U.S. patent application number 10/094042 was filed with the patent office on 2002-07-18 for foamed fracturing fluids, additives and methods of fracturing subterranean zones.
Invention is credited to Chatterji, Jiten, Crook, Ron, King, Karen L..
Application Number | 20020092652 10/094042 |
Document ID | / |
Family ID | 24798993 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020092652 |
Kind Code |
A1 |
Chatterji, Jiten ; et
al. |
July 18, 2002 |
Foamed fracturing fluids, additives and methods of fracturing
subterranean zones
Abstract
The present invention provides environmentally safe foamed
fracturing fluids, additives for foaming and stabilizing foamed
fracturing fluids and methods of fracturing subterranean zones. The
foamed fracturing fluids of this invention are basically comprised
of water, a gelling agent for forming the water into gelled water
and increasing the viscosity thereof, sufficient gas to form a
foam, and an effective amount of an additive for foaming and
stabilizing the gelled water comprised of hydrolyzed keratin.
Inventors: |
Chatterji, Jiten; (Duncan,
OK) ; Crook, Ron; (Duncan, OK) ; King, Karen
L.; (Duncan, OK) |
Correspondence
Address: |
Robert A. Kent
Halliburton Energy Services
2600 South 2nd Street
Duncan
OK
73536
US
|
Family ID: |
24798993 |
Appl. No.: |
10/094042 |
Filed: |
March 8, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10094042 |
Mar 8, 2002 |
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09696902 |
Oct 25, 2000 |
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6367550 |
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Current U.S.
Class: |
166/308.5 ;
166/309; 507/202; 507/215; 507/216; 507/217; 507/922 |
Current CPC
Class: |
C04B 22/0026 20130101;
C04B 22/147 20130101; C04B 38/10 20130101; Y10S 507/922 20130101;
C09K 8/905 20130101; C09K 8/703 20130101; C04B 24/14 20130101; C04B
40/0039 20130101; C04B 2111/00017 20130101; C04B 24/14 20130101;
C04B 28/02 20130101; C04B 38/10 20130101; Y10S 507/903 20130101;
C09K 8/473 20130101; C04B 40/0039 20130101; C04B 2111/00146
20130101; Y10S 507/924 20130101; C04B 28/02 20130101; C09K 8/46
20130101; C09K 8/685 20130101; C04B 22/143 20130101; C04B 20/023
20130101; C04B 22/124 20130101; C04B 24/02 20130101; C04B 22/142
20130101; C04B 24/14 20130101; C04B 24/14 20130101 |
Class at
Publication: |
166/308 ;
166/309; 507/202; 507/215; 507/216; 507/217; 507/922 |
International
Class: |
E21B 043/26; C09K
003/00 |
Claims
What is claimed is:
1. An improved foamed fracturing fluid for forming fractures in a
subterranean zone comprising: water; a gelling agent for forming
said water into gelled water and increasing the viscosity thereof,
sufficient gas to form a foam; and an effective amount of an
additive for foaming and stabilizing said gelled water comprised of
hydrolyzed keratin.
2. The foamed fracturing fluid of claim 1 wherein said water is
selected from the group consisting of fresh water and salt
water.
3. The foamed fracturing fluid of claim 1 wherein said gelling
agent is selected from the group consisting of galactomannans,
cellulose derivatives and biopolymers.
4. The foamed fracturing fluid of claim 1 wherein said gelling
agent is a galactomannan selected from the group consisting of
guar, hydroxypropylguar and carboxymethylhydroxypropylguar.
5. The foamed fracturing fluid of claim 1 wherein said gelling
agent is a cellulose derivative selected from the group consisting
of hydroxyethylcellulose, carboxymethylhydroxyethylcellulose and
hydroxyethylcellulose grafted with vinyl phosphonic acid.
6. The foamed fracturing fluid of claim 1 wherein said gelling
agent is xanthan gum.
7. The foamed fracturing fluid of claim 1 wherein said gelling
agent in said foamed fracturing fluid is present in an amount in
the range of from about 0.125% to about 0.375% by weight of said
water therein.
8. The foamed fracturing fluid of claim 1 wherein said gas is
selected from the group of air and nitrogen.
9. The foamed fracturing fluid of claim 1 wherein said gas in said
foamed fracturing fluid is present in an amount in the range of
from about 20% to about 80% by volume of water therein.
