U.S. patent application number 14/869624 was filed with the patent office on 2016-01-21 for methods, systems, and compositions for the controlled crosslinking of well servicing fluids.
The applicant listed for this patent is TUCC Technology, LLC. Invention is credited to James W. Dobson, JR., Shauna L. Hayden, Kimberly A. Pierce Dobson.
Application Number | 20160017211 14/869624 |
Document ID | / |
Family ID | 40790441 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160017211 |
Kind Code |
A1 |
Dobson, JR.; James W. ; et
al. |
January 21, 2016 |
Methods, Systems, and Compositions for the Controlled Crosslinking
of Well Servicing Fluids
Abstract
Treating fluid compositions for use in hydrocarbon recovery
operations from subterranean formations are described, as well as
methods for their preparation and use. In particular, treating
fluid compositions are described which comprise a liquid, a
crosslinkable organic polymer material that is at least partially
soluble in the liquid, a crosslinking agent that is capable of
increasing the viscosity of the treating fluid by crosslinking the
organic polymer material in the liquid, and a crosslinking modifier
additive which can delay or accelerate the crosslinking of the
treating fluid composition. Such compositions may be used in a
variety of hydrocarbon recovery operations including fracturing
operations, drilling operations, gravel packing operations, water
control operations, and the like.
Inventors: |
Dobson, JR.; James W.;
(Houston, TX) ; Hayden; Shauna L.; (Houston,
TX) ; Pierce Dobson; Kimberly A.; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TUCC Technology, LLC |
Houston |
TX |
US |
|
|
Family ID: |
40790441 |
Appl. No.: |
14/869624 |
Filed: |
September 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12395406 |
Feb 27, 2009 |
9181469 |
|
|
14869624 |
|
|
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|
61032703 |
Feb 29, 2008 |
|
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Current U.S.
Class: |
507/211 |
Current CPC
Class: |
C09K 8/685 20130101;
E21B 43/25 20130101 |
International
Class: |
C09K 8/68 20060101
C09K008/68 |
Claims
1. A method of treating a subterranean formation, the method
comprising: generating a treating fluid by mixing an aqueous base
fluid and a crosslinking additive, and delivering the treating
fluid into a subterranean formation; wherein the aqueous base fluid
comprises a crosslinkable organic polymer, and wherein the
crosslinking additive comprises a borate crosslinking agent
premixed with one or more salt-based crosslinking modifiers.
2. The method of claim 1, wherein the borate crosslinking agent is
an alkaline earth metal borate, an alkali metal-alkaline earth
metal borate, or an alkali metal borate containing at least 2 boron
atoms per molecule.
3. The method of claim 2 wherein the borate is selected from the
group consisting of ulexite, colemanite, probertite, and mixtures
thereof.
4. The method of claim 1, further comprising delivering an
inorganic or organic peroxide breaker into the subterranean
formation.
5. The method of claim 4, wherein the inorganic or organic peroxide
breaker is slightly soluble in water.
6. The method of claim 1, wherein the crosslinking additive
comprises a freeze-point depressant.
7. The method of claim 1, wherein the crosslinking additive further
comprises a suspension agent selected from the group consisting of
clays, polymers, and combinations thereof.
8. The method of claim 7, wherein the suspension agent is selected
from the group consisting of palygorskite-type clays consisting of
attapulgite, smectite, sepiolite, and composite mixtures
thereof.
9. The method of claim 7, wherein the polymer is a water-soluble
polymer selected from the group consisting of biopolymers,
naturally-occurring polymers, derivatives thereof, and combinations
thereof.
10. The method of claim 1, wherein the crosslinking additive
comprises a deflocculant.
11. The method of claim 1, wherein the crosslinking additive
comprises one or more chelating agents.
12. The method of claim 1, wherein the crosslinking additive
comprises a friction reducer.
13. A composition for crosslinking an aqueous, crosslinkable
organic polymer solution, the composition comprising: a water-based
crosslinking additive comprising a sparingly-soluble borate
crosslinking agent and a salt-based crosslinking modifier; wherein
the crosslinking additive is capable of crosslinking the organic
polymer at a modified rate compared to a water-based crosslinking
additive having the same borate concentration but lacking the
crosslinking modifier.
14. The composition of claim 13, wherein the crosslinkable
viscosifying organic polymer is a polysaccharide.
15. The composition of claim 14, wherein the polysaccharide is
guar, cellulose, starch, galactomannan gum, xanthan, succinoglycan
or scleroglucan or a derivative thereof.
16. The composition of claim 15, wherein the polysaccharide is
selected from the group consisting of guar, hydroxypropyl guar,
carboxymethylhydroxypropyl guar, methyl cellulose, hydroxyethyl
cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose,
hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose,
hydroxybutylmethyl cellulose, methylhydroxyethyl cellulose,
methylhydroxypropyl cellulose, ethylhydroxyethyl cellulose,
carboxyethylcellulose, carboxymethylcellulose or
carboxymethylhydroxyethyl cellulose.
17. The composition of claim 13, wherein the sparingly-soluble
borate is an alkaline earth metal borate, an alkali metal-alkaline
earth metal borate, or an alkali metal borate containing at least
two boron atoms per molecule.
18. The composition of claim 17, wherein the sparingly-soluble
borate is selected from the group consisting of ulexite,
colemanite, probertite, and mixtures thereof.
19. The composition of claim 13, wherein the concentration of
sparingly-soluble borate is in the range from about from about 0.1
kg/m.sup.3 to about 5 kg/m.sup.3.
20. The composition of claim 13, wherein the composition further
comprises a suspension agent selected from the group consisting of
clays, polymers, and combinations thereof.
21. The composition of claim 20, wherein the suspension agent is
selected from the group consisting of palygorskite-type clays
consisting of attapulgite, smectite, sepiolite, and composite
mixtures thereof.
22. The composition of claim 20, wherein the polymer is a
water-soluble polymer selected from the group consisting of
biopolymers, naturally-occurring polymers, derivatives thereof, and
combinations thereof.
23. The composition of claim 13, wherein the crosslinking additive
comprises a freeze-point depressant.
24. The composition of claim 13, wherein the crosslinking additive
comprises a clay, a polymer, or combinations thereof.
25. The composition of claim 24, wherein the crosslinking additive
comprises a clay selected from the group consisting of
palygorskite-type clays consisting of attapulgite, smectite,
sepiolite, and composite mixtures thereof.
26. The composition of claim 24, wherein the crosslinking additive
comprises a water-soluble polymer selected from the group
consisting of biopolymers, naturally-occurring polymers,
derivatives thereof, and combinations thereof.
27. The composition of claim 13, wherein the crosslinking additive
comprises a deflocculant.
28. The composition of claim 13, wherein the crosslinking additive
comprises one or more chelating agents.
29. The composition of claim 13, wherein the crosslinking additive
comprises a friction reducer.
30. A composition for crosslinking aqueous, crosslinkable organic
polymer solutions, wherein the composition is prepared by a process
comprising: mixing a borate-containing crosslinking agent and a
salt-based crosslinking modifier.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of U.S. patent
application Ser. No. 12/395,406, filed Feb. 27, 2009 (allowed),
which claims priority to U.S. Provisional Patent Application Ser.
No. 61/032,703, filed Feb. 29, 2008, which both are incorporated by
reference, and to which priority is claimed.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The inventions disclosed and taught herein relate generally
to compositions and methods for controlling the gelation rate in
aqueous-based fluids useful in treating subterranean formations.
More specifically, the present disclosure is related to improved
compositions for use in the controlled gelation, or crosslinking,
of polysaccharides in aqueous solutions with sparingly-soluble
borates, as well as methods for their use in subterranean,
hydrocarbon-recovery operations.
[0004] 2. Description of the Related Art
[0005] Many subterranean, hydrocarbon-containing and/or producing
reservoirs require one or more stimulation operations, such as
hydraulic fracturing, in order to be effectively produced. Borates
were some of the earliest crosslinking agents used to increase the
viscosity and proppant-transport capabilities of aqueous,
guar-based stimulation fluids, and have been used successfully in
numerous low- to moderate-temperature (<200.degree. F.)
reservoirs. However, as hydrocarbon exploration capabilities
expanded, the number of subterranean reservoirs being developed
with temperatures greater than 200.degree. F. increased, the
conventional borate-salts used, and the resulting crosslinked
fluids, were found to provide inadequate rheological stability.
[0006] Thus, as the development of high-temperature
(>200.degree. F.) well stimulation fluids were developed, an
emphasis was placed on the maximization of the thermal stability of
the rheological properties of the fluids. In particular, titanium
and zirconium crosslinking agents were developed for their ability
to provide stable, somewhat controlled, bonding in high-temperature
subterranean environments.
[0007] Fracturing fluids that are crosslinked with titanate,
zirconate, and/or borate ions (using compounds which generate these
ions in the fluid), sometimes contain additives that are designed
to delay the timing of the crosslinking reactions. Such
crosslinking time delay agents permit the fracturing fluid to be
pumped down hole to the subterranean formation before the
crosslinking reaction begins to occur, thereby permitting more
adaptability, versatility or flexibility in the fracturing fluid.
Additionally, the use of these gelation control additives can be
beneficial from an operational standpoint in completion operations,
particularly because their use allows for a decrease in the amount
of pressure required for pumping the well treating fluids. This in
turn can result in reduced equipment requirements and decreased
maintenance costs associated with pumps and pumping equipment.
Examples of early crosslinking time delay agents that have been
reported and have been incorporated into water-based fracturing
fluids include organic polyols, such as sodium gluconate, sodium
glucoheptonate, sorbitol, glyoxal, mannitol, phosphonates, and
aminocarboxylic acids and their salts (EDTA, DTPA, etc.).
[0008] A number of additional classes of previously used delay
additives and compounds for use in controlling the delay time and
the ultimate viscosity of treating fluids, such as fracturing
fluids, have been previously reported. As can be imagined, the
gelation control additives and methods vary, depending upon whether
the crosslinking agent is a borate-based crosslinker or a
transition metal crosslinker (e.g., Zr or Ti). Generally, the
agents used to slow the crosslinking of guar and guar-type fluids
are polyfunctional organic materials which have chelating
capabilities and can form strong bonds with the crosslinking agent
itself. Several classes of agents have been described to date,
especially for the controlled crosslinking by zirconium and
titantium. For example, a hybrid delay agent having the trade name
TYZOR.RTM. (DuPont) for the delay of viscosity development in
fracturing fluids based on guar derivatives crosslinked with a
variety of common zirconate and titanate crosslinkers under a wide
pH range and under a variety of fluid conditions has been described
by Putzig, et al [SPE Paper No. 105066, 2007]. Other delay agents
for such organic transition-metal based crosslinkers include
hydroxycarboxylic acids, such as those described in U.S. Pat. No.
4,797,216 and U.S. Pat. No. 4,861,500 to Hodge, selected
polyhydroxycarboxylic acid having from 3 to 7 carbon atoms as
described by Conway in U.S. Pat. No. 4,470,915, and alkanolamines
such as triethanolamine-based delay agents available under the
trade name TYZOR.RTM. (E.I. du Pont de Nemours and Co., Inc.).
However, the use of many of these transition-metal based
crosslinkers, and their often-times costly crosslink time delay
additives have occasionally been associated with significant damage
(often greater than 80%) to the permeability of the proppant pack
when used in hydraulic fracturing operations, especially in
formations having elevated temperatures [Penny, G. S., SPE 16900
(1987); Investigation of the Effects of Fracturing Fluids Upon the
Conductivity of Proppants, Final Report, (1987) STIM-LAB Inc.
Proppant Consortium (1988)].
[0009] A number of approaches to the control of the crosslinking
process in fluids comprising fully-soluble borate crosslinkers have
also been described. For example, a number of polyhydroxy compounds
such as sugars, reduced sugars, and polyols such as glycerol have
been reported to be delay agents for crosslinkers based on boron.
Functionalized aldehyde-based and dialdehyde-based delay agents for
fully-soluble borates, such as those described in U.S. Pat. Nos.
5,082,579 and 5,160,643 to Dawson, have also been reported.
However, numerous of these gelation control agents for use in
boron-based crosslinker compositions are highly pH and temperature
dependent, and cannot be used reliably in subterranean environments
having elevated pHs, e.g., a pH greater than 9 and/or temperatures
greater than about 200.degree. F.
[0010] The mechanism for delay in crosslinking time of organic
polymer in fluids comprising sparingly-soluble borate-based
crosslinkers has also been documented to some extent. As was
described in U.S. Pat. No. 4,619,776 to Mondshine, the unique
solubility characteristics of the alkaline earth metal borates or
alkali metal alkaline earth metal borates enables them to be used
in the controlled crosslinking of aqueous systems containing guar
polymers. The rate of crosslinking could be controlled by suitable
adjustment of one or more of the following variables--initial pH of
the aqueous system, relative concentrations of one or more of the
sparingly-soluble borates, temperature of the aqueous system, and
particle size of the borate. However, there are several limitations
in the aforementioned art for sparingly soluble borates which are
incorporated in water-base crosslinking suspensions for fracturing
operations--particle size/concentrations of the borate solids, and
the initial pH of the guar solution.
[0011] At present, the primary method for varying crosslink times
of a treatment fluid utilizing sparingly soluble borate is with
modification of the borate particle size alone. Operational
requirements for delayed crosslink times as fast as 30-45 seconds
have not been accomplished with present technology. Smaller
particles may sometimes decrease crosslink times, but even with
milling and air classification, the size is often not sufficiently
fine or small enough to produce the desired rapid crosslink times.
Additionally, limited solubility borate solids exhibit a major
change as the pH of the base guar solution is changed. For example,
when the alkalinity is incrementally increased from a more acidic
pH to a basic pH 10.0, the crosslink time is faster. At pH values
greater than about pH 10.0, the crosslink time reverses and becomes
slower as the alkalinity is increased. As a result, higher pH
values (e.g., about 11.6) which are utilized to provide gel
viscosity stability at elevated temperatures exhibit crosslink
times greater than 12 minutes even with very fine borate solids.
Accelerating crosslink times using finer particles with more
surface area, or increased concentrations of sparingly-soluble
borate is not feasible due to gelation of the crosslinking
concentrate caused by more solids and their subsequent
interaction.
