Controlled hydraulic fracturing via nonaqueous solutions containing low charge density polyampholytes

A process for fracturing a subterranean formation surrounding a gas or oil well which comprises: PA0 (a) injecting into said subterranean formation under hydraulic pressure a fluid comprising a solution of terpolymer dissolved in a solvent system, said solvent system comprising an organic liquid and a polar cosolvent, said polar cosolvent being less than about 15 weight percent of said solvent system, said terpolymer comprising a water-insoluble, oil-soluble terpolymer dissolved in said solvent system, the concentration of said terpolymer in said solution being about 0.2 to about 10 weight percent and the viscosity of said solution being less than about 2,000 cps, said terpolymer having the formula: ##STR1## wherein R.sub.1 =C.sub.6 H.sub.5, C.sub.6 H.sub.4 --CH.sub.3, C.sub.6 H.sub.4 --(CH.sub.3).sub.3, Cn H.sub.2 NH; wherein n=1-30; wherein x is about 50 to about 98 mole percent; y is about 1 to about 50 mole percent; z is about 1 to about 50 mole percent; wherein y and z are less than 60 mole percent; and M is an amine or a metal cation selected from the group consisting of antimony, tin, lead, Groups IA, IIA, IB and IIB of the Periodic Table of Elements; and PA0 (b) adding water to said solution of said polymer, said polar cosolvent transferring from said organic liquid to said water, thereby causing said organic liquid to gel within the fractures of said subterranean formation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for the hydraulic fracturing of 
subterranean formations surrounding oil wells and gas wells by means of 
injection of a fracturing fluid into the well, wherein the fracturing 
fluid comprises a solution of non-polar organic liquid or oil, a 
polyampholyte and, possibly, a polar cosolvent and water. 
2. Description of the Prior Art 
Hydraulic fracturing has been widely used for stimulating the production of 
crude oil and natural gas from wells completed in low permeability 
reservoirs. The methods employed normally require the injection of a 
fracturing fluid containing a suspended propping agent into a well at a 
rate sufficient to open a fracture in the exposed formation. Continued 
pumping of fluid into the well at a high rate extends the fracture and 
leads to the buildup of a bed of propping agent particles between the 
fracture walls. These particles prevent complete closure of the fracture, 
as the fluid subsequently leaks off into the adjacent formation, and 
result in a permeable channel extending from the wellbore into the 
formation. The conductivity of this channel depends upon the fracture 
dimensions, the size of the propping agent particles, the particle spacing 
and the confining pressures. Studies of conventional fracturing operations 
indicate that fracture widths seldom exceed about one-fourth inch and that 
conductivities in excess of about 250,000 millidarcy-inches are rarely 
obtained. The average width and conductivity are considerably lower than 
these values. 
With the advent of declining reserves, the drilling and stimulation of 
higher temperature wells in increasing the drilling and completion of 
light dry gas and water sensitive formation is also on the rise. The 
industry is relying to a greater extent on hydrocarbon fluids to drill and 
complete these wells which cannot be treated with the normal water-based 
fluids, therefore, there has been a substantial need for hydrocarbon-based 
viscosifiers which exhibit good performance at high temperatures. 
A desirable formulation, both for drilling fluids and hydraulic fracturing 
fluids, would be a homogeneous fluid which possesses adequate viscosity of 
30-1,000 cps-A non-polar, organic-liquid-based, fluid-containing polymer 
viscosifiers would meet the above-stated requirements. 
Since the beginning of recorded oil well production hydrocarbon-based 
viscosifiers have played an important role in hydraulic fracturing fluids. 
Some of these viscosifiers have been either metal soaps of fatty acids, or 
metal soaps of partially esterified phosphates. Both of these impart 
viscosity to hydrocarbons, but the metal soaps of fatty acids have 
inherent thermal thinning properties, which give them limited utility at 
higher temperatures. The metal soaps of partially esterified phosphates 
have the disadvantage of being extremely pH sensitive, along with being 
thermally thinning. 
