U.S. patent application number 13/444921 was filed with the patent office on 2013-10-17 for acidizing fluids comprising a salt block inhibitor and methods for use thereof.
This patent application is currently assigned to Halliburton Energy Services, Inc.. The applicant listed for this patent is Enrique A. Reyes. Invention is credited to Enrique A. Reyes.
Application Number | 20130269937 13/444921 |
Document ID | / |
Family ID | 47913626 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130269937 |
Kind Code |
A1 |
Reyes; Enrique A. |
October 17, 2013 |
Acidizing Fluids Comprising a Salt Block Inhibitor and Methods for
Use Thereof
Abstract
Treatment fluids comprising hydrofluoric acid, a hydrofluoric
acid-generating compound, or any combination thereof can be used in
conjunction with acidizing a subterranean formation that contains a
siliceous material. Inclusion of a salt block inhibitor in the
treatment fluids may eliminate or reduce the formation of insoluble
fluorosilicates and aluminosilicates that can occur when an
acidizing operation is conducted. Methods for treating a
subterranean formation can comprise: providing a treatment fluid
that comprises a salt block inhibitor comprising a fructan, and
hydrofluoric acid, a hydrofluoric acid-generating compound, or any
combination thereof; and introducing the treatment fluid into a
subterranean formation.
Inventors: |
Reyes; Enrique A.; (Duncan,
OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Reyes; Enrique A. |
Duncan |
OK |
US |
|
|
Assignee: |
Halliburton Energy Services,
Inc.
Houston
TX
|
Family ID: |
47913626 |
Appl. No.: |
13/444921 |
Filed: |
April 12, 2012 |
Current U.S.
Class: |
166/279 |
Current CPC
Class: |
C09K 8/74 20130101 |
Class at
Publication: |
166/279 |
International
Class: |
E21B 43/00 20060101
E21B043/00 |
Claims
1. A method comprising: providing a treatment fluid that comprises:
a salt block inhibitor comprising a fructan; and hydrofluoric acid,
a hydrofluoric acid-generating compound, or any combination
thereof; and introducing the treatment fluid into a subterranean
formation.
2. The method of claim 1, further comprising: allowing the fructan
to interact with an alkali metal ion.
3. The method of claim 2, wherein the interaction between the
fructan and the alkali metal ion reduces or eliminates the
formation of insoluble fluorosilicates or aluminosilicates in the
subterranean formation, relative to a like treatment fluid lacking
the fructan.
4. The method of claim 1, wherein the fructan comprises an inulin,
a levan, a graminin, any salt thereof, any derivative thereof, or
any combination thereof.
5. The method of claim 4, wherein the fructan comprises
carboxymethylinulin, carboxyethylinulin, any salt thereof, or any
combination thereof.
6. The method of claim 1, wherein the treatment fluid further
comprises a carrier fluid comprising alkali metal ions.
7. The method of claim 1, wherein the treatment fluid further
comprises a chelating agent, an alkali metal salt of a chelating
agent, a non-alkali metal salt of a chelating agent, or any
combination thereof.
8. The method of claim 1, wherein the treatment fluid has a pH of
about 8 or less.
9. The method of claim 1, wherein the treatment fluid has a pH
ranging between about 0 and about 8.
10. A method comprising: providing a treatment fluid having a pH
ranging between about 0 and about 8 that comprises: a salt block
inhibitor comprising a fructan; and hydrofluoric acid, a
hydrofluoric acid-generating compound, or any combination thereof;
introducing the treatment fluid into a subterranean formation; and
performing an acidizing operation in the subterranean
formation.
11. The method of claim 10, wherein performing an acidizing
operation in the subterranean formation comprises at least
partially dissolving a silicate or an aluminosilicate in the
subterranean formation.
12. The method of claim 10, wherein the treatment fluid further
comprises a carrier fluid comprising alkali metal ions.
13. The method of claim 10, wherein the treatment fluid further
comprises another acid, an acid-generating compound, or any
combination thereof.
14. The method of claim 10, wherein the acidizing operation is
performed in the absence of an NH.sub.4.sup.+ salt.
15. The method of claim 10, wherein the treatment fluid performs
the acidizing operation.
16. The method of claim 10, wherein the fructan interacts with an
alkali metal ion in the subterranean formation so as to reduce or
eliminate the formation of insoluble fluorosilicates or
aluminosilicates, relative to a like treatment fluid lacking the
fructan; wherein the insoluble fluorosilicates or aluminosilicates
are generated during the acidizing operation.
17. The method of claim 10, wherein the treatment fluid further
comprises a chelating agent, an alkali metal salt of a chelating
agent, a non-alkali metal salt of a chelating agent, or any
combination thereof.
18. The method of claim 10, wherein the fructan comprises an
inulin, a levan, a graminan, any salt thereof, any derivative
thereof, or any combination thereof.
19. The method of claim 18, wherein the fructan comprises
carboxymethylinulin, carboxyethylinulin, or any combination
thereof.
