CA1113235A

CA1113235A - Corrosion inhibitor for aqueous brines

Info

Publication number: CA1113235A
Application number: CA332,464A
Authority: CA
Inventors: Mitchael D. Coffey
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1978-08-11
Filing date: 1979-07-24
Publication date: 1981-12-01
Also published as: NO792606L; NO155973B; DE2932560A1; GB2027686B; NL7906139A; GB2027686A; NO155973C

Abstract

ABSTRACT OF THE DISCLOSURE

Corrosion of ferrous metals by aqueous brines is inhibited by including in the brine, an effective amount of a dispersible sulfur compound wherein the sulfur has an oxidation state of zero or less. Preferably, a quaternary pyridinium, quino-linium, or isoquinolinium salt is also employed.
Inclusion of a cobalt salt is also sometimes de-sirable.

27,321-F

Description

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.
,.

.`~
27, 321-F

.

... ~ . ~ .
' ,: ,.
- , .. . .
....

.

-2 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 `
'~
27,321-F

. ' . . , - . ~ - ~ . . ~

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
B

. ` ~
`; . .

, . ~

-3a-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 27,321-F

~3 ' '''' ....
.. - .. .. . .
..
", . . , , , ., . -. . : - . . . : . :

., ~ ' ' . ' 4 ~3 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"
"
;~

.~ .
27,321-F
'.: .:, -, , . . :

:. :. .

-5~ 5 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

. . .

27,321-F
.

~ .

: . . ~ . .
, . ,:

f~

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 27,321-F

r ` ' ~ ;
. .

~ ~ , ' ' "'' , ', . ' " ' . , ~' ' ~7~ 3~

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 , 27,321-F

, , : :
.. . . . ~ - . ~ .
.. . . .~ , . - . .
. - , ,. .
.
;. . ..

-8~ 5 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

.. ~ . . . : .
. . . . :
: ~ .
.~
' .' , ' ~ , , , ' ' . . . . . .
.

_9~

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.

,, .~ .
~ 27,321-F

.. .

:

-lo- ~$~s~

_ -o ,, -~ O r~ O r-~ ~ N ~ ~ a~ ~ ~ t~ ~ ~') ~ u~ ~ ~
o ~ ~ o ~ o ~ o ~1 o o o o ,~ o o o o o ~a ~oo ooo ooo ooo ooo o oo o ~oo ooo ooo ooo ooo o oo .' V ,~
o o U
u~ o o ~I N ,1 ,_1 h ~ ~
~ ~ ~ rl rl I I I I I ~0 ~0 1 n X o, X
O z; Zi ~0 'I ~o V V

~ ~ ~ 0 ~
1:~ O ~ ~) h~ ~ ~ h h V Z V V
~ ~ ~3 o o o o o o o o o ~
pj ~ v ~ $~ m~
u ~ o ,~ E~
o o o o o o o o o o o o o ,, ~
~ ~ _ _ ,, ~ _ ~ ~ m m a~ m ~ m ~
~1 ~ P~P~ O= ~ ~ ~0

3 ~ ~a a a E-~ w m a a ~ ~ a n o V V V Q Q
~ O ,1 ~ ~ h .. h ~ 5~ ~ h S~ h S~
O R P~ 4 h h ~ ~1 ~ ~1 ~1~ 0 0 ~ i3 m ~ ~ ~ ~ ~ ~ ~ Z Z; Ln 01 0 0o o o o o o o o o o o o a~ ~

27, 321-F

:

... . , ~:
.
,. . - ~ : .

. ,.......... - , . ~ ~ . . . : . :
- - . .