[0012] In view of the above, the need exists for compositions,
systems, and methods for providing more precise control of delays
over the crosslinking reaction of borated aqueous subterranean
treating fluids, such as fracturing fluids. The inventions
disclosed and taught herein are directed to improved compositions
and methods for the selective control of the rates of crosslinking
reactions within aqueous subterranean treating fluids, especially
at varying pH and over a wide range of formation temperatures,
including formation temperatures greater than 200.degree. F.
BRIEF SUMMARY
[0013] The present disclosure provides novel compositions and
systems for producing a controlled delayed crosslinking interaction
in an aqueous solution as well as methods for the manufacture and
use of such compositions, the compositions comprising a
crosslinkable organic polymer and a crosslinking additive
consisting of a sparingly-soluble borate crosslinking agent
suspended in an aqueous crosslink modifier of fully-solubilized
salts, acids, or alkali components which are capable of adjusting
the rate at which gelation of the organic polymer occurs without
substantially altering the final pH or other characteristics of the
crosslinked system.
[0014] In accordance with a first embodiment of the present
disclosure, compositions for controlling the gelation rate of an
organic polymer-containing well treatment fluid are described,
wherein the compositions comprise a crosslinkable organic polymer,
a sparingly-soluble borate crosslinking agent; and a crosslink
modifier composition capable of controlling the rate at which the
crosslinking additive promotes the gelation of the crosslinkable
organic polymer, wherein the crosslink modifier is a salt, an
alkaline or acidic chemical, or a combination thereof. In
accordance with further non-limiting aspects of this embodiment,
the crosslink modifier is selected from the group consisting of
KCO.sub.2H, KC.sub.2H.sub.3O.sub.2, CH.sub.3CO.sub.2H, HCO.sub.2H,
KCO.sub.2H, NaCO.sub.2H, NaC.sub.2H.sub.3O.sub.2, NaCO.sub.2H, and
combinations thereof. In a further aspect of this embodiment, the
composition may further comprise a chelating agent.
[0015] In a further embodiment of the present disclosure, well
treatment fluid compositions are described comprising an aqueous
solution consisting of a crosslinkable organic polymer, a
crosslinking additive containing a sparingly-soluble borate
crosslinking agent, and a crosslink modifier, wherein the crosslink
modifier is capable of controlling the rate at which the
sparingly-soluble borate promotes the gelation, or crosslinking, of
the crosslinkable organic polymer at pH values greater than about
7. In accordance with this aspect of the present disclosure, the
crosslink modifier is a salt, an alkaline chemical or acidic
chemical, or a combination thereof.
[0016] In yet another embodiment of the present disclosure, methods
of treating a subterranean formation are described, wherein the
method generates a well treatment fluid comprising a blend of an
aqueous solution and a crosslinkable organic polymer material that
is at least partially soluble in the aqueous solution; hydrating
the organic polymer in the aqueous solution; formulating a
crosslinking additive comprising a borate-containing crosslinking
agent and crosslink modifiers; adding the crosslinking additive to
the hydrated treating fluid so as to crosslink the organic polymer
in a controlled manner; and delivering the treating fluid into a
subterranean formation.
[0017] In accordance with further embodiments of the present
disclosure, compositions for controllably crosslinking aqueous well
treatment solutions is described, wherein the compositions comprise
a crosslinkable, viscosifying organic polymer; a sparingly-soluble
borate crosslinking agent; and a crosslink modifier agent capable
of controlling the rate at which the crosslinking agent promotes
the gelation of the crosslinkable organic polymer at a pH greater
than about 7, wherein the crosslink modifier agent is a salt, an
acidic agent, or an alkaline agent, or combinations thereof. In
further accordance with aspects of this embodiment, the crosslink
modifier has a +1 or +2 valence state. In accordance with further
aspects of this embodiment, the crosslink modifier is selected from
the group consisting of KCO.sub.2H, KC.sub.2H.sub.3O.sub.2,
CH.sub.3CO.sub.2H, HCO.sub.2H, KCO.sub.2H, NaCO.sub.2H,
NaC.sub.2H.sub.3O.sub.2, NaCO.sub.2H, and combinations thereof.
[0018] In accordance with further embodiments of the present
disclosure, a fracturing fluid composition for use in a
subterranean formation is described, wherein the fracturing fluid
comprises an aqueous liquid, such as an aqueous brine; a
crosslinkable viscosifying organic polymer; a sparingly-soluble
borate crosslinking agent; and, a crosslinking modifier
composition, wherein the crosslinking modifier composition is
capable of controlling the rate at which sparingly-soluble borate
crosslinking agent crosslinks the organic polymer at pH values
greater than about 7. In accordance with aspects of this
embodiment, the crosslink modifier is a salt, an alkaline chemical
or acidic chemical, or a combination thereof. In further accordance
with this embodiment, the composition may further comprise one or
more chelating agents and/or friction reducers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is Table A, showing crosslink time comparisons for
water-base and oil-base crosslinking additives.
[0020] FIG. 2 is Tables B-E, showing crosslink time comparisons for
potassium acetate/potassium carbonate crosslinking additives (guar
pH 7, borate particles D.sub.50 of 36 microns).
[0021] FIG. 3 is Tables F-I, showing crosslink time comparisons for
potassium formate/potassium carbonate crosslinking additives (guar
pH 7, borate particles D.sub.50 of 36 microns).
[0022] FIG. 4 is Table J, providing a summary of crosslink time
comparison studies for the crosslinking additives of Example 5
(guar pH 7).
[0023] FIG. 5 is Table K, showing alkaline chemical comparisons for
potassium acetate crosslinking additives (guar pH 7, borate
particles D.sub.50 of 36 microns).
[0024] FIG. 6 is Table L, showing alkaline chemical comparisons for
potassium formate crosslinking additives (guar pH 7, borate
particles D.sub.50 of 36 microns).
[0025] FIG. 7 is Table M, showing the effect of incremental
increases of acetic acid in a potassium acetate crosslinking
additive (HPG pH 11.6, borate particles D.sub.50 of 11
microns).
[0026] FIG. 8 is Table N, showing the effect of incremental
increases of formic acid in a potassium formate crosslinking
additive (HPG pH 11.6, borate particles D.sub.50 of 11
microns).
[0027] FIG. 9 is Table O, showing acidic chemical comparisons for
potassium acetate crosslinking additives (HPG pH 11.6, borate
particles D.sub.50 of 11 microns).
[0028] FIG. 10 is Table P, showing acidic chemical comparisons for
potassium formate crossliking additives (HPG pH 11.6, borate
particles D.sub.50 of 11 microns).
[0029] FIG. 11 is Table Q, showing the results of incremental
increases of potassium carbonate content in potassium acetate
crosslinking additives (HPG pH 11.6, borate particles D.sub.50 of
11 microns).
[0030] FIG. 12 is Table R, showing the results of incremental
increases of acetic acid content in potassium acetate crosslinking
additives (HPG pH 11.6, borate particles D.sub.50 of 11
microns).
[0031] FIG. 13 is Table S, showing the effect of sparingly-soluble
borate particle size on crosslink time (HPG pH 11.6, borate
particles D.sub.50 of 36 microns).
DESCRIPTION
[0032] The written description of specific structures and functions
set forth below are not presented to limit the scope of what the
Applicants have invented or the scope of the appended claims.
Rather, the written description is provided to teach any person
skilled in the art to make and use the invention for which patent
protection is sought. Those skilled in the art will appreciate that
not all features of a commercial embodiment of the inventions are
described or shown for the sake of clarity and understanding.
Persons of skill in this art will also appreciate that the
development of an actual commercial embodiment incorporating
aspects of the present inventions will require numerous
implementation-specific decisions to achieve the developer's
ultimate goal for the commercial embodiment. Such
implementation-specific decisions may include, and likely are not
limited to, compliance with system-related, business-related and
government-related factors, and other constraints, which may vary
by specific implementation, location and time. While a developer's
efforts might be complex and time-consuming in an absolute sense,
such efforts would be, nevertheless, a routine undertaking for
those of skill in this art and having benefit of this disclosure.
It must be understood that the inventions disclosed and taught
herein are susceptible to numerous and various modifications and
alternative forms. Lastly, the use of a singular term, such as, but
not limited to, "a," is not intended as limiting of the number of
items. Also, the use of relational terms, such as, but not limited
to, "top," "bottom," "left," "right," "upper," "lower," "down,"
"up," "side," and the like are used in the written description for
clarity and are not intended to limit the scope of the inventions
or the appended claims.
[0033] Applicants have created compositions and related methods for
the controlled crosslinking of crosslinkable organic polymers in
well treatment fluids using sparingly-soluble, borate-containing
water-base suspensions and crosslink modifier compositions, as well
as the application of such compositions and methods to a number of
hydrocarbon recovery operations.
[0034] In accordance with aspects of the present disclosure, well
treatment fluid compositions and systems are described which are
suitable for use in conjunction with the compositions and methods
of these inventions, and which are useful to control the
crosslinking rate of the fluids in a variety of subterranean
environments, over a wide pH range. These well treatment fluid
compositions, such as fracturing fluid compositions, comprise at
least an aqueous base liquid, a crosslinkable organic polymer, a
sparingly-soluble borate-containing crosslinking agent, and a
crosslink modifier composition, wherein the crosslink modifier is
capable of controlling the rate at which the sparingly-soluble
borate-containing crosslinking additive promotes the gelation of
the organic polymer at stabilized pH values greater than about
7.
[0035] In accordance with one embodiment of the present disclosure,
the controlled crosslinking compositions and systems may be used in
subterranean hydrocarbon recovery operations wherein the
composition or system is contact with a subterranean formation in
which the temperature ranges from about 150.degree. F. (66.degree.
C.) to about 500.degree. F. (260.degree. C.), including formation
temperature ranges from about 170.degree. F. (77.degree. C.) to
about 450.degree. F. (232.degree. C.), and from about 200.degree.
F. (93.degree. C.) to about 400.degree. F. (204.degree. C.),
inclusive.
[0036] The typical crosslinkable organic polymers, sometimes
referred to equivalently herein as "gelling agents", that may be
included in the treatment fluids and systems described herein,
particularly aqueous fluids and systems, and that may be used in
connection with the presently disclosed inventions, typically
comprise biopolymers, synthetic polymers, or a combination thereof,
wherein the `gelling agents` or crosslinkable organic polymers are
at least slightly soluble in water (wherein slightly soluble means
having a solubility of at least about 0.01 kg/m.sup.3). Without
limitation, these crosslinkable organic polymers may serve to
increase the viscosity of the treatment fluid during application. A
variety of gelling agents can be used in conjunction with the
methods and compositions of the present inventions, including, but
not limited to, hydratable polymers that contain one or more
functional groups such as hydroxyl, cis-hydroxyl, carboxylic acids,
derivatives of carboxylic acids, sulfate, sulfonate, phosphate,
phosphonate, amino, or amide. The gelling agents may also be
biopolymers comprising natural, modified and derivatized
polysaccharides, and derivatives thereof that contain one or more
of the monosaccharide units selected from the group consisting of
galactose, mannose, glucoside, glucose, xylose, arabinose,
fructose, glucuronic acid, or pyranosyl sulfate. Suitable gelling
agents which may be used in accordance with the present disclosure
include, but are not limited to, guar, hydroxypropyl guar (HPG),
cellulose, carboxymethyl cellulose (CMC), carboxymethyl
hydroxyethyl cellulose (CMHEC), hydroxyethylcellulose (HEC),
carboxymethylhydroxypropyl guar (CMHPG), other derivatives of guar
gum, xanthan, galactomannan gums and gums comprising
galactomannans, cellulose, and other cellulose derivatives,
derivatives thereof, and combinations thereof, such as various
carboxyalkylcellulose ethers, such as carboxyethylcellulose; mixed
ethers such as carboxyalkylethers; hydroxyalkylcelluloses such as
hydroxypropylcellulose; alkylhydroxyalkylcelluloses such as
methylhydroxypropylcellulose; alkylcelluloses such as
methylcellulose, ethylcellulose and propylcellulose;
alkylcarboxyalkylcelluloses such as ethylcarboxymethylcellulose;
alkylalkylcelluloses such as methylethylcellulose;
hydroxyalkylalkylcelluloses such as hydroxypropylmethylcellulose;
combinations thereof, and the like. Preferably, in accordance with
one non-limiting embodiment of the present disclosure, the gelling
agent is guar, hydroxypropyl guar (HPG), or
carboxymethylhydroxypropyl guar (CMHPG), alone or in
combination.
[0037] Additional natural polymers suitable for use as
crosslinkable organic polymers/gelling agents in accordance with
the present disclosure include, but are not limited to, locust bean
gum, tara (Cesalpinia spinosa lin) gum, konjac (Amorphophallus
konjac) gum, starch, cellulose, karaya gum, xanthan gum, tragacanth
gum, arabic gum, ghatti gum, tamarind gum, carrageenan and
derivatives thereof. Additionally, synthetic polymers and
copolymers that contain any of the above-mentioned functional
groups may also be used. Examples of such synthetic polymers
include, but are not limited to, polyacrylate, polymethacrylate,
polyacrylamide, polyvinyl alcohol, maleic anhydride, methylvinyl
ether copolymers, and polyvinylpyrrolidone.