So a viscosifier that has the advantage of maintaining viscosity at high 
temperatures and/or is not susceptible to variations in pH would represent 
an advancement over the prior art. 
The instant invention differs from a number of applications, U.S. Ser. No. 
223,482, U.S. Pat. No. 4,361,658; U.S. Ser. No. 136,837, U.S. Pat. No. 
4,322,329, and U.S. Ser. No. 106,027, U.S. Pat. No. 4,282,130, filed by 
Robert D. Lundberg, one of the instant inventors, et al. These 
previously-filed applications were directed to the gelling of the organic 
liquid by a water insoluble, neutralized, sulfonated polymer, whereas the 
instant invention is directed to fracturing fluids formed from a 
non-polar, organic liquid and a polyampholyte. 
In U.S. Ser. No. 547,955, filed Nov. 2, 1983, abandoned, two polymers are 
mixed to produce an interpolymer complex which at relatively low 
concentrations forms a three-dimensional network with a gel-like behavior. 
Interpolymer complexes are much more effective in forming a network than 
are single associating polymers, leading to gels of higher strength. The 
instant polyampholytes are not a polymeric complex as defined in U.S. Ser. 
No. 547,955. 
In U.S. Ser. No. 547,955 the interpolymer complexes in hydrocarbon 
solutions are obtained by mixing two polymers which are strongly 
associated with each other. One polymer will contain anionic groups along 
or pendant to its backbone; and the other polymer will contain cationic 
groups. The coulombic interaction between cationic and anionic groups 
leads to network formation, if each chain contains interacting groups in 
multiple locations. 
In the instant invention low charge density polyampholytes are formed in 
nonaqueous solutions by sulfonation of a preformed base-containing 
copolymer, such as styrene-4 vinylpyridine. In a polyampholyte the 
cationic and anionic moieties which are located on the same chain 
backbone, i.e., sulfonate and 4-vinylpyridine units, interact very 
strongly with each other. Therefore, these polyampholytes strongly 
interact with each other, forming a tight networks, i.e., gel, since each 
chain contains interacting groups in multiple locations. The gel 
structure, to a first approximation, more tightly bound than its low 
charge density sulfonate ionomer counterpart and, more importantly, the 
properties of these gels are improved over the interpolymer complexes. 
Even more importantly, these polyampholytic gel systems are formed without 
having to mix oppositely-charged copolymers, as taught in U.S. Ser. No. 
547,955. 
A solution of polyampholyte and a non-polar organic solvent will have a 
relatively high viscosity. This can be used as is, if the solution 
viscosity is not excessive, and, if excessive, the solution viscosity can 
be modified by the incremental addition of a variety of polar cosolvents, 
modifying the solution's rheological properties. If by the co-mining water 
with a solution of polyampholytes and a non-polar solvent, the polar 
cosolvent is extracted into the water phase, an increase in viscosity or 
gelling would result in the ampholyte solution during injection into a 
well. This viscous gel can then be used as a fracturing fluid. 
SUMMARY OF THE INVENTION 
The fracturing method of this invention is carried out by injecting a 
fracturing fluid through a sting of tubing or casing into a fracture. The 
fracturing fluid is composed of a non-polar organic liquid, a polar 
cosolvent and the polyampholyte. When water is mixed with the fracturing 
fluid, the polar cosolvent is extracted from the fracturing fluid into the 
water phase and the viscosity of the fracturing fluid will increase and a 
gel will be formed. The water can be added to the fracturing fluid prior 
to its injection into the fracture or the water is obtained from the 
naturally occuring water within the fracture itself. If the water is mixed 
with the fracturing fluid prior to injection into the casing mixing 
occurings during injection through the tubing. Injection of the high 
viscosity fluid is continued until a fracture of sufficient width to 
produce a highly conductive channel has been formed, wherein the gel which 
is formed is contained within the fracture and keeps the fracture open. 
