U.S. patent application number 17/072644 was filed with the patent office on 2021-09-02 for chlorine dioxide precursor and methods of using same.
The applicant listed for this patent is Sabre Intellectual Property Holdings. Invention is credited to John Y. Mason.
Application Number | 20210269308 17/072644 |
Document ID | / |
Family ID | 1000005594863 |
Filed Date | 2021-09-02 |
United States Patent
Application |
20210269308 |
Kind Code |
A1 |
Mason; John Y. |
September 2, 2021 |
CHLORINE DIOXIDE PRECURSOR AND METHODS OF USING SAME
Abstract
According to one aspect of the invention, a method of converting
an oxy halide salt into a halide dioxide in a reaction zone under
certain conditions is provided. More specifically, the method
includes generating chlorine dioxide from a stable composition
comprising an oxy halide salt by introducing said composition to a
reducing agent and minimum temperature within the reaction zone.
According to another aspect of the invention, a composition for a
stable chlorine dioxide precursor comprising an oxy halide salt is
provided.
Inventors: |
Mason; John Y.;
(Slingerlands, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sabre Intellectual Property Holdings |
Slingerlands |
NY |
US |
|
|
Family ID: |
1000005594863 |
Appl. No.: |
17/072644 |
Filed: |
October 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16806242 |
Mar 2, 2020 |
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17072644 |
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16518600 |
Jul 22, 2019 |
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16806242 |
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15875301 |
Jan 19, 2018 |
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16518600 |
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14958381 |
Dec 3, 2015 |
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15875301 |
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14196207 |
Mar 4, 2014 |
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14958381 |
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13427544 |
Mar 22, 2012 |
8703656 |
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14196207 |
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61466258 |
Mar 22, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 8/845 20130101;
C09K 8/86 20130101; C09K 8/605 20130101; C07C 7/20 20130101; E21B
41/02 20130101; C09K 8/524 20130101; C01B 11/023 20130101; C09K
8/032 20130101; C09K 8/532 20130101; C09K 2208/20 20130101; A01N
59/00 20130101 |
International
Class: |
C01B 11/02 20060101
C01B011/02; C09K 8/60 20060101 C09K008/60; C09K 8/532 20060101
C09K008/532; C09K 8/03 20060101 C09K008/03; C09K 8/524 20060101
C09K008/524; A01N 59/00 20060101 A01N059/00; C07C 7/20 20060101
C07C007/20; C09K 8/84 20060101 C09K008/84; C09K 8/86 20060101
C09K008/86; E21B 41/02 20060101 E21B041/02 |
Claims
1-46. (canceled)
47. A chlorine dioxide precursor composition comprising an aqueous
solution of 5% to 40% by weight of a chlorate salt and 5% to 20% by
weight of a weak acid, wherein the composition is stable at a
temperature below about 90.degree. F. and wherein the composition
reacts to form chlorine dioxide when exposed to a reducing agent in
combination with a temperature of about 110.degree. F. or
greater.
48. The composition of claim 47, wherein the chlorate salt
comprises sodium chlorate and the weak acid comprises citric
acid.
49. The composition of claim 48, wherein the composition does not
comprise a strong acid.
50. The composition of claim 48, wherein the composition further
comprises a strong acid at a concentration of about 0.1% to 2% by
weight.
51. The composition of claim 50, wherein the strong acid is
hydrochloric acid, hydrofluoric acid, or a mixture thereof.
52. The composition of claim 47, wherein the reducing agent is iron
sulfide.
53. A well fluid to which the precursor composition of claim 47 is
added at a concentration from about 100 to 10,000 mg/l.
54. A chlorine dioxide precursor composition comprising an aqueous
solution of sodium chlorate at 5% to 40% by weight and citric acid
at 5% to 20% by weight, wherein the composition is stable at a
temperature below about 90.degree. F. and wherein the composition
reacts to form chlorine dioxide when exposed to iron sulfide in
combination with a temperature of about 115.degree. F. or
greater.
55. A well fluid to which the precursor composition of claim 54 is
added at a concentration from about 100 to 10,000 mg/l.
