Note: Descriptions are shown in the official language in which they were submitted.
3~
The present invcntion relate to macrolnolecular composi~i.cns
crosslinked by a novel bridge having the forrnula
~NTIX-CH~N-CO-. This novel bridge is obtained by recoin
a macro molecule, preferably a polymer, having at least t~Jo
arnidocarbonyl groups with a compoullc~ havillg at least two
formylamido grouts in an aqueous medium under highly acidic
conditions. Tlle crosslinkin~ bridge wormed by the reaction
ox this invention is produced in accord with the following
formula:
R-NRX-C~ H2N-CO R'
Ho
X~C13=N-CO~ 120
Compositions containing macromolecules havi.ng at least two
nmicloc~rbonyl ~,roups an a compound havl.n~, at lest two
~ormylc~ ido groups ,can act as viscos~n~ or gellin~ agents for
~qlleous ails wllerc ken died to aqucous acid, crosslinkill~
occurs. Acids gelled in this manner have important use in the
recovery of oil and natural gas from subterranean formations..
The art of well stimulation can employ a technique called
frac~ure-ac~iæing Jo enhance the recovery o either oil or
gas from subterranean carbonate formations. Carbonate formations
include limestone, dolomites, or other reservoir ogle r!~iC~
contain calcarious material. normally, fracture-acidizing
involves the injection of an aqueous acid, which rnay or may no
contain a ~rop~ant, .into a wellbore at such a rate and pressure
-- 2 --
3~7
.
as to exceed the formation stresses whereby causlng rock
fa~i~ue and inducing new fractures in the formation.
Fractures are natural or induced cracks or channels ln the
formation matrix. Stimulstion by this technique is
achieved by allowing the acid to etch the fracture face
Since the face is a heterogeneous cotnposition, the acid
reaction rates will vary on the exposed surface. After
the exerted pressure has been relieved, fracture closure
will occur but the fracture face is no longer uniform and
in most cases Jill not perfectly align due to the action
of the acid. If a proppant is pumped with the acid, the
acid will again preferentially act on the formation face.
However, since the formation is heterogeneous, some areas
of the face will be nonreactive to the acid. After fracture
closure, the etched, non uniform localities of the face
again will not align while areas not etched will be "propped"
open by that proppant.
In each case, a more conductive channel is provided to
allow the oil or gas to flow to the wellbore aEter the
injection pressure is relieved. When an aqueous acid is
injected into a wellbore in a fracture-acidi~ing application,
it is often advantageous to use a viscosiEying or jelling
agent in the 1uid (c~fo U.S. patents 3,415,319; 3,434,971;
3,749,169; 3,236,305 and 3,252,904). Viscous fluids possess
several properties ha are favorable to fracture acidizing.
For example, the fluid viscosity is proportionally related
to the created fracture volume end racture width, wherefore
higher fluid viscosities will generate larger fracture
volumes and fracture widths In additlo~, vlscous fluids
: - 3
\~
decrease the rate of the acid etching on the formation allowing
the acid to penetrate deeply into the fracture and viscous fluids
serve as efficient proppant transporting media necessary to
place proppant into the etched fracture.
Normally viscous fluids contain homo or copolymer
compositions as the viscosifying agents. In particular,
copolymer compositions containing amidocarbonyl pendent groups,
such as polyacrylamide, are commonly used as viscosifying agents
in fracture acidizing fluids. Normally, low polymer concentra-
tions, usually less -than 1.0% by weigh-t, are used. To enhance
the viscosity of the fluid, it is known from German O~fenlegung-
sschrift 2,657,443 that copolymers of acrylamide are readily
crosslinked by the addition of aldehydes such as formaldehyde,
acetaldehyde or glyoxal. The crosslinkiny reaction normally
occurs at ambient temperatures in alkaline solutions or between
40 and 30C in acidic media. However, heating the fluid to
initiate crosslinking and the time necessary to complete the
crosslinking, sometimes in excess of 45 minutes, make this fluid
impractical in fracture acidizing applications.
The present invention relates to a composition cross-
linkable in an aqueous acidic medium comprising a compound having
at least two formylamido groups and a different compound having
at least two amidocarbonyl groups, the formylamido group and the
amidocarbonyl group of said compounds being capable of reac-ting
in an aqueous acidic medium to form crosslink bridges of the
formula -NR -CH=N-CO-, wherein R represents hydrogen, alkyl
having 1 to 4 carbon atoms or -CH2OH.
The present invention may also be defined as a cross-
linked polymer composition obtained by reactiny in a highly
acidic aqueous medium amidocarbonyl groups of component A) with
-- 4 --
l ., .i .:~;
23~
formylamido groups of component s), component A) comprising a
water-soluble homo- or copolymer having amidocarbonyl groups in
an amount of more than 10%, calculated on the weight of the
polymer and component B) comprising a member selected from the
group consisting of (a) a bis-acylamido-compound of the formula I
O O
H-c-N-cnH2n-(ocnH2n)m-N-c-H (I)
R R
wherein
Rl and R represent hydrogen, alkyl having 1 -to carbon
atoms or -CH2OH, n represents a number from 1 to 3 and m
represents a number from 0 to 1, and (b) a water-soluble homo-
or copolymer having formylamido groups of the formula
-N-C /
R9 \ H
wherein R stands for hydrogen or alkyl having 1 to carbon
atoms or -CH2OH, the amount of formylamido groups being not less
than 1 mol per 500 g o:E the polymer.
In another aspect, the invention compr:Lses a methocl
of forming a crosslinked composition having c:rosslin]c briclyes
of the formula NR -CH=N-CO in which R represents hydrogen,
alkyl having 1 to 4 carbon atoms or -CH2OH comprising reacting
a compound having at least two formylamido groups with a compound
having at least two amidocarbonyl groups in an aqueous acidic
medium.
In a further aspect, the invention comprises in the
process for well stimulation by fracture acidizing with an
aqueous acidic solution containing a viscosifying amount of a
polymer composition, the improvement comprises the aqueous acidic
- 4a -
Z37
solution containing as a viscosifier a crosslinked polymer
composition as hereinbefore defined.
