CA1302003C - Acid viscosifier compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Cationic, anionic and amphoteric polymers suitable for the preparation of acid viscosifier compositions and the acid viscosified compositions are provided. The polymers are water soluble or water dispersible and are based on acrylyl monomers having the stated ionic charge. They are capable of viscosifying acid solutions that have important use in recovery of gas and oil from subterranean formations.

Description

~L3C~

ACID ~ISCOSIFIER COMPOSITIONS
The use of polymeric compositions to thicken or viscosify acid compositions is well known and commonly practiced in the gas and oil recovery field.
Though many polymers are used, problems are often encountered~ e~g., loss of viscosity of the acid composition, precipitation of the polymer from solution, degradation resulting from exposure to elevated temperatures in the subterranean formation, and sensitivity to calcium ions. The polymers of this invention have been found to alleviate some of the problems.
Canadian Patent No. 1,133,788, issued to K.
G. Phillips et al., on October 19, 1982, discloses water-in-oil emulsions of MAPTAC and acrylamide cationic polymers but does not disclose their use as acid viscosifying agents.
U.S. Patent No. 3,943,966, issued to Lo J.
Guildbault on March 16, 1976, discloses use of MAPTAC-containing polymers in cements.
U.S. Patent No. 4,022,731, issued to J. M.
Schmitt on May 10, 1977, discloses MAPTAC-AM polymers but does not disclose use as an acid viscosifying agent.
U.S. Patent No. 4,191,657, issued to B. L.
Swanson on March 4, 1980, discloses the use Or water ~,i."! dispersible polymers based on acrylamide or methacrylamide, the hydrolyzed polymers thereof? the crosslinked polymers thereof, the hydrolyzed crosslinked polymers thereof, and copolymers thereof with other monomers, in the production of acid compositions suitable for matrix-acidizing or ~L3~ 3 fracture-acidizing subterranean formations. However, it nowhere discloses our claimed polymers~
U.S. Patent No. 4J452~940~ issued to M. R.
Rosen on June 5, 1984 and U.S. Patent No. 4~529,782, issued to Y. L. ~an et al. on July 16t 1985, disclose the producton of water-in-oil emulsions and water soluble polymers. However, they do not disclose the polymers of this invention nor their use in producing viscosified acid compositions.
European Patent Application 0122073, published on October 17, 1984, discloses a terpolymer of acrylamide/sodium styrene sulfonate/methacryl-amidopropyltrimethylammonium chloride and its use in drilling muds having a basio pH of about 10 to 10.5.
Not only are the polymers different than those of this invention, but it is not concerned with highly acidic viscosified acid compositions.
The cationic, anionic and amphoteric polymers of this invention are essentially water soluble and can be used to prepare viscosified acid compositions having improved properties.

T~E INVENTION
_ This invention is directed to polymers useful as viscosifying agents to thicken acid solutions that are employed in gas and oil well acidizing operations. The polymers are those cationic polymers (Group A), anionic polymers (Group B) and amphoteric polymers (Group C) hereinafter defined.

~3~26)~3 Acid treating or acidizing of porous subterranean formations is an accepted procedure for increasing the yield and/or production of fluids from the well, be they liquid or gaseous. These procedures are so well known and so extensively practiced that detailed explanation is neither necessary nor o~ assistance to one of ordinary skill in this field. Suffice it to say it is an internationally practiced procedure to acid treat wells and the patent and related published technical literature is replete with material detailing the procedure.
Though there is an abundance of published material and commercial compositions available, the industry is continuously looking for improvements.
Among the problems that still exist are inadequate penetration of the acid into the formation, fluid loss in the more porous ~ones of the formation and leak-off at the fracture faces1 any one of which may have a deleterious effect on the well's production.
Among the attempts ~hat have been made to resolve some of these problems has been the addition of various polymeric thickening agents. These agents seem to thicken the acid solution and increase its viscosity and in many instances the higher viscosity or thickened acid solutions have reduced fluid loss properties. In this regard attention is directed to U.S. Patent No. 3,415,319 (B. L. Gibson) and U.S.
Patent No. 3,434,971 (B. L. Atkins). It has also been indicated that these thickened acid solutions show a lesser reaction rate with the acid-soluble portions of the formation. In this regard attention ~3~2~3 is directed to U.S. Patent No. 3,749,169 (J. F.
Tate), U.S. Patent No. 3,236,305 (C. F. Parks) and U.S. Patent No. 3,252,904 (N. F. Carpanter).
The higher viscosities additionally have an advantage in fracture-acîdizing operations because these thicker and more viscous acid solutions produce longer and wider fractures. They are also more effective in carring propping agents into the formation when they are employed.
A problem existing in acidizing operations is the instability of the viscosifier in the acid solution to heat. This problem can be particularly troublesome when using acidizing solutions that contain thickening or viscosifying agents. Stability to heat, the retention of the increased or higher viscosity properties of the acidizing mixture under the conditions existing in the well or formation is important. The most satisfactory acidizing mixtures or compositions are those which are sufficiently stable to resist degradation by the heat in the well and, particularly, in the formation for a period of time sufficient to accomplish the intended purposes of good penetration andtor significant etching of the formation. The degree of stability will vary from one formation to another, as is known, and is dependent on many factors present during the operation. For instance the siæe and depth of the well, the type of subterranean formation present, the concentration of the acid in the acidizing solution, the temperature conditions existing throughout the well bore and the formation, etc. All of these factors as well as many others are known to affect ~3~ 3 the stability of the acidizing solution with the temperature, which can be as high as 4000F or more, having a pronounced effect and is considered one of the most important operating variables when considering stabiliSy. Increased temperature not only hastens degradation with resultant decrease in viscosity but also increases the rate o~ reaction of the acid in the formation resulting in treatment of a smaller area of the formation; both being undesireable. Thermal degradation must be distinguished from loss of viscosity (thermal thinning) due to increased temperature, also a common phenomenon.
The present invention generally alleviates several of the problems discussed and provides polymers useful for the production of thickened or , viscosified acid solutions, and new thickened or j viscosified acid solutions containing said polymers.
The following glossary is presented to facilitate an understanding of the designations used to identify the various compounds:
MAPTAC - methacrylamidopropyltrimethylammonium chloride MAPDMOAC - methacrylamidopropyldimethyl-n-octyl-ammonium chloride MAPDMDAC - methacrylamidopropyldimethyl-n-dodecyl-ammonium chloride MAPDMCAC - methacrylylamidopropyldimethylcetyl-ammonium chloride AM - acrylamide MAM ~ methacrylamide NAM - N-methylacrylamide D-153~7 ~ 3 NND~AM - N,N-dimethylacrylamide DMAPA - dimethylaminopropylmethacrylamide ~aAMP ~ - s~dium 2-acrylamido-2-methylpr~pane sulfonate NPPE~, ~ n~nylphenoxyp~ly(ethyleneoxy)ethylmeth-acrylate DMDAAC - dimethyldiallylammonium ~hl~ride SPP - N~(3-sulropropyl)~ ethacrylamid~propyl-- N,N-dimethyl ammonium betain YAZO 33~ - 2,2'-az~b-is(2,4-dimethyl-4~methoxy valeronitrile) VAZO 52~ - 2,2'-azobis(294-di~ethyl valeronitrile) TERGITOL ~P10~ - 10 mole ethoxylate of nonylphenol VERSO~X 80a - pentasodium salt of diethylene-triamine pentaacetic acid Santonox R~ - a phenolic thioether Ionol~ - di-t-butyl-p-cresol Isopar M6 _ hydrooarbon oil The Group A ca:ionic polymers ar~ the polymers presented ~y Generic Formula A. They are produced by polymerizing monomer ~i) alone or in`
com~ination with one or ~ore ~S the ~onomers (ii), (iii) and/or (iv):
(i) an acrylamidoalkyltrialkylammonium halide or a ~ethacrylamidoalkyltrialkylammonium halide;
(ii) acrylamide, an N-alkylacrylamide or an N,N-dialkylacryla~ide;
(iii) a hydrophobic acrylamidoalkYltrialkYlammonium - halide or ~e~hacrylamidoalkyltr~alkylammonium halide dirSere~t than that ~hich ~as used as ~3~Z al~3 monomer (i); as (iii) is defined in Generic Formula A; and (iv) a polyunsaturated monomer.
The cationic polymers of this group appear to perform well in the laboratory under acidizing conditions usually encountered in the field. They exhibit good solubility and stability in acid - solutions at only moderate cationic levels, they exhibit good viscosity retention after thermal aging in acid, they are capable of forming very high molecular weight polymers thus giving rise to high viscosif`ying efficiencies, the polymers containing the polyunsaturated monomer modifier in the molecule often exhibit improved thermal thinning behavior over the corresponding unmodified versions, and they are compatible with other cationic additives generally used in the field. Those containing the hydrophobe (iii) and/or polyunsaturated monomer (iv) are novel polymers.
GENERIC FORMULA A
R R R
~CH2-C~fcH2-c~cH2_c~G~
- C =O C =O C -O
s Q N Q
/ ~ l R' R R R' 1~
R"-N-R" R"-N-R"
X~ I X~
R" R"' !
I