The injected fluid is then permitted to leak off into the formation until 
the fracture has closed sufficiently to hold the gel in place and, if 
applicable, propellant and other materials are used, as desired. 
Thereafter, the fluid remaining in the fracture may be produced back into 
the wellbore. 
Accordingly, it is a primary object of the instant invention to describe an 
economical fracturing process for fracturing a subterranean formation by 
means of a fracturing fluid which comprises a solution of non-polar 
organic liquid, a polar cosolvent and a polyampholyte. 
GENERAL DESCRIPTION 
The present invention relates to a process for the fracturing of a 
subterranean formation surrounding an oil well or gas well in order to 
increase the recovery of the oil or gas. The process includes the steps of 
forming a solvent system of a non-polar, organic liquid or oil and a polar 
cosolvent, the polar cosolvent being less than about 15 weight percent of 
the solvent system, the viscosity of solvent system being less than about 
1,000 cps; dissolving a polyampholyte in the solvent system to form a 
solution; and injecting the solution in the well under hydraulic pressure 
to fracture the subterranean formation. The viscosity needed to accomplish 
this can be achieved in a number of ways: 
1. The first method being the variation of ampholytic concentration of 
and/or ampholytic density to obtain a variety of rheological properties. 
2. Certain polar cosolvents in incremental amounts can be added to the 
non-polar solvent-polyampholyte solution, modifying and controlling its 
rheological properties. 
3. Certain polar cosolvents can be added to the non-polar 
solvent-polyampholyte solution, reducing its viscosity. This solution 
would then be pumped and co-mingled in surface tubular mixers with water, 
extracting the polar solvent from the polyampholyte solution, forming a 
gel of high viscosity. 
4. A concentrate of the polyampholyte in the non-polar hydrocarbon solvent 
containing a polar cosolvent to render the solution of a low viscosity. 
This would then be co-mingled during pumping through tubular mixers, with 
additional non-polar solvent diluting the polyampholyte solution and 
forming a gel of high viscosity which in all cases may be used as 
fracturing fluid. 
The gelled polymer solution, having a viscosity greater than 50 cps, acts 
as a propping means within the fractures of the subterranean formation. 
The gel is formed by the addition of water to the polymer solution, 
wherein the polymer solution comprises a water-insoluble, oil-soluble 
polyampholyte, a non-polar organic liquid and a polar cosolvent, wherein 
the the solution has a viscosity of less than 2,000 cps. The concentration 
of polyampholyte in the solution is 0.2 to 10 weight percent, more 
preferably about 0.3 to about 9, and most preferably about 0.4 to about 8. 
Upon the addition of water to the solution of the polyampholyte the polar 
cosolvent may, in one instance, transfer from the solution of the 
polyampholyte, non-polar organic liquid and the polar cosolvent to the 
aqueous phase, causing gelation of the non-polar organic liquid. 
The component materials of the instant process generally include a 
water-insoluble, oil-soluble polyampholyte at a concentration level of 0.2 
to 10 weight percent, more preferably about 0.3 to about 9.0, and most 
preferably about 0.2 to about 8.0, a non-polar organic liquid and a polar 
cosolvent to which water is subsequently added. 
The polyampholytes of the instant invention are water-insoluble, 
oil-soluble terpolymers of a nonionic monomer, a sulfonate-containing 
monomer and an amine-containing monomer. The terpolymers of the instant 
invention are formed by a free radical emulsion polymerization of the 
amine-containing monomer and the nonionic monomer to form a copolymer of 
the nonionic monomer and the amine-containing monomer. This copolymer is 
subsequently sulfonated according to the procedures of U.S. Pat. No. 
3,836,511, which is hereby incorporated by reference, to form the 
terpolymer of the nonionic monomer, the sulfonate-containing monomer and 
the amine-containing monomer. 
