Note: Descriptions are shown in the official language in which they were submitted.
11,4~8
7056
This invention is concerned with wRter systems
which are employed in subterranean processe3 such as the
drilling of oil wells, or in the enhanced recovery of oil.
More generally, thls invention i9 concerned with the treat-
ment of water systems to which are provided water-soluble
polymeric materials having the capability of enhancing or
increasing the viscosity of water in which they are pro-
~ided. In particular, the inYention is concerned withproviding a polyalkylene polyamine, an alicyclic amine
and/or a alkanolamine in an aqueous system to which has
been provided a water-soluble, polymeric material which
increases the viscosity of the aqueous medium.
It ~s well recognized that one of the ser~ous
problems in the drilling of oil wells or in the enhanced
recovery of oil, such as occurs in ~econdary and tertiary
recovery of oil using water as the pushing medium,is the
attack of metal materials utilized in those processes by
dissolvet oxygen in the water. The oxygen causes corrosion
of the metal thereby depositing salts of the metal or
:: :
a~ hydroxide9 o the metal lnto the aqueous media where the
ame can ~e eventually oxidized and caused to precipitate
as ~olids to adversely affect the ability to drill the
depogit or to utilize the queous medium for enhanced oil
. s
~ recovery. With respect to enhanced recovery of oil, such
, ~
as secondary and tertiary recovery,water is employed as a
2.
' ~ ' ' : ',
11 1408
~97~5t;
driving medium for displacement of additional oil from the
oil reservoir. This displacing medium is in~ected in the
reservoir by means of one or more of the original wells or
by means of entirely new wells and the o~l in the reservoir
is displaced toward and withdrawn from one or m~re of the
other rema~ning wells. Because water ~ Q generally readily
available in many regions, it has been extensively employed
as a driving or pushin medium ~n secondary and tertiary
oil recovery programs. In a typical case, water under pres-
sure is in~ected at various points into a partially depleted
oil-bearing reservoir rock fon~ation to displace portions
of the residual oil therein and the displaced oil is driven
towards a producLng well from which it is recovered by
p-~ing. It is then ~eparated from the water which has been
pumped from the producing well ~nd this water is conveyed
to a storage reservoir from which it can again be pumped
into the in~ection well or wells. Supplementary water from
other sources may be used in conjunction with the produced
water. When the storage reservo~r is opened to the atmos-
phere and the water i9 sub~ected to aeration, this type of
water-flooding system is referred ~o as an open water-
flooding system as contrasted fr~m a closed water flooding
system in which the water is recirculated in a closed system
without substantial aeration. The last mentioned system
thus generally operates under anaerobic conditions.
Two general types of water are employed for
secondary or tertiary oil recovery. Probably the most
, 11,408
ln~7~ss
w~dely used type is fresh ground water obtained from
rivers, lakes, welLs, etc. In some places, however, brine
waters from producing oil wells are used because of the
limited supply of fresh ground water, BS well as due to
the large requirements of water in repre~suriz~ng opera-
tions. In some areas, ~t hRs been found convenient to use
a mixture of brine waters and fre~h ground waters.
It is well recognized that there is a corrosion
problem caused by the presence of dissolved oxygen in the
water. The presence of even very small amounts of dis-
solved oxygen in the waters uQed in the waterflooding or
water containing medium serving to drive the oil w~ll cause
corrosion of metal pipes used in the operation and this
; corrosion is particularly exemplified by pitting of the
metal parts. This pitting occurs in closed waterflooding
systems, l.e., those which operate under anaerobic con-
ditions, because even under ~uch operating conditions the
100ding waters have small concentrations of oxygen dis-
solved therein, these concentrations being nevertheless
sufficient to cau~e the above pitting type of pipe ~urfsce
corrosion. Even with only trace concentrations of oxygen,
; e.g., 0.1 part per million (ppm) or even lesser amounts of
oxygen, which may be present in the driving medium used ~n
~econdary or tertiary oil recovery under anaerobic con-
ditions the large volumes of such water moving through the
pipes makes significant amoun~s of oxygen ~vailable to
large cathodic areas surrounding very 9mall anodic spots
11,408
7~)56
thus causing considerable pitting corrosion.
The floo~ing or driving medium which usually
comprises water or oil field brine have added to them
various conditioning materials, for example, surface
_ active agents or deter~ents which promote the desorption
of the residual oil from the formation, sequestering
agents which prevent the deposition of calcium and/or
magnesium compounds in the interstices of the formation,
bactericides which prevent the ormation from becoming
plugged by bacterial or algae growth, corrosion inhi-
bitors which prevent corrosion of the metallic well
equipment and the consequent deposition of corrosion
products in the formation, and like.
Conventional waterflooding of a subterranean
oil reservoir to obtain additional oil has a nu~ber of
shortcomings which detract seriously from its value.
Foremost among the shortcomings is a tendency of flood
water to "finger" through a reservoir and to by-pass
substantial portions of the reservoir. Noreover, a
water drive has a less than perfect "sweep efficiency"
in that i~ does not contact all portions of the reservoir
and therefor channels through reservoir formation.
Furthermore, it does not normally displace as much oil
in the portions of the reservoir which it contacts
as it theoretically is capable of doing.
The channelling tendency of a waterflood is
usually explained by the fact that oil reservoirs
possess regions and strata that have different perme-
abilities and this has become very well recognized
~97056 11,408
in the application of enhanced oil recovery technology.
The wate~ flaws more rapidly through those regions in
,strsta having a greater relative permeability to water
~than in other portions of the reservoir. As a result,
the water achieves an inefficient displacement of the
oil.
