Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
STABLE FOAMS AND METHODS OF USE
This invention pertains to novel foams and
methods of use. This invention pertains in particular
to novel ~oams having enhanced stability and their use
in treatment of subterranean earthen formations (e.g.
fracturing).
Foams have a wide variety of commercial uses.
For example, foams have been used as cleaning mediums
in industry and at home to clean hard surfaces, soiled
linens, etc. Foams have also been used commercially to
clean scale and other debris from boiler tubes and the
like; these procedures capitalize on the foam's capacity
to carry solids. See USP 3,037,887 and 3 212,762 which
illustrate this utility.
The capacity of foam to carry solids has also
been recently utili~ed in the oilfield. Hydraulic
Eracturing of subterranean earthen formations with
proppant laden foam has been described by Blauer et al.
in USP 3,937,283 and by Plummer et al. in USP 3~980,136.
The state of the art is represen~ed by Blauer et al, supra.
Foam fracturing is a substantial advance in fracturing
technology because the low liquid content causes less form-
ation damage and the high gas content supplies energy
to return fracturing fluids to the surface. The net
result is faster and better c]eanup.
29,267-F
- 2 - ~5~
The state of the art has been enhanced further
by the recent discovery by Zingg of a slurry concentrator
that can be used to make more concentrated proppant
slurries prior to ~oaming. This slurry concentrator is
described in a commonly owned, copending Canadian patent
application, serial no. 391,517, filed December 4, 1981.
Another such device was described by Black in USP
4,126,181 which allegedly has a similar use in the
treatment of wells.
The essential components of a foam are well
known and comprise (a) a foamable liquid, and (b) a
blowing agent. The foamable liquid is usually an aqueous
liquid containing a surfactant or surfactant mixture.
In foam fracturing, the surfactant is usually a nonionic
or cationic surfactant (or a mixture thereof), or an
amphoteric surfactant. A wide variety of such surfactants
are known and commercially available, as illustrated by
-the above referenced materials and by the handbook of
McCutcheorls, Combined Edition (published by McCutcheons'
Division, MC Publishing Company, Glen Rock, N~Jo)~
The surEactants described by J.L. Thompson in USP 4,018,689;
USP 4,028,257; USP 4,108,782; and USP 4,113,631 are of
particular interest i.n the present invention insofar as
it pertains to treatment (e.g. foam fracturing) of
subterranean formations.
Foam stability is an important property in
most commercial applications. Various additives have
been used to enhance this property. For example, certain
alcohols have given excellent results in enhancing foamed
aqueous acids (as shown by Scherubel in a co~unonly owned
Canadian patent 1,138,309 entitled "Foamable Acid
Compositions", granted December 28, 1982 and various
polymers have also given good results (e.g. the hetero-
polysaccharide marketed by Kelco and described in the
Kelco product bulletin entitled "Xanthan Gum", Second
Edition.
.r .
29,267~F - 2 -
~B5~78
The blowing agents used to gene~ate foam are
normally gases or compounds which genera-te gas in situ.
Most commonly, the blowing agent is a gas (e.g. air,
nitrogen, carbon dioxide, etc.). Such gases are
usually available from co~mercial sources in pressure
cylinders or other cryogenic containers and in truck
load quantities (e.g. as liquid nitrogen).
It is surprising that even in the fac~ of the
extensive literature on foams and the commerical demand
for foams that there is still a need for a foam having
enhanced foam stability, yet that need exits, particularly
for foams used in hydraulic fracturing.
A novel foam has now been discovered which
has excellent foam stability. The novel foamable liquid
composition comprising:
(a) an aqueous medium, (b) a viscosity increasing amount
of xanthan gum, (c) a cationic surfactant, and (d) a minor
Eoam stabi]izing amount o~ water-soluble inorganic salt.
The invention also resides in a foam suitable
eor use in fracturing a subterranean earth formation
comprls1ng:
(a) an aqueous medium, (b) a viscosity increasing amount
o xanthan yum, (c) a cationic surfactant, (d) a minor,
foamable stabilizing amount of a water-soluble inorganic
salt, and (e) a blowing agent.
29,267-F - 3 -
7~3
~4--
The new foam has excellent stability and
proppant-carrying capaciky which makes it particularly
useful in foam fracturing of subterranean formations.
The foamable liquid comprises an aqueous
medium, which is usually water or dilute acid ~.g.
dilute HCl). Water is the medium of choice in most
instances although dilute acid ~e.g. about 1-5 percent
HCl~ can be advantageous in foam fracturing of some
formations. The aqueous medium can also contain other
addi~ives, such as lower alkanols (e y. methanol,
ethanol isopropanol, etc.~ to aid dissolution,
compatible inhibitors, and the like, if desired.