Suitable oil-soluble and water-insoluble terpolymers of the instant 
invention generally have the formula: 
##STR2## 
wherein R.sub.1 =C.sub.6 H.sub.5, C.sub.6 H.sub.4 --CH.sub.3, C.sub.6 
H.sub.4 --(CH.sub.3).sub.3, Cn H.sub.2 NH' wherein n=1-30; wherein x is 
about 40 to about about 98 mole percent, more preferably about 50 to about 
95 mole percent, and most preferably about 80 to about 90; y is about 1 to 
about 50 mole percent, more preferably about 2 to about 20 mole percent, 
and most preferably about 2 to about 10 mole percent; z is about 1 to 
about 50 mole percent, more preferably about 2 to about 20, and most 
preferably about 2 to about 10; wherein y and z are less than 60 mole 
percent; and M is an amine or a metal cation selected from the group 
consisting of antimony, aluminum, tin, lead, Groups IA, IIA, IVA, VII, 
VII, VIA, IB and IIB of the Periodic Table of Elements. 
The molecular weight, as derived from intrinsic viscosities, for the 
terpolymers of styrene/metal styrene sulfonate/vinyl pyridine is about 
1.times.10.sup.3 to about 5.times.10.sup.7, more preferably about 
1.times.10.sup.4 to about 2.times.10.sup.7, and most preferably about 
1.times.10.sub.5 to about 1.times.10.sup.7. The means for determining the 
molecular weights of the oil-soluble and water-insoluble terpolymers from 
the viscosity of the solutions of the terpolymers comprises the initial 
isolation of the hydrocarbon-soluble terpolymers, purification and 
redissolving the terpolymers in a nonaqueous solvent to give solutions 
with well known concentrations. The flow times of the solutions and the 
pure solvent were measured in a standard Ubbelhold viscometer. 
Subsequently the reduced viscosity is calculated through standard methods 
utilizing these values. Extrapolation to zero polymer concentration leads 
to the intrinsic viscosity of the polymer solution. The intrinsic 
viscosity is directly related to the molecular weight through the well 
known Mark Houwink relationship. Polymerization process is generally 
preferred, but other processes are also acceptable. 
The vinyl pyridine content of the preferred copolymer of styrene and 
vinylpyridine is about 1 to about 50 mole percent, more preferably about 2 
to about 20 mole percent, and most preferably about 2 to about 10 mole 
percent. The number average molecular weight, as measured by GPC, is about 
10,000 to about 10,000,000, preferably about 20,000 to about 5,000,000, 
and most preferably about 30,000 to about 2,000,000. 
The amine-containing polymer is typically a polymeric backbone where the 
nitrogen elements are in the chain or pendant to it. Such a polymer may be 
obtained by direct copolymerization of a monomer containing the basic 
moiety with other monomers, or by grafting a monomer containing the basic 
moiety on to a polymerized chain. Monomers can be chosen from vinyl 
monomers leading to hydrocarbon-soluble polymers, such as styrene, t-butyl 
styrene, acrylonitrile, isoprene, butadiene, acrylates, methacrylates and 
vinyl acetate. Monomers containing a basic moiety will be those which 
contain amine or alkyl amine groups, or pyridine groups, such as vinyl 
pyridine. 
The amount of vinyl pyridine in the amine-containing copolymer can vary 
widely, but should range from about 0.01 mole percent to about 25 mole 
percent. 
Preferably, the amine content in the amine-containing copolymer is 
expressed in terms of basic nitrogen. In this respect, the nitrogen 
content in amides and similar non-basic nitrogen functionality is not part 
of the interacting species. 
A minimum of three basic groups must be present on the average per polymer 
molecule and the basic nitrogen content generally will range from 4 meq. 
per 100 grams of polymer up to 500 meq. per 100 grams. A range of 80 to 
200 meq. per 100 grams is preferred. 