[0038] Generally speaking, the amount of a gelling
agent/crosslinkable organic polymer that may be included in a
treatment fluid for use in conjunction with the present inventions
depends on the viscosity desired. Thus, the amount to include will
be an amount effective to achieve a desired viscosity effect. In
certain exemplary embodiments of the present inventions, the
gelling agent may be present in the treatment fluid in an amount in
the range of from about 0.1% to about 60% by weight of the
treatment fluid. In other exemplary embodiments, the gelling agent
may be present in the range of from about 0.1% to about 20% by
weight of the treatment fluid. In general, however, the amount of
crosslinkable organic polymer included in the well treatment fluids
described herein is not particularly critical so long as the
viscosity of the fluid is sufficiently high to keep the proppant
particles or other additives suspended therein during the fluid
injecting step into the subterranean formation. Thus, depending on
the specific application of the treatment fluid, the crosslinkable
organic polymer may be added to the aqueous base fluid in
concentrations ranging from about 15 to 60 pounds per thousand
gallons (pptg) by volume of the total aqueous fluid (1.8 to 7.2
kg/m.sup.3). In a further non-limiting range for the present
inventions, the concentration may range from about 20 pptg (2.4
kg/m.sup.3) to about 40 pptg (4.8 kg/m.sup.3). In further,
non-restrictive aspects of the present disclosure, the
crosslinkable organic polymer/gelling agent present in the aqueous
base fluid may range from about 25 pptg (about 3 kg/m.sup.3) to
about 40 pptg (about 4.8 kg/m.sup.3) of total fluid. One skilled in
the art, with the benefit of this disclosure, will recognize the
appropriate gelling agent and amount of the gelling agent to use
for a particular application. Preferably, in accordance with one
aspect of the present disclosure, the fluid composition or well
treatment system will contain from about 1.2 kg/m.sup.3 (0.075
lb/ft.sup.3) to about 12 kg/m3 (0.75 lb/ft.sup.3) of the gelling
agent/crosslinkable organic polymer, most preferably from about 2.4
kg/m.sup.3 (0.15 lb/ft.sup.3) to about 7.2 kg/m.sup.3 (0.45
lb/ft.sup.3).
[0039] The crosslink modifier compositions useful in the treatment
fluid formulations of the present disclosure comprise one or more
crosslinking control additives, which are preferably selected from
the group consisting of acidic agents, alkaline agents, salts,
combinations of any of these agents (e.g., salts and alkaline
agents), combinations of which may also serve as freeze-point
depressants. Freeze point depressants themselves may also
optionally be included in the crosslinking additive composition in
accordance with the present disclosure, separately and distinct
from the crosslink modifiers.
[0040] Acidic agents which may be used as crosslink modifiers in
accordance with the present disclosure include inorganic and
organic acids, as well as combinations thereof. Exemplary acidic
agents suitable for use herein include acetic acid
(CH.sub.3CO.sub.2H), boric acid (H.sub.3BO.sub.3), carbonic acid
(H.sub.2CO.sub.3), hydrochloric acid (HCl), nitric acid
(HNO.sub.3), hydrochloric acid gas (HCl(g)), perchloric acid
(HC.sub.1O.sub.4), hydrobromic acid (HBr), hydroiodic acid (HI),
phosphoric acid (H.sub.3PO.sub.4), formic acid (HCO.sub.2H),
sulfuric acid (H.sub.2SO.sub.4), fluorosulfuric acid (FSO.sub.3H),
fluoroantimonic acid (HFSbF.sub.5), p-toluene sulfonic acid (pTSA),
trifluoroacetic acid (TFA), triflic acid (CF.sub.3SO.sub.3H),
ethanesulfonic acid, methanesulfonic acid (MSA), malic acid, maleic
acid, oxalic acid (C.sub.2H.sub.2O.sub.4), salicylic acid,
trifluoromethane sulfonic acid, citric acid, succinic acid,
tartaric acid and heavy sulphate expressed by the general formula
XHSO.sub.4 (wherein X is an alkali metal, such as Li, Na, and
K).
[0041] Alkaline agents which may be used as crosslink modifiers in
accordance with the present disclosure include, but are not limited
to, inorganic and organic alkaline agents (bases), as well as
combinations thereof. Exemplary alkaline agents suitable for use
herein include, but are not limited to, amines and
nitrogen-containing heterocyclic compounds such as ammonia, methyl
amine, pyridine, imidazole, histidine, and benzimidazole;
hydroxides of alkali metals and alkaline earth metals, including,
but not limited to, potassium hydroxide (KOH), sodium hydroxide
(NaOH), barium hydroxide (Ba(OH).sub.2), cesium hydroxide (CsOH),
strontium hydroxide (Sr(OH).sub.2), calcium hydroxide
(Ca(OH).sub.2), lithium hydroxide (LiOH), and rubidium hydroxide
(RbOH); oxides such as magnesium oxide (MgO), calcium oxide (CaO),
and barium oxide; carbonates and bicarbonates of alkali metals,
alkaline earth metals, and transition metals including sodium
bicarbonate (NaHCO.sub.3), sodium carbonate (Na.sub.2CO.sub.3),
potassium carbonate (K.sub.2CO.sub.3), potassium bicarbonate
(KHCO.sub.3), lithium carbonate (LiCO.sub.3), rubidium carbonate
(Rb.sub.2CO.sub.3), cesium carbonate (Cs.sub.2CO.sub.3), beryllium
carbonate (BeCO.sub.3), magnesium carbonate (MgCO.sub.3), calcium
carbonate (CaCO.sub.3), strontium carbonate (SrCO.sub.3), barium
carbonate (BaCO.sub.3), manganese (II) carbonate (MnCO.sub.3), iron
(II) carbonate (FeCO.sub.3), cobalt carbonate (CoCO.sub.3), nickel
(II) carbonate (NiCO.sub.3), copper (II) carbonate (CuCO.sub.3),
zinc carbonate (ZnCO.sub.3), silver carbonate (Ag.sub.2CO.sub.3),
cadmium carbonate (CdCO.sub.3), and lead carbonate
(Pb.sub.2CO.sub.3); phosphate salts such as potassium dihydrogen
phosphate (KH.sub.2PO.sub.4), di-potassium monohydrogen phosphate
(K.sub.2HPO.sub.4) and tribasic potassium phosphate
(K.sub.3PO.sub.4); acetates of alkali metals, alkaline earth
metals, and transition metals, such as potassium acetate
(KC.sub.2H.sub.3O.sub.2), sodium acetate, lithium acetate, rubidium
acetate, cesium acetate, beryllium acetate, magnesium acetate,
calcium acetate, calcium-magnesium acetate, strontium acetate,
barium acetate, aluminum acetate, manganese (III) acetate, iron
(II) acetate, iron (III) acetate, cobalt acetate, nickel acetate,
copper (II) acetate, chromium acetate, zinc acetate, silver acetate
acetate, cadmium acetate, and lead (II) acetate; formates of alkali
metals, alkaline earth metals, and transition metals, such as
potassium formate (KCO.sub.2H), sodium formate (NaCO.sub.2H), and
cesium formate (CsCO.sub.2H); and alkoxides (conjugate bases of an
alcohol), including, but not limited to, sodium alkoxide, potassium
alkoxide, potassium tert-butoxide, titanium isopropoxide
(Ti[OCH(CH.sub.3).sub.2].sub.4), aluminum isopropoxide
Al(O-i-Pr).sub.3, where i-Pr is the isopropyl group
--CH(CH.sub.3).sub.2, and tetraethylorthosilicate (TEOS,
Si(OC.sub.2H.sub.5).sub.4).
[0042] Salts which may be used as crosslink modifiers in accordance
with the present disclosure include, but are not limited to, both
inorganic salts such as alkali metal salts, alkaline earth metal
salts, and transition metal salts such as halide salts like sodium
chloride, potassium chloride, magnesium chloride, calcium chloride,
and zinc chloride; as well as organic salts such as sodium citrate.
The term "salt(s)", as used herein, denotes both acidic salts
formed with inorganic and/or organic acids, as well as basic salts
formed with inorganic and/or organic bases. Exemplary acid addition
salts include acetates like potassium acetate, ascorbates,
benzoates, benzenesulfonates, bisulfates, borates, butyrates,
citrates, camphorates, camphorsulfonates, fumarates,
hydrochlorides, hydrobromides, hydroiodides, lactates, maleates,
methanesulfonates, naphthalenesulfonates, nitrates, oxalates,
phosphates, propionates, salicylates, succinates, sulfates,
tartarates, thiocyanates, toluenesulfonates (also known as
tosylates,) and the like.
[0043] Exemplary basic salts include ammonium salts, alkali metal
salts such as sodium, lithium, and potassium salts, alkaline earth
metal salts such as calcium and magnesium salts, salts with organic
bases (e.g., organic amines) such as dicyclohexylamines, t-butyl
amines, and salts with amino acids such as arginine, lysine and the
like. Basic nitrogen-containing groups of organic compounds may
also be quarternized with agents such as lower alkyl halides (e.g.,
methyl, ethyl, and butyl chlorides, bromides and iodides), dialkyl
sulfates (e.g., dimethyl, diethyl, and dibutyl sulfates), long
chain halides (e.g., decyl, lauryl, and stearyl chlorides, bromides
and, iodides), aralkyl halides (e.g., benzyl and phenethyl
bromides), and others, so as to form basic organic salts.
[0044] As used herein, the term "alkali metal" refers to the series
of elements comprising Group 1 of the Periodic Table of the
Elements, and the term "alkaline earth metal" refers to the series
of elements comprising Group 2 of the Periodic Table of the
Elements, wherein Group 1 and Group 2 are the Periodic Table
classifications according to the International Union of Pure and
Applied Chemistry, (2002). The preferable crosslink modifiers
suitable for use in the compositions described herein are alkali
metal carbonates, alkali metal formates, alkali metal acetates, and
alkali metal hydroxides. Typical crosslink modifiers include
potassium carbonate, potassium formate, potassium acetate,
potassium hydroxide, and combinations thereof. In accordance with
one aspect of the present disclosure, the crosslink modifier is a
monovalent salt, acidic agent, or alkaline agent that lowers the
pour point of the aqueous composition, such as lithium, sodium,
potassium, or cesium salts, acidic agents, or alkaline agents. In
accordance with a further aspect of the present disclosure, the
crosslink modifier is a divalent salt, acidic agent, or alkaline
agent that lowers the pour point of the aqueous composition, such
as calcium or magnesium salts, acidic agents or alkaline
agents.
[0045] Freeze-point depressants which may be used as a crosslink
modifier, in accordance with aspects of the present disclosure,
include, but are not limited to, metal salts, including alkali
metal, alkali earth metal, and transition metal salts of organic
acids, linear sulphonate detergents, metal salts of caprylic acid,
succinamic acid or salts thereof, N-laurylsarcosine metal salts,
alkyl naphthalenes, polymethacrylates, such as Viscoplex.RTM. [Rohm
RohMax] and LZ.RTM. 7749B, 7742, and 7748 [all from Lubrizol
Corp.], vinyl acetate, vinyl fumarate, styrene/maleate co-polymers,
and other freeze point depressants known in the art.
[0046] The amount of crosslink modifier present in the crosslinking
additive compositions ranges from about 0.01 wt. % to about 80 wt.
%, by weight of the total solution, and more preferably from about
0.1 wt. % to about 65 wt. %. The amount of crosslink modifier to be
used may be determined based on the ratio of the crosslink modifier
to the sparingly-soluble borate crosslinking agent, and ranges from
about 1:1 to about 10:1, more preferably from about 1:1 to about
5:1, including ratios between these ranges, such as about 2:1,
about 2.5:1, about 3:1, about 3.5:1, about 4:1, and about 4.5:1,
inclusive.
[0047] The base fluid of the well treatment fluids that may be used
in conjunction with the compositions and methods of these
inventions preferably comprise an aqueous-based fluid, although
they may optionally also further comprise an oil-based fluid, or an
emulsion as appropriate. The base fluid may be from any source
provided that it does not contain compounds that may adversely
affect other components in the treatment fluid. The base fluid may
comprise a fluid from a natural or synthetic source. In certain
exemplary embodiments of the present inventions, an aqueous-based
fluid may comprise fresh water or salt water depending upon the
particular density of the composition required. The term "salt
water" as used herein may include unsaturated salt water or
saturated salt water "brine systems", such as a NaCl, or KCl brine,
as well as heavy brines including CaCl.sub.2, CaBr.sub.2 and
KCO.sub.2H. The brine systems suitable for use herein may comprise
from about 1% to about 75% by weight of an appropriate salt,
including about 3 wt. %, about 5 wt. %, about 10 wt. %, about 15
wt. %, about 20 wt. %, about 25 wt. %, about 30 wt. %, about 35 wt.
%, about 40 wt. %, about 45 wt. %, about 50 wt. %, about 55 wt. %,
about 60 wt. %, about 65 wt. %, about 70 wt. %, and about 75 wt. %
salt, without limitation, as well as concentrations falling between
any two of these values, such as from about 21 wt. % to about 66
wt. % salt, inclusive. Generally speaking, the base fluid will be
present in the well treatment fluid in an amount in the range of
from about 2% to about 99.5% by weight. In other exemplary
embodiments, the base fluid may be present in the well treatment
fluid in an amount in the range of from about 70% to about 99% by
weight. Depending upon the desired viscosity of the treatment
fluid, more or less of the base fluid may be included, as
appropriate. One of ordinary skill in the art, with the benefit of
this disclosure, will recognize an appropriate base fluid and the
appropriate amount to use for a chosen application.
[0048] In accordance with exemplary methods of the present
disclosure, an aqueous fracturing fluid, as a non-limiting example,
is first prepared by blending one or more crosslinkable organic
polymers into an aqueous base fluid. The aqueous base fluid may be,
for example, water, brine (e.g., a NaCl or KCl brine),
aqueous-based foams or water-alcohol mixtures. The brine base fluid
may be any brine, conventional or to be developed which serves as a
suitable media for the various components. As a matter of
convenience, in many cases the brine base fluid may be the brine
available at the site used in the completion fluid, for a
non-limiting example.
[0049] Any suitable mixing apparatus may be used for this
procedure. In the case of batch mixing, the crosslinkable organic
polymer, such as guar or a guar derivative, and the aqueous fluid
are blended for a period of time sufficient to form a gelled or
viscosifled solution. The organic polymer that is useful in the
present inventions is preferably any of the hydratable
polysaccharides, as described herein above, and in particular those
hydratable polysaccharides which are capable of gelling in the
presence of a crosslinking agent to form a gelled base fluid. The
most preferred hydratable polymers for the present inventions are
guar gums, carboxymethyl hydroxypropyl guar and hydroxypropyl guar,
as well as combinations thereof. In other embodiments of the
present disclosure, the crosslinkable organic polymer, or gelling
agent, may be depolymerized, as necessary. The term
"depolymerized," as used herein, generally refers to a decrease in
the molecular weight of the gelling agent. Depolymerized polymers
are described in U.S. Pat. No. 6,488,091, the relevant disclosure
of which is incorporated herein by reference as appropriate.