It should be recognized that crude oils vary
greatly in viscosity, from being as low as one or two
centipoises (cps) and some ranging up to 1,000 cps and
even more. It has been established that simple water
flooding performs less sat~sfactorily with ~iscouq crude
oils than with relatively non-viscou~ oils. In other
words, the fingering and by-passing tendencies of the
water drive are more or less directly related to the ratio
of the viscosity of the reservoir oil to the viscosity of
the aqueous driving medium. me following equation con-
~titutes a m~thematical relationship which can be employed
to explain the behavior of fluids flowing through porous
media ~uch as oil reservoirs:
Mo , e x Ko
Me mO Ke
wherein Mo ~s the mobility of the oil to the reservoir in
question;
Me is the mobility of the flooding medium to the
reservoir in question;
mO is the viscosity of the driven oil;
6.
lC~5~7~S~ 11,408
me is the ~i~cosity of the flooding medium;
Ke i~ the relative permeability of the reservoir
toward the flooding medium in the presence of resldual
oil; ~nd
Ko is the relative permeability of the reservoir
toward the oil in the presence of driving water.
The equation i perhaps best explained by seating
that when the mobility ratio of oil to the driving fluid
within the reservoir is equal to one, the oil ancl driving
fluid move through the reservo~r with equal ease. Sub-
8tantially equilibrium proportions of driv~ng fluid and oil
rema~n within the reservoir as soon as the driving fluid
has passed therethrough. Expressed otherwise, the mobility
ratio ter~ affords a measure of the volume of driving fluid
and the amount of time that is required to reduce the oil
content of the reservoir to an ultlmate equilibrium ~alue.
For example, a given volume of dr~ing fluit operated at a
mobil~ty rat~o of one or greater will displace a markedly
greater volume of oil from a reservoir than will an equal
volume of driv~ng fluid operating at a mobility ratio of
le~s than one.
A procedure which h~s been employed to reduce the
degree of fingering and by-passing has been to increase the
visc~sity of the water tri~e medium rel~tive to the oil by
lncorpora~ng into the water, of a water soluble polymeric
mobility control agent, that is, a material which can in-
crea~e the viscosity of the ~ater ~ufficient to pro~ide an
11,408
~97056
effective viscosity (or reciprocal of the mobility within
the reservoir) which is at least substantially equal to ~nd
preferably greater than that of the reservoir oil and/or
any oil displacing liquid (such as an aqueous or oil ex-
ternal surfactant system) that i~ injected ahead of the
viscosity enhanced solution. This mobility ratio, the
measure of the volume of displacing fluid which will be
required to reduce the oil content of a reservoir to an
ultimate equilibrium value, has also been defined by another
equation, that is -
vo~
MR- V
wherein K designates the reservoir permeability, V repre-
sents the viscosity and the subscripts w and o denote water
~nd oil respecti~ely. According ~o this equation, a mobil-
ity ratio of unity indicates that the water and the oil will
mo~e through the reservoir in the presence of one another
with equal ease and a given volu~e of water at a mobility
ratio of less than one will displace a markedly greater
volume of oil from a reservoir than will the sRme amount of
water at a mobility ratio greater ~han one.
A variety of water soluble polymeric materials
csn be used as mobility control-agents in water or the
purpose of enhancing oil recovery such as is the case in
secondary and ~ertiary oil recovery system~. Suitable for
these purposes are the hydro~yethycelluloses illustrated
by Cellosize ~ brand hydroxyethylcellulose such as numbers
' 11,408
10~7056
Q]?3, 300 t 4400, 15,000, 30,000, 52,000, and 100 M,
,.,anufactured and sold by Union Carbide Corporation, the
partially hydrolyzed polyacryamides such as those
described in U.S. Patent No. 3,039,529, patented June
_ 19, 1962, and illustrated by a polyacryl~mide which
has been hydrolyzed to pro~ide from about lO to about
40 wei~ht percent of the nmide group having been
hydrolyzed to sodium carboxylate groups (see U.S. Patent
3,343,603, patented September 26, 1967).
Another class of water-soluble polymeric mobility
control agents are the polyacrylamide copolymers of acryl-
amide with acrylic acid, methacrylic acid and alkali metal
salts of the acids. Other polymeric mobllity co~trol
agents are the water-soluble alkylene oxide polymers,
polymeric sulfonates, polyvinyl alcohols~ and esters and
amides of styrene-maleic anhydride copolymers. In this
respect references made to U.S. Patents Nos. 2,731,414;
2,827,964; 2,842,492; 3,018,826; 3,079,337; and 3,085,063.
U.S. Pstent No. 3,079,336, patented February 26, 1963, des-
cribes a ~umber of useful polymers such as a styrene maleic
anhytride copolymer and ~ half methyl es~er derivatl~e of
that copolymer which as a salt csn be dissolv~d in reservoir
water utilizing an alkali metal hydro~ide sueh as sodium
hydro~:ide. Other useful materials characterized are poly-
acrylic acid and polyethylene oxide s~ch as the high molec-
ular weight polymers of ethylene oxi~-s characteri~ed as
Polyox ~ rfsins, manufactured and so_d by Union Carbide
Corporation. Other polymers which have been ~haracterized
1097056 11, 408-C
as water soluble, polymeric mobility control agents are
the sulfonated polystyrenes and the sulfonated polyvinyl
toluenes.
As pointed out in U. S. Patent 3,292,696, hydroxy-
ethylcellulose is an effective mobility control agent.
Polysaccharides, as a class, are known to be water-soluble
polymeric mobility control agents. For example, dextran
and ionic and non-ionic polysaccharides had been recognized
for some time as suitable water soluble polymeric mobility
control agents (see U. S. Patents Nos. 3,084,122, patented
April 2, 1963 and 3,766,983, patented October 23, 1973),
Carboxymethyl cellulose has been described as a water
soluble mobility control agent in U. S. Patent No. 2,731,414,
patented January 17, 1956.
Other water-soluble carbohydrates include guar
gum and substituted guar gums such as hydroxyethyl, hydroxy-
propyl, carboxymethyl, hydroxypropyl carboxymethyl, and
ether derivatives thereof, guar gums. Other carbohydrates
including locust beam gums may be suitably employed.
