Note: Descriptions are shown in the official language in which they were submitted.
CORROSION INHIBITOR FOR AQUEOUS BRINES
The invention relates to inhibiting cor-
rosion of ferrous metals by aqueous brines. In a
specific application for the petroleum industry,
it relates to reducing corrosion of iron and steel
casing, tubing, and other ferrous subterranean well
structural parts exposed to agueous brines used as
completion, work over, or packer fluids.
In well treating operations, brines are
utilized for various purposes, especially where a
relatively dense aqueous fluid is desired. Alkali
metal salt brines may be employed, but more typically,
calcium chloride brines, calcium bromide brines, or
a mixture thereof are employed because solutions of
greater specific gravity may be obtained. Such brines
are corrosive to the metal goods in the wellbore, even
in the absence of substantially any oxygen. Such
corrosion is relatively insignificant at tempera-
tures of about 200F, but becomes fairly signifi-
cant at temperatures of at least 250F, especially
above about 300F.
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Although some corrosion inhibitors well
suited for inhibiting HCl may find some utility in
inhibiting brines, it cannot be said that a hydro-
chloric acid inhibitor will necessarily be effective
in inhibiting brines, at least not to a practical
degree.
Canadian Patent No. 983,041 teaches a
water soluble corrosiorl inhibitor for brines com-
prising the reaction product of certain aliphatic
saturated carboxylic acids with substituted imidazo-
lines.
U.S. Patent No. 3,215,637 teaches that a
mixture of sodium silicate and zinc chloride inhibits
corrosion by sodium chloride and calcium chloride
brines. The patent also discusses shortcomings of
other known brine inhibitors such as sodium nitrate,
hydrazine, pyrogallol, or sulphite.
U.S. Patent No. 4,010,111 discloses a
corrosion inhibiting composition for aqueous brines
wherein the inhibitor contains a reaction product
of a carboxylic acid and a polyamine, an alcohol,
and an alkylbenzene sulfonic acid.
At the time of this invention, it is
believed that among the most widely used commercial
inhibitors for heavy brines--at least in the United
States petroleum industry--were Baroid~ Coat B-1400
~; inhibitor and Corexit~ 7720 inhibitor. Analysis
~; of a sample of the Baroid~ product indicates it
` contains about 14 percent by weight of a volatile
amine, about 19 percent by weight of isopropyl
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alcohol, about 45 percent by weight of water, and the
balance predominately ethoxylated amide with a small
amount of car~oxylic acid salt.
The present invention is based on the
dlscovery that ferrous metals can be at least partially
protected from corrosion by aqueous brines by including
in the brine, an effective amount of a sulfur compound
wherein the oxidation state of the sulfur is zero or
less, which is uniformly dispersible in, and preferably
solu~le in, said brine and which is capable of making
sulfur available for reaction with the ferrous metal to
be protected to form a protective iron sulfide film on
the surface of the metal exposed to the inhibited brine.
Preferably, at least one quaternary pyridinium, quinolinium,
or isoquinolinium salt which is soluble in the brine is
also employed as an inhibitor aid.
The invention resides in a method of reducing
the corrosive effect of aqueous brine on ferrous metal
surfaces which are contacted by the brine comprising add-
ing to the brine, a corrosion inhibiting quantity of asulfur compound wherein the oxidation state of the sulfur
is zero or less, said sulfur compound being uniformly
dispersible in the brine.
The invention further resides in an aqueous
brine composition which has a reduced corrosive effect on
ferrous metal surfaces which are contacted by the brine,
the brine containing a corrosion inhibiting quantity of a
sulfur compound wherein the oxidation state of the sulfur
is 0 or less, said sulfur compound being uniformly dis-
persed in the brine.