O ~1 ~ Ul 0 0 ~ r l r l - rl - rl 1~
U~ ~ O O O O O O O O r~ O O 0 ~1 O ~ O O h h~ u~
h o O O O O O o o o r~l U U~1 o~ a)P~
rO
O 0~4 h ~ ~arl O
a) I , o O
t~ Q) tJ~ N tJ~ N~H ~ S l ~ ~ I I I I I U~ U~ U~ O O al ~ r l O U ~ ~1 I t7) N ~O N ~ ~
v~ o ~ o z o æ ~ u ~-r O O rl S
h P~
O O h O
O rl rl 111 ~ `
U U 0~
Q~
S~
~ ~ ~UO~ .
~0 U~
Z Z Z Z ~ Z Z ~ ~ 0 O U~
h ~ ~ ~ ~ ~ ~ ~ d' R. P
O ~ tl~ t~l !li ~i h~! ~trl. ~1 ~ o rl O ~ 2 !;~ !Z~ ~ I I N S ~D
O r j 1--i tn t~ 0 ~i ~ ~ N ~3 H E-l O O O O O O 0 0 0 p~
_ 0~ 0~ ~
~ h h ~ ~ 3t m ~ m h E-l h ~ ~ ~
0 14 r-l 14 a ~ ~ h h ~o _~ o ,~ a ~ ~h :5 ~3 ~I H 0 0 0 r-l O
~:: :0 ~ ~ O
rl ~ ~ ~ ~ ~ O
0 1~ la-rl O Ll ~4 h P~ h h ~1 ~1~ ~1~ 0 h O
~ ~1 ~1 1 1 1rl rl h al h ~3 r l ~ r l r l ~--1 ~I h r-l ~1 0 $ u~
O ~ ~ ~ 111 ~ ~ ~ O
O O O O 0 0 0 ~q 0 0 0 ~ 0 rl ~
o ~I N ~ d~D t~ O rl ~ ~
U~ p; rl N ~1 N N N N N N ~Zi ~ ~ ~

`, 27, 321-F
, ,.

: : ~ ~ ` ::

: : :
::: l ~ :

o O ~` u~ In ~ ~ U~ ~0 ~) G~ ~ ~ ~ ~
U~ ~ o o o o o o o o o o o o o o o~ ooo ooo ooo ooo o o h 1~ ... ... ... ...
~1 ~ ' O O O O O O O O O O O O O O
o 1.
a ~ , I, ,,, ,,, , o C) U~
,~ al a) h q) a V~ U~

Z . ~1 ~h ~
~1 O O O OO O rl O O O O O O 0 3 ~1 0~ ~
u ~
~rl o n V ~ ~ ~ ~o ~ ~ ~ ~
E~ ooo ~oo ooo ooo 'S
_ ~
~1--~ ~ ~
~ ~ m m ~ m ~ ~ o ~ _ ~, ~ --m o ~ , m ~ m ~ ~ v n o v ul ~1 P ~I-rl r-l ~1 5~1 h a~ ~1 ~ ~ ~ ~ ~ 1~ 4 h a~
U~
~ ~D Id ~1 ~ L~O ~ N~ ~ U)u) Ln U~
u~ 1 ~ ... .- .-- - o O OOOr-lOO OOO OOO U~
a) ~
o ~ ~ oD ~ o ~ o ~1 . .

. ~ .
~, , 27, 321-F
.
. j .

. . .

,: , : . .-O ~ t~ ~O O ~ O ~ ~ ~D a~ ~ co ~n ~) o o o o o o o o o o o o 0~ ooo ooo oo o ooo O ooo ooo oo o ooo V

, 0~ I ~ I I I I I I I I I I
~ .
U~ o o~
o ~ O

rl X
td ~O O Q~ ~ O ~O O ~n I I I o v os~ o X a~ 5~
~I ~ O O o ,~ ,1 ~, ;~ ~s a~ v Z
n ~1 ~ u~ o O ~ ~1 ~
{3 h ~ O ~ VVV ZVV VZ VZZv ~ ' `I O U~
n d'd'~ ~ d' ~d'~ t~
~!~ Z ~zm~z ~ :
o U~ P r~ ~ ~ ~ ~ ~ .
-. ~ ~ -~ ~ ~ ~ O ~
V ~ _~ O O s~
r~ ~ ~ h ~I m m o u ~ m ~
P~
O ---- h h ---- ~ rl ~10 0 V ~ W u~ a) ~ l4 ~ ~
LI~ ,q ~
.. ~ Sl I I I ~I h 0 ~ ~ ~ ~0~o ~ ~ 1:4 ~ I
. m ~ h ~1 Z Z z zO ~ ~1 ~
t~ Ul U) ~ U) O
d ~ ' ' ~ a) ., , :~ ~ O O o V~ U~ o o o ,~
,' O ~ ~

, ., .i!
27, 321-F
:: , ....... - ` - ~. ~ . . ` ` ' `
` . . ` - . .

