WO2006136262A1

WO2006136262A1 - Corrosion inhibitor for acids

Info

Publication number: WO2006136262A1
Application number: PCT/EP2006/005009
Authority: WO
Inventors: Antoni PUÑET PLENSA; Lluís LOZANO SALVATELLA
Original assignee: Kao Corp SA
Current assignee: Kao Corp SA
Priority date: 2005-06-23
Filing date: 2006-05-25
Publication date: 2006-12-28
Anticipated expiration: 2007-12-23
Also published as: GB2441727A; GB2441727B; NO341782B1; GB0800854D0; NO20080427L; AR055056A1; ES2273581B1; ES2273581A1

Abstract

New compositions for inhibiting corrosion in pipes, pumps and other metallic materials that may be in contact with highly acidic solutions used in the stimulation of oil wells and the like are described. Said compositions contain (a) cinnamaldehyde and/or substituted cinnamaldehyde, and (b) urea.

Description

CORROSION INHIBITOR FOR ACIDS

SPECIFICATION

Field of the Invention

The present invention belongs to the field of corrosion inhibitors and to the methods for inhibiting corrosion m pipes, pumps and other metallic materials that can be in contact with highly acidic solutions used in the stimulation of oil wells and the like.

State of the Art

Hydrocarbons (petroleum, natural gas, etc) are obtained from an underground geological formation (in other words, a deposit) by drilling a well that penetrates the geological formation containing said hydrocarbons. A deposit is an underground rocky body that is sufficiently porous and permeable to store and transmit fluids.

The recovery of hydrocarbons varies due to factors related to the heterogeneity of the deposit (type of rocky body forming it), the type of fluid produced, the drainage mechanisms, etc.

Hydrocarbon producers normally carry out stimulation techniques with acid to increase the overall permeability of the deposit, creating conducting routes from the deposit to the well and passing through the area surrounding the well which has been damaged during the drilling and foundation .

The stimulation techniques include: (1) injecting chemical products into the well to react with and to dissolve the area surrounding the well which has been damaged; (2) injecting chemical products through the well and into the geological formation to react with and to dissolve small portions of rock to create small conducting channels (conducting wormholes) through which the hydrocarbon will flow (so that rather than eliminating the damaged areas, the hydrocarbon is re-directed through said areas);

(3) injecting chemical products through the well and forming pressures sufficient to really break up the rock, thus creating a large flow channel allowing the hydrocarbon to migrate rapidly from the rock to the well.

Normally, acids or acid-based liquids are used for this purpose due to their ability to dissolve minerals and pollutants introduced in the well during drilling or recovery operations. The most common agents used in well stimulation with acids are mineral acids such as hydrochloric (HCl) and/or hydrofluoric acid (HF), generally in the form of 15% by weight acid solutions.

A problem inherent to stimulation with acids is the corrosion of the pump equipment and of the pipes of the well caused by contact with the acid, although the petroleum and natural gas or the water entrained therewith also contain corrosive components, for example, CO₂ or H₂S and salts, leading to severe corrosion of the metallic surfaces. Furthermore, the working liquids used in this field, for example, the sludge for the sweeping of the drillings, contribute to corrosion.

Therefore, the so-called corrosion inhibitors are used for protection against corrosion, and are added to the liquids which come into contact with metallic surfaces. Corrosion inhibitors either form a film on the metallic surface or reduce the corrosion process by means of physical and chemical reactions on metallic surfaces. Additives for very acidic solutions which, on one hand, are not only effective as corrosion inhibitors but also do not increase the environmental risks of the process, have been sought for some time. Innumerable compositions containing amines, quaternary ammonium compounds, acetylene alcohols and/or ethoxylated phenol type surfactants, are described in the state of the art. Said compounds are considered to be to be hazardous for the environment. On the other hand, patent US-A-3589860 describes the use of cinnamaldehyde or derivatives thereof as a corrosion inhibitor for equipment used in chemical processes and for petroleum extraction equipment in contact with acid media.

Patent US-A-4734259 describes a composition and a method for inhibiting corrosive aqueous fluid attack on metals by means of a composition including an α, β- unsaturated aldehyde and a surfactant. Cinnamaldehyde and derivatives thereof are included among the preferred α, β- unsaturated aldehydes. Alkylaryl sulphonates, quaternary ammonium compounds and alkyl and alkylaryl polyether alcohols are among the preferred surfactants.

Patent US-A-5120471 describes a composition for inhibiting steel corrosion containing more than 9% of chromium in the presence of at least one mineral acid, said composition comprising: a) an organic inhibitor selected from the group consisting of phenylacetone, phenylacetone with a quaternary ammonium salt of a heterocyclic aromatic compound, and cinnamaldehyde with a quaternary ammonium salt of a heterocyclic aromatic compound; and b) a compound soluble in acid of antimony or bismuth type.

