Note: Descriptions are shown in the official language in which they were submitted.
7~73
GL-198
CORROSION INHIB~
BACKGROUND OF THE I NVENT I ON
Field Of The Invention. This invention relates
to well bore servicing fluids and more particularly to a
corrosion inhibited high density fluid that may be
employed under rigorous service conditions.
Description Of The Prior Art. Drilling fluids
have conventionally been used to maintain control during
perforation, completion, or workover operations in oil
and gas wells. Drilling fluids that have heretofore been
employed for such purposes include mud, saltwater, water,
or oil. The use of these fluids during drilling opera-
tions has per se been generally satisfactory and has
actually enhanced drilling efficacy. However, the same
materials have been employed during completion and work-
over operations with undesirable consequences.
For example, use of drilling muds during well
perforation has freguently resulted in plugging of the
perforations. Solids present in such drilling fluids
have caused plugging and have made the completion process
unduly complex, expensive and unre:Liable. Similarly, use
of drilling muds and other drilling fluids as packer
fluids has resulted in unwanted settling of solids.
Moreover, drilling media may be somewhat corrosive under
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long-term, static operating conditions thereby further
rendering them unsuitable for use other than as transi-
tory drilling aids.
Among the efforts that have been made to over-
come the foregoing problems has been the utilization ofhigh density clear salt solutions. Clear fluids comp.ris-
ing solutions of zinc bromide~calcium bromide, and,
optionally, calcium chloride having densities in the
range o about 15.0 up to about 20.0 ppg are disclosed in
U. s. Patents 4,292,183 and 4,304,677. While such solu-
tions are highly satisfactory materials for use in the
completion, packing and perforation of oil and gas wells,
these solutions have not heretofore been usable where
down-hole temperatures exceed about 300F.(149C.) because
of the high rate of corrosion of the iron and steel under
such conditions. Thus, under high temperature conditions,
it heretofore has only been possible to employ less
desirable fluids such as modified drilling muds and the
like. However, at high temperature, the solids contained
in the drilling mud settle to the bottom of the well
bore, solidify and make workover of the well far more
costly and difficult to achieve.
The zinc ion in a 19.2 ppg clear fluid may only
be maintained in solution by maintaining a pH in the
range of about 1.0 to about 1.3, normally by the addition
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of excess hydrobromic acid. While pH's in this range
achieve the desired solubility of the weighting salt, the
resulting fluid is highly corrosive. Even where a 19.2
ppg zinc bromide/calcium bromide solution is blended with
calcium bromide/calcium chloride solution to produce
; ultimate fluids of lower density, the pH remains in the
highly acidic area, never rising above about 5.5. The
resulting fluids thus remain strongly acidic and very
corrosive at temperatures exceeding 300F.
U. S. Patent No. 4,292,183 describes the use of
a film-forming amine-based corrosion inhibitor. However,
the corrosion inhibition system disclosed in that patent
is useful in the range only of up to about 300F. and
cannot be used at the higher temperatures to which the
subject invention is directed.
The prior art has suggested several corrosion
inhibition systems for use in strong acid environments.
However, only a few have proved to be satisfactory and
fewer still have even been commercially employed. Thus,
arsenic and/or arsenic compounds have been suggested to
provide corrosion protection in strong acid solutions
used to acidize new and producing wells. However, the
toxic nature of arsenic compounds to humans and the
"poisoning" of the catalysts used in refineries have made
arsenic compounds undesirable.
'
, -, .
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A strong acid inhibitor is described in U. S.
Patent No. 3,077,454. The inhibitor contains an organic
ketone, an aliphatic aldehyde, and a fatty acid. Protec-
tion up to 350F. (177C.) is suggested, but only for
5 short periods of time (i.e., no longer than 16 hours.
A similar composition is described in U. S.
Patent No. 3,634,270. A synergistic mixture of organic
nitrogen and sulfur compounds that prevents the attack of
the corrosive ingredient of the solution on metal is
claimed. Application to industrial boiler and heat
exchanger cleaning is suggested. Sulfur compounds
selected from the group thiourea, allyl thiourea, sodium
mercaptobenzothiazole, mercaptothioazoline, sodium thio-
cyanate and mixtures are disclosed to be particularly
effective. However, the disclosed operating range for
the inhibitor systems included low temperatures no greater
than 300 F. and short time periods, no longer than 16
hours.
