Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
HIGH TEMPERATURE AQUEOUS-BASED
ZIRCONIUM FRACTURING FLUID AND USE
FIELD OF THE INVENTION
The present invention relates to zirconium-based crosslinking
compositions and their use in oil field applications such as hydraulic
fracturing and plugging of permeable zones.
BACKGROUND OF THE INVENTION
The production of oil and natural gas from an underground well
(subterranean formation) can be stimulated by a technique called
hydraulic fracturing, in which a viscous fluid composition (fracturing fluid)
containing a suspended proppant (e.g., sand, bauxite) is introduced into
an oil or gas well via a conduit, such as tubing or casing, at a flow rate and
a pressure which create, reopen and/or extend a fracture into the oil- or
gas-containing formation. The proppant is carried into the fracture by the
fluid composition and prevents closure of the formation after pressure is
released. Leak-off of the fluid composition into the formation is limited by
the fluid viscosity of the composition. Fluid viscosity also permits
suspension of the proppant in the composition during the fracturing
operation. Cross-linking agents, such as borates, titanates or zirconates,
are usually incorporated into the fluid composition to control viscosity.
Typically, less than one third of available oil is extracted from a well
after it has been fractured before production rates decrease to a point at
which recovery becomes uneconomical. Enhanced recovery of oil from
such subterranean formations frequently involves attempting to displace
the remaining crude oil with a driving fluid, e.g., gas, water, brine, steam,
polymer solution, foam, or micellar solution. Ideally, such techniques
(commonly called flooding techniques) provide a bank of oil of substantial
depth being driven into a producing well; however, in practice this is
frequently not the case. Oil-bearing strata are usually heterogeneous,
some parts of them being more permeable than others. As a
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consequence, channeling frequently occurs, so that the driving fluid flows
preferentially through permeable zones depleted of oil (so-called "thief
zones") rather than through those parts of the strata which contain
sufficient oil to make oil-recovery operations profitable.
Difficulties in oil recovery due to thief zones may be corrected by
injecting an aqueous solution of an organic polymer and a cross-linking
agent into a subterranean formation under conditions where the polymer
will be cross-linked to produce a gel, thus reducing permeability of the
subterranean formation to driving fluid (gas, water, etc.). Polysaccharide-
or partially hydrolyzed polyacrylamide-based fluids cross-linked with
certain aluminum, titanium, zirconium, and boron based compounds are
used in these enhanced oil recovery applications.
Cross-linked fluids or gels, whether for fracturing a subterranean
formation or for reducing permeability of zones in subterranean formation,
are now being used in hotter and deeper wells under a variety of
temperature and pH conditions, where rates of cross-linking with known
cross-linking compositions may be unacceptable.
Commercially available zirconium complexes of triethanolamine do
not cross-link at desirable rates for all organic polymers, for example, too
fast, or they do not maintain adequate viscosity in the cross-linked fluid
under high pH conditions and/or temperatures of about 275 F (135 C) and
higher, causing a significant loss in viscosity due to shear degradation,
which can also result in a sand out. Sand out refers to a situation in which
sand (proppant) deposits at the bottom of a wellbore due to lack of
viscosity development of the cross-linked fluid before the fluid reaches the
fracture zone.
U.S. Patent 4,801,389 discloses a fracturing fluid consisting of a
natural guar gum useful at high temperature (250 to 325 F, 121 to 163 C).
The fluid pH is controlled using a bicarbonate salt at a pH of 8 to 10 and
further comprises a zirconium crosslinking agent such as zirconium
lactate, sodium thiosulfate, brine (KCI). Use of bicarbonate shows
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acceptable viscosity (113 cp at 170 sec-1 at 1 hour, 121 C, 250 F). In
contrast, use of sodium carbonate shows poor viscosity (23 cp) under the
same conditions.
U.S. Patent 6,737,386 discloses a fracturing fluid comprising
natural guar and temperatures of 250 to 340 F (121 to 171 C). The fluid
has a pH range of 9 to 12 and comprises zirconium crosslinker, brine,
sodium thiosulfate, a buffer and citric acid. The fracturing fluids provide a
4-hour viscosity between 200-300 cp at 340 F at a shear rate of 40 sec-1
using natural guar.