Patent US-A-5854180 describes a composition for inhibiting corrosion caused by hydrochloride acid solutions used for acidifying petroleum wells, in which said composition comprises a) 10-30% by weight of cinnamaldehyde or substituted cinnamaldehyde; b) 20-50% by weight of ethylene glycol; c) 5-20% by weight of C₈-Ci2 ethoxylated alcohols; d) 1-15% by weight of a composition containing 10-40% by weight of isopropanol and of a reaction product of a ketone with 3-9 carbon atoms, urea, thiourea or alkyl- substituted thiourea, benzaldehyde or formaldehyde and hydrochloric acid.

Finally, patents US-A-6068056 and US-B-6399547 describe compositions used for stimulating petroleum wells comprising: an acid, such as hydrochloric acid, water, an aliphatic aldehyde with 1-10 carbon atoms and an aromatic aldehyde with 7-20 carbon atoms. Preferred aliphatic aldehydes are glyoxalic acid and glyoxal. A preferred aromatic aldehyde is cinnamaldehyde.

Although some compositions from the state of the art have reached a certain degree of effectiveness against corrosion, they are questionable from an environmental point of view in some cases. On the other hand, given that cinnamaldehyde and/or substituted cinnamaldehyde are quite expensive, it is necessary to develop corrosion inhibitors for acids that provide an efficient technical performance that overcome the environmental and financial drawbacks set forth. Object of the Invention

Surprisingly, the combination of cinnamaldehyde and/or substituted cinnamaldehyde with urea provides a corrosion inhibiting composition reducing the attack of several aqueous fluids, such as aqueous acids, against ferrous metals, such as iron and steel, as well as against non- ferrous metals, such as aluminium, zinc and copper.

The inventors have observed a synergistic effect when the components of the composition of the invention are combined, providing corrosion inhibition thereof order or greater than the ones of compositions containing only cinnamaldehyde and/or substituted cinnamaldehyde and much greater than compositions containing only urea Therefore, it is an object of the present invention to provide a composition for inhibiting the corrosion of metals in a fluid aqueous medium comprising:

(a) cinnamaldehyde and/or substituted cinnamaldehyde, and (b) urea.

Another object of the present invention relates to an acid-type aqueous solution comprising a composition for inhibiting metal corrosion according to the invention and an acid. A method for stimulating an underground rocky formation consisting of placing an acid-type aqueous solution of the invention into contact with an underground rocky formation forms part of the object of the invention. Description of the Invention Cinnamaldehyde or substituted cinnamaldehyde

Cinnamaldehyde or 3-phenyl-2-propen-l-al is obtained naturally from cinnamon oil.

A conjugated double bond (C₆H₅CH=CHCHO) causes the geometry of the compound to be planar and, therefore, a mixture of isomers (cis and trans) can be found.

According to the present invention, cinnamaldehyde can be substituted or unsubstituted. Examples of cmnamaldehydes that can be used in the present invention are: dicinnamaldehyde; p-hydroxycinnamaldehyde; p- methylcinnamaldehyde; p-ethylcinnamaldehyde; p- methoxycinnamaldehyde; p-dimethylaminocinnamaldehyde; p- diethylaminocmnamaldehyde; p-nitrocmnamaldehyde; o- nitrocinnamaldehyde; 4- ( 3-propenal) cinnamaldehyde; sodium p-sulphocinnamaldehyde; p-tnmethylammoniumcinnamaldehyde sulphate; p-trimethylammoniumcmnamaldehyde o- methylsulphate; p-thiocyanocinnamaldehyde; p-(S- acetyl ) thiocinnamaldehyde; p- (S-N, N- dimethylcarbamoylthio) cinnamaldehyde ; p- chlorocinnamaldehyde ; α-methylcinnamaldehyde; β- methylcinnamaldehyde; α-chlorocinnamaldehyde; α- bromocinnamaldehyde; α-butylcinnamaldehyde; α- amylcinnamaldehyde; α-hexylcinnamaldehyde; α-bromo-p- cyanocinnamaldehyde; α-ethyl-p-methylcinnamaldehyde and p- methyl-α-pentylcinnamaldehyde .

Cinnamaldehyde is preferred according to the present invention. It is preferred that cinnamaldehyde should be mainly trans-cinnamaldehyde . In this context, "mainly" means that if cinnamaldehyde contains a mixture of isomers, trans-cinnamaldehyde is present in a proportion greater than 50% by weight of said mixture Urea

Urea or carbonyldiamide is a colourless crystalline chemical compound, with formula CO (NH₂) ₂- It is found abundantly in human and mammal urine.