3~ 3 where R = H or CH3;
R~ = a linear or branched alkylene radical having ~rom 2 to 10 carbon ato~s, pre~erably from 2 to 6 carbon atoms, most prererably from 2 to 4 ¢arbon atoms;
R" - H or alkyl, llnear or branched, having - from 1 to 3 carbon atoms, preferably from 1 to 2 carbon atoms;
R"' ~ an alkyl groupt linear or branched, having about 8 to about 25 carbon atoms, preferably from 4 to 18 carbon ~toms;
aryl, alkaryl or aralkyl having from 6 to lB carbon atoms;
Q = -NR- or -0-;
G = a residual unit derived from a polyunsaturated monomer;
X~ - a halogen ion (F, Cl, Br1 I) or a methyl sulfate ion;
b _ from about 10 to 100 mole percent, preferably from 20 to 50 mole perc~nt, most pre~erably ~rom 30 to 50 mole percent; ~ith the proviso that (b) i~
not more than 9g.9DS when (d) is greater than zero c - ~rom about O to 90 ~ole percent, preferably from 50 to 80 ~ole percent, most prererably from 50 to 70 mole percent;
d ~ from O to about 10 ~ole percent, pre~erably rrom 0.1 to about 2 ~le peroent; and e ~ rrom O ~o 2 ~ole p~rcent, preferably ~ro= O te 0~5 ~ole percentO

~_153B7 .

; . .
i ~ 1 , r ~ !, ~L3~)2~3 g Illustrative type (i) water-soluble monomers include methacrylamidopropyltrimethylammonium chloride ? methacrylamidopropyltrimethylammonium ~ethylsulfate, methacrylamidopropylhydroxyethyl-dimethylammonium acetate, methacrylamidopropyli~o-propylammonium chloride, methacryloyllethyltrimethyl-ammonium chloride, acryloylethyltrimethylammonium chloride~ methacryloylethyltrimethylammonium methylsulfate, acrylolethyldimethylethylammonium ethylsulfate and the like.
Illustrative type (ii) monomers include acrylamide, N-methylacrylamide and dimethylacryl-amide, alpha-methyl acrylamide, alpha-methyl-N-methylacrylamide, alpha-methyl-N,N-dimethylacryl-amide.
Illustrative type (iii) hydrophobic ~onomers include methacrylamidopropyldimethyl-n-octylammonium chloride, methacrylamido-propyldimethyl-n-dodecyl ammonium chloride, me~hacrylamidopropyldimethyl_ cetylammonium chloride, methacryoylethyldimethyl-octylam~onium chloride, methacryloylethyldimethyl-cetylammonium chloride, acryloylethyldimethyldodecyl-ammonium chloride, acryloylethyldimethyloctylammonium chloride, methacrylamidopropyldi~ethylhexylammonium chloride, methacryloylethyldimethylstearylammonium chloride and the like.
Illustrative type (iv) monomers include ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, ethylene glycvl dimethacrylate, diethylene glycol dimethacrylate, diurethane di~ethacrylate, I)_15387 ~2~3 -- 1 o --1,4-butandiol dimethacrylate, polyglycol-400 dimeth-acrylate, neopentyl glycol dimethacrylate, triethyl-ene glycol dimethacrylate, N,N'-isovalerylidene-bis methacrylamide, N,N'-methylene-bis-methacrylamide and the like.
These Group A Cationic Polymers pos~sess good solubility, can be made to have high molecular ~ weights and can be used over a wide temperature range in viscosified acid solutions in subterranean formations.

The Group B Anionic Polymers The Group B anionic polymers are the copolymers represented by Generic Formula B. They are produced by copolymerizing three or more of the ~ monomers:
:~ (i) an acrylamidoalkyl sulfonic acid or a methacrylamidoalkyl sulfonic acid or the salts thereof;
t (ii) acrylamide, N-alkylacrylamide or N,N-dialkylacrylamide;
(iii) a hydrophobic acrylic acid ester or methacrylic acid ester or acrylamidohydrocarbyl wherein the hydrocarbyl group is as defined by R" in Generic Formula B; and (iv) a polyunsaturated monomer.

~;~1)2~4D3 GENERIC FORMULA ~
R R R
~CH2-C~cH2_c~cH2_c - ~G~
I f \ I /h I i ~ / k C=O C=O C=û
Q N Q
/ \
R' R R R"

(I) where R = H or CH3;
R' = a linear or branched alkylene or arylene radioal having from 2 to 10 carbon atoms, preferably from 2 to 6 carbon atoms, most preferably from 2 to 4 carbon atoms;
M~ = H+, Na+, NH4~, or other j monovalent metal atom (Mef);
G = a unit derived from a polyunsaturated monomer;
Q = a divalent radical such as -O-, -NR-;
R" = C4-C1g alkyl, C7-C24 aralkyl or an ethoxylated C7-C24 aralkyl;
f = from about 10 to 60 mole percent, preferably from 20 to 50 mole percent;
h = from about 39.99 to 89.99 mole percent, preferably from 49.9 to 79.9 mole percent;
j = from 0.01 to 10 mole percent, preferably from 0.1 to about 2 mole percent; and k = from O to 2 mole percent, preferably from 0.1 to 0.5 mole percent.

Illustrative type (i) monomers include sodium 2-acryla~ido-2-methylpropane sul~onate, sodium 2-acrylamidoethane sulfonate, potassium 3~methacryl-amidopropane sulfonate, ammonium p-acrylamidobenzene-sulfonate, potassium 6-acrylamidonaphthalene sulfonate, disodium 4-methacrylamidobenzenedisul-fonate-1,3, tripotassium 3-acrylamidonaphthalene trisulfonate-1,5,6~ and the like.
Illustrative type (ii) monomers include acrylamide, N-methylacrylamide, N,N-dimethylacryl-amide, alpha-methylacrylamide, alpha-methyl-N-meth-acrylamide, alpha-methyl-N,N-dimethy;acrylamide.
Illustrative type ~iii) hydrophobic monomers include N-butylacrylamide, N-t-butyl-acrylamide, N-decylacrylamide, N-stearylacrylamide, the N-pentyl-acrylamides, N-butylmethacrylamide, N-decylmethacryl-amide, N-benzylacrylamide, N-tolylacrylamide, N-benzylmethacrylamide, N-tolylmethacrylamide, N-t-butylmethacrylamide, the butyl acrylates, the decyl acrylates, phenyl acrylate, tolyl acrylate, t-butyl methacrylate, octyl methacrylate, phenyl methacrylate, nonylphenoxypoly(ethyleneoxy)ethylmeth-acrylate, and the like.
Illustrative type (iv) polyunsaturated monomers include ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, diurethane dimethacrylate, 1,4-butandiol dimethacrylate, polyglycol-400 dimethacrylate, neopentylglycol dimethacrylate, triethyleneglycoldimethacrylate, N,N'-isovalerylidene-bis-methacrylamide, N,N'~methylene-bis-methylacrylamide, and the like.