There is a need for fracturing fluids which can function at high
temperatures (>_ 275 F, 135 C) and provide sufficient viscosity at these
temperatures when using hydroxypropyl guar. HPG is a solvatable
polysaccharide that is commercially available. Compared to natural guar,
HPG is more soluble in water, which may minimize damage to a
subterranean formation. HPG also has a faster hydration rate, which may
minimize agglomerate formation when dissolving in water. However,
when HPG is crosslinked using a zirconium crosslinker under certain
conditions, such as at high temperature, viscosity is unacceptably low.
SUMMARY OF THE INVENTION
The present invention provides a fracturing fluid or crosslinking
composition suitable for use at high temperature comprising (a) an
aqueous liquid, (b) brine, (c) a thermal stabilizer, (d) a non-delaying
alkaline buffer sufficient to provide a pH of less than 9, (e) an organic
acid,
(f) hydroxypropyl guar and (g) a zirconium crosslinking agent. Preferably
pH is from 7.5 to 8.9, more preferably from 8.0 to 8.9. Preferably the
buffer is sodium carbonate or potassium carbonate. More preferably the
buffer is sodium carbonate. The fracturing fluid is particularly suitable for
use at high temperature, i.e., at temperatures of about 275 F (135 C) or
higher, for example, at a temperature of 275-340 F (135-171 C).
The present invention further provides methods for using the
fracturing fluid of this invention in oil field applications, for example, for
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hydraulically fracturing a subterranean formation. The fracturing fluid of
this invention is further useful for plugging permeable zones or leaks in
subterranean formations.
DETAILED DESCRIPTION OF THE INVENTION
Trademarks and tradenames are shown herein in upper case.
The present invention provides a fracturing fluid comprising HPG
having sufficient viscosity for use in high temperature wells. Furthermore,
sufficient viscosity is maintained for a sufficient time for treating a
subterranean zone. More specifically, the present invention provides a
fracturing fluid or cross-linking composition comprising (a) an aqueous
liquid, (b) brine, (c) a thermal stabilizer, (d) a non-delaying alkaline
buffer
sufficient to provide a pH of less than 9, (e) an organic acid, (f)
hydroxypropyl guar and (g) a zirconium crosslinking agent. Each
component is present in an amount sufficient to provide a viscosity of at
least 100 centipoise (cp), 90 minutes after contacting the components a
temperature of at least 275 F (135 C).
The aqueous liquid (a) is typically selected from the group
consisting of water and aqueous alcohol. Preferably, the aqueous liquid
is water, aqueous methanol or aqueous ethanol.
By brine (b), it is meant one or more components, preferably salts
that act as clay stabilizers. Brine may comprise, for example, hydrochloric
acid and chloride salts, such as, tetramethylammonium chloride (TMAC),
sodium chloride or potassium chloride. Aqueous brine solutions may be
used and comprise, for example, 0.5 to 5.0 weight % of the clay stabilizer,
based on the total weight of the fracturing fluid. Preferably the brine is
tetramethylammonium chloride or potassium chloride.
Thermal stabilizers (c) include, for example, methanol, alkali metal
thiosulfate, and ammonium thiosulfate. Preferably the thermal stabilizer is
an alkali metal thiosulfate, more preferably sodium thiosulfate. The
concentration of thermal stabilizer in the fracturing fluid is 0.1 to 0.5
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weight %, preferably 0.2 to 0.4 weight % of the thermal stabilizers based
on the total weight of the fracturing fluid.
The fracturing fluid comprises an effective amount of a pH buffer
(d), which is a non-delaying alkaline buffer, to control pH at a pH less
than 9. By "non-delaying alkaline buffer" it is meant a buffer, which upon
addition to the composition does not delay the rate of cross-linking. The
preferred buffer is sodium carbonate or potassium carbonate, more
preferred is sodium carbonate. Preferably pH is from 7.5 to 8.9, more
preferably from 8.0 to 8.9. The fracturing fluid comprises 0.05 to 0.2
weight %, preferably 0.05 to 0.15 weight %, based on the total weight of
the fracturing fluid.
The fracturing fluid comprises an organic acid (e). The organic acid
is defined as a carboxylic acid. The preferred organic acids are formic
acid, acetic acid, lactic acid and fumaric acid. Preferably the acid is
fumaric acid. The fracturing fluid comprises 0.01 to 0.15 weight %,
preferably 0.02% to 0.1 weight %, and most preferably 0.04 weight % to
0.08 weight % organic acid based on the total weight of the fracturing fluid.
