JP2000219980A - Method for suppressing local corrosion of metals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the local corrosion by adding an organic inhibitor and a hydrocarbon oil to suppress the cathodic reaction. SOLUTION: Objective metals include iron, low alloy steel, and stainless steel, and are particularly effective to an excavation pipe to be used in exploration and development of oil and natural gas. An organic solvent to be used is preferably amines for iron (steel), and fatty acids for iron (steel) passivated by oxides. More specifically, long-chain amines and long-chain fatty acids, and their salts and derivatives are preferable, and the carbon number of alkyl groups of the long-chain fatty acids is 11 to 18. The hydrocarbon oil to be used has the hydrophobic interaction with the organic inhibitor, and includes paraffin hydrocarbon, naphthene hydrocarbon, aromatic hydrocarbon, and mixed oil thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing local corrosion of metals by suppressing the cathodic reaction of corrosion in controlling local corrosion of metals. The present invention relates to a method for suppressing local corrosion on the outer surface of a digging pipe used for digging.

[0002]

2. Description of the Related Art Generally, localized corrosion in metal corrosion is corrosion that occurs in a corrosion-resistant material, and most of the surfaces actually exhibit corrosion resistance among combinations of materials and environments that are originally expected to have corrosion resistance. Regardless of the phenomenon, the progress of corrosion is concentrated at a specific place,
Changes in the environment during use, defects in the design of structures and equipment, defects in materials caused by defective manufacturing conditions, local loss of anticorrosion means, and the like can be cited. In particular, with the deepening of wells targeted for oil and natural gas exploration and development in recent years, high-temperature polymer mud has come to be used. Local corrosion is an important problem.

[0003] The corrosion reaction consists of a cathodic reaction in which hydrogen ions or oxygen removes electrons from the metal, and an anodic reaction in which the metal is dissolved. Since the total amount of the cathodic reaction is equal to the total amount of the anodic reaction, the means for suppressing the corrosion reaction is to directly suppress the anodic reaction in which the metal is eluted or to suppress the cathodic reaction. Good. However, it is recognized that it is difficult to suppress the anodic dissolution reaction due to the internal solution composition and complicated form of the anodic dissolution pits due to the anodic reaction.

As mentioned above, high temperature polymer mud is used for drilling of oil and natural gas. Local corrosion on the outer surface of the pipe is caused by dissolved oxygen in the mud and high temperature deterioration of the mud. (The formation temperature at which the drilling mud encounters is a high temperature exceeding 200 ° C.). Therefore, the following method is considered as a conventional countermeasure against corrosion. Removal of oxygen by addition of oxygen scavenger Solidification and separation of carbon dioxide by addition of calcium Addition of amine-based corrosion inhibitor Addition of organic phosphoric acid-based inhibitor In these methods, the above methods are used when polymer muddy water tends to gel. Was not applicable and was not appropriate in the case of anionic polymer muds. And it was decomposed at a high temperature such as 200 ° C. and was not effective. In Europe and the United States, oil-based mud is mainly used for drilling in harsh environments where the formation temperature at which the drilled mud encounters exceeds 200 ° C. However, this method involves pollution problems, price, and transportation and storage. From this point, polymer mud has begun to be used. As described above, none of the conventional corrosion countermeasures is an effective method. The group of the present inventors previously reported that corrosion was greatly suppressed by the attachment of the hydrophobic group of the liquid hydrocarbon to the hydrophobic group of the organic inhibitor.

[0005]