, . ` - - . :
; . - . .:
` ' .. `: ` ` : " : : ','' ` `. "` ' - :~ , : ~ ` `
, -~ O ~r~ O
h ~ ~ ~ N Ll~ U') ~/ ) U~ ~D ~ N ~ ~1 O
~ U

O ~ ~ o ~ ~ o co u~ D O
U~ ~ O ~ IS~ O C~ ~ N ~ r` ~O Ln ao ~D a) O ~ N ~ ~1 ~ O ~1 ~1 0 0 ~1 ~1 ~1 ~I r l h ~ 000 000 000 000 00 h ~ O O o O O O O O o O O O O O
C~

h ~ .
U
N
O ,.
~ ~3 ~ U~

~ ~ ~ ` Z Z Z Z
W ~ ~ Z X Z; U U U U
v~ a~ u o ~) u u~
o ~ ~ z~ `:
~n ~ .. ......
,U~ ,q h h ~i ~I m ~ ~ m ,, ~ m ~
~ ~ o o o o ~I H O O O O
V ~ ~1 ~-1 ~ . ......
.... ... - ~ D ~
V d~ ~ NN N N O O O N N
.. ...... ooo r~r~
O O O O O O O O ~ ep ~
N ~ ~ ~ X X
O ~ ~ ~ h ~I h ~ a~
a) O s.~ ~ ~ h h ~ ~4 h ~ m ~ v v ~ r l r-l N dl D ~I N ~ ~D N ~ ~ N d~
,~ h O O O O O O O O O O O O O
~` o a) ~
U~ ~ t~ OD a~ o ~1 N ~ U~

` 27,321-F
:, .~

., .

, ~ , . . . . .
: ` . , . ~ ;
:: : : . .: :
, .: . , . . ~ i 3~3~

~t ~ 0 a~ , a~ ,~ ~ ~ ~ ~ o o ~ o u~
~-1 rl~ N ~ `1 ~1 ~1 u~
O
.) m ~
v a ~ ~ .
Ul o ,~~ O U. ~ t~ O ~ ~ ~
,~ o t~ ~ ~ ~ o 03 co ~ ~ In o ~ t~
O U~ ~ ~ O O O O ~ O O O O O ~ O O ~, o~ ooo ooo ooo ooo oo ... ... ... ... .. O
O O O O O O O O O O O O O O N
¦ o ~ . . .
~ U~
U~ N
¦ ~ ææ â ~
~ V~
; ,, s~m m~ o O Z; Z Z Z
ua m m m a:~ $
., ~ o P~o o .~. .~ ~ .
~ o .~ ~d ~ ~ O
~ ,~ I N ~~ ~ o o o : ~ .a o o o 1~ t~
rl O OO O ~ ~ d' t` t` r~ ~1 ~1 ,~
- ~ ~~ o ~4 ~4 ~ ~ ~ ~ .~ X

o Q~ P~ ~ ~ O O O a~
~ OJ O ~ h h ~ 3: 3 3 - ~1 ~ J O O O O O O
~: .. g ~ m ~q m o u ~ a ~ a ,t: ~y g h o o o o o o o o o o o o o O rl ~ , o ,t ~ol ~1 *
.
;~ 27, 321-E~
~ B 1~
. . .
.

. . .. ~ . . ... ..... .... . .

`. . . . . . .. .
. . . . ~ .
~ .. . . .
, .

.
~ ~ O O
o ~ ~ oo h-r~
~ ~ ~ U

o Lr) n r`
.,~ ~ ~ O d' U~ ~ ~ O ~ o ~ U~
O ~ O O O O -~ O
.. .. ..

U

~ _ _ ~ UZ UZ
U~
.. .. ..
m a: m P~ O P~
o .. .. ..
~1 ~D ~ ~
.4 ~ N N
.,.1 ~ l O l O l O
1--1 H ~
lXI ~
P
U~
d' d' d' . , O O O ' .

N ~`1 N N N N
m~ ~ ~ m UU UU UU
S~ ~ ;~
o O O
U~ O
N N N N N N
11 ~ ~ h h ~1 o :4 ~ ~ m~ ~N
N N N W N

I~
~1 ~1 ~I N N U~

~:
27, 321-F

;.. ;. ........... ', . , ' ' :

,' . : . : ` . ,

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of reducing the corrosive effect of aqueous brine on ferrous metal surfaces which are contacted by the brine comprising adding the brine, a corrosion inhibiting quantity of a sulfur compound wherein the oxidation state of the sulfur is zero or less, said sulfur compound being uniformly dispersible in the brine.