The literature contains references to the
inhibition of acid corrosion of steel by thiourea and its
derivatives. T. P. Hoar and R. D. Holliday in J. Appl.
Chem. 3 (11): 502-13 (1953); B. Donnelly, T. C. Downie,
G. Grzeskowiak, H. R. Hamburg and D. Short in Corrosion
Science, 14:597-606 (1974); E. Jackson and I. J. Wilkinson
in British Corrosion J., 11:208-11 (1976); and M. B. Lawson
DWV20-C/cs
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in Corrosion, 36:493-7 (1980) are representative examples
of the extensive literature.
U. S. Patent No. 4,100,100 describes the use of
the combination of a quaternary pyridinium salt and an
organic thiamide or water soluble thiocyanate to reduce
the corrosion or iron and steel by an aqueous sour gas
conditioning solution. The same mixture is described in
U. K. Patent 2,027,686 as a corrosion inhibitor for
agueous brines in a well bore.
U. S. Patent 4,100,100 and U. K. Patent 2,027,686
report that the addition of a small amount of a water
soluble cobalt salt to the inhibitor combination improves
its effectiveness. The sulfur compound of the mixture is
preferably ammonium thiocyanate or thiourea. The corro-
sion tests described in the patents are for moderately
high temperatures (i.e., 350F (177~C)) and short time
periods (i.e., no more than 118 hours).
A corrosion inhibitor mixture suitable for use
in calcium chloride and sodium chloride brines is described
in U. 5. Patent 3,215,637. The mixture is composed of
sodium silicate, zinc chloride and sodium chromate. A
mixture of inhibitors is required because no single
composition proved effective in preventing general and
localized corrosion. The effectiveness of the inhibitor
composition was evaluated for longer time periods, lO
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days, but at a low temperature, 68F (20~C).
A method ox corrosion inhibition in well drill-
ing operations is described in U. S. Patent 4,250,042.
The agueous drilling fluid is treated with at least one
water-soluble ammonium carboxylate salt. The corrosion
tests described are carried out in an atmosphere of air
and oxygen at 185F for 20 hours.
The short term, low temperature protection of
the foregoing prior art is of little value in an oil well
completion, workover, or packer fluid.
Japan 75 03,741 describes an oxide film remover
and corrosion inhibitor for copper and copper alloys
comprising 2 20 volume percent of an aqueous solution of
sodium or ammonium thioglycolate containing benzotriazole,
sodium mercaptobenzothiazole and/or imidazole derivatives.
Japan Kokai 76 92,735 describes metal rinsing compositions
for cleaning air conditioner pipes or internal con~ustion
radiators in shorter periods of time without corroding
the piping by using water soluble thioglycolate, halogenated
alykl metal or halogenated ammonium thioglycolate. Japan
Kokai Tokkyo Koho 79 120,007 describes compositions of
coloring agents, wetting agents, annino acid derivatives
and ammonium thioglycolate as jet printing inks having
good storageability and corrosion inhibition.
None of the prior art has thus described a
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suitable corrosion inhibition system for high density
fluids that permits their application under hiyh tempera-
ture down-hole operating conditions.
Accordingly, a primary object of this invention
is to provide a corrosion inhibition system for zinc
bromide/calcium bromide solutions optionally containing
calcium chloride permitting their use in oil and gas
wells as a well-servicing fluids at temperatures as high
as 400~. (204C).
A further object is to provide a composition of
the character described that is successfully usable with
solutions having densities in the range of about 15.0 up
to about 20.0 ppg.
A still further object is to provide corrosion
protection in such systems for extended periods of time
up to 90 days or more.
A still further object is to provide a cor-
rosion inhibitor that is sufficiently soluble in high
density fluids that it can be provided in a base solution
which can be blended down to lower densities for field
use.
SUMMARY OF I~ENTION
The foregoing and other objects, advantages,
and features of this invention may be achieved with a
corrosion inhibited, clear, high density composition
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capable of long term use as a well servicing fluid under
conditions of elevated temperature comprising a solution
of zinc bromide and calcium bromide, and, optionally,
calcium chloride in water having a density in the range
of about 15.0 to about 20.0 ppg and a corrosion inhibit-
ing amount of a member selected from the group consisting
of ammomium thioglycolat , calcium thioglycolate, -thio-
glycerol and mixtures thereof. Desirably, the corrosion
inhibitor is provided at a level of about 0.01-5.00
percent by weight of the clear solution.