The fracturing fluid comprises a cross-linkable organic polymer (f),
which is hydroxypropyl guar (HPG). The fracturing fluid comprises 0.2 to
1.0 weight %, preferably 0.4 to 0.7 weight % of HPG, based on the total
weight of the fracturing fluid.
The fracturing fluid comprises a zirconium crosslinking agent (g).
The zirconium crosslinking agents are zirconium containing compounds
that enable polymerization compounds to form three-dimensional
networks. Examples of zirconium crosslinking agents include zirconium
alkanolamine complex, zirconium alkanolamine polyol complex and salts
of zirconium lactate, including sodium, ammonium and alkanolamine salt.
Zirconium alkanolamine complex may be prepared by reacting a
tetraalkyl zirconate with alkanolamine. Zirconium alkanolamine polyol
complex may be prepared by reacting a tetraalkyl zirconate with
alkanolamine and a suitable polyol. The tetraalkyl zirconate is typically
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expressed by the general formula Zr(OR)4 where each R is individually
selected from an alkyl, cycloalkyl, alkaryl, hydrocarbyl radical containing
from 1 to about 30, preferably 2 to about 18, and most preferably 2 to 12
carbon atoms per radical and each R can be the same or different. In
reaction of a tetraalkyl zirconate with alkanolamine, the alkanolamine
replaces four of the OR groups in the tetraalkyl zirconate. Zirconium
alkanolamine complex and zirconium alkanolamine polyol complex are
commercially available, e.g., from E. I. du Pont de Nemours and
Company, Wilmington, DE.
Zirconium lactate can be prepared by reacting a zirconium
oxychloride with lactic acid. The reaction can be followed by neutralization
with a base such as ammonia, an alkali metal hydroxide, alkanolamine or
by reaction with a quaternary ammonium hydroxide. The preferred
zirconium lactate salts are zirconium tris-ammonium lactate or its sodium
salt analogue, zirconium tris-sodium lactate. Zirconium lactates are
commercially available, e.g., from E. I. du Pont de Nemours and
Company, Wilmington, DE.
Preferably the zirconium crosslinking agent is selected from the
group consisting of alkanolamine complex, zirconium alkanolamine polyol
complex, zirconium tris-ammonium lactate, and zirconium tris-sodium
lactate.
The zirconium crosslinking agent is generally dissolved in an
organic, aqueous or mixed aqueous/organic solvent, providing a zirconium
solution. Typical solvents include water and alcohols, such as ethanol, n-
propanol, and isopropanol.
The fracturing fluid comprises between 10 to 50 ppm (pg/g),
preferably 30-40 ppm zirconium (as Zr), based on the total weight of the
fracturing fluid.
The fracturing fluid may comprise optional components, including
those which are common additives for oil field applications. Thus, the
fracturing fluid may further comprise one or more of proppants, friction
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reducers, bactericides, organic solvents, chemical breakers, surfactants,
formation control agents, and the like. Proppants include sand, bauxite,
glass beads, nylon pellets, aluminum pellets and similar materials.
Friction reducers include polyacrylamides. Organic solvents that may be
used include alcohols, glycols, polyols, and hydrocarbons such as diesel.
Chemical breakers break the cross-linked polymer (gel) in a controlled
manner and include enzymes, alkali metal persulfate, and ammonium
persulfate.
These optional components are added in an effective amount
sufficient to achieve the desired cross-linking performance based on the
individual components, desired cross-linking time, temperature and other
conditions present in the formation being fractured or permeable zone
being plugged.
The fracturing fluid is prepared by a process comprising contacting
the cross-linkable polymer (HPG), typically with mixing, with the aqueous
liquid to form a base gel. The base gel and zirconium crosslinking agent
are then contacted to provide the fracturing fluid. Other components,
including optional components can be added to the base gel, the
zirconium crosslinking agent or both.
While there is no particular order of addition that is required to
prepare the fracturing fluid of the present invention, it may be convenient
to first combine the aqueous liquid and brine to provide an aqueous brine.