10. The foamed fracturing fluid of claim 1 wherein said hydrolyzed
keratin in a 40% by weight aqueous solution is present in said
foamed fracturing fluid in an amount in the range of from about
0.2% to about 1.0% by volume of water therein.
11. The foamed fracturing fluid of claim 1 which further comprises
a cross-linking agent for cross-linking said gelled water.
12. The foamed fracturing fluid of claim 11 wherein said
cross-linking agent is selected from the group consisting of boron
compounds and compounds that can supply zirconium IV ions, titanium
IV ions, aluminum ions and antimony ions.
13. The foamed fracturing fluid of claim 11 wherein said
cross-linking agent in said foamed fracturing fluid is present in
an amount in the range of from about 0.001% to about 0.1% by weight
of said gelling agent therein.
14. The foamed fracturing fluid of claim 1 which further comprises
a foam viscosity and stability increasing additive selected from
the group consisting of iodine, hydrogen peroxide, cupric sulfate
and zinc bromide.
15. A method of fracturing a subterranean zone penetrated by a well
bore comprising the steps of: (a) preparing a foamed fracturing
fluid comprised of water, a gelling agent for forming said water
into gelled water and thereby increasing the viscosity of said
water, sufficient gas to form a foam and an effective amount of an
additive for foaming and stabilizing said gelled water comprised of
hydrolyzed keratin; and (b) contacting said subterranean zone with
said foamed fracturing fluid under conditions effective to create
at least one fracture therein.
16. The method of claim 15 wherein said water in said foamed
fracturing fluid is selected from the group consisting of fresh
water and salt water.
17. The method of claim 15 wherein said gelling agent in said
foamed fracturing fluid is selected from the group consisting of
galactomannans, cellulose derivatives and biopolymers.
18. The method of claim 15 wherein said gelling agent in said
foamed fracturing fluid is a galactomannan selected from the group
consisting of guar, hydroxypropylguar and
carboxymethylhydroxypropylguar.
19. The method of claim 15 wherein said gelling agent in said
foamed fracturing fluid is a cellulose derivative selected from the
group consisting of hydroxyethylcellulose,
carboxymethylhydroxyethylcellulose and hydroxyethylcellulose
grafted with vinyl phosphonic acid.
20. The method of claim 15 wherein said gelling agent in said
foamed fracturing fluid is xanthan gum.
21. The method of claim 15 wherein said gelling agent in said
foamed fracturing fluid is present in an amount in the range of
from about 0.125% to about 0.375% by weight of said water
therein.
22. The method of claim 15 wherein said gas in said foamed
fracturing fluid is selected from the group of air and
nitrogen.
23. The method of claim 15 wherein said gas in said foamed
fracturing fluid is present in an amount in the range of from about
20% to about 80% by volume of water therein.
24. The method of claim 15 wherein said hydrolyzed keratin in a 40%
by weight aqueous solution is present in said foamed fracturing
fluid in an amount in the range of from about 0.2% to about 1.0% by
volume of water therein.
25. The method of claim 15 wherein said foamed fracturing fluid
further comprises a cross-linking agent for cross-linking said
gelled water.
26. The method of claim 25 wherein said cross-linking agent in said
foamed fracturing fluid is selected from the group consisting of
boron compounds and compounds that can supply zirconium IV ions,
titanium IV ions, aluminum ions and antimony ions.
27. The method of claim 25 wherein said cross-linking agent in said
foamed fracturing fluid is present in an amount in the range of
from about 0.001% to about 0.1% by weight of said gelling agent
therein.
28. The method of claim 15 wherein said foamed fracturing fluid
further comprises a foam viscosity and stability increasing
additive selected from the group consisting of iodine, hydrogen
peroxide, cupric sulfate and zinc bromide.
29. The method of claim 15 wherein said foamed fracturing fluid
further comprises proppant material.
30. The method of claim 29 wherein said proppant material is
selected from the group consisting of resin coated or uncoated
sand, sintered bauxite, ceramic materials and glass beads.
31. The method of claim 30 wherein said proppant material in said
foamed fracturing fluid is present in an amount in the range of
from about 1 to about 10 pounds of proppant material per gallon of
said foamed fracturing fluid.
32. An additive for foaming and stabilizing a gelled water
fracturing fluid containing gas comprising hydrolyzed keratin.