56. A method of treating an aqueous fluid for introduction into a
reaction zone having a temperature of at least about 110.degree. F.
and comprising one or more reducing agents, the method comprising
adding to the aqueous fluid a chlorine dioxide precursor
composition comprising an aqueous solution of a chlorate salt at a
concentration of 5 to 40% by weight and an acid at a concentration
of 5 to 20% by weight, wherein the composition is stable at a
temperature below about 90.degree. F. and wherein the composition
reacts to form chlorine dioxide when exposed to a reducing agent in
combination with a temperature of about 110.degree. F. or
greater.
57. The method of claim 56, wherein the chlorate salt comprises
sodium chlorate and the weak acid comprises citric acid.
58. The method of claim 56, wherein the composition does not
comprise a strong acid.
59. The method of claim 56, wherein the composition further
comprises a strong acid at a concentration of about 0.1% to 2% by
weight.
60. The method of claim 59, wherein the strong acid is hydrochloric
acid, hydrofluoric acid, or a mixture thereof
61. The method of claim 56, wherein the chlorine dioxide precursor
composition is added to the aqueous fluid at a concentration from
about 100 to 10,000 mg/l.
62. The method of claim 56, further comprising introducing the
aqueous fluid into a subterranean formation such that it enters a
reaction zone within the subterranean formation that has a
temperature of at least about 110.degree. F. and comprises a target
reducing agent.
63. The method of claim 62, wherein said target reducing agent
comprises one or more of elemental sulfur, a reduced sulfur
compound, a reduced organic compound, and a reduced metal ion.
64. The method of claim 62, wherein the chlorine dioxide precursor
composition is added to the aqueous fluid at a ratio of
approximately 2.5 to 5:1 by weight of chlorine dioxide precursor
composition to target reducing agent, and wherein said target
reducing agent comprises one or more reduced sulfur compounds or
reduced metal ions.
Description
RELATED APPLICATION(S)
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/806,242 filed Mar. 2, 2020 which is a
continuation of U.S. patent application Ser. No. 16/518,600 filed
Jul. 22, 2019, now abandoned which is a continuation of U.S. patent
application Ser. No. 15/875,301 filed Jan. 19, 2018, now abandoned,
which is a continuation of U.S. patent application Ser. No.
14/958,381 filed Dec. 3, 2015, now abandoned, which is a
continuation of U.S. patent application Ser. No. 14/196,207, filed
Mar. 4, 2014, now abandoned, which is a Divisional of U.S. patent
application Ser. No. 13/427,544, filed Mar. 22, 2012, and issued on
Apr. 22, 2014 as U.S. Pat. No. 8,703,656, which claims the benefit
of priority from U.S. Provisional Application No. 61/466,258, filed
Mar. 22, 2011. The entire teachings of the above application(s) are
incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates to a composition for a stable,
chlorine dioxide precursor and method for using the same to
generate chlorine dioxide for petroleum applications, such as, but
not limited to, the use of chlorine dioxide in petroleum formations
and high temperature gas or liquid streams. More particularly, this
invention relates to a composition comprising an oxy halide salt,
(e.g., sodium chlorate) as a stable chlorine dioxide precursor for
use in petroleum applications.
BACKGROUND
[0003] In the petroleum industry, numerous agents or contaminants
can cause damage to or restriction of the production process.
Examples of such contaminates can be high-molecular weight polymers
(e.g. polyacrylamides, carboxymethylcellulose,
hydroxyethylcellulose, CMC, HPG, and Zanthan), bacteria, sulfur,
iron sulfide, hydrogen sulfide and similar compounds.
[0004] These contaminants can, in some cases, occur naturally in
the formation or be present from prior human interactions. For
example, bacteria are commonly introduced to the formation during
drilling and workover (e.g. the repair or stimulation of an
existing production well) operations. Similarly, during the
fracturing process, bacteria are often introduced into the wellbore
and forced deep into the formation. More specifically, polymers
such as CMC, HPG, Zanthan, and polyacrilomides are added to the
fracturing fluid to maintain the proppant in suspension and to
reduce the friction of the fluid. Bacteria entrained within this
fluid penetrate deep into the formation, and once frac pressure is
released, become embedded within the strata in the same manner as
the proppant deployed. Additionally, the polymer can also be
deposited within the formation, causing damage in its own right.
Typically, conventional "breakers" are added to the fracturing
fluid along with the polymer to prevent this problem, but damage to
producing wells due to the incomplete destruction of the polymer
remains a common occurrence.