To the aqueous brine may be added simultaneously or sequentially the
thermal stabilizer, acid and hydroxypropyl guar. By "simultaneous"
addition, it is meant herein that two or more components are added at the
same time or less than 60 seconds apart, for example, not more than 30
seconds apart. Typically, the aqueous liquid, brine, thermal stabilizer, acid,
and hydroxypropyl guar are mixed and allowed to stand for a period of
time, typically less than 60 minutes, preferably for 10-40 minutes, such as
for 30 minutes, prior to adding the buffer. The buffer (preferably sodium
carbonate or potassium carbonate) is added to the mixture and the
mixture is allowed to stand for a period of time, typically less than 60
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minutes, preferably for 10-40 minutes, such as for 30 minutes. prior to
adding the zirconium crosslinking agent. The zirconium crosslinking agent
is generally the final component added to the fracturing fluid.
This invention provides a method for hydraulically fracturing a
subterranean formation, which comprises introducing into the formation at
a flow rate and pressure sufficient to create, reopen, and/or extend one or
more fractures in the formation, a fracturing fluid which comprises (a) an
aqueous liquid, (b) brine, (c) a thermal stabilizer, (d) a non-delaying
alkaline buffer sufficient to provide a pH of less than 9, (e) an organic
acid,
(f) hydroxypropyl guar (HPG) and (g) a zirconium crosslinking agent. The
preferred embodiments of the fracturing fluid are described hereinabove.
In one embodiment of the method for hydraulically fracturing a
subterranean formation, the aqueous liquid, brine, thermal stabilizer,
buffer, acid, hydroxypropyl guar, and the zirconium crosslinking agent are
premixed and introduced into the subterranean formation as a single
stream. In this embodiment, a zirconium crosslinking agent and HPG are
contacted prior to their introduction into the formation, such that the
crosslinking agent and HPG polymer react to form a crosslinked gel.
Preferably, the zirconium crosslinking agent is introduced as a zirconium
solution. The cross-linked gel is then introduced into the formation at a
flow rate and pressure sufficient to create, reopen, and/or extend a
fracture in the formation. In this method, a base gel is prepared by mixing
HPG with the aqueous liquid. A crosslinked gel is prepared by mixing the
base gel with a solution of the zirconium crosslinking agent (zirconium
solution). In this embodiment, the additional components - the brine,
thermal stabilizer, buffer, and acid, and any optional components, may be
added to the base gel, the zirconium solution or both. For example, the
HPG may be mixed with the aqueous liquid, brine, thermal stabilizer,
buffer and acid to provide the base gel. This base gel is mixed with the
zirconium solution to produce a crosslinked gel, which is then introduced
into the formation.
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In a second embodiment of the method for hydraulically fracturing a
subterranean formation, zirconium crosslinking agent and HPG are not
contacted prior to their introduction into the formation. This method
comprises (a) preparing a base gel by mixing HPG with an aqueous liquid;
(b) introducing the base gel into the into the formation, (c) simultaneously
with or sequentially after introducing the base gel into the into the
formation, introducing the zirconium crosslinking agent into the formation;
and (d) permitting the base gel and the crosslinking agent to react to form
a crosslinked gel in the formation. Preferably, the zirconium crosslinking
agent is introduced as a zirconium solution. The additional components -
the brine, thermal stabilizer, buffer, and acid - and any optional
components, can be added to the base gel, the zirconium crosslinking
agent or both. For example, the HPG may be mixed with the aqueous
liquid, brine, thermal stabilizer, buffer and acid to provide the base gel.
This base gel is mixed with the zirconium crosslinking agent in the
formation to produce a crosslinked gel.
In an alternative when zirconium crosslinking agent and HPG are
not contacted prior to their introduction into the subterranean formation,
the formation is penetrated by a wellbore. A zirconium crosslinking agent,
preferably in the form of a zirconium solution, is contacted with a base gel
in the wellbore to form a crosslinked gel. The crosslinked gel is introduced
into the formation from the wellbore. A zirconium solution is prepared by
dissolving a zirconium crosslinking agent in a solvent such as water or an
alcohol. This method of hydraulically fracturing a subterranean formation
penetrated by a wellbore comprises (a) preparing a base gel by contacting
hydroxypropyl guar with an aqueous liquid; (b) introducing the base gel
into the wellbore; (c) simultaneously with or sequentially after introducing
the base gel into the wellbore, introducing the zirconium crosslinking agent
into the wellbore; (d) permitting the base gel and the zirconium
crosslinking agent to react to form a crosslinked gel in the wellbore; and
(e) introducing the crosslinked gel into the formation from the wellbore at a
flow rate and pressure sufficient to create, reopen, and/or extend a
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fracture in the formation. Additional components - the brine, thermal
stabilizer, buffer, and acid - and any optional components, are
independently admixed with the base gel, the zirconium crosslinking agent
or both prior to introducing the base gel and the zirconium crosslinking
agent into the wellbore. For example, the HPG may be mixed with the
aqueous liquid, brine, thermal stabilizer, buffer and acid to provide the
base gel. This base gel is mixed with the zirconium crosslinking agent to
produce a crosslinked gel, which is then introduced into the formation.
