Method and composition for protecting metal surfaces from oxidative environments

The present invention relates to a method of inhibiting the oxidative effect of an oxidative environment upon a metal surface utilizing a composition comprising an inhibiting effective amount of an acetylenic alcohol, a quaternary ammonium compound, an aromatic hydrocarbon, an antimony compound, and an aqueous fluid. The metal surface to be protected is contacted with the composition whereby a deposit or coating of at least a portion of the composition constituents is formed on the metal surface.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and composition for protecting a 
metal surface exposed to an oxidative environment. 
Acidizing and fracturing treatments using aqueous acidic solutions commonly 
are carried out in hydrocarbon-containing subterranean formations 
penetrated by a well bore to accomplish a number of purposes, one of which 
is to increase the permeability of the formation. The increase in 
formation permeability normally results in an increase in the recovery of 
hydrocarbons from the formation. 
In acidizing treatments, aqueous acidic solutions are introduced into the 
subterranean formation under pressure so that the acidic solution flows 
into the pore spaces of the formation. The acidic solution reacts with 
acid-soluble materials contained in the formation which results in an 
increase in the size of the pore spaces and an increase in the 
permeability of the formation. 
In fracture acidizing treatments, one or more fractures are produced in the 
formation and the acidic solution is introduced into the fracture to etch 
flow channels in the fracture face. The acid also enlarges the pore spaces 
in the fracture face and in the formation. 
A problem associated with acidizing subterranean formations is the 
oxidation or attack by the solution on the tubular goods in the well bore 
and the other equipment used to carry out the treatment. The expense of 
repairing or replacing damaged equipment is extremely high. 
It would be desirable to provide a composition and method for treating a 
metal surface which reduces at least some of the oxidation problem 
resulting from contact of the oxidative environment with ferrous and other 
metals. 
SUMMARY OF THE INVENTION 
The present invention relates to a method and composition for protecting 
metal surfaces, and particularly ferrous metals, from the effects of 
oxidative environments. The method is accomplished by introducing the 
metal surface to be protected into contact with the composition of the 
present invention. The contacting may be effected in any manner that coats 
the metal surface to be protected with the composition. The contacting of 
the metal surface with the composition results in the formation of a 
surface deposit upon the metal surface to be protected comprised of 
constituents contained in the composition. 
The composition comprises an aqueous solution containing effective amounts 
of one or more acetylenic alcohols, a quaternary ammonium compound, an 
aromatic hydrocarbon having high oil-wetting characteristics and an 
antimony compound. The aqueous solution can have a pH of from about 0 to 
about 9. The antimony compound can comprise any antimony compound which is 
capable of activation by the other constituents of the inhibitor. The 
composition is effective in reducing the oxidative effects of acidic 
solutions in contact with ferrous metals where the temperature at which 
the metal and acid are in contact is between about ambient and 500.degree. 
F. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
In accordance with the present invention, there is provided a composition 
comprising an aqueous fluid and effective amounts of one or more 
acetylenic alcohols, a quaternary ammonium compound, an aromatic 
hydrocarbon having high oil-wetting characteristics and an antimony 
compound which is capable of activation by the other constituents of the 
composition. 
The aqueous fluid can comprise any aqueous solution which does not 
adversely react with the constituents. The aqueous fluid can have a pH in 
the range of from about 0 to about 9. Preferably, the aqueous fluid has a 
pH level in the range of from about 1 to about 4. The pH of the aqueous 
fluid can be adjusted with the use of various acids or bases. The acids 
employed in the practice of the present invention can comprise 
hydrochloric acid or mixtures of hydrochloric acid with hydrofluoric and 
formic acid, acetic acid, formic acid, hydrofluoric acid or mixtures of 
these acids and the like. The bases can comprise various alkali metal 
hydroxides or the like. 
The antimony compound which is employed in the present invention can 
comprise any antimony compound which is activated by the other 
constituents of the composition to cause the composition to form a 
protective deposit on the exposed metal surface to substantially reduce 
the oxidative effect of an oxidative environment on ferrous metals, 
copper, brass, duplex metals and the like in contact with the acidic 
solution. The antimony compound can comprise, for example, antimony 
trichloride, antimony pentachloride, alkali metal salts of antimony 
tartrate, antimony adducts of ethylene glycol, solutions containing 
ethylene glycol, water and the oxidized product of hydrogen peroxide and 
antimony trioxide or any other trivalent antimony compound and the like. 