The invention also relates to mixtures of ingredients,
one comprising macromolecules having at least two amidocarbonyl
groups and another comprising a compound having at least two
formylamido groups, said mixtures being suitable for reaction
in an aqueous medium under highly acidic condi-tions to cross-
link with the formation of the -NRX-CH=~-CO-bridge. The
invention further relates to methods of crosslinking such
mixtures. The invention also relates to the use of the
resulting crosslinked polymer compositions as
- 4b -
I.-
`;
viscosifiers for acids that do not have the disadvantagesof the known polymers used for this purpose in fracture
acidizing stimulation. I^~ile the new crosslin}<ed polymer
compositions of this invention have particular utility as
viscosifiers in fracture acidizing stimulation, they may
also be used whenever it is desired to increase the
viscosity of aqueous acids such as ln the art of metal
cleaning.
The compositions according to the present invention
when employed in acid fracturing have the advantage that
little or no precipitants are formed in ~h2 acid
environment as is typical of previously known gelling
agents. Precipitants, if formed, tend to plug the
underground formations and can severely limit the efficiency
of the stimulation. In the present invention, if the
crosslinked pol.ymer composition degrades, the resulting
polymer residues are solul~le in the aqueous acld. This
is because the crosslinking bridge decomposes leav:Ln~-
amino functions attached to the polymer haclcbone. These
amino functions impart solubillty to the polymer residues.
Crosslinkable mixtures of this invention prei~err~bly
comprise:
a) a water-soluble homo- or copolymer having
amidocarbonyl groups and
by a bis~acylamido-compound of the formula I
O O
H-c-N-cnH2n-~ocnH2n)m-N-c~H I
Rl ' R2
wherein
Rl and R2 represent hydrogen, alkyl having 1 to carbon
atoms or -CH20H,
~2~7
.. .
represents a number from 1 to 3 end
m represents a number from 0 to 1
or a water-soluble homo- or copol~ner having o~nyl~mldo
groups of the formula
NO
9 .~ Al
wheroln stands for hydrogen or alkyl having 1 to
carbon atoms or Cll2OH. The cros~llnk~5bl~ mlxtur~s rnay
contain ox or more of thy componen ts n together wi if one
or more components by
' Component a) oE the crosslinkahLe mixtures this
i.nven~ion and component by are resent in a ratio by
weight ox from IØ2 Jo 1:20, preferably 1:0.2 to 1:1.
In genera he homo- or copolyln~r of colrlr)on~n~
a) prior to crosslinking may be any macromoleculc,
preferably a polymer, which is su~iciently solllble in
water end contains in the polymer an amount of amino-
carbonyl groups (a least two) suficient to allow k
formation of the novel cro~slinklng brid,e,
-N~X-C~l~N-CO- D in to m~cromolec~ 3~ Ox C~I
crossllnking agent i* pr~s~nt in thy compositlons llX rivals
, or R . Thy ~olu~ility 1ll wator should bo not lets
than lO g/l and lie content ox amidoc~rbonyl groups shoulcl
be above lo preferably above 15%, calculntcd on the weigtlt
of the macromolecul~O
Particularly suitable homo- or copolymers of the
component a) prior to ~rosslinklng comprise 50 to 100%
by welght of entities of the formllla II
R4
2 SIX)
CONH2
-- 6 --
3~
.
wherein R4 stands for hydrogen or methyl and of O to 50%
by weight of entities of the formula III
R5
-CHIC-
. (III)
wherein
R5 stands for hydrogen, alkyl having 1 to 3 carbon atoms,
hydrogen and methyl being preferred, and
Y stands for formylamido; ~-suhstituted
formylamido where the N-substitutent is methyl or hydroxy
methyl, cyano, carboxyl or its alka~, or ammorlium
salts; the alkoxycarbonyl group having 1 to 6, preferably
1 to 3 carbon atoms; the hydroxy-alkoxycarbonyl group
having 1 to 3 carbon atoms; the N-methylolamidocarbonyl
group HOCH2~H-CO-, thy methyl group of which may optionally
be etherified with alkanols having 1 to 4 carbon atoms; the
allcanoylamino group having 1 to 4 carbon atoms which may
optionally be N-substltuted with methylol or alkyl having
1 to 4 carbon atoms; ~yrrolldonyl~ phenylj pyridinium;
the sulfonic acid group; the sulfoalkylamidocarbonyl
group having 1 to 4 carbon atoms; the phosphonic acid group,
it being possible for sulfonic and phosphonic acid groups
to occur as alkali or ammo~i~ salts; for a radlcal of the
formula IV
~7
~PH2~ R~
or for a radical of the formula V
~7
-CONH-CpH2p-N (V3
8~23'7
and the quaterni~ed compounds of (IVY and (V) quaternized with CH3-Cl or
dimethyl sulfate, wherein R7 and R8 are the same or different and stand :Eor
alkyl having l to 4, preferably l or 2; carbon atoms and p represents a
number from l to 4.
Preferred homo- or copolymers of component a) prior to crosslink-
ing comprise 60 to 85% by weight of entities oE the formula II and 15 to ~0%
by weight of entities of the formula III.
Furthermore, it is preferable to use as component a) homo- or
copolymers in which R5 signifies hydrogen or methyl and
Y signifies the carboxyl group; the sulfonic acid group, 3-sulfo-2-methyl-
propyl-(2)-amidocarbonyl of the :Eormula,
C,~13
-CON1-1-C-CH2-S03H
CH3
an alkanoylamino group having l to 4 carbon atoms which may optionally bc
N-substituted with methylol or alkyl having l to carbon atoms; pyrrolidonyl-
(l) or a radical of the formulas IV and V given and defined above, wl1ere
each acid group can also occur as Na-, I- or NH~-salt.
From among the group of compositions of this invcnt:ion prior to
crosslinking containing a bis-acylamido compound o:f the ~Eormu1fl 1: thosc arc
prc:Eerred which conta:i.n a comL)ol1nd of the :formula :[ where
Rl and R represent hydrogen or -C11201-1, and
n represents the number l.
It is possible to use as homo- or copolymer of component b) prior
to crosslinking any polymer that is
-- 8 --
r
g;237
sufficiently soluble in water, i.e. not less than 10 g/l which
in audition to formylamido groups also has an amount of
amidocarbonyl groups su~icient to give stable crosslinked
polymers of -the novel chemical structure. Stated differently,
it is possible that component a) and component b) each contains
the required amounts ox amidocarbonyl and formylamido groups.
