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Description  |
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Many treatments and procedures are carried out in industry utilizing high
viscosity fluids to accomplish a number of purposes. For example, in the
oil industry, high viscosity aqueous well treating fluids are utilized in
treatments to increase the recovery of hydrocarbons from subterranean
formations such as by creating fractures in the formations, acidizing the
formations, etc. High viscosity aqueous fluids are also commonly utilized
in well completion procedures. For example, during the completion of a
well, a high viscosity aqueous completion fluid having a high density is
introduced into the well to maintain hydrostatic pressure on the formation
which is higher than the pressure exerted by fluids contained in the
formation thereby preventing the formation fluids from flowing into the
wellbore.
Heretofore, in preparing high viscosity treating fluids it has been
necessary to utilize a number of dry additives which are mixed with water
or other aqueous fluid at the job site. A number of disadvantages are
inherent in such mixing procedures, particularly when large volumes of
treating fluids are prepared. For example, special mixing equipment for
mixing the dry additives with water is required and problems such as
chemical dusting, uneven mixing, lumping of gels while mixing and extended
preparation and mixing time are involved. In addition, the mixing and
physical handling of large quantitites of dry chemicals require a great
deal of manpower, and where continuous mixing is required, the accurate
and efficient handling of chemicals such as salts, gelling agents, gel
breakers, fluid loss control additives, complexers and surfactants is
extremely difficult.
By the present invention an aqueous liquid concentrate of gelling agents
(hydratable polymers or copolymers which yield viscosity upon hydration),
salts and other additives is provided. The concentrate is inhibited from
yielding viscosity, i.e., the hydration rate of the gelling agent or
agents is retarded in a manner whereby the concentrate can be premixed and
stored either at the job site or at locations away from the job site. When
the concentrate is combined with additional water, either in a batch
mixing procedure or a continuous mixing procedure in a proper ratio and
under proper pH and/or temperature conditions, the inhibition of the
hydration of the gelling agent or agents contained in the concentrate is
reversed and a high viscosity aqueous fluid is produced. The concentrate
can also be utilized directly, i.e., to produce a high viscosity fluid
without the addition of water, and in such use the inhibition of the
hydration of the gelling agent or agents in the concentrate is reversed by
changing the pH or temperature of the concentrate. In some instances,
either when the concentrate is used directly or diluted with additional
water, the inhibition of the hydration of the gelling agent or agents
therein is reversed by combining a chemical with the concentrate which
reacts therewith to reverse or supplement the reversal of the inhibition.
Thus, the liquid gel concentrate of the present invention and the use
thereof for the preparation of high viscosity fluids substantially reduces
the manpower and equipment which has been heretofore required and obviates
the problems and disadvantages mentioned above.
The liquid gel concentrate of the present invention is comprised of water,
a hydratable polymer or mixture of polymers which yield viscosity upon
hydration and an inhibitor having the property of reversibly reacting with
the hydratable polymer or polymers in a manner whereby the rate of
hydration of the polymer is retarded. Upon a change in the pH condition of
the concentrate such as by dilution and/or the addition of pH changing
chemicals to the concentrate, upon increasing the temperature of the
concentrate, or upon the change of other selected condition of the
concentrate the inhibition reaction is reversed and the polymer or
polymers hydrate to yield viscosity.
Hydratable polymers which are suitable for use in accordance with the
present invention include polymers which contain, in sufficient
concentration and reactive position, one or more of the functional groups
hydroxyl, cis-hydroxyl, carboxyl, sulfate, sulfonate, amino or amide.
Particularly suitable such polymers are polysaccharides and derivatives
thereof which contain one or more of the following monosaccharide units:
galactose, mannose, glucoside, glucose, xylose, arabinose, fructose,
glucuronic acid or pyranosyl sulfate. Natural hydratable polymers
containing the foregoing functional groups and units include guar gum and
derivatives thereof, locust bean gum, tara, konjak, tamarind, starch,
cellulose and derivatives thereof, karaya, xanthan, tragacanth and
carrageenan.
Hydratable synthetic polymers and copolymers which contain the
above-mentioned functional groups and which can be utilized in accordance
with the present invention include, but are not limited to, polyacrylate,
polymethacrylate, polyacrylamide, maleic anhydride methylvinyl ether
copolymers, polyvinyl alcohol, and polyvinylpyrrolidone.