Accordingly, the present inventor has made the above-mentioned knowledge on the suppression of local corrosion, particularly the local corrosion of the outer surface of a drilling pipe used in oil and natural gas wells, based on the local corrosion cathod. After various investigations as to whether or not it can be applied to the reaction, it was found that the hydrophobic interaction between the organic inhibitor and the hydrocarbon drastically suppressed the cathodic reaction of local corrosion and consequently the local corrosion. It is an object of the present invention to provide a method for suppressing local corrosion of metals by suppressing a cathodic reaction.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for suppressing local corrosion of metals, which comprises adding an organic inhibitor and a hydrocarbon oil in suppressing local corrosion of metals. That is, in the present invention, the interaction between the hydrophobic group of the organic inhibitor and the hydrophobicity of the hydrocarbon oil acts on the site of local corrosion to thoroughly suppress the cathodic reaction, thereby suppressing local corrosion. It is understood that. Conventionally, oil may be injected into the drilling mud for the purpose of lubricating the bit (drilling edge), but in this case, the drilling mud flows and cannot have an anticorrosive effect, and is insoluble in water. In some cases, oil is injected together with the inhibitor as a solvent for the organic inhibitor, but in the present invention, a water-soluble inhibitor such as salts of lauric acid is dissolved in water and injected as an inhibitor. It is also possible to form an anticorrosion film of lauric acid ions on the surface of the excavated pipe, and a high anticorrosion effect is exhibited by the oil binding to the anticorrosion film with hydrophobic affinity.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. The metals that can suppress local corrosion according to the present invention include iron,
Any metal such as low alloy steel, stainless steel, copper, and copper alloy may be used, but it is particularly effective for drilling pipes used in oil and gas exploration and development. Drilling pipes used for oil and natural gas exploration and development are used under severe conditions of 200 ° C with formation temperature of polymer and muddy water, so local corrosion easily occurs on the outer surface of the drilling pipes, and this local corrosion is suppressed. It is effective to do.

As the organic inhibitor used in the present invention, an organic inhibitor having good compatibility with the metal surface is preferable. Here, an organic inhibitor having good compatibility with the metal surface means an organic inhibitor having a strong adsorption power to the metal. In an environment where local corrosion occurs, the corroded portion is actively dissolved, whereas the metal surface is covered with an oxide or the like, and although there is a difference in strength, it is considered to be passivated. Therefore, it is considered that an organic inhibitor having good compatibility with a passive metal is effective as an inhibitor for preventing local corrosion. Specifically, an inhibitor of amines is preferable for iron (steel), and an inhibitor of fatty acids is preferable for iron (steel) passivated by an oxide. As inhibitors for amines, there are long-chain amines and long-chain imidazolines, and as inhibitors for fatty acids, long-chain fatty acids (R-COOH
R: represents an alkyl group. ) And salts and derivatives thereof, and a long-chain fatty acid having 11 to 17 carbon atoms of R is preferable. When the passivation is weak, a long-chain nitrogen-containing compound and its derivative are effective. Benzotriazole inhibitors are preferred for copper and copper alloys.

The hydrocarbon oil used in the present invention is a hydrocarbon oil having a hydrophobic interaction with an organic inhibitor. Normally, organic inhibitors are composed of an adsorbing group (polar group) and a hydrophobic group (lipophilic group), and are used for the metal surface in an oil / water (oil-in-water) liquid. In, the organic inhibitor is adsorbed on the metal surface by an adsorbing group (polar group), and the hydrophobic group is oriented toward the liquid. Oil adheres to this hydrophobic group. This adhesion is due to a weak interaction between those excluded by water, and this interaction is called a hydrophobic interaction. In the present invention, a hydrocarbon oil having an interaction with the hydrophobic group of the organic inhibitor is used. However, if hydrocarbons are present as a gas, it is impossible to adhere to the hydrophobic groups of the organic inhibitor by hydrophobic interaction, so it is desirable to use hydrocarbons having a high boiling point. The hydrocarbon oil used in the present invention may be any of paraffinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, and mixed oils thereof. However, when applying to an actual system, it is necessary to select the one that exists as a liquid in consideration of the temperature of the system.