20. A method comprising: providing a treatment fluid that
comprises: a carrier fluid comprising alkali metal ions; a salt
block inhibitor comprising a fructan; and hydrofluoric acid, a
hydrofluoric acid-generating compound, or any combination thereof;
introducing the treatment fluid into a subterranean formation
having a siliceous material present therein; and allowing the
hydrofluoric acid, hydrofluoric acid-generating compound, or any
combination thereof to at least partially dissolve the siliceous
material in the subterranean formation.
21. The method of claim 20, wherein the treatment fluid further
comprises a chelating agent, an alkali metal salt of a chelating
agent, a non-alkali metal salt of a chelating agent, or any
combination thereof.
22. The method of claim 20, wherein the fructan comprises an
inulin, a levan, a graminan, any salt thereof, any derivative
thereof, or any combination thereof.
Description
BACKGROUND
[0001] The present disclosure relates to matrix acidizing of
subterranean formations, and, more specifically, to treatment
fluids that can eliminate or reduce the production of insoluble
fluorosilicates and aluminosilicates that may occur in conjunction
with an acidizing operation.
[0002] Treatment fluids can be used in a variety of subterranean
treatment operations. Such treatment operations can include,
without limitation, drilling operations, stimulation operations,
production operations, sand control treatments, and the like. As
used herein, the terms "treat," "treatment," "treating," and
grammatical equivalents thereof refer to any subterranean operation
that uses a fluid in conjunction with achieving a desired function
and/or for a desired purpose. Use of these terms does not imply any
particular action by the treatment fluid. Illustrative treatment
operations can include, for example, fracturing operations, gravel
packing operations, acidizing operations, scale dissolution and
removal, consolidation operations, and the like.
[0003] In acidizing operations, a subterranean formation containing
an acid-soluble material can be treated with an acid to dissolve at
least a portion of the material. Formation components of the
formation matrix may comprise the acid-soluble material in some
cases. In other cases, the acid-soluble material may have been
deliberately introduced into the subterranean formation in
conjunction with a stimulation operation (e.g., proppant
particulates). Illustrative examples of formation components that
may be dissolved by an acid include, for example, carbonates,
silicates, and aluminosilicates. Dissolution of these formation
components can desirably open voids and conductive flow pathways in
the formation that can improve the formation's rate of hydrocarbon
production, for example. In a similar motif, acidization may be
used to remove like types of precipitation damage that can be
present in the formation.
[0004] Carbonate formations often contain minerals that comprise a
carbonate anion (e.g., calcite). When acidizing a carbonate
formation, the acidity of the treatment fluid alone can be
sufficient to solubilize the formation components. Both mineral
acids (e.g., hydrochloric acid) and organic acids (e.g., acetic and
formic acids) can be used to treat a carbonate formation, often
with similar degrees of success.
[0005] Siliceous formations can include minerals such as, for
example, zeolites, clays, and feldspars. Most sandstone formations
contain about 40% to about 98% sand quartz particles (i.e.,
silica), bonded together by various amounts of cementing material
including carbonates (e.g., calcite), aluminosilicates, and other
silicates. As used herein, the term "siliceous" refers to a
substance having the characteristics of silica, including silicates
and/or aluminosilicates.
[0006] Acidizing a siliceous formation (e.g., a sandstone formation
or a clay-containing formation) is thought to be considerably
different than acidizing a carbonate formation. Specifically, the
treatment of a siliceous formation with the treatment fluids
commonly used for acidizing a carbonate formation may have little
to no effect, because mineral acids and organic acids do not
effectively react with siliceous materials. In contrast to mineral
acids and organic acids, hydrofluoric acid can react very readily
with siliceous materials to produce soluble substances. Oftentimes,
a mineral acid or an organic acid can be used in conjunction with a
hydrofluoric acid-containing treatment fluid to maintain the
treatment fluid in a low pH state as the hydrofluoric acid becomes
spent. In some instances, the low pH of the treatment fluid may
promote initial silicon dissolution and aid in maintaining the
silicon in a dissolved state. At higher subterranean formation
temperatures (e.g., above about 200.degree. F.), it may be
undesirable to lower the pH much below about 1 due to mineral
instability that can occur as a result. Additionally, regardless of
the formation temperature, corrosion can be an inevitable problem
that occurs when very low pH treatment fluids are used.
[0007] Although low pH treatment fluids may be desirable to aid in
silicon dissolution, precipitation of insoluble fluorosilicates and
aluminosilicates can still become problematic in the presence of
certain metal ions. Specifically, under low pH conditions (e.g.,
below a pH of about 3), dissolved silicon can react with Group 1
metal ions (e.g., Na.sup.+ and K.sup.+) to produce insoluble
fluorosilicates and aluminosilicates. The terms "Group 1 metal
ions" and "alkali metal ions" will be used synonymously herein.