[0050] In addition to the aqueous base fluid and crosslinkable
organic polymer, the treatment fluid comprises a crosslinking
agent, which is used to crosslink the organic polymer and create a
viscosified treatment fluid. While any crosslinking agent may be
used, it is preferred that the crosslinking agent is a
sparingly-soluble borate. For the purposes of the present
disclosure, "sparingly-soluble" is defined as having a solubility
in water at 22.degree. C. (71.6.degree. F.) of less than about 10
kg/m.sup.3, as may be determined using procedures known in the arts
such as those described by Giiilensoy, et al. [M. T. A. Bull., no.
86, pp. 77-94 (1976); M. T. A. Bull., no. 87, pp. 36-47 (1978)].
For example, and without limitation, sparingly-soluble borates
having a solubility in water at 22.degree. C. (71.6.degree. F.)
ranging from about 0.1 kg/m3 to about 10 kg/m.sup.3 are appropriate
for use in the compositions disclosed herein. Generally, in
accordance with the present disclosure, the sparingly-soluble
borate crosslinking agent may be any material that supplies and/or
releases borate ions in solution. Exemplary sparingly-soluble
borates suitable for use as crosslinkers in the compositions in
accordance with the present disclosure include, but are not limited
to, boric acid, alkali metal, alkali metal-alkaline earth metal
borates, and the alkaline earth metal borates such as disodium
octaborate tetrahydrate, sodium diborate, as well as boron
containing minerals and ores. In accordance with certain aspects of
the present disclosure, the concentration of the sparingly-soluble
borate crosslinking agent described herein ranges from about from
about 0.01 kg/m3 to about 10 kg/m.sup.3, preferably from about 0.1
kg/m.sup.3 to about 5 kg/m.sup.3, and more preferably from about
0.25 kg/m.sup.3 to about 2.5 kg/m.sup.3 in the well treatment
fluid.
[0051] Boron-containing minerals suitable for use as
sparingly-soluble borate crosslinking agent in accordance with the
present disclosure are those ores containing 5 wt. % or more boron,
including both naturally-occurring and synthetic boron-containing
minerals and ores. Exemplary naturally-occurring, boron-containing
minerals and ores suitable for use herein include but are not
limited to boron oxide (B.sub.2O.sub.3), boric acid
(H.sub.3BO.sub.3), borax (Na.sub.2B.sub.4O.sub.7-10H.sub.2O),
colemanite (Ca.sub.2B.sub.6O.sub.11-5H.sub.2O), frolovite
Ca.sub.2B.sub.4O.sub.8-7H.sub.2O, ginorite
(Ca.sub.2B.sub.14O.sub.23-8H.sub.2O), gowerite
(CaB.sub.6O.sub.10-5H.sub.2O), howlite
(Ca.sub.4B.sub.10O.sub.23Si.sub.2-5H.sub.2O), hydroboracite
(CaMgB.sub.6O.sub.11-6H.sub.2O), inderborite
(CaMgB.sub.6O.sub.11-11H.sub.2O), inderite
(Mg.sub.2B.sub.6O.sub.11-15H.sub.2O), inyoite
(Ca.sub.2B.sub.6O.sub.11-13H.sub.2O), kaliborite (Heintzite)
(KMg.sub.2B.sub.11O.sub.19-9H.sub.2O), kernite (rasorite)
(Na.sub.2B.sub.4O.sub.7-4H.sub.2O), kumakovite
(MgB.sub.3O.sub.3(OH).sub.5-15H.sub.2O), meyerhofferite
(Ca.sub.2B.sub.6O.sub.11-7H.sub.2O), nobleite
(CaB.sub.6O.sub.10-4H.sub.2O), pandermite
(Ca.sub.4B.sub.10O.sub.19-7H.sub.2O), patemoite
(MgB.sub.2O.sub.13-4H.sub.2O), pinnoite
(MgB.sub.2O.sub.4-3H.sub.2O), priceite
(Ca.sub.4B.sub.10O.sub.19-7H.sub.2O), preobrazhenskite
(Mg.sub.3B.sub.10O.sub.18-4.5H.sub.2O), (probertite
NaCaB.sub.5O.sub.9-5H.sub.2O), tertschite
(Ca.sub.4B.sub.10O.sub.19-20H.sub.2O), tincalconite
(Na.sub.2B.sub.4O.sub.7-5H.sub.2O), tunellite
(SrB.sub.6O.sub.10-4H.sub.2O), ulexite
(Na.sub.2Ca.sub.2B.sub.10O.sub.18-16H.sub.2O), and veatchite
Sr.sub.4B.sub.22O.sub.37-7H.sub.2O, as well as any of the Class
V-26 Dana Classification borates, hydrated borates containing
hydroxyl or halogen, as described and referenced in Gaines, R. V.,
et al. [Dana's New Mineralogy, John Wiley & Sons, Inc., NY,
(1997)], or the class V/G, V/H, V/J or V/K borates according to the
Strunz classification system [Hugo Strunz; Ernest Nickel: Strunz
Mineralogical Tables, Ninth Edition, Stuttgart: Schweizerbart,
(2001)]. Any of these may be hydrated and have variable amounts of
water of hydration, including but not limited to tetrahydrades,
hemihydrates, sesquihydrates, and pentahydrates. Further, in
accordance with some aspects of the present disclosure, it is
preferred that the sparingly-soluble borates be borates containing
at least 3 boron atoms per molecule, such as, triborates,
tetraborates, pentaborates, hexaborates, heptaborates, decaborates,
and the like. In accordance with one aspect of the present
disclosure, the preferred crosslinking agent is a sparingly-soluble
borate selected from the group consisting of ulexite, colemanite,
probertite, and mixtures thereof.
[0052] Synthetic sparingly-soluble borates which may be used as
crosslinking agents in accordance with the presently disclosed well
treatment fluids and associated methods include, but are not
limited to, nobleite and gowerite, all of which may be prepared
according to known procedures. For example, the production of
synthetic colemanite, inyoite, gowerite, and meyerhofferite is
described in U.S. Pat. No. 3,332,738, assigned to the U.S. Navy
Department, in which sodium borate or boric acid are reacted with
compounds such as Ca(IO.sub.3).sub.2, CaCl.sub.2,
Ca(C.sub.2H.sub.3O.sub.2).sub.2 for a period of from 1 to 8 days.
The synthesis of ulexite from borax and CaCl.sub.2 has also been
reported [Gulensoy, H., et al., Bull. Miner. Res. Explor. Inst.
Turk., Vol. 86, pp. 75-78 (1976)]. Similarly, synthetic nobleite
can be produced by the hydrothermal treatment of meyerhofferite
(2CaO.sub.3B.sub.2O.sub.3-7H.sub.2O) in boric acid solution for 8
days at 85.degree. C., as reported in U.S. Pat. No. 3,337,292.
Nobleite may also be prepared in accordance with the processes of
Erd, McAllister and Vlisidis [American Mineralogist, Vol. 46, pp.
560-571 (1961)], reporting the laboratory synthesis of nobleite by
stirring CaO and boric acid in water for 30 hours at 48.degree. C.,
followed by holding the product at 68.degree. C. for 10 days. Other
techniques which may be used to generate synthetic boron-containing
materials suitable for use in the process of the present disclosure
include hydrothermal techniques, such as described by Yu, Z.-T., et
al. [J. Chem. Soc., Dalton Transaction, pp. 2031-2035 (2002)], as
well as sol-gel techniques [see, for example, Komatsu, R., et al.,
J. Jpn. Assoc. Cryst. Growth., Vol. 15, pp. 12-18 (1988)] and
fusion techniques. However, while, synthetic sparingly-soluble
borates may be used in the compositions and well treatment fluids
described herein, naturally-occurring sparingly-soluble borates are
preferred. This is due, in part, to the fact that although the
synthetic compositions have the potential of being of higher purity
than the naturally-occurring materials since they lack the mineral
impurities found in naturally occurring specimens, they are
generally relatively low in borate content by comparison.
[0053] The amount of borate ions in the treatment solution will
often be dependent upon the pH of the solution. In one non-limiting
embodiment of the present disclosure, the crosslinking agent is
preferably one of the boron-containing ores selected from the group
consisting of ulexite, colemanite, probertite, and mixtures
thereof, present in the range from about 0.5 to in excess of about
45.0 pptg (pounds per thousand gallons) of the well treatment
fluid. In another non-restrictive embodiment, the concentration of
sparingly-soluble borate crosslinking agent is in the range from
about 3.0 pptg to about 20.0 pptg of the well treatment fluid.
[0054] The compositions of the present disclosure may further
contain a number of optionally-included additives, as appropriate
or desired, such optional additives including, but not limited to,
suspending agents/anti-settling agents, stabilizers, deflocculants,
breakers, chelators/sequestrants, non-emulsifiers, fluid loss
additives, biocides, proppants, buffering agents, weighting agents,
wetting agents, lubricants, friction reducers, anti-oxidants, pH
control agents, oxygen scavengers, surfactants, fines stabilizers,
metal chelators, metal complexors, antioxidants, polymer
stabilizers, clay stabilizers, freezing point depressants, scale
inhibitors, scale dissolvers, shale stabilizing agents, corrosion
inhibitors, wax inhibitors, wax dissolvers, asphaltene
precipitation inhibitors, waterflow inhibitors, sand consolidation
chemicals, leak-off control agents, permeability modifiers,
micro-organisms, viscoelastic fluids, gases, foaming agents, and
nutrients for micro-organisms and combinations thereof, such that
none of the optionally-included additives adversely react or effect
the other constituents of these inventions. Various breaking agents
may also be used with the methods and compositions of the present
disclosure in order to reduce or "break" the gel of the fluid,
including but not necessarily limited to enzymes, oxidizers,
polyols, aminocarboxylic acids, and the like, along with gel
breaker aids. One of ordinary skill in the art will recognize the
appropriate type of additive useful for a particular subterranean
treatment operation. Further, all such optional additives may be
included as needed, provided that they do not disrupt the
structure, stability, mechanism of controlled delay, or subsequent
degradability of the crosslinked gels at the end of their use.
[0055] In accordance with typical aspects of the present
disclosure, the crosslinking agent (or agents, if appropriate) is
maintained in a suspended manner in the crosslinking additive by
the inclusion of one or more suspending agents in the crosslinking
additive composition. The suspending agent typically acts to
increase the viscosity of the fluid and prevent the settling-out of
the crosslinking agent. Suspending agents may also minimize
syneresis, the separation of the liquid medium so as to form a
layer on top of the concentrated crosslinking additive upon aging.
Suitable suspending agents for use in accordance with the present
disclosure include both high-gravity and low-gravity solids, the
latter of which may include both active solids, such as clays,
polymers, and combinations thereof, and inactive solids. In a
non-limiting aspect of the disclosure, the suspending agent may be
any appropriate clay, including, but not limited to,
palygorskite-type clays such as sepiolite, attapulgite, and
combinations thereof, smectite clays such as hectorite,
montmorillonite, kaolinite, saponite, bentonite, and combinations
thereof, Fuller's earth, micas, such as muscovite and phologopite,
as well as synthetic clays, such as laponite. The suspending agent
may also be a water-soluble polymer which will hydrate in the
treatment fluids described herein upon addition. Suitable
water-soluble polymers which may be used in these treatment fluids
include, but are not limited to, synthesized biopolymers, such as
xanthan gum, cellulose derivatives, naturally-occurring polymers,
and/or derivative of any of these water-soluble polymers, such as
the gums derived from plant seeds. Various combinations of these
suspending agents may be utilized in the crosslinking additive
compositions of the present disclosure. Preferably, in accordance
with certain aspects of the present disclosure, the suspending
agent is a clay selected from the group consisting of attapulgite,
sepiolite, montmorillonite, kaolinite, bentonite, and combinations
thereof.
[0056] The amount of suspending agent which may be included in the
crosslinking additive compositions described herein, when they are
included, range in concentration from about 1 pound per 42 gallon
barrel (bbl) to about 50 pounds per barrel (ppb), or more
preferably from about 2 pounds per barrel to about 20 pounds per
barrel, including about 3 ppb, about 4 ppb, about 5 ppb, about 6
ppb, about 7 ppb, about 8 ppb, about 9 ppb, about 10 ppb, about 11
ppb, about 12 ppb, about 13 ppb, about 14 ppb, about 15 ppb, about
16 ppb, about 17 ppb, about 18 ppb, about 19 ppb, and ranges
between any two of these values, e.g., from about 2 ppb to about 12
ppb, inclusive. For purposes of the present disclosure, it is to be
noted that one lbm/bbl is the equivalent of one pound of additive
in 42 US gallons of liquid; the "m" is used to denote mass so as to
avoid possible confusion with pounds force (denoted by "lbf"). Note
that lbm/bbl may equivalently be written as PPB or ppb, but such
notation as used herein is not to be confused with `parts per
billion`. In SI units, the conversion factor is one pound per
barrel equals 2.85 kilograms per cubic meter; for example, 10
lbm/bbl=28.5 kg/m.sup.3).
[0057] A deflocculant is a thinning agent used to reduce viscosity
or prevent flocculation, sometimes (incorrectly) referred to as a
"dispersant". Most deflocculants are low-molecular weight anionic
polymers that neutralize positive charges on clay edges. Examples
of deflocculants suitable for use in the compositions of the
present disclosure include, but are not limited to, polyphosphates,
lignosulfonates, quebracho (a powdered form of tannic acid extract
from the bark of the quebracho tree, used as a high-pH and lime-mud
deflocculant) and various water-soluble synthetic polymers.
[0058] The aqueous well treatment fluids of the present disclosure
may optionally and advantageously comprise one or more friction
reducers, in an amount ranging from about 10 wt. % to about 95 wt.
% as appropriate. As used herein, the term "friction reducer"
refers to chemical additives that act to reduce frictional losses
due to friction between the aqueous treatment fluid in turbulent
flow and tubular goods (e.g. pipes, coiled tubing, etc.) and/or the
formation. Suitable friction reducing agents for use with the
aqueous treatment fluid compositions of the present disclosure
include but are not limited to water-soluble non-ionic compounds
such as polyalkylene glycols and polyethylene oxide, and polymers
and copolymers including but not limited to acrylamide and/or
acrylamide copolymers, poly(dimethylaminomethyl acrylamide),
polystyrene sulfonate sodium salt, and combinations thereof. In
accordance with this aspect of the disclosure, the term
"copolymer," as used herein, is not limited to polymers comprising
two types of monomeric units, but is meant to include any
combination of monomeric units, e.g., terpolymers, tetrapolymers,
and the like.