The amine-containing copolymer of styrene and vinyl pyridine is sulfonated 
according to the procedures of U.S. Pat. No. 3,836,511, which is herein 
incorporated by reference, to form the terpolymer of styrene/styrene 
sulfonic acid/vinylpyridien, which is subsequently neutralized with an 
amine or metal cation to form the terpolymer of styrene/neutralized 
styrene sulfonate/vinylpyridine. 
The number of sulfonate groups contained in the terpolymer is a critical 
parameter affecting this invention. The number of sulfonate groups present 
in the polymer can be described in a variety of ways, such as weight 
percent, mole percent, number per polymer chain, etc. For most polymer 
systems of interest in this invention it is desirable to employ mole 
percent. An alternate way of expressing this is to state the sulfonate 
level in terms of milliequivalents of sulfonic acid groups per 100 grams 
of polymer. This latter procedure provides a rapid and independent measure 
of sulfonic acid content in a polymer through simple titration. 
Both mole percent sulfonate and meq. of sulfonate will be employed to 
describe the sulfonate polymers employed in this invention. 
In general, the terpolymer will comprise from about 1 meq. up to 500 meq. 
of sulfonate groups per 100 grams of polymer, more preferably about 5 meq. 
to about 300 meq. of sulfonate groups, and most preferably about 10 to 
about 100. The unneutralized sulfonate terpolymers in the instant 
invention are neutralized with the basic materials selected from the group 
consisting of Groups IA, IIA, IVA, VIA, VIIA, VIIIA, IB and IIB of the 
Periodic Table of Elements and lead, aluminum, tin and antimony. A 
preferred counter-ion for this invention is zinc. 
Neutralization of the unneutralized sulfonated terpolymers with appropriate 
metal hydroxides, metal acetates, metal oxides, etc. can be conducted by 
means well-known in the art. For example, the sulfonation process of the 
copolymer containing a small 0.3 to 1.0 mole percent unsaturation can be 
conducted in a suitable solvent, such as 1,2-dichloroethane with acetyl 
sulfate as the sulfonating agent. The resulting sulfonic acid derivative 
can then be neutralized with a number of different neutralization agents, 
such as sodium phenolate and similar metal salts. The amounts of such 
neutralization agents employed will normally be stoichiometrically equal 
or, in some cases, excess to the amount of free acid in the polymer, plus 
any reacted reagent which still is present. It is preferred that the 
amount of neutralizing agent be equal to the molar amount of sulfonating 
agent originally employed, plus 10% more to ensure full neutralization. 
The use of more of such neutralization agent is not critical. Sufficient 
neutralization agent is necessary to affect at least 50% neutralization of 
the sulfonic acid groups present in the polymer, preferably at least 90%, 
and most preferably essentially complete neutralization of such acid 
groups should be effected. 
The degree of neutralization of said sulfonate groups may vary from 50 to 
500 mole percent, preferably 90 to 200%. It is preferred that the degree 
of neutralization can be substantially complete, that is, with no 
substantial free acid present and without substantial excess of the base 
other than that needed to ensure neutralization. Thus, it is clear that 
the polymers which are utilized in the instant invention comprise 
substantially neutralized pendant groups and, in fact, an excess of the 
neutralization material may be utilized without defeating the objects of 
the instant invention. 
We have surprisingly found that a very important factor in determining the 
strength of the interaction between the sulfonate groups and 
amine-containing groups in the terpolymer is the nature of the counterion. 
There are, broadly speaking, three major classes of such counterions. The 
first class, which are less preferred, are those metals of Group I and 
Group IIA, which include Li, Na, K, etc., Be, Mg, Ca, etc. We have found 
that these species do not interact as strongly with amine groups as the 
more preferred species described below. Those metals are commonly defined 
as members of the transition elements (see chemical text, Chemical 
Principles and Properties by J. M. Sienko and R. A. Plane, McGraw Hill 
Book Company, 1974, page 19). These metal cations are best exemplified by 
zinc and interact strongly with pyridine and similar amines. As a 
consequence, a zinc neutralized sulfonate group interacts much more 
strongly with the vinylpyridine in the terpolymer than does a magnesium or 
sodium neutralized system. It is for this reason that the transition 
elements are preferred, with zinc, copper, titanium, firconium, chromium, 
iron, nickel and cobalt being especially preferred. We also include 
aluminum, antimony and lead as suitable cations. 