[0005] Many bacteria are facultative, that is they can exist in
both aerobic or anaerobic conditions using either molecular oxygen
or other oxygen sources to support their metabolic processes. For
example, under the right conditions, facultative bacteria can use
sulfate as an oxygen source and respire hydrogen sulfide, which is
highly toxic to humans in addition to being corrosive to steel.
Additionally, in a process known in the art as Microbiologically
Induced Corrosion (MIC), bacteria will attach to a substrate, such
as the wall of a pipe in the wellbore, and form a "biomass" shield
around them. Underneath, the bacteria metabolize the substrate
(e.g. a mixture of hydrocarbon and metallic iron) and respire
hydrogen sulfide, resulting in the metal becoming severely corroded
in the wellbore and, eventually, pipe failure and damage to
downhole equipment. The respiration and presence of hydrogen
sulfide also complicates the refining and transportation process,
and attenuates the economic value of the produced hydrocarbon.
[0006] The traditional methods used to address these problems has
one or more drawbacks. For example, the present industry practice
is to add conventional organic and inorganic biocides, such as
quaternary ammonium compounds, chloramines, aldehydes, such as
Gluteraldehyde, THPS and sodium hypochlorite, to fracturing fluids
with other additives to control bacteria. The efficacy of these
conventional biocides, however, is minimal due to the type of
bacteria that typically are found in hydrocarbon-bearing formations
and petroleum production environments. More particularly, only a
small percentage of these bacteria, which are often found in
volcanic vents, geysers, and ancient tombs, are active at any one
time; the remainder of the population is present in dormant and
spore states. The aforementioned conventional biocides have no, or
limited, effect on dormant and spore forming bacteria. Thus, while
the active bacteria are killed to some extent, the inactive
bacteria survive and thrive once they reach the environmental
conditions found within the formation. Additionally, these biocides
become inactivated when exposed to many of the components found in
petroleum production formations. And, furthermore, microorganisms
build resistance to these biocides, thus limiting their utility
over time.
[0007] Chlorine dioxide, on the other hand, can inactivate or kill
active, dormant and spore forming microorganisms. Unlike
conventional biocides, microorganisms do not build a resistance to
chlorine dioxide, and it has a low residual toxicity and produces
benign end products. Chlorine dioxide is therefore an efficacious
biocide, however certain applications have not been possible prior
to the invention. For example, although chlorine dioxide can be
applied directly to well fluids (for example, fracturing water) for
disinfection, it can only be applied at a low dosage to prevent
degradation of polymer(s) or other drag reduction additives.
[0008] Embodiments of this invention provide for a stable chlorine
dioxide precursor additive. The inventor has found that this
chlorine dioxide precursor will remain stable within, for example,
well fluids (e.g. a fracturing fluid) or other fluid streams or
systems until it enters a zone (e.g. within a subterranean
formation) that satisfies certain conditions and reaches a minimum
temperature of about 100.degree. F.-110.degree. F. One or more
embodiments of the invention, which incorporate this chlorine
dioxide precursor into a fracturing fluid, thus provide an in situ
method for generating and using chlorine dioxide as a polymer
oxidant and downhole biocide that does not deplete or attenuate the
friction-reducing components of the fracturing fluid until the
chlorine dioxide precursor is dispersed into the target zone of the
subterranean, hydrocarbon-bearing formation. In these embodiments,
the chlorine dioxide precursor reacts with components in the
subterranean formation at a certain temperature to form chlorine
dioxide therein, which then acts as a polymer oxidant and downhole
biocide.
[0009] The inventor has found that the embodiments of the invention
provide for results that cannot be accomplished with ex situ
generated halogen dioxides, such as chlorine dioxide, or other
halogen dioxide precursors, such as sodium chlorite. For example,
chlorine dioxide cannot be added to well fluids (e.g. fracturing
fluid) at high concentrations prior to injection into the wellbore
because the chlorine dioxide will prematurely oxidize the polymers
and friction-control additives within the fracturing fluid.
Similarly, sodium chlorite, sometimes referred to as "stabilized
chlorine dioxide," is limited in that it immediately begins to
react with weak acids and other components of the fracturing fluids
at ambient temperatures, thereby generating chlorine dioxide too
soon, which in turn will prematurely oxidize the polymers and
friction-control additives within the fracturing fluid. By
contrast, embodiments of the present invention remain generally
stable until exposed to a minimum temperature and reducing agents
(e.g., contaminants) located within a subterranean formation or
otherwise provided in a target reaction zone.