The acetylenic alcohols employed in the present invention may suitably 
include substantially any of the acetylenic compounds having the general 
formula: 
##STR1## 
wherein R.sub.1, R.sub.2 and R.sub.3 are hydrogen, alkyl, phenyl, 
substituted phenyl or hydroxy-alkyl radicals. Preferably, R.sub.1 
comprises hydrogen. Preferably, R.sub.2 comprises hydrogen, methyl, ethyl 
or propyl radicals. Preferably, R.sub.3 comprises an alkyl radical having 
the general formula C.sub.n H.sub.2n where n is an integer from 1 to 10. 
Some examples of acetylenic alcohols which can be employed in accordance 
with the present invention are, for example, methyl butynol, methyl 
pentynol, hexynol, ethyl octynol, propargyl alcohol, benzylbutynol, 
ethynylcyclohexanol and the like. Preferred alcohols are hexynol, 
propargyl alcohol, methyl butynol and ethyl octynol. 
The quaternary ammonium compounds employed in the present invention 
comprise aromatic nitrogen compounds which may be illustrated by alkyl 
pyridine-N-methyl chloride quaternary, alkyl pyridine-N-benzyl chloride 
quaternary, quinoline-N-methyl chloride quaternary, quinoline-N-benzyl 
chloride quaternary, isoquinoline quaternaries, benzoquinoline 
quaternaries, chloromethyl naphthalene quaternaries of the above, 
admixtures of the compounds and the like. 
The hydrocarbon compound can comprise substantially any aromatic compound 
which exhibits high oil-wetting characteristics. The aromatic hydrocarbon 
compound can comprise, for example, xylenes, saturated biphenyl-xylenes 
admixtures, heavy aromatic naphtha, heavy aromatic solvent, tetralene, 
tetrahydroquinoline, tetrahydronaphthalene and the like. 
The acetylenic alcohol, aromatic hydrocarbon and quaternary amine are 
present in the composition in an amount sufficient to effect an activation 
of the antimony compound whereby the composition can significantly reduce 
the oxidative effect of an oxidative environment on a ferrous metal or 
other metal. Preferably, the acetylenic alcohol is present in the 
composition in an amount sufficient to comprise at least five percent by 
volume of the non-aqueous constituents of the composition. Most 
preferably, the acetylenic alcohol comprises from about 5 to about 35 
percent of the non-aqueous constituents of the composition. Preferably, 
the ratio of the volume of acetylenic alcohol to the volume of aromatic 
hydrocarbons is at least about 0.05:1.0. Most preferably, the ratio of 
acetylenic alcohol to aromatic hydrocarbon is in the range of from about 
0.08:1.0 to about 1.66:1.0. The quaternary amine and any additional 
additives constitute the remainder of the non-aqueous constituents of the 
composition. Preferably, a sufficient quantity of the antimony compound is 
added to obtain a solution having a concentration of from about 0.007 to 
about 0.1 molar. Larger quantities of the antimony compound may be 
utilized to form the protective coating, however, such quantities 
generally are unnecessary to achieve effective protection. The antimony 
compound may be admixed with the other constituents of the composition to 
form a premixed solution or it may be formulated in situ in an acidic 
solution by the addition of a sufficient quantity of the antimony compound 
and a quantity of the other constituents which may be premixed. 
Additional additives which can be present in the aqueous solution of the 
composition can comprise, for example, a solvent such as an alkanol to 
assist in maintaining the constituents of the composition as a homogeneous 
admixture. 
Alkanols which can be employed in the present invention are, for example, 
methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl and 
the higher liquid members of these aliphatic alcohols. Preferably, the 
quantity of alkanol employed is that which merely is sufficient to 
maintain the constituents in homogeneous admixture as excess quantities 
have no demonstrable effect on the effectiveness of the composition. 
Preferably, the alkanol comprises less than about fifteen percent by 
volume of the composition to avoid unnecessary dilution of the 
composition. 
The composition also can include a non-ionic surfactant which facilitates 
dispersion of the organic constituents of the composition in the aqueous 
solution. 