The mobility control agents described in the
goregoing patents may be used in the practice of this inven-
tion.
Though some prior art has failed to recognize any
problems associated with the use of these water soluble
polymeric mobility control agents is enhanced oil recovery,
10.
lQ370S6 11, 408
there is a substantial body of literature which points to
the fact that these agents tend to degrade when they are
so utilized. A number of factors have been cited for the
cause of this degradation. For example, some authors have
referred to one or more of the following as the basis for
causing the degradation of one or more of the various water
soluble polymeric mobility control agents described pre-
viously: oxidation, heat, bacteria, reactions with metals
and metal salts, and coreaction with other additives. In
the main, the factors which are considered to be the most
significant in causing the degradation of these water
soluble polymeric mobility control agents are the combina-
tion of heat, oxygen ~even in minute quantities) and
reaction with or through the agency of metals and metal
salts present in the oil reservoir, or dissolved or carried
in the water medium. A number cf provisions have been taken
by the art to eliminate the oxygen problem and these include
the addition of a number of sulfites and phosphonates. In
particular, sodium sulfite and sodium hydrosulfite
(sodium dithionite) have been found to be effective in
eliminating oxygen in the water employed in the enhanced
oil recovery effort. The materials are regarded to be
lower-cost, more-reactive oxygen scavengers, and hence,
are regarded to be desirable materials to employ, if
possible. However, it has been established by Knight,
infra. that the use of sodium hydrosulfite in combination
with for example the hydrolyzed polyacrylamide mobility
X
. .
~ 70S6 11,408
control agent in the presence of oxygen adversely affects
the stability of the agent causing it ~o be rapidly
degraded and resulting in a substantial viscosity re-
duction and loss of the possibility of enhanced oil
recovery. However, Knight, infra, clearly indicates
that if the water is first treated with the sodium
hydrosulfite and the hydrolyzed polyacrylamide is
subsequently introduced to the well then the degradation
problem is materially reduced so long as oxygen is not
re-introduced. In fact, the degradation of the polymer
becomes significantly less of a problem than would
occur in the absence of any treatment with sodium
hydrosulfite. Materials such as thiosulfates, formal-
dehyde, dialdehyde, and the like, have been disclosed
as additives for improving the stability of the partially
hydrolyzed acrylamides against thermal and oxidative
degradation. Another procedure which is em~loyed to
avoid degradation of these polymers is to maintain a
proper solution pH in the water drive fluid so as to
avoid any potential for acid hydrolysis of the polymer.
There is described herein a procedure by which
the problems associated with oxidative degradation of the
water soluble polymeric mobility control agents can be
materially reduced while at the same time providing better
control over solution pH conditions whereby to avoid acid
hydrolysis and also minimize the adverse effects which can
be derived from the presence of metal salts în the reservoir
such as those obtained by the oxidative corrosion o~ metal
parts in the well piping
1~7056 11, 408-C
This invention relates to additives which can be
employed under realistic application conditions to provide
viscosity stabili.y for water-soluble poly~eric mobility
control agents in aqueous solutions with a reasonable
degree of reproducability. This invention is also concerned
with the viscosity stability of water soluble polymers in
aqueous solution which can be used as a drilling fluid
(such as described in German Patent Application,
P 25 24 991.6). Moreover, this invention involves additives
which deal with the problems of dissolved oxygen and the
sequestering of transition metal ions, effects a maximum cost-
thickening efficiency of synthetic polyelectrolytes by
minimizing the need for io~ic scavengers and/or by moderat-
ing their activity, and provides solution pH control
which inhibits biological degradation under aerobic con-
ditions of non-synthetic water soluble polymers containing
multiple acetal linkages.
It has been discovered that al~ylene polyamines
(and in select cases, alkanolamines) (collectively -
"amines") effectively eliminate or minimize viscositylosses of aqueous solutions containing water-soluble
polymer mobility control agents which appear to be
caused by thermal, oxidative, hydrolytic and biological
degradation.
13O
~0~7056
11,408
It also has been discovered in accordance with the
present invention that such alkylene polyamines (in select
cases, alkanolamines) moderate the activity of lower-
cost, more-reactive oxygen scavengers so that the latter
materials may be used with the mobility control agents even
- in the presence of trace amounts of residual and re-
introduced o~ygen without causing the substantial viscosity
losses which have been known to those skilled in the art of
polymer waterflooding. In accordance with this invention,
these alkylene polyamines ~and in select cases, alkan-
olamines) can be used with lower-cost, more-reactive oxygen
scavengers to effect more economical formulations for
eliminating or minimizing viscosity losses of aqueous
solutions containing small amounts of water-soluble polymeric
mobility control agents. The oxides or hydroxides of non-
transition metals, within their solubility limitations, may
also be used in aqueous solution compositions for more
economical manipulations of the solution's pH.
Hereto~ore, e~ployment of the lower-cost, more-
reactive oxygen scavengers has not proven effective under
realistic application conditions ~or stabilizing the
viscosities of aqueous solutions containing small amounts
of polymeric mobility control agents which had been employed
originally in amounts to increase the viscosity of the
water driving medium. These active reducing agents are
effective in converting ferric hydroxide into soluble ferrous
14.
_ ,.
11,408
~C~970S~
salts but thi~ reducing component (ferrou~ lon) is believed
to form an activated complex with residual ~mounts of dis-
solved oxygen, usually introduced ~n the polymer post-
addition step, which is more reactive towards degradation
of the polymeric thickener than oxygen alone. The inter-
action of the sulfite, dithionite, etc., with oxygen is
detrimental to solution viscosity stability, even with less
than 0.2 ppm of transition metal ions present. The
addition of the amines el~minates or minimizes these --
causes for visc09ity losses. The minimum amount of the
amine required is proportional to the amount of reducing
agent employed, the quantity of residual oxygen introduced
in the various stages of solution preparation and its
injection into the oil reservoir, and the amount of transi-
tion metal ion contamination expected during preparation
and transmission of the thickened fluids through wellbore
casing into the reservoir and in recovery. These criteria
are best evaluated by injecting the thickened fluid into
the su~terranean formation for each in~ection we~l and
then analyzing the fluid recovered by backflushing from
the reservoir after an approximate th~rty d~y interval.