The following table sets forth the specific functional groups and
structural monosaccharide units contained in the polymers mentioned above.
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Monosaccharide Functional
Polymer Units Groups
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Guar Gum and
Galactose and Hydroxyl and cis-
Derivatives
Mannose hydroxyl
thereof
Locust Bean Gum
Galactose and Hydroxyl and cis-
Mannose hydroxyl
Tara Galactose and Hydroxyl and cis-
Mannose hydroxyl
Konjak Glucose and Mannose
Hydroxyl and cis-
hydroxyl
Tamarind Galactose, Xylose and
Hydroxyl
Glucose
Starch Glucose Hydroxyl
Cellulose Glucose Hydroxyl
Starch Glucose Hydroxyl, sulfate,
derivative sulfonate and carboxyl
Cellulose Glucose Hydroxyl, sulfate,
derivative sulfonate and carboxyl
Karaya Galactose Hydroxyl and carboxyl
Xanthan Glucose and Mannose
Hydroxyl, carboxyl
and cis-hydroxyl
Tragacanth Galactose, Xylose,
Hydroxyl, carboxyl
Arabinose, Fructose
and cis-hydroxyl
and Glucuronic Acid
Carrageenan
Galactose and Pyra-
Hydroxyl and sulfate
nosyl Sulfate
Polyacrylamide
-- Amide, carboxyl,
amino and sulfate
Polyacrylate
-- Carboxyl
Maleic anhydride
-- Carboxyl
methylvinyl ether
copolymers
Polyvinyl alcohol
-- Hydroxyl
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Various compounds can be utilized with the above-mentioned hydratable
polymers in an aqueous concentrate composition to inhibit or retard the
hydration rate of the polymers, and therefore, delay a viscosity increase
in the concentrate for a required period of time. Depending upon the
particular functional groups contained in the polymer, different
inhibitors react with the functional groups to inhibit hydration. For
example, inhibitors for cis-hydroxyl functional groups include compounds
containing multivalent metals which are capable of releasing the metal
ions in an aqueous solution, borates, silicates, and aldehydes. Examples
of the multivalent metal ions are chromium, zirconium, antimony, titanium,
iron (ferrous or ferric), tin, zinc and aluminum. Inhibitors for hydroxyl
functional groups include mono- and di-functional aldehydes containing
from about 1 to about 5 carbon atoms and multivalent metal salts that form
hydroxide. Multivalent metal salts or compounds can be utilized as
inhibitors for the hydroxyl functional groups in polyvinyl alcohol and
sulfate functional groups. Inhibitors for amides include aldehydes and
multivalent metal salts or compounds. Generally, any compound can be used
as an inhibitor for a hydratable polymer if the compound reacts or
otherwise combines with the polymer to cross-link, form a complex or
otherwise tie-up the functional groups of the polymer whereby the rate of
hydration of the polymer is retarded.
As stated above, the functional groups contained in the polymer or polymers
utilized must be in sufficient concentration and in a reactive position to
interact with the inhibitors. Preferred hydratable polymers which yield
high viscosities upon hydration, i.e., apparent viscosities in the range
of from about 10 centipoises to about 80 centipoises at a concentration in
the range of from about 10 lbs/1000 gals. to about 80 lbs/1000 gals. in
water, are guar gum and guar derivatives such as hydroxypropyl guar and
carboxymethylguar, cellulose derivatives such as hydroxyethylcellulose,
carboxymethylcellulose, and carboxymethylhydroxyethylcellulose, locust
bean gum, carrageenan gum and xanthan gum. Xanthan gum is a
biopolysaccharide produced by the action of bacteria of the genus
Xanthonomas. Generally, such polymers can be present in the aqueous
concentrate of this invention in an amount in the range of from about 100
to about 3000 lbs/1000 gals. of water used and the hydration of the
polymers can be inhibited or retarded by various inhibitors present in the
concentrate in an amount in the range of from about 0.03 to about 1000
lbs/ 1000 gals. of water used. The reversal of the inhibition of such
polymers by the inhibitors can be accomplished by a change in the pH of
the concentrate or by heating the concentrate to an appropriate
temperature, generally above about 140.degree. F. At lower concentrations
of inhibitor, the resulting concentrate is less retarded from hydration
and has a shorter storage life. At higher inhibitor concentrations, the
retardation and storage life are increased, but the retardation may be
more difficult to reverse, i.e., a greater change in pH or heating to a
higher temperature may be required.