33. The additive of claim 32 which further comprises water present
in an amount sufficient to dissolve said hydrolyzed keratin.
34. The additive of claim 33 wherein said water is present in an
amount such that the resulting solution contains hydrolyzed keratin
in an amount of about 40% by weight of said solution.
35. The additive of claim 34 wherein said solution further
comprises one or more freezing and pour point depressants therein.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of application
Ser. No. 09/696,902 filed on Oct. 25, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to foamed fracturing fluids,
additives for foaming the fracturing fluids and methods of using
the fracturing fluids.
[0004] 2. Description of the Prior Art
[0005] Viscous gelled fracturing fluids are commonly utilized in
the hydraulic fracturing of subterranean zones penetrated by well
bores to increase the production of hydrocarbons from the
subterranean zones. That is, a viscous fracturing fluid is pumped
through the well bore into a subterranean zone to be stimulated at
a rate and pressure such that fractures are formed and extended
into the subterranean zone. The fracturing fluid also carries
particulate proppant material, e.g., graded sand, into the formed
fractures. The proppant material is suspended in the viscous
fracturing fluid so that the proppant material is deposited in the
fractures when the viscous fracturing fluid is broken and
recovered. The proppant material functions to prevent the fractures
from closing whereby conductive channels are formed through which
produced fluids can flow to the well bore.
[0006] After the viscous fracturing fluid has been pumped into a
subterranean zone in a formation and fracturing of the zone has
taken place, the fracturing fluid is removed from the formation to
allow produced hydrocarbons to flow through the created fractures.
Generally, the removal of the viscous fracturing fluid is
accomplished by converting the fracturing fluid into a low
viscosity fluid. This has been accomplished by adding a delayed
breaker, i.e., a viscosity reducing agent, to the fracturing fluid
prior to pumping it into the subterranean zone. Examples of delayed
breakers that can be used include, but are not limited to, enzymes,
acids and oxidizing agents.
[0007] In carrying out hydraulic fracturing, the fracturing fluids
must often be lightweight to prevent excessive hydrostatic pressure
from being exerted on subterranean formations penetrated by the
well bore. As a result, a variety of lightweight fracturing fluids
have heretofore been developed and used including foamed fracturing
fluids.
[0008] Foamed fracturing fluids have heretofore included various
surfactants known as foaming and foam stabilizing agents for
facilitating the foaming and stabilization of the foam produced
when a gas is mixed with the fracturing fluid. However, the foaming
and stabilizing surfactants have not met complete environmental
requirements. That is, when the foaming and stabilizing surfactants
find their way into water in the environment, they do not fully
degrade which can result in interference with aquatic life
cycles.
[0009] Thus, there are needs for improved foamed fracturing fluids,
improved fracturing fluid foaming and stabilizing additives which
degrade completely in the environment and are harmless thereto and
improved methods of utilizing the foamed fracturing fluids.
SUMMARY OF THE INVENTION
[0010] The present invention provides improved foamed fracturing
fluids, improved foaming additives for foaming and stabilizing the
fracturing fluids which are harmless to the environment and methods
of using the improved foamed fracturing fluids which meet the needs
described above and overcome the deficiencies of the prior art. The
improved foamed fracturing fluids for forming fractures in
subterranean zones are basically comprised of water, a gelling
agent for forming the water into gelled water and increasing the
viscosity thereof, sufficient gas to form a foam and an effective
amount of an environmentally harmless additive for foaming and
stabilizing the gelled water comprised of hydrolyzed keratin.
[0011] The gelled water fracturing fluid foaming and stabilizing
additive of this invention which is harmless to the environment is
hydrolyzed keratin. The additive is preferably predissolved in
water to form an aqueous solution which is added to a fracturing
fluid to be foamed along with a gas for foaming the fracturing
fluid.
[0012] The methods of the present invention for fracturing
subterranean zones penetrated by well bores are basically comprised
of the following steps. A foamed fracturing fluid comprised of
water, a gelling agent for forming the water into gelled water and
thereby increasing the viscosity of the water, sufficient gas to
form a foam and an effective amount of an additive for foaming and
stabilizing the gelled water comprised of hydrolyzed keratin.
Thereafter, the subterranean zone is contacted with the foamed
fracturing fluid under conditions effective to create at least one
fracture therein.