The present invention also includes novel
methods for ormulating such corrosion inhibited clear
solutions as well as for their use in well servicing
operations.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As noted, those skilled in the art have long
but unsuccessfully sought a corrosion inhibited zinc
bromide/calcium bromide solution that would permit its
use in down-hole operating temperatures as high as 400F.
By employing a corrosion inhibitor in accordance with
this invention, it is possible to achieve high density
agueous brines for use as completion, workover or packer
fluids in deep, high pressure, high temperature oil, gas,
or geothermal wells. The objectives of this invention
are achieved with a corrosion inhibitor that is completely
DWV2Q-C/cs
soluble in aqueous solutions o zinc bromide, calcium
bromide and calcium chloride in the density range of
about 15.0 ppg to 20.0 ppg.
In addition to having the desired solubility,
the corrosion inhibitor must be able to provide signifi-
cant corrosion inhibition at temperatures up to and
including 400F. The corrosion protection must be main-
tained for extended periods of time of at least 30 days
and preferably as much as 90 days or more. It is also
important that the corrosion inhibition minimize pitting
corrosion so that the small amount of corrosion that does
occur is of a generalized rather than a highly specific
nature. In addition, the corrosion inhibitor must be
compatible with other chemical additives commonly employed
with high density agueous brine such as viscosifiers,
suspending agents, and defoamers.
In accordance with this invention it has been
found that ammonium thioglycolate, calcium thioglycolate,
thioglycerol, or mixtures thereof permit these objectives
to be achieved when provided in corrosion inhibiting
amounts. Corrosion inhibited clear fluids in accordance
with this invention not only may be satisfactorily
employed at high temperatures in the well-servicing
environment, but it has also been demonstrated that they
may be used over relatively long periods of time of up to
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1~76~3
90 days or more.
The formulation of zinc bromide/calcium bromide
solutions, which may optionally contain calcium chloride
as well, is not per se a part of the present invention.
Satisfactory methods of preparing and blending such
solutions with densities lying in the range of about 15.0
up to about 20.0 ppg are described in U. S. Patent
4,292,183 and U. S. Patent 4,304,677.
Typically such high density fluids are formul-
ated with a base fluid of relatively high density ~e.g.,a zinc bromide/calcium bromide solution having a density
of about 19.2 ppg containing about 54.7 weight percent
zinc bromide and about 20.6 percent calcium bromide).
Such a base solution may then be blended with calcium
bromide or calcium bromide and calcium chloride solutions
in the field to the desired density required for a given
application.
The corrosion inhibitor in accordance with this
invention may be added to the resulting clear fluid at
substantially any point in the preparation cycle. Thus,
it may be provided in the base so].ution and in one or
more of the auxiliary solutions of calcium bromide or
calcium bromide and calcium chloride, or the corrosion
inhibitor may be separately added to the blended solution
at the well location.
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Preferably, however, the corrosion inhibitor is
provided in the base solutivn (e.g., 19.2 ppg zinc bromide/
calcium bromide solution in sufficient quantity to
provide the ultimate level desired under all feasible
conditions of use. Thus ! sufficient inhibition is sup-
plied to ensure adequate protection where the 19.2 ppg
base solution is blended down to an ultimate density of
about 15.0 ppg.
In general, the solution to be employed in a
lQ well-servicing operation should contain about 0.01-5.0
percent of one or more of the corrosion inhibitors of
-this invention, preferably about 0.1~3.0 percent.
Where the corrosion inhibitors are provided in
the high density base solution (e.g., 19.2 ppg zinc
bromide/calcium bromide solution), the amount of cor-
rosion inhibitor employed is preferably about 0.1- 3.0
percent by weight of the base solution.
As indicated, the desired degree of corrosion
inhibition may be obtained in accordance with this inven-
tion through the use of ammonium thioglycolate, calciumthioglycolate, thioglycerol or mixtures of these agents.