Upon creation of a fracture or fractures, the method may further
comprise introducing a fracturing fluid comprising a zirconium crosslinking
agent, a cross-linkable organic polymer and proppant into the fracture or
fractures. This second introduction of zirconium is preferably performed in
the event the cross-linking composition used to create the fracture or
fractures did not comprise proppant. The cross-linkable organic polymer
in this second addition may be hydroxypropyl guar or any other suitable
cross-linkable organic polymer.
This invention further provides a method for selectively plugging
permeable zones and leaks in subterranean formations, which comprises
introducing into the permeable zone or the site of the subterranean leak, a
fracturing fluid comprising (a) an aqueous liquid, (b) brine, (c) a thermal
stabilizer, (d) a non-delaying alkaline buffer sufficient to provide a pH of
less than 9, (e) an organic acid, (f) hydroxypropyl guar and (g) a zirconium
crosslinking agent. Optional components as described hereinabove, can
be added to the fracturing fluid prior to introducing the fracturing fluid
into
the permeable zone or site of the leak.
In one embodiment of the method for plugging a permeable zone or
a leak in a subterranean formation, the aqueous liquid, brine, thermal
stabilizer, buffer, acid, hydroxypropyl guar, and the zirconium crosslinking
agent are premixed and introduced into the subterranean formation as a
single stream. In this embodiment, a zirconium crosslinking agent and
HPG are contacted prior to their introduction into the subterranean
formation, such that the HPG polymer and zirconium crosslinking agent
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react to form a crosslinked gel. Preferably, the zirconium crosslinking
agent is introduced as a zirconium solution. The crosslinked gel is then
introduced into the formation. In this method, a base gel is prepared by
mixing HPG with the aqueous liquid. A crosslinked gel is prepared by
mixing the base gel with a zirconium crosslinking agent (preferably as a
zirconium solution). In this embodiment, the additional components - the
brine, thermal stabilizer, buffer, and acid, and any optional components,
may be added to the base gel, the zirconium crosslinking agent or both.
For example, the HPG may be mixed with the aqueous liquid, brine,
thermal stabilizer, buffer and acid to provide the base gel. This base gel is
mixed with the zirconium crosslinking agent to produce a crosslinked gel,
which is then introduced into the formation.
In a second embodiment of the method for plugging a permeable
zone or a leak in a subterranean formation, zirconium crosslinking agent
and HPG are not contacted prior to their introduction into the formation
and crosslinking occurs within the subterranean formation. Preferably, the
zirconium crosslinking agent is introduced as a zirconium solution. This
method comprises (a) preparing a base gel by mixing HPG with an
aqueous liquid; (b) introducing the base gel into the into the permeable
zone or the site of the subterranean leak, (c) simultaneously with or
sequentially after introducing the base gel into the into the permeable zone
or the site of the subterranean leak, introducing the zirconium crosslinking
agent into the permeable zone or the site of the subterranean leak; and
(d) permitting the base gel and the crosslinking agent to react to form a
crosslinked gel to plug the zone and/or leak. In this embodiment, the
additional components - the brine, thermal stabilizer, buffer, and acid -
and any optional components, can be added to the base gel, with the
zirconium crosslinking agent, or both. For example, the HPG may be
mixed with the aqueous liquid, brine, thermal stabilizer, buffer and acid to
provide the base gel. This base gel is mixed with the zirconium
crosslinking agent in the formation to produce a crosslinked gel.