[0059] In accordance with certain, non-limiting aspects of the
present disclosure, the aqueous well-treatment fluids described
herein may optionally include one or more chelating agents, in
order to remedy instances which have the potential to detrimentally
affect the controlled crosslinking of solutions as described
herein, e.g., to remedy contaminated water situations. As used
herein, the term `chelating agent` refers to compounds containing
one or more donor atoms that can combine by coordinate binding with
a single metal ion to form a cyclic structure known equivalently as
a chelating complex, or chelate, thereby inactivating the metal
ions so that they cannot normally react with other elements or ions
to produce precipitates or scale. Such chelates have the structural
essentials of one or more coordinate bonds formed between a metal
ion and two or more atoms in the molecule of the chelating agent,
alternatively referred to as a `ligand`. Suitable chelating agents
for use herein may be monodentate, bidentate, tridentate,
hexadentate, octadentate, and the like, without limitation. The
amount of chelating agent used in the compositions described herein
will depend upon the type and amount of ion or ions to be chelated
or sequestered. Similarly, when chelating agents are included in
the compositions of the present disclosure, it is preferable that
the pH of the well treatment fluids described herein be kept above
the pH at which the free acid of the chelating agent would
precipitate; generally, this means keeping the pH of the
composition above about 1, prior to delivering the treatment fluid
downhole.
[0060] Exemplary chelating agents suitable for use with the
compositions and well treating fluids of the present disclosure
include, but are not limited to, acetic acid; acrylic polymers;
aminopolycarboxylic acids and phosphonic acids and sodium,
potassium and ammonium salts thereof; ascorbic acid; BayPure.RTM.
CX 100 (tetrasodium iminodisuccinate, available from LANXESS
Corporation, Pittsburgh, Pa.) and similar biodegradable chelating
agents; carbonates, such as sodium and potassium carbonate; citric
acid; dicarboxymethylglutamic acid; aminopolycarboxylic acid type
chelating agents, including but not limited to
cyclohexylenediamintetraacetic acid (CDTA),
diethylenetriamine-pentaacetic acid (DTPA),
ethylenediaminedisuccinic acid (EDDS); ethylenediaminetetraacetic
acid (EDTA), hydroxyethylethylenediaminetriacetic acid (HEDTA),
hydroxyethyliminodiacetic acid (HEIDA), nitrilotriacetic acid
(NTA), and the sesquisodium salt of diethylene triamine penta
(methylene phosphonic acid) (DTPMP.Na.sub.7), or mixtures thereof,
inulins (e.g. sodium carboxymethyl inulin); malic acid; nonpolar
amino acids, such as methionine and the like; oxalic acid;
phosphoric acids; phosphonates, in particular organic phosphonates
such as sodium aminotrismethylenephosphonate; phosphonic acids and
their salts, including but not limited to ATMP
(aminotri-(methylenephosphonic acid)), HEDP
(1-hydroxyethylidene-1,1-phosphonic acid), HDTMPA
(hexamethylenediaminetetra-(methylenephosphonic acid)), DTPMPA
(diethylenediaminepenta-(methylenephosphonic acid)), and
2-phosphonobutane-1,2,4-tricarboxylic acid, such as the
commercially available DEQUEST.TM. phosphonates (Solutia, Inc., St.
Louis, Mo.); phosphate esters; polyaminocarboxylic acids;
polyacrylamines; polycarboxylic acids; polysulphonic acids;
phosphate esters; inorganic phosphates; polyacrylic acids; phytic
acid and derivatives thereof (especially carboxylic derivatives);
polyaspartates; polyacrylades; polar amino acids (both alph- and
beta-form), including but not limited to arginine, asparagine,
aspartic acid, glutamic acid, glutamine, lysine, and ornithine;
siderophores, including but not limited to the desferrioxamine
siderophores Desferrioxamine B (DFB, a specific iron complexing
agent originally obtained from an iron-bearing metabolite of
Actinomycetes (Streptomyces pilosus), and the cyclic trihydroxamate
produced by P. stutzeri, Desferrioxamine E (DFE)); succinic acid;
trihydroxamic acid and derivatives thereof, as well as combinations
of the above-listed chelating agents, and the free acids of such
chelating agents (as appropriate) and their water-soluble salts
(e.g., their Na.sup.+, K.sup.+, NH.sub.4.sup.+, and Ca.sup.2+
salts).
[0061] Non-limiting exemplary chelating agent/metal complexes which
may be formed by the chelating agents of the present disclosure
with suitable metal ions include chelates of the salts of barium
(II), calcium (II), strontium (II), magnesium (II), chromium (II),
titanium (IV), aluminum (III), iron (II), iron (III), zinc (II),
nickel (II), tin (II), or tin (IV) as the metal and
nitrilotriacetic acid,
1,2-cylohexane-diamine-N,N,N',N'-tetra-acetic acid,
diethylenetriamine-pentaacetic acid,
ethylenedioxy-bis(ethylene-nitrilo)-tetraacetic acid,
N-(2-hydroxyethyl)-ethylenediamino-N,N',N'-triacetic acid,
triethylene-tetraamine-hexaacetic acid or
N-(hydroxyethyl)ethylenediamine-triacetic acid or a mixture thereof
as a ligand.
[0062] The well treatment fluid of the present disclosure may also
optionally comprise proppants for use in subterranean applications,
such as hydraulic fracturing. Suitable proppants include, but are
not limited to, gravel, natural sand, quartz sand, particulate
garnet, glass, ground walnut hulls, nylon pellets, aluminum
pellets, bauxite, ceramics, polymeric materials, combinations
thereof, and the like, all of which may further optionally be
coated with resins, tackifiers, surface modification agents, or
combinations thereof. If used, these coatings should not
undesirably interact with the proppant particulates or any other
components of the treatment fluids of the present inventions. One
having ordinary skill in the art, with the benefit of this
disclosure, will recognize the appropriate type, size, and amount
of proppant particulates to use in conjunction with the well
treatment fluids of the present disclosure, so as to achieve a
desired result. In certain non-limiting embodiments, the proppant
particulates used may be included in a well treatment fluid of the
present inventions to form a gravel pack downhole or as a proppant
in fracturing operations.
[0063] The treatment fluids of the present inventions may
optionally further comprise one or more pH buffers, as necessary,
and depending upon the characteristics of the subterranean
formation to be treated. The pH buffer is typically included in the
treatment fluids of the present inventions to maintain pH in a
desired range, inter alia, to enhance the stability of the
treatment fluid. Examples of suitable pH buffers include, but are
not limited to, alkaline buffers, acidic buffers, and neutral
buffers, as appropriate. Alkaline buffers may include those
comprising, without limitation, ammonium, potassium and sodium
carbonates, bicarbonates, sesquicarbonates, and hydrogen
phosphates, in an amount sufficient to provide a pH in the
treatment fluid greater than about pH 7, and more preferably from
about pH 9 to about pH 12. Further exemplary alkaline pH buffers
include sodium carbonate, potassium carbonate, sodium bicarbonate,
potassium bicarbonate, sodium or potassium diacetate, sodium or
potassium phosphate, sodium or potassium hydrogen phosphate, sodium
or potassium dihydrogen phosphate, sodium borate, sodium or
ammonium diacetate, or combinations thereof, and the like.
Advantageously, the present inventions do not modify the pH,
allowing the pH of the treatment fluid to remain at a desired
level.
[0064] Acidic buffers may also be used with the formulation of
treatment fluids in accordance with the present disclosure. An
acidic buffer solution is one which has a pH less than 7. Acidic
buffer solutions may be made from a weak acid and one of its salts,
such as a sodium salt, or may be obtained from a commercial source.
An example would be a mixture of ethanoic acid and sodium ethanoate
in solution. In this case, if the solution contained equal molar
concentrations of both the acid and the salt, it would have a pH of
4.76. Thus, as used herein, "acidic buffer" means a compound or
compounds that, when added to an aqueous solution, reduces the pH
and causes the resulting solution to resist an increase in pH when
the solution is mixed with solutions of higher pH. The acidic
buffer must have a pKa below about 7. Some currently preferred
ranges of pKa of the acidic buffer are below about 7, below about
6, below about 5, below about 4 and below about 3. Acidic buffers
with all individual values and ranges of pKa below about 7 are
included in the present disclosure. Examples of acidic buffers
suitable for use with the treatment fluids described herein
include, but are not limited to, phosphate, citrate, iso-citrate,
acetate, succinate, ascorbic, formic, lactic, sulfuric,
hydrochloric, nitric, benzoic, boric, butyric, capric, caprilic,
carbonic, carboxylic, oxalic, pyruvic, phthalic, adipic,
citramalic, fumaric, glycolic, tartaric, isotartaric, lauric,
maleic, isomalic, malonic, orotic, propionic, methylpropionic,
polyacrylic, succinic, salicylic, 5-sulfosalicylic, valeric,
isovaleric, uric, and combinations thereof, such as a combination
of phosphoric acid and one or more sugars that has a pH between
about 1 and about 3, as well as other suitable acids and bases, as
known in the art and described in the Kirk-Othmer Encyclopedia of
Chemical Technology, 5.sup.th Edition, John Wiley & Sons, Inc.,
(2008). Other suitable acidic buffers are mixtures of an acid and
one or more salts. For example, an acidic buffer suitable for use
herein may be prepared using potassium chloride or potassium
hydrogen phthalate in combination with hydrochloric acid in
appropriate concentrations.
[0065] Oxygen scavengers may also be included in the aqueous well
treatment fluids of the present disclosure. As used herein, the
term `oxygen scavenger` refers to those chemical agents that react
with dissolved oxygen (02) in the solution compositions in order to
reduce corrosion resulting from, or exacerbated by, dissolved
oxygen (such as by sulfite and/or bisulfite ions combining with
oxygen to form sulfate). Oxygen scavengers typically work by
capturing or complexing the dissolved oxygen in a fluid to be
circulated in a wellbore in a harmless chemical reaction that
renders the oxygen unavailable for corrosive reactions. Exemplary
oxygen scavengers suitable for use herein include, but are not
limited to, metal-containing agents such as organotin compounds,
nickel compounds, copper compounds, cobalt compounds, and the like;
hydrazines; ascorbic acids; sulfates, such as sodium thiosulfate
pentahydrate; sulfites such as potassium bisulfite, potassium
meta-bisulfite, and sodium sulfite; and combinations of two or more
of such oxygen scavengers, as appropriate, and depending upon the
particular characteristics of the subterranean formation to be
treated with a treatment fluid of the present disclosure. In order
to improve the solubility of oxygen scavengers, such as stannous
chloride or other suitable agents, so that they may be readily
combined with the compositions of the present disclosure on the
fly, the oxygen scavenger(s) may be pre-dissolved in an appropriate
aqueous solution, e.g., when stannous chloride is used as an oxygen
scavenger, it may be dissolved in a dilute, aqueous acid (e.g.,
hydrochloric acid) solution in an appropriate weight (e.g., from
about 0.1 wt. % to about 20 wt. %), prior to introduction into the
well treatment fluids described herein.
[0066] Other common additives which may be employed in the well
treatment fluids described herein include gel stabilizers that
stabilize the crosslinked organic polymer (typically a
polysaccharide crosslinked with a borate) for a sufficient period
of time so that the fluid may be pumped to the target subterranean
formation. Suitable crosslinked gel stabilizers which may be used
in the treatment fluids described herein include, but are not
necessarily limited to, sodium thiosulfate, diethanolamine,
triethanolamine, methanol, hydroxyethylglycine,
tetraethylenepentamine, ethylenediamine and mixtures thereof.
[0067] The compositions of the present disclosure may also comprise
one or more breakers, added at the appropriate time during the
treatment of a subterranean formation that is penetrated by a
wellbore. Typically, once a proppant has been placed in a
subterranean fracture following a fracturing operation, the
crosslinked support fluid for the proppant (such as those described
herein) must be thinned, and the high-molecular weight filter cake
on the fracture faces must be destroyed in order to facilitate
clean-up prior to producing from the formation. This is commonly
accomplished through the use of "breakers"--chemicals that
literally `break` the crosslinked polymer molecules into smaller
pieces of lower molecular weight enabling a viscous fluid (such as
a fracturing fluid) to be degraded controllably to a thin fluid
that can be produced back out of the formation [see, for example,
Ely, J. W., Fracturing Fluids and Additives, in Recent Advances in
Hydraulic Fracturing, Society of Petroleum Engineers, Inc.; Gidley,
J. L., et al., Eds., Ch. 7, pp. 131-146 (1989); and Rae, P., and
DiLullo, G., SPE Paper No. 37359 (1996).]. In accordance with this
disclosure, the breaker(s) which are suitable for use in the
presently described compositions and associated treatment methods
for subterranean formations may be either an organic or inorganic
peroxide, both of which may be either soluble in water or only
slightly soluble in water. As used in this disclosure, the term
"organic peroxide" refers to both organic peroxides (those
compounds containing an oxygen-oxygen (--O--O--) linkage or bond
(peroxy group)) and organic hydroperoxides, while the term
"inorganic peroxide" refers to those inorganic compounds containing
an element at its highest state of oxidation (such as perchloric
acid, HClO.sub.4), or containing the peroxy group (--O--O--). The
term "slightly water soluble" as used herein with reference to
breakers refers to the solubility of either an organic peroxide or
an inorganic peroxide in water of about 1 gram/100 grams of water
or less at room temperature and pressure. Preferably, the
solubility is about 0.10 gram or less of peroxide per 100 grams of
water. The solubility determination of peroxides for use as
breakers in accordance with the present disclosure may be measured
by any appropriate method including, but not limited to, HPLC
methods, voltammetric methods, and titration methods such as the
iodometric titrations described in Vogel's Textbook of Quantitative
Chemical Analysis, 6.sup.th Ed., Prentice Hall, (2000).