It was unexpected and unpredictable to discover that the viscosifying ability of the Group B
Anionic Polymers was enhanced rather than impaired by the incorporation of the hydrophobic component and that even a weak hydrophobe, such as a C4-al~yl moiety benefited the acid-solution viscosity. These polymers also exhibited good solubility in acid.
Applicants do not intend to be bound by the above theoretical explanation. The viscosifying ability of the hydrophobe-modified anionic polymers was found to be better than the counterpart hydrophobe free polymer. Theoretically this may be explained as being caused by an association of the hydrophobe group.
,, The Group C Amphoteric Polymers The Group G amphoteric polymers are those represented by Generic Formulas C and D. These poly-ampholyte copolymers are particularly useful acid viscosifiers in acid solutions used where a high degree of tolerance to calcium ions is required.
During the course of an acidizing operation an increasingly higher concentration of calcium chloride generally forms due to the reaction of hydrochloric acid with limestone or dolemite formations. The presence of high concentrations of calcium ions is usually detrimental to the stability of many poly-electrolytes leading to either a loss of solution 1 viscosity or polymer precipitation or both. We have found these polyampholytes provide the required solu-bility and stability in acid solution and as shown in the data below are stable in the presence of calcium.

The Generic Formula C polymers are produced by copolymerizing three or more of the monomers;
(i) a cationic polymerizable monomer;
(ii) an anionic polymerizable monomer;
(iii) a hydrophobic acrylic acid ester or methacrylic acid ester or acrylamidohydrocarbyl wherein the hydrocarbyl group is as defined by R";
~ (iv) acrylamide; and (v) a polyunsaturated monomer.
The Generic Formula D polymers are produced by copolymerizing at least three of the monomers;
(i) a Zwitter-ion polymerizable monomer;
(ii) a hydrophobic acrylic acid ester or methacrylic acid ester or acrylamidohydrocarbyl wherein the hydrocarbyl group i9 as de~ined by R";
(iii) acrylamide; and (iv) a polyunsaturated monomer.
l GENERIC FORMULA C
, R R
A ~ 1 B ~ CH2-C ~ CH2-C ~ G t \ ¦ /m \ ¦ n\ I P\ I q r ~9 ~3 C=O C=O
Q N
/ \
R" R R

GENERIC FORMULA D
_ R R
~ C ~ CH2-C ~ CH2-C _ ~ G
- ~ C=O C-O
Q N
R" R R

where A- ~ = the residue of a cationic monomer;
B- 0 = the residue of an anionic monomer;
C- ~ - 0 = the residue of a Zwitter-ion monomer;
R, R'l, Q and G are the same as previously defined from Generic Formula B;
m = 10-49.99 mole percent; prePerably 20-35 mole percent;
n = 10-49.99 mole percent, preferably 20-35 mole percent;
p = 0.01-10 mole percent; preferably 0.1-2 mole percent;
q = 0-80 mole percent, preferably 30-60 mole percent;
r - 0-2 mole percent, preferably 0-0.5 mole percent;
s = 5-99.99 mole percent, preferably 10-50 mole percent; and ,~ t = 0-95 mole percent, preferably 50-90 mole percent with the previso that the sum thereof equals 100 mole percent.
Of course one can use a mixture oP A-0, B-~and C~ type monomers in a single copolymer and this is considered with the scope of our claimed invention. In such instances, the copolymers can be represented by the following formula wherein the variable x is modified to produce an appropriate viscosifying agent.
R R
~A~1B- ~ LC~CH2_C~CH2C~G~
\ I Jx \ I lx \ I ~x l /x I x ~x ~3 9 ~ C=O 1=0 Q N
R'l R R

~3~ 3 The cationic, anionic and Zwitter ionmonomers are well known to the ordinary skilled polymer chemist; any suitable monomer can be used.
Illustrative suitable cationic polymerizable monomers include dimethyldiallylammonium chloride, methacryloylethyl trimethylammonium chloride, acryloylethyl trimethylammonium methylsulfate, methacryloylethyldimethylethylammonium ethyl sulfate, methacrylamidopropyltrimethylammonium chloride, vinylmethylpyridinium chloride, and the like.
Illustrative suitable anionic polymerizable monomers include sodium 2-acrylamido-2-methylpropane sulfonic acid, sodium acrylate, potassium methacrylate, sodium 2-acrylamidoethane sulfonate, potassium 3-methacrylamidopropane sulfonate, and the like.
The cationic and anionic monomers may be present in the form of an ion-pair such that no other counter ions are present. The ion-pair monomers ! would enter the polymerization as if they were a ' single entity. Illustrative ion-pair monomers include dimethylaminopropylmethacrylamide, and 2-acrylamido 2-methylpropane sulfonic acid and the like.
; Illustrative suitable Zwitter-ion polymerizable monomers include N-(3-sulfopropyl)-N-methacrylamido-propyl-N,N-dimethyl ammonium betain, N-(3~sulfo-propyl)-N-methacryloxyethyl-N,N-dimethylammonium ~ betain 7 and the like.
! The suitable hydrophobic monomers and polyunsaturated monomers are those set forth as illustrative for types ~iii) and (iv) for Generic ~3~ 33 Formula B. Illustrative type (iii) hydrophobic monomers include N-butylacrylamide, N-t-butylacryl-amide~ N-decylacrylamide, N-stearylacrylamide, the N-pentylacrylamides, N-butylmethacrylamide, N-decyl-methacryla~ide, N-benzylacrylamide, N-tolylacryl-amide, N-benzylmethacrylamide, N-tolyl~ethacrylamide, N-t-butylmethacrylamide~ the butyl acrylates, the decyl acrylates, phenyl acrylate, tolyl acrylate, t-butyl methacrylate, octyl methacrylate, phenyl methacrylate, nonylphenoxypoly(ethyleneoxy)ethylmeth-acrylate. Illustrative type (iv) monomers include ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacryl-ate, diurethane di~ethacrylate, 1,4-butandiol dimeth-acrylate, polyglycol-400 dimethacrylate, neopentyl glycol dimethacrylate, triethylene glycol dimeth-acrylate, N,N'-isovalerylidene-bis-methacrylamide, N,N'-methylene-bis-methacr~lamide, and the like.
It is recognized that small amounts of other polymerizable monomers can be present in any polymer discussed above.
The polymerization reactions for producing the above polymers can be carried out using any of the methods known in the art. For example as disclosed in U.S. Patent No. 4,191,657 (B. L. Swanson), U.S.
Patent No. 4,452,940 (M. R~ Rosen), U.S. Patent No.
4,485,209 (Y. L. Fan et al.), U.S. Patent No.
4,529,782 (Y. L. Fan et al.) and South African Patent No. 84-01784 (Y. L. Fan et al.). The preferred method, however, is that which was used to produce the polymers in the examples.
i ~3~ 3 In a typical polymerization process the method comprises;
ta) combining the monomers, an oil soluble surfactant, water and hydrophobic- liquid ~edium in the conventional manner;
(b) homogenizing the mixture from (a) to form a water-in-oil emulsion;
(c) deoxygenating the emulsion from ~b);
(d) adding initiator(s) to the deoxygenatd emulsion from (c);
(e) heating and stirring the mixture from (d) under polymerization conditions so as to form a water-in-oil polymer emulsion; and (f) recovering the polymer in whatever physical form desired.

In this procedure, the aqueous phase generally comprises from about 60 weight percent to about 85 weight percent, preferably from about 70 weight percent to about 80 weight percent, of the total composition .
The hydrophobic medium suitable fGr use in ~his invention includes benzene, xylene, toluene, mineral oils, petroleum and mixtures~ hereof. A preferred hydrophobic medium is Isopar'~h~ Any oil-soluble surfactant that supports a water-in-oil emulsion and does not have an unduly harmful e~fect on the polymerization reaction can be used. The pre~erred surractant3 are those ha~ing a Hydrophile-Lipophile Balance (HLB) of ~rom about 1 to about 10, pre~erably rrom about 2 to about 6. These ~urfactants are well known and include She fatty acid ester~, and aq ~L3~2~3 ~ g sorbitan monolaurate, sorbit n monostearate, sorbitan monooleate, sorbitan trioleate; mono- and diglycer-ides, such as those obtained from the glycerolysis of edible ~ats; polyoxyethyleneated fatty acid e~ters, such as polyoxyethylene-(4)-sorbiSan monostearate;
polyoxyethyleneated linear alcohols, such as TERGITOL$ 15-S~3 and SERGITOL0 ~25=L-3; polyoxyethyl-ene sorbitol esters, such as polyoxyethylene sorbitol beeswax derivatives; polyoxyethyleneated alcohols, such as polyoxyethylene-(2)-c ~ l ether; polyester ether copolymers (e.g. Rapiso -246, ICI); and the like, or mixtures thereof.
Any of the known free radical initiators can be used at catalytic amounts sufficient to carry out the polymeri~ation, generally from about 0.05 to about 0.5, preferably from about 0.1 to about 0.25 weight percent, based on the weight of monomers charged. The initiator can be added directly or diluted with solvent and can be incrementally added during the course of the reaction if desired.
Illustrative initiators include the peroxides, such as t butyl hydroperoxide, t-butyl perbenzoate, benzoyl peroxide, ammonium persulfate, cumene f~
hydr~ eroxide~the azo compounds, such as VA~0~ 3, VA~0~ 2, VAZ0~4; redox catalysts; and others known to those of ordinary skill in the art.
The polymerization is carried out at a temperature ~rom about 30C to about 800C, preferably from about 40C to about 600C. The time will vary depending upon the particular reactants being employed, the temperature, the size of the batch and other corditions pr~valent during the poly~eri2ation.
Normally cooling ~ r~quired.