The non-ionic surfacant can comprise an ethoxylated oleate, tall oils or 
ethoxylated fatty acids. The 8 to 20 moles of ethylene oxide adducts of 
octyl phenol, nonyl phenol, tridecyl phenol and the like are preferred. 
Sufficient non-ionic surfactant is admixed with the other constituents of 
the composition to facilitate dispersion of the constituents in the 
aqueous solution. Preferably, the surfactant comprises less than about 20 
percent by volume of the non-aqueous constituents of the composition to 
avoid unnecessary dilution of the composition. 
The method of the present invention is carried out in one embodiment by 
first admixing effective amounts of the acetylenic alcohol, quaternary 
ammonium compound aromatic compound having oil-wetting characteristics and 
antimony compound in an aqueous solution. If necessary, the pH of the 
aqueous solution can be adjusted by the addition of a suitable acid or 
base to provide a solution pH in the range of from about 0 to about 4. 
While no particular order of addition of the constituents to the aqueous 
fluid is necessary, preferably the acetylenic alcohol, quarternary 
ammonium compound and aromatic compound are admixed with the aqueous prior 
to addition of the antimony compound. The amount of the non-aqueous 
constituents present in the composition can vary over a substantial range. 
Preferably, the non-aqueous constituents are present in an amount of at 
least about 5 gallons per 1000 gallons of aqueous fluid and, preferably, 
in an amount of from about 10 to 30 gallons per 1000 gallons of aqueous 
fluid. 
The composition of the present invention can be prepared in any suitable 
mixing tank equipped with suitable mixing means well known to individuals 
skilled in the art. 
The metal surface to be protected can be contacted with the composition by 
immersion therein or by flowing the composition across the metal surface 
to be protected. The contacting of the metal surface with the composition 
results in the formation or deposition of a surface coating upon the metal 
surface. The composition preferably is contacted with the metal surface to 
be protected for from about 15 minutes to over several hours. At elevated 
contacting temperatures, a satisfactory protective coating can be formed 
by immersion in the composition for from about 1 to 4 hours. When a metal 
is merely immersed in the composition, agitation of the composition by 
some conventional means is desirable as this reduces the total time 
required for a satisfactory protective coating to form. The surface 
deposit is comprised of constituents contained in the composition. The 
contacting can be effected at a temperature of from about ambient to in 
excess of about 400.degree. F. While the specific mechanism of the present 
invention is unclear, it is believed that an antimony metal deposit is 
formed in response to a moderated change in the oxidation state of the 
metal surface when in contact with the composition of the present 
invention. Surprisingly, it has been found that while the composition of 
the present invention is capable of protecting a metal surface in contact 
with an aqueous acidic solution at temperatures in excess of 400.degree. 
F., it also will protect the metal surface for extended periods of time 
when placed in other oxidative environments. The composition of the 
present invention is capable of protecting a metal surface against the 
oxidative effects of moist air having humidity levels in excess of 40 
percent for months. 
In another embodiment of the present invention, the composition is utilized 
to protect the metal surface of a cased well bore during treatment of a 
subterranean formation with an acidic solution and to provide residual 
oxidation protection to the casing subsequent to the treatment. The 
composition is prepared in accordance with the method of the present 
invention. The aqueous fluid comprises a 15 percent hydrochloric acid 
solution. The acidic solution containing the composition of the present 
invention is introduced into the well bore, pumped therethrough and 
introduced into the subterranean formation. During contacting of said 
casing comprising a ferrous metal with said composition, a protective 
coating is formed upon the metal surface exposed to the acidic solution. 
The protective coating substantially protects the metal surface of the 
casing from corrosion by the acid present in the solution. The injected 
acidic solution dissolves soluble constituents within the subterranean 
formation whereby at least a portion of the acidic content of the solution 
is neutralized. 
The partially neutralized acidic solution then can be flowed back through 
the well bore for removal at the earth's surface. Thereafter, the well 
bore may be placed in production to produce, for example, a mixture of 
conate water and oil from the subterranean formation. The protective 
coating on the casing in the well bore provides residual protection to the 
metal casing's surface contacted by the water to protect the surface from 
the oxidative environment caused by the presence of the water. 
To further illustrate the effectiveness of the composition of the present 
invention in preventing the oxidation of a metal surface, but not by way 
of limitation, the following examples are provided.

