Corrosion inhibitor formulation for geothermal reinjection wells

Abstract

A method for inhibiting corrosion of metal surfaces in contact with geothermal systems is provided. The method may include contacting the metal surface with a corrosion inhibitor composition by adding the composition to geothermal process water. The corrosion inhibitor composition may include an organic phosphonate, an orthophosphate, and zinc or a salt thereof.

Description

Technical Field

[0001] The present invention generally relates to corrosion inhibition. More particularly, the present disclosure relates to compositions for inhibiting corrosion in geothermal systems.

Background Art

[0002] Geothermal energy is a form of energy in the heat within the Earth and can be developed using geothermal wells. The interior of the Earth contains an enormous supply of heat, but challenges remain in the extraction of heat for energy generation. Geothermal energy moves towards the Earth's surface by heat conduction through rock formations. Thermal energy can also be transmitted towards the Earth's surface by the movement of magma or the circulation of fluids (H2O as steam or water) through interconnected fractures and pores. In either case, geothermal wells are relatively deep wells.

[0003] Geothermal brine and steam are generally used as energy sources. Geothermal brine is used in power generation, heating, and electrical processes. The temperature of geothermal steam ranges from about 185°C to about 370°C (about 365°F to about 700°F). Steam is separated from brine using a flashing unit. Low-temperature brine can also be used to produce an electrical binary unit (secondary fluid unit). Geothermal brine can have a salt content of less than about 1000 ppm to several hundred thousand ppm and a non-condensable gas content of up to about 6 percent. Depending on the salt content and application, geothermal fluids can be used directly or via a secondary fluid cycle. As the abundance of other energy sources decreases and they become more expensive, the use of geothermal energy as an energy source is increasing in importance. This is a sustainable and renewable energy source, and unlike other renewable energy sources, geothermal energy is always available.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Corrosion of metal surfaces in aqueous media is a problem in the geothermal industry. For example, geothermal operations involve contacting metal surfaces where corrosive components such as brine are present. These harsh conditions can cause severe corrosion, as evidenced by pitting, embrittlement, and general metal loss on the surface. The metal surface can be composed of high-alloy steels including chromium steel, ferritic alloy steel, austenitic stainless steel, precipitation - 45 hardened stainless steel, and high nickel-containing steel.

Means for Solving the Problem

[0005] A method for suppressing corrosion of a metal surface in contact with a geothermal system is provided. This method may include contacting the metal surface with a corrosion inhibitor composition. The corrosion inhibitor composition may include an organic phosphonate, orthophosphate, and zinc or its salt.

[0006] In some embodiments, the organic phosphonate can be 2,2'-(hydroxyphosphoryl) disuccinic acid (PSO), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), ((dimethylamino)methylene) bis(phosphonic acid) (DMAMDP), N,N-dimethyl-1,1-diphosphonomethaneamine oxide (DMAMDPO), (morpholinomethylene) bis(phosphonic acid) (MMDP), 4-(diphosphonomethyl) morpholine 4-oxide (MMDPO), hydroxyphosphonoacetic acid (HPA), phosphinocarboxylic acid (PCA), or any combination thereof.

[0007] In some embodiments, the corrosion inhibitor composition can include from about 1 wt% to about 20 wt% of an organic phosphonate.

[0008] In some embodiments, the corrosion inhibitor composition can include from about 10 wt% to about 40 wt% of orthophosphate.

[0009] In some embodiments, the corrosion inhibitor composition can include from about 2 wt% to about 15 wt% of zinc or its salt.

[0010] In some embodiments, the corrosion inhibitor composition may further include a fluorescent tracer.

[0011] In some embodiments, the corrosion inhibitor composition may include from about 0.01 wt% to about 0.5 wt% of a fluorescent tracer.

[0012] In some embodiments, the method may include passivating a metal surface with a corrosion inhibitor composition.

[0013] In some embodiments, the metal surface may be contacted with an aqueous medium containing from about 50 ppm to about 400 ppm of the corrosion inhibitor composition.

[0014] In some embodiments, the metal surface may be contacted with an aqueous medium having a pH of from about 4 to about 8.

[0015] In some embodiments, the corrosion inhibitor composition may be added to the aqueous medium at a dosage rate of from about 0.01 ppm to about 500 ppm.