[0013] The objects, features and advantages of the present
invention will be readily apparent to those skilled in the art upon
a reading of the description of preferred embodiments which
follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0014] The improved foamed fracturing fluids of this invention are
useful for fracturing subterranean zones penetrated by well bores
to increase the production of hydrocarbons therefrom. The foamed
fracturing fluids are basically comprised of water, a gelling agent
for forming the water into gelled water and increasing the
viscosity thereof, sufficient gas to form a foam and an effective
amount of an environment harmless additive for foaming and
stabilizing the gelled water comprised of hydrolyzed keratin.
[0015] The water utilized for forming the foamed fracturing fluid
of this invention can be fresh water or salt water. The term "salt
water" is used herein to mean unsaturated salt solutions and
saturated salt solutions including brines and seawater. The gelling
agent is added to the water for forming the water into gelled water
and increasing the viscosity thereof. A variety of gelling agents
can be used including natural or derivatized polysaccharides which
are soluble, dispersible or swellable in an aqueous liquid to yield
viscosity to the aqueous liquid. One group, for example, of
polysaccharides which are suitable for use in accordance with the
present invention includes galactomannan gums such as gum arabic,
gum ghatti, gum karaya, tamarind gum, tragacanth gum, guar gum,
locust beam gum and the like. Modified gums such as carboxyalkyl
derivatives, like carboxymethylguar and hydroxyalkyl derivatives,
like hydroxypropylguar can also be employed. Doubly derivatized
gums such as carboxymethylhydroxypropylguar can also be used.
[0016] Modified celluloses and derivatives thereof can also be
employed as gelling agents in accordance with the present
invention. Examples of water-soluble cellulose ethers which can be
used include, but are not limited to, carboxymethylcellulose,
carboxymethylhydroxyethylcellulose, hydroxyethylcellulose,
methylhydroxypropylcellulose, methylcellulose, ethylcellulose,
propylcellulose, ethylcarboxymethylcellulose, methylethylcellulose,
hydroxypropylmethylcellulose and the like. Of these,
hydroxyethylcellulose and carboxymethylhydroxyethylcellulose are
preferred. The most preferred cellulose derivative is
hydroxyethylcellulose grafted with vinyl phosphonic acid as
described in U.S. Pat. No. 5,067,565 issued on Nov. 26, 1991 to
Holtmyer et al., the disclosure of which is incorporated herein by
reference.
[0017] Other gelling agents which can be used include, but are not
limited to, biopolymers such as xanthan gum, welan gum and a
biopolymer commercially available from Halliburton Energy Services
of Duncan, Okla. under the tradename "FloBack.TM.". Of these,
xanthan biopolymer is preferred.
[0018] Additional gelling agents include water dispersible
hydrophillic organic polymers having molecular weights greater than
100,000 such as polyacrylamide and polymethacrylamide wherein about
5% to about 75% of the carboxamides are hydrolyzed to carboxyl
groups and a copolymer of about 5% to about 70% by weight acrylic
acid or methacrylic acid copolymerized with acrylamide or
methacrylamide. These water dispersible organic hydrophillic
polymers can be cross-linked with a cross-linking composition
comprising water, a zirconium compound having a valence of 4.sup.+,
an alpha-hydroxy acid and an amine compound as more fully described
in U.S. Pat. No. 4,524,829 issued to Hanlon et al. on Jun. 25, 1985
which is incorporated herein by reference.
[0019] Still other gelling agents which can be used include, but
are not limited to, a chelated organic gelling agent comprised of a
metal ion chelated water soluble polyalkylene imine, such as
polyethylene or polypropylene imine, and a water soluble polymer
capable of being cross-linked by the gelling agent. Such polymers
capable of being cross-linked by the gelling agent include a
terpolymer of an ethylenically unsaturated polar monomer, an
ethylenically unsaturated ester and a monomer selected from
2-acrylamido-2-methylpropane sulfonic acid (AMPS.RTM.) or
N-vinylpyrrolidone or a tetrapolymer of an ethylenically
unsaturated polar monomer, an ethylenically unsaturated ester,
AMPS.RTM. and N-vinylpyrrolidone as more fully described in U.S.
Pat. No. 6,196,317 B1 issued to Hardy on Mar. 6, 2001 which is
incorporated herein by reference. Polymerizable water soluble
monomers such as acrylic acid, methacrylic acid, acrylamide,
methacrylamide and the like cross-linked with a cross-linker
selected from glycerol dimethacrylate, glycerol diacrylate and
others can also be utilized as more fully described in U.S. Pat.