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In an alternative when zirconium crosslinking agent and HPG are
not contacted prior to their introduction into the permeable zone or the leak
in a subterranean formation, the zone or formation is penetrated by a
wellbore. A zirconium crosslinking agent, preferably in the form of a
zirconium solution, is contacted with a base gel in the wellbore to form a
crosslinked gel. The crosslinked gel is introduced into the formation from
the wellbore. A zirconium solution is prepared by dissolving a zirconium
crosslinking agent in a solvent such as water or an alcohol. This method
of plugging a permeable zone or a leak in a subterranean formation,
wherein the zone or leak is penetrated by a wellbore comprises (a)
preparing a base gel by mixing hydroxypropyl guar with an aqueous liquid;
(b) introducing the base gel into the wellbore; (c) simultaneously with or
sequentially after introducing the base gel into the wellbore, introducing a
zirconium crosslinking agent into the wellbore; (d) permitting the base gel
and the zirconium crosslinking agent to react to form a crosslinked gel in
the wellbore; and (e) introducing the crosslinked gel from the wellbore into
the zone or formation. Additional components - the brine, thermal
stabilizer, buffer, and acid - and any optional components, are
independently admixed with the base gel, the zirconium crosslinking agent
or both prior to introducing the base gel and the zirconium crosslinking
agent into the wellbore. For example, the HPG may be mixed with the
aqueous liquid, brine, thermal stabilizer, buffer and acid to provide the
base gel. This base gel is mixed with the zirconium crosslinking agent to
produce a crosslinked gel in the wellbore, which is then introduced into the
formation.
The relative amounts of HPG and the zirconium crosslinking agent
complex may vary. One uses small but effective amounts which for both
will vary with the conditions, e.g., the type of subterranean formation, the
depth at which the method (e.g., fluid fracturing, permeable zone plugging
or leak plugging) is to be performed, temperature, pH, etc. Generally one
uses as small an amount of each component as will provide the viscosity
level necessary, such as a viscosity of at least 100 cp at 90 minutes after
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forming the crosslinked gel to effect the desired result, i.e., fracturing of
the subterranean formation, or plugging permeable zones or leaks to the
extent necessary to promote adequate recovery of oil or gas from the
formation.
Surprisingly, addition of acid to a base gel for a fracturing fluid and
maintaining pH at less than 9 using an alkaline buffer, allows HPG to be
used as cross-linkable organic polymer at a temperature of about 275 F
(135 C) or higher in a method for hydraulically fracturing a subterranean
formation or in a method for selectively plugging permeable zones or leaks
in subterranean formations.
EXAMPLES
The zirconium crosslinkers, zirconium lactate sodium salt (TYZOR
217 organic zirconate), alkanolamino zirconate (TYZOR 212 organic
zirconate) and triethanolamino zirconate (TYZOR TEAZ organic
zirconate), are all commercially available from E. I. du Pont de Nemours
and Company, Wilmington, DE. Zirconium lactate ammonium salt was
made by reacting zirconium oxychloride with lactic acid, followed by
neutralization with ammonium hydroxide.
Carboxymethylhydroxypropylguar (CMHPG), hydroxypropylguar
(HPG) and natural guar are commercially available from Rhodia, Inc., NJ.
All other chemicals used herein were purchased from Aldrich Chemical
Company, Milwaukee, WI.
Comparative Examples Al and A2
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and KCI brine (20 g). The solution was agitated and
hydroxypropylguar (HPG, 4.2 g) was added to the vortex of the agitating
solution. The solution was agitated for 30 minutes. Sodium bicarbonate
buffer (1.45 g) and sodium thiosulfate pentahydrate (1.2 g) were added to
the solution. The solution was mixed for 30 minutes. The resulting gel
was allowed to stand for at least one hour prior to adding zirconium
crosslinker to produce a fracturing fluid.
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Comparative Example B
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and sodium thiosulfate pentahydrate (3.6 g). The solution was
agitated and hydroxypropyl guar (HPG, 6.6 g) was added to the vortex of
the agitating solution. The solution was agitated for 30 minutes. Sodium
carbonate buffer was added to adjust pH to 9.5. Then sodium hydroxide
was added to adjust pH to 10. The solution was agitated for 5 minutes
and citric acid water solution (25%, 0.75g) was added. The solution was
agitated for 5 minutes. The resulting gel was allowed to stand for 30
minutes prior to adding zirconium crosslinker to produce a fracturing fluid.