[0068] In accordance with this aspect of the present disclosure,
processes are described for delivering a well treatment fluid (such
as a fracturing fluid) comprising a polysaccharide, a
sparingly-soluble borate crosslinking agent, and a crosslink
modifier into a subterranean formation that is penetrated by a
wellbore, contacting the borate-stabilized crosslinked fluid with
an organic or inorganic breaker which is soluble or only
slightly-soluble, wherein the breaker is present in an amount
sufficient to reduce the viscosity. In accordance with such
processes, either individual batches of the crosslinked fluids may
be periodically treated with the organic or inorganic breaker so
that the breaker is provided intermittently to the well, or
alternatively and equally acceptable, all of the crosslinked fluid
used in a given operation may be treated so that the breaker in
effect is continuously provided to the well.
[0069] The organic peroxides suitable for use as breakers in
accordance with the present disclosure may have large activation
energies for peroxy radical formation and relatively high storage
temperatures that usually exceed about 80.degree. F. High
activation energies and storage temperatures of the organic
peroxides suitable for use with the compositions herein lend
stability to the compositions, which can in turn provide a
practical shelf life. Preferred organic peroxides suitable for use
as breakers include, but are not limited to, cumene hydroperoxide,
t-butyl hydroperoxide, t-butyl cumyl peroxide, di-t-butyl peroxide,
di-(2-t-butylperoxyisopropyl)benzene,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-isopropylbenzene
monohydroperoxide, di-cumylperoxide, 2,2-di-(t-butyl peroxy)
butane, t-amyl hydroperoxide, benzoyl peroxide, mixtures thereof,
and mixtures of organic peroxides with one or more additional
agents, such as potassium persulfate, nitrogen ligands (e.g., EDTA
or 1,10-phenatroline). For example, cumene hydroperoxide has a
slight water solubility of about 0.07 gram/100 grams water, an
activation energy of about 121 kJ/mole in toluene, and a half life
of about 10 hours at 318.degree. F.
[0070] Slightly water-soluble inorganic and organic peroxides are
preferred for use in applications where they may have better
retention in the fracture during injection than water-soluble
inorganic or organic peroxides. While not limiting the reason for
this to a single theory, such retainment may likely be due to the
polysaccharide filter cake itself. The cake, when exposed to a
pressure differential during pumping into the subterranean
formation, allows the water phase to filter through the cake
thickness. After passing through the filter cake, the water, and
any associated water-soluble solutes, can enter into the formation
matrix. Consequently, water-soluble peroxides can behave in a
manner similar to persulfates with a sizeable fraction degrading in
the formation matrix. In contrast, most of the slightly
water-soluble inorganic and organic peroxides suggested for use
herein are not in the water phase and consequently do not filter
through the polysaccharide filter cake into the formation. Most of
the inorganic and organic peroxides described herein as being
suitable for use with the fluids of the present disclosure can
become trapped within the cake matrix. Therefore, the inorganic or
organic peroxide concentration should increase within the fracture
at nearly the same rate as the polysaccharide while retaining
amounts sufficient to degrade both the fluid and the filter
cake.
[0071] The rate of the slightly water-soluble inorganic or organic
peroxide degradation will depend on both temperature and the
concentration of the inorganic or organic peroxide. The amount of
slightly water-soluble organic peroxide used is an amount
sufficient to decrease viscosity or break a gel without a premature
reduction of viscosity. For example, if the average gelled
polysaccharide polymer has a molecular weight of about two million,
and the desired molecular weight reduction is about 200,000 or
less, then the reduction would entail about ten cuts. A
concentration of 20 ppm of organic peroxide should degrade the
polysaccharide without a premature reduction of viscosity.
Preferably, the amount of organic peroxide ranges from about 5 ppm
to about 15,000 ppm based on the fluid. Typically, the
concentration depends on both polysaccharide content, preferably
about 0.24% to about 0.72% (weight/volume) and the temperature. The
applicable temperature range suitable for use with these peroxides
ranges from about 125.degree. F. to about 275.degree. F., while the
applicable pH can range from about pH 3 to about pH 11.
Additionally, the average particle size of the peroxide breaker may
range from about 20 mesh to about 200 mesh, and more preferably
from about 60 mesh to about 180 mesh.
[0072] Inorganic peroxides suitable for use as breakers in a
combination with the compositions of the present disclosure
include, but are not limited to, alkali metal peroxides, alkaline
earth metal peroxides, transition metal peroxides, and combinations
thereof, such as those described by Skiner, N. and Eul, W., in
Kirk-Othmer Encyclopedia of Chemical Technology, J. Wiley &
Sons, Inc., (2001). Exemplary alkali metal peroxides suitable for
use in association with the present disclosure include, but are not
limited to, sodium peroxide, sodium hypochlorite, potassium
peroxide, potassium persulfate, potassium superoxide, lithium
peroxide, and mixtures of such peroxides such as sodium/potassium
peroxide. Exemplary alkaline earth metal peroxides include
magnesium peroxide, calcium peroxide, strontium peroxide, and
barium peroxide, as well as mixed peroxides such as
calcium/magnesium peroxide. Transition metal peroxides which may be
used in the compositions described herein include any peroxide
comprising a metal from Group 4 to Group 12 of the Periodic Table
of the Elements, such as zinc peroxide.
[0073] Additional common additives which may be used in conjunction
with the presently described well treatment fluids are enzyme
breaker (protein) stabilizers. These compounds may act to stabilize
any enzymes and/or proteins used in the treating fluids to
eventually `break` the gel after the subterranean formation is
treated, so that they are still effective at the time it is desired
to break the gel. If the enzymes degrade too early, they will not
be available to effectively break the gel at the appropriate time.
Nonlimiting examples of enzyme breaker stabilizers which may be
incorporated into the well treatment fluids of the present
disclosure include sorbitol, mannitol, glycerol, citrates,
aminocarboxylic acids and their salts (EDTA, DTPA, NTA, etc.),
phosphonates, sulphonates and mixtures thereof.
[0074] The delayed crosslinking additives and treatment fluids of
the present disclosure may be used in any subterranean treating
operation wherein such a treatment fluid would be appropriate, such
as a stimulation or completion operation, and where the viscosity
and crosslinking of that treatment fluid will be advantageously
controlled or modified. Exemplary types of treating subterranean
formations include, without limitation, drilling a well bore,
completing a well, stimulating a subterranean formation with
treatment operations such as fracturing (including hydraulic and
foam fracturing) and/or acidizing (including matrix acidizing
processes and acid fracturing processes), diverting operations,
water control operations, and sand control operations (such as
gravel packing processes), as well as numerous other subterranean
treating operations, preferably those associated with hydrocarbon
recovery operations. As used herein, the term "treatment," or
"treating," refers to any subterranean operation that uses a fluid
in conjunction with a desired function and/or for a desired
purpose. The term "treatment," or "treating," does not imply any
particular action by the fluids of the present disclosure.
[0075] Other and further embodiments utilizing one or more aspects
of the inventions described above can be devised without departing
from the spirit of the Applicants' inventions. Further, the various
methods and embodiments of the well treatment fluids and
application methods described herein can be included in combination
with each other to produce variations of the disclosed methods and
embodiments. Discussion of singular elements can include plural
elements and vice-versa.
[0076] The following examples are included to demonstrate preferred
embodiments of the inventions. It should be appreciated by those of
skill in the art that the techniques disclosed in the examples
which follow represent techniques discovered by the inventors to
function well in the practice of the inventions, and thus can be
considered to constitute preferred modes for its practice. However,
those of skill in the art should, in light of the present
disclosure, appreciate that many changes can be made in the
specific embodiments which are disclosed and still obtain a like or
similar result without departing from the scope of the
inventions.
EXAMPLES
Example 1
General Crosslinking Evaluation Procedure
[0077] The degree of crosslinking of several of the
boron-containing ores was determined using standard methods, as
described, for example, in U.S. Pat. No. 7,018,956. In general, to
conduct the crosslinking tests, a 2% KCl-guar solution was prepared
by dissolving 5 grams of potassium chloride (KCl) in 250 mL of
distilled or tap water, followed by adding 0.7 grams of guar
polymer, such as WG-35.TM. (available from Halliburton Energy
Services, Inc., Duncan, Okla.), or the equivalent. The resulting
mixture was agitated using an overhead mixer for 30 to 60 minutes,
to allow hydration. Once the guar had completely hydrated, the pH
of the solution was determined with a standard pH probe, and the
temperature was recorded. Typically, the initial guar mixture had a
pH that was in the range from about 7.5 to about 8.0, and had an
initial viscosity (as determined on a FANN.RTM. Model 35A
viscometer, available from the Fann Instrument Company, Houston,
Tex.) ranging from about 16 cP to about 18 cP at 77.degree. F. A
volume of 250 mL of the guar solution was placed in a clean, dry
glass Waring blender jar and the mixing speed of the blender motor
was adjusted using a rheostat (e.g., a Variac voltage controller)
to form a vortex in the guar solution so that the acorn nut (the
blender blade bolt) and a small area of the blade, that surrounds
the acorn nut in the bottom of the blender jar was fully exposed,
yet not so high as to entrain significant amounts of air in the
guar solution. While maintaining mixing at this speed, 0.44 mL of
crosslinking additive solution containing sparingly-soluble borate
was added to the guar mixture to effect crosslinking Upon addition
of the entire boron-containing material sample to the guar
solution, a timer was simultaneously started. The crosslinking rate
is expressed by three different time recordings: vortex closure,
T.sub.1, static top, T.sub.2, and hang lip time, T.sub.3. T.sub.1
is defined herein as the time that has elapsed between the time
that the crosslinker/boron-containing material is added and the
time when the acorn nut in the blender jar just becomes fully
covered by fluid. T.sub.2 is defined as the time that has elapsed
between the time that the crosslinker/boron-containing material is
added and the time when the top surface of the fluid in the blender
jar has stopped rolling/moving and becomes substantially static.
These two measurements are indicated in the tables herein as VC
(for "vortex closure") and ST (for "static top"), respectively. The
blender mixing speed setting remained constant throughout this test
(although the actual mixing speed may be reduced as the viscosity
of the crosslinked fluid increases). Optionally, after T.sub.2 was
recorded, the mixing was stopped and the fluid was manually
agitated back and forth between two beakers to observe the
consistency of the crosslinked composition. This optional third
measurement (T.sub.3), referred to generally as the hang lip time,
is defined herein as the time that has elapsed between the time
that the crosslinker is added and the time when the crosslinked
fluid forms a stiff lip that can hang on the edge of the beaker.
Those of ordinary skill in the art of evaluating fracturing fluids
will quickly recognize the fundamental tenants of evaluating such
fluids in the manner described in these Examples, although
individual testing practices and procedures may vary from those
described herein.
Example 2
Comparison of Water-Base and Oil-Base Crosslink Times
[0078] The initial crosslinking concentrates were prepared in both
water and diesel, according to known, general procedures. In
particular, the water-based concentrate was prepared by mixing
together 2 grams of attapulgite clay (FLORIGEL.RTM. HY, available
from the Floridan Company, Quincy, Fla.), 0.857 grams of low
viscosity polyanionic cellulose (GABROIL.RTM. LV, available from
Akzo Nobel, The Netherlands), 0.857 mL of NALCO.RTM. 9762 viscosity
modifier/deflocculant (available from the Nalco Company, Sugarland,
Tex.), and 49.97 grams of ground (D.sub.50=11 or 36) ulexite from
the Bigadic region of Turkey in 72.82 mL of Houston, Tex. tap
water. The diesel-based concentrate was prepared by mixing together
2.14 grams of a suspending agent, such as CLAYTONE.RTM. AF or
TIXOGEL.RTM. MP-100 (both available from Southern Clay Products,
Inc., Gonzales, Tex.), 1.31 mL of an emulsifier such as Witco 605A
(available from the Chemtura Corp., Middlebury, Conn.), and 49.97
grams of ground (D.sub.50.apprxeq.11 or 36) ulexite from the
Bigadic region of Turkey in 72.36 mL of diesel.
[0079] A 2% KCl-guar mixture for use with both the water-based and
diesel-based concentrates was prepared as a model of typical well
treatment fluids, and comprised a mixture of 5 grams of KCl and 0.7
grams of guar gum (WG-35.TM., available from Halliburton Energy
Services, Inc., Duncan, Okla.) in 250 mL of Houston, Tex. tap
water. The pH of the resultant guar mixture was then adjusted to 7
pH with dilute acetic acid (CH.sub.3CO.sub.2H). A concentration of
0.44 mL of either water-base or oil-base solutions with suspended
sparingly-soluble borate was admixed with 250 mL of a guar solution
and the crosslinking time determined at 100.degree. F.
(37.78.degree. C.). The results of these comparisons are shown in
Table A (FIG. 1).
[0080] Table A demonstrates that particle size distributions with a
high percentage of fines suspended in a saturated borate mineral
water have little impact on crosslink times when mixed in a low pH
guar composition. Varying the D-50 particle size of the borate from
11 to 36 microns only changes the crosslink time by 3-5%, whereas
the same solids mixed in an oil-base concentrate alters the
crosslink time by 22%.
Example 3
Crosslink Time Comparison for Potassium Acetate/Potassium Carbonate
Crosslinking Additives
[0081] A series of crosslinking additive compositions comprising
varying amounts of the crosslink modifiers potassium acetate
(KC.sub.2H.sub.3O.sub.2) and potassium carbonate (K.sub.2CO.sub.3)
were prepared and their crosslink times evaluated. In general, a 2%
KCl-guar mixture, as described above, was prepared. Separately, 100
mL of crosslinking additive solution was prepared having the ratio
of an aqueous KC.sub.2H.sub.3O.sub.2 solution-to-K.sub.2CO.sub.3
recited in Tables B-E (FIG. 2). For example, in the preparation of
a 93.76 vol. % KC.sub.2H.sub.3O.sub.2/6.24 vol. % K.sub.2CO.sub.3
crosslink modifier solution (Table B, FIG. 2), 68.29 mL of a 10.22
lb. gal. potassium acetate solution (available from NA-CHURS/ALPINE
Solutions, Marion, Ohio) was added to 4.54 mL of an 11.75 lb. gal.
solution of potassium carbonate (available from NA-CHURS/ALPINE
Solutions, Marion, Ohio) and the mixture was stirred to effect a
completely mixed solution. To this
KC.sub.2H.sub.3O.sub.2/K.sub.2CO.sub.3 solution was added 2 grams
of attapulgite clay (FLORIGEL.RTM. HY, available from the Floridan
Company, Quincy, Fla.), and the solution mixed in a Hamilton Beach
mixer for approximately 15 minutes. Subsequently, 0.857 grams of
low viscosity polyanionic cellulose (GABROIL.RTM. LV, available
from Akzo Nobel, The Netherlands) was added, and the solution mixed
for an additional 15 minutes. To this mixture was added 0.857 mL of
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and 49.97 grams of finely ground
(D.sub.50.apprxeq.36) ulexite from the Bigadic region of Turkey,
completing the crosslinking additive composition. A concentration
of 0.44 mL of KC.sub.2H.sub.3O.sub.2/K.sub.2CO.sub.3 crosslinking
additive with suspended sparingly-soluble borate was then admixed
with 250 mL of a guar solution and the crosslinking time determined
at 100.degree. F. (37.78.degree. C.). The results of these
comparisons are shown in Tables B, C, D and E, shown in FIG. 2.