It is observed that these amines do not interfere
with the ~cavenging reaction of dithionite anions at 72C.
or above or of sulfite anions at elevated temperatures.
The ami~es serve to modify the activity of these ~aterials
to avoid the rapid degradation of the polymer as compared
to when the amine is not employed. The use of non-
transition metal oxides and/or mono-~mines, to a lesser
degree, help to dify the activ:Lty of ~uch materials.
The additLon of polymeric th~ckeners prior to the oxy~en
~c~veng~ng co~pone~ts repre~entq a~ unexpected advantage
15.
11,408
10970S6
of this invention [e.g., see Knight, J. of Petroleum
Technology, pp 618-626 (May 1973); Note the discussion
at p. 621, col. 2}. By incorporating the polymers which
p~ossess good dispersing characteri~tics into neutral pH
_ solutions before such materials are added will facilitate
good di~solution of sl~ch materials, with less applied
shear to ~olubilize the polymer. This can achieve better
tissolution of the water soluble polymers with fewer gel
structures in the solution and less strenuous criteria for
filtration of the thickened solutions. A significant aspect
of this invention is the stability imparted to synthetic
polyelectrolytes without compromising their cost-thickening
efficiency. Also important is the ability to achiev~ high
alkalinity in the aqueous driving fluid in those instances
when polysaccharides are employed aR the mobility control-
agent. This materially minimizes biological and hydrolytic
degradations of 3uch agents.
Examples of alkylene polyamines useful in practi-
cing this invention include the following: ethylene-
diamine, 1,2-propylene diamine, 1,4-butylene diamine, `
diethylene triamine~ dipropylene triamine, triethylene
tetramine, trlpropylene tetramine, tetraethylene pentamine,
tetrapropylene pentamine, cycloalkyleneamines, such as
piperazine and N-Qubstituted piperazines, polyalkylene-
imines, i.e., the higher molecular weight amines derived
from alkyleneimine such as polyethyleneimines, polypropyl-
eneimines, for example, hav~ng 50, 100 or more alkylene
amino unitQ, etc. Mixtures of the above polyamineS and
those polyamines containing both ethylene and propylene
. groups, for e~ample:
16.
1~97056 11, 408
CH
H ~ H
NH2CH2C~12N - M CH2N - CH2CH~NH2
H H
NH2cH2cH2N - (CH2 ) 2 ~ N ~ CH2CH2NH2
These include the following:
H
2 ( CH2CH21~) 2H
2 (CH2CH2N)3 H
H
NH2- (CH2C~12N)4-H
H
NH2- (CH2CH~N)5 -H
( f H~
NH2 ~ CH~ -N ~ H
~ ¦ 3 H~
NH2 ~ CH2-N 7L~ H
3 H~
NH2 ~ CH - CH2 - N~ H, etc.
H
NH2 ~CH2CH2CH2N) 2 ~ H
H
( 2CH2CH2N)3 - H
H
NH2 (CH2cH2cy.2N)4 - H, etc .
17.
~970S6 11,408
In addition, the starting polyamine may be of a
technical grade such as "Amine E-100" from Dow Chemical
Company. Amine E-100 is the still bottoms fr~m a poly-
alkylene polyamine pr~cess with the ollowing approximate
COmpoQition:
Percent
H
Tetraethylene pentamine (H2N(CH2CH2N)4H) 10
Pentaethylene hexamine (H2N(CH2CH2N)5H) 40
Cyclics (piperazines) 20
Branched Structure 20
Polymers (chains with more than five ethylene 10
amine groups)
Also included within the terms alkylene poly-
amine are substituted polyamines such as N-alkyl,-N-aryl,
etc., compositions
H
(AN)nH and
H H
RN (AN)nH
where R is alkyl, aryl, elkenyl, etc., such as hexyl,
dodecyl, etc., n is a positive number and A is alkylene.
Alkanol amines suitable for use in the practice
of thi~ in~ention include those ha~ing the following
average formul~:
(I 3)a Ic (IH3)a
2 CH--~CH2 ~ N--~X--~CHCH--OH)~
18.
. 11,408
~(~97056
wherein each a is 0 or 1; b is 0 to 6, inclusive;
c is 0 to 2 inclusi~ei d is 3-z; x is 0 to 4 inclusiYe;
and z re 1 to 3, inclusive, and when c is greater
than 0, ~ is 3-c. Illustrati~e compounds include ~he
_ following:
(HOCH2CH2)3N, (HOC~2CH~)2NH, HOCH2CH2NH2,
1 3
(HOCH2CH2)3N, tHoCHCH2)2NH, HOCHCH2NH2,
(HOCH2CH2)2NCH2 2 2 H0CH2CH2NHCH2CH2NH2,
2 2)2 NCH2CH2NHCH2CH2NH2, HOCH2CH2NHCH2CH2NHCH2~H NH
and the like.
The preferred amines are the alkylene polyamines
in which the alkylene contains 1 to about 3 carbon atoms,
and the most preferred amines are polyalkylene polyamines,
that is, amines which contain more than 2 nitrogen atoms.
A standard test for preselecting a suitable
alkylene polyamine (including the alkanolamine~ additive
for use in eliminating or minimizing the visocity losses
of aqueous solutions containing these water soluble poly-
meric mobility control agents is the effectiveness of the
additive at 300 ppm concentration in a hydroxyethycellulose
(Cellosize ~ 100 M) solution (having a 90 cps viscosity,
see Experimental Procedure, infra), to achieve a solution
maintained at 35 DC . (95F.) which retains at least 60% of
its measured ~iscosity af~er 24 hours and thereafter there
i6 lecs than 30% additional measured viscosity loss at the
end of 10 days. In this test, the oxygen concentration
of the solution is reduced to approximately 1 ppm by
19 .