[0010] Next, an experimental example shows a state in which the anodic reaction and the cathodic reaction are suppressed when the organic inhibitor of the present invention and a hydrocarbon oil are used. For comparison, a case where only the organic inhibitor is used and a case where no organic inhibitor is added are also described. In addition,
The method for measuring the polarization curve will be described later. Experiment 1 STPG38 was used as a test piece, and at a temperature of 70 ° C. and a pressure CO2 of 2.0 MPa (70 ° C.), 500 ppm of an amine organic inhibitor as an organic inhibitor and 20 ml (milliliter) of isooctane as a hydrocarbon oil were added. The polarization curve in the prepared medium was measured. The measurement results are shown in FIG. In the polarization curve of FIG. 1, the vertical axis represents the potential, and the horizontal axis represents the flowing current. The noble (potential: high potential) upward-sloping curve basically corresponds to the metal leaching reaction rate (anodic reaction) due to corrosion, while the noble (low potential) downward-sloping curve corresponds to This corresponds to the strength of the substance in the solution taking away electrons from the metal (cathodic reaction). Their intensity, the horizontal axis, is the logarithm of the current density. In FIG. 1, the current density was high in both the anodic reaction and the cathodic reaction when no organic inhibitor was added (curve c).
Both the cathodic reaction and the cathodic reaction are actively proceeding. On the other hand, when an amine-based inhibitor is added (curve b), both the anodic reaction and the cathodic reaction shift to the low current density side, and both reactions are suppressed. Notable on the side. Further, when isooctane was added as a hydrocarbon oil thereto, both the anodic reaction and the cathodic reaction were drastically suppressed, and the degree was two orders of magnitude in current density.

Experiment 2 A test similar to that of Test Example 1 was carried out using lauric acid in place of the amine organic inhibitor of Experiment 1 and xylene in place of the hydrocarbon oil, and the results are shown in FIG. 2, in the case of the fatty acid inhibitor (curve b), both the anodic and cathodic reactions were greatly suppressed by the addition of xylene (hydrocarbon oil) (curve c), similarly to the amine-based inhibitor of Experiment 1. . In particular, the cathodic reaction caused by the addition of xylene was dramatically suppressed.
In addition, the curve c is a case without addition.

According to these experiments, the remarkable suppression of the cathodic reaction by the addition of hydrocarbons (oils) was caused by the hydrocarbons (oils) attached to the hydrophobic groups of the organic inhibitor by hydrophobic interaction. it is conceivable that. In the present invention, the hydrophobic group of such an organic inhibitor and the hydrocarbon (oil) thoroughly suppress the cathodic reaction by hydrophobic interaction, thereby suppressing local corrosion.

[0013]

Next, the present invention will be described in detail with reference to examples. In Examples, the following three types of laboratory tests and evaluation tests in actual wells were performed as evaluation tests of the organic inhibitor of the present invention. Autoclave test using mud with 1/2 concentration of real mud Electrochemical measurement in saline solution (polarization measurement) Thermal curing cell test using real mud Autoclave test Low temperature mud flows inside the drilling pipe and outside The high temperature mud flows through the tube, and the tube wall is considered to be a heat transfer surface. Therefore, a corrosion prevention experiment was conducted by forming a heat transfer surface in an autoclave having a 1.8 L capacity and a superalloy Hastelloy C-276 lining. The test device is shown in FIG. That is, tap water (cooling water) was passed through the inside of the stainless steel pipe, and a cylindrical test piece of carbon steel was attached so as to contact the outer surface of the pipe. A corrosion acceleration test was performed by bringing a carbon steel test piece into contact with a stainless steel pipe. 1.3 solution obtained by diluting the polymer muddy water for high temperature actually used by half with ion-exchanged water
L was injected into the autoclave, so that the test piece was immersed in the solution. As the corrosive substances, dissolved oxygen and carbon dioxide gas were considered, so that deoxidation was not performed. Further, sodium bicarbonate is used as carbon dioxide gas,
000 ppm was added. The drill pipe was kept at 95 ° C., which is the estimated temperature of mud at the depth of the most severely corroded area in the actual well, for 20 hours, and the corrosion rate was determined from the weight loss of the test pieces before and after the test. The experiment was performed under the condition of adding fatty acids and fatty acids + oil. In addition, an experiment was also performed on a sample obtained by subjecting some fatty acids to high-temperature deterioration at 180 ° C. for 3 days. A similar experiment was performed at 120 ° C. During the test, the solution was stirred at a speed of 350 rpm.