[0016] In some embodiments, the metal surface may be iron, copper, an iron alloy, a copper alloy, admiralty brass, about 90% copper and about 10% nickel, about 80% copper and about 20% nickel, about 70% copper and about 30% nickel, aluminum brass, manganese brass, leaded naval bronze, phosphor bronze, carbon, and any combination thereof.

[0017] In some embodiments, the metal surface may include iron.

[0018] In some embodiments, the metal surface may be mild steel or carbon steel.

[0019] In some embodiments, the corrosion rate of the metal surface may be less than about 3 mpy.

[0020] In some embodiments, the corrosion rate of the metal surface may be less than about 1 mpy.

[0021] In some embodiments, the corrosion inhibitor composition may include a water-miscible co-solvent.

[0022] In some embodiments, the water-miscible co-solvent may be selected from the group consisting of acetone, methanol, ethanol, propanol, formic acid, formamide, propylene glycol, ethylene glycol, and any combination thereof.

[0023] In some embodiments, the corrosion inhibitor composition may include additives selected from the group consisting of additional corrosion inhibitors, treatment polymers, antibacterial agents, scale inhibitors, colorants, fillers, buffers, surfactants, viscosity modifiers, chelating agents, dispersants, deodorants, masking agents, deoxidizers, indicator dyes, and any combination thereof.

[0024] Also provided is the use of a corrosion inhibitor composition for inhibiting corrosion of a metal surface in contact with an aqueous medium in a geothermal system. The corrosion inhibitor composition may include an organic phosphonate, orthophosphate, and zinc or a salt thereof.

[0025] The foregoing has outlined the features and technical advantages of the present disclosure so as to better understand the manner in which the following invention is practiced. Additional features and advantages of the present disclosure, which form the subject of the claims of this application, will be described below. It should be understood by those skilled in the art that the disclosed concepts and specific embodiments may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present disclosure. It should also be recognized by those skilled in the art that such equivalent embodiments do not depart from the spirit and scope of the present disclosure as set forth in the appended claims.

Brief Description of the Drawings

[0026] A detailed description of the invention will be set forth hereinbelow with specific reference to the following drawings.

[0027]

Figure 1

[0028]

Figure 2

[0029] Various embodiments are described below. The relationships and functions of the various elements of the embodiments can be better understood by referring to the following detailed description. However, the embodiments are not limited to those illustrated below. In certain examples, details not necessary for understanding the embodiments disclosed herein can be omitted.

[0030] A method for suppressing corrosion of a metal surface in contact with a geothermal system is provided. The method can include contacting the metal surface with a corrosion inhibitor composition. The corrosion inhibitor composition can include an organic phosphonate, an orthophosphate, and zinc or a salt thereof.

[0031] In some embodiments, the organic phosphonate can be 2,2'-(hydroxyphosphoryl) disuccinic acid (PSO), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), ((dimethylamino)methylene) bis(phosphonic acid) (DMAMDP), N,N-dimethyl-1,1-diphosphonomethaneamine oxide (DMAMDPO), (morpholinomethylene) bis(phosphonic acid) (MMDP), 4-(diphosphonomethyl) morpholine 4-oxide (MMDPO), hydroxyphosphonoacetic acid (HPA), phosphinocarboxylic acid (PCA), or any combination thereof.

[0032] In some embodiments, the organic phosphonate can be PSO. In some embodiments, the organic phosphonate can be PBTC. In some embodiments, the organic phosphonate can be DMAMDP. In some embodiments, the organic phosphonate can be DMAMDPO. In some embodiments, the organic phosphonate can be MMDP. In some embodiments, the organic phosphonate can be MMDPO. In some embodiments, the organic phosphonate can be HPA. In some embodiments, the organic phosphonate can be PCA.

[0033] The corrosion inhibitor composition can include an effective amount of an organic phosphate to maximize corrosion inhibition. The amount of the organic phosphonate in the composition can be from about 1 wt% to about 20 wt% of the organic phosphonate. In some embodiments, the amount of the organic phosphonate in the corrosion inhibitor composition can be about 2 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, about 10 wt%, about 11 wt%, about 12 wt%, about 13 wt%, about 14 wt%, about 15 wt%, about 16 wt%, about 17 wt%, about 18 wt%, or about 19 wt%.