10970S6 11!408
nitrogen purging prior to polymer addition, and a primary
oxygen scavenger, e.g., sodium sulfite or sodium dithionite,
at a 25 ppm and 5 ppm concentration, respectively, are
post-added in slurry or solution form to the thickened
solution at ambient temperatures. The preferred amines
of this invention are those which by the same test, but
operated at 57.22C. ~135F.) achieve the same viscosity
retention.
A more stringent test is the ability of a pre-
10 selected amine at a 1000 ppm concentration to inhibitdegradation, i.e. approximately 70% viscosity retention
after 24 hours with 30% or less viscosity loss over the
following 10 days of time, of the same hydroxyethyl cellu-
lose polymer in oxygen saturated (8.5 ppm) solutions
(same viscosity) at 90.56C. (195F.).
A secondary test in preselecting an amine is
its ability to scavenge greater than forty percent of the
oxygen in an oxygen saturated aqueous solution maintained
at 90.56C. for 10 days. An additional secondary test is
20 the ability of a preselected amine at 250 ppm concentration
to sequester the viscosity degrading effects of 10 ppm
ferrous ion on the same hydroxyethyl cellulose solutions
(same viscosity~ in aqueous, oxygen saturated solutions
maintained at 57.22C. These or a similar set of criteria
can be used to preselect amine stabilizers, alone or in
combination with other more reactive oxygen scavengers
and/or in combination with basic oxides or hydroxides of
non-transition metals, in eliminating or minimizing (at
high temperatures) the viscosity losses of aqueous water-
soluble polymer solutions caused by thermal, oxidative,
hydrolytic and biological degradation.
20.
X
'
1 ~9 7~ S~ 11,408
It h~s been found that the amines, as described
herein, when empLoyed in ~queous solutions thickened with
water-soluble polymeric mobility control agents can
simultaneously sca~enge dlQsolved oxygen from aqueous
solurions, complex transition metal ~ons capable of form- i
ing insoluble hydroxide compounds, which may plug wellbore
configurations, and complex the lower valence states of
transition metal ions, which RS discussed below can be
very detrimental to maintaining polymer solution vis-
cosit~es. In addition, the amines serve to facilitate
alkaline solution conditions, for inhibiting biological
degradation of the non-synthe~ic water-soluble polymers
(e.g., the polysaccharides) under aerobic conditions.
Some of the amines possess biocidal properties in their
own right and this is desirable.
Because of this effectiveness of th~ amines, one
may ~lso employ several low-cost components as supplements
in minimizing aqueous water-soluble polymer solution
viscosity los~es. For example, the ~mines tend to
moderate the reactivity of lower-cost, oxygen scsvengers,
i.e. ~ulfite, dithionite anions, etc., in regards to the
degradation of ~he water-soluble polymeric mobility con-
trol agents in the presence o~ low dissolved oxygen
concentrations, with or withou~ significant amo~ts of
ferrous ion present. The resulting lower coct formula-
tions may also include components for more economical
21.
11,408
10970S~i
control of solution pH without detrimentally affecting
solution viscosity.
The amount of the water-soluble-polymeric
mobility control agent to be supplied to an aqueous
driving medium is that amount which is typically con-
sidered useful by the ~rt. me amount employed will be
dependent upon a number of considerations, such as,
whether the medium comprises fresh water or brine, the
nature of the salts in the medium and/or the reservoirs,
the particul~r mobility control agen~ chosen, the tempera~
ture at the time of addition and in the oil reservoir, the
viscosity of the oil to be recovered, the presence of a
slug (or if this medium is to be the slug) and its vis-
cosity re~uirements, the permeability of the reservoir,
and the like. As a rule, the amount of the water-soluble
polymeric mobility control agent will be such as to cause
the water in contact w~th the oil in the reservoir to have
a viscosity, while in the reservoir, which is at least
equal to the ~iscosity of the oil. In the preferred oper-
ation, the amount of the water-soluble polymeric mobility
control agent provided in the aqueous drive medium shoult
not be 80 great as to c~use the thickened medium to have
undesirable r~duction in ability to permeate the reservoir.
In the case where the agent i8 hydroxyrthyl
cellulose, even slight amounts of it are effective for the
purpose slnce the water viscosity is increased by the
presence of the additive, however it is preferred that a
1097~56 11 408
sufficient amount be added to sttain a water viscosity of
at least about 1 centipoise or greater at the reservoir
temperature. When posAible, ~t is preferred to add
hydroxyethyl cellulose in ~n smount sufflcient to achieve
a water viscosity between ~bout 10 and 1000 centipoises.
The exact amount necessary to provide these viscosities is
dependent on the reservoir temperature, the molecular
weight and substitution of the hydroxyethyl cellulose, as
well as the nature and amount of in~urities and ~alts in
the flood waters. Usually, however, this amount is between
about 0.~1 and 1.0 weight percent of the solution.
In the case where the agent is a natural poly-
saccharide, the amount may range between about 0.001 to
about 1.0 weight per cent of the ~olution. The poly-
acrylamides may be used in Emounts of between about 0.001
to about 1.0 weight per cent of the solution. me other
mobility control ~gent~ described above ma~ be effectively
employed in ~mount of between about 0.001 to about 1.O
weight percent.
The amount of the amine provided in the aqueous
m~dium i~ that amount that causes the reduction in the
degradation of the mobility control agent as evidenced
by a reduction in the loss of viscosity of the medium,
as described above. The amount of the amine should be
correlated with the amount of any other component added
to the medium for the s~me or similar purposes. For
example, if there is added sodium dithionite as an
oxygen scavenger, then the function of the amine as
an oxygen scavenger is not as critical a feature of
23.