2. The method of Claim 1 wherein the sulfur compound is employed in an amount of at least about 0.3 grams per liter of brine.

3. The method of Claim 1 wherein the sulfur compound is a water soluble thiocyanate or thioamide.

4. The method of Claim 1, 2 or 3, wherein the brine contains at least one of calcium chloride, calcium bromide, calcium iodide, zinc chloride, zinc bromide, or zinc iodide.

5. The method of Claim 1 wherein an effec-tive amount of at least one quaternary pyridinium, quinolinium, or isoquinolinium salt is added to the 27,321-F

brine to further reduce the corrosive effect of the brine, said quaternary salt being selected so as to be sufficiently soluble in the brine so that an effective amount can be dissolved in in the brine.

6. The method of Claim 5, wherein the combined weight of said sulfur compound plus any quaternary salt present does not exceed about 3 grams per liter.

7 The method of Claim 5 wherein the quaternary salt is employed in an amount of from 0.1 to 10 parts per part by weight of the sulfur' compound.

8. The method of Claim 5 wherein the total concentration of the sulfur compound and the quaternary salt is from 0.5 to 2 grams per liter of brine, and the weight ratio of said quaternary compound to sulfur is from 0.125:1 to 4:1.

9. The method of Claim 5 wherein the quaternary salt has the formula X- , X- , or 27,321-F

X- , 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 alkyl or alkoxy radical of 1-6 carbon atoms, and X is an anionic radical.

10. The method of Claim 9 wherein R
is an alkyl radical of 6-16 carbon atoms.

11. The method of Claim 10 wherein X is bromine.

12. The method of Claim 11 wherein each R' is hydrogen.

13. The method of Claim 12 wherein the quaternary compound is a pyridinium salt.

14. The method of Claim 13 wherein the total concentration of the sulfur compound and the pyridinium salt is from 0.5 to 2 grams per liter of brine, and the weight ratio of said pyridinium salt to sulfur compound is from 0.125:1 to 4:1.

15. The method of Claim 14 wherein the pyridinium salt is octylpyridinium bromide and wherein the sulfur compound is a thiocyanate or thioamide.

27,321-F

16. The method of Claim 15 wherein the weight ratio of the pyridinium salt to sulfur com-pound is from 0.125:1 to 4:1 and wherein the sulfur compound is ammonium thiocyanate or thiourea.

17. The method of Claim 1 wherein an effective amount of a water soluble cobalt salt is added to the brine to still further reduce the corrosive effect of the brine.

18. An aqueous brine composition which has a reduced corrosive effect on ferrous meta1 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 dispersed in the brine.

19. The composition of Claim 18 wherein the sulfur compound is contained therein in an amount of at least 0.3 grams per liter of brine.

20. The composition of Claim 17 or 18 wherein the sulfur compound is a water soluble thiocyanate or thioamide.

21. The composition of Claim 19 wherein the sulfur compound is ammonium thiocyanate or thiourea.

22. The composition of Claim 18 wherein the aqueous brine contains at least one of calcium chloride, calcium bromide, calcium iodide, zinc chloride, zinc bromide, and zinc iodide.

27,321-F

23. The composition of Claim 18 wherein an effective amount of at least one quaternary pyridinium, quinolinium or isoquinolinium salt is also added to the brine to further reduce the corrosive effect of the brine, the quaternary salt being selected so as to be sufficiently soluble in the brine so that an effective amount can be dissolved in the brine.

24. The composition of Claim 23 wherein the combined weight of said sulfur compound plus any quaternary salt present does not exceed 3 grams per liter.

25. The composition of Claim 22 wherein the quaternary salt is contained in an amount of from 0.1 to 10 partsper part by weight of the sulfur com-pound.

26. The composition of Claim 24 wherein the total concentration of the sulfur compound and the quaternary salt is from 0.5 to 2 grams per liter of brine, and the weight ratio of said quaternary compound to sulfur is from 0.125:1 to 4:1.

27. A well treating operation involving the use of brine as claimed in Claim 18.

27,321-F