Example 4
Crosslink Time Comparison for Potassium Formate/Potassium Carbonate
Crosslinking Additives
[0082] A series of crosslinking additive compositions comprising
varying amounts of the crosslink modifiers potassium formate
(KCO.sub.2H) and potassium carbonate (K.sub.2CO.sub.3) were
prepared and their crosslink times evaluated. In general, a 2%
KCl-guar mixture having a pH of 7, as described above, was
prepared. Separately, 100 ml of crosslinking additive solution was
prepared having the ratio of an aqueous KCO.sub.2H solution to
K.sub.2CO.sub.3 solution recited in Tables F-I, shown in FIG. 3.
For example, in the preparation of the mixture at entry 2 of Table
F, 67.31 mL of 11.22 lb. gal. potassium formate (KCO.sub.2H,
available from NA-CHURS/APLINE Solutions, Marion, Ohio) was stirred
with 5.06 mL of Houston, Tex. tap water generating an 11.0 lb. gal.
mixture. Added to this was 0.457 mL of an 11.75 lb. gal. solution
of potassium carbonate (K.sub.2CO.sub.3, available from
NA-CHURS/ALPINE Solutions, Marion, Ohio) and the mixture was
stirred to effect a completely mixed solution. To this
KCO.sub.2H/K.sub.2CO.sub.3 solution was added 2 grams of
attapulgite clay (FLORIGEL.RTM. HY, available from the Floridan
Company, Quincy, Fla.), and the solution was mixed with a Hamilton
Beach mixer for approximately 15 minutes. Subsequently, 0.857 grams
of low viscosity polyanionic cellulose (GABROIL.RTM. LV, available
from Akzo Nobel, The Netherlands) was added, and the solution mixed
for an additional 15 minutes. To this mixture was added 0.857 mL of
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and 49.97 grams of finely ground
(D.sub.50.apprxeq.36) ulexite from the Bigadic region of Turkey.
The pH of the resultant crosslinking additive mixture was 10.71.
The pH of the guar solution, such as described above, was adjusted
to pH 7 with dilute formic acid (HCO.sub.2H). A concentration of
0.44 mL of KCO.sub.2H/K.sub.2CO.sub.3 crosslinking additive with
suspended sparingly-soluble borate was then admixed with 250 mL of
a guar solution, and the crosslinking time determined at
100.degree. F. (37.78.degree. C.). The results of these comparisons
are shown in Tables F, G, H and I, shown in FIG. 3.
Example 5
Crosslink Time Comparison for Crosslinking Additives with Acetate
Chloride Acetate/Acetic and an Acetate/Sparingly-Soluble Borate
without Fines
[0083] A series of crosslinking additive compositions containing a
variety of crosslink modifiers were prepared and their crosslink
times evaluated. In particular, mixtures comprising potassium
acetate, potassium chloride, potassium acetate with the pH adjusted
to 7.5 with acetic acid, and potassium acetate with greater than
325 mesh particles of sparingly-soluble borate were prepared and
their crosslink times evaluated, using the methodology described
herein. First, a guar solution was prepared by admixing 250 mL of
Houston, Tex. tap water, 5 grams of potassium chloride (KCl,
available from Univar USA, Inc., Houston, Tex.), and 0.7 grams of
guar gum (WG-35.TM., available from Halliburton Energy Services,
Inc., Duncan, Okla.). This guar solution had an initial viscosity
of 16 cP @ 77.degree. F. (25.degree. C.), as measured on a
FANN.RTM. Model 35A viscometer, (available from the Fann Instrument
Company, Houston, Tex.). The pH of the resultant guar mixture was
then adjusted to pH 7 with dilute acetic acid
(CH.sub.3CO.sub.2H).
[0084] The 62.29 wt. % KC.sub.2H.sub.3O.sub.2 crosslinking additive
was prepared by admixing 72.83 mL of a 10.22 lb. gal.
KC.sub.2H.sub.3O.sub.2 solution, and 2 grams of attapulgite clay
(FLORIGEL.RTM. HY, available from the Floridan Company, Quincy,
Fla.). The solution was then blended with a Hamilton Beach mixer
for approximately 15 minutes. Subsequently, 0.857 grams of low
viscosity polyanionic cellulose (GABROIL.RTM. LV, available from
Akzo Nobel, The Netherlands) was added, and the solution mixed for
an additional 15 minutes. To this mixture was added 0.857 mL of
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and 49.97 grams of finely ground
(D.sub.50.apprxeq.36 or D.sub.50.apprxeq.36, retained on a 325 mesh
screen) ulexite from the Bigadic region of Turkey.
[0085] Similarly, the KCl solution was prepared by combining 98.7
grams of KCl (available from Univar USA, Inc., Houston, Tex.) with
308.35 mL of Houston, Tex. tap water. The solution was mixed, and
filtered through sharkskin filter paper, the filtrate being a
saturated KCl solution. A base solution was then prepared using
72.83 mL of the 9.7 lb. gal. KCl solution, 2 grams of attapulgite
clay (FLORIGEL.RTM. HY, available from the Floridan Company,
Quincy, Fla.), 0.857 grams of low viscosity polyanionic cellulose
(GABROIL.RTM. LV, available from Akzo Nobel, The Netherlands),
0.857 mL of NALCO.RTM. 9762 viscosity modifier/deflocculant
(available from the Nalco Company, Sugarland, Tex.), and 49.97
grams of finely ground (D.sub.50.apprxeq.36) ulexite, as described
in previous aspects.
[0086] The 61.46 wt. % KC.sub.2H.sub.3O.sub.2/0.84 wt. %
CH.sub.3CO.sub.2H crosslinking additive was prepared by admixing
71.69 mL of a 10.22 lb. gal. KC.sub.2H.sub.3O.sub.2 solution, 1.14
mL of an 8.75 lb. gal. CH.sub.3CO.sub.2H solution, and 2 grams of
attapulgite clay (Florigel.RTM. HY, available from the Floridan
Company, Quincy, Fla.). The solution was then blended with a
Hamilton Beach mixer for approximately 15 minutes. Subsequently,
0.857 grams of low viscosity polyanionic cellulose (GABROIL.RTM.
LV, available from Akzo Nobel, The Netherlands) was added, and the
solution mixed for an additional 15 minutes, To this mixture was
added 0.857 mL of NALCO.RTM. 9762 viscosity modifier/deflocculant
(available from the Nalco Company, Sugarland, Tex.), and 49.97
grams of finely ground (D.sub.50.apprxeq.36) ulexite from the
Bigadic region of Turkey.
[0087] A concentration of 0.44 mL of KC.sub.2H.sub.3O.sub.2, KCl,
and KC.sub.2H.sub.3O.sub.2/CH.sub.3CO.sub.2H crosslinking additives
with suspended sparingly-soluble borates was then admixed with 250
mL of a guar solution and the crosslinking time determined at
100.degree. F. (37.78.degree. C.). The results of these experiments
are summarized in Table J, shown in FIG. 4.
Example 6
Alkaline Chemical Comparisons for Potassium Acetate and Potassium
Formate Crosslinking Additives
[0088] A series of crosslinking additive compositions comprising
varying amounts of the crosslink modifiers potassium acetate
(KC.sub.2H.sub.3O.sub.2) and potassium formate (KCO.sub.2H) were
prepared and their crosslink times evaluated in a guar solution. In
general, a guar solution having a pH of 7 was prepared as described
previously herein, using a WG-35.TM. guar (available from
Halliburton Energy Services, Inc., Duncan, Okla.), and had an
initial viscosity at 300 rpm of 16-18 cP at 77.degree. F.
(25.degree. C.), as measured on a FANN.RTM. model 35A viscometer.
The KC.sub.2H.sub.3O.sub.2 and KCO.sub.2H crosslinking additives
were prepared, in the concentrations shown in Tables K and L (FIGS.
5 and 6, respectively), using the general methods described herein.
For example, 100 mL of the 60.58 wt. % KC.sub.2H.sub.3O.sub.2/1.87
wt. % K.sub.2CO.sub.3 crosslinking additive in Table K was prepared
by admixing 71 mL of 10.22 lb. gal. KC.sub.2H.sub.3O.sub.2
solution, 1.83 mL of an 11.75 K.sub.2CO.sub.3 solution, and 2 grams
of attapulgite clay (FLORIGEL.RTM. HY, available from the Floridan
Company, Quincy, Fla.). The solution was then blended with a
Hamilton Beach mixer for approximately 15 minutes. Subsequently,
0.857 grams of low viscosity polyanionic cellulose (GABROIL.RTM.
LV, available from Akzo Nobel, The Netherlands) was added, and the
solution mixed for an additional 15 minutes. To this mixture was
added 0.857 mL of NALCO.RTM. 9762 viscosity modifier/deflocculant
(available from the Nalco Company, Sugarland, Tex.), and 49.97
grams of finely ground (D.sub.50.apprxeq.36) ulexite from the
Bigadic region of Turkey. The resultant crosslinking additive
mixture had a pH of about 10.99.
[0089] The remaining compositions described in Tables K and L were
prepared in a similar manner as this, with appropriate
modifications regarding amounts of reagents depending upon the
final composition of the crosslinking additive to be tested.
[0090] A concentration of 0.44 mL of KC.sub.2H.sub.3O.sub.2 and
KCO.sub.2H crosslinking additives with suspended sparingly-soluble
borate was then admixed with 250 mL of a guar solution and the
crosslinking time determined at 100.degree. F. (37.78.degree. C.).
The results of these experiments are shown in Tables K and L (FIGS.
5 and 6, respectively).
[0091] Observations Based on Low pH (pH 7.0) Guar Solution
Experiments.
[0092] The results of Examples 3-6 herein, which studied the effect
of a number of crosslink modifiers (e.g., salt, alkaline or acidic
chemicals) in accordance with the present disclosure on the
crosslinking rates/times of guar solutions at low pH (e.g., about
pH 7.0), illustrate the ability of the compositions described
herein to produce dramatic changes in crosslink times of well
treatment fluids without altering the crosslinked system
characteristics. For example, Tables C and G illustrate that the
addition of salts, such as potassium acetate or potassium formate,
into a water-based crosslinking additive composition reduces the
crosslink time by 65.1% and 49.6%, respectively. Additionally,
Table C also shows that a salt/alkaline chemical crosslink modifier
solution ((e.g. 97.49 vol. % KC.sub.2H.sub.3O.sub.2 (8.90 lb.
gal.)/2.51 vol. % K.sub.2CO.sub.3 (11.75 lb. gal.)) in the
crosslinking additive composition alters the crosslink time by
about 66.9% while the final pH of the crosslinked system varies
only 0.1%. Similarly, Table G illustrates that a 97.49 vol. %
KCO.sub.2H (11 lb. gal.)/2.51 vol. % K.sub.2CO.sub.3 (11.75 lb.
gal.) crosslink modifier solution in the crosslinking additive
composition varies the crosslink time by about 53.3% while the
final pH of the crosslinked system remains unchanged.
[0093] Tables B and F illustrate several additional, important
features when used with low pH guar solutions. For example, Table B
illustrates that, as the level of K.sub.2CO.sub.3 is increased to
about 0.47 wt. % in the potassium acetate crosslinking additive,
the crosslink time is increased, but when the level of
K.sub.2CO.sub.3 increases above about 0.47 wt. %, the crosslink
time is reduced as the amount of K.sub.2CO.sub.3 is increased by
addition. In Table F, it is clear that, as the level of
K.sub.2CO.sub.3 is increased in the potassium formate crosslinking
additive, the crosslink time is reduced. Finally, Tables B and F
clearly show that the addition of a salt and an alkaline reaction
chemical can reduce the crosslink time to about 35 seconds even
though the borate crosslinking agent has a D.sub.50 particle size
of 36 microns.
[0094] The crosslink comparison studies for Table J illustrate
several important observations regarding the present disclosure.
For example, it can be seen from the table that when salt is added
into a water-base composition with sparingly-soluble borate and
then admixed with a guar solution the crosslink times are reduced.
However, the addition of an acidic chemical into the salt mixture
composition will increase the crosslink time. The experiment
utilizing coarse borate salt particles without fines also appears
to be able to increase the crosslink time for all of the
compositions studied. Finally, Table J illustrates that, in
accordance with the present disclosure, salts other than acetate
and formate can be used to change the crosslink times, with similar
beneficial effects.
[0095] Tables K and L also demonstrate that other alkaline
chemicals (e.g., potassium hydroxide) mixed in
KC.sub.2H.sub.3O.sub.2 and KCO.sub.2H solutions can be used to
accelerate crosslink times in low pH guar solutions. For example,
crosslink modifier solutions of 97.49 vol. % KC.sub.2H.sub.3O.sub.2
(8.90 lb. gal.)/2.51 vol. % KOH (9.06 lb. gal.) and 97.49 vol. %
KCO.sub.2H (11 lb. gal.)/2.51 vol. % KOH (9.06 lb. gal.) in the
crosslinking additive compositions can alter the crosslink time by
72.9% and 60.7%, respectively, as compared to a system crosslinked
by a water-based crosslinking additive.