Urea is also present in fungus mould as well as in leaves and seeds of a number of legumes and cereals. It is soluble in water and in alcohol and slightly soluble in ether.

According to the present invention, it is preferred that the weight ratio between cinnamaldehyde and/or substituted cinnamaldehyde (a) and urea (b) is comprised between 50:1 and 1:6, preferably between 35:1 and 1:4, more preferably between 15:1 and 1:3, and most preferably between 8:1 and 1:2. A surfactant (c) can further be incorporated in the composition for inhibiting metal corrosion of the present invention .

Cationic, non-ionic and amphoteric surfactants can be used together with cinnamaldehyde and/or substituted cinnamaldehyde (a) and urea (b) in the compositions for inhibiting metal corrosion of the present invention. Said surfactants can be dissolved in liquids, normally water.

According to the present invention, the surfactants are considered to have 100% of active substance (active ingredient) .

Suitable cationic surfactants according to the present invention are:

C_e-C₂2 alkyl amines (R-NH₂) , di C₆-C₂₂ alkyl amines (R₂-NH) or tri C₆-C₂₂ alkyl amines (R₃-N) (such as fatty coconut, tallow or oleic monoalkyl amines and dialkyl amines), in the form of an addition salt from the neutralization with organic (acetic, citric, oleic, etc.) or inorganic (hydrochloric, etc.) acids - C₆-C₂₂ alkyl dimethyl amines (R-N(CH₃J₂) and di C₆- C₂₂ alkyl methyl amines (R₂-NCH₃) from coconut, tallow or oleic fats, in the form of an addition salt from the neutralization of organic (acetic, citric, oleic, etc.) or inorganic (hydrochloric, etc.) acids - Alcoxylated C₅-C₂₂ alkyl amines (R-NH₂), di C₆-C₂₂ alkyl amines (R₂-NH) or tri C₆-C₂₂ alkyl amines (R₃-N), generally ethoxylated and/or propoxylated (such as fatty coconut, tallow or oleic monoalkyl amines and dialkyl amines with 2-30 moles of ethylene and/or propylene oxide), optionally quaternized with suitable alkylating agents such as dimethyl sulphate, methyl chloride or benzyl chloride, or in the form of an addition salt from the neutralization with organic (acetic, citric, oleic, etc.) or inorganic (hydrochloric, etc.) acids

Alkylene polyamines, such as C₆-C₂₂ alkyl propylene diamines (R-NH-(CH₂J₃-NH₂), C₆-C₂₂ alkyl propylene triamines (R-NH- (CH₂) ₃-NH- (CH₂) ₃-NH₂) , C₆-C₂₂ alkyl propylene tetraamines (linear and branched), in the form of an addition salt from the neutralization of organic (acetic, citric, oleic, etc.) or inorganic (hydrochloric, etc.) acids - alcoxylated alkylene polyamines, generally ethoxylated and/or propoxylated, such as fatty coconut, tallow or . oleic Cg-C₂₂ alkyl propylene diamines (R-NH-(CH₂J₃-NH₂), fatty coconut, tallow or oleic C₆-C₂₂ alkyl propylene triamines (R-NH-(CH₂J₃-NH- (CH₂J₃-NH₂), fatty coconut, tallow or oleic C₆-C₂₂ alkyl propylene tetraamines (linear and branched), with 2 to 30 moles of ethylene and/or propylene oxide, optionally quaternized with suitable alkylating agents such as dimethyl sulphate, methyl chloride or benzyl chloride, or in the form of an addition salt from the neutralization with organic (acetic, citric, oleic, etc.) or inorganic (hydrochloric, etc.) acids C₆-C₂₂ alkyl ether amines C₆-C₂₂ alkyl imidazolines - C₆-C₂₂ alkyl amidoamines amines of colophony acids (mainly monobasic carboxylic acids containing a phenanthrene skeleton with 20 carbon atoms in the molecule) or of tall oil quaternary ammonium compounds, such as C₆-C₂₂ alkyl dimethyl amines (R-N(CH₃J₂) and C₆-C₂₂ dialkyl methyl amines (R₂-NCH₃) quaternized with suitable alkylating agents such as dimethyl sulphate, methyl chloride or benzyl chloride, as well as heterocyclic ammonium salts. Examples of quaternary ammonium compounds are C₆-C₂₂ alkyl trimethyl ammonium (R- N( + ) (CH₃)₃) chloride or methosulphate, preferably Cio~ Ci₈ alkyl trimethyl ammonium, C₆-C₂₂ dialkyl dimethyl ammonium (R₂-N ( + ) (CH₃) ₂) chloride or methosulphate, preferably Cio-Ciβ dialkyl dimethyl ammonium, C₆-C₂₂ alkyl benzyl dimethyl ammonium chloride, quaternized alkylene polyamines (such as quaternized C₆-C₂₂ alkyl propylene diamines, quaternized C₆-C₂₂ alkyl propylene triamines or quaternized Ce-C₂₂ alkyl propylene tetraamines ) , N-C₅-C₂₂ alkyl pyridinium bromide or chloride (such as N-octyl pyridinium bromide, N-nonyl pyridinium bromide, N-decyl pyridinium bromide, N- dodecyl pyridinium bromide, N-tetradecyl pyridinium bromide, N-dodecyl pyridinium chloride), N-cyclohexyl pyridinium bromide, naphthyl methyl quinolinium chloride, Cg-C₂₂ alkyl methyl quinolinium chloride, naphthyl methyl pyridinium chloride or C₆-C₂₂ alkyl methyl quinolinium chloride. Suitable amphoteric surfactants according to the invention are betaine-type compounds such as: :