[0010] Thus, embodiments of the invention provide for, inter alia,
a composition that is stable under ambient conditions within a
fluid stream or system (for example, the well fluids applied during
drilling, completion, workover and fracturing operations), but
subsequently reacts within a target reaction zone under specified
conditions to produce a halide oxide that is capable of 1)
degrading polymers within the target zone (i.e. the subterranean
formation); 2) reducing toxic and unwanted sulfur compounds within
the target zone (i.e. the subterranean formation and hydrocarbon
deposits), and 3) functioning as a biocide that kills or destroys
bacteria in active, dormant and spore forms.
BRIEF DESCRIPTION OF THE INVENTION
[0011] One aspect of the invention includes a method for
introducing an oxy halide salt into a zone wherein the oxy halide
salt comes into contact with a reducing agent resulting in
conversion of the oxy halide salt into a halide dioxide, comprising
applying or injecting an oxy halide salt into a zone with a
reducing agent under conditions in which all or a part of the oxy
halide salt is converted into the halide dioxide.
[0012] Another aspect of the invention includes a method of
reducing, inactivating, destroying, or eliminating one or more
reduced sulfur compounds, comprising the steps of contacting the
reduced sulfur compound with an oxy halide salt under conditions in
which all or a part of the oxy halide salt is converted into the
halide dioxide, thereby reducing, inactivating, destroying, or
eliminating one or more reduced sulfur compounds.
[0013] In another aspect of the invention, a method for oxidizing
one or more polymers, one or more reduced sulfur compounds or one
or more reduced metals, comprises the steps of contacting the
polymer, reduced sulfur compound or reduced metal with an oxy
halide salt in a reaction zone under conditions in which all or a
part of the oxy halide salt is converted into the halide dioxide,
thereby oxidizing one or more polymers, one or more reduced sulfur
compounds or one or more reduced metals.
[0014] Another aspect of the invention includes a method for
inactivating, destroying or killing one or more microbes,
comprising contacting the microbe with an oxy halide salt under
conditions in which all or a part of the oxy halide salt is
converted into the halide dioxide, thereby inactivating, destroying
or killing one or more microbes.
1. DETAILED DESCRIPTION
[0015] The following terms as used herein have the following
meanings:
[0016] As used herein, the words "comprise," "has," and "include,"
and all grammatical variations thereof are each intended to have an
open, non-limiting meaning that does not exclude additional
elements or parts.
[0017] As used herein, a biocide, or bactericide, is a substance
that inhibits, destroys or kills bacteria.
[0018] As used herein, free residual level or residual is the
amount of oxidant in a fluid present and available for
microbiological control at a given time after the oxidant has
reacted with background impurities and contaminants in the fluid.
Generally described in units of percentage or ppm.
[0019] As used herein, well fluid is any fluid used in any of the
drilling, completion, work over, fracturing and production of
subterranean oil and gas wells.
[0020] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to
embodiments of the invention and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, and
any alterations and further modifications in the described
embodiments, and any further applications of the principles of the
invention as illustrated therein as would normally occur to one
skilled in the art to which the invention relates are contemplated
an protected.
[0021] According to one or more embodiments of the invention, a
halide dioxide, preferably chlorine dioxide, is generated in situ
in a target reaction zone. According to one aspect of the
invention, the target reaction zone is found within a
hydrocarbon-bearing subterranean formation and is the zone within
the formation where the target compounds, or contaminants, are
located. Furthermore, the target zone may comprise a hydrocarbon
deposit, a petroleum deposit, a hydrocarbon or petroleum product
formation, or a hydrocarbon or petroleum processing product or
equipment. As used herein, the target compounds, or contaminants,
are agents located within the subterranean formation that have the
potential or propensity to cause damage to or restriction of the
petroleum production process, and include high-molecular weight
polymers (e.g. polyacrylamides, carboxy-methylcellulose,
hydroxyethylcellulose, CMC, HPG, and Zanthan), microbes (e.g.
anaerobic and aerobic bacteria), sulfur, iron sulfide, hydrogen
sulfide and similar compounds.