A third species which is preferred is the free sulfonic acid of the 
terpolymer, which will also interact with the vinylpyridine. In this 
latter case, it is clear that the interaction is a classic acid-base 
interaction, while with the transition metals a true coordination complex 
is created, which is due to the donation of the electron pair of the 
nitrogen element. This distinction is a very important one and sets these 
polyampholytes apart from classic acid-base interactions. The surprising 
observation is that such coordination complexes can form in such extreme 
dilution insofar as interacting groups are concerned, and that they are 
apparently formed so far removed from their expected stoichiometry (based 
on small molecule analogs). Therefore, only those polymer backbones (i.e., 
as measured in the absence of ionic groups) having a solubility parameter 
less than 10.5 are suitable in this invention. 
The organic liquids which may be utilized in the instant invention are 
selected with relation to the anionic and cationic moieties of the 
polyampholyte and vice versa. The organic liquid is selected from the 
group consisting of crude or refined paraffinic, naphthenic and aromatic 
hydrocarbons, cyclic aliphatic ethers, aliphatic ethers, or organic 
aliphatic esters and mixtures thereof. 
The method of the instant invention includes incorporating a polar 
cosolvent, for example an alcohol, in the solution of the nonpolar organic 
liquid and a water-insoluble, oil-soluble polyampholyte in order to 
solubilize the pendant sulfonate groups. The polar cosolvent will in one 
case have a solubility parameter of at least 10.0, more preferably at 
least 11.0, and is water miscible. Additionally, the polar solvent will 
have a solubility parameter of about or less than 10 and is hydrocarbon 
miscible. The polar solvent comprises from 0.1 to 15.0 weight percent, 
more preferably 0.1 to 5.0 weight percent, of the total mixture of the 
non-polar organic liquid-water insoluble, oil-soluble polyampholyte and 
polar cosolvent. The viscosity of the solvent system measured at room 
temperature is less than about 1,000 cps, more preferably less than about 
800 cps, and most preferably less than about 500 cps. 
Normally, the polar cosolvent will be a liquid at room temperature, 
however, this is not a requirement. It is preferred, but not required, 
that the polar cosolvent be soluble or miscible with the organic liquid at 
the levels employed in this invention. The polar cosolvent is selected 
from the group consisting of soluble alcohols, amines, di- or 
tri-functional alcohols, amides, acetamides, phosphates or lactones and 
mixtures thereof. Especially preferred polar coslovents are aliphatic 
alcohols having about 1 to about 20 carbon atoms, such as methanol, 
ethanol, n-propanol, isopropanol, oleyl and 1,2-propane diol. 
The amount of water added to the solution of water-insoluble, oil-soluble 
polyampholyte, organic liquid and polar cosolvent having a viscosity of 
less than about 2,000 cps is about 0.5 to about 500 volume percent of 
water, more preferably about 1.0 to about 300 volume percent water, most 
preferably about 2 to about 200 volume percent water. 
The water can be added to the solution of the polyampholyte, organic liquid 
and polar cosolvent by one of three methods. In the first method the water 
is added to and mixed with the solution of the polyampholyte, organic 
liquid and polar cosolvent above ground and prior to pumping through the 
string of tubing or casing into the fracture. The second method comprises 
pumping the solution of the polyampholyte, organic liquid and polar 
cosolvent through the string of tubing or casing into the fracture and 
subsequently pumping water through the string of tubing or casing into the 
fracturing such that the water is added to the solution of the 
polyampholyte, organic liquid and polar cosolvent within the fracture. The 
third method comprises pumping the solution of the polyampholyte, the 
organic liquid and polar cosolvent through the string of tubing or casing 
into the fracture, wherein water contained naturally within the fracture 
or earth formation mixes with the solution of the polyampholyte, organic 
liquid and polar cosolvent.