C₆-C₂₂ alkyl dimethyl betaines (R-N (CH₃) ₂ (⁺) - CH₂COO^"), obtained from a C₆-C₂₂ alkyl dimethyl amine which is reacted with sodium monochloroacetate, such as Ci₂-Ci₄ dimethyl betaine (carboxylate methyl Ci₂-Ci₄ alkyl dimethylammonium) ,

C₆-C₂₂ alkyl amido betaines (R-CO-NH-CH₂CH₂CH₂- N (CH₃) ₂ (⁺) -CH₂COO^") , obtained by the reaction of sodium monochloroacetate with the reaction product of dimethyl amino propylamine with C₆-C₂₂ fatty acids or its methyl esters, such as Ci₀-Ci₈ amidopropyl dimethylamino betaine, C₆-C₂₂ alkyl and C₆-C₂₂ alkyl amido sulphobetaines

(R-CO-NH-CH₂CH₂CH₂-N (CH₃) ₂ (⁺ ) -CH₂CHOH-CH₂SO₃ ^") , similar products to those previously described in which the carboxylic group has been substituted by a sulphonic group, such as Cio-Ciβ dimethyl sulphohydroxybetaine,

CiO-Ci₈ amido propyl dimethylamino sulphohydroxybetaine, betaine-type imidazoline derivatives, these are products obtained by reaction of a fatty-type alkyl imidazoline with sodium monochloroacetate . In the case of adding 1 mole of sodium monochloroacetate, monocarboxylated derivatives are obtained, whereas if 2 moles of sodium monochloroacetate are added, dicarboxylated derivatives are obtained - C₆-C₂₂ alkyl amino monopropionates and C₆-C₂₂ alkyl amino dipropionates

C₆-C₂₂ alkyl amino amphoacetates and C₆-C₂₂ alkyl amino diamphoacetates, such as sodium coco amino amphoacetate or disodium coco amino diamphoacetate - soybean lecithin.

Suitable non-ionic surfactants according to the invention are: alcohols alkanolamides - amides derived from alkanolamides (coconut fatty acid monoethanolamide, coconut fatty acid diethanolamide, oleic acid diethanolamide, vegetable oil fatty acid diethanolamide) alcoxylated fatty amides, generally ethoxylated and/or propoxylated (such as coconut fatty acid monoethanolamide with 4 moles of ethylene oxide), amine oxides, such as N-cocoamidopropyl dimethyl amine oxide, dimethyl C6-C22 amine oxide, such as dimethyl coco amine oxide,

Esters, such as ethoxylated and/or propoxylated fatty acids (castor oil with 2 to 40 moles of ethylene oxide), ethoxylated and/or propoxylated glycerides (PEG-24 glyceryl monostearate) , glycol esters and derivatives, monoglyceπdes, polyglyceryl esters, esters and ethers of polyalcohols, sorbitan/sorbitol esters and phosphoric acid trimesters

Ethers such as ethoxylated and/or propoxylated fatty alcohols (cetyl stearyl alcohol with 2 to 40 moles of ethylene oxide, lauric alcohol with 2 to 40 moles of ethylene oxide, oleic alcohol with 2 to 40 moles of ethylene oxide, ethoxylated lanoline derivatives, ethoxylated polysiloxanes , PEG propoxylated ethers ( PPG-l-PEG-9-lauryl glycol ether), ethoxylated and/or propoxylated alkylphenols . Preferably, surfactant (c) is selected from alkylene polyammes, optionally alcoxylated, quaternary ammonium compounds, betaine-type amphoteric surfactants, and mixtures thereof.