Do15387 .~ .

~3~2 [)~3 _ 20 -The pressure is not critical and can be subatmospheric, atmospheric or superatmospheric. The polymerization i5 preferably carried out under an lnert atmosphere. However, at times, small quantities of air or oxygen may be ~parged into t~e reaction mixture to assist in controlling the polymerization reaction rate; the amount of dissolved oxygen in the aqueous pha~e is usually less than about 1 part per million.
After the polymerization is complete, an antioxidant, or any other desired additive, can be added to the reaction mass, generally in an amount of from about 0.05 to about 5 parts per hundred parts of resin. Any organic antioxidant suitable for the product can be used; it is generally added in the form o~ a solution in a suitable solvent. Suit~ble antioxidants include substituted phenols, such as Ionol; thiobisphenols, such as Santonox R~;
hydroquinone derivatives, ~uch as the monomethyl ether of hydroquinone; benzothiazole; ammonium or sodium thiosulfate; alkaline metal thiocyanates;
aminocarboxylic acids; or any of the other antioxidants known to those skilled in the art~
An inverting sur~actant, e.g. TERGITO~NP10, may be added to the water in-oil emulsion at the conclusion of the reaction. The surfactants which may be used include polyoxyethylene alkyl phenol, polyoxyethylene (10 mole) cetyl ether, polyoxyethyl-ene alkyl-aryl ether1 quaternary ammonium derivatives, potassium oleate, N-cetyl N-ethyl ~orpholinium ethosul~ate, sodium lauryl ~ulfate, condensation productg ~r higher fatty alcohol~ with D-1~387 . ," .

)3 ethylene oxide, such as the reaction product of oleyl alcohol with 10 ethylene oxide units; condensation products of alkylphenols and ethylene oxide, such as the reaction products of isooctylphenol with 12 ethylene oxide units; condensation products of higher fatty acid amines with five, or more, ethylene oxide units; ethylene oxide condensation products of polyhydric alcohol partial higher fatty esters, and their inner anhydrides (mannitolanhydride, called Mannitan, and sorbitol-anhydride, called Sorbitan).
The preferred surfactants are ethoxylated nonyl phenols, ethoxylated nonyl phenol formaldehyde resins, and the like.
The inverting surfactant is used in amounts of from about 0.1 to about 20, preferably from about 1 to about 10 parts per one hundred parts of the polymer.
The water-in-oil emulsion containing the inverting surfactant is solubilized or inverted in the presence of water. The polymer-containing emulsion releases the polymer in the aqueous solution in a very short period of time.
The polymers of this invention have reduced viscosity of from about 1 dl/g to about 20 dl/g~
preferably from about 3 dl/g to about 15 dl/g in 1N
NaCl solution at 25C.
The acidizing solutions generally are based on aqueous hydrochloric acid. The acid concentration usually varies from about 3 to about 2~ weight percent ~Cl. The amount of viscosifying agent of this invention present in the acidizing solution will depend upon the viscosity desired. Suitable polymer ~L3~ 3 concentrations are from about 0.25 to about 3 weight percent of the acidizing solution. Commonly about 0.5 to 1.5 weight percent is employed. The preparation of the~e solutions is well known to one of ordinary skill in this art and can contaln any of the additives normally and conventionally uqed in this art. Any of the other commonly used acids oan be employed, e.g., hydrofluoric acid, formic acid, acetic acid, etc., as is known in the art, as well as mixtures. It is also known that higher concentra-tions of the acid can be used and these are within the scope of our invention. Any concen~ration of acidizing acid adequate to have an acidizing effect in the formation can be used.
The following examples serve to give specific illustrations of this invention but they are not intended in any way to limit the scope of this invention.

Example 1 Into a one-liter pyrex~ lass reactor, equipped with a turbine agitator, thermometer, addition funnel, condenser, nitrogen inlet and outlet, and an external heating or cooling bath, there was charged 704 g of a monomeric ~ater-in~oil emulsion. The latter was prepared by emulsifying an aqueouQ solution that consisted of 245.2 g of a 50S
aqueous solution of ~MAPTAC) methacrylamidopropyltri-~ethyla~moniu~ chloride, 184.4 g of a 50~ aqueous solution of (AM) acryla~ide, ~ 6 B g of deionized water, and 0.17 g o~ Versenex~0 with an oil olution consisting of 157.9 g of Isopar~ oil and 9~ g of D~153B7 ~ 3 Span 80~ (sorbitan mon~oleate). The monomeric emulsion was deaerated by sparging with nitrogen for 30 m~nutes. Thereafter, an i ~tiator solution consisting of 0.012 g of VAZO ~ 3 and 1.5 g Or sylene was introduced. The reactor was heated to 50DC with the external heating bath. ~nce the polymerization initiated, an external cooling bath was employed and the polymerization temperature was maintained at 50 2~C. In the meantime, a second initiator solution consisted of 0.18 g of VAZ~ 2 and 7.5 g of xylene was added in six equal portions with a 10 minute interval between addltions. Upon completing the addition of the second initiator1 the polymerization mixture was heated for an additional 4 hours at 50 +
2C. At the end of polymerization, the reactor was cooled t~ room temperature and a solution of 0.2 g of Santonox~ in 2.5 g of xylene together with 10.7 g of TERGITOL~ P10 was added to the mixture. The ~inished polymeric emulsion was milky white in appearance and exhibited a Brookfield viscosity of 1560 cps (Model HBT, 10 rpm at 25C). The recovered polymer possessed a reduced viscosity in 1N NaCl solution of 9,7 dlJg.

Examples 2-9 Using the equip~ent and procedure described in Example 1, a series of (MAPTAC-AM) copolymers having different degrees o~ ionic characters was prepared. The compositions and general characteris-tics of these polymers are listed in Table I. For completion; data for Example 1 is also ~rcluded.

3 ~ 3 - 24 ~

TABLE I
CATIONIC POLYMERS DERIVED FR M MAPTAC
Composition, Mole ~ RV1 3~ Solution2 Example MAPTAC AM dl/g ViscosityL cps 2 17.6 82046.2 4650 3 20 80 10.4 7550 4 25 75 11.0 7250 - 1 30 7Q 9.7 5450 9.5 5800 6 40 60 7.9 2850 7 40 60 9.1 5800 8 50 50 7.6 3160 9 100 - 1.1 low 1) Measured in lN NaCl solution at 25C, C = 0.0126 g/dl.
2) Measured in distilled water, Brookfield Viscometer Model L.VT, 0.6 rpm, at 25C.
Example 10 This example illustrates a general procedure for the preparation of a hydrophobe-modified cationic monomer using an alkylating agent. Into a 100-ml, 3~necked pyrex flask, equipped with a mechanic stirrer, thermometer, condenser, addition funnel and an external cooling bath, there was charged 34.7 g of the amino monomer, dimethylamino-propylmethacrylamide (DMAPMA). The flask was cooled to about 10C with the cooling bath, and 29.9 g of n-octyl chloride was added in a dropwise manner over a one-hour period. The reaction mixture was stirred for another hour at room temperature. The product, methacrylamidopropyldimethyl-n-octylammonium chloride, was used for polymerization without further purification.