[0022] In one or more embodiments, a composition comprises a
stable, halogen dioxide precursor concentrate that does not react
with the target compounds prior to entering the target reaction
zone within the subterranean formation. The halogen dioxide
precursor comprises an oxy halide salt, such as sodium chlorate, in
solution at a concentration up to about 50% by weight, preferably
about 5% to 40% by weight. Although the embodiments and examples
disclosed herein refer to sodium chlorate as the oxy halide salt,
one of ordinary skill in the art would recognize that other oxy
halide salts containing a chlorine in the plus five valence or
oxidation state, such as potassium chlorate, calcium chlorate, or
magnesium chlorate, would fall within the embodiments of this
invention. The stable precursor concentrate will typically be added
to a fluid stream (e.g. well fluid) at concentrations ranging from
about 100 to 10,000 mg/l.
[0023] Although not required, in one or more embodiments, the
composition or concentrate comprising the stable chlorine dioxide
precursor further comprises additives selected to benefit the type
of treatment that is targeted. For example, in certain embodiments,
the halogen dioxide precursor further comprises and is premixed
with additives, preferably chelants or weak acids, such as citric
acid, or wetting agents such as ethylene glycol monobutyl
ether.
[0024] More specifically, in one embodiment, the composition
comprises up to about 40% by weight sodium chlorate, up to 20% by
weight of a chelating agent, and up to about 10% by weight of a
surface active agent. In other embodiments, the composition
comprises an aqueous solution of an oxy halide salt and a weak
acid, wherein the concentration of the oxy halide salt is between
about 5% and 40% and the concentration of the weak acid is between
about 5% and 20%. In still other embodiments, more specifically in
embodiments wherein the target reaction zone alone supplies a
sufficient amount hydrogen ions to allow for the generation of
chlorine dioxide, the stable precursor composition does not include
any chelating agent.
[0025] Because the target compounds within the target zone react
with the stable precursor to form a halogen dioxide, preferably
chlorine dioxide, as an end-product of the reaction, a free
residual of said halide oxide is generated in situ and is available
to oxidize other compounds, function as a biocide and control or
inactivate microbes located either within or around the target
zone. Therefore, in one or more embodiments of this invention, no
ex situ generator or process is required to generate chlorine
dioxide for injection into the subterranean formation and/or gas or
liquid streams in order to destroy or reduce polymers, sulfur,
reduced sulfur compounds, phenols and other compounds.
[0026] More specifically, in one or more embodiments of the present
invention, the premixed composition, or concentrate, comprising
said halogen dioxide precursor is stable and not reactive in
solutions of polymer, sulfides, and/or weak acids at ambient
conditions and temperatures, and more specifically is stable in
solutions of polymer, sulfides, and/or weak acids at temperatures
in the range of less than about 90.degree. F. to 110.degree. F.,
and more preferably does not react to form chlorine dioxide until
the temperature reaches or exceeds about 110.degree. F. to
115.degree. F. More specifically, and in the embodiments disclosed
herein, the composition is stable at ambient temperatures in, for
example, drilling, fracturing, completion, and operational well
fluids, including but not limited to drilling muds, fracturing
fluids, produced or fresh water, or blends thereof. In still other
embodiments of the invention, the composition or concentrate also
remains stable at temperatures in the range of less than about
90.degree. F. to 110.degree. F. when premixed with a low
concentration of a strong acid, such as hydrochloric or
hydrofluoric acid, wherein the concentration of the strong acid can
be in the range of about 0.1% to 2%, more preferably 0.2% to 0.5%.
In accordance with the invention, both the selection and
concentration of a weak or strong acid is determined by the
concentration at which said acid will not react to form chlorine
dioxide when it is mixed directly with the oxy halide salt at
temperatures in the range of less than about 90.degree. F. to
110.degree. F.
[0027] According to the invention, the composition comprising the
stable halogen dioxide precursor therefore remains stable until it
reaches a target reaction zone, wherein the composition is then
exposed to temperatures of at least about 90.degree. F. to
110.degree. F., and preferably reaches or exceeds about 110.degree.
F. to 115.degree. F., and wherein the composition is further
exposed or introduced to at least one of or a combination of one or
more of the following: a hydrocarbon containing formation, reduced
sulfur compounds, elemental sulfur, sulfite, polymer, biomass (i.e.
microbes or bacteria), reduced metal ions, and other easily
oxidized organic and inorganic compounds. For example, in one or
more embodiments, the reduced sulfur compounds are present in a
target reaction zone within a subterranean geological formation or
material that contains one or more solid, liquid, or gaseous
hydrocarbons, or a hydrocarbon deposit, a petroleum deposit, a
hydrocarbon or petroleum product formation, or a hydrocarbon or
petroleum processing product or equipment. In another embodiment,
microbes and reduced sulfur compounds are present in a target
reaction zone within a petroleum processing piece of equipment. In
still another embodiment, polymers and reduced sulfur compounds are
present in a target reaction zone within the fractures of
hydrocarbon-bearing subterranean formation.