EXAMPLE I 
To determine the effectiveness of the composition of the present invention 
in inhibiting oxidation of a metal surface, the following tests were 
performed. An aqueous acidic solution is prepared by adding a sufficient 
quantity of concentrated hydrochloric acid or hydrochloric acid and 
hydrofluoric acid to water to form a solution having the concentrations 
set forth in Table I. The composition of the present invention is prepared 
as previously described by admixing the following constituents: a 
quaternary ammonium compound, a heavy aromatic hydrocarbon compound, 
acetylenic alcohol, a surfactant comprising an ethoxylated phenol and a 
solvent comprising an alkanol. A sufficient quantity of the non-aqueous 
constituents then is added to the aqueous acid to comprise two percent by 
volume of the solution. Sufficient antimony compound is dissolved in the 
solution to provide a 0.04 molar antimony concentration. The solution then 
is heated to a temperature of about 400.degree. F. under a 500 psig over 
pressure of an inert heat transfer fluid and a weighed sample coupon is 
suspended in the solution. After the period of time indicated in Table I, 
the sample coupon is removed from the heated acid solution, washed and 
visually inspected to determine whether a protective coating had formed 
upon the metal sample coupon by the acidic solution. Several samples then 
were kept in an oxidative environment at a temperature of about 60.degree. 
to 78.degree. F. and a humidity level of about 40 to 90 percent for over 
266 days. The coupons then were inspected for visual signs of oxidation. A 
control coupon was tested in each instance in an equivalent acidic 
solution without the composition of the present invention. Table II sets 
forth the results of tests performed in accordance with the foregoing 
procedure to determine whether or not a surface coating forms on other 
metals. 
TABLE I 
__________________________________________________________________________ 
Duration of Oxidation 
Acidic 
Exposure 
Protective 
Inhibition to 
Sample Coupon 
Solution 
to Compo- 
Coating 
Humidity 
Material Constituent 
sition 
Formed 
Exposure 
__________________________________________________________________________ 
Type N-80 Steel 
15% HCl 
2 (Control) 
-- Extensive oxidation 
Type N-80 Steel 
pH4 (HCl) 
2 (Control) 
-- Extensive oxidation 
Type N-80 Steel 
15% HCl 
2 yes No apparent oxidation 
Type N-80 Steel 
pH4 (HCl) 
2 yes No apparent oxidation 
__________________________________________________________________________ 
TABLE II 
______________________________________ 
Duration of 
Acidic Exposure Protective 
Sample Coupon 
Solution to Compo- Coating 
Material Constituent sition Formed 
______________________________________ 
Hastelloy C276 
15% HCl 4 yes 
Hastelloy C276 
12% HCl, 3% HF 
4 yes 
Monel K500 
15% HC 4 yes 
Monel K500 
12% HCl, 3% HF 
4 yes 
Incoloy 925 
15% HC 4 yes 
Incoloy 925 
12% HCl, 3% HF 
4 yes 
______________________________________ 
The results clearly illustrate the ability of the composition of the 
present invention to form a protective coating upon a metal surface. The 
data also illustrates that the protective coating will protect the metal 
surface from oxidation over an extended period of time. 
EXAMPLE II 
To illustrate the pH levels at which the protective coating can be formed, 
the following tests were performed. Aqueous solutions having a pH of about 
0, 4.5 and 7 were prepared. The pH of zero was obtained with hydrochloric 
acid, pH of 4.5 with acetic acid and 7 with hydrochloric acid and sodium 
hydroxide. The composition of the present invention then is prepared 
utilizing the various aqueous solutions as previously described by 
admixing the following constituents with the aqueous solutions: a 
quaternary ammonium compound, a heavy aromatic hydrocarbon compound, 
acetylenic alcohol, a surfactant comprising an ethoxylated phenol and a 
solvent comprising an alkanol. A sufficient quantity of the non-aqueous 
constituents are admixed with the aqueous solutions to comprise two 
percent by volume of the solutions. Sufficient antimony compound is 
dissolved in the solutions to provide a 0.04 molar antimony concentration. 
The solutions then are heated to a temperature of about 350.degree. F. 
under a 500 psig over pressure of an inert heat transfer fluid and a type 
N-80 steel coupon is placed in each solution. After 4 hours the coupons 
are removed from the solution and examined for the presence of a 
protective surface coating. Each coupon was found to have a protective 
coating formed upon its surface. 