Polarization Measurement As shown in FIG.
The carbon steel test electrode and the counter electrode of platinum are immersed therein. By scanning the potential difference between a reference electrode showing a constant potential by immersing the Ag / AgCl electrode in a saturated KCl solution and a test electrode with a potentiostat,
At this time, a current flowing between the test electrode and the counter electrode is measured with a potentiostat. The reference electrode and the electrolytic cell were connected by a salt bridge so as not to hinder the flow of current. Sodium bicarbonate was added to the saline solution in the electrolytic cell so as to have a bicarbonate ion concentration of 10,000 ppm. During the measurement, the solution was stirred with a stirrer. No deoxygenation was performed. For the measurement of the polarization curve, first, a cathode curve was obtained at a scan speed of 20 mV / min from the corrosion potential in a noisy direction, and then an anode curve was obtained at the same speed from the corrosion potential in a noble direction. The measurement was performed at room temperature under three conditions of no addition of lauric acid, addition of 0.1% lauric acid, and addition of 10 mL of xylene.

Thermal curing cell test 400 mL of actual muddy water was injected into a cylindrical stainless steel thermal curing cell having an internal volume of 500 mL, and the bicarbonate ion concentration was 1%.
Sodium bicarbonate was added to reach 000 ppm. The stainless steel jig was covered directly with a carbon steel test piece, and the test piece was immersed in muddy water. The cell was placed horizontally in a thermostat and rotated at a speed of 35 rpm in the circumferential direction. Raise the temperature of the thermostat to 95 ° C,
Maintained for 8 hours. The corrosion rate was determined from the weight loss before and after the test. An experiment was performed in which 0.1% lauric acid + 0.5% xylene was added, and the anticorrosion effect was examined.

Experimental Results Autoclave Test The anticorrosion effects of lauric acid and stearic acid are shown in FIG. The anticorrosion rate was determined by the following equation. From FIG. 5, it was found that both lauric acid and stearic acid exhibited a good anticorrosion effect of 60% or more. In particular, at 120 ° C., stearic acid showed a high anticorrosion effect of 95%. Table 1 shows the effect of oil (xylene) on the anticorrosive effect of lauric acid and the effect of high-temperature deterioration of lauric acid. FIG. 6 shows that the acid and its salt have the same level of corrosion inhibitory effect.

[0017]

From Table 1, the anticorrosion rate of lauric acid alone is 63%.
However, a high anticorrosion rate of 88% was achieved by the addition of oil. The lauric acid concentration tested was only one point of 0.1%, but a higher concentration may provide a higher anticorrosion effect. In addition, although the anticorrosion rate decreases due to high temperature deterioration of lauric acid, 54%
The anticorrosion effect was obtained. In the case of an organic inhibitor, there is a compound that accelerates corrosion by high-temperature deterioration, but it was an evaluation result that the anti-corrosion effect was exhibited even at high temperature.

Polarization measurement The results are as shown in FIG. Cathode reaction (−30) considered to be mainly a reduction reaction of dissolved oxygen
(Lower than 0 mV), the decrease in current density due to the addition of lauric acid was small. That is, lauric acid alone does not significantly suppress the reduction reaction of oxygen, which takes away electrons from carbon steel. However, a significant decrease in the cathode current density (approximately two orders of magnitude lower at portions near the corrosion potential) was observed with the addition of oil. The coexistence of lauric acid and oil greatly suppressed the oxygen reduction reaction. On the other hand, the anodic reaction which is the elution reaction of carbon steel (part noble than -300 mV)
Was suppressed stepwise by the addition of lauric acid and further by the addition of oil.

Heat Curing Cell Test After the test, the steel was removed from the heat curing cell, and the appearance of the steel test after washing with ion-exchanged water was observed. Corrosion had occurred. On the other hand, when lauric acid and oil were added, almost no corrosion was observed.
Incidentally, the anticorrosion rate was 75%. Although anodic reaction (elution of carbon steel) is likely to occur in the gap, lauric acid (+ oil) is difficult to access. It is considered that the anticorrosion effect in this experiment was achieved because the cathodic reaction was suppressed at a high rate by lauric acid + oil. Excavation using muddy water is required to exhibit the following functions against muddy water. Cleaning and transportation (dispersant, thickener) Cooling and lubrication (lubricant) and adjustment of specific gravity (weighting agent) Mud wall formation (thickener) For this purpose, various water-soluble polymers are added to muddy water.
The water-soluble polymer is considered to hinder the adsorption of the organic inhibitor on the metal surface. Therefore, in the polymer-drilled mud, the anticorrosion rate was only 75%, but it could be evaluated.