[0028] Embodiments of the present invention also provide that the
concentrate or composition comprising said halogen dioxide
precursor is either added to or premixed with a fluid stream, for
example a fluid stream being injected into a subterranean wellbore,
wherein said fluid stream may include other additives, such as
friction reducers, wetting agents, polymers, corrosion inhibitors,
sand, proppants, biocides, breakers and other chemicals and wherein
the chlorine dioxide precursor is and remains stable in the
presence of these additives until it reaches the target reaction
zone. Once it reaches the target reaction zone, the halogen dioxide
precursor is introduced to a high temperature liquid or gas stream
that contains one or more of sulfides, reduced sulfur compounds,
polymers, microbial matter or other target compounds. In accordance
with the invention, the high temperature fluid or gas stream is at
or brought up to temperatures above about 90.degree. F. to
115.degree. F., and preferably above about 110.degree. F. to
115.degree. F. According to embodiments of this invention, when the
halogen dioxide precursor solution reaches the target reaction zone
within the formation that contains the conditions set forth above,
said precursor composition will react spontaneously to form halogen
dioxide (e.g., chlorine dioxide) in said zone. The in situ
generated halogen dioxide will then destroy polymers and other
target compounds, such as reduced sulfur compounds, biomass (e.g.
microbes, bacteria), sulfur, phenols, either within, around or
after said zone, such that the halogen dioxide formation reaction
that initiates in said zone will consume the contaminants.
[0029] In one embodiment, said stable composition or concentrate is
premixed offsite and is then transported to the work site. In other
embodiments, for example during a hydraulic fracturing operation,
said composition can be premixed at the work site in one of the
frac tanks or in the blender. The premixed concentrate comprising
the stable chlorine dioxide precursor and other additives is then
injected into the process stream via a chemical injector system
and/or other method that is known to those skilled in the art.
[0030] The dosage rate and concentration of the composition
comprising the stable precursor is calculated based on the quantity
of chlorine dioxide, or other halogen oxide, that needs to be
generated and/or the amount of contaminants that need to be
consumed. More specifically, the dosage rate and concentration can
be determined based on the nature of the treatment, the
characteristics of the fluid or gas stream, the characteristics of
the subterranean formation (if applicable), and the contaminants
contained therein, as would be determined by those skilled in the
art. For example, and in one embodiment, the application ratio to
eliminate reduced sulfur compounds and oxidate reduced metal ions
is approximately 2.5 to 5:1 chlorine dioxide precursor to target
compound by weight.
[0031] When chlorine dioxide or other halogen dioxides are added
directly to well fluids (i.e. fracturing fluids) or other fluid
streams, they can initially react with dissolved organic and
inorganic compounds in the water, thus depleting the amount of free
residual available as a biocide and for other intended treatment
purposes. Therefore, in one or more embodiments of the present
invention, it will be necessary to add an excess of the stable
precursor in order to produce a free residual of the halogen
dioxide sufficient to achieve the desired bacterial control and/or
oxidation of complex organics. In yet another embodiment, if
instant biocidal control is desired or required, the stable
precursor of the present invention may be incorporated into a water
or fluid stream that has already has been dosed with a generated
solution of chlorine dioxide or other biocidal agent. More
specifically, and by way of example only, chlorine dioxide
concentrations of 10 to 20 mg/l or less do not impact the
performance of the additives, such polymer(s) or other drag
reduction additives, in fracturing fluids. Therefore, in certain
embodiments, the composition comprising the stable precursor can be
added to raw fracturing water that contains a sufficient residual
of chlorine dioxide, for example from about 0.02 to 5 mg/l, and
preferably from about 1-2 mg/l, to provide primary disinfection of
the raw water without prematurely depleting or effecting the
performance of the other additives. The addition of this
low-residual, generated chlorine dioxide provides primary
disinfection and inhibits or prevents biofouling of the mixing and
pumping equipment. As described herein, and in accordance with the
invention, the composition comprising the stable precursor will not
provide appreciable biocidal control until activation it is
introduced to the appropriate conditions within the reaction zone,
including one or more reducing agents and fluid temperatures at a
minimum of about 90.degree. F. to 110.degree. F., and preferably at
or above about 110.degree. F. to 115.degree. F.