2~)3 Using the equipment and procedures described in Example 10 and the appropriate molar quantities of reactants, two additional hydrophobe modi~ied cationic monomers were prepared. The results of Examples 10 to 12 are summarized in Table II.
TABLE II
HYDROPHOBE-MODIFIED CATIONIC MONOMERS
Example Amino Alkylating Number ~ ABent _ 1 O DMAPMA n-octyl methacrylamidopropyl-chloride dimethyl-n-octyl-ammonium chloride 11 DMAPMA n-dodecyl methacrylamidopropyl-chloride dimethyl-n-dodecyl-am~onium chloride 12 DMAPMA cetyl methacrylamidopropyl-chloride dimethylcetylammonium-chloride Example 13 A polymer was prepared using the equipment and procedure described in Example 1 with the exception that the agueous solution was composed of 24~.3 g of a 50g aqueous solution of MAPTAC, 185.7 g of a 50S a~ueous ~olution of acrylamide, 1.19 g of methacrylamidopropyldimethyl-n-octylamm~n ~ ~ chloride prepared in Example 10, 0.18 g of Versene~~~0, and 104.2 g of deicni~ed water. The finished polymeric emulsion exhibited a Brook~ield ViQCosity o~ 1560 cps (Model H~T, 10 rpm at 25C). The recovered polymer pOSQ~S ed a reduced vi~cosity of 8.1 dl/g in lN NaCl ~olution at 25C.

L~
.~s; .~ ~

~;~0;~ 33 Examples 14 and 15 Using the procedure described in Example 13, a (MAPTAC-AM-methac,rylamidopropyldimethyl-n-dodecyl-ammonium chloride) terpolymer and a (MAPTAC-AM-methacrylamidopropyldimethylcetylammonium chloride) terpolymer were prepared. The compositions and general characteristics of the polymers are shown in Table III.
TABLE III
HYDROPHOBE-MODIFIED CATIONIC MONOMERS
Example Compo~ M~le ~ RV2 O.3~ Solution3 Number Hydrophobel MAPTAC AM dl/~ Viscosity, cps 13 0.2 29.8 70 8.1 900 (Example 10) : 14 0.2 29.8 70 8.42500 (Example 11) 0.2 29.8 70 8.6 950 (Example 12) 1) As indicated by the Example number 2) Measured in 1N NaCl solution at 25C, C - 0.0125 g/dl.
3) Measured in distilled water at 25C with a Brookfield Model LVT Viscometer at 0.6 rpm, Example 16 A polymer was prepared using the equipment and procedure described in Example 1 with the exception that the aqueous solution was composed of 243.1 g of a 50~ aqueous solution of MAPTAC, 181.6 g of a 50~ aqueous solution of acrylamide, 1.4 g of the monomeric product prepared in Example 11, 1.1 g of ~L3~2~03 ~7 .
ethylene dimethacrylate, 0.18 ~ of ~er~enex ao, and 109.2 g of deionized water. The finished polymeric emulsion was milky white in appearance and exhibited a Brookfield viscosity o~ 3760 cps. The recovered polymer possessed a reduced viscosity o~ 1.3 dl/g in lN NaCl solution at 25C. This tetrapolymer contained 0.3 mole ~ of the difuncti.or;al monomer-ethylene glycol dimethacrylate.

Examples 17-26 The viscosifying efficiencies of these polymers in 15~ aqueous HCl solution were measured with a Fann 35 viscometer (Fann Instrument Co., Houston, Texas) at 300 rpm and 25C at a concentration of 35 gallons of emulsion per 1000 gallons Or acid rluid tequivalent to 1.05~ by weight of active polymer in the acid solution). The higher the viscosity, the more efficient is the polymer.
For comparative purposes a commercially available copolymer of acrylamide and sodium acrylate was tested in the same manner (Control A). The improved properties obtained with the viscosirying polymers of this invention are clearly e~ident.

J~
~ .,. ;),~

TAB
VISCOSIFYING EFFICIENCIES IN 15% HCl SOBUTION
Polymer Initial oP Mole ~ Viscosity in Example Example MAPTAC AM Other 15~ HCl, cps _ 17 2 17.6 82.4 - 51 1~ 3 20 80 - 82 24 13 29.8 70 0.2 42 14 29.8 70 0.2 42 26 15 29.8 70 Q.2 42 Control A 3 Examples 27-33 I'he thermal-thinning behavior, or viscosity retention at elevated temperatures, of these polymers was measured with a Fann 50 viscometer. The sample was subjected to a constant shear rate of 170 sec 1 and was heated at a programmed rate of 12F/min.
Viscosity retention values at 225, 250 and 300F
were expressed in Table V as ~ of 100F viscosity. In all cases studied, the polymers of the present invention showed significantly greater viscosity retentions at elevated temperatures when compared to Control B. Control B used a commercially available polacrylamide of the type employed by drillers.

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~ 30 -Exa~ple 34 Into a one-liter pyrex glass reactor, equipped with a turbine agitator, thermometer, addition funnel, condenser, nitrogen inlet and outlet, and an external heating or cooling bath, there was charged 708 g of a water-in--oil monomers emulsion. The latter was prepared by emulsifying, with a Waring blender, an aqueous solution consisting of 249.8 g of a 50S aqueous solution o~ sodium 2-acrylamido-2-methylpropane sulfor.ate (NaAMPS~
178.8 g of a 50S aqueous solution of acrylami(e (AM), 1.g g of N-decylacrylamide, 0.17 g of Ver~enex ~0 and 105.8 g of deionized water with an oil solution comp~sed of 157.8 g of Isopar~ solvent and 14.2 g of Span~ O surfactant (sorbitan monooleate). The monomeric emulsion was deaerated by sparging with nitrogen for 30 minutes. Thereafter,~n initiator solution consisting of 0.012 g of VAZ ~ 3 (2,2'-azobis-t2,4-di~ethyl-4-methoxy valeronitrile]) and 1.5 g of xylene was introduced. The reactor was heated to 50C. Once the polymerization initiated, an @xternal cooling bath was used to maintain the reactor temperature at 50 ~ 2~C. In the meantime, a second initiator solution, consisting of 0.18 g of VA2 ~ 2 (2,2'-azobis-[2,4-dimethyl valeronitrile]) and 7.5 g of xylene, was added in six equal portions with a 10-minute interval between additions. Upon completion of the addition of She ~econd initiator, the polymerization was heated for 4 more hours at 50 + 2C. At the end of polymerization, the reactor was cooled to room temperature and a ~olution of 0.1g g Or Santonox~ in 2.5 g of xylene, together with ,..~. ~,~ ,, ~3~ 3 ~) 10.8 g of TERGITOL NP10 surfactant, was added to the mixture. ~he finished polymeric emulsion was milky white in appearance and exhibited a Brookfield viscosity of 1200 cps (Model HBT, 10 rpm at 25C).
The recovered polymer showed a reduced vi~cosity of 10.8 dl/g in 1N NaCl solution at 25C, Examples 35-40 Using the equipment and procedure described in Example 34, six additional terpolymers containing N decylacrylamide were prepared. The compositions and general characteristics of these polymers are listed in Table VI.

TABLE VI
ANIONIC_(NaAMP ~ M-NDAM) TERPOLYMERS
Example Mole ~1 RV2 0.3~ Solution3 _N!_ ~ ~ Vis~oslty, c~
69 1 10 . 3 9000 34 30 69.5 0.511.7 7950 36 30 69.9 0.111.B 8350 37 40 59 . 8 0 . 2 10 . 2 4000 38 50 49 1 8.6 1BOO
39 50 49.5 ~.5 8,8 1g50 ' 49.8 0.2 9.7 3550 1) Monomer feed composition 2) Measured in lN NaCl ~olution at 25C, C = 0.0125 g/dl.
3) Measured in distilled water at 25C using a Brookfield Model LVT Viscometer at 0.6 rpm and 25C.

f'~ ' ~3~ 3 ~ 32 ~

Examples 41-47 Using the equipment and procedure de~cribed in Example 34, terpolymers containing dif~erent types of hydrophobes were prepared. The compositions and general characteristics of these polymers are listed in Tabl~ VII. Also included in Table VII are two (NaAMPS~ M) copolymer used as eontrols.