Examples of some of the inhibitors which can be utilized depending upon the
particular polymer or polymers used in the concentrate are sodium
sulfite-sodium dichromate, aluminum sulfate, triethanol amine titanium
chelate, basic potassium pyroantimonate, zinc chloride, iron chloride, tin
chloride, zirconium oxychloride in hydrochloric acid solution, sodium
tetraborate and glyoxal. Basic compounds such as sodium hydroxide,
potassium hydroxide, amines and organic bases are utilized in certain of
the liquid gel concentrates of this invention to adjust the pH of the
concentrates to the range where the inhibitor or inhibitors utilized
inhibit the hydration of the polymer or polymers used. In addition, in
some of the concentrates, the basic compound or compounds function to
inhibit or supplement the inhibition of the polymer or polymers.
In order to give the liquid gel concentrate an initial viscosity,
preferably within the range of from about 15 centipoises to about 300
centipoises, whereby suspended materials in the concentrate are maintained
in suspension during the storage and handling thereof, a quantity of
hydrated polymer is preferably included in the concentrate. The same
polymer can be utilized to impart initial viscosity to the concentrate as
the inhibited polymer in the concentrate, but in this event, the quantity
of polymer utilized to impart initial viscosity to the concentrate must be
combined with the water used so that it will hydrate prior to combining
the inhibitor utilized and additional polymer. For those polymers where
hydration takes place most rapidly at pH conditions below neutral, a weak
acid such as fumaric can be added to the water-polymer mixture to lower
the pH thereof to the desired level. For those polymers where hydration
takes place most rapidly at a pH above neutral, a suitable base such as
sodium hydroxide can be added to the mixture.
An alternate and more preferred technique is to utilize a polymer for
imparting viscosity to the concentrate which is not inhibited by the
particular inhibitor utilized. In this technique, the polymer for
imparting initial viscosity to the concentrate does not have to be added
to the water prior to the inhibitor making the addition of other additives
to the concentrate less difficult. Other additives which can be utilized
in the concentrate include salts, surfactants, fluid loss control
additives, freezing point depressants such as alcohols, complexing agents,
etc.
A liquid gel concentrate of this invention is comprised of water,
hydroxypropyl guar present in the concentrate in an amount in the range of
from about 300 to about 3000 lbs/1000 gals. of water, sodium tetraborate
present in the concentrate in an amount in the range of from about 0.1 to
about 1000 lbs/1000 gals. of water and a base such as sodium hydroxide
present in the concentrate in an amount sufficient to adjust the pH
thereof to a value in the range of from about 9 to about 14. A more
preferred concentrate of this type contains hydroxypropyl guar in an
amount in the range of from about 500 to about 1500 lbs/1000 gals. of
water, most preferably from about 700 to about 900 lbs/1000 gals. of
water, sodium tetraborate in an amount in the range of from about 2 to
about 20 lbs/1000 gals. of water, most preferably from about 6 to about 12
lbs/1000 gals. of water, and a base such as sodium hydroxide present in an
amount to adjust the pH of the concentrate to a value in the range of from
about 9 to about 14. For the most preferred concentrate described above, a
quantity of sodium hydroxide of about 30-50 lbs/1000 gals. of water is
utilized.
In preparing the above-described concentrate, the sodium tetraborate
inhibitor is combined with the water used followed by the sodium hydroxide
to adjust the pH of the mixture to a value in the range of from about 9 to
about 14. The hydroxypropyl guar is then combined with the mixture to
produce an aqueous hydration inhibited concentrate having a storage life
in the range of from about 1 to about 90 days depending on the
quantitative ratio of hydratable polymer to inhibitor utilized. The sodium
tetraborate inhibitor retards the rate of hydration of the hydroxypropyl
guar in the concentrate, but hydration of the hydroxypropyl guar gradually
occurs with time. Thus, the effective storage life of the concentrate is
the time period between when the concentrate is initially prepared and
when the concentrate attains a viscosity such that it cannot effectively
be handled or pumped, i.e., a viscosity above about 500 centipoises. The
term "storage life" is used hereinafter to mean the time period between
preparation of a concentrate and when the concentrate reaches a viscosity
of about 500 centipoises.