[0034] The corrosion inhibitor composition can include an effective amount of orthophosphate to maximize corrosion inhibition. The corrosion inhibitor composition can include from about 10 wt% to about 40 wt% of orthophosphate. In some embodiments, the amount of orthophosphate in the composition can be about 15 wt%, about 20 wt%, about 25 wt%, about 30 wt%, about 35 wt%, or about 40 wt%.

[0035] The corrosion inhibitor composition can include an effective amount of zinc or its salt to maximize corrosion inhibition. In some embodiments, the corrosion inhibitor composition can include from about 2 wt% to about 15 wt% of zinc or its salt. In some embodiments, the amount of zinc in the composition can be about 3 wt%, about 4 wt%, about 5 wt%, about 6 wt%, about 7 wt%, about 8 wt%, about 9 wt%, about 10 wt%, about 11 wt%, about 12 wt%, about 13 wt%, about 14 wt%, or about 15 wt%.

[0036] In some embodiments, the corrosion inhibitor composition may further include a fluorescent tracer. In some embodiments, the composition may be made compatible with a fluorescence tracking technology, such as the TRASAR® technology (available from Nalco® Company, Naperville, Ill., USA), by including an inert tracer. In other embodiments, an inert fluorescent tracer may be included in the composition to provide a means for determining the dosage level. A fluorescent tracer in a known ratio may be added simultaneously or continuously with the corrosion inhibitor. An effective inert fluorescent tracer may include a substance that is chemically non-reactive with other components in the system and does not significantly deteriorate over time.

[0037] Representative inert fluorescent tracers include fluorescein or fluorescein derivatives; rhodamine or rhodamine derivatives; naphthalenesulfonic acids (mono, di, tri, etc.); pyrenesulfonic acids (mono, di, tri, tetra, etc.); stilbene derivatives containing sulfonic acids (including optical brighteners); biphenylsulfonic acids; phenylalanine; tryptophan; tyrosine; vitamin B2 (riboflavin); vitamin B6 (pyridoxine); vitamin E (α-tocopherol); ethoxyquin; caffeine; vanillin; naphthalenesulfonic acid formaldehyde condensation polymers; phenylsulfonic acid formaldehyde condensates; ligninsulfonic acids; polycyclic aromatic hydrocarbons; (poly)cyclic aromatic hydrocarbons containing amine, phenol, sulfonic acid, and carboxylic acid functional groups in any combination; (poly)heterocyclic aromatic hydrocarbons having N, O, or S; and polymers containing at least one moiety of naphthalenesulfonic acid, pyrenesulfonic acid, biphenylsulfonic acid, or stilbenesulfonic acid.

[0038] In some embodiments, the corrosion inhibitor composition may include from about 0.01 wt% to about 0.5 wt% of a fluorescent tracer. The amount of fluorescent tracer included in the composition or added separately from the composition may be sufficient to track the dosage level of the corrosion inhibitor in the aqueous system.

[0039] In some embodiments, the metal surface can be iron, copper, an iron alloy, a copper alloy, admiralty brass, about 90% copper and about 10% nickel, about 80% copper and about 20% nickel, about 70% copper and about 30% nickel, aluminum brass, manganese brass, leaded naval bronze, phosphor bronze, carbon, and any combination thereof. In some embodiments, the metal surface can include iron. In some embodiments, the metal surface can be mild steel or carbon steel.

[0040] In some embodiments, the method can include passivating the metal surface with a corrosion inhibitor composition. Passivating the metal surface can include adding the composition directly to the metal surface or adding the composition to an aqueous system at a higher dosage for a period of time and then reducing the dosage to a maintenance dosage.

[0041] In some embodiments, the metal surface can be contacted with an aqueous medium containing about 50 ppm to about 400 ppm of the corrosion inhibitor composition.

[0042] In some embodiments, the corrosion inhibitor can be added to the aqueous medium at a concentration of about 1 ppm to about 1000 ppm, about 1 ppm to about 800 ppm, about 1 ppm to about 600 ppm, about 1 ppm to about 500 ppm, about 1 ppm to about 400 ppm, about 1 ppm to about 200 ppm, about 5 ppm to about 1000 ppm, about 5 ppm to about 800 ppm, about 5 ppm to about 600 ppm, about 5 ppm to about 500 ppm, about 5 ppm to about 400 ppm, or about 5 ppm to about 200 ppm. In some embodiments, the corrosion inhibitor composition can be added to the aqueous medium at a dosing rate of about 0.01 ppm to about 500 ppm.