The exact amount of agent to be employed is dependent
upon the specific material that is used. Thus, where
ammonium thioglycolate is employed, the preferred range
is about 0.1-1.0 percent by weight of the base solution;
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for calcium thioglycolate, the preferred range is about
0.3-3.0 percent by weight of the base solution; and where
thioglycerol i5 employed, the desired amount is about
0.1-0.5 percent by weight of the base solution.
It is especially preferred to employ ammonium
thioglycolate as the corrosion inhibitor in accordance
with this invention.
The corrosion inhibitors in accordance with
- this invention may be added in any convenient form.
Calcium thioglycolate may be supplied in solid or solu
tion form. Thioglycerol is a liquid at room temperature
and is normally used in that form. Ammonium thioglyco-
late is desirably employed as a 60% agueous solution.
Where used herein, the amounts of inhibitor are stated as
amounts of active agent.
Exemplary corrosion inhibited high density
fluids are disclosed in the foIlowing examples.
EXAMPLE I
A 19.2 ppg zinc bromide, calcium bromide solu-
tion was prepared in the following manner: The pH of anuninhibited 19.2 ppg zinc bromide/calcium bromide base
solution was adjusted using a slur:ry of zinc oxide,
calcium bromide and water or with 54% hydrogen bromide to
1.2 0.1. The density was adjusted to 19.20 0.05 ppg
with 14.2 ppg calcium bromide. The solution was filtered
DWV20-C/cs
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through a medium sintered glass funnel coated with filter
aid. The filtered, density- and pH-adjusted fluid was
heated to 95 5C (203F~. The desired amount of corro-
sion inhibitor was added to the hot fluid. After stirrlng
for 30 minutes, the solution was filtered hot through a
medium sintered glass funnel coated with filter aid. The
solution was allowed to cool to room temperature.
EXAMPLE_II
An 18.0 ppg uninhibited zinc bromide/calcium
bromide base solution was prepared by dissolving 224.9
pounds of zinc bromide and 306.1 pounds calcium bromide
in 226.0 pounds of water. This prepared one barrel of
18.0 ppg zinc bromide/calcium bromide fluid. The pH was
adjusted with a slurry of zinc oxide, calcium oxide and
water or with 54% hydrogen bromide to 2.3 0.1. The
density was adjusted to 18.0 0.05 with 14.2 ppg calcium
bromide or with solid zinc bromide. The solution was
filtered through a medium sintered glass funnel coated
with filter aid. The filtered, density-adjusted fluid
was heated to 95 i 5C ~203F). The desired amount of
corrosion inhibitor was added to the hot fluid. After
stirring for 30 minutes, the solution was flltered hot
through a medium sintered glass funnel coated with filter
aid. The solution was allowed to cool to room temperature.
.
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EXAMPLE III
A 14.5 ppg uninhibited zinc bromide/calcium
bromide base solution was prepared by dissolving 29.4
pounds of zinc bromide and ~8.9 pounds of calcium bromide
in 280.7 pounds of water. This prepared one barrel of
14.5 ppg zinc bromide/calcium bromide base solution. The
pH was adjusted with a slurry of zinc oxide, calcium
oxide and water to 6.0 0.1. The density was adjusted
to 14.50 0.05 with 14.2 ppg calcium bromide or solid
zinc bromide. The solution was filtered through a medium
sintered glass funnel coated with filter aid. The fil-
tered, density adjusted fluid was heated to 95 5C
(203F). The desired amount of corrosion inhibitor was
added to the hot fluid. After stirring for 30 minutes,
the solution was filtered hot through a medium sintered
glass funnel coated with filter aid. The solution was
allowed to cool to room temperature.
EXAMPLE IV
A 19.2 ppg zinc bromide/calcium bromide solu-
tion was prepared containing 1.0 weight percent ammonium
thioglycolate by the procedure of Example I. One barrel
of a 17.5 ppg blend of uninhibited 19.2 ppg zinc bromide/
calcium bromide was prepared by mixing 0.660 barrels
(532.2 pounds) of inhibited 19.2 ppg zinc bromide, calcium
bromide and 0.340 barrels (202.8 pounds) of 14.2 ppg
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calcium bromide. After stirring for 30 minutes, the
fluid was filtered thiough a medium sintered glass funnel
coated with filter aid.