Other metal ions, including Group 2 metal ions (e.g., Ca.sup.2+ and
Mg.sup.2+), may also be problematic in this regard. The
precipitation of insoluble fluorosilicates and aluminosilicates can
block pore throats and undo the desirable permeability increase
initially achieved by the acidizing operation. That is, the
formation of insoluble fluorosilicates and aluminosilicates can
damage the subterranean formation. In many instances, the damage
produced by insoluble fluorosilicates and aluminosilicates can be
more problematic than if the acidizing operation had not been
conducted in the first place. In contrast to many metal ions,
ammonium ions (NH.sub.4.sup.+) are not believed to promote the
formation of insoluble fluorosilicates and aluminosilicates.
Accordingly, treatment fluids comprising an ammonium salt are
frequently used in conjunction with acidizing a siliceous
formation, as discussed further below.
[0008] Problematic alkali metal ions or other metal ions can come
from any source including, for example, the treatment fluid, a
component of the treatment fluid, or the subterranean formation
itself. For example, the carrier fluid of a treatment fluid may
contain some sodium or potassium ions unless costly measures (e.g.,
deionization), are taken to limit their presence. Alkali metal
ions, in particular, are widely distributed in the environment and
can be especially difficult to avoid completely when conducting a
subterranean treatment operation. As discussed further below, a
variety of strategies have been developed to address the most
common sources of problematic metal ions encountered when
conducting subterranean treatment operations.
[0009] One strategy that has been used with some success to avoid
the damaging effects of metal ions includes introducing a sequence
of pre-flush treatment fluids into the subterranean formation prior
to performing an acidizing operation with a hydrofluoric
acid-containing treatment fluid. For example, a pre-flush treatment
fluid comprising a mineral acid or an organic acid can be used to
dissolve acid-soluble formation components and remove at least a
portion of the problematic metal ions from the formation.
Thereafter, another pre-flush treatment fluid comprising an
ammonium salt can be introduced into the subterranean formation to
displace the remaining formation metal ions and leave the formation
enriched in ammonium ions. Although this approach can be used
successfully, it can considerably add to the time and expense
needed to perform an acidizing operation.
[0010] Another strategy that can be used to mitigate the effects of
metal ions in acidizing operations is to introduce a chelating
agent into the subterranean formation. Although this strategy can
be successful for Group 2 metal ions and transition metal ions, for
example, chelation is believed to be somewhat less effective for
alkali metal ions. In addition, many chelating agents are utilized
in their salt form, which is many times their Na.sup.+ or K.sup.+
salt form. Thus, use of a chelating agent, although reducing
precipitation effects from certain metal ions, can actually
exacerbate the precipitation effects of alkali metal ions.
[0011] Sometimes the free acid or ammonium salt forms of chelating
agents can be used to avoid this issue, at least in principle, but
the free acid and/or ammonium salt forms of many chelating agents
are either unknown or not commercially available at a reasonable
cost. Furthermore, many common chelating agents are not
biodegradable or present other toxicity concerns that can make
their use in a subterranean formation problematic.
[0012] At higher concentrations, alkali metal salts themselves can
sometimes precipitate in a subterranean formation. Precipitated
alkali metal salts can also damage a subterranean formation and
reduce its permeability. Remediation operations using an aqueous
cleanup fluid may need to be conducted to remove any precipitated
salt. As above, these remediation operations may also add to the
time and expense needed to perform a treatment operation. One
method that has been used to retard the precipitation of Group 1
metal salts in a subterranean formation is to utilize a salt block
inhibitor. Examples of salt block inhibitors are described in U.S.
Pat. Nos. 7,028,776 and 7,977,283. Salt block inhibitors can
effectively increase the concentration of salt in a treatment fluid
and reduce the likelihood of precipitation.
SUMMARY OF THE INVENTION
[0013] The present disclosure relates to matrix acidizing of
subterranean formations, and, more specifically, to treatment
fluids that can eliminate or reduce the production of insoluble
fluorosilicates and aluminosilicates that may occur in conjunction
with an acidizing operation.
[0014] In some embodiments, the present invention provides a method
comprising: providing a treatment fluid that comprises: a salt
block inhibitor comprising a fructan; and hydrofluoric acid, a
hydrofluoric acid-generating compound, or any combination thereof;
and introducing the treatment fluid into a subterranean
formation.
[0015] In some embodiments, the present invention provides a method
comprising: providing a treatment fluid having a pH ranging between
about 0 and about 8 that comprises: a salt block inhibitor
comprising a fructan; and hydrofluoric acid, a hydrofluoric
acid-generating compound, or any combination thereof; introducing
the treatment fluid into a subterranean formation; and performing
an acidizing operation in the subterranean formation.
[0016] In some embodiments, the present invention provides a method
comprising: providing a treatment fluid that comprises: a carrier
fluid comprising alkali metal ions; a salt block inhibitor
comprising a fructan; and hydrofluoric acid, a hydrofluoric
acid-generating compound, or any combination thereof; introducing
the treatment fluid into a subterranean formation having a
siliceous material present therein; and allowing the hydrofluoric
acid, hydrofluoric acid-generating compound, or any combination
thereof to at least partially dissolve the siliceous material in
the subterranean formation.