The heteropolysaccharides form a known cla5S
of polymeric compounds, any of which can be used herein
so long as the compound(s) chosen uniformly thickens
the agueous medium (i.e. increases i~s viscosity) and
enhances khe stability of the foam. A simple experimental
~xocedure will be described below for evaluating such
compounds. The biopolymers produced by the microorganism
anthomonas campestris are preferred heteropolysaccharides
and are commercially available (e.g. from Kelco Division
of Merck & Co.). Such biopolymPrs may be used as they
are formed in the fermentation process (containing live
bacteria) or as they are commercially marketed. The
commexcially marketed materials have been pasterurized
with heat to kill the ~acteria, precipitated with a
lower alkanol (e.g. isopropanol), and recovered by
iltration.
The heteropolysaccharides are normally used
in amounts of up to about 60 lbs/1300 gal. of a~ueous
liquid medium. However, in most instances,
29,267-F ~4
~5--
~uantities of from 20 to 40 lbs/1000 yal~ are adequate,
and preferred.
Other viscosifiers or gelling agents (e.g.
locust bean gums, guar gums, etc.~ can also be added to
the foam~ble liquid if desired so long as they ax~
compatible in the foamable liquid and do not distabilize
the foam.
The cationic surfactants likewise form a
known class of compounds, any member (or mixture) of
which can be used herein so long as a stable foam is
generated. The cationic sur~actant can be used as such
or as a blend with a nonionic surfactant. Such blends
are advantageous and usually preferred. The nonionic
surfactants are, of course, a known class of compounds.
When the foam is to be used in foam fracturing, it is
customary for the operator to check the ~oam (and its
components) for compatibility with the formation fluids.
Such compatibility screening is done routinely in the
~ield. Selection of a su~fac~ant is therefQre important,
bu~ can be varied and is within the skill of the art.
The surackanks described by J. L. Thompson in USP
4,018,689; USP 4,028,257 and ~SP 4,108,782 are especially
useul in foam fracturing applications and are pxeferred
in such instances.
The water soluble inorganic salts are a known
class of compounds, any member of mixture of which can
be used herein so long as the salt(s) is compatible
with the remaining components o~ the foam. Obviously,
the salt will not be chosen in a manner tha~ would
render the foam unacceptable for its intended purpose
by virtue of the effect of the anion and/or cation on
29,267-F ~5-
--6--
the substrate ~o be cleaned, fractured, etc. For
example, one would normally tend to choose a salt
having an anion other than chloride if the foam was to
be used in cleaning a stainless steel surface. Similarly,
some salts might be undesirable in foam fracturing
because of potential formation damage and would be
avoided. Such information and knowledge is within the
skill of the art and is readily determined by routine
experimentation. Examples of suitable such salts
include: alkali and alkaline earth metal halides (such
as NaF, NaCl, KCl, NaBr, KBr, CaC12) etc.), alkali
metal carbonates (such as Na2C03, etc.), alkali metal
bicarbonates (such as NaHC03, etcc), alkali metal nitrates
(such as NaN02, etc.), and the like. NaCl and KCl are
presently preferred salts for use in foam fracturing
fluids, and KCl is most preferred.
Applicants were surprised to learn that minor
amounts o~ dissolved inorganic salts substantially
enhanced the foam stability of the presen~ foams. The
~alts are included in the foams in foam stabilizing
amounts (as d~termined by the foam half-lie test below).
The salts are normally included in amounts of up to
about 5 w~ight percent, based on the weight of the
liquid aqueous medium, and are preferably included in
amounts o~ from 2 to 3 weight percent, with amounts
o from 2 to 2.5 weight percent being most preferred.
The ~Iblowing agent" used herein is an inert
gas (i.e. not reactive with the constitutents in the
foam) and can be added as such or generated in situ by
adding a compound which reacts with water to evolve a
gas (e.g. C02). Most commonly, the blowing agent is
29,267-F -6-
~85~
_7,
added as a gas. E~amples of such blowing agents include
air, nitrogen, carbon dioxide, normally gaseous hydro-
carbons (e.g. propane~, etc. Nitrogen is the blowing
agent of choice because of economics, availability and
handling safety. ~he ~oam "quality" is defined and
calculated according to the procedure set forth in
Blauer et al., supra. A Mitchell foam ~uality of
from 0.60 to 0.85 (at fonmation temperature and pres-
sure) is preferred when the foam is to be used in
foam fracturing of subterranean formations.
The novel foams are conveniently prepared by
blending the components necessary to make a foam~le
liquid composition and ~hereafter adding the foaming
agent. The foamable li~uid composition,can be prepared
in one blending step or in multiple blending steps.