If it is desired to impart initial viscosity to the above-described
concentrate, prior to combining other components of the concentrate with
the water used, fumaric or other acid can be combined with the water in an
amount sufficient to lower the pH thereof to a value less than about 6.5
followed by combining an initial quantity of hydroxypropyl guar therewith
in an amount in the range of from about 10 to about 25 lbs/1000 gals. of
water. The initially combined hydroxypropyl guar is allowed to hydrate to
produce a base fluid having a viscosity in the range of from about 3 to
about 15 centipoises.
When the concentrate is utilized to produce subterranean formation treating
fluids, it preferably contains one or more clay stabilizers such as
potassium chloride, sodium chloride, calcium chloride, ammonium chloride,
water soluble potassium and aluminum salts and/or compatible organic ionic
polymers. The clay stabilizer or stabilizers can be present in the
concentrate in amounts up to about 2500 lbs/1000 gals. of water. Other
additives such as alcohols to lower freezing point, surfactants, fluid
loss control agents, complexors, etc., can also be included in the
concentrate to bring about desired results.
In preparing the concentrate having initial viscosity, the acid and initial
quantity of hydroxypropyl guar for increasing the viscosity of the
concentrate are thoroughly mixed with the water used. If a clay stabilizer
such as potassium chloride is included in the concentrate, it is next
combined with the hydrated hydroxypropyl guar-water mixture. The sodium
tetraborate inhibitor is next combined with the mixture and the pH thereof
is adjusted to a value in the range of from about 9 to about 14 by
combining a base, e.g., sodium hydroxide therewith. The hydroxypropyl guar
to be inhibited by the sodium tetraborate is combined with the mixture
last to produce a concentrate having a viscosity in the range of from
about 10 to about 100 centipoises and having a storage life in the range
of from about 1 to about 90 days.
Another liquid gel concentrate of this invention is comprised of water,
hydrated hydroxyethylcellulose or other polymer which is inhibited by
sodium tetraborate-decahydrate present in the concentrate in an amount in
the range of from about 10 to about 80 lbs/1000 gals. of water,
hydroxypropyl guar present in the concentrate in an amount in the range of
from about 300 to about 3000 lbs/1000 gals. of water, sodium tetraborate
inhibitor present in the concentrate in an amount in the range of from
about 0.1 to about 1000 lbs/1000 gals. of water and a base, e.g., sodium
hydroxide present in the concentrate in an amount sufficient to adjust the
pH thereof to a value in the range of from about 9 to about 14. A more
preferred concentrate of this type contains hydroxypropyl guar in an
amount in the range of from about 500 to about 1500 lbs/1000 gals. of
water, most preferably from about 700 to about 900 lbs/1000 gals. of
water, and sodium tetraborate in an amount in the range of from about 2 to
about 20 lbs/1000 gals. of water, most preferably from about 6 to about 12
lbs/1000 gals. of water. If desired, the concentrate can include a clay
stabilizer in an amount up to about 2500 lbs/1000 gals. of water and other
additives of the type mentioned above.
In preparing the foregoing concentrate, the hydroxyethylcellulose or other
uninhibited polymer utilized to impart initial viscosity to the
concentrate can be combined therewith last. A preferred procedure for
preparing this concentrate is to first combine the clay stabilizer, if
included, with the water utilized, followed by the addition of the sodium
tetraborate inhibitor to the water-stabilizer mixture. The sodium
hydroxide or other base is next combined with the mixture followed by the
hydroxypropyl guar. After hydroxypropyl guar has been combined with the
mixture, the hydroxyethylcellulose or other uninhibited polymer is
combined therewith. If a fluid loss control additive is included in the
concentrate it is preferably combined with the mixture prior to the
hydroxyethylcellulose to minimize mixing difficulties, and if a surfactant
is included, it is preferably combined with the concentrate after the
hydroxyethylcellulose to minimize foaming. The resulting liquid gel
concentrate has an initial viscosity in the range of from about 10 to
about 100 centipoises and a storage life of from about 1 to about 90 days.