[0017] The features and advantages of the present invention will be
readily apparent to one having ordinary skill in the art upon a
reading of the description of the preferred embodiments that
follows.
DETAILED DESCRIPTION
[0018] The present disclosure relates to matrix acidizing of
subterranean formations, and, more specifically, to treatment
fluids that can eliminate or reduce the production of insoluble
fluorosilicates and aluminosilicates that may occur in conjunction
with an acidizing operation.
[0019] As described above, metal ions, especially alkali metal
ions, can lead to a number of issues when present during an
acidizing operation. Particularly in the presence of dissolved
silicon (e.g., in the form of SiF.sub.4, SiF.sub.5.sup.-, or
SiF.sub.6.sup.2-), alkali metal ions can result in damaging alkali
fluorosilicate precipitates. Current approaches to dealing with the
issue of fluorosilicate and aluminosilicate precipitation can be
costly and may be insufficient in some cases.
[0020] The present disclosure describes that salt block inhibitors
may be included in treatment fluids comprising a hydrofluoric acid
source (e.g., hydrofluoric acid, a hydrofluoric acid-generating
compound, or a combination thereof) in order to address the issue
of fluorosilicate and aluminosilicate precipitation. Without being
bound by any theory or mechanism, it is believed that the salt
block inhibitor may increase the effective interaction of alkali
metal salts with aqueous treatment fluids, such that the salts are
less readily available to cause precipitation of fluorosilicates
and aluminosilicates. In addition, the salt block inhibitors may
also increase the solubility of alkali metal fluorosilicates that
do form. Applicant does not believe that there has been any
recognition in the art to use salt block inhibitors in either of
the foregoing manners.
[0021] A number of advantages can be realized when using treatment
fluids that comprise a salt block inhibitor and a hydrofluoric acid
source, as described herein, for acidizing a subterranean
formation. A primary advantage is that significantly fewer
precautions may need to be taken to exclude alkali metal ions from
the subterranean environment. For example, it may not be necessary
to conduct a pre-flush treatment with an NH.sub.4.sup.+-containing
treatment fluid prior to acidizing or fewer pre-flush treatment
cycles may be needed. This can reduce the time and expense needed
to conduct the acidizing operation. Likewise, there may be more
tolerance for alkali metal ions in the carrier fluid used to
formulate the treatment fluids, thereby allowing saltier water
sources to be used.
[0022] Use of treatment fluids that comprise a salt block
inhibitor, as described herein, may also significantly expand the
breadth of chelating agents that may be used in conjunction with
sequestering metal ions in a subterranean formation. Specifically,
use of a salt block inhibitor in treatment fluids may
advantageously allow sodium or potassium salts of a chelating agent
to be used in lieu of the free acid or ammonium salt forms, which
may be unknown, not commercially available, or expensive. In this
regard, some of the more common chelating agents known in the art
are available in their ammonium salt forms, but the chelating
agents are not biodegradable. In contrast, only a limited number of
biodegradable chelating agents are available in their free acid or
ammonium salt forms. Thus, use of a salt block inhibitor in
treatment fluids, as described herein, may allow a wider breadth of
biodegradable chelating agents to be used in conjunction with an
acidizing operation, which can improve the environmental profile of
the acidizing operation and lower the costs associated with the
chelating agent. Further discussion of biodegradable chelating
agents follows hereinbelow.
[0023] In some embodiments of the present invention, the salt block
inhibitor can be a fructan or any derivative thereof, particularly
an inulin, a levan, a graminin, or any derivative thereof. Fructans
are a class of polysaccharides comprising oligomers of the
monosaccharide fructose. Fructans are available from a number of
natural sources at a relatively low cost, and therefore do not
greatly increase the expense of a treatment fluid in which they are
included. Furthermore, because fructans are biodegradable
polysaccharides, they are not believed to detrimentally impact the
environmental profile of a treatment fluid in which they are
included.
[0024] In some embodiments of the present invention, treatment
fluids described herein may comprise a salt block inhibitor
comprising a fructan; and hydrofluoric acid, a hydrofluoric
acid-generating compound, or any combination thereof.
[0025] In some embodiments of the present invention, treatment
fluids described herein may comprise an aqueous carrier fluid as
their continuous phase. Suitable aqueous carrier fluids may
include, for example, fresh water, acidified water, salt water,
seawater, brine (e.g., a saturated salt solution), or an aqueous
salt solution (e.g., a non-saturated salt solution). Aqueous
carrier fluids can be obtained from any suitable source. In more
preferred embodiments of the present invention, the treatment
fluids may comprise an aqueous carrier fluid that is substantially
free of alkali metal ions or contains as low a concentration of
alkali metal ions as attainable at a reasonable cost. Choice of a
low salt or salt-free aqueous carrier fluid may allow a lower
concentration of the salt block inhibitor to be used in the
treatment fluids, allow saltier subterranean formations to be
treated, and/or permit greater quantities of alkali metal salts of
chelating agents to be used. In general, use of a salt block
inhibitor may allow greater levity to be realized in choosing an
aqueous carrier fluid for an acidizing treatment fluid than would
otherwise be possible. In some embodiments of the present
invention, the treatment fluids may further comprise a carrier
fluid that comprises alkali metal ions. In other embodiments of the
present invention, the treatment fluids may further comprise a
carrier fluid that is substantially free of alkali metal ions.