No. 5,335,726 issued to Rodrigues on Aug. 9, 1994 which is
incorporated herein by reference.
[0020] Of the foregoing gelling agents, a gelling agent selected
from the group consisting of galactomannans, cellulose derivatives
and biopolymers are preferred. Of the galactomannans that can be
utilized, guar, hydroxypropylguar and
carboxymethylhydroxypropylguar are preferred. Of the cellulose
derivatives that can be utilized, hydroxyethylcellulose,
carboxymethylhydroxyethylcellulose and hydroxyethylcellulose
grafted with vinyl phosphonic acid are preferred. Of the
biopolymers which can be utilized, xanthan gum is preferred. The
gelling agent utilized in the foamed fracturing fluid of this
invention is generally included in the foamed fracturing fluid in
an amount in the range of from about 0.125% to about 0.375% by
weight of the water therein.
[0021] The gas utilized for forming the foamed fracturing fluid can
be air or nitrogen, with nitrogen being preferred. The gas is
present in an amount sufficient to foam the fracturing fluid,
generally in an amount in the range of from about 20% to about 80%
by volume of the water therein.
[0022] The environmentally harmless hydrolyzed keratin additive for
foaming and stabilizing a gelled water fracturing fluid is
manufactured by the base hydrolysis of hoof and horn meal. That is,
the hoof and horn meal is heated with lime in an autoclave to
produce a hydrolyzed protein. The protein is commercially available
as a free-flowing powder that contains about 85% protein. The
non-protein portion of the powder consists of about 0.58% insoluble
material with the remainder being soluble non-protein materials
primarily made up of calcium sulfate, magnesium sulfate and
potassium sulfate.
[0023] The hydrolyzed keratin protein powder is preferably
predissolved in fresh water in an amount of about 40% by weight of
the solution. In addition to water for dissolving the hydrolyzed
keratin, the additive can include other components such as one or
more freezing and pour point depressants to prevent it from
freezing during storage or handling in cold weather and lower its
pour point. Preferably, such depressants are selected from the
group of propylene glycol, sodium chloride and mixtures thereof.
The depressant or depressants utilized are generally present in the
additive solution in an amount in the range of from about 0.1% to
about 0.125% by weight of the solution.
[0024] The hydrolyzed keratin in a 40% by weight aqueous solution
is preferably included in a foamed fracturing fluid of this
invention in an amount in the range of from about 0.2% to about
1.0% by volume of water in the foamed fracturing fluid.
[0025] In order to further enhance the development of the viscosity
of the gelled water in the foamed fracturing fluid of this
invention, the gelling agent utilized can be cross-linked by a
cross-linking agent added to the gelled water. The cross-linking
agent can comprise a borate releasing compound or any of the well
known transition metal ions which are capable of creating a
cross-linked structure with the particular gelling agent utilized.
Preferred cross-linking agents for use with the above described
gelling agents include, but are not limited to, borate releasing
compounds, a source of zirconium IV ions, a source of titanium IV
ions, a source of aluminum ions and a source of antimony ions. When
used, the cross-linking agent is included in the gelled water in an
amount in the range of from about 0.001% to about 0.1% by weight of
the gelling agent therein.
[0026] When it is desirable to increase the viscosity and stability
of a foamed fracturing fluid of this invention even further, a foam
viscosity and stability increasing additive can be included in the
foamed fracturing fluid. Examples of such foam viscosity and
stability increasing additives include, but are not limited to,
iodine, hydrogen peroxide, cupric sulfate and zinc bromide.
[0027] As mentioned, the foamed fracturing fluid can also include a
proppant material for preventing formed fractures from closing. A
variety of proppant materials can be utilized including, but not
limited to, resin coated or un-coated sand, sintered bauxite,
ceramic materials and glass beads. When included, the proppant
material is generally present in the foamed fracturing fluid in an
amount in the range of from about 1 to about 10 pounds of proppant
material per gallon of the foamed fracturing fluid.
[0028] The methods of the present invention for fracturing a
subterranean zone penetrated by a well bore are basically comprised
of the following steps. A foamed fracturing fluid comprised of
water, a gelling agent for forming the water into gelled water and
thereby increasing the viscosity of the water, sufficient gas to
form a foam and an effective amount of an additive for foaming and
stabilizing the gelled water comprised of hydrolyzed keratin.
