) is monitored in the step 4), and the specific steps are: the gas phase medium in the upper gas phase space in the alloy kettle cavity (11) is collected by the fidelity sampler (18) and transported to the supercritical fluid chromatography analysis (19), and the solubility of water in supercritical CO2 is measured by the supercritical fluid chromatography analysis (19); the liquid phase medium in the lower liquid phase space in the alloy kettle cavity (11) is monitored in the step 4), and the specific steps are: the liquid phase medium in the lower liquid phase space in the alloy kettle cavity (11) is injected into the titration cell (22), and the CO3 in the solution in the titration cell is measured. 2- or HCO3 - concentration; monitoring contents include: solubility of formation water in supercritical CO2 in the upper gas phase environment in the alloy kettle chamber (11) changes with pressure; solubility of formation water in supercritical CO2 in the lower liquid phase environment in the alloy kettle chamber (11) changes with pressure; dynamic changes of the corrosive medium in which the test piece is located; 5) After the experiment, the test piece was taken out for characterization test. The corrosion mechanism was analyzed and explored by combining the characterization test results with the above monitoring results.

2. The experimental method for simulating corrosion evaluation of metal pipe column materials according to claim 1, characterized in that: The test piece is a metal test piece made of the same material as the on-site production oil and gas well pipe string to be simulated and evaluated. Multiple groups of parallel test pieces are connected to the upper clamp (13) and the lower clamp (14), and the number of parallel test pieces in each group is more than 3.

3. The experimental method for simulating corrosion evaluation of metal pipe string materials according to claim 1, characterized in that: The heights of the upper clamp (13) and the lower clamp (14) can be adjusted up and down.

4. The experimental method for simulating corrosion evaluation of metal pipe string materials according to claim 1, characterized in that: The step 2) checks the air tightness of the alloy kettle cavity (11) and discharges all the O2 in the alloy kettle cavity (11). The specific steps are: injecting N2 into the alloy kettle cavity (11), increasing the pressure in the alloy kettle cavity (11) to a set pressure and then stabilizing it, and after confirming that there is no pressure reduction or gas leakage, completely discharges the O2 in the alloy kettle cavity (11).

5. The experimental method for simulating corrosion evaluation of metal pipe materials according to claim 1, characterized in that: The step 3) prepares a mixture of supercritical CO2 and water, and the specific steps are: heating and pressurizing the CO2 gas to a supercritical phase, and mixing the supercritical CO2 with water to obtain a mixture of supercritical CO2 and water; the water is deionized water or mineralized formation water.

6. The experimental method for simulating corrosion evaluation of metal pipe string materials according to claim 1, characterized in that: Step 5) After the experiment is completed, the steps for taking out the test piece are as follows: after the experiment is completed, the temperature in the alloy kettle chamber (11) is lowered to room temperature, the mixed gas in the alloy kettle chamber (11) is discharged, and when the pressure in the alloy kettle chamber (11) drops to normal pressure, the test piece is taken out.

7. The experimental method for simulating corrosion evaluation of metal pipe string materials according to claim 1, characterized in that: Step 5) Characterization test includes: observing the macroscopic morphology of the corrosion of the test piece; analyzing the phase composition of the corrosion product by XRD; observing the microscopic morphology of the corrosion product by SEM and qualitatively analyzing the composition of the corrosion product by EDS scanning; cleaning and removing the corrosion product film, weighing and calculating the weight difference, and calculating the weight loss uniform corrosion rate; measuring the maximum pitting depth of the substrate surface of the test piece and calculating the pitting rate.

8. The experimental method for simulating corrosion evaluation of metal pipe string materials according to claim 1, characterized in that: The test piece fixture (12) rotates during the experiment, and the rotation speed is determined according to the flow rate in actual working conditions.

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