[0026] In some or other embodiments of the present invention, the
treatment fluids may comprise an organic solvent, such as
hydrocarbons, as at least a portion of its continuous phase.
[0027] The volume of the carrier fluid to be used in the treatment
fluids described herein may be dictated by certain characteristics
of the subterranean formation being treated such as, for example,
the quantity of siliceous material needing removal, the chemistry
of the siliceous material, and the formation porosity.
Determination of an appropriate volume of carrier fluid to be used
in the treatment fluids may also be influenced by other factors, as
will be understood by one having ordinary skill in the art.
[0028] In various embodiments of the present invention, the
treatment fluids may have a pH of about 8 or below. We have found
that such pH values, and especially pH values of about 3 or below,
may be effective for dissolving silicates and/or aluminosilicates
in a siliceous formation and/or maintaining dissolved silicon in
the treatment fluids. In addition, in embodiments in which a
chelating agent is present, the chelating agent may be more
effective in forming a metal complex that can sequester a metal ion
at certain pH values. In some embodiments of the present invention,
the treatment fluids may have a pH ranging between about 0 and
about 8. In other embodiments of the present invention, the
treatment fluids may have a pH ranging between about 0 and about 6,
or between about 0 and about 4, or between about 1 and about 6, or
between about 1 and about 4, or between about 2 and about 5, or
between about 0 and about 3, or between about 3 and about 6. One of
ordinary skill in the art will be able to determine an effective
working pH for the treatment fluids described herein to maintain
silicon in a dissolved state through routine experimentation and
given the benefit of this disclosure.
[0029] In various embodiments of the present invention, treatment
fluids comprising a salt block inhibitor comprising a fructan; and
hydrofluoric acid, a hydrofluoric acid-generating compound, or any
combination thereof may be used in conjunction with treating a
subterranean formation. More specifically, in some embodiments, the
treatment fluids described herein may be used in conjunction with
an acidizing operation, particularly an acidizing operation
conducted in a siliceous formation containing silicates and/or
aluminosilicates.
[0030] In some embodiments of the present invention, methods
described herein can comprise: providing a treatment fluid that
comprises a salt block inhibitor comprising a fructan; and
hydrofluoric acid, a hydrofluoric acid-generating compound, or any
combination thereof; and introducing the treatment fluid into a
subterranean formation.
[0031] In some embodiments of the present invention, methods
described herein can comprise: providing a treatment fluid having a
pH ranging between about 0 and about 8 that comprises a salt block
inhibitor comprising a fructan; and hydrofluoric acid, a
hydrofluoric acid-generating compound, or any combination thereof;
introducing the treatment fluid into a subterranean formation; and
performing an acidizing operation in the subterranean
formation.
[0032] In some embodiments of the present invention, methods
described herein can comprise: providing a treatment fluid that
comprises a carrier fluid comprising alkali metal ions; a salt
block inhibitor comprising a fructan; and hydrofluoric acid, a
hydrofluoric acid-generating compound, or any combination thereof;
introducing the treatment fluid into a subterranean formation
having a siliceous material present therein; and allowing the
hydrofluoric acid, hydrofluoric acid-generating compound, or any
combination thereof to at least partially dissolve the siliceous
material in the subterranean formation.
[0033] The treatment fluids described herein can comprise
hydrofluoric acid, a hydrofluoric acid-generating compound, or any
combination thereof. Suitable hydrofluoric acid-generating
compounds may include, for example, fluoroboric acid,
fluorosulfuric acid, hexafluorophosphoric acid, hexafluoroantimonic
acid, difluorophosphoric acid, hexafluorosilicic acid, potassium
hydrogen difluoride, sodium hydrogen difluoride, boron trifluoride
acetonitrile complex, boron trifluoride acetic acid complex, boron
trifluoride dimethyl ether complex, boron trifluoride diethyl ether
complex, boron trifluoride dipropyl ether complex, boron
trifluoride dibutyl ether complex, boron trifluoride t-butyl methyl
ether complex, boron trifluoride phosphoric acid complex, boron
trifluoride dihydrate, boron trifluoride methanol complex, boron
trifluoride ethanol complex, boron trifluoride propanol complex,
boron trifluoride isopropanol complex, boron trifluoride phenol
complex, boron trifluoride propionic acid complex, boron
trifluoride tetrahydrofuran complex, boron trifluoride piperidine
complex, boron trifluoride ethylamine complex, boron trifluoride
methylamine complex, boron trifluoride triethanolamine complex,
polyvinylammonium fluoride, polyvinylpyridinium fluoride,
pyridinium fluoride, imidazolium fluoride, ammonium fluoride,
ammonium bifluoride, tetrafluoroborate salts, hexafluoroantimonate
salts, hexafluorophosphate salts, bifluoride salts, and any
combination thereof.