Example 7
Evaluation of the Effect of Incremental Increases in the Amount of
Acetic Acid and Formic Acid in Potassium Acetate and Potassium
Formate Crosslinking Additives
[0096] A series of crosslinking additive compositions comprising
varying amounts of the crosslink modifiers potassium acetate
(KC.sub.2H.sub.3O.sub.2)/acetic acid (CH.sub.3CO.sub.2H) and
potassium formate (KCO.sub.2H)/formic acid (HCO.sub.2H) were
prepared and their crosslink times evaluated in HPG solutions. In
general, a hydroxypropyl guar (HPG) solution was prepared, by
combining 0.96 grams of HPG (GW-32.TM., available from BJ Services,
Tomball, Tex.) in 200 mL of Houston, Tex. tap water. The HPG
solution had an initial viscosity as measured by a FANN.RTM. model
35A viscometer at 300 rpm of 29-33 cP @77.degree. F., and a pH of
8.0-8.4 before adjusting to a pH of 11.6 using dilute NaOH.
[0097] The KC.sub.2H.sub.3O.sub.2/CH.sub.3CO.sub.2H and
KCO.sub.2H/HCO.sub.2H crosslinking additives were prepared as
generally described herein, by combining the required amounts of
10.22 lb. gal. KC.sub.2H.sub.3O.sub.2 or 11 lb. gal. KCO.sub.2H
with from 0% to 1.97 wt. % of acetic acid or formic acid, an
attapulgite clay (FLORIGEL.RTM. HY, available from the Floridan
Company, Quincy, Fla.), a low viscosity polyanionic cellulose
(GABROIL.RTM. LV, available from Akzo Nobel, The Netherlands),
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and very finely ground
(D.sub.50.apprxeq.11) ulexite, from the Bigadic region of
Turkey.
[0098] A concentration of 0.50 mL of
KC.sub.2H.sub.3O.sub.2/CH.sub.3CO.sub.2H and KCO.sub.2H/HCO.sub.2H
crosslinking additives with suspended sparingly-soluble borate was
then admixed with 200 mL of the HPG solution and the crosslinking
time was determined at 80.degree. F. (26.67.degree. C.). The
results of these experiments are shown in Tables M and N, (FIGS. 7
and 8, respectively).
Example 8
Acidic Chemical Comparisons for Potassium Acetate and Potassium
Formate Crosslinking Additives
[0099] A series of crosslinking additive compositions comprising
varying amounts of the crosslink modifiers potassium acetate
(KC.sub.2H.sub.3O.sub.2) and potassium formate (KCO.sub.2H) with
acids were prepared and their crosslink times evaluated in HPG
solutions. In general, the HPG solution was prepared as described
in Example 7, herein, using GW-32.TM., (available from BJ Services,
Tomball, Tex.) and had an initial viscosity at 300 rpm of 29-33 cP
at 77.degree. F. (25.degree. C.), as measured on a FANN.RTM. model
35A viscometer, and an initial pH of 8.0-8.4 prior to adjustment to
pH 11.6 with dilute NaOH. The KC.sub.2H.sub.3O.sub.2 and KCO.sub.2H
crosslinking additive solutions were prepared, in the
concentrations shown in Tables O and P (FIGS. 9 and 10,
respectively), using the general methods described herein. For
example, 100 mL of the 60.30 wt. % KC.sub.2H.sub.3O.sub.2/1.97 wt.
% HCl crosslinking additive in Table O was prepared by admixing
70.4 mL of 10.22 lb. gal. KC.sub.2H.sub.3O.sub.2 solution, 2.43 mL
of a 9.83 lb. gal. HCl solution, and 2 grams of attapulgite clay
(FLORIGEL.RTM. HY, available from the Floridan Company, Quincy,
Fla.). The solution was then blended with a Hamilton Beach mixer
for approximately 15 minutes. Subsequently, 0.857 grams of
polyanionic cellulose (GABROIL.RTM. LV, available from Akzo Nobel,
The Netherlands) was added, and the solution mixed for an
additional 15 minutes. To this mixture was added 0.857 mL of
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and 49.97 grams of very finely
ground (D.sub.50.apprxeq.11) ulexite from the Bigadic region of
Turkey. The resultant crosslinking additive mixture had a pH of
about 8.04.
[0100] The remaining compositions described in Tables O and P were
prepared in a similar manner as this, with appropriate
modifications regarding amounts of reagents (e.g., HCl,
CH.sub.3CO.sub.2H, or HCO.sub.2H), depending upon the final
composition of the crosslinking additive to be tested.
[0101] A concentration of 0.50 mL of KC.sub.2H.sub.3O.sub.2 and
KCO.sub.2H crosslinking additives with suspended sparingly-soluble
borate was then admixed with 200 mL of the HPG solution and the
crosslinking time was determined at 80.degree. F. (26.67.degree.
C.). The results of these experiments are shown in Tables O and P
(FIGS. 9 and 10, respectively).
Example 9
Evaluation of the Incremental Increase of Potassium Carbonate or
Acetic Acid in Potassium Acetate Crosslinking Additives
[0102] A series of crosslinking additive compositions comprising
the crosslink modifiers potassium acetate (KC.sub.2H.sub.3O.sub.2)
and varying amounts of potassium carbonate (K.sub.2CO.sub.3) or
acetic acid (CH.sub.3CO.sub.2H) were prepared and their crosslink
times evaluated in HPG solutions. In general, the HPG
(hydroxypropyl guar) solution was prepared as described in Example
7, herein, using GW-32.TM., (available from BJ Services, Tomball,
Tex.) and had an initial viscosity at 300 rpm of 29-33 cP at
77.degree. F. (25.degree. C.), as measured on a FANN.RTM. model 35A
viscometer, and an initial pH of 8.0-8.4 prior to adjustment to pH
11.6 with dilute NaOH. The KC.sub.2H.sub.3O.sub.2 crosslinking
additive solutions were prepared, in the concentrations shown in
Tables Q and R (FIGS. 11 and 12, respectively), using the general
methods described herein. For example, 100 mL of the 61.28 wt. %
KC.sub.2H.sub.3O.sub.2/0.88 wt. % CH.sub.3CO.sub.2H crosslinking
additive in Table R was prepared by admixing 71.54 mL of 10.22 lb.
gal. KC.sub.2H.sub.3O.sub.2 solution, 1.29 mL of an 8.75 lb. gal.
CH.sub.3CO.sub.2H solution, and 2 grams of attapulgite clay
(FLORIGEL.RTM. HY, available from the Floridan Company, Quincy,
Fla.). The solution was then blended with a Hamilton Beach mixer
for approximately 15 minutes. Subsequently, 0.857 grams of
polyanionic cellulose (GABROIL.RTM. LV, available from Akzo Nobel,
The Netherlands) was added, and the solution mixed for an
additional 15 minutes. To this mixture was added 0.857 mL of
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and 49.97 grams of very finely
ground (D.sub.50.apprxeq.11) ulexite from the Bigadic region of
Turkey. The resultant crosslinking additive mixture had a pH of
about 8.81.
[0103] The remaining compositions described in Tables Q and R were
prepared in a similar manner as this, with appropriate
modifications regarding amounts of reagents (e.g., K.sub.2CO.sub.3
or CH.sub.3CO.sub.2H), depending upon the final composition of the
crosslinking additive to be tested.
[0104] A concentration of 0.50 mL of
KC.sub.2H.sub.3O.sub.2/K.sub.2CO.sub.3 or
KC.sub.2H.sub.3O.sub.2/CH.sub.3CO.sub.2H crosslinking additives
with suspended sparingly-soluble borate was then admixed with 200
mL of the HPG (hydroxypropyl guar) solution and the crosslinking
time was determined at 80.degree. F. (26.67.degree. C.). The
results of these experiments are shown in Tables Q and R (FIGS. 11
and 12, respectively).
Example 10
Evaluation of Increased Particle Size in Potassium
Acetate/Potassium Carbonate Crosslinking Additives
[0105] A series of crosslinking additive compositions comprising
the crosslink modifiers potassium acetate (KC.sub.2H.sub.3O.sub.2)
and varying amounts of potassium carbonate (K.sub.2CO.sub.3) with a
larger particle size distribution of sparingly-soluble borates was
prepared and their crosslink times evaluated in HPG (hydroxypropyl
guar) solutions. In general, the HPG solution was prepared as
described herein, using GW-32.TM., (available from BJ Services,
Tomball, Tex.) and had an initial viscosity at 300 rpm of 29-33 cP
at 77.degree. F. (25.degree. C.), as measured on a FANN.RTM. model
35A viscometer, and an initial pH of 8.0-8.4 prior to adjustment to
pH 11.6 with dilute NaOH. The
KC.sub.2H.sub.3O.sub.2/K.sub.2CO.sub.3 crosslinking additives were
prepared, in the concentrations shown in Table S (FIG. 13), using
the general methods described herein. For example, 100 mL of the
58.0 wt. % KC.sub.2H.sub.3O.sub.2/4.44 wt. % K.sub.2CO.sub.3
crosslinking additive in Table S was prepared by admixing 68.29 mL
of 10.22 lb. gal. KC.sub.2H.sub.3O.sub.2 solution, 4.54 mL of an
11.75 lb. gal. K.sub.2CO.sub.3 solution, and 2 grams of attapulgite
clay (FLORIGEL.RTM. HY, available from the Floridan Company,
Quincy, Fla.). The solution was then blended with a Hamilton Beach
mixer for approximately 15 minutes. Subsequently, 0.857 grams of
polyanionic cellulose (GABROIL.RTM. LV, available from Akzo Nobel,
The Netherlands) was added, and the solution mixed for an
additional 15 minutes. To this mixture was added 0.857 mL of
NALCO.RTM. 9762 viscosity modifier/deflocculant (available from the
Nalco Company, Sugarland, Tex.), and 49.97 grams of finely ground
(D.sub.50.apprxeq.36) ulexite from the Bigadic region of Turkey.
The resultant crosslinking additive mixture had a pH of about
11.35.
[0106] The remaining compositions described in Table S were
prepared in a similar manner as this, with appropriate
modifications regarding amounts of reagents (e.g.,
KC.sub.2H.sub.3O.sub.2 or K.sub.2CO.sub.3), depending upon the
final composition of the crosslinking additive to be tested.
[0107] A concentration of 0.50 mL of
KC.sub.2H.sub.3O.sub.2/K.sub.2CO.sub.3 crosslinking additive with
suspended sparingly-soluble borate was then admixed with 200 mL of
the HPG solution and the crosslinking time was determined at
80.degree. F. (26.67.degree. C.). The results of these experiments
are shown in Table S, shown in FIG. 13.
[0108] Observations Based on High pH (pH 11.6) HPG Solution
Experiments.
[0109] The results of Examples 7-10 herein, which studied the
effect of a number of crosslink modifiers (e.g., salt, alkaline or
acidic chemicals) in accordance with the present disclosure on the
crosslinking rates/times of HPG solutions. At high pH (e.g., about
pH 11.6), the examples also illustrate the ability of the
compositions described herein to produce dramatic changes in
crosslink times of well treatment fluids without altering the
crosslinked system characteristics.
[0110] Tables M and N illustrate that at high pH values, such as at
a pH value of 11.6, crosslinking times for HPG solutions system are
greater than 12 minutes with very fine particles in the water-based
crosslinking additives. These tables also illustrate that the
addition of a salt, such as potassium formate, into a water-based
crosslinking additive composition, will reduce crosslink times over
30%, and the addition of both a salt and an acid into the
crosslinking additive composition reduces the crosslink times by
greater than 80% (compared with the water-based composition), to
below 1:45. Additionally, Table M shows that a 96.67 vol. %
KC.sub.2H.sub.3O.sub.2 (10.22 lb. gal)/3.33 vol. %
CH.sub.3CO.sub.2H (8.75 lb. gal.) crosslink modifier solution in
the crosslinking additive composition alters the crosslink time by
86.4% while the final pH of the crosslinked system varies only
5.4%. Similarly, Table N illustrates that a 96.67 vol. % KCO.sub.2H
(11 lb. gal.)/3.33 vol. % HCO.sub.2H (10.16 lb. gal.) crosslink
modifier solution in the crosslinking additive composition varies
the crosslink time by 89.6% while the final pH of the crosslinked
system changes only 3.0%.
[0111] The crosslink comparison studies for Tables O and P
illustrate that acids, other than acetic or formic (e.g.,
hydrochloric) can be used to accelerate the crosslink times of
water-based HPG systems. For example, crosslink modifier solutions
of 96.67 vol. % KC.sub.2H.sub.3O.sub.2 (10.22 lb. gal)/3.33 vol. %
HCl (9.83 lb. gal.) and 96.67 vol. % KCO.sub.2H (11 lb. gal.)/3.33
vol. % HCl (9.83 lb. gal.) in the crosslinking additive
compositions can alter the crosslink time by over 80% as compared
to a system crosslinked by a water-based crosslinking additive.
[0112] Tables Q and R demonstrate that incremental increases of the
crosslink modifiers K.sub.2CO.sub.3 and CH.sub.3CO.sub.2H with
decreasing amounts of KC.sub.2H.sub.3O.sub.2 will progressively
accelerate crosslink times in HPG solutions at high pH.
[0113] The results of the experiments in Table S, indicate that, in
contrast to the results shown in Table Q, high pH HPG solutions are
affected by the particle size of the sparingly-soluble borate
crosslinking agent. As exemplified in entry 1 of Tables Q and S,
the vortex closure (VC) time is extended 32.3% by varying the
D.sub.50 particle size from 11 microns to 36 microns in a
water-based crosslinking additive.
[0114] The order of steps described herein can occur in a variety
of sequences unless otherwise specifically limited. The various
steps described herein can also optionally be combined with other
steps, interlineated with the stated steps, and/or split into
multiple steps. Similarly, elements have been described
functionally and can be embodied as separate components or can be
combined into components having multiple functions.
[0115] The inventions have been described in the context of
preferred and other embodiments, but not every embodiment of the
inventions has been described. Obvious modifications and
alterations to the described embodiments are available to those of
ordinary skill in the art. The disclosed and undisclosed
embodiments are not intended to limit or restrict the scope or
applicability of the inventions conceived of by the Applicants, but
rather, in conformity with the patent laws, Applicants intend to
fully protect all such modifications and improvements that come
within the scope or range of equivalent of the following
claims.
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