[0043] In some embodiments, the metal surface can be contacted with an aqueous medium having a pH of about 4 to about 8. In some embodiments, the pH of the aqueous medium is about 4.5, about 5, about 5.5, about 6, about 6.5, about 7, or about 7.5.

[0044] The compositions disclosed herein can reduce the corrosion rate of metal surfaces that come into contact with an aqueous medium in a geothermal system. The corrosion rate of the metal surface can be less than about 3 mpy. In some embodiments, the corrosion rate of the metal surface can be less than about 2.5 mpy, about 2 mpy, 1.5 mpy, or about 1 mpy.

[0045] In some embodiments, the corrosion inhibitor composition can include a water-miscible co-solvent. Examples of water-miscible co-solvents include, but are not limited to, acetone, methanol, ethanol, propanol, formic acid, formamide, propylene glycol, or ethylene glycol.

[0046] The corrosion inhibitor composition can include additives. Examples of additives include, but are not limited to, additional corrosion inhibitors, treatment polymers, antibacterial agents, scale inhibitors, colorants, fillers, buffers, surfactants, deoxidizers, chelating agents, dispersants, deodorants, masking agents, deoxidizers, indicator dyes, or defoamers.

[0047] In some embodiments, the method can include adding a defoamer to the process water used in a geothermal system. The process water can be geothermal cooling water or geothermal condensate. Examples of defoamers include, but are not limited to, C5-C 25 alkyl alcohols, C5-C 25 alkyl alcohol ethoxylates, aluminum monostearate, stearic acid, polydimethylsiloxane, sorbitan monostearate, hydrated silica, ethoxylated sorbitan monostearate, xanthan gum, and amorphous silica. In some embodiments, the defoamer can include water, polydimethylsiloxane, and sorbitan monostearate. In other embodiments, the defoamer can consist of water, polydimethylsiloxane, sorbitan monostearate, hydrated silica, ethoxylated sorbitan monostearate, and xanthan gum.

[0048] In some embodiments, the antifoaming agent can be added to the process water in an amount from about 0.001 ppm to about 100 ppm. In some embodiments, the antifoaming agent can be added to the process water in an amount from about 0.001 ppm to about 10 ppm, from about 0.001 ppm to about 5 ppm, from about 0.01 ppm to about 10 ppm, from about 0.05 ppm to about 5 ppm, from about 0.05 ppm to about 2 ppm, from about 0.05 ppm to about 10 ppm, or from about 0.1 ppm to about 1 ppm.

[0049] In certain embodiments, an iron catalyst can be added to the process water. In other embodiments, an iron catalyst is not added to the process water. The iron catalyst can include an iron salt, an iron complex, or a combination thereof. The iron catalyst can be, for example, ferrous sulfate, ferric sulfate, ferric chloride, ferrous gluconate, ferric nitrate, iron(III) oxyhydroxide [FeO(OH)], ferrous chloride, ferrous iodide, iron sulfide, iron 4-cyclohexyl-butyrate, ferric oxide, ferric bromide, ferrous fluoride, iron powder, ferrous acetate, ferrous oxalate, ferric oxalate, etc.

[0050] In certain embodiments, hydrogen peroxide can be added to the process water. In other embodiments, hydrogen peroxide is not added to the process water.

[0051] Additional corrosion inhibitors that can be included in the composition or added separately to the process water include C 14 ~C 22 monomeric or oligomeric fatty acids such as saturated and unsaturated fatty acids, and dimer, trimer, and oligomeric products obtained by polymerizing one or more of such fatty acids. The corrosion inhibitor can be a triazole. Examples of triazoles include, but are not limited to, benzotriazole, tolyltriazole, butylbenzotriazole, halobenzotriazole, halo-tolyltriazole, or nitrated triazole. In some embodiments, the additional corrosion inhibitor can be a 2-substituted benzimidazole.