1(~970S6 11,408
its use as is its role of stabilizing the affect of
the sodium dithionite addition on the rate of degra-
dation of the water-soluble polymeric mobility control
agent. Typically, the amount of the amine ranges
between about 0.0001 to 1.0 weight percent of the
weight of the aqueous medium containing the mobility
control agent.
/
/
/
24.
11,408
loa70s6
BRIEF DESCRIPTION O~ THE DRAWINGS
Figures 1 through 19 serve to give further
illustration of the practice of this invention and the
following outlines the matters and legends contained
in them:
Fig. 1 Percent retained ViscOfiity dependence on time
in oxygen saturated (8.5 ppm), water-soluble
polymer (W-SP) aqueous solutions, 195F.(90-56~C.):
W-SP: - - - - Acrylaminde/acrylic acid
copolymer (PAMC from Dow Chemical Co.);
- -, PAMC from Calgon Corp.;
- - - , Xanthomonas Cam~estris
polysaccharide from ~elco Corp.;
x x , Hydroxypropyl guar gum from
Celanese Corp.; - , Hydroxyethyl
cellulose from Vnion Carbide Corp.
Fig. 2 Percent retained viscosity dependence on
time in oxygen saturated (8.S ppm), water-
~oluble polymer (W-SP) aqueous solutions
150F.(65.56C.)
W-SP~ PAMC from Dow Chemical Co.;
- - - , Xanthomonas Campestris
polysaccharide from Kelco Corp.i
, Hydroxyethyl cellulose from
Union Carbide Corp.
11,408
10970X6
Fig. 3 Percent retained visc~sity dependence on
time in oxygen saturated ~8.5 ppm~, water-
601uble polymer (W-SP) aqueous solutions,
135F.(57.22C.):
W-SP: ~ PAMC from Dow Chemical Co.
or Calgon Corp.; ~ , Xanthomonas
Campestris polysaccharide from Kelco Corp.;
---~ , Hydroxyethyl cellulose from Union
Carbide Corp.
Fig. 4 Percent retained viscosity dependence on
time in oxygen saturated (8.5 ppm), acrylamide/
acrylic acid copolymer (post-addition)
: aqueous solutions, 150F.(65.5~C.)
Additive: Sodium dithionite - ~, 50 ppm
0 75 ppm;
A 100 ppm;
n 250 ppm;
~ 500 ppm
Hydrazine - 10 ppm;
100 ppm
Fig. 5 Percent retained viscosity depentence on
time in oxygen saturated (8.5 ppm), hydroxy-
ethyl cellulose aqueous solutiDns, 195F.(90.56C.)
Additives tlO00 ppm): O , hexaethylenehept2mine;
O , tetraethylenepentamine; ~ ,
triethanolamine; V, sodium tripolyphosphate;
O , ethylenediamine; n , hexamethylene-
diamine; ~ , tetrapropylenepentamine;
, 30% sodiu~ chloride.
26.
:1~97~s6 11,408
Fig. 6 Percent retained viscosity dependence on
time in oxygen saturated t8.5 ppm), hydroxy-
ethyl cellulose (HEC~ aqueous solutions:
O HEC with 500 ppm hexaethyleneheptamine
(HEHA) aqueous solution viscosity loss
characteristics as a function ~f tem-
perature, 135**:HEC with 500 ppm
Poly(ethylene ~mine)(PEI) or penta-
ethylene hexamine (PEHA)
Fi~. 7 Percent retained viscosity dependence on time
in oxygen saturated (8.5 ppm), hydroxyethyl
cellulose ~HEC) aqueous solutions;
1~
0 : HEC aqueous solution viscosity loss
characteristics as a function of
temperature.
: HEC with 1000 ppm hexaethyleneheptamine
(HEHA) aqueous solution viscosity loss
characteristicQ as a function of tem-
perature. 135**:HEC with 1000 ppm
PEI or PEHA.
Fig. 8 Percent retained visc~si~,y dependence on time in oxygen saturated (8.5 ppm), water-s~luble
; polymer (W-SP) aqueous solutiQns with 1000 ppm
hexaethylenehepeamine~ 1~0F.(65.56C.)
W-SP: 0 , Hydroxyethyl cellulose
6a . Hydroxypropyl guar gum
~ , Xanthomonas Campestris polysaccharide
11,408
~(~97~)S6
~ig. 9 Percent ret~ined viscosity dependence on time
in low oxygen (~ 1.0 ppm) hydroxyethyl
cellulose aqueous ~olutions, 135F, contain-
~ng ferric ion at:
O , O.S ppm; O , 1.O ppm: A , 5.9 ppm;
, 10.0 ppm with 250 ppm HEHA; O , 17.0 ppm;
o , 17.0 ppm with 250 ppm HEHA. (The 10
ppm without HEHA lost 80% of original
viscosity at room temperature.)
Fig. 10 Percent retained viscosity dependence on time
in low oxygen (~ 1.0 ppm) hydroxyethyl
cellulose aqueous solut~ ns, 135F, contain-
ing ferrous ion at:
o , 0-5 pp~; O , 1.0 pFm; A , 5.0 ppm;
~ s 10.0 ppm; O 10.0 ppF ~ith 250 ppm HEHA.
Fig. 11 Percent retained viscosity dependence on time
in oxygen saturated (8.5 ppm), hydroxyethyl
cellulose aqueous solutions, 150F. ~65.56C.):
Additives: o , 10 ppm Hydrazi~e (Hz);
<D . 100 ppm Hz;
~ , 50 ppm Hz, 500 ppm HEHA:
, 100 Hz, 500 HEHA;
, 250 Hz, 500 HEHA.
~8.
109705~ 11, 408
Fig. 12 Percent ret~ined viscos~ty dependence on time
in low oxygen (- 1 ppm), pre-addition hydroxy-
ethyl cellulose aqueous solutions, 72F.(22.22C.): .