TABLE VII
ANIONIC (NaAMPS-AM-HYDROPHOBE) TERPOLYMERS
Example ~ Mole ~ RV2 0.3~ Solution3 No. ~ 1 dl/g Viscosity,_cps 41 30 69.9NPPEM 0.111.6 10800 42 30 69.~NPPEM 0.58.1 9050 43 30 6909NBMA 0.112.4 gOOO
44 30 69.~NBMA 0.511.4 9300 69NBMA 1.0 11.4 10750 46 30 69.9NTBMA 0~111.1 7050 47 30 69NTBMA 1.0 11.3 7850 Cont. C 40 60 -- 10.4 6400 Cont. D 30 70 -- 10.4 9900 1) NPPEM = Nonylphenoxypoly(ethyleneoxy)ethylmeth-acrylate; NBMA = N-benzylmethacrylamide;
NTBMA _ N-t-butylmethacrylamide.
2) Measuned in 1N NaCl solution at 25DC, C ~ 0~0125 g/dlo 3) Measured in distilled water at 25C using a Brookfield Model LVT Yiscometer ~t 0.6 rpm and 25C.

Using the equipment and procedures des~ribed in Exa~ple 34, tetrapolymers containing bot~ a hydro-phobic comonomer and a multi~unctional oomonomer were prepared. The ~Gmposi~ions and general ~haract~ris-tics b~ the e polymers are listed in Table YIII.

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E .1 ~ o~ O ~ 8 b:l ~0 K Z ,-- ~ r~ =r .,~i ~3(~ 3 - 3~ -Examples 55 60 __ The examples shown in Table IX illu trate the benefit of incorporating a quitable poly~erizable hydrophobe monomer into an anionic acid ~i~cos~f$er.
In all cases studied, the N-decylacrylamide-modified polymers produced noticeably hiBher viscosities in acid fluid than their corresponding unmodified versions.
TABLE IX

Initial1 Example Polymer of ~ L~_ _ Viscosity in No. Example No. NaAMP_~J-- NDAM 15~ HCl, cps 55Control D 30 70 - 30 57 34 30 69.5 0.5 42 58 36 30 ~9.9 0.1 39 59Control C 40 60 - 23 38 40 59.8 0.2 30 1) Measured with a Fann 35 Viscometer (Fann Instrument Co., Houston, Texas) at room temperature and 300 rpm and a concentration ~f 1.05S by weight of polymer.
Examples 61-68 The examples shown in Table X further illustrate the benefit of this in~ention with di~ferent types of hydrophobic comonomers.

......

TABLE X
~al1 Yi~cosity Example Polymer of MQle ~in 15 No. Exam~le No. 1~1}5~quo~ 3 ~ e 61 Control D 30 70 --- 3~
62 41 30 69.9NPPEM 0.1 58 63 42 30 69.5NPPEM 0.5 47 64 43 30 69.9NBMA 0.1 39 44 30 69.5NBMA 0.5 44 66 45 30 69.0N~MA 0.1 45 67 46 30 69.9NTBMA 0.1 37 68 47 30 69.0NTBMA 1.0 37 1) Measured with a Fann 35 Yiscometer at room temperature and 300 rpm and a concentration of 1.05~ ~y weight o~ polymer.
The data in Tables IX and X show the polymers of this invention, whioh contain the hydrophobe monomers, when used as acid viscosifiers produce acid solutions having higher initial viscosities than are obtained when using a polymer that does not contain the hydrophobe in the molecule.

Exam ~
The benefit of retaining a higher portion of its initial viscosity in acid fluid is accomplished by the incorporation of the multi~unctional comonomers described in this patent. Data in Table XI show the viscosity retention as a function o~
temperature and time when the various level~ of polyrunctional monomer are employed.

D-1~387 "

~3~2~3 TABLE XI
VISCOSITY RETENTION OF
ANIONIC ACID VISCOSIFIERS CONTAINING
DIFFERENT LEVELS O F EDMA
Example No. 40 51 50 49 EDMA, Mole % - 0.1 0.3 0.6 Initial Viscosity1 at 100F, cps48 23 28 11 Retained1,2 Viscosity, ~
at 150F 75 67 72 42 at 200F 56 43 53 36 at 225F 47 37 53 32 at 250F 38 40 65 29 at 250F ~ 5 min. 38 57 116 57 at 250F ~ 15 min. - - 222 217 ' at 250F ~ 30 min. - - - 629 ;~ after cooling1 !~ back to 100F78 113 250 >1000 1) Measured at a polymer concentration of 2.1% by ' weight using a Fann 50 Viscometer at 100 rpm.
I 2) Viscosity at 100F = 100%.

2~3 ~e~
Into a one-liter pyrex~ lass reactor9 equipped with a turbine agitator, ther~ometer, addition funnel, condenser, nitrogen inlet and outlet, and an external heating or cooling ~ath, there was charged about 700 g of a water~in-oil monomeric emulsion. The latter ~as prepared by emulsifying, with a Waring blender, an aqueous solution consisting of 162.4 g of sodium 2-~crylamido-2-methylpropane sulfonate as the anionic monomer, 92 g of a 62~ aqueous solution of dimethyldiallylam~onium chloride as the cationic monomer, 150.3 g of a 50~ aqueous solution of acrylamide as the water soluble monomer, 1.4 g o~
nonylphenoxypoly(ethyleneoxy)ethylmetha~ylate as the hydrophobic monomer, 0.14 g of Versenex ~0, and 130.2 g of deionized water with an oil solution comp~sed o~ 157.8 g of Isopar~ solvent and 9.5 g of Span~O surfactant (sorbitan monooleate). The monomeric emulsion was deaerated by nitrogen sparging for 30 minutes. Thereafter,j~n initiator solution consisting of 0.012 g of VAZ ~ 3 (2,2'-azobis[2,4-dimethyl-4-~ethoxy valeronitrile]) and 1.5 g of xylene was introduced. The reactor was heated to 50C. Once the polymerization initiated, an external cooling bath was used to maintain the reactor temperature at 50 ~ 2C. In the meantime, a seco~d initiator solution consi~tiDg of 0.18 g of VAZ ~ 2 (2,2'-azobisL2~4-dimethyl valeronitrileJ) and 7.5 g o~ xylene was added in six equal portions with a 10-minute interval between additions. Upon completion o~ the addition of the 3econd initlator, 2~3 38 ~

the polymerization was heated ~or 4 more hours at 50 2C. At the end o~ the polymerization, the reactor ~as cooled to room~temperature and a solution of 0.19 g of Santono ~ in 2.5 g of xylene together with 10.8 g Or TERGIT0~-~P10 surfactant was added to the mixture. The finished polymeric emulsion was milky white in appearance and exhibited a Brookfield vi~cosity of 880 cps tModel HBT, 10 rpm at 25C).
The reco~ered polymer pos~essed a reduced viscosity of 6.2 dl/g in lN NaCl solution.

A polymer was prepared using the equipment and procedures described in Example 72, with the exception that the aqueous solution consisted of 163.4 g of a 50% aqueous solution of sodium 2-acrylamido-2-methylpropane ~ulfonate as the anionic monomer, 92.5 g of a 62S aqueous solution of (DMDAAC) dimethyldiallylammonium ~hloride as the cationic monomer, 151.5 g of a 5C~ aqueous solution of acrylami~e as the water soluble monomer, 0.14 g of Ver~enex 80, and 12B.9 B Or deionized water. The ~inished polymeric e~ulQion exhibited a Brookfield viscosity of 1500 cps (Model HBT, 10 rpm at 25DC).
The reco~ered poly~er pos~essed a r-educed viscosity of 7.6 dl/g in 1N NaCl solution at 25C.

Example 74 An acid fluid containing 1.05 g of active polymer Or Example 72 in 15S HCl was heated in a 180F water bath ~or 60 mlnutes. The acid ~luid ~howed no visible polymeric precipitate. ~eaction 3g -wit~ limestone showed no significant change in viscosity nor any evidence of precipation. Under the ~ame te~ing conditions, elther the corr~ponding (NaAMPS~M) copolymer (at 20/80 molar ratio) or (DMDAAC-AM~ copolymer (at 20/80 molar ratio) resulted in precipitation of the polymer on heating.
.
Exam?le 75 An acid fluid containing 1.05 g of active polymer of Example 72 in 15~ HCl produced a solution viscosity of 40 cps (Fann 35 viscometer ~easured at 300 rpm and 25C). A control fluid made with the ~ame amount of polymer of Example 73 gave a solution viscosity of 3l~ ~ps.