27,321-F
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Aqueous solutions of alkali metal halides
may be inhibited using the composition of the present
invention, although its greatest benefit is realized
where the brine contains at least one polyvalent
metal halide salt, such as calcium chloride, bromide,
or iodide, zinc chloride, bromide, or iodide, or
a mixture of such salts. Such brines are commonly
used in oil field applications, as well as in other
industries. For example, such brines may be used
in separation processes wherein solids of different
densities are separated by flotation. In addition
to the corrosion inhibitor, such brines may contain
various functional additives, if desired, such as
fluid loss additives, gelling agents, friction
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reducers, or surfactants. Brine solutions which
may be inhibited according to the present inven-
tion include aqueous organic acid solutions
weighted with a suitable metal halide salt to in-
crease the specific gravity thereof, although inmost instances, solutions treated according to the
present invention will normally have a slightly
basic pH and will consist substantially of aqueous
solutions of calcium or zinc halides or mixtures
thereof.
The corrosion inhibitor system of the
present invention has good inhibitive properties,
especially at the higher temperatures where the
corrosion caused by brines would otherwise become
relatively serious. It is also compatible with a
wide range of functional additives. Moveover,
particularly the most preferred embodiments act
as a defoaming agent, thereby simplifying field
mixing procedures.
The sulfur compound is preferably a water-
-soluble thio compound, e.g. a thiocyanate such as
an alkali metal thiocyanate or, most preferably,
ammonium thiocyanate. It can also be an organic
thioamide and essentially any such compound is
operable. This class of compounds includes thio-
urea, a polythiourea, a hydrocarbon substituted
derivative thereof, or a thioamide having the
- formula:
S
A-C-N- R
~ R"
"
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27,321-F
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wherein A is a hydrocarbon radical of 1-12 carbon
atoms or a pyridyl radical and each R" is a hydrogen
atom or an alkyl radical of 1-8 carbon atoms.
Thioamides such as thiourea, 1,2-diethylthiourea,
propylthiourea, 1,1-diphenylthiourea, thiocarbanilide,
1,2-dibutylthiourea, dithiobiurea, thioacetamide,
thionicotinamide, or thiobenzamide are represen-
tative of this class. Water soluble sulfides such
as ammonium sulfide, an alkali metal sulfide, or
corresponding hydrosulfide including H2S are other
operable thio compounds. Elemental sulfur which is
dispersible in the brines is also operable, although
the above mentioned soluble thio compounds are pre-
ferred.
Preferably, a quaternary pyridinium,
quinolinium, or isoquinolinium salt which is
stable in the aqueous brine solution is also em-
ployed as the inhibitor acid. Preferably, this
salt has the formula:
' R' R'
~ X~ ~ X , or
R R' R
R' ~ X
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27,321-F
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where R is an alkyl radical of 1-20 carbon atoms,
a benzyl radical, or an alkylated benzyl radical
wherein the aromatic ring has one or more alkyl
substituents totalling 1-20 carbon atoms, each R'
is a hydrogen atom or an al~yl or alkoxy radical
of 1-6 carbon atoms, and X is any convenient anionic
radical such as halide, sulfate, acetate, or nitrate.
Obviously, those skilled in the art will realize
that the various parameters should not be selected
to provide a compound having such a high carbon
content that the compound is not soluble in the
brine at at least an effective concentration. In
the above general formulae, X is preferably a bromine
or chlorine atom, and most preferably bromine.
Preferably, R is a higher alkyl radical of about
6-16 carbon atoms. Also, R' is preferably hydrogen.
Pyridinium salts are generally preferred. The most
preferred embodiment considering both performance
and solubility is n-octylpyridinium bromide. Mix-
tures of such salts may be employed if desired.
While any significant quantity of thesulfur compound will provide some degree of inhi-
bition of corrosion, at least about 0.3 grams of
the sulfur compound per liter of brine solution
is usually required to provide practical pro-
tection. Concentrations as high as 20 grams of
the inhibitor per liter are, for the most part,
not detrimental. More than about 3 grams of the
inhibitor per liter of brine, however, usually
provides little or no additional protection, and
in some cases may actually provide less protection
than smaller amounts. The preferred upper limit
of 3 grams per liter applies whether the sulfur
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compound is ~mployed alone or in combination with
the heterocycllc quaternar~ compound, i.e. when
the guaternary compound is employed, the total
concentration o tlle quaternary and sulfur compounds
preferably does not exceed 3 g/liter. Most pre-
ferably, the total concentration of sulfur compound
and quaternary salt is from about 0.5-2 grams per
liter of brine.