Preferred cationic surfactants according to the invention are son C₁₀-Ci₈ alkyl trimethyl ammonium chloride or methosulphate, C1₀-C₁₈ dialkyl dimethyl ammonium chloride or methosulphate, C₆-C₂₂ alkyl benzyl dimethyl ammonium chloride, quatermzed C6-C22 alkyl propylene diamine chloride or methosulphate, N-C₆-C₂₂ alkyl pyridinium bromide or chloride, optionally alcoxylated C₆-C₂₂ alkyl propylene diamines, optionally alcoxylated C₆-C₂₂ alkyl propylene triamines, optionally alcoxylated C₆-C2₂ alkyl propylene tetraamines (linear and branched) , and mixtures thereof. Preferred amphoteric surfactants according to the invention are Ci₂-C₁₂ alkyl dimethyl betaine, Ci₀-Ci_S alkyl amidopropyl dimethylamino betaine, Ci₀-CiS dimethyl sulphohydroxybetaine, Ci₀-CiS amido propyl dimethylamino sulphohydroxybetaine, sodium Ci₀-Ci_S alkyl amino amphoacetate, disodium Ci₀-Ci₈ alkyl ammo diamphoacetate, and mixtures thereof.

According to the present invention, the weight ratio between cinnamaldehyde and/or substituted cinnamaldehyde (a) and surfactant (c) is comprised between 50:1 and 1:6, preferably between 35:1 and 1:3, even more preferably between 30:1 and 1:2.

On the other hand, the weight ratio between urea (b) and surfactant (c) is comprised between 30:1 and 1:20, preferably between 20:1 and 1:10.

A solvent (d) can be incorporated into the composition for inhibiting metal corrosion of the present invention with the purpose of solubilizing the cinnamaldehyde and/or substituted cinnamaldehyde (a) , urea (b) or surfactant (c) . Said solvent (d) is selected from water, aprotic polar solvents, aromatic solvents, terpinols, alcohols with 1 to 18 carbon atoms and polyols (polyhydroxylated alcohols) with 2 to 18 carbon atoms and mixtures thereof.

The preferred solvents according to the invention are water, aprotic polar solvents such as formamide, dimethyl formamide (DMF), dimethyl acetamide (DMA) and mixtures thereof, linear or branched alcohols (mono-alcohols, ether- alcohols, etc) with 1 to 18 carbon atoms, optionally alcoxylated, preferably with ethylene oxide and/or propylene oxide, and polyols (polyhydroxylated alcohols) with 2 to 18 carbon atoms, both aromatic, such as pyrocatechol ( 1, 2-benzenediol) , resorcinol (1,3- benzenediol ) , hydroquinone ( 1 , 4-benzenediol ) , or bisphenol A ( 4 , 4 ' -isopropylidenediphenol ) and aliphatic.

Preferably, the alcohols with 1 to 18 carbon atoms used are alcohols and ether-alcohols such as methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n- pentanol, methylglycol , ethylglycol, propylglycol, butylglycol and n-pentylglycol, as well as natural fatty alcohols such as lauric, palmitic, cetylic, stearic, and oleic alcohols, etc. Preferably, the polyols used are polyhydroxylated alcohols with a linear or branched chain containing 2 to 18 carbon atoms. Suitable polyols are: diols, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, tnmethylene glycol, 1 , 4-butanediol , 1 , 6-hexanediol triols, such as glycerol, tetrols, such as pentaerythritol, diglycerol hexols, such as manitol, sorbitol and similar polyols . Preferably, solvent (d) is selected from water, formamide, dimethylformamide, dirnethylacetamide, methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n- pentanol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1 , 4-butanediol, 1,6- hexanediol, methylglycol, ethylglycol, propylglycol, butylglycol, glycerol and mixtures thereof.

A composition for inhibiting metal corrosion in a fluid aqueous medium is preferred, comprising with respect to the total weight of said composition: (a) between 5-45%, preferably between 10-30% by weight of cmnamaldehyde and/or substituted cmnamaldehyde

(b) between 0.1-30%, preferably between 2-20% by weight of urea (c) between 0-25%, preferably between 1-20% by weight of 100% surfactant or mixtures thereof

(d) between 20-90%, preferably between 55-80% by weight of a solvent or mixtures thereof. According to the invention, it is preferable that the active substance thereof is comprised, with respect to the total weight thereof, between 10% and 80% by weight, preferably between 15% and 50%, more preferably between 20% and 45%. The active substance of the composition for inhibiting metal corrosion of the invention is substantially provided by components (a) cmnamaldehyde and/or substituted cmnamaldehyde, (b) urea, and optionally (c) surfactant/s . pH regulating agents, viscosity modifying agents, ion chelating or trapping agents such as EDTA (ethylene diammo tetraacetic acid) , DPTA (diethylene triamino pentaacetic acid) , HEDTA (hydroxyethylene diamino triacetic acid) , EDDHA (ethylene diammo di-ortho-hydroxy-phenyl acetic acid) , EDDHMA (ethylene diamino di-ortho-hydroxy-para- methyl phenyl acetic acid) , EDDCHA (ethylene diamino di- ortho-hydroxy-para-carboxy-phenyl acetic acid), stabilizing agents, corrosion inhibition intensifying or enhancing agents, corrosion inhibitors, dispersing agents or mixtures thereof can be incorporated in the composition for inhibiting metal corrosion of the present invention.