[0052] In some embodiments, the additional corrosion inhibitor is benzyl-(C12 ~C 16 can include (alkyl)-dimethyl-ammonium chloride. In some embodiments, the corrosion inhibitor is benzyl-(C 12 ~C 16 alkyl)-dimethyl-ammonium chloride, ethoxylated alcohol phosphate salt, imidazoline salt, 2-mercaptoethanol, ethylene glycol, diethylene glycol, methanol, 2-butoxyethanol, and water. In some embodiments, the corrosion inhibitor includes sodium gluconate.

Examples

[0053] Example 1

[0054] The compounds used in these examples include phosphonate (CAS number 770734-50-4), phosphoric acid (CAS number 7664-38-2), zinc chloride (CAS number 7646-85-7), and a fluorescent tracer (CAS number 59572-10-0). Composition 1 includes PSO, phosphoric acid, zinc chloride, and a fluorescent tracer. Composition 2 includes imidazoline acetate of tall oil, a quaternary ammonium compound, and a substituted carboxylic acid.

[0055] A composition containing molybdate (MoO4) as a corrosion inhibitor was tested under conditions mimicking geothermal reinjection well water. However, high doses of molybdate were required to achieve acceptable corrosion inhibition. Unexpectedly, it was discovered that a composition containing phosphonate, phosphoric acid, and zinc provides the best corrosion inhibition even at a pH of about 5 - 6.5 in geothermal reinjection wells. Gamry corrosion data was performed by mimicking reinjection well conditions at lower pH. The measured corrosion rate was less than about 1 mpy.

[0056] Figure 1 shows the corrosion rates for different chemicals. The average corrosion rate of the blank was 7.35 mpy. Composition 1 exceeded the other chemicals with a corrosion rate of 0.67 mpy (the coupon appeared transparent with no corrosion). The metal coupon was passivated for 18 hours using approximately 100 ppm of Composition 1, and then the dosage was lowered to approximately 15 ppm over 24 hours. The coupon treated with MoO4 had started to visibly corrode. The average corrosion rate was 2.1 mpy for 30 ppm of MoO4 and 1.32 mpy for 50 ppm of MoO4. The MoO4-treated coupon was passivated for 18 hours using 100 ppm of MoO4, and then the dosage was lowered to 30 ppm and 50 ppm of MoO4.

[0057] Example 2

[0058] Water containing 1.3 ppm Ca, 0.1 ppm Mg, 68 ppm alkalinity as CaCO3, and 93 ppm sulfate as ions was prepared to simulate geothermal reinjection well water. Dilute sulfuric acid was used to adjust the pH of the water to 6.3. According to Table 1, approximately 1 liter of water was added to a gum cell, an inhibitor was added for passivation, and the corrosion rate was measured for approximately 18 hours. Then the water was exchanged for fresh water with a maintained dosage of the inhibitor and heated to approximately 40 °C. The pH was maintained at approximately 6 - 6.3 for approximately 24 hours.

Table 1

[0059] The metal was mild steel, and Composition 1 provided the best corrosion control at a dosage of approximately 15 ppm. No corrosion was observed on the coupon treated with Composition 1. The average corrosion rate was approximately 0.6 mpy. Figure 2 shows the corrosion rates for different tests over time.

[0060] The average corrosion rate for MoO4 at a dosage of 50 ppm was about 1.3 mpy, but the coupons began to corrode, which was relatively better than that for 30 ppm MoO4. The metal coupons treated with Composition 2 began to corrode during the passivation step of 100 ppm, and the average corrosion rate was 4.0 mpy. The blank corrosion rate exceeded about 5 mpy even at room temperature.

[0061] Any composition disclosed herein can comprise, consist of, or consist essentially of any of the compounds / components disclosed herein. According to the present disclosure, phrases such as "consist essentially of", "consists essentially of", "consisting essentially of" limit the scope of the claims to specific materials or steps and materials or steps that do not substantially affect the basic and novel characteristics of the claimed invention.

[0062] As used herein, the term "about" refers to a quoted value that is within the error resulting from the standard deviation found in their respective test measurements, and where such error cannot be determined, "about" refers to within 5% of the quoted value.

[0063] Any method disclosed herein can comprise, consist of, or consist essentially of any of the method steps disclosed herein, or any combination of two or more of the method steps disclosed herein.

[0064] Unless otherwise specified, all molecular weights referred to herein are weight-average molecular weights, and all viscosities were measured at 25 °C using neat (undiluted) polymers.