[0034] When used, a hydrofluoric acid-generating compound can be
present in the treatment fluids described herein in an amount
ranging between about 0.1% to about 20% by weight of the treatment
fluid. In other embodiments of the present invention, an amount of
the hydrofluoric acid-generating compound can range between about
0.5% to about 10% or between about 0.5% to about 8% by weight of
the treatment fluid. Hydrofluoric acid, when present, may be used
in similar concentration ranges.
[0035] In some embodiments of the present invention, another acid,
an acid-generating compound, or any combination thereof can be
present in the treatment fluids in addition to hydrofluoric acid or
a hydrofluoric acid-generating compound. In some embodiments of the
present invention, the additional acid can be a mineral acid such
as, for example, hydrochloric acid, or an organic acid such as, for
example, acetic acid or formic acid. Other acids that also may be
suitable for use include, for example, chloroacetic acid,
dichloroacetic acid, trichloroacetic acid, or methanesulfonic acid.
Examples of suitable acid-generating compounds can include, for
example, esters, aliphatic polyesters, orthoesters, poly(ortho
esters), poly(lactides), poly(glycolides), poly(c-caprolactones),
poly(hydroxybutyrates), poly(anhydrides), ethylene glycol
monoformate, ethylene glycol diformate, diethylene glycol
diformate, glyceryl monoformate, glyceryl diformate, glyceryl
triformate, triethylene glycol diformate, and formate esters of
pentaerythritol. Among other things, the additional acid or
acid-generating compound can maintain the pH of the treatment
fluids at a desired low level as the hydrofluoric acid or
hydrofluoric acid-generating compound becomes spent. As described
below, when a chelating agent is present, the additional acid or
acid-generating compound may also help maintain the pH of the
treatment fluids at a level where the chelating agent is more
active for chelation to occur.
[0036] In some embodiments of the present invention, a suitable
salt block inhibitor for inclusion in the treatment fluids
described herein may comprise a fructan or a derivative thereof.
Suitable fructans may include, for example, an inulin, a levan, a
graminin, any derivative thereof, or any combination thereof.
Inulins are linear fructans that are generally linked by
.beta.(2.fwdarw.1) glycosidic bonds. Levans are linear fructans
that are generally linked by .beta.(2.fwdarw.6) glycosidic bonds.
Graminins are branched fructans that are linked by both
.beta.(2.fwdarw.1) and .beta.(2.fwdarw.6) glycosidic bonds. In more
specific embodiments of the present invention, the salt block
inhibitor may comprise an inulin derivative. Particularly suitable
inulin derivatives may include, for example, carboxymethylinulin,
carboxyethylinulin, or any combination thereof.
[0037] In some embodiments of the present invention, other types of
salt block inhibitors may be included in addition to or in
combination with a fructan. In some embodiments of the present
invention, a suitable salt block inhibitor may comprise
nitrilotriacetamide, which is described in U.S. Pat. No.
7,028,776.
[0038] In some embodiments of the present invention, a chelating
agent, an alkali metal salt thereof, a non-alkali metal salt
thereof, or any combination thereof may be included in the
treatment fluids. As described above, a chelating agent may be
included in the treatment fluids, for example, when it is desirable
to provide additional sequestration of metal ions in a subterranean
formation. One of ordinary skill in the art will be able to choose
an appropriate chelating agent and amount thereof to include in a
treatment fluid intended for a particular application, given the
benefit of the present disclosure.
[0039] In some embodiments of the present invention, the chelating
agent may be biodegradable. Although use of a biodegradable
chelating agent may be particularly advantageous in some
embodiments of the present disclosure, there is no requirement to
do so, and, in general, any suitable chelating agent may be used.
As used herein, the term "biodegradable" refers to a substance that
can be broken down by exposure to environmental conditions
including native or non-native microbes, sunlight, air, heat, and
the like. Use of the term "biodegradable" does not imply a
particular degree of biodegradability, mechanism of
biodegradability, or a specified biodegradation half-life.
[0040] In some embodiments of the present invention, suitable
chelating agents may include common chelating agent compounds such
as, for example, ethylenediaminetetraacetic acid (EDTA),
propylenediaminetetraacetic acid (PDTA), nitrilotriacetic acid
(NTA), N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA),
diethylenetriaminepentaacetic acid (DTPA),
hydroxyethyliminodiacetic acid (HEIDA),
cyclohexylenediaminetetraacetic acid (CDTA), diphenylaminesulfonic
acid (DPAS), ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA),
glucoheptonic acid, gluconic acid, citric acid, any salt thereof,
any derivative thereof, and the like. It is to be noted that NTA
may be considered to be a biodegradable compound, but it may have
undesirable toxicity issues.