Using the equipment and general procedures described in Example 72, a copolymer composed of 30 m~le percent of N-(3-sulfopropyl)-N-methacrylamido-propyl-N,N-dimethylammonium-betain (SPP) and 70 mole percent Or acrylamide was prepared. The resu}tant polymeric emulsion exhibited a ~rookfield vi cosity of 1,4~G cps. The recovered polymer possessed a reduced viscosity (RV) of i.5 dl/g in lN NaCl solution at 25C.

Example 76 was repeated wi'ch the exception that a ~mall amount of a hydrophobic comonomer, nonylphenoxy~-psly(ethyleneoxy)ethyllDethacrylata (NPPEM), ~a~ incorporated into the polymerizatlDn ~ormulation 30 that ths resul'cant product was 8 , ... .

(NPPEM-SPP-AM) terpolymer containing 0.1, 30; and 6g.9 mole percent of these monomers, respectively.
The resultant polymeric emulsion exhibited a Brookfield viscosity of 1,600 cps. The recovered polymer possessed a reduced viscosity of 6.7 dl~g.

Exampl_ 78 - The thermal-thinning behavior in 15% HCl solution of the polymers prepared in Example 76 and 77 were measured using a Fann 50 viscometer operating at 130 rpm and a programmed heating rate of 12F/min.
A polymer concentration of 1.05 weight percent was employed.

Initial % Retention of I Polymer o~ Viscosity at 100F Visco.sity at Example RV100F, cps150 200 250 300 ¦ 76 7.5 51 72 43 23 9 77 6.9 67 82 50 3~ 27 The polymer in Example 77, which contained a small amount of hydrophobic monomer NPPEM, produced a significantly higher degrees of viscosity retention at elevated temperatures than its corresponding polymer without the hydrophobic comonomer indicating it was more stable to heat.

Claims (38)

1. A polymer selected from the group consisting of (A), (B), (C), and (D) wherein; (A) is a cationic polymer of the general formula:

where R = H or CH3;
R' = a linear or branched alkylene radical having from 2 to 10 carbon atoms;
R" = H or alkyl, linear or branched, having from 1 to 3 carbon atoms;
R''' = an alkyl group, linear or branched, having about 8 to about 25 carbon atoms, aryl, alkaryl or aralkyl having from 6 to 18 carbon atoms;
Q = -NR- or -O-;
G = a residual unit derived from a polyunsaturated monomer;
X? = a halogen ion (F, Cl, Br, I) or an alkyl sulfate ion;
b = from about 10 to 99.9 mole percent;
c = from about 0 to 90 mole percent;
d = from 0.1 to about 10 mole percent; and e = from 0 to 2 mole percent;

(B) is an anionic polymer of the general formula;

(I) where R = H or CH3;
R' = a linear or branched alkylene or arylene radical having from 2 to 10 carbon atoms;
M+ = H+, Na+, NH4+, or other monovalent metal atom (Me+);
G = a unit derived from a polyunsaturated monomer;
Q = a divalent radical -O- or -NR-;
R" = C8-C18 alkyl, C7-C24 aralkyl or an ethoxylated C7-C24 aralkyl;
f = from about 10 to 60 mole percent;
h = from about 39.99 to 89.99 mole percent;
j = from 0.01 to 10 mole percent; and k = from 0 to 2 mole percent;

(C) is an amphoteric polymer of the general formula;

(D) is an amphoteric polymer of the general formula:

where A- ? = the residue of a cationic monomer;
B- ? = the residue of an anionic monomer;
C- ? - ? = the residue of a Zwitter-ion monomer;
R, R", Q and G are the same as previously defined under (B);
m = 10-49.99 mole percent;
n = 10-49.99 mole percent;
p = 0.01-10 mole percent;
q = 0-80 mole percent;
r = 0-2 mole percent;
s = 5-99.99 mole percent;
t = 0-95 mole percent, with the proviso that the sum thereof equals 100 mole percent.

2. A cationic polymer (A) as claimed in claim 1 wherein:
R = H or CH3;
R' = a linear or branched alkylene radical having from 2 to 4 carbon atoms;
R'' = H or alkyl, linear or branched, having from 1 to 2 carbon atoms;
R''' = an alkyl group, linear or branched, having from 8 to about 18 carbon atoms, aryl, alkaryl or aralkyl having from 6 to 18 carbon atoms;
Q = -NR- or -O-;
G = a residual unit derived from a polyunsaturated monomer;
X? = a halogen ion (F, Cl, Br, I) or an alkyl sulfate ion;
b = from about 30 to 50 mole percent;
c = from about 50 to 70 mole percent;
d = from 0.1 to about 2 mole percent; and e = from 0 to 0,5 mole percent.

3. An anionic polymer (B) as claimed in claim 1 wherein:
R = H or CH3;
R' = a linear or branched alkylene radical having from 2 to 4 carbon atoms;
M+ = H+, Na+ NH4+, or other monovalent metal atom (Me+);
G = a unit derived from a polyunsaturated monomer;
Q = a divalent radical -O- or -NR-;

R" = C8-C18 alkyl, C7-C24 aralkyl or an ethoxylated C7-C24 aralkyl;
f = from about 29 to 50 mole percent;
h = from about 49.9 to 79.9 mole percent;
j = from 0.1 to about 2 mole percent; and k = from 0 to 0.5 mole percent.

4. An amphoteric polymer (C) as claimed in claim 1 wherein:
A- ? - the residue of a cationic monomer;
B- ? - the residue of an anionic monomer;
R, R", Q and G are the same as previously defined in claim 1;
m = 20-35 mole percent;
n = 20-35 mole percent;
p = 0.1-2 mole percent;
q = 30-60 mole percent;
r = 0-0.5 mole percent; and with the proviso that the sum thereof equals 100 mole percent.

5. An amphoteric polymer (D) as claimed in claim 1 wherein:
C- ? - ? = the residue of a Zwitter-ion monomer; R, R", Q and G are the same as previously defined in claim 1;
p = 0.1-2 mole percent;
r = 0-0.5 mole percent;
s = 10-50 mole percent;
t = 50-90 mole percent; and with the proviso that the sum thereof equals 100 mole percent.

6. A cationic polymer (A) as claimed in claim 1 comprising (i) methacrylamidopropyl-tri-methylammonium chloride; (ii) acrylamide and (iii) methacrylamidopropyldimethyl-C8-16 alkyl-ammonium chloride units.

7. A cationic polymer (A) as claimed in claim 1 comprising (i) methacrylamidopropyl-tri-methylammonium chloride; (ii) acrylamide, and (iii) methacrylamidopropyldimethyl-n-stearyl-ammonium chloride units.

8. A cationic polymer as claimed in claim 6 wherein component (iii) is methacrylamidopropyldi-methylcetylammonium chloride units.

9. A cationic polymer as claimed in claim 6 wherein component (iii) is methacrylamidopropyldi-methyl-n-dodecylammonium chloride units.

10. A cationic polymer as claimed in claim 1 comprising (i) methacrylamidopropyltrimethylammonium chloride, (ii) acrylamide, (iii) methacrylamidopropyl-dimethyl-n-dodecylammonium chloride and (iv) ethyleneglycol dimethacrylate units.

11. An anionic polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide and (iii) N-decylacrylamide units.

12. An anionic polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, and (iii) nonylphenoxypoly(ethyleneoxy)ethyl methacrylate units.

13. An anionic polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, and (iii) N-benzylmeth-acrylamide units.

14. An anionic polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, and (iii) N-t-butylmeth-acrylamide units.

15. An anionic polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, (iii) N-decylacrylamide and (iv) ethyleneglycol dimethacrylate units.

16. An anionic polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, (iii) N-decylacrylamide and (iv) trimethylolpropane trimethacrylate units.

17. An amphoteric polymer as claimed in claim 1 comprising (i) sodium 2-acrylamido-2-methyl-propane sulfonate, (ii) dimethyldiallylammonium chloride, (iii) acrylamide and (iv) nonylphenoxypoly-(ethyleneoxy)ethylmethacrylate units.