Comparative Examples C1 and D1
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and a 50% aqueous solution of tetramethylammonium chloride
brine (TMAC, 2 g). The solution was agitated and
carboxymethylhydroxypropyl guar (CMHPG, 6 g) was sprinkled into the
vortex of the agitating solution. The pH of the resultant slurry was
adjusted to 6 with sodium diacetate (buffer) and agitated for 30 minutes.
The pH was then adjusted to 10 with 10% sodium hydroxide solution.
Agitation was stopped and the gel was allowed to stand for 30 minutes
prior to adding zirconium crosslinker to produce a fracturing fluid.
Comparative Examples C2 and D2
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and a 50% aqueous solution of tetramethylammonium chloride
brine (2 g) was added. The solution was agitated and hydroxypropyl guar
(HPG, 6 g) was added to the vortex of the agitating solution. The pH of
the resultant slurry was adjusted to 6 with sodium diacetate and agitated
for 30 minutes. The pH was then adjusted to 10 with sodium hydroxide
solution (10%). The gel was allowed to stand for 30 minutes prior to
adding zirconium crosslinker to produce a fracturing fluid.
Comparative Example E
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A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and KCI brine (20 g) was added. The solution was agitated.
Sodium thiosulfate pentahydrate (2.4 g), fumaric acid (0.55 g) and natural
guar (6.0 g) were added to the solution and the solution was agitated for
30 minutes. The pH was then adjusted to pH 8.8 with sodium carbonate
(buffer). The agitation was stopped and the gel was allowed to stand for
30 minutes prior to adding zirconium crosslinker to produce a fracturing
fluid.
Examples 1-5
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and KCI brine (20 g) was added. The solution was agitated.
Sodium thiosulfate pentahydrate (2.4 g), fumaric acid (0.55 g) and
hydroxypropyl guar (HPG, 6.0 g) were added to the solution
simultaneously (i.e., less than 60 seconds for the addition) and the
solution was agitated for 30 minutes. The pH was then adjusted to pH
7.8-8.8 with sodium carbonate (buffer). The agitation was stopped and the
gel was allowed to stand for 30 minutes prior to adding zirconium
crosslinker to produce a fracturing fluid.
Example 6
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and KCI brine (20 g) was added. The solution was agitated.
Sodium thiosulfate pentahydrate (2.4 g), acetic acid (0.58 g) and
hydroxypropyl guar (HPG, 6.0 g) were added to the solution and the
solution was agitated for 30 minutes. The pH was then adjusted to pH 8.8
with sodium carbonate (buffer). The agitation was stopped and the gel
was allowed to stand for 30 minutes prior to adding zirconium crosslinker
to produce a fracturing fluid.
Example 7
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and KCI brine (20 g) was added. The solution was agitated.
Sodium thiosulfate pentahydrate (2.4 g), lactic acid (0.76 g) and
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hydroxypropyl guar (HPG, 6.0 g) were added to the solution and the
solution was agitated for 30 minutes. The pH was then adjusted to pH 8.8
with sodium carbonate (buffer). The agitation was stopped and the gel
was allowed to stand for 30 minutes prior to adding zirconium crosslinker
to produce a fracturing fluid.
Example 8
A base gel was prepared by adding distilled water (1 L) to a Waring
blender jar and KCI brine (20 g) was added. The solution was agitated.
Sodium thiosulfate pentahydrate (2.4 g), formic acid (0.44 g) and
hydroxypropyl guar (HPG, 6.0 g) were added to the solution and the
solution was agitated for 30 minutes. The pH was then adjusted to pH 8.8
with sodium carbonate (buffer). The agitation was stopped and the gel
was allowed to stand for 30 minutes prior to adding zirconium crosslinker
to produce a fracturing fluid.
Viscosity measurement of zirconate cross-linked base gels
After preparation of base gels, the desired amount of zirconium
crosslinker (32-148 ppm) was added to each base gel (250 ml) and the
resulting solution was then agitated for 30 seconds. The fracturing fluid,
i.e., agitated base gel containing crosslinker (25 ml), was placed into the
cup of the FANN 50 Viscometer, unless the fracturing had gelled in the
blender. The viscosity was measured at a continuous shear rate of 170
reciprocal seconds of shear and between 275-340 F (135-171 C).
Viscosity measurements were recorded after 10, 30, 60 and 90 minutes
when possible.