[0065] All of the compositions and methods disclosed and claimed in this specification can be made and executed without undue experimentation in light of the present disclosure. The present invention can be embodied in many different forms, and specific preferred embodiments of the invention are described in detail herein. This disclosure is illustrative of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. In addition, unless expressly stated to the contrary, the use of the term "a" is intended to include "at least one" or "one or more." For example, "a dispersant" is intended to include "at least one dispersant" or "one or more dispersants."

[0066] Any range given in either absolute or approximate terms is intended to cover both, and any definitions used herein are intended to be clarifying and not limiting. Numerical ranges and parameters setting forth the broad scope of the invention are approximations, although the numerical values set forth in specific examples are reported as accurately as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective test measurements. Further, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein (including all fractional and whole values).

[0067] Furthermore, the present invention encompasses any and all possible combinations of some or all of the various embodiments described herein. It is also to be understood that various changes and modifications to the preferred embodiments of the invention described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the invention and without diminishing its intended advantages. Accordingly, such changes and modifications are intended to be covered by the appended claims. Examples of embodiments of the present disclosure are listed in the following items [1] to

[20] . [1] A method for suppressing corrosion of a metal surface in contact with a geothermal system, comprising contacting the metal surface with a corrosion inhibitor composition, the corrosion inhibitor composition being composed of an organic phosphonate, an orthophosphate, and zinc or a salt thereof. [2] The method according to item 1, wherein the organic phosphonate is 2,2'-(hydroxyphosphoryl) disuccinic acid (PSO), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), ((dimethylamino)methylene) bis(phosphonic acid) (DMAMDP), N,N-dimethyl-1,1-diphosphonomethaneamine oxide (DMAMDPO), (morpholinomethylene) bis(phosphonic acid) (MMDP), 4-(diphosphonomethyl) morpholine 4-oxide (MMDPO), hydroxyphosphonoacetic acid (HPA), phosphinocarboxylic acid (PCA), or any combination thereof. [3] The method according to item 1 or 2, wherein the corrosion inhibitor composition contains about 1 wt% to about 20 wt% of the organic phosphonate. [4] The method according to any one of items 1 to 3, wherein the corrosion inhibitor composition contains about 10 wt% to about 40 wt% of the orthophosphate. [5] The method according to any one of items 1 to 4, wherein the corrosion inhibitor composition contains about 2 wt% to about 15 wt% of the zinc or a salt thereof. [6] The method according to any one of items 1 to 5, wherein the corrosion inhibitor composition further contains a fluorescent tracer. [7] The method according to item 6, wherein the corrosion inhibitor composition contains about 0.01 wt% to about 0.5 wt% of the fluorescent tracer. [8] The method according to any one of items 1 to 7, further comprising passivating the metal surface with the corrosion inhibitor composition. [9] The method according to any one of items 1 to 8, wherein the metal surface is in contact with an aqueous medium containing about 50 ppm to about 400 ppm of the corrosion inhibitor composition.

[10] The method according to any one of items 1 to 9, wherein the metal surface is in contact with an aqueous medium having a pH of about 4 to about 8.

[11] The method according to any one of items 1 to 10, wherein the corrosion inhibitor composition is added to the aqueous medium at a dosing rate of about 0.01 ppm to about 500 ppm.

[12] The method according to any one of items 1 to 11, wherein the metal surface comprises iron, copper, iron alloy, copper alloy, admiralty brass, about 90% copper and about 10% nickel, about 80% copper and about 20% nickel, about 70% copper and about 30% nickel, aluminum brass, manganese brass, leaded naval bronze, phosphor bronze, carbon, and any combination thereof.

[13] The method according to any one of items 1 to 12, wherein the metal surface comprises iron.

[14] The method according to any one of items 1 to 13, wherein the metal surface is mild steel or carbon steel.

[15] The method according to any one of items 1 to 14, wherein the corrosion rate of the metal surface is less than about 3 mpy.

[16] The method according to any one of items 1 to 15, wherein the corrosion rate of the metal surface is less than about 1 mpy.

[17] The method according to any one of items 1 to 16, wherein the corrosion inhibitor composition comprises a water-miscible co-solvent.

[18] The method according to item 17, wherein the water-miscible co-solvent is selected from the group consisting of acetone, methanol, ethanol, propanol, formic acid, formamide, propylene glycol, ethylene glycol, and any combination thereof.