18. A viscosified acidic composition suitable for acidizing a porous subterranean formation susceptible to attack by an acid, comprising (i) water; (ii) from about 0.25 to 3 weight percent, based on the total weight of said acidic composition of a polymer selected from the group consisting of (A), (B), (C), and (D) wherein;
(A) is a cationic polymer of the general formula:

where R = H or CH3;
R' = a linear or branched alkylene radical having from 2 to 10 carbon atoms;
R" = H or alkyl, linear or branched, having from 1 to 3 carbon atoms;
R''' = an alkyl group, linear or branched, having about 8 to about 25 carbon atoms, aryl, alkaryl or aralkyl having from 6 to 18 carbon atoms;
Q = -NR or -O-;
G = a residual unit derived from a polyunsaturated monomer;
X? = a halogen ion (F, Cl, Br, I) or an alkyl sulfate ion having 1 to 4 carbon atoms;
b = from about 10 to 100 mole percent;
c = from about 0 to 90 mole percent;
d = from 0 to about 10 mole percent; and e = from 0 to 2 mole percent;

(B) is an anionic polymer of the general formula;

(I) where R = H or CH3;
R' = a linear or branched alkylene or arylene radical having from 2 to 10 carbon atoms;
M+ = H+, Na+, NH4+, or other monovalent metal atom (Me+);
G = a unit derived from a polyunsaturated monomer;
Q = a divalent radical -O- or -NR-;
R" = C8-C18 alkyl, C7-C24 aralkyl or an ethoxylated C7-C24 aralkyl;
f = from about 10 to 60 mole percent;
h = from about 39.99 to 89.99 mole percent;
j = from 0.01 to 10 mole percent; and k = from 0 to 2 mole percent;

(C) is an amphoteric polymer of the general formula;

(D) is an amphoteric polymer of the general formula:

where A-? = the residue of a cationic monomer;
B-? = the residue of an anionic monomer;
C-?-?= the residue of a Zwitter-ion monomer;
R, R", Q and G are the same as previously defined under (B);
m = 10-49.99 mole percent;
n = 10-49.99 mole percent;
p = 0.01-10 mole percent;
q = 0-80 mole percent;
r = 0-2 mole percent;
s = 5-99.99 mole percent;
t = 0-95 mole percent, with the proviso that the sum thereof equals 100 mole percent; and (iii) from 3 to about 28 weight percent of acid.

19. A viscosified acidic composition as claimed in claim 18 wherein the concentration of component (ii) is from 0.5 to 1.5 weight percent.

20. A viscosified acidic composition as claimed in claim 18 wherein component (ii) is a cationic polymer (A) wherein:
R = H or CH3;
R' = a linear or branched alkylene radical having from 2 to 4 carbon atoms;
R" = H or alkyl, linear or branched, having from 1 to 2 carbon atoms;
R''' = an alkyl group, linear or branched, having from 8 to about 18 carbon atoms, aryl, alkaryl or aralkyl having from 6 to 18 carbon atoms;
Q = -NR- or -O-;
G = a residual unit derived from a polyunsaturated monomer;
X? = a halogen ion (F, Cl, Br, I) or an alkyl sulfate ion having 1-4 carbon atoms;
b = from about 30 to 50 mole percent;
c = from about 50 to 70 mole percent;
d = from 0.1 to about 2 mole percent; and e = from 0 to 0.5 mole percent.

21. A viscosified acidic composition as claimed in claim 18 wherein component (ii) is an anionic polymer (B) wherein:
R = H or CH3;
R' = a linear or branched alkylene radical having from 2 to 4 carbon atoms;

M+ = H+, Na+, NH4+, or other monovalent metal atom (Me+);
G = a unit derived from a polyunsaturated monomer;
Q = a divalent radical -O- or -NR-;
R" = C8-C18 alkyl, C7-C24 aralkyl or an ethoxylated C7-C24 aralkyl;
f = from about 20 to 50 mole percent;
h = from about 49.9 to 79.9 mole percent;
j = from 0.1 to about 2 mole percent; and k = from 0 to 0.5 mole percent.

22. A viscosified acidic composition as claimed in claim 18 wherein component (ii) is an amphoteric polymer (C) wherein:
A-? = the residue of a cationic monomer;
B-? = the residue of an anionic monomer;
R, R", Q and G are the same as previously defined in claim 18;
m = 20-35 mole percent;
n = 20-35 mole percent;
p = 0.1-2 mole percent;
q - 30-60 mole percent;
r = 0-0.5 mole percent; and with the proviso that the sum thereof equals 100 mole percent.

23. A viscosified acidic composition as claimed in claim 18 wherein component (ii) is an amphoteric polymer (D) wherein:
C-?-? = the residue of a Zwitter-ion monomer; R, R", Q and G are the name as previously defined in claim 18;

p = 0.1-2 mole percent;
r = 0 0.5 mole percent;
s = 10-50 mole percent;
t = 50-90 mole percent; and with the proviso that the sum thereof equals 100 mole percent.

24. A viscosified acidic composition as claimed in claim 18 wherein the cationic polymer comprises (i) methacrylamidopropyl-trimethylammonium chloride; (ii) acrylamide and (iii) methacrylamido-propyldimethyl-n-octyl-ammonium chloride units.

25. A viscosified acidic composition as claimed in claim 18 wherein the cationic polymer comprises (i) methacrylamidopropyl-trimethylammonium chloride; (ii) acrylamide; and (iii) methacrylamido-propyldimethyl-n-stearyl-ammonium chloride units.

26. A viscosified acidic composition as claimed in claim 18 wherein the cationic polymer comprises (i) methacrylamidopropyl-trimethylammonium chloride; (ii) acrylamide; and (iii) methacrylamido-propyldimethylcetylammonium chloride units.

27. A viscosified acidic composition as claimed in claim 18 wherein the cationic polymer comprises (i) methacrylamidopropyl-trimethylammonium chloride; (ii) acrylamide; and (iii) methacrylamido-propyldimethyl-n-dodecylammonium chloride units.

28. A viscosified acidic composition as claimed in claim 18 wherein the cationic polymer comprises (i) methacrylamidopropyltrimethylammonium chloride, (ii) acrylamide, (iii) methacrylamidopro-pyldimethyl-n-dodecylammonium chloride and (iv) ethyleneglycol dimethacrylate units.

29. A viscosified acidic composition as claimed in claim 18 wherein the anionic polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide and (iii) N-decylacryl-amide units.

30. A viscosified acidic composition as claimed in claim 18 wherein the anionic polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide; and (iii) nonylphenoxy-poly(ethyleneoxy)ethyl methacrylate units.

31. A viscosified acidic composition as claimed in claim 18 wherein the anionic polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide; and (iii) N-benzyl-methacrylamide units.

32. A viscosified acidic composition as claimed in claim 18 wherein the anionic polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide; and (iii) N-t-butylmeth-acrylamide units.

33. A viscosified acidic composition as claimed in claim 18 wherein the anionic polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, (iii) N-decylacrylamide and (iv) ethyleneglycol dimethacrylate units.

34. A viscosified composition as claimed in claim 18 wherein the anionic polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) acrylamide, (iii) N-decylacrylamide, and (iv) trimethylolpropane trimethacrylate units.

35. A viscosified acidic composition as claimed in claim 18 wherein the amphoteric polymer comprises (i) sodium 2-acrylamido-2-methylpropane sulfonate, (ii) dimethyldiallylammonium chloride, (iii) acrylamide and (iv) nonylphenoxypoly(ethylene-oxy)ethylmethacrylate units.

36. A viscosified acidic composition as claimed in claim 18 wherein the cationic polymer comprises (i) methacrylamidopropyltrimethylammonium chloride, and (ii) acrylamide.

37. A viscosified acidic composition as claimed in claim 36 wherein the cationic polymer comprises (i) methacrylamidopropyltrimethylammonium chloride and (ii) acrylamide; b = from 30 to 50 mole percent and c = from 50 to 70 mole percent.

38. A viscosified acidic composition as claimed in claim 18 wherein the concentration of acid in the composition is an amount sufficient to have an acidizing effect on the formation.