For example, the foamable liquid composition which is
used in foam racturing is advantageously prepared by
blending the hydratable heteropolysaccharide wi~h the
aqueous medium containing dissolved salt(s) and subse-
~uently blending in the surfactant and blowing agent tomake the ~oam. Product uniformity seems to be enhanced
if the het~ropolysaccharide is introduced in this
matter but different blending methods can also be used,
with good results. For example, a dry blend of salt
and heteropolysaccharide can be blended with the aqueous
medium and then foamed by adding surfactant and a
blowing agent. Other blending methods will be apparent
to the skilled artisan.
It has been found advantageous but not critical
to pressurize the foamable li~uid composition before
adding the blowing agent if the resultant foam is to be
used at elevated pxessures ~e~g. in fracturing)O In
this manner, pumping is facilitated.
29,267-F -7~
778
--8
Experimental
The following experiments will further illustrate
the invention:
Experiments 1-4
An aqueous stock solution containing 2 weight
percent KCl and 0.80 volume percent of a blend of
commercial surfactants.(0.48 percent F7~ and 0.32
percent F75N, products of The Dow Chemical Company) was
prepared. Various polymeric gelling agents and inorganic
salts were then addPd to 100 milliliter aliguots of the
stock solution and the resulting mixture was stirred
for 30 seconds at high speed in a commercial Waring
Blender. The oamed contents were then transferred
quickly to a graduated cylinder. The foam half-life was
measured by recording the length of time required for
50 milliliters of liquid to separate out of the foam.
The longer the ~oam half~life, of course, the more
stable the foam.
This series of experiments was conducted to
show the performance of xanthan ~Im (a heteropolysac-
charide) r~lative to other polymeric thickening agents.
TABLE I
Half-Life (minutes) at
Experiment ~y~Polymer Conc. (lbs/1000 qal.)
. 20 30 40
1 guar gum 14 20 41
2 hydroxy~ 7 14 28
propyl guar
3 hydroxy- 15 26 52
ethyl
cellulose
4 xanthan 210 315 441.5
gum
29,267~F -8-
_9_
A foam prepared from the stock solution
without any thickening agent had a half-life of about 3
minutes.
Experiments 5-39
This series of experiments was designed to
show ~he e~fect o~ various amounts of KCl in an aqueous
stock solution containing xanthan gum (20, 30 or 40
lbs/lO00 gal. of solution), 0.80 weight percent of
the blend of surfactants identified in Experiments l 4.
TABLE II
Xanthan Gum - 0 _ gal
Initial Foam Fo~m Half-Life
xperlment KCl (wt. %) Volume ~mll_ (minutes~
0 350 2.6
6 0.25 310 2.5
7 0.50 270 2.0
8 0.75 280 1.8
9 1.00 300 1.7
1.50 N.A. 50.7
20 11 2.00 290 77.5
12 2.25 350 86.5
13 2.50 295 81.0
14 2.75 350 92.5
3.00 385 87.5
25 16 3.25 360 28.5
* N.A. means data not acquired.
29,267-F -9-
~10--
TABLE I I ( continued )
Xanthan Gum - 20 lb~/1000 yal
Initial FaomFoam Half~Life
Experiment KCl (wt. ~O) Volume (ml ~ (minutes )_
17 3 . 50 320 27 . 0
1~ 3 . 75 325 21 . 5
19 4. 00 385 2~ . ~
4 . 50 28~ 25 . 0
21 5 . 00 300 26 . 0
TABLE I I I
X~Atha~ 30 lb~1000 ~al
Initial Foam Foam Hal~Life
.KCl (wt. %) Volume (ml ) _(miIlutes )
22 0 2~0 0 . 7
15 23 0 . 25 240 1 . 9
24 a . 5 280 10 . 5
0 . 75 325 13 . 1
26 1 . 0 325 17 . 5
27 2 . 0 325 191 . 0
20 28 3 . 0 N.A. 231. 0
29 4.0 N.A. 57.0
5 . 0 265 57 . 0
29, 267-F -10-
7~
TABL~ IV
Initial Foam Foam Half-Life
Experiment KCl (wt~_~ Volume lm].) (minutes)
31 0 240 15.0
32 0.25 300 40.5
33 0.5 300 55.5
34 0O75 300 77.5
1.0 300 90.5
36 2.0 300 441.5
37 3.0 N.A~ 410.0
38 4.0 N.A. 118.0
39 5.0 200 137.0
~ lments 40-51
1$ This ser.ies of experiments was conducted in a
manner essenti.ally identical to those above except NaCl
was used in place of KCl.
29,~67-F 11
577~
--12--
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29, 267-F -12-
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Experiments _5 - 6 0
This series o experiments was conducted in a
manner essentially identical to those above except CaC12
was used in place of KCl.
29, 267-F 13 -
14-
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29, 267 F -14-
7~3
--15--
Experiments 61-69
This series of experiments was conducted in a
manner essentially identical to those above except ~gC12
was used in place of KCl.