Indeed, component a) and component b) may be the same. Self-
crosslinkable copolymers ox this special class are described in
a concurrently filed Canadian application Serial No. 392,248
entitled "Water-soluble Copolymers" in the names ox Friedrich
Engelhardt, Klaus Kuhlein, Ulrich Riegel, Sigmar P. Von Halasz,
Jeffrey C. Dawson and Anthony R. Reed.
Component b) must contain a sufficient amount of
formylamido groups to form the desired crosslink bridge. A
sufficient amount of formylamido groups should not be less than
1 yram mole of formylamido group (i.e., 71 grams of N-vinyl
formamide) per 500 grams of the polymer.
Particularly suitable homo- or copolymers of -the
component b) prior to crossllnking comprise 50 -to 100~ by
weight of entities of the formula VI
-CH -CH-
N O (VI)
' \H
R
wherein R stands for hydrogen, methyl or hydroxymethyl, hydrogen
and methyl being preferred, and of 0 to 50% by weight oE
entities of the formula VII
Rll
-CH2C- (VII)
X
g _
~8~37
wherein
R stands for hydrogen or methyl and
X stands for cyano; the carboxyl group or its alkali or ammonium salts; the
alkoxycarbonyl group having l to 6, preferably l to 3 carbon atoms; the
hydroxy-alkoxycarbonyl group having l to 3 carbon atoms; the amidocarbonyl
group, the N-methylolamidocarbonyl group HOC112N11-CO-, the methylol group of
which may optionally be etherified with alkanols having l to 4 carbon atoms;
an alkanoylamino group having l to 4 carbon atoms which may optionally be
N-substituted with methylol or alkyl having l to 4 carbon atoms;
pyrrolidonyl-(l); phenyl; pyridinium; the sulfonic acid group, a sulfoalkyl-
amidocarbonyl group having l to carbon atoms; the phosphonic acid group;
it being possible for sulfonic and phosphonic acid groups to occur as alkali
or ammonium salts; for a radical of the formula VIII
o
-C~l2~l2--P-R (VIII)
R13
whereir1 R and R are the same or different and stand for alkyl having l
to 4J preferably l or 2 carbon atoms; for a radical of the formula IX
R12
-COO-Cpl12p-N \ Rl3 ~1:X)
wherein R and R have the mean:ings given above and p rep-rese1l~s a tl~1mbe:r
from l to 4; or for a radical of the formula X
R L
-CON11-CpH2p-N Rl5 OX)
and the quaternized compounds of SIX) and OX) quaternized with ~13Cl or
dimethyl sulfate, wherein Rl4 and Rl5 are the same or different and stand
for alkyl having l to I, preferably l or 2 carbon atoms and p has the mean-
ing given above.
Preferred homo- or copolymers of the component b) prior to cross-
linking comprise 60 to 95% by weight of entities of the formula (VI) and
- 10 -
; -
~L~89~3~
5 to 40% by weight of entities of the formula ~VII).
Furthermore, it is preferable to use as component b) prior tocrosslinking homo- or copolymers in which X signifies the carboxyl group,
the sulfonic acid group, 3-sulfo-2-methyl-propyl-(2)-amidocarbonyl of the
formula
c,~l3
-CONH-C-C112-S03H
C~13
an alkanoylamino group having 1 to carbon atoms which may optionally be
N-substituted with methylol or alkyl having 1 to carbon atoms,
pyrrolidonyl-(l) or a radical oE the formulas IX and X glven and defined
above, where each acid group can also occur as Na-, K- or NH~-sal~.
Preferably, copolymers are used as components a) and b) prior to
crosslinking having K-values of from 15 to 300 (cf. ~ikentscher
"Cellulosechemie" Vol 13, page 5~ (1932).
It stands to reason that the copolymers may contain several differ-
ent radicals X and Y respectively. As a rule, the radicals X and Y when
present in a single macromolecule have not more than 3, preferably 2, diEEer-
ent meanings. Copolymers oE this kind are prepared using several clitforont
comonomers carrying a radical X and Y respec-tively, as a file not nlore tlu
3, preEerably 2.
The homo- or copolymer con~positions oE-this invention prior -to
crosslink:ing are readily soluble in water to give solutions of` a meclium de-
gree of viscosity. Hence these solutions can be handled easily. The com-
positions prior to crosslinking retain this property unless they are treated
with acids at a pH of 3 or below. Unlike the known polymer-aldehyde combina-
tions, the compositions of this invention are storable for an unlimited
period of time. Acids are used to induce the novel crosslinking reaction be-
tween the amidocarbonyl groups of component a) and the formylamido groups of
component b) which results in a drastic rise in viscosity due to the forma-
.
9Z37
tion of -NR -C~l=N-C0-linkages forming a three dimensional novel polymer net-
work according to this invention. This is why these compositions are used
to increase the viscosity of acids. Depending upon the amount of the com-
position added, the viscosity may be varied within a wide range. The lower
limit of this range is the viscosity of the pure acid free from copolymers.
If, on the other hand, a sufficient amount of a composition of this inven-
tion is added, gels of the novel cross linked polymer composition may be ob-
tained which do not flow spontaneously but keep any shape given to them. Be-
tween these extremes any viscosity may be obtained by varying the composi-
tion contents of the acid.
In fracture-acidi~ing applications, the concentration of the
acrylamido homo or copolymer (component a) usually ranges from 0.24% to
0.72% by weight on total fracturing or treating fluid depending of the
polymer properties, well treating conditions or reservoir characteristics.
The crosslinking agent (component b) will have a concentration range from
0.05% to 1%, preferably 0.25% to 0.6%, based on total weight of the fractur-
ing or treating Eluid. The acrylamido homo or copolymers are introduced
into the aqueous phase as a fine solid powder, a hydrocarbon dispersion con-
taining 20% to 50% by weight of component a, or as an oil in water or water
in oil emulsion normally containing 20% to 50% by weight of component a.
The preferred system is an emulsion containing the highest possible percent-
age of component a to produce a stable emulsion, normally 35% to 75% by
weight. Suitable oils useful in such water in oil emulsions include normal
or branched paraffinic hydrocarbons having a boiling point of 150C. to
250C.