[0041] In some embodiments of the present invention, suitable
chelating agents may include biodegradable chelating agents such
as, for example, glutamic acid diacetic acid (GLDA), methylglycine
diacetic acid (MGDA), .beta.-alanine diacetic acid (.beta.-ADA),
ethylenediaminedisuccinic acid, S,S-ethylenediaminedisuccinic acid
(EDDS), iminodisuccinic acid (IDS), hydroxyiminodisuccinic acid
(HIDS), polyamino disuccinic acids,
N-bis[2-(1,2-dicarboxyethoxy)ethyl]glycine (BCA6),
N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA5),
N-bis[2-(1,2-dicarboxyethoxy)ethyl]methylglycine (MCBA5),
N-tris[(1,2-dicarboxyethoxy)ethyl]amine (TCA6),
N-methyliminodiacetic acid (MIDA), iminodiacetic acid (IDA),
N-(2-acetamido)iminodiacetic acid (ADA),
hydroxymethyl-iminodiacetic acid, 2-(2-carboxyethylamino) succinic
acid (CEAA), 2-(2-carboxymethylamino) succinic acid (CMAA),
diethylenetriamine-N,N''-disuccinic acid,
triethylenetetramine-N,N'''-disuccinic acid,
1,6-hexamethylenediamine-N,N'-disuccinic acid,
tetraethylenepentamine-N,N''''-disuccinic acid,
2-hydroxypropylene-1,3-diamine-N,N'-disuccinic acid,
1,2-propylenediamine-N,N'-disuccinic acid,
1,3-propylenediamine-N,N'-disuccinic acid,
cis-cyclohexanediamine-N,N'-disuccinic acid,
trans-cyclohexanediamine-N,N'-disuccinic acid,
ethylenebis(oxyethylenenitrilo)-N,N'-disuccinic acid,
glucoheptanoic acid, cysteic acid-N,N-diacetic acid, cysteic
acid-N-monoacetic acid, alanine-N-monoacetic acid,
N-(3-hydroxysuccinyl) aspartic acid,
N-[2-(3-hydroxysuccinyl)]-L-serine, aspartic acid-N,N-diacetic
acid, aspartic acid-N-monoacetic acid, any salt thereof, any
derivative thereof, or any combination thereof.
[0042] When present, the chelating agent can comprise about 1% to
about 50% by weight of the treatment fluids. In other embodiments
of the present invention, the chelating agent can comprise about 3%
to about 40% by weight of the treatment fluids.
[0043] When present, the acid dissociation constants of the
chelating agent can dictate the pH range over which the treatment
fluids can be most effectively used. GLDA, for instance, has a pK,
value of about 2.6 for its most acidic carboxylic acid
functionality. Below a pH value of about 2.6, dissolution of metal
ions will be promoted primarily by the acidity of a treatment fluid
containing GLDA, rather than by chelation, since the chelating
agent will be in a fully protonated state. MGDA, in contrast, has a
pK, value in the range of about 1.5 to 1.6 for its most acidic
carboxylic acid group, and it will not become fully protonated
until the pH is lowered to below about 1.5 to 1.6. In this respect,
MGDA can be particularly beneficial for use in acidic treatment
fluids, since it can extend the acidity range by nearly a full pH
unit over which the chelating agent is an active chelant. The lower
pH of the treatment fluid can beneficially allow for a more
vigorous acidizing operation to take place.
[0044] In further embodiments of the present invention, the
treatment fluids described herein may optionally further comprise
any number of additional additives commonly used in treatment
fluids including, for example, surfactants, gel stabilizers,
anti-oxidants, polymer degradation prevention additives, relative
permeability modifiers, scale inhibitors, corrosion inhibitors,
foaming agents, defoaming agents, antifoaming agents, emulsifying
agents, de-emulsifying agents, iron control agents, proppants or
other particulates, particulate diverters, salts, acids, fluid loss
control additives, gas, catalysts, clay control agents,
dispersants, flocculants, scavengers (e.g., H.sub.2S scavengers,
CO.sub.2 scavengers or O.sub.2 scavengers), gelling agents,
lubricants, breakers, friction reducers, bridging agents,
viscosifiers, weighting agents, solubilizers, pH control agents
(e.g., buffers), hydrate inhibitors, consolidating agents,
bactericides, catalysts, clay stabilizers, and the like.
Combinations of these additives can be used as well.