[0032] Although the embodiments disclosed hereinabove often refer
to the target reaction zone as located within a subterranean
formation, in accordance with alternate embodiments that are within
the scope of the invention, the reaction zone can also equipment, a
pipeline or vessel for extracting, processing, refining,
transporting or storage of hydrocarbons. In order to oxidize
contaminants in a fluid or gas stream in accordance with the
invention in these embodiments, a stable precursor composition or
concentrate will comprise up to about 40% of a oxy halide salt,
preferably sodium chlorate and may also comprise up to about 20% by
weight of a chelating agent. The composition is then introduced via
the fluid or gas stream to an environment with a minimum
temperature of about 90.degree. F. to 100.degree. F., ideally over
about 100.degree. F., and more preferably over about 110.degree. F.
to 115.degree. F., wherein said fluid or gas stream further
comprises contaminants such as reduced metal ions, biomass, reduced
sulfur compounds, or other reduced organics such as phenols or
tertiary alcohols or amines.
[0033] The inventor has also found that, due to the oxidation of
sulfides and other contaminants, the generation of chlorine dioxide
within a formation in accordance with this invention will affect
the affinity of hydrocarbons to non-hydrocarbons, such that the
embodiments disclosed herein result in hydrocarbons being released
from the subterranean formation in amounts greater than would have
occurred without the generation of chlorine dioxide within the
formation. More specifically, in situ generated chlorine dioxide
via the stable precursor composition disclosed herein effectuates
the removal of hydrocarbons from subterranean formation material,
while other oxidants such as hydrogen peroxide, sodium persulfate,
sodium peroxide, sodium chlorite, and sodium hypochlorite do
not.
EXAMPLES
Example 1
[0034] This example illustrates a representative reaction in which
chlorine dioxide is formed from a precursor. A chlorine dioxide
precursor reacts with reduced contaminant to form chlorine dioxide
by gaining an electron from the contaminant.
ClO.sub.3.sup.-+Rx.fwdarw.ClO.sub.2+RxO.sup.-;
where Rx is the reducing agent providing an electron in the
reduction of chlorate to chlorine dioxide.
[0035] The formed chlorine dioxide competes with the stable
precursor in the oxidation of the contaminants, and as a reactive
free radical oxidizes additional compounds that are non reactive
with the precursor. Neither chlorine dioxide nor chlorate react via
electrophilic substitution and do not thus form chlorinated organic
compounds. One known pathway for chlorate to form chlorine is in
the absence of a reducing agent under strong acid conditions, as
represented by the following reaction:
ClO.sub.3.sup.-+2HCl.fwdarw.ClO.sub.2+1/2Cl.sub.2+H.sub.2O
[0036] No strong acids are present in the media during the
application of the present invention and reducing agents are always
present during the chlorine dioxide formation. Mixture of the
chlorine dioxide precursor with a strong acid is generally avoided
to prevent chlorination and corrosive effects from the resultant
chlorine.
Example 2
[0037] A solution was made up of 10% by weight of sodium chlorate,
10% citric acid, and 0.15% hydrochloric acid. Samples of the
solution were stored at 80.degree. F., 90.degree. F., 100.degree.
F., 110.degree. F., 120.degree. F. and 150.degree. F. and monitored
for sixty days using spectrophotometric analysis for the presence
of chlorine dioxide. At no time during the test period was there a
physical change in the solution, evidence of off-gassing or
evidence of chlorine dioxide production. At the end of the
observation period the samples were analyzed for sodium chlorate.
No significant change in the concentration was observed. The
foregoing study demonstrates that solutions of an oxy halide salt
can be formulated with weak acids or low concentrations of strong
acids (e.g., hydrochloric acid) without the resultant formation of
chlorine dioxide that would prevent their transportation under DOT
regulations, or degradation of the product within a normal shelf
life period.
Example 3
[0038] Identical examples of the solution used in Example 2 were
mixed with the addition of 0.5% Iron Sulfide. Samples of the final
solution were stored at 80.degree. F., 90.degree. F., 100.degree.