29,267-F ~ 15-
~5~7~
--16--
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29, 267 F -16-
-17-
Experiments 70-78
This series of experiments was conducted in a
manner essentially identical to those above except NH4Cl
was used in place of KCl.
29,267-F -17-
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29, 267-F
~ 8~i77~3
--19--
E~periments 79-85
This series of experiments was desiyned to
show the effect of various ratios of cationic surfactants
(F78) to nonionic surfac~ants (F75N). The li~uid in
each instance contained 2 percent KCl, xanthan gum
(20 lbs/lO00 yal.) and the surfactant (8 gal/lO00 gal)
dissolved in water. In parallel experiments in which
KCl was omitted, li~uids containing the cationic surfactant
formed a gummy precipitate. The f3ams were, of course,
generated and evaluated as shown above.
29,267-F -19-
'7~3
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29, 267-F -20~
-21-
Experiments 86-91
This series of experiments was designed to show
the effectivene s of cationic surfactants in the present
foam sys-tem relative to anionic surfactants (F52 -
commercial product from The Dow Chemical Company) andnonionic surfactants (Igepal~ CO 730 ~ commercial product
from GAF Corp.). The liquid in each instance contained
xanthan gum (40 lbs/lOOO gal.), the indicated surfactant
(5 gal/lOOO gal.) and KCl (in amounts as indicated~
dissolved in water. The foams were, of course, generated
and evaluated as shown above.
29,267-F --21-
--22--
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29, 267-F -22-
~5~
-23-
Experiment 92
The slurry concentrator illustrated by Figures
1 and 2 in Zingg et al., supra, was used in a fracturing
system as shown in Figure 3 of Zingg et al. in a foam
5 fracturing treatment of a well located in the Luling
Branyon Field in Guadalupe County, Texas. The well was
approximately 2,000 feet deep and it has a bottom hole
static pressure of 700 psi and a permeability of 0.21
millidarcies (average).
In this trea~ment, S,000 gal. of an a~leous
carrier fluid (2 percent KCl brine gelled with a
commercial ~anthan gum, Dowell~ J312 (20 lbs/1000 gal.
brine) and 5,000 gal. of carrier fluid wexe blended
with 5,000 lbs. of 100 mesh sand and then 2,500 gal. of
carrier fluid wexe sequentially pumped through the
slurry concentrator with the choke assembly valved off
so that no li~uid was removed from the fluids passing
through at a rate of 20 barrels per minute (bpm~i a
blend of commercial surfactants [Dowell~ F78 t3 parts by
volume) and Dowell~ F75N (2 parts by volume] dissolved
in dilute HCl was added at rate of 0.5 bpm (i.e. 5 gal.
of surfactant concentrated per 1000 gal. of carrier
~luid), and the fluids were then foamed with gaseous
nitrogen (13 bpm, liquid basis) to give a foam guality
of 65 (i.e. a Mitchell valve of 65) and injected into
the well. The valve on the choke assembly was then
opened and a slurry of carrier fluid blended with
increasing amounts 20 to 40 mesh sand was then pumped
through the system (20 bpm) concentrated and foamed
using the same blend of surfactants and nitrogen at the
same rates shown above. The slurry was blended at a
concentration designed to give 1 lb. sand/gal. of
liquid in the foam initially and then to rise steadily
29,267-F -23-
~577~3
-24-
to a final concentration of 5 to 6 lbs. sand/gal. of
liquid in the foam over a short period of time (e.g. 3
to 4 minutes). This schedule was easily achieved. The
slurry going into the concentrator thus varied from an
absolute density of 9.4 to 13.1 lbs/gal. and the slurry
discharged from the concentrator had an absolute density
that varied correspondingly from 9.9 to 14~6 lbs/gal.
These dat are correlated in Table XI.
TABLE XI
.
Proppa-nt-conc. ~ luid3
Initial SlurryDischarge Slurry Foam
g.a~ 9.9
10.4 11.1 2
11.0 12.~ 3
1516.6 13.0 4
12.2 13.7 5
13.1 14.6 6-~
To illustrate the data in another way commonly
used in the ~ield, 12.2 and 13.7 lbs/gal. absolute
density correspond to 8.8 and 14.3 lbs. of sand added
per gallon of fluid, respectively. Without the slurry
concentrator and the dynamics of the system, it would
generally be thought impossible, for e~ample, for 1
gallon of this carrier fluid to hold 14.3 lbs. of sand,
much less the 18.5 lbs. which was achieved during the
course of this fracturing treatment. In total, 235,000
lbs. of proppant were emplaced using 89,000 gals. of
carrier fluid and 647,369 standard cubic feet of nitrogen.
The well was shut in for a period and brought back
29,267-F -24-
~5~8
-25-
slowly, according to s~andard procedures. The fracture
treatmen-t was extremely successful according to initial
production data.
29,267-F -25-