The results clearly illustrate the wide pH range over which the protective 
coating can be formed to protect a metal surface from an oxidative 
environment. 
EXAMPLE III 
To determine the cohesiveness of the protective coating of the present 
invention, the following tests were performed. The composition of the 
present invention is prepared as in Examples I and II utilizing an aqueous 
solution comprised of 71/2 percent hydrochloric acid. The composition is 
heated to a temperature of 400.degree. F. under a 500 psig over pressure 
of an inert heat transfer fluid. Several type N-80 steel coupons then are 
immersed in the composition for four hours. The coupons then are removed, 
washed and inspected for protecting coating formation. Each coupon has 
developed a protective coating. The coated coupons then are placed in 
acidic solutions having the following pH levels: 2, 4 and 6. The solutions 
are prepared by admixing concentrated hydrochloric acid with ordinary tap 
water. The acidic solutions are heated to a temperature of 400.degree. F. 
under a 500 psig over pressure of an inert heat transfer fluid. After 64 
hours, the coupons are removed and inspected to determine whether the 
protective coating has adhered to the coupon and whether or not the 
coating is protecting the metal surface of the coupon from oxidation. Each 
coupon was found to have the coating tightly adhering to the metal 
coupon's surface and each coupon showed no visual signs of oxidation. 
The results clearly illustrate the cohesiveness of the protective plate or 
coating produced by the practice of the method of the present invention. 
EXAMPLE IV 
To determine the effectiveness of the composition of the present invention 
in protecting a metal surface exposed to an oxidative environment, the 
following tests were performed. An aqueous acidic solution was prepared by 
adding a sufficient quantity of hydrochloric acid to water to form a 15% 
solution. This solution was divided into three samples. In the first 
sample, a sufficient quantity of an antimony compound was dissolved in the 
solution to provide a 0.04 molar antimony concentration. In the second 
sample, a composition comprising the following constituents: a quaternary 
ammonium compound, a heavy aromatic hydrocarbon compound, acetylenic 
alcohol, a surfactant comprising an ethoxylated phenol and a solvent 
comprising an alkanol was admixed in an amount sufficient to comprise two 
percent by volume of the solution. In the third sample, a sufficient 
quantity of the antimony compound used in the first sample was dissolved 
in the solution to provide a 0.04 molar antimony concentration and a 
sufficient quantity of the organic constituent-containing composition used 
in the second sample to comprise twp percent by volume of the solution. A 
metal coupon comprising type N-80 steel then was placed in each of the 
three samples for four hours. The solutions are heated to a temperature of 
about 400.degree. F. under a 500 psig over pressure of an inert heat 
transfer fluid. After the 4 hour period of exposure, the coupons are 
removed from the solutions, washed and visually inspected for formation of 
the protective coating and to determine the extent of corrosion of the 
coupon. The coupons then are kept in an oxidative environment at a 
temperature of about 70.degree. to 78.degree. F. and a humidity level of 
about 40 to 90 percent to determine if any residual protection against 
oxidation occurs. 
Upon inspection, the coupon in the first sample solution containing only 
the antimony compound was found to be extensively corroded and no residual 
coating was present. Upon exposure to the oxidative environment, the 
coupon was found to rapidly form rust on the coupon surface. 
The coupon in the second sample solution containing the organic 
constituents and no antimony was found to have protected the metal coupon 
to some extent against corrosion, however, no residul coating was present 
upon the coupon. Upon exposure to the oxidative environment the coupon was 
found to rapidly rust. 
The coupon in the third sample solution containing the antimony and organic 
constituents of the composition of the present invention was found to have 
provided better protection to the metal coupon against corrosion than the 
second sample solution and a residual coating was present upon the coupon. 
Upon exposure to the oxidative environment the coupon was found to show no 
apparent signs of rust for the duration of the exposure to the oxidative 
environment. 
While particular embodiments of the invention have been described, it is to 
be understood that such descriptions are presented for purposes of 
illustration only and that the invention is not limited thereto and that 
reasonable variations and modifications, which will be apparent to those 
skilled in the art, can be made without departing from the spirit of scope 
of the invention as set forth in the appended claims.