EXAMPLE V
A 19.2 ppg zinc bromide/calcium bromide solu-
tion was prepared containing 1.0 weight percent calcium
thioglycolate by the procedure of Example I. One barrel
of a 15.5 ppg zinc bromide/calcium bromide, calcium
chloride solution was prepared by mixing 0.119 barrels
(96 pounds) of inhibited 19.2 ppg zinc bromide/calcium
bromide solution with 0.881 barrels (555.0 pounds) of
15.0 ppg calcium bromide, calcium chloride solution.
After stirring for 30 minutes, the fluid was filtered
through a medium sintered glass funnel coated with filter
lS aid.
EXAMPLE VI
A 19.2 ppg zinc bromide/calcium bromide solution
was prepared containing 2.0 weight percent thioglycerol
by the procedure of Example I. One barrel of 16.5 ppg
æinc bromide/calcium bromide was prepared by mixing 0.460
barrels (370.9 pounds) of inhibite:d 19.2 ppg zinc bromide/
calcium bromide solution with 0.540 barrels (322.1 pounds
of 14.2 ppg calcium bromide solution. After stirring for
30 minutes, the fluid was filtered through a medium
sintered glass funnel coated with filter aid.
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EXAMPLE VII
A 19.2 ppg zinc bromide/calcium bromide solu
tion was prepared containing 0.5 weight percent ammonium
thioglycolate and 0.5 weight percent thioglycerol using
the procedure of Example I. One barrel of 18.5 ppg zinc
bromide/calcium bromide/calcium chloride fluid was pre-
pared by blending 0.833 barrels (671.7 pounds of inhib-
ited 1~.2 ppg zinc bromide, calcium bromide and 0.167
barrels (105.2 pounds) of 15.0 ppg c.alcium bromide,
calcium chloride solution. After stirring for 30 minutes,
the fluid was filtered through a medium sintered glass
funnel coated with filter aid.
The effectiveness of the corrosion inhibitors
of this invention has been demonstrated experimentally
using the following test procedure. The density of a pH
adjusted uninhibited base fluid was first determined.
The solution was then heated to 95 + 5C., and the desired
amount of corrosion inhibitor added to the hot uninhibited
base fluid. The solution was filtered hot through a
medium sintered glass funnel coated with filter aid, and
the solution allowed to cool to room temperature. The
base fluid was then blended to the desired density accord-
ing to blending tables, and the blended fluid was filtered
through a medium sintered glass funnel coated with filter
aid. The fluid density at 60~F. was determined, and the
DWV20-C/cs
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pH of thy fluid measured using a pH meter.
The test fluid was then added to a high tempera-
ture axing cell so as to cover a test coupon. The test
cells were pressurizPd with nitrogen and placed in an
oven for the desired time and temperature. At the end of
the test, the test cells were xemoved from the oven and
allowed to cool for at least two hours. The coupons were
weighed before and after the test, with the weight loss
being an indication of corrosion.
The corrosion rate in mils per year was calcu-
lated using the formula:
mpy = (534) (WL)
(MD) (SA) (T)
where WL = weight loss in mg 3
MD = metal density in g/cm 2
SA = coupon surface area in in
T - time in hours
To provide base line data, seven day mild steel
corrosion rates of blends of uninhibited zinc bromide and
calcium bromide solutions having densities in the range
of 15.5 ppg up to 18.5 ppg were determined and are given
in Table I. These data demonstrate that corrosion rates
vary from a relatively low rate at low temperatures and
densities to extremely high rates at high temperatures
and densities.
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TABL
Seven Day Mild Steel Corrosion Rates
Uninhibited Blends of 19.2 pp~ ænBr2/CaBr2
_ and _4 2 pp Car _
Fluid Corrosion Rate lmpy) Density
(ppg) 250 F300 F350 F _ 400 F
15 5 1.0 1.7 4.1 13.3
16 5 4.4 7.6 17.6 28.3
17 5 22.3 24.8 49.4 56.6
18 5 55.5 85.4 94.7 90.3
Seven day corrosion rates were obtained at
400F for 17.5 ppg zinc bromide/calcium bromide blend
(39.6 percent zinc bromide, 29.5 percent calcium bromide
containing 0.3 weight percent of the inhibitors of this
invention. These data are reported in Table II.