Suitable corrosion inhibition intensifying or enhancing agents are formic acid (HCOOH) , methyl formiate (HCOOCH₃) , ethyl formiate (HCOOCH₂CH₃) , benzyl formiate (HCOOCH₂C₆H₅), formamide (CH₃NO), dimethyl formamide (HCON(CH₃J₂), 1, l'-azobisformamide (NH₂CON=NCONH₂), and metal halides such as sodium fluoride (NaF) or potassium fluoride (KF), sodium chloride (NaCl) or potassium chloride (KCl), sodium bromide (NaBr) or potassium bromide (KBr), sodium iodide (NaI) or potassium iodide (KI), copper (I) chloride (I) (CuCl or Cu₂Cl₂), copper (I) iodide (CuI or

Cu₂I₂), copper (II) chloride (CuCl₂), copper (II) iodide

(CuI₂), antimony chloride (SbCl₃) or mixtures thereof. Preferred corrosion inhibition intensifying or enhancing agents according to the invention are KI, CuI or Cu₂I₂, or mixtures thereof.

Suitable corrosion inhibition agents are propargylic alcohol (CHCCH₂OH), Pent-4-m-l-ol (CHC(CH₂J₃OH), hexinol, ethyl octmol, octinol, 3-phenyl-2-propin-l-ol, crotonaldehyde, furfural, p-anisaldehyde, phenyl vinyl ketone, β-hydroxypropiophenone, piperazine, hexamethylene tetramme, or mixtures thereof.

Also forming part of the object of the invention is an acid-type aqueous solution comprising:

(a) an acid selected from hydrochloric acid (HCl), hydrofluoric acid (HF), formic acid (HCOOH), acetic acid (CH₃CH₂CHOOH), sulphuric acid (H₂SO₄), and mixtures thereof

(b) an effective amount of a composition according to the present invention for inhibiting the corrosion caused by said acid.

The previously described acids are frequently in aqueous solution form at 3%, 7.5%, 15%, 28% and 37% by weight for hydrochloric acid and for mixtures of hydrochloric acid and hydrofluoric acid. According to the present invention, hydrochloric acid and the mixture of hydrochloric acid and hydrofluoric acid is preferred, said mixture preferably contains from 6% to 15% by weight of hydrochloric acid and from 1% to 6% by weight of hydrofluoric acid.

The composition for inhibiting metal corrosion of the present invention is added to the acid (or to an aqueous solution thereof) obtaining an acid-type aqueous solution, such that the composition for inhibiting metal corrosion is present between 0.01-10% (active substance), preferably between 0.1-5% with respect to the total weight of the acid-type aqueous solution. The composition for inhibiting metal corrosion of the present invention can be used, in the intervals specified previously, at temperatures ranging between 20°C and 200⁰C.

The present invention also provides a method for stimulating an underground rocky formation consisting of placing said underground rocky formation into contact with an acid-type aqueous solution according to the invention.

Preferably, an acid-type aqueous solution according to the invention is pumped through a well.

The following examples are set forth with the purpose of providing a sufficiently clear and complete explanation of the present invention to the person skilled in the art, but they must not be considered as limiting to the essential aspects of the object of the invention as they have been set forth in the foregoing sections of this description. Examples Example 1

A test is carried out to determine the corrosion inhibition properties, as described below: 1. Cold-rolled, low carbon content steel test pieces, of the Fill-type according to the UNE (a Spanish standard) denomination, with dimensions of 40x20x2 mm (height x width x thickness) are taken and the surface thereof is polished with sandpaper. Then, they are degreased by introducing them into a container with isopropyl alcohol and they are left in an ultrasound bath for 3 minutes. They are air- dried and weighed in a balance with an accuracy of ± 0.001 g- 2. 70 ml of concentrated 15% HCl (obtained by diluting commercial concentrated 37% HCl) is added in Pyrex glass bottles with screw-on closure. Then 1.0% (700 microlitres) of the corrosion inhibitor, the compositions of which are shown in Table 1, is added.

3. The previous mixture is shaken manually and subsequently a degreased and weighed (according to 1) steel test piece is introduced into each glass bottle in a vertical position such that it is completely covered by the acid solution.