Post-addition adtitives, slurry addition:
5 ppm Na2S2O4 with 300 ppm:
O , ethylene diamine; O ,
tetraethylene pentamine (TEPA);
O , ethanolamine; ~ , triethanol-
amine; ~ , tetrapropylene pentamine;
V , hexamethylenediami~e; o ,
magnesium oxide.
, 25 ppm Na2S03 with 300 ppm TEPA.
Fig. 13 Percent retained viscosity dependence on time
in low oxygen (~1 ppm), pre-additlon hydroxy-
ethyl cellulose aqueous solutions, 135F.(57.22C.):
Post-addition additives, slurry adtition:
5 ppm Na2S2O4 with 300 ppm:
O ethylene dia~ine; ,
tetrsethylenepentamine (TEPA);
O , ethanolamine; ~ , triethanol--
amine; ~ , tetrapropylenepentsmine;
~ , hexamethylenediamine; O ,
magnesium oxide.
29.
~ 9~056 11,408
Fig. 14 Percent retained viscosity dependence on
time in low oxygen (x~l.O ppm) hydroxy-
e~hyl cellulose aqueous solutions, 135~F.,
containing mixed ~dditives:
o , 5-0 ppm Na2S204, 250 ppm CaO;
~ , 5.0 ppm Fe 2,5.o ppm Na2S204,
250 ppm CaO; O , 5.0 ppm Fe+2,5.0 ppm
Na2S204, 125 ppm CaO; 125 ppm TEPA;
O , 5.0 ppm Fe+2,5.0 ppm Na2S2O4,
-` 250 ppm TEPA.
Fig. 15 Percent retained viscosity dependence on
time in low oxygen (~ 1.0 ppm) hydroxy-
ethyl cellulose aqueous solutions, 195F
containing mixet additives:
O , 5.0 ppm Na2S2O4, 250 ppm CaO;
, 5.0 ppm Fe ~,5.0 ppm Na2S2O4,
250 ppm CaO; o , 5.0 ppm Fel2,5.0 ppm
Na2S2O4, 125 ppm CaO; 125 ppm TEPA;
~ ~ 5-0 ppm Fe ,5.0 ppm Na2S2O4, 250
ppm TEPA.
Fig. 16 Percent retained viscosity dependence on
~ime in oxygen saturated (8.5 ppm), hydro-
ethyl cellulose aqueous 801utions, 135~F.:
Mixed Additives: ~ , 250 ppm Na~S2O4 (DT),
500 hexaethylene heptsmine ~HE~); ffl , 250 ppm
DT, 250 ppm YEHA; m, 1OO ppm DT, 250 HEHA;
D , 50 ppm DT, 250 ppm HEHA; 4~ , 250 DT,
500 aminoethylpiperazine; o , 50 ppm DT,
alone; ~ , 100 ppm DT, alone.
30.
.
1(~970.~6 11, 408
Fig. 17 Percent retained viscosity dependence on
time in oxygen saturated (8.5 ppm), hydroxy-
ethyl cellul~se aqueous solutions, 135~
~lixed Additives: ~ , 250 ppm, Na2SO3 (SS),
_ 500 ppm HDHAi ~ , 250 ppm SS, 250 ppm HEHA;
O , 250 ppm DT, 125 ppm Boric Acid,
125 ppm Sodium Borate buffer; ~ , 100 ppm
250 ppm DT, 250 ppm Boric Acid,
250 ppm Sodium Borate buffer.
Nitrogen purged aqueous solutions, aqueous
solution oxygen ca, 1 ppm:
Additives: E3. 50 ppm SS, 250 ppm HEHA;
0 , 10 ppm SS, 250 ppm HEHA.
Fig. 18 Percent retained viscosi~y dependence on
time in low oxygen (ca. ~ ppm) hydroxy-
e~hyl cellu: se a~ueous solut~ons, 135F.:
Mixed Additives: O , 3 ppm DT, 250 TEPA;
~ , 3.0 DT, 250 HEHA; ~ , 100 ppm SS,
250 TEPA; O , 50 ppm SS~ 250 TEPA;
Q , 50 ppm SS, 250 HEHA; A , 3 pp~ DT,
slone.
Fig. 19 Percent retained ~iscosity dependence on
t~me in low oxygen (ca. 1 ppm) hydroxy-
ethyl cellulose aqueous solutions, 135F.: -
Mixed Additives: O , O , 5 ppm DT, 300 ppm
TEPA; ~ , o , 5 ppm DT, 300 ppm triethanol-
am~ne
W-S Polymer: Closed symbols, acrylamide/
acrylic acid copolymer; Open symbols,
hydroxyethyl cellulose.
'''
1 ~9~V S 6 11,408
The degree of confidence that can be expected
in stabilizing viscosities of ~n aqueous solution of a
water-soluble polymeric mobili~y control agent ~ria the
prior art iQ reflected in the dithionite studies in
Figure 4. For example 75 ppm of sodium dithionite is
capable of removing 8.5 ppm of dis solved oxygen, yet the
solution viscosities of the polymer thickened fluid are
below those of the acrylamide/acrylic acid copolymer
colutions where no attempt at stabilization was made.
Only one of the five stabilization efforts resulted in
adequate long-term ~olution ~iscosities. This is due
primarily to the difficulty of dissolving the polymers
without re-introducing oxygen into the solution, and to a
lesser extent, to trace amounts of metal ions in all poly-
mers. Hydrazine also was investigated in this study.
Hydrazine will sca~enge oxygen from aqueous 301utions and
has been disclosed as a corrosion inhibitor for boilers
(U.S. 3,983,048) via this mechanism. Polymer degradation
was observed to be very rapid with this scavenger.