The crosslinking agents (component b) are normally introduced as
aqueous solutions containing up to 50% by weight of crosslinking agent, a
fine solid powder, a hydrocarbon, dispersion containing 20% to 50% by weight
of crosslinking agent or water in oil or oil in water emulsions containing
20% to 50% by weight of crosslinking agent. The preferred state would be as
I ,/ 's,
~8~Z37
an aqueous solution containing 50% by weight active crosslinking agent.
When the preferred concentration of acrylamido homo or copolymer,
0.2~% to 0.72%, and preferred concentration of the crosslinking compositions
of this invention, 0.25% to 0.5%, are placed together in water only a
medium viscosity is obtained. A Fann 35 viscometer at a shear rate of 511
sec 1 will indicate a viscosity between 20 and 60 centipoise. The composi-
tions will retain this viscosity until they are treated wikh a Bronsted-
Lowery acid. The acids are used to induce the crosslinking reaction between
the acrylamido homo or copolymer and the formylamido compositions leading to
the new crosslinked polymers of this invention by the formation of linkages
according to the following chemical structure -NRX-CII=N-CO- producing a
drastic rise in viscosity usually exceeding 300 cps at a shear rate of 511
sec 1 on a Fann 35 viscometer.
The normal method oE preparing the novel acid gel according to
this invention is to add the preferred concentration of acrylamido homo or
copolymer to an acidic solution allowing the polymer to hydrate for usually
3 min. to ~5 min. Generally, any acid or aqueous acid solution may be
thickened accordlng to the present invention. In fracture-acidizing applica-
tions, acid strengths normal range from l to 28% by weight of either
hydrochloric, acetic or formic acid. The preferred strength is 3% to 15%
depending on the well treating conditions and reservoir characteristics.
After 90% of the viscosity from the hydrating polymer has been obtained the
acidic solution is treated with the preferred concentration of crosslinking
agent, 0.25% to 0.5% by weight, a substantial increase in viscosity occurs
according to the formation of the new crosslinked polymer. It stands to rea-
son that any other way of combining the components of this invention with
the acrylamido homo or copolymer and the acid likewise yields acid gels or
highly viscous acid preparations.
The viscosity of the acid thickened with the compositions of this
invention is maintained at room temperature for long periods of time, e.g.,
- 13 -
`'
3~
exceeding 3 months. At elevated temperatures, e.g., above 50C., preferably
above 80C., the viscosity diminishes and the highly viscous, gelled acids
turn to liquids of low viscosity.
This change is due to a hydrolytical degradation of the novel
three dimensional crosslinked polymer -to linear polymer chains. The time
necessary for the change from the gel to the liquid state depends, to a cer-
tain extent, on the composition of the polymer molecule and hence, may be
varied within certain limits, but not exceeding 12 hours, by selection of
appropriate monomer compounds and monomer ratios.
Generally, any acid or aqueous acid solution may be thickened
according to the present invention by Eorming the novel crosslinked three
dimensional polymer. Acids being solid at normal temperatures, e.g.,
aromatic sulfonic acids, have to be used as aqueous solutions. Preferred
acids are those which are normally liquid and9 with respect to economical
use in the field of oil recovery, are strong and inexpensive. I-lence in the
first place, inorganic and strong lower organic acids are taken into con-
sideration .
Examples of acids which may be thickened according to this ;nvcn-
tion are hydrochloric acid, sulEuric acid, ni-tric acid, l~erchloric acid,
phosplloric acid, formic acid, acetic acid, monocllloroacetic ceil dicllLoro-
acetic acicl ~uld trichloroacetic acid.
Preferred acids Eor oil recoveriTIg pur~)oscs are hydrocllloric acld,
Eormic acid auld acetic acid
The homo or copolymers of the component a) prior to crosslinking
are produced by (co-)polymerizing 50 to 100%, preferably 60 to 85% by weight
of acrylamide or methacrylamide and 0 to 50%, preferably 15 to ~0% by weight
of a comonomer of the formula IIIa
,R5
CH2=C-Y (IIIa)
wherein R and Y have the meanings given above.
- l -
Z3~7
1onomers having the ormul~ (IIla) and suitable
for copolymeriza~ion with acrylamide or methacrylamide
include the following:
R 5~ C11~
- -CHO
5¦-CH3 -I ~3 3
_ _ . __ . . . _ .. __ _ _ _ _ _
Y -COOC~3 -CO~C2H5 COOC2~5 -COOC' E1 -COOC~
~5 CH3 c~3
. __ ., _ . . . _
Y -C~C6~13 2 4 -COOC2H~OH 3 6V~1 1~CC3H6VrI
R5 c~3 -H ~~3
_ I, ................ .~ . .
y CO~H.C~20~ -~O~IC~20~ -CONHCF~20C~I3 -CO~'~C~OC~13
R5 ~~ ~3 ~~
,. . . - . - .
Y ~COI~CH20C2H5 -CONHC~20C~H5 ~COl~Hc~2
R5 CH3
_ I__ __I
Y ~HCOC~3 -~COC2~5 ~COC3~7 7 WHO
CH20H
~5
..~_
%37
R5 1 -I ¦ Of
Y -N-COC~3 -~COC2~1$ -N-COC3~7 -~-CHO -N-CHO
l l l
~2 C~2 C~2~I C~13 CH2 -OH
. .
~,5 _~ -El _~
______ _ _ _
Y COC E~3 -X'-CC~ 3H~; - N C OC 2E~5
CE~3 CE~3 C2H5
~5 -El -CE~3
__ __ __ _ ___ _
Y a 3 -N? SO3
R5 a H `;`El OH
_ J _ ____ 3
-S03~) 'P3~2~ P~3~2
~,5 -H _}~
-e~OhV~-C~I2SC\;~ -CN~C~2C~2CH~;3~)
R5 _~
. Y -CO~EIC2~-S03~) -~o~HCH-C~32~$03~)
~3
.. ..