16
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O I I Q
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17
CA 02704542 2010-05-03
WO 2009/059160 PCT/US2008/082024
o o o LO 00 N o ~ LO
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18
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Results
Tables 1 and 2 provide Performance Results for Comparative
Examples and Examples of this invention. Tables 1 and 2 list the
zirconium crosslinker type, guar type and strength, brine used, the organic
acid, when used, temperatures, pH, and measured viscosity results for
each of the Comparative Examples and Examples of this invention. Guar
strength is measured in pptg (lbs per 1000 gal), and in weight % in
parentheses. "Zr loading" refers to the amount of zirconium added in parts
per million (ppm) based on the total weight of the fracturing fluid. The
viscosity measurements are measured in centipoise (cp) at time interval
indicated. Zirconium crosslinked base gels perform well if the gel remains
at acceptable viscosity levels for 90 minutes, for example, greater than
100 cp. Zirconium cross-linked gels are considered "failed" if viscosity is
less than 100 cp after 90 minutes or if viscosity is listed as "-", indicating
the viscosity was so low that the gel degraded during the measurements
(prior to the 90 minutes). Alternatively, the fracturing fluids failed if the
fracturing fluid gelled prior to measuring viscosity (i.e. Table recites,
"Gelled in blender").
Comparative Examples Al and A2 were base gels cross-linked with
zirconium lactate, also referred to as fracturing fluids, prepared using
conditions described in US Patent 4,801,389. The fracturing fluid had an
initial high viscosity but after 10 minutes, the viscosity was lower than
desired and the fracturing fluid failed before 20 minutes. The fracturing
fluids of Comparative Examples Al and A2 failed at 275 F (135 C) and
340 F 171 C), respectively.
A base gel cross-linked with zirconium lactate prepared according
to US Patent 6,737,386, but using HPG rather than natural guar, was used
in Comparative Example B. The fracturing fluid gelled immediately, so no
viscosity measurements . Surprisingly, the conditions which worked for
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natural guar in U.S. Patent 4,801,389 or 6,737,386 were not effective
when natural guar was replaced with the derivatized guar, HPG.
A base gel cross-linked with zirconium lactate prepared using
conditions in this invention using natural guar in place of HPG, was used
in Comparative Example E. Surprisingly, the crosslinking composition
gelled immediately.
Comparative Examples C1 and C2 were base gels prepared using
CMHPG and HPG, respectively, and cross-linked with alkanolamine
zirconate to produce fracturing fluids. The CMHPG-fluid performed well at
high temperatures through 90 minutes, but the HPG-fluid showed low
viscosity at 10 minutes and failed at 250 F. Thus, when it is desirable to
use HPG rather than CMHPG, or if CMHPG is not available, conditions
that work for CMHPG cannot always be used successfully with HPG.
Comparative Examples D1 and D2 were base gels prepared using
CMHPG and HPG, respectively, and cross-linked with triethanolamine
zirconate to produce fracturing fluids. The CMHPG-fluid performed well at
high temperatures through 60 minutes, but the HPG-fluid showed failed
after 10 minutes at 275 F (135 C). Again, these Comparative Examples
show HPG and CMHPG are not interchangeable in fracturing fluids.
Examples 1-8, fracturing fluids of this invention, were prepared
using HPG and zirconium lactate sodium salt, zirconium lactate
ammonium salt and alkanolamino zirconate at temperatures between 275
and 340 F (135 and 171 C). Examples 1-8 exhibited desirable viscosities
over the 90 minute time period (viscosity of greater than 100 cp after 90
minutes) and did not show premature degradation caused by shearing as
shown in Comparative Examples using HPG. Viscosity and maintenance
of viscosity over time, using HPG in the fracturing fluids of this invention
were comparable to each other at the high temperatures of the tests and
comparable to Comparative Examples that used CMHPG in fracturing
fluids using triethanolamine zirconates.
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Thus, it has been shown that fracturing fluids of this invention
comprising zirconium crosslinking agent, brine (KCI), a stabilizer, a non-
delayed alkaline buffer (sodium carbonate), an acid, a pH less than 9, and
a temperature in the range of 275-340 F (135-171 C) are useful as the
hydraulic fracturing fluids. These fracturing fluids may be used in the field
for fracturing or plugging of deep, hot wells in areas where HPG is the
predominant guar used.
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