TABLE II
Seven Day Corrosion Rates
17.5 ppg Blend of Zinc Bromide/Calcium Bromide
168 Hours, 400~F.
Inhibitor Corroslon Rate (mpy~
20 Ammonium Thioglycolate 11.1
Calcium Thiogycolate 10.7
Thioglycerol 17.3
Seven day mild steel corrosion rates were
measured for various solution blends containing 0.6
percent ammonium thioglycolate and 1.0 percent calcium
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thioglycolate are given in Tables III and IV. These data
demonstrated significant reductions in corxosion rates in
comparison to the uninhibited solutions reported in
Table I.
S TABLE III
Seven Day Mild Steel Corrosion Rates
Blends of 19.2 ppg ZnBr /CaBr (containing
O.6_wt.% Ammonium Thioglxcol~te an 14.2 ppg._CaBr~
Fluid Corrosion Rate (mpy)
Density
(ppq) 250 F 300 F350 F 400 F
15.5 3~1 3O5 3.4 6.6
16 5 6.6 5.~ 7.1 19.
17 5 16.3 21.1 13.0 23.3
18.5 28.9 32.7 40.6 68.7
TABLE IV
Seven Day Mild Steel Corrosion Rates
Blends of 19.2 ppg ZnBr /CaBr containing
1.0 wt.% Calcium Thioglycol~te) and 14.2 ~pg CaBr~
Fluid Corrosion Rate (mpy)
Dens ty 250 F _300~ F 350 F_400 F
15.5 - - 36 1
16 5 _ _ 26 0
18.5 _ 95 3
Thirty day corrosion tests demonstrate even
better results. Tables V and VI report respectively
thirty day corrosion rates for blends of 19.2 ppg zinc
bromide and calcium bromide (containing 0.6 weight per-
cent respectively of ammonium thioglycolate and calcium
--19--
DWV20-C/cs
thioglycolate) with 14.2 ppg calcium bromide. In all
cases, corrosion rates of less than 10 mil per year were
observed for solutions having densities less than about
18.0 ppg. The 10 mil per year corrosion rate on a thirty
day test period is generally accepted as an industry
standard for use in determining the acceptability of
corrosion inhibition.
TABLE V
Thirty Day Mild Steel Corrosion Rates
Blends of 19.2 ppg ZnBr /CaBr (Containing 0.6 wt.%
Ammonium Thio~lycol2ate) and 14.2 pi CaBr
Fluid Corrosion Rate (mpy)
Density
(PPg~ 250 F 300 F 350 F400 F
15.5 1.9 3.7 7.1 1.6
16.5 1.2 2.8 7.6 ~.3
17 5 5.3 3.5 7.9 6.7
18 5 42.4 33.0 9.9 4~.2
Table VI
Thirty Day Mild Steel Corrosion Rates
Blends of 19.2 ppg ZnBr /CaBr~ (containing 1~0 wt.%
Calcium Thio~lycola~e) an 14.2 pPq CaBr~
Fluid Corrosion Rate (mpy)
Denslty 250 F 300 F 350 F400 F
15 5 0.5 - 2.9
16 5 1.0 - - 2.5
17 5 5.8
18 5 15.3 - - 111.1
While the corrosion levels on a 30 day standard
at 18.5 ppg fall somewhat above the desired level, they
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nevertheless are a significant improvement in comparison
with the unhibited solution. (See Table I.) Moreover,
high density solutions ranging at the 18.5 ppg level and
above are typically blended down to lower density ranges
in actual use. Thus, the corrosion inhibitors of this
invention are effective at virtually all commercially
useful conditions.
Table VII gives seven and 30 day mild corrosion
rates for various high density fluid blends at various
densities between 18.0 and 18.5 ppg demonstrating the
rapid increase in corrosion experienced as densities
increase above 18.0 ppg.
TABLE VII
.
Seven and Thirty Day Mild Steel Corrosion Rates
18.1 to 18.5 Blends of 19.2 ppg ZnBr~/CaBr
(Containing 0.6 wt.% Ammonium Thioglyco~ate) 2and
14.2 ppg CaBrj~ at 400~F.