_
Y -coy H2c~2~H~c ~2 S03 O C~-C~2~H2 5~3
~3
P~5 . EI
.-
Y C O SO
, 3
~:~13
3123~7
R~ H3 -CII
..... _ , ,
go c2lI4so3~ 1 C~13
c~3
R5 CEI
_ _ _ _ _ A _ , . ' . . . _
-Cot 2c~2-N 3 coo-c~2c~l2-l~ 3
Y ~COO-c8~cH2 2 5 1 ~COOa CE~2C~-N 3 7
R5
.--~ _______--_
. CH~C~2-N 4 9 -COO-C~I~CE~2-N 4 9
~R5~ -I O
_ 3
y -coo~cE~2c~ 2c~l2~N 3 C~3~C~2t~2_N 3
OR 5 O
Y O ~C2E~i -COC~o~c~ 3
~:~32~5 ~3 ~C~3
. a .,,
_
Y -coy 2c~ N 3 CON~-C~1~2C~N~
237
5 -El O
_ ___ _ _ j 3
Y -CO~;R~CE~2C~2-N~c . 2C~12 My C l
_
~CON~I-CE12C~ N ' 32 ~2 No C
R5
Y2 H:~ No i Oh'H-CEI2C~2~2~N 3
R 5 -CE13 HI
_
Y -CO~R-CR2C~2CH2-~ 3 -CONH-C WCH 2_N~ 2
y I -CONH-C13-cH2~J 3 CONH-C-CR 11 ~H3
~N~ l coo 2c~N 2 5 H2-~ 3 7
Since N-vinyl amides are no stable under acidic conditions
reaction mixtures containing acidic substances mus t be
neutralized prior to the polymerizn~lon such as with the
above men~oned basic comonvmers.
m e homo or copolymers of the col-nponent b) p-ior to cross-
lin~;in~ are prod-lced by (co-)pol~ncri~ing 50 to 100/~,
preferably 60 to 95~/~ by weight of a monomer having the formula
VIa:
,~,0
Cl~=CII-N-C (via)
R9 H
wherein Pi has the meaning given above and
O T O 50%, preferably 5 to 40% by weight ox a comono~er of
he formula VIIa:
pll
I (VIIa~
CH2 = C-X
herein Rll and Ye have the neanings given above.
.onomers having the formula (VIa) and suitable for the
production of homopolymers of component b or copolymerization
with monomers of the fo~ula vIra to forTn copolyners of
component b are N-vinyl-formamide, N-vinyl N-methyl-formrlmide
ancl N-vinyl-~-hydroxymethyl-folmamide. Monomers having the
fonnula VIIa include acrylrlmide/al~e monomers illustrrltecl above
for formula IIIa.
Crosslinling of component a may also be achieved by
employing compounds of formula I as a crosslinking agent.
Specific compounds of the formula I include the following species:
_ _
3~7
Rl ' R2 n
. . . _
H H 1 0
H H 1
c~3 C~13 1 0
CH3 CH3
~H5 G2H5 1 0
C~H5 ~2H5
C3H7 C3H7 1 0
C4Hg C~Hg 1 o
C4~29 CH3 1 0
C3H7 C2~I5 1 0
H H 2 0
CH3 C~23 2 0
H H 2
Ci~3 C~13 2
C2H5 C2~5 2 0
C3~17 : C3}27 2 0
H H 3 0
C~13 C''3 3
}I H 3
C2H5 C2H5 3
C3H7 C3~7 3 o
Preferred compounds ox ormula I ore:
O
,. ..
H-C-NH-CH2-NII-C-H ~Methylene-bis-for~amide) Fmd
o o
H-C-NIl-CH2-0-C}l2-N~I-CH (Bis-(N-fol~yl-aminomethyl) ether).
The compounds of formula I can easily be produced according
to British Patent 1,410,722.
If copol~ners having several different radios Y and X
in components a and b respectively are desired, several
different comonomers of the fonnula IIIa and VIIa respectively
are used in the copoly~erization, as a rule 3 or preferably 2.
The polymerization to procluce coMponents a or b may be
performed according to any known polymerizing process. Ion one
of the monomers is a vinyl-form~mide monomer, R pal range from
6 to 12, preferably 7 to 9 shou].d be employed.
To adjust the pll value, allcaline reacting salts of alkali
metals, e.g., alkalicarbonates, alkalihydrop,encarl~onates,
alkaliborates, di- or trialkaliphospha~es , alkali-
hydroxides, ammonia or organic amines of the formula NR316
are used, wherein R16 is hydrogell, alkyl hazing 1 to 4 carbon
atoms or hydroxyethyl whereby at l.east one of the radicals Rl6
is differënt prom hydrogen. Preferred bases fol: adjus~in~-
the pi value are the alkali compounds mentioned above,
especially sodium hydroxide, potassi.um hydroxide, sodium
carbonate and hydrogen carbon~lte, potassium carbonaLe and
hydrogen carbonate and sodium- alld potassium bora~es. ~.nother
preferred base is NH3.
The polymerization reaction can be initiated by energetic
electromagnetic or corpuscular radiation or by all substances
which form radicals. Accordingly, possible polymerization
initiators are organic per-compounds such as, for example,
benzoyl peroxide, alkyl hydroperoxides, such as, for example,
butyl hydroperoxide, cuTnene hydroperoxide, p-mentllane hydro-
peroxide, dialkyl peroxides, such as di-tert.-butyl peroxide,
or inorganic per-compounds such as, for example, potassium,
sodium or am~onium persulfate and hydrogen peroxide, and azo
,~(
compounds such as, for example, azobisisobutyronitrile~2,2'
azobis(2-amidinopropane)hydrochloride or azobisisobutyramide.
It is advantageous to employ the organic or i.norganic per-
compounds in combination with reducing agents. Examples of
suitable reducing agellts are sodium ~yrosul~hite, ~odiu~
bisul~hite or condensation products of formaldehyde with
sulphoxylates. The polymerization reaction can be carried out
particularly advantageously using ~lannich adducts of sulphinic
acids, aldehydes and amino compounds, such as are described in
German Patent 1,301,566.
It is know furthermore to add to thy pol~nerization batches
small amounts of moderators, which harmonize the course of the
reaction by flattening the reaction rat~/time di~t,ram,
improve the reproduciblll~ of the reaction anal hence foal
to uniform products with extremely little variation in q~lali.ty.