Yet another liquid gel concentrate of the present invention is comprised of
water, guar gum present in the concentrate in an amount in the range of
from about 300 to about 1500 lbs/1000 gals. of water, aluminum sulfate
present in the concentrate in an amount in the range of from about 20 to
about 350 lbs/1000 gals. of water, and a base, e.g., sodium hydroxide
present in the concentrate in an amount sufficient to adjust the pH
thereof to a value in the range of from about 9 to about 13. A more
preferred concentrate of this type contains guar gum in an amount in the
range of from about 500 to about 1000 lbs/1000 gals. of water, most
preferably from about 700 to about 900 lbs/1000 gals. of water, and
aluminum sulfate in an amount in the range of from about 100 to about 300
lbs/1000 gals. of water, most preferably from about 200 to about 300
lbs/1000 gals. of water.
In preparing the guar gum-aluminum sulfate concentrate, the aluminum
sulfate is combined with the water used first, followed by the addition of
the base followed by the addition of the guar gum. The concentrate can
also include hydrated hydroxyethylcellulose or other polymer which is
uninhibited by aluminum sulfate to impart initial viscosity thereto in an
amount in the range of from about 10 to about 80 lbs/1000 gals. of water
as well as other additives. As described above in connection with the
hydroxypropyl guar-sodium tetraborate concentrate, the
hydroxyethylcellulose or other uninhibited polymer can be added to the
concentrate last to produce a concentrate having an initial viscosity in
the range of from about 10 to about 100 centipoises and a storage life of
from about 1 to about 90 days.
Still another liquid gel concentrate of this invention is comprised of
water, carboxymethylcellulose present in the concentrate in an amount in
the range of from about 300 to about 3000 lbs/1000 gals. of water and
aluminum sulfate present in the concentrate in an amount in the range of
from about 75 to about 750 lbs/1000 gals. of water. The resulting
concentrate has a pH in the range of from about 2.5 to about 4.5 and the
inhibition of the hydration of the carboxymethylcellulose by the aluminum
sulfate can be reversed by increasing the pH as will be described further
hereinbelow. A more preferred concentrate of this type contains
carboxymethylcellulose in an amount in the range of from about 500 to
about 1500 lbs/1000 gals. of water, most preferably from about 700 to
about 1100 lbs/1000 gals. of water and aluminum sulfate in an amount in
the range of from about 100 to about 375 lbs/1000 gals. of water, most
preferably from about 150 to about 250 lbs/1000 gals. of water.
In preparing this concentrate, the aluminum sulfate inhibitor is first
combined with the water used followed by the addition of the
carboxymethylcellulose to produce a concentrate having a storage life of
from about 1 to about 120 days. Like the other concentrates described
above, the carboxymethylcellulose-aluminum sulfate concentrate can include
hydrated hydroxyethylcellulose or other polymer which is uninhibited by
aluminum sulfate to impart initial viscosity thereto present in the
concentrate in an amount in the range of from about 10 to about 80
lbs/1000 gals. of water as well as other additives. The resulting liquid
gel concentrate has an initial viscosity in the range of from about 10 to
about 100 centipoises.
In utilizing the above-described liquid gel concentrates to produce a large
volume of highly viscous treating fluid, the concentrate is diluted with
additional water and the pH of the resulting fluid is lowered or raised or
the fluid is heated whereby the innibition reaction between the hydratable
polymer and inhibitor contained in the concentrate is reversed and the
hydratable polymer yields viscosity. In order to reverse the inhibition of
concentrates such as the hydroxypropyl guar-sodium tetraborate concentrate
and guar gum-aluminum sulfate concentrates described above, the pH can be
lowered to a value in the range of from about 5 to about 9 during or after
the concentrate is diluted with water by combining an acid therewith. In
order to reverse the inhibition of concentrates such as the
carboxymethylcellulose-aluminum sulfate concentrate described above, the
pH can be raised to a value in the range of from about 8 to about 13
during or after the concentrate is diluted with water by combining a base
therewith. As stated above, the liquid concentrates can be utilized to
form a high viscosity fluid without dilution with additional water, and in
this event, the same procedure as described above can be used to reverse
the inhibition of the concentrates. As also stated above, the concentrates
or diluted concentrates can be caused to yield viscosity by heating to a
temperature of about 140.degree. F. without changing the pH thereof.