[19] The method according to any one of items 1 to 18, wherein the corrosion inhibitor composition comprises an additive selected from the group consisting of additional corrosion inhibitors, treatment polymers, antibacterial agents, scale inhibitors, colorants, fillers, buffers, surfactants, viscosity modifiers, chelating agents, dispersants, deodorants, masking agents, deoxidizers, indicator dyes, and any combination thereof.

[20] Use of a corrosion inhibitor composition for inhibiting corrosion of a metal surface in contact with an aqueous medium in a geothermal system, the corrosion inhibitor composition comprising an organic phosphonate, orthophosphate, and zinc or a salt thereof.

Claims

1. A method for suppressing corrosion of a metal surface in contact with an aqueous medium of a geothermal system, comprising contacting the metal surface with a corrosion inhibitor composition, the corrosion inhibitor composition being composed of an organic phosphonate, an orthophosphate, and zinc or a salt thereof, the organic phosphonate being 2,2'-(hydroxyphosphoryl)disuccinic acid (PSO), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), hydroxyphosphonoacetic acid (HPA), phosphinocarboxylic acid (PCA), or any combination thereof, the aqueous medium having a pH of 4 to 6.

5.

2. The method according to claim 1, wherein the corrosion inhibitor composition contains 1% to 20% by weight of the organic phosphonate.

3. The method according to claim 1 or 2, wherein the corrosion inhibitor composition contains 10% to 40% by weight of the orthophosphate.

4. The method according to any one of claims 1 to 3, wherein the corrosion inhibitor composition contains 2% to 15% by weight of the zinc or a salt thereof.

5. The method according to any one of claims 1 to 4, wherein the corrosion inhibitor composition further contains a fluorescent tracer.

6. The method according to claim 5, wherein the corrosion inhibitor composition contains 0.01% to 0.5% by weight of the fluorescent tracer.

7. The method according to any one of claims 1 to 6, further comprising passivating the metal surface with the corrosion inhibitor composition.

8. The method according to any one of claims 1 to 7, wherein the metal surface is in contact with an aqueous medium containing 50 ppm to 400 ppm of the corrosion inhibitor composition.

9. The method according to any one of claims 1 to 8, wherein the corrosion inhibitor composition is added to the aqueous medium at a dosing rate of 0.01 ppm to 500 ppm.

10. The method according to any one of claims 1 to 9, wherein the metal surface comprises iron, copper, iron alloy, copper alloy, admiralty brass, 90% copper and 10% nickel, 80% copper and 20% nickel, 70% copper and 30% nickel, aluminum brass, manganese brass, leaded naval bronze, phosphor bronze, carbon, and any combination thereof.

11. The method according to any one of claims 1 to 10, wherein the metal surface comprises iron.

12. The method according to any one of claims 1 to 11, wherein the metal surface is mild steel or carbon steel.

13. The method according to any one of claims 1 to 12, wherein the corrosion rate of the metal surface is less than 3 mpy.

14. The method according to any one of claims 1 to 13, wherein the corrosion rate of the metal surface is less than 1 mpy.

15. The method according to any one of claims 1 to 14, wherein the corrosion inhibitor composition comprises a water-miscible co-solvent.

16. The method according to claim 15, wherein the water-miscible co-solvent is selected from the group consisting of acetone, methanol, ethanol, propanol, formic acid, formamide, propylene glycol, ethylene glycol, and any combination thereof.

17. The method according to any one of claims 1 to 16, wherein the corrosion inhibitor composition comprises an additive selected from the group consisting of additional corrosion inhibitors, treatment polymers, antibacterial agents, scale inhibitors, colorants, fillers, buffers, surfactants, viscosity modifiers, chelating agents, dispersants, deodorants, masking agents, deoxidizers, indicator dyes, and any combination thereof.

18. Use of a corrosion inhibitor composition for suppressing corrosion of a metal surface in contact with an aqueous medium having a pH of 4 to 6.5 in a geothermal system, wherein the corrosion inhibitor composition comprises an organic phosphonate, orthophosphate, and zinc or a salt thereof, wherein the organic phosphonate is 2,2'-(hydroxyphosphoryl) disuccinic acid (PSO), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), hydroxyphosphonoacetic acid (HPA), phosphinocarboxylic acid (PCA), or any combination thereof.

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