Examples of suitable moderators of this type are ni~rilo-tris-
propionylamide or hydrohalides of monoalkylamines) d:ialkyl-
amines or.~ri~lkylamines, such as, for example, dibu~yl~ i.ne
hydrochloride. In m.anufacturin~ the copolymers ox the
i.nvention, such compounds can also be present with advantage.
urthermore, scatted regulators can be added to the
polymerization batches, that Is Jo say compounds itch influenee
the molecular weight of the polymers formed. Usable known
regulators are, for examp~ e, alcohols such as methan~1,
ethanol, propanol, isopropanol, n-butanol, sec.-butanol and
amyl alcohol, alkylmercaptans 6uch as dodecylmercaptan and
tert.-dodecylmercap~an, lsooctyl ~hioglycola~e, and Rome
halogen compounds, ah as carbon tetrachloride, chloroform
and methylene chloride.
o2~2
3~7
As usual, the polymerization is carried out in an atmosphere
of protective was, preferably nitrogen.
The reaction may be perfonned in solution, in emulsion or
under the conditions of precipitative polymerization at a
temperature of from 20 to 1~0C., preferably from 40 to 100C.
If water is used as a solvcnt for the reaction, the
polymerization is run ln sollltion and a viscous, aqueotls solution
of the (co-)polymerizates is obtained. The product can be
isolated either by distilling off the waxer from the solution
or by mixing the aqueous solution with organic solvcllts
miscible with water, whereby the (co-)polymer precipitates
ànd can be separated from the liquid phase, e.g., by filtration.
It is preferred, however, to use the aqueous solution of
the (co-~pol,~ner obtained directly, optiona11y after having
adjusted a certain desired concentration.
If (co-)polymerizing is performed in an organic solvent, as
for instarlce in a lower alkanol, prefera~)ly, e.g., in Bert.
butanol, the reaction runs under the con~:i.tions oE rrecini~ativ~
polymerization. In this case, the (co-)polymer Honed pre
cipitates from the starting solution as a solid com~ouncl
during the course of the reaction. it eon be easily isolated
in the usual nlanner, e.g,., by iiltration under suctiorl an-l
drying the jilter residue. 0~ course, it is also possible,
and sometimes referred, -to distill off the organic solvent.
The following working examples demonstrate the use of
compositions according to the invention or the production
of hi~h~viscous acid compositions, especially acld gels.
further illustrative~worklng examples of the preparation of
the polymers of component b, as well as pol~ners of component a
here Y is formylamido, can be found in the aforesaid application
ox Engelhardt et al entitled "later Soluble Copolymers".
ale abbreviations used in the examplcs and in the included
tables have the following meanings:
AM: acrylamide
vinyl-N-methylacetamide
A~IPS: 2-acryla~ido-2-methylpropane sulionic acid
where the exponent
1 signifies khe a~onium salt,
2 signifies the salt with dimethyl- ~-hydroxyl-
ethylamine,
AS; acrylic acid
BIAS: methacrylic acid
N~A: N-methylol-acrylamide
VSSNa: sodi~n salt of vinylsulfonic acid
era: N me~hylol-vinylaceta~ide
VA: vinylacetamide
VF. vinylformamide
N~F: N-methylol-vinylforma~ide
VPA: vinylphosphonic acid
I: ammoniu~eroxidisulfate
B: a combination of a oniumperoxidisulfate + dib~l~yl-
ammoniuDI hydrochloridet
CH3 SO2-CH-NH-COOCH3
COOH
C: azo-isobutylronitrile
VIP: vinyl~yrrolidone.
~923~7
Example 1
a) To 100 g of a 1% by weight aqueous solution of a copolymer of 80%
by weight of acrylamide, 15% by weight of AMYS and 5% by weight of vinyl-
pyrrolidone (K = 201) 5 g of N-methylene-bis-formamide are added. The clear,
slightly viscous solution thus obtained is stable and storable for an un-
limited period of time. Upon mixing this solution with 100 ml of concen-
trated hydrochloric acid the viscosity rises rapidly and within 30 minutes
a gel is formed. At ordinary temperatures of 20 to 25C. the acid gel does
practically not change its property over a period of more than 15 days. At
80 to 90C., however, the gel degrades within 20 minutes to give a slightly
yellowish brown, clear liquid of low viscosity.
The copolymer used in this Example can be produced as follows:
b) 600 ml of deionised water are Eirst introduced into a 2 1 polymer-
isation vessel equipped with a stirrer, thermometer, gas inlet tube, dropp-
ing funnel and heating bath, and the following monomers are then introduced,
while stirring the mixture and passing a slight stream oE nitrogen through
it:
80 g oE acrylamide,
15 g of AMPS and
5 g of vinylpyrrolidone.
ThereaEter 0.5 g oE azodiisobutyronitrile is aclcled ancl the tempera-
ture of the reaction mixture is brought to 50C. by means oE a heating bath.
One ml of a 10% solution of benzoyl peroxide in acetone is then adcled to
cause the polymerisation to commence, with a rise in temperature and in
viscosity, a maximum temperature oE 58C. being reached.
AEter completion of the reaction, the mixture is stirred or a
further hour at 80C. The highly viscous polymer mass is now diluted to 1%
strength by adding water, while stirring.
c) Gels of similar properties are obtained if the copolymer used
above is replaced by a copolymer of 55% by weight of acrylamide, ~0% by
- 25 -
~9~37
weight of AMPS and 5% by weight of vinyl-methylacetamide (K = 165) or with a
copolymer of 60% by weight of acrylamide, 35% by weight of AMPS and 5% of
vinyl-methyl-acetamide (K = 179).
Example 2
To a 3.5% by weight aqueous solution of a copolymer of 70% by
weight of acrylamide, 10% by weight of AMPS, 15% by weight of vinylformamide
and 5% by weight of vinylpyrrolidone (K-value = 152) was admixed, with stirr-
ing, 1% by weight of N-methylene-bis-formamide. The clear solution obtained
was storable without change for an unlimited period of time. Upon adding
thereto the same volume of concentrated hydrochloric acid there was obtained,
within a period of 20 minutes an acid gel which does not alter its state
within a 10 day's period at 20 to 25C.
At 80 to 90C., however, the gel "fuses" within 20 minutes to give
a clear liquid of low viscosity.
Acid gels of similar behavior may be obtained if the copolymer used
in this Example is replaced by the copolymers given in the following table:
AM AMPS net k-value
. . .
20 VIP
25 VIP
20 VIP 39.~6 2l5
20 VIP 30.3 206
20 VIP 32.6 208
All amounts given in this table are parts by weight.