Higher temperatures may be required depending upon the particular
polymer-inhibitor combination used.
A preferred method of utilizing the liquid concentrates of this invention
in the treatment of subterranean formations is to mix the concentrate used
with additional water containing a quantity of acid such as acetic acid or
a base such as sodium carbonate or sodium hydroxide whereby the pH of the
resulting mixture is changed to an appropriate value for reversing the
inhibition reaction. The mixing of the concentrate with the additional
water containing acid or base can be carried out in a batch process or a
continuous process. Preferably, the mixing of the concentrate with
additional water containing acid or base is carried out continuously as
the high viscosity treating fluid produced is introduced into the
formation. If the formation to be treated has a temperature such that the
diluted gel concentrate will be heated to an appropriate temperature and
the treatment lends itself to allowing the treating fluid to heat up prior
to yielding viscosity, the pH of the fluid need not be adjusted prior to
introducing the fluid into the formation. The particular quantity of water
combined with the concentrate depends on the quantity and type of
hydratable polymer contained in the concentrate as well as the viscosity
of the resulting treating fluid. By way of example, a concentrate
containing 800 lbs. of hydroxypropyl guar per 1000 gallons of water can be
diluted with 15 parts of additional water per part of concentrate to
produce a fluid having a viscosity in the range of from about 30 to about
35 centipoises.
Examples of other hydratable polymer-inhibitor combinations which can be
utilized in the aqueous gel concentrates of this invention and which are
pH and/or temperature reversible are as follows:
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Polymer or Polymers Inhibitor
______________________________________
Guar gum Sodium sulfite and sodium
dichromate mixture
Guar Gum and Hydroxypropyl guar
Sodium sulfite and sodium
dichromate mixture
Hydroxypropyl guar and carra-
Sodium hydroxide
geenan gum
Guar gum and hydroxypropyl guar
Basic potassium
pyroantimonate
Guar gum and hydroxypropyl guar
Zinc chloride
Guar gum and hydroxypropyl guar
Iron chloride
Guar gum Iron chloride
Hydroxypropyl guar and locust
Tin chloride
bean gum
Hydroxypropyl guar, locust bean
Zirconium oxychloride in
gum and carrageenan gum
hydrochloric acid solution
Guar gum, hydroxypropyl guar and
Sodium silicate
carrageenan gum
Guar, hydroxypropyl guar, locust
Sodium tetraborate
bean gum and carrageenan gum
Hydroxypropyl guar, hydroxyethyl-
Glyoxal
cellulose, and xanthan gum
Polyacrylate Chrome alum
polyacrylamide Chrome alum
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The liquid gel concentrates of this invention and high viscosity fluids
produced therefrom can be utilized in a great variety of applications
including, but not limited to, suspending explosive materials used in
mining, drilling and other similar applications, carrying out production
stimulation procedures in oil, gas and water wells, carrying out
subterranean well completions, transporting proppant or other materials
into desired areas in subterranean well formations, diverting fluids in
subterranean well formations and carrying out cleaning procedures such as
in cleaning tubular goods, production equipment and industrial equipment.
The high viscosity aqueous fluids produced using the liquid gel
concentrates are particularly suitable as treating fluids in carrying out
subterranean well formation acidizing, fracturing, fracture-acidizing and
other procedures. In these applications, the liquid gel concentrates of
this invention provide particular advantages in addition to those
mentioned above. More particularly, a variety of techniques can be
utilized to control the viscosity of the treating fluids produced from the
liquid gel concentrates during use. For example, when concentrates are
utilized which yield viscosity, i.e., the inhibition reaction is reversed,
upon changing the pH of the concentrates as well as upon heating the
concentrates and with the passage of time, the pH of the concentrates can
be changed at the surface to a level whereby only partial hydration of t | | |