Evaluation Results in Actual Wells In a corrosion prevention test in a laboratory, lauric acid + oil showed a good anticorrosion effect. Therefore, in an actual well, the anticorrosion effect of lauric acid + heavy oil was examined. In an actual well, mud enters the borehole at about 70 ° C from the ground and returns to the ground at about 80 ° C. During this time the maximum temperature reaches 140-150 ° C. The temperature of the excavated formation is well above 200 ° C. Before adding lauric acid and heavy oil (when drilling 5,000 m), about 200
The occurrence of corrosion was observed over a wide range from m to 4,600 m. However, with the addition of 0.8% lauric acid and 3% heavy oil (when drilling at 6,000 m), the depth of occurrence of corrosion is narrowed to about 1,000 to 1,800 m,
The degree of corrosion has also been greatly reduced. In particular, a strong anticorrosive film of lauric acid and heavy oil was formed in the shallow portion up to 1,000 m, and high water repellency was recognized. The present invention showed an excellent anticorrosion effect even in an actual well.

[0022]

As described above, the present invention can suppress the local corrosion of metals by a combination of an organic inhibitor and a hydrocarbon oil, especially a combination of a long-chain fatty acid and a hydrocarbon oil. -Local corrosion on the outer surface of the excavation pipe used in a natural gas well can be easily suppressed.

[Brief description of the drawings]

FIG. 1 is a measurement diagram of a polarization test result of Experiment 1.

FIG. 2 is a measurement diagram of a polarization test result of Experiment 2.

FIG. 3 is a schematic diagram of an autoclave test apparatus.

FIG. 4 is a schematic diagram of a polarization measuring device.

FIG. 5 is a diagram showing the results of a corrosion / corrosion test using an autoclave.

FIG. 6 is a diagram of the corrosion inhibiting effect of lauric acid and its salt in 1/2 muddy water.

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[Procedure amendment]

[Submission date] December 8, 1999 (1999.12.
8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. The metals that can suppress local corrosion according to the present invention include iron,
Although any metal such as low alloy steel and stainless steel may be used, it is particularly effective for drilling pipes used for oil and natural gas exploration and development. Drilling pipes used for oil and natural gas exploration and development are used under severe conditions of 200 ° C with formation temperature of polymer and muddy water, so local corrosion easily occurs on the outer surface of the drilling pipes, and this local corrosion is suppressed. It is effective to do.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

As the organic inhibitor used in the present invention, an organic inhibitor having good compatibility with the metal surface is preferable. Here, an organic inhibitor having good compatibility with the metal surface means an organic inhibitor having a strong absorption power for the metal. In an environment where local corrosion occurs, the corroded portion is actively dissolved, whereas the other metal surfaces are covered with oxides and the like, and although there is a difference in strength, it is considered to be passivated. Therefore, it is considered that an organic inhibitor having good compatibility with a passive metal is effective as an inhibitor for preventing local corrosion. Specifically, an inhibitor of amines is preferable for iron (steel), and an inhibitor of fatty acids is preferable for iron (steel) passivated by an oxide. As inhibitors for amines, there are long-chain amines and long-chain imidazolines, and as inhibitors for fatty acids, long-chain fatty acids (R-
COOH R: represents an alkyl group. ) And salts and derivatives thereof, and a long-chain fatty acid having 11 to 18 carbon atoms of R is preferable. When the passivation is weak, a long-chain nitrogen-containing compound and its derivative are effective.

Claims (3)

[Claims] 1. In suppressing local corrosion of metals,
A method for inhibiting local corrosion of metals, comprising adding an organic inhibitor and a hydrocarbon oil. 2. The method according to claim 1, wherein the metal is a drilling pipe. 3. The organic inhibitor is a long-chain fatty acid and / or a derivative thereof, and the hydrocarbon oil is a paraffinic oil,
The method for suppressing local corrosion of metals according to any one of claims 1 to 2, wherein the method is at least one selected from the group consisting of a naphthene type, an aromatic type, and a mixed oil thereof.