Fluid
Density 7 Day 30 Day
(PPq) (mpy~ (my)
18.10 60.8 12.7
18.25 23.4 31.8
1~,40 36.0 35.4
18.50 6~.7 46.2
The effect of altering the inhibitor level is
demonstrated by the data in Table VIII which shows thirty
day mild steel corrosion rates for 17.5 ppg blends inhib-
ited with ammonium thioglycolate, calcium thioglycolate
and thioglycerol.
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TABLE VIII
Thirty Day Mild Steel Corrosion Rates. 17.5 ppg
ZnBr2 Fluid, at Various Inhibitor Levels
_ _ in the 19.2 ppg ZnBr~/CaBr~ _
Corrosion Rates (mpy) at Various Inhibi-
tor Levels in the 19.2 ppg ZnBr2/CaBr2
__ _
0.3 0.5 0.6 1.0 1.5 2.0 2.5 3.0
Inhibitor wt.% wt.% wt.~_wt.% wt.% wt.% wt.% wt.
Ammonium 5.2 -- 6.7 -- 16.1 -I
Thioglycolate
Calcium
Thioglycolate -- 9.3 -- 3.5 -- 7.0 -- 5.2
Thioglycerol-- 50.7 -- 44.3 - 35.3
These data demonstrate the preferred and opera-
tive ranges for the inhibitors of this invention.
By using the inhibitoxs of this invention, it
is possible to achieve very low levels of corrosion
throughout long periods of operation. Table IX gives
ninety day corrosion dates on mild steel for blends of
19.2 ppg zinc bromide/ calcium bromide (containing ammo
nium thioglycolate) with 14.2 ppg calcium bromide at four
densities in the range of 15.5 to 18.5 ppg at 400~F.
These data show that, at densities below about 18.0 ppg,
extremely low corrosion rates are experienced. Only
above 18.0 ppg does the corrosion rate rise above the 10
mil per year objective. Although reduced levels of
protection are obtained at densities above 18.0 ppg,
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substantial improvement is obtained as compared to
uninhibitied 19.0 ppg fluids.
TABLE IX
Ninety Day Mild Steel Corrosion Rates
Winter Blends of 19.2 ppg ZnBr /CaBr2 (Containing 0.6 wt. %
Ammonlum Thio~ycolate) 2and 14.2 ppg CaBr~
Fluid Corrosion Rate (mpy)
Density
(ppg) 400DF
15.5 3.9
1~.5 2.1
17.5 5.0
18.5 56.7
Utilization of the composition of the present
invention in servicing well bores is shown in the follow-
ing example.
EXAMPLE VIII
When a zinc bromide/calcium bromide fluid is
used as a packer fluid in an oil well, its purpose is to
minimize the pressure drop across the packer in the
wellbore. The packer serves to isolate the hydrocarbon
producing interval from the remainder of the wellbore.
The advantage of using a clear fluid as a packer fluid is
the minimization of solids in the well annulus. Solids
will settle out over time and build up on the packer
making removal of the packer difficult. Therefore,
cleanup of the wellbore and all surface equipment before
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DWV20-C/cs ~g
the solids free fluid is placed in the wellbore is impor-
tant. All equipment, pumps, lines and storage tanks must
be clean. The wellbore must be scraped and flushed with
water. A fluid density is chosen to meet the requirements
of the well. (In many cases, a fluid density providing a
hydrostatic pressure in the wellbore at the packer 200
psi greater Han the formation pressure is employed).
The fluid is blended from the base fluids (which, prefer-
ably, include a 19.? ppg zinc bromide/calcium bromide fluid
and a 15.0 ppg calcium bromide/calcium chloride or a 14.2
ppg calcium bromide fluid) containing corrosion inhibitors
in accordance with this invention, and placed in appro-
priate storage tanks at the rig site. At the proper time,
the fluid is placed in the well annulus by displacement of
the fluid in the well annulus. The fluid will remain in
the well until remedial work is reguired to stimulate oil
production from the well.
In accordance with this invention there are
provided clear high densiky fluids which may be safely
and effectively employed as well-completion, packing and
perforating media. They are non-corrosive to equipment
and personnel, remain stable and may be satisfactorily
used on a long term basis. The solution should fulfill a
-~4-
DWV20-C/cs
~9~
long felt want in the well service field for clear solu-
tions having high densities that are capable of being
employed at high well bore operating temperatures.
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