DETAILED DESCRIPTION OF THE INVENTION 
The following Examples illustrate the present invention without, however, 
limiting the same hereto. 
EXAMPLE 1 
A representative example for the synthesis of styrene-4-vinylpyridine 
copolymer, which is subsequently sulfonated, is described below. 
Into a 1 liter, 4 neck flask was added: 
50 grams styrene 
3.2 grams sodium lauryl sulfate 
120 ml distilled water 
0.2 grams potassium persulfate 
0.5 grams dodecylthiol 
1.1 grams 4-vinylpyridine. 
The solution was purged with nitrogen gas for 1 hour to remove dissolved 
oxygen. As the nitrogen gas purging began the solution was heated to 
50.degree. C. After 24 hours the polymer was precipitated from solution 
with a large excess of acetone. Subsequently, the polymer was washed with 
acetone and dried in a vacuum oven at 60.degree. C. for 24 hours. 
Elemental analysis showed that the copolymer contained 2.5 mole percent 
4-vinylpyridine. 
EXAMPLE 2 
A representative example for the sulfonation of the styrene-4-vinylpyridine 
copolymer is described below. 
The following procedure was generally followed: 50 grams of the copolymer 
of styrene-4-vinyl-pyridine was dissolved in 500 ml of 1,2-dichloroethane. 
The solution was heated to 50.degree. C., and the requisite amount of 
acetyl sulfate was added, in this case, 34.6 ml of 9.996M acetyl sulfate 
(24.5 meq.). The solution was stirred for 60 minutes at 50.degree. C. and 
the reaction was terminated by the addition of 40 ml of methanol. 
Sufficient zinc acetate (diluted with methanol) was added to neutralize 
all acid present. The polymer solution was precipitated into a substantial 
excess of methanol with vigorous agitation, followed by filtration and 
washing with methanol. The product was then vacuum dried. Analyses were 
conducted for sulfur and sodium. The level of sulfonate incorporated was 
determined by sulfur analysis. 
Elemental analysis shows that 1.6 mole percent sulfonate groups were 
incorporated into the polymer chain structure. 
EXAMPLE 3 
Presented in Tables I and II are representative data on the rheological 
properties of hydrocarbon soluble ampholyte polymer composed of 
approximately 35 mole percent t-butyl styrene, 60 mole percent styrene, 3 
mole percent styrene sulfonate and 2 mole percent 4-vinylpyridine 
dissolved in xylene. 
Subsequently, the samples were heated under constant shears and fann 
50.degree. C. rheometer at (170 sec.sup.-1) and periodically the shear was 
reduced to (85 sec.sup.-1) for rheological property measurement. The 
testing was completed by cooling the sample and measuring a final 
rheology. The viscosities yielded show that these hydrocarbon ampholytes 
are very effective at enhancing rheological properties of hydrocarbons 
with relatively good viscosity stability. 
TABLE I 
______________________________________ 
1% w/w Ampholyte in Xylene 
1% w/w Oleyl Alcohol in Xylene 
Time Temperature 
(Minutes) +(F..degree.) 
Viscosity at 170 Sec.sup.-1 
______________________________________ 
0 75 23 
15 150 19 
30 150 19 
60 150 19 
90 75 22 
______________________________________ 
TABLE II 
______________________________________ 
2% w/w Ampholyte in Xylene 
1% w/w Oleyl Alcohol in Xylene 
Time Temperature 
(Minutes) +(F..degree.) 
Viscosity at 170 Sec.sup.-1 
______________________________________ 
0 75 567 
18 150 38 
30 150 25 
45 150 19 
60 150 18 
75 250 8 
90 250 7 
168 75 431 
______________________________________