4. Once the test piece is introduced into the glass bottle containing the acid solution, the bottle is closed by screwing on the cap and introduced into an autoclave containing water. It is kept for 2 hours at a pressure of 1.2 bar and 120⁰C. Subsequently, it is cooled for 2 more hours inside the autoclave. When the bottle is removed, it is at about 60-70⁰C.

5. Subsequently, the steel test piece is removed with pincers, is introduced in a 10% sodium bicarbonate bath so as to neutralize the remaining acid and then it is cleaned by rubbing the surface of the plate with a brush and soapy water. Afterwards, it is cleaned first with limonene and then with isopropyl alcohol. It is air-dried and then weighed with an accuracy of ± 0.001 g. Corrosion (corrosion rate) is presented as the loss of mass in grams per square metre and hour (g/m².h) .

The lesser the difference in mass between before and after the treatment with acid in the autoclave, the greater is the inhibiting power of the evaluated composition. Table 2 shows the average values obtained for the compositions detailed in Table 1 when tests are carried out in duplicate. Table 1

⁵ Alkyl (fatty chain with 12 and 14 carbon atoms), ( (carboxylate methyl) al kyldimethylammonium) betaine. Active substance: 32%

Table 2

It can be seen in Table 2 that by combining cmnamaldehyde ( trans-cinnamaldehyde) and urea, values of protection against corrosion are obtained that are higher than the ones obtained with only cmnamaldehyde or with urea .

On the other hand, adding a surfactant (of the alkyl betaine type) to the cinnamaldehyde-urea mixture allows increasing the protection against corrosion.

Example 2

A new series of experiments is carried out in the same experimental conditions as the ones described in Example 1. The differences are the composition of the corrosion inhibitors detailed in Table 3 and the dose used of said inhibitors, in this case, 0.75% (525 microlitres) to 70 ml of the 15% hydrochloric acid solution.

Furthermore, 3% (2.1 g) of KI has been used as an intensifying agent in this new series of experiments.

Table 4 shows the values obtained for the compositions detailed in Table 3 when the tests are carried out in duplicate .

Table 3

Table 4

It can be observed in Table 4 that the intensifying agent allows obtaining values of protection against corrosion that are higher than the ones obtained in its absence

On the other hand, sample 14 has values of protection against corrosion of the same order as the ones obtained with only cmnamaldehyde (sample C3), which involves obtaining equally efficient and more economical formulations

Finally, samples 11, 12 and 13 achieve a significant decrease in the corrosion rate, which involves obtaining more efficient and economical formulations.

Example 3

A new series of experiments is carried out in the same experimental conditions as the ones described in Example 2. The only difference is the composition of the corrosion inhibitors detailed in Table 3. In this new series of corrosion inhibitor samples, the cmnamaldehyde and urea of sample 13 have been proportionally substituted with other components, maintaining the total sum of active components in the formulation. Table 6 shows the values obtained for the compositions detailed in Table 5 when the tests are carried out in duplicate.

Table 5

¹ Polypropylene polyamine from tallow ethoxylated with 3 moles of ethylene oxide. Active substance: 100%

' Monoamine with coconut fatty chain ethoxylated with 5 moles of ethylene oxide. Active substance: 100%

³ Quaternary alkyl (coconut fatty chain) benzyl dimethyl ammonium chloride. Active substance: ⁴ Mixture of fatty alcohols with 12 to 14 carbon atoms ethoxylated with 7 moles of ethylene oxide. Active substance: 100% ⁵ Alkyl (fatty chain with 12 and 14 carbon atoms), ( (carboxylate methyl) alkyldimethylammonium) betaine. Active substance: 32% ⁶ Alkyl propylene diamine from tallow quaternized with methyl chloride. Active substance: 50% Tabl e 6

In Table 6, it can be observed how the fatty polyamine-type surfactants, quaternary ammonium compounds and betaines combined with the cinnamaldehyde-urea mixture are preferred.

Any modifications which do not alter, change or modify the essential aspects of the described compositions are included within the scope of the present invention.

Claims

1. A composition for inhibiting metal corrosion in a fluid aqueous medium, comprising: (a) cinnamaldehyde and/or substituted cinnamaldehyde, and (b) urea.

2. A composition according to claim 1, characterized in that the weight ratio between cinnamaldehyde and/or substituted cinnamaldehyde (a) and urea (b) is comprised between 50:1 and 1:6.

3. A composition according to any of claims 1 to 2, characterized in that the weight ratio between cinnamaldehyde and/or substituted cinnamaldehyde (a) and urea (b) is comprised between 35:1 and 1:4, preferably between 15:1 and 1:3.