[0045] In some embodiments of the present invention, the present
methods may further comprise allowing the fructan to interact with
an alkali metal ion. The type of interaction between the fructan
and the alkali metal ion may vary without limitation, and no
mechanistic explanation of the interaction is set forth or implied
herein. In some embodiments of the present invention, the
interaction between the alkali metal ion and the fructan can be of
a type that increases the effective solubility of alkali metal
ions, such as that which occurs when the fructan is used in
traditional salt block inhibition applications. As described above,
the same interactions that inhibit salt deposition are also
believed to reduce the propensity for alkali metal ions to react
with dissolved silicon and form insoluble fluorosilicates and
aluminosilicates. In some embodiments of the present invention, the
interaction between the fructan and the alkali metal ion may reduce
or eliminate the formation of insoluble fluorosilicates or
aluminosilicates in a subterranean formation, relative to a like
treatment fluid lacking the fructan. As used herein, the term "like
treatment fluid" refers to a treatment fluid having a similar
composition to another treatment fluid but lacking at least one
component thereof. In some embodiments of the present invention,
the fructan may increase the effective solubility of alkali metal
fluorosilicates by an interaction occurring therewith.
[0046] In some embodiments of the present invention, the treatment
fluids described herein may be used for performing an acidizing
operation in a subterranean formation, particularly a subterranean
formation that comprises a siliceous mineral or has had a siliceous
material introduced thereto. In some embodiments of the present
invention, the subterranean formation being treated by the
acidizing operation can comprise a sandstone and/or a
clay-containing formation. In some or other embodiments of the
present invention, the subterranean formation can have had a
silicate or aluminosilicate introduced thereto. For example, in a
fracturing operation, sand particulates (a silicate) or a ceramic
propping material may be introduced to the subterranean formation.
Accordingly, silicate and aluminosilicate particulates that were
introduced into a non-siliceous subterranean formation may also be
effectively treated according to the methods described herein as
well.
[0047] In some embodiments of the present invention, acidizing
operations conducted using the treatment fluids described herein
may be performed in the absence of an NH.sub.4.sup.+ salt. As
described above, use of a salt block inhibitor in treatment fluids
in conjunction with hydrofluoric acid or a hydrofluoric
acid-generating compound may allow at least some alkali metal ions
to be present. In alternative embodiments of the present invention,
the treatment fluids described herein may comprise an
NH.sub.4.sup.+ salt or be used in conjunction with another
treatment fluid that comprises an NH.sub.4.sup.+ salt. For example,
one might choose to use a treatment fluid comprising an
NH.sub.4.sup.+ salt in conjunction with a treatment fluid
comprising a salt block inhibitor if the amount of alkali metal
ions in the subterranean formation is high enough that salt block
inhibitor alone cannot effectively reduce or eliminate the
formation of insoluble fluorosilicates or aluminosilicates when
performing an acidizing operation.
[0048] In some embodiments of the present invention, treatment
fluids described herein may be used for performing an acidizing
operation. That is, treatment fluids comprising a salt block
inhibitor; and hydrofluoric acid, a hydrofluoric acid-generating
compound, or a combination thereof may be used to acidize a
subterranean formation by dissolving a silicate or aluminosilicate
in the subterranean formation. In alternative embodiments of the
present invention, treatment fluids comprising a salt block
inhibitor may be used in conjunction with an acidizing operation
that is conducted with a separate treatment fluid comprising
hydrofluoric acid, a hydrofluoric acid-generating compound, or any
combination thereof. For example, treatment fluids comprising a
salt block inhibitor may be introduced into a subterranean
formation ahead of a fluoride-containing acidizing fluid (i.e., a
treatment fluid comprising hydrofluoric acid or a hydrofluoric
acid-generating compound) to achieve a like effect to the combined
treatment fluids described hereinabove.
[0049] Therefore, the present invention is well adapted to attain
the ends and advantages mentioned as well as those that are
inherent therein. The particular embodiments disclosed above are
illustrative only, as the present invention may be modified and
practiced in different but equivalent manners apparent to those
skilled in the art having the benefit of the teachings herein.
Furthermore, no limitations are intended to the details of
construction or design herein shown, other than as described in the
claims below. It is therefore evident that the particular
illustrative embodiments disclosed above may be altered, combined,
or modified and all such variations are considered within the scope
and spirit of the present invention. The invention illustratively
disclosed herein suitably may be practiced in the absence of any
element that is not specifically disclosed herein and/or any
optional element disclosed herein. While compositions and methods
are described in terms of "comprising," "containing," or
"including" various components or steps, the compositions and
methods can also "consist essentially of" or "consist of" the
various components and steps. All numbers and ranges disclosed
above may vary by some amount. Whenever a numerical range with a
lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically disclosed.
In particular, every range of values (of the form, "from about a to
about b," or, equivalently, "from approximately a to b," or,
equivalently, "from approximately a-b") disclosed herein is to be
understood to set forth every number and range encompassed within
the broader range of values. Also, the terms in the claims have
their plain, ordinary meaning unless otherwise explicitly and
clearly defined by the patentee. Moreover, the indefinite articles
"a" or "an," as used in the claims, are defined herein to mean one
or more than one of the element that it introduces. If there is any
conflict in the usages of a word or term in this specification and
one or more patent or other documents that may be incorporated
herein by reference, the definitions that are consistent with this
specification should be adopted.
* * * * *