Example 3
To 100 ml of a 1% by weight aqueous solution of a copolymer of
65% by weight of acrylamide and 35% by weight of sodium acrylate (K = 203)
100 ml of concentrated hydrochloric acid are added. The strongly acidic mix-
ture obtained represents a slightly viscous liquid which can be stored em-
changed for an unlimited period of time. Upon adding to it 0.5% by weight
- 26 -
f
237
of methylene-bis-formamide, a gel s-table in shape is formed wi-thin a period
of 10 minutes. At 20 to 25C. the acid gel remains unchanged for at least
12 days, while at 80 to 90 C. a clear liquid of low viscosity is formed
within 30 minutes. A similar acid gel may be produced if the methylene-bis-
formamide used above is replaced by the same amount of a compound having the
formula
~C-NH-CH2-0-CH -Nll-C~
The aqueous polymer solution used can be obtained by adding, under
vigorous stirring, 2.6 ml of a copolymer emulsion produced as described be-
low, into 97.5 ml of water.
The copolymer emulsion is produced as Eollows:
1.85 g of sorbitan monostearate are dissolved in 30 g of a technical
isomeric hydrocarbon solvent having a boiling range of from 200 to 2~0C.
The solution is introduced into a 2-liter reaction vessel fitted
with a mechanical stirrer, thermometer and gas inlet for nitrogen. A solu-
-tion of monomers is produced by dissolving 33.9 g of acrylamide and 18.2 g
of acrylic acid in 50 ml of deionized water and the pll-value of the mixture
is adjusted to 8.5 by adding a 20% aqueous solution of sodium hyclroxkle.
Then the aqueous monomeric solution is slowly added to -the orgallic sorbitan
monostearate solution while vigorously stirring and the air -in tlle react:io
vessel :is replaced by nitrogen.
0,07 g of 2,2'-Azobis-iso-butyronitrile, dissolved in ace-tone, are
added to the emulsion of the monomers and then the reaction vessel is gen-tly
heated to 60 C. while stirring. The polymerising reaction was finished with-
in 2.5 hours resulting in a stable 39% by weight strength emulsion of the
copolymer having a K-value of 203.
1% by weight aqueous solution of a copolymer of 90% acrylamide and
10% of dimethylaminoethyl-methacrylate (used for polymerising as the acetate)
- 27 -
'. '
237
containing 5% by weight of N-methylene-bis-formamide was mixed, at a volume
ratio of 1 19 with concentrated hydrochloric acid which results in an acid
gel within 10 minutes. At 20 to 30C., the gel obtained remains unchanged
for more than 8 days but collapses to give a clear liquid of low viscosity
at 80 to 90C.
Replacement of the N-methylene-bis-formamide by the same amount of
a compound having the formula
C - N - CH - N - O
H - CH3 C113 CH3
leads to a similar result.
The aqueous polymer solution used can be obtained by adding, under
vigorous stirring, 4.8 g of a copolymer emulsion produced as described below,
into 95.2 ml of water and subsequent addition of 5 g of N-methylene-bis-
formamide.
The copolymer emulsion is produced as follows:
185.0 g oE a mi.xture of 84% strength saturated aliphatic hydrocarbons and
16% strength naphthenic hydrocarbons (boiling point of the mixture: 192 to
254C.), 188.3 g of a chloroalkane having a chlorine content of 66.5 and a
density of 1.575 kg/m3 and 32 g of sorbitan monooleate are mixed in a vessel
equipped with a stirrer, a thermometer and a nitrogen inlet and outlet.
After having well intermixed the constituents, a solution of 180 g
of acrylamide and 20 g of dimethylaminoethyl-methacrylate-acetate in 387.5
parts of water is added and the aqueous phase is emulsified in the organic
phase. Nitrogen is allowed to pass through the mixture for 30 minutes,
which is then heated within 15 minutes to a temperature of 60C. At this
temperature a solution of 0.212 parts of 2,2'-azo-bis-isobutyronitrile in a
slight amount of acetone is added. After having heated the mixture to 60 C.
for 3 hours the polymerization is complete.
A dispersion is obtained which does not clot, is safe against sedi-
mentation, has a viscosity of 710 m Pa sec. at 29.3 sec. 1 and contains a
,"~ - 28 -
237
polymer having a value of 201. Polymer contents: 20.8%.
Example _
a) 1.85 g of sorbitan monostearate are dissolved in 28 g of Isopar* M,
a technical isomeric hydrocarbon solvent having a boiling range of from 200
to 240 C., sold by Exxon Corporation. The solution is introduced into a
2-liter reaction vessel fitted with a mechanical stirrer, thermo~leter and
gas inlet for nitrogen. A solution of monomers is produced by dissolving
33.9 g of acrylamide and 2,4 g of acrylic acid in 40 ml of deionized water
and the pH-value of the mixture is adjusted to 8.5 by adding a 20% aqueous
solution of sodiumhydroxide.
Then the aqueous monomeric solution is slowly added to the organic
sorbitan monostearate solution while vigorously stirring and the air in the
reaction vessel is replaced by nitrogen.
0.07 g of 2,2'-azobis-iso-butyronitrile, dissolved in acetone, are
added to the emulsion of the monomers and then the reaction vesscl is gently
heated to 60 C. while stirring. ale polymerising reaction was finished wi-th-
in 2.5 hours resulting in a stable emulsion oE the copolymer.
by 67 g of Isopar M are introduced into a l-liter polymerization
Elask and heated to a temperature of 60C., with weak stirring, 0.27 g of
sorbitan monolaurate, 1.3 g of sorbitan monostearate, 0.17 g of sorl)itall
monooleate and 4.3 g oE polyoxyethylene sorbitan monostcarate bring SLlCCeS-
sively added and dissolved. With further weak s-tirring a s-tream oE nitroge
is passed into the solution and the temperature is adjus-tecl-to 60 C.
94 ml of water are given into a separate vessel and 2.9 g oE AMPS,
10.0 g of VIMA, 10.0 g of vinyl ~yrrolidone and l0.~ g of N-vinyl formamide
are added and dissolved while stirring. This solution is adjusted to a pll-
value of 8 to 10 by the dropwise addition of 10% strength aqueous solution
oE sodium hydroxide, 0.1 g of ammonium persulfate being subsequently added.