4. A composition according to any of the previous claims, characterized in that it further comprises a surfactant (c) .

5. A composition according to claim 4, characterized in that the weight ratio between cinnamaldehyde and/or substituted cinnamaldehyde (a) and the surfactant (c) is comprised between 50:1 and 1:6, preferably between 35:1 and 1:3.

6. A composition according to claim 4, characterized in that the weight ratio between urea (b) and the surfactant (c) is comprised between 30:1 and 1:20, preferably between 20:1 and 1:10.

7. A composition according to any of claims 4 to 6, characterized in that the surfactant (c) is selected from alkylene polyammes, optionally alcoxylated, quaternary ammonium compounds, betaine-type amphoteric surfactants, and mixtures thereof.

8. A composition according to claim 7, characterized in that the surfactant (c) is selected from Ci₀-Ci₈ alkyl tnmethyl ammonium chloride or methosulphate, Ci₀-Ci₈ dialkyl dimethyl ammonium chloride or methosulphate, C₆-C₂₂ alkyl benzyl dimethyl ammonium chloride, quaternized C₆-C₂₂ alkyl propylene diamine chloride or methosulphate, N-C6-C22 alkyl pyridinium bromide or chloride, optionally alcoxylated C₆-C₂₂ alkyl propylene diamines, optionally alcoxylated C₆-C₂₂ alkyl propylene tπamines, optionally alcoxylated C₆-C₂₂ alkyl propylene tetraamines (linear and branched), and mixtures thereof.

9. A composition according to claim 7, characterized in that the surfactant (c) is selected from Ci₀-Ci₈ alkyl dimethyl betaine, Ci₀-Ci₈ alkyl amidopropyl dimethylammo betaine, Ci₀-Ci₈ dimethyl sulphohydroxybetame, Ci₀-Ci₈ amido propyl dimethylammo sulphohydroxybetame, sodium Ci₀-Ci₈ alkyl ammo amphoacetate, disodium Ci₀-Ci₈ alkyl ammo diamphoacetate, and mixtures thereof.

10. A composition according to any of the previous claims, characterized in that it further comprises a solvent (d) .

11. A composition according to claim 10, characterized in that solvent (d) is selected from water, aprotic polar solvents, aromatic solvents, terpinols, alcohols with 1 to 18 carbon atoms and polyols with 2 to 18 carbon atoms and mixtures thereof.

12. A composition according to any of claims 10 to 11, characterized in that solvent (d) is selected from water, formamide, dimethyl formamide, dimethyl acetamide, methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n-pentanol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1 , 4-butanediol, 1, 6-hexanediol, methylglycol, ethylglycol, propylglycol , butylglycol, glycerol and mixtures thereof.

13. A composition according to any of claims 1 to 12, characterized in that it comprises, with respect to the total weight of the composition:

(a) between 5-45%, preferable between 10-30% by weight of cinnamaldehyde and/or substituted cinnamaldehyde ;

(b) between 0.1-30%, preferably between 2-20% by weight of urea;

(c) between 0-25%, preferably between 1-20% by weight of a 100% surfactant or mixtures thereof; and

(d) between 20-90%, preferably between 55-80% by weight of solvent.

14. A composition according to any of the previous claims, characterized in that the cinnamaldehyde and/or substituted cinnamaldehyde (a) is trans-cmnamaldehyde .

15. A composition according to any of the previous claims, characterized in that it further comprises corrosion inhibition intensifying or enhancing agents, pH regulating agents, viscosity modifying agents, ion chelating or trapping agents, stabilizing agents, corrosion inhibitors, dispersing agents or mixtures thereof.

16. An acid-type agueous solution, characterized in that it comprises:

(a) an acid selected from hydrochloric acid (HCl), hydrofluoric acid (HF) , formic acid (HCOOH) , acetic acid (CH₃CH₂CHOOH), sulphuric acid (H₂SO₄), and mixtures thereof, and (b) an effective amount of a composition according to any of claims 1 to 15 for inhibiting the corrosion caused by said acid.

17. An acid-type aqueous solution according to claim 16, characterized in that said composition according to any of claims 1 to 15 is present between 0.01-10%, preferably between 0.1-5% with respect to the total weight of the acid-type aqueous solution.

18. An acid-type aqueous solution according to any of claims 16 to 17, characterized in that the acid is hydrochloric acid or a mixture of hydrochloric acid and hydrofluoric acid.

19. A method for stimulating an underground rocky formation, characterized in that it consists of placing said underground rocky formation into contact with an acid- type aqueous solution according to any of claims 16 to 18.

20. A method according to claim 19, characterized in that an acid-type aqueous solution according to any of claims 16 to 18 is pumped through a well.