If employed, the ~laternary salt is employed
in an amount which is effective to improve the over-
all inhibition of the system. The optimum ratio
of the quaternary salt to the sulfur compound will
vary somewhat from system to system, but generally,
benefit is realized when the two components are
employed in a weight ratio of from 0.1:1 to 10:1,
although a ratio of from 0.125:1 to 4:1 is more
preferred. A ratio of 0.2:1 to 1:1 is most pre-
ferred, especially where the concentration of the
components approaches the upper or lower limits
recommended in the preceding paragraph. For any
given brine system and combination of inhibitor
components, those skilled in the art will be able
to arrive at an optimum concentration and ratio.
The addition of a small but effective
amount--e.g., from 0.05 to 0.5 gram Co+2 per liter
of brine--of a water soluble cobalt salt to the
system also improves its effectiveness, but is not
necessary for an operable or even commercially
acceptable performance. Consequently, though some-
` 30 what better performance is obtained with the cobalt,
it is not normally a preferred embodiment for routine
applications because of somewhat increased toxicity
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and environmental concerns. If employed, the co-
balt may be provided by essentially any cobaltous
compound which is sufficiently soluble in the
aqueous brine solution to provide the desired con-
centration of cobaltous ions. Salts such as CoCl2,CoBr2, CoSO4~ Co(NO3)2, cobaltous acetate, or co-
baltous benzoate are all suitable sources of co-
baltous ions. Salts such as the acetate, benzoate,
or bromide are particularly preferred.
The present invention is further illu-
strated by the following examples and comparison
runs.
Test procedure. In preparation for the
corrasion tests hereinafter described, coupons were
cut from 2-3/8" O.D. N80 steel tubing. The coupons
were cleaned by tumbling in aluminum oxide grit
after which they were exposed to an ultrasonic tri-
chloroethylene bath, rinsed in acetone, dried, and
stored in a desiccator. In carrying out the tests,
the coupon was placed in the test solution in an
autoclave and the test temperature and pressure
were established as rapidly as was practical.
Stated test times are the times for which the
coupon was exposed to the solution at the speci-
fied temperature and pressure. All tests werecarried out under static conditions, i.e. without
agitation, at 1000 psi. After permitting the test
bath to cool to about 150F, the coupon was removed
from the bath, rinsed in acetone, and washed in
inhibited 15% aqueous HCl for about 3-4 minutes
with agitation to dissolve the iron sulfide film
which forms during the test. The coupon was then
27,321-F
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washed in water, scrubbed wl~h a brass brush and
pumice soap, heated in hot water to accelerate
acetone evaporation, rinsed in acetone, dried,
cooled, and weighed.
In all corrosion tests, the various ad-
ditives in the quantities stated were added to
100 ml of the brine. In all tables, "Corrosion
Rate" is expressed as pounds per square foot per
the stated test time. "Percent Inhibition" is the
following quantity:
Corrosion rate with no inhibitor - Corrosion rateof test
solution x 100.
Corrosion rate with no inhibitor
Various quaternary salt solutions were pre-
pared and used as follows
Prep. A: Decylquinolinium bromide (DQBr)
Prep. B: Dodecylquinolinium bromide (DodQBr)
Prep. C: Tetradecylpyridinium bromide (TdPBr)
Prep. D: Hexadecylpyridinium bromide (HdPBr)
Prep. E: Decylpyridinium bromide (DPBr)
Prep. F: Dodecylpyridinium bromide (DodPBr)
Prep. G: Alkyl substituted tetradecylpyridinium
bromide (AlkTdPB)
Prep. H: Hexylpyridinium bromide (HPBr)
Prep. I: Octylpyridinium bromide (OPBr)
Prep. J: 0.4:1 OPBr:Ammonium thiocyanate
Prep. K: 0.26:1 OPBr:Ammonium thiocyanate
Several series of corrosion tests sum-
marized in the following tables were carried out.
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