This monomeric solution is then emulsified in the organic phase via a dropp-
ing funnel in the reaction flask, with rapid stirring. The polymerization
* Trade Mark - 29 -
23~
reaction starts after approx. 30 minutes, which is recognizable by a rise in
the temperature. In the course of 15 minutes the reaction temperature rises
to 80 - 90C. The polymerizing reaction having faded out, the solution is
heated for another two hours at 80C. A stable emulsion having a polymeric
content of 30 percent by weight is obtained. The molecular weight of the
polymer is 1.5 . 106.
The two emulsions obtained under items a) and b) of this Example
are intermixed and thoroughly homogenised by vigorously stirring the mixture
for 5 Minutes. The copolymer composition thus obtained has a copolymer con-
tent of about 27% and represents a highly active, valuable thickening agent
for aqueous acids.
Example 6
a) 185.0 parts of a mixture of 8~% strength saturated aliphatic hydro-
carbons and 16% strength naphthenic hydrocarbons boiling point of the mix-
ture: 192 to 25~C.), 188.3 parts of a chloroalkane having a chlorine con-
tent of 66.5 and a density of 1,575 kg/m3 and 32 parts of sorbitan mono-
oleate are mixed in a vessel equipped with a stirrer, a thermometer and a
nitrogen inlet and outlet.
After having well intermixed the constituents, a solution of
212.5 parts of acrylamide in 387.5 parts of water is added and the aqueous
phase is emulsified in the organic phase. Nitrogen is allowed to pass
through the mixture for 30 minutes, which is then heated within 15 minutes
to a temperature of 60 C. At this temperature a solution of 0.212 parts of
2~2'-azo-bis-isobutyronitrile in a slight amount of acetone is added. After
having heated the mixture to 60C. for 3 hours the polymerization is com-
plete.
A dispersion is obtained which does not clot, is safe against sedi-
mentation, has a viscosity of 710 m Pa sec. at 29.3 sec. 1 and contains a
polymer having a K value of 201.
b) 150 g of Exsol* D, a deodorized kerosene boiling between 190 to
* rrade Mark _ 30 -
Phi
23~7
240 O sold by Esso Chemie of Germany, are introduced into a l-liter poly-
merization flask and hea-ted to a temperature of 60C., with weak stirring,
1.3 g of sorbitan monolaurate~ 6.5 g of sorbitan monostearate, 0.8 g of
sorbitan monooleate and 22 g of polyoxyethlene sorbitan monostearata being
successively added and dissolved. With further weak stirring a stream of
nitrogen is passed into the solution and the temperature is adjusted to 60 C.
150 ml of water are given into a separate vessel and 30 g of AMPS, 45 g of
vinyl pyrrolidone and 55 g of N-vinyl formamide are added and dissolved
while stirring. This solution is adjusted to a pH value of 8 to 10 by the
dropwise addition of 10% strength aqueous solution of sodium hydroxide, 0.3 g
of atmmonium persulfate being subsequently added. rhis monomeric solution is
then emulsified in the orgculic phase via a dropping funnel in the reaction
flask, with rapid stirring. The polymerization reaction starts after approx.
30 minutes, which is recognizable by a rise in the temperature. In the
course oE 15 minutes the reaction temperature rises to 80 - 90 C. The poly-
merizing reaction having Eaded out, the solution is heated for another two
hours at 80C. A staple emulsion having a polymeric content of 30% by
weight is obtained. The molecular weight of the polymer is 95,000.
The two emulsions obtained under items a) and b) of this example
are intermixed and thoroughly homogenised by vigorously stirring the mixture
for 5 minutes. The copolymer composition thus obtained has a copolymer con-
tent of about 27% and represents a highly active, valuable thickening agent
for aqueous acids.
A gas well in West Texas is selected to fracture-acidize. The
well has production interval from a depth of 9~650 to 9,740 feet. At this
interval, the bottom hole static temperature is 170F while the formation
permeability averaged 0.1 md. The well productivity prior to treatment is
4 MCF/day and 5 barrels of condensate by natural flow.
The fracture-acidizing fluid is prepared by blending 40,000
- 31 -
3~7
gallons of a 15% hydrochloric acid solution containing 80 gallons, 0.2% by
weight, of a common corrosion inhibitor with 1,600 pounds (40 lb per 1000
gallons) of a fine powdered (lOO-120 mesh) copolymer. The copolymer con-
tains 55% by weight acrylamide, 40% by weight oE AMPS and 5% by weight of
N-methyl-N-vinyl acetamide (K = 165). In addition, 80 gallons, 0.2% by
weight, of a nonionic fluorosurfactant is also blended into the treating
fluid. After one hour of storage in two frac tanks, a low viscosity fluid
(I 35 cps at 511 sec. 1 on a Fann 35) is obtained. Upon injection of the
fluid into the well bore, the aqueous crosslinking solution containing 50%
by weight of active polymer from a composition of 80% N-vinyl formamide, 10%
acrylic acid and 10% N-vinylpyrrolidone is added at a rate of 4 gallons per
1000 gallons of treating fluid. The injection rate is 12 barrels per minute
at a surface treating pressure of 6000 psi. After approximately 85 minutes,
the well is shut-in for 6 hours to allow the acid to react. After this time,
the well head pressure is relieved and the well is placed back into a flow-
ing status. The well productivity is tested and found to be significantly
improved.
In its broadest aspects, highly viscous acid preparations or acid
gels of the present invention may contain from 70 to 99.8% by weight of one
or more of the aforementioned acids and 0.2 to 30% by weight of the cross-
linked polymer composition having characteristic -NR -CH=N-CO- bridges. It
is generally preferred that substantially all (at least 50% and preferably
at least 70%) crosslink bridges have the aforesaid formula. Other known
crosslink bridges may also appear in the final product depending upon the
presence of other moieties in components a or b) and/or the addition of
known crosslinking agents reactive with such moieties.
As stated earlier, the amidocarbonyl groups of component a) are
carried on macromolecules. This is because the macromolecule seems to
stablize the resulting bridge. Where the molecule to which the amido-
carbonyl groups are attached is of insufficient size, no or only a small
- 32 -
,
~8~Z37
number of desired bridges are stabilized, and the bridges appear to be de-
graded to formic acid, ammonium ion, amine, carboxylic acid and possibly
other degradation products by hydrolytic action.
- 33 -
..