Thereafter, the subterranean zone is contacted with the foamed
fracturing fluid under conditions effective to create at least one
fracture therein.
[0029] A preferred foamed fracturing fluid of this invention for
forming fractures in a subterranean zone comprises: water; a
gelling agent selected from the group consisting of galactomannans,
cellulose derivatives and biopolymers for forming the water into
gelled water and increasing the viscosity thereof; sufficient
nitrogen to form a foam and an effective amount of an additive for
foaming and stabilizing the gelled water comprised of hydrolyzed
keratin.
[0030] A preferred method of this invention for fracturing a
subterranean zone penetrated by a well bore comprises the steps of:
(a) preparing a foamed fracturing fluid comprised of water, a
gelling agent selected from the group consisting of galactomannans,
cellulose derivatives and biopolymers for forming the water into
gelled water and thereby increasing the viscosity of the water,
sufficient nitrogen to form a foam and an effective amount of an
additive for foaming and stabilizing the gelled water comprised of
hydrolyzed keratin; and (b) contacting the subterranean zone with
the foamed fracturing fluid under conditions effective to create at
least one fracture therein.
[0031] In order to further illustrate the improved foamed
fracturing fluids, additives and methods of this invention, the
following examples are given.
EXAMPLE 1
[0032] One liter of tap water was placed in a Waring blender and 2%
potassium chloride was added. 2.4 grams of hydroxypropyl guar (20
pounds per 1000 gallons) were stirred into the 2% potassium
chloride solution. The solution was adjusted to a pH of 6.0 by the
addition of sodium diacetate. The solution was stirred vigorously
for 20 minutes to allow the guar to hydrate fully. The gel yielded
a viscosity of 12 centipoises at 300 rpm on a Fann model 35
viscometer.
[0033] 100 milliliters of the hydrated gel were placed in a Waring
blender jar. 0.5 milliliters of keratin foaming agent were added to
the blender jar at a very low blender speed to give the foam
sufficient time to build. The speed of the blender and the shear
rate were increased until the foam reached a maximum height in the
blender jar. 60 grams of 20/40 sand (5 pounds per gallon) were
added to the blender jar with stirring to equally disperse the sand
throughout the foam.
[0034] The resulting 70 quality foam was poured into a 500
milliliter graduated cylinder so that settling of the sand could be
observed. Approximately 5% of the 20/40 sand settled after one hour
at room temperature. Stated another way, 95% of the 20/40 sand
stayed suspended in the foam for one hour.
EXAMPLE 2
[0035] One liter of tap water was placed in a Waring blender and 2%
potassium chloride was added. 2.4 grams of hydroxypropyl guar (220
pounds per 1000 gallons) were stirred into the 2% potassium
chloride solution. The solution was adjusted to a pH of 6.0 by the
addition of sodium diacetate. The solution was stirred vigorously
for 20 minutes to allow the guar to hydrate fully. The gel yielded
a viscosity of 12 centipoises at 300 rpm on a Fann model 35
viscometer.
[0036] A solution of 10 milliliters of tap water, a foam stabilizer
comprised of 2 grams of potassium iodine and 1.66 grams of iodine
was prepared. 100 milliliters of the above described hydrated gel
were placed in a Waring blender jar and stirring was started. 0.5
milliliters of the above described foam stabilizer were added and
allowed to disperse followed by the addition of 0.5 milliliters of
keratin foaming agent added at a very low blender speed to give the
foam sufficient time to build. The mixing and the shear rate were
increased until the foam reached the maximum height in the blender
jar. 60 grams of 20/40 sand were added while stirring to allow the
sand to be equally dispersed throughout the foam.
[0037] The resulting 70 quality foam containing the dispersed sand
was poured into a 500 milliliter graduated cylinder to observe sand
settling. Trace quantities of the 20/40 sand settled after one hour
at room temperature. Stated another way, greater than 99% of the
20/40 sand stayed suspended in the foam for one hour.
[0038] Thus, the present invention is well adapted to carry out the
objects and attain the ends and advantages mentioned as well as
those which are inherent therein. While numerous changes may be
made by those skilled in the art, such changes are encompassed
within the spirit of this invention as defined by the appended
claims.
* * * * *