F., 110.degree. F., 120.degree. F. and 150.degree. F. and monitored
for sixty days using spectrophotometric analysis for the presence
of chlorine dioxide. At temperatures of up to 110.degree. F., no
evidence of reaction or chlorine dioxide formation was observed and
hydrogen sulfide gas was evolved into the head space of the
samples. At the end of the sixty day cycle chlorate analysis
indicated no significant change. The 120.degree. F. samples showed
a slow degradation of the hydrogen sulfide and yellowing of the
solution over a 48 hour period. After 48 hours there was no
remaining sulfide within the sample and there was a slight residual
of 8-10 ppm chlorine dioxide. The 150.degree. F. sample immediately
yellowed and consumed the iron sulfide without a release of
hydrogen sulfide upon addition and formed a slight 10 to 15 ppm
residual of chlorine dioxide. Once iron sulfide was consumed
formation of chlorine dioxide ceased. Additional aliquots of iron
sulfide resulted in complete destruction of the sulfide and
oxidation of the iron to the ferric state. Subsequent analysis of
the residual chlorate revealed that chlorate was consumed by
approximately a 2.7 chlorate to sulfide weight ratio. The foregoing
study demonstrates that the stable chlorine precursor will react at
typical production formation conditions to form chlorine dioxide
and consume the target contaminants and form sufficient residual
chlorine dioxide to kill, inactivate or destroy more stable or
resilient contaminants such as bacteria and polymers.
Example 4
[0039] Identical examples of the solution used in Example 2 were
mixed with the addition of 5% by weight ground up core material.
The materials were sandstone and dolomite in nature, and contained
approximately 10 mg/kg of iron sulfide. Samples of the final
solution were stored at 80.degree. F., 90.degree. F., 100.degree.
F., 110.degree. F., 120.degree. F. and 150.degree. F. and monitored
for sixty days using spectrophotometric analysis for the presence
of chlorine dioxide. At temperatures of up to 100.degree. F., there
was no evidence of reaction or chlorine dioxide formation, and
hydrogen sulfide gas was evolved into the head space of the
samples. At the end of the sixty day cycle, chlorate analysis
indicated no significant change in chlorate concentration. The
110.degree. F., 120.degree. F. and 150.degree. F. samples showed a
slow degradation of the hydrogen sulfide and yellowing of the
solution over a 48 hour period. After 48 hours, there was no
remaining sulfide within the sample and there was a slight residual
of 8-10 ppm chlorine dioxide. The 150.degree. F. sample immediately
yellowed and consumed the iron sulfide without a release of
hydrogen sulfide upon addition, and formed a slight 10 to 15 ppm
residual of chlorine dioxide. Subsequent analysis of the residual
chlorate revealed that chlorate was consumed by approximately a 3.2
chlorate to sulfide weight ratio. The foregoing study demonstrates
that production zone material can provide sufficient reducing
materials for the conversion of a precursor to chlorine dioxide to
occur.
Example 5
[0040] In this example, a first flask contained a 0.5 percent
solution of sodium sulfide. A second flask contained a solution of
10% sodium chlorate and 10% citric acid. A third flask contained a
5% solution of ferric (iron) sulfate. An inert gas stream purged
gases from flask to flask through a gas train. Hydrochloric acid
was added to the first flask to evolve hydrogen sulfide gas. The
study was conducted at 100.degree. F., 150.degree. F., 175.degree.
F. and 200.degree. F. At 100.degree. F. and 150.degree. F., no
reaction was observed within the second flask and hydrogen sulfide
reacted with the iron sulfate solution to form iron sulfide in the
third flask. Some hydrogen sulfide vented from the third flask. At
175.degree. F., iron sulfide was still formed in the third flask
and some hydrogen sulfide vented, but to a much lesser extent.
Flask 2 remained clear at the end of the study, but evolved some
chlorine dioxide. At 200.degree. F., no iron sulfide formed within
the third flask or was vented from the gas train. The solution in
flask 2 displayed evidence of chlorine dioxide formation and had a
slight residual of chlorine dioxide of approximately 5 mg/l at the
conclusion of the study the foregoing study demonstrates that an
elevated temperature gas stream has sufficient reducing properties
to trigger the conversion of precursor to chlorine dioxide, and
that reducing agents within the contaminants can be used as the
reductant (hydrogen sulfide) to trigger the conversion with
sufficient halo dioxide to result in the elimination of the
reductant.
[0041] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
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