In the studies wherein stabilization was not
attempted, the polysaccharides ~the biosynthesis product
from Xanthomonas Cæmpestris (XCPS) snd hydroxyethyl cellu-
lsse (HEC)]exhibited greater ~nstability at the lower
temperatures than the scrylamide/acryl~c acid copolymer
(PAMC), Polysaccharides contain multiple acetal units sub-
~ect to acid hydrolysis. Consequently, in the static
laboratory ~olu~ions, ~utoaccelerstive degradation could
9~0~i6 11,408
have accounted for the greater instability noted. Initial
acid generation could occur through oxygen extraction of
the hydrogen bonded to the carbon of the acetal linkage.
To combat the acid hydrolysis autoacceleration pos~ibillty,
.
a polymeric base, polycethylene imine) (PEI), was added to
polysaccharide solutions. The improved ~tability, i.e.
solution viscosities, noted when PEI was employed at 500
and 1000 ppm was far greater than m~ght have been expected
by interpretation of academic studies [Brandon, R. E.,
et. al~, ACS Symp. Ser., 10, (1975); Aspinall, G. 0.,
Biochem. Soc. Sym~., 11, 42 (1953~; Major, W. D., ~ , 41,
530 (1958~; Kuzmina, 0. P., J. Polym. Sci., C16, 4225
(1968)] on c~rbohydrate decomposition rates at elevated
temperatures. The use of PEI improved viscosity stabilities
of PAMC aqueous solutions, which were proportional, with
little reproducibility variance, to the amount of additive
used. During these studies it was observed that the dis-
solved oxygen content decreased as the amo~nt of PEI was
increased.
Another ~creening test (1000 ppm additive in
aqueous, oxygen saturated solutions at 195F - Table I)
showed a general agreement between the screening results
and the ab~lity of the additives to stabilize agueous
HEC solution viscosities (Figure 5). Solution pH
control ha~ been found an insufficient cr~teria
11,408
~3~056
TABLE I
ADDITIVE EFFECT ON PERCENT OXYGEN
REMOVED FROM AQUEOUS SOLUTIONS
% Oxygen Removedd
_ Solution i~ 24 hrs. at
ADDITIVE (7?F)e 72~ 104oe 1350e 1950e
. .
Urea 7 3 0 0
Formaldehyde 6.9 ~ O OO <10
lOZ Sodlum Chloride 7.1 - - - 13
15% Sodium Chloride 7.1 - - - -~1
Sodium Tripolyphosphate 9.5 0 0 - ~10
Ethylenedinitrilo-tetracetic 3.5 0 - - O
acid
Ethylenedinltrilo- 10.5 - - - O
tetracetic acid,
tetrasodium salt
Triethanolamineb 9.8 0 0 41
Aminoethylpiperazine 8.0 0 0 22
N-Methyl Morpholine 8.0 0 0 '10
Hydroxylamine Hydrochloride 6.9 10 203~
Ethylenediamine 10.8 0 0 19
Diethylenetriamineb 10.7 0 8 5290
Tetraethylenepentamineb 10.5 0 21 5581
Pentaethylenehexamineb 10.6 9 21 5783
Hexaethyleneheptamineb 10.4 33 60 9090
1,6 Hexamethylenediam~-ne 9.6 - - ~10
Tetrapropylenepentamineb 11.0 0 C10 32
Poly(ethylene imine) 8.5 10 20 6075
a) 1000 ppm unless otherwise indicated.
~) Predominant component in complex mixture.
c) pH (inltial water). 5.7.
d) ~8% error in measurements.
e) 22.22~C.(72F.); 40C.(104F.~;
57.22C.(135F.); 90.56C.(195F.)
34.
~97~ 5~ 11.408
for estimating significant, long-term impro~ements in
solution viscosity stabilities. A pr~mary criteria that
can be used for est~mating the significance of additives
to effect long-term ~olution viscosity stability improve-
ments is reflected ~n Figure 5. For example, in oxygen
6atursted, hydroxyethyl cellulose thickened ~queous solu-
t~ons, those add~tives which effect approximately 70% ~r
greater retention of the original viscosity after 24 hours
a~ 195~F. (90.56C.) solution temperatures, and wherein
the rate of viscosity loss during the first ten day
interval is approximate to or less than 30% can be
expected to impart a significant stabilizing influence
under an actual well bore test.
Based upon ~he greater oxygen scavenging ability
(Table I) and good performance in HEC solu;ion viscosity
studies, hexaethylene heptamine tHEHA) was examined in
greater detail Over a broad temperature range, 500 ppm
(Figure 6) and 1000 ppm CFigure 7), HEHA was noted to
significantly improve the viscosity stabillty of HEC 801u-
tions beyond that noted in the absence of the additive
CFigure 7). The addition of HEHA also was obser~ed to
impart the s2me degree of stability in other carbohydrates
~Figure 8) in fresh or brine solutions and to synthe~ic
water-soluble polymers such as PAMC. The unusual viscosity
~ncrease with XCPS is probably associated with its slight
11, 408
i~7~S6
polyelectrolyte and complex biological solution ch~racter-
istics.
In a period of thirty to fifty-days,gels are
observed in the stabilized carbohydrate thickened ~olutions
with an associated drop in 801u ion ~iQcos~ty. Gels are
not obserYed in the PAMC-HEHA solutlons. T~e cross-
linking of c~rbohydrate chains via decomposition protuct
group, i.e., aldehyde and aids and reactions with
Emine, are the probable cause of the gelation phenom-
enon. As such, the phenomenon has Potential as a time
dependent flow diversion technique. mere are mRny dis-
closures on flow d~version agentQ in the area of the well-
bore, but few (e.g. U.S. 3,926,258) pertaining to time
dependent reactions which function beneficially far beyond
the well ~ite to inhibit "line-driving9', i.e. channeling,
between in~ection and producing wells. In separate studies
it was observed that gelation is shear rate dependent.
Consequently, the phenomenon can be inhibited by incre~sing
the frontal velocity of a subterranean sweep; an applica-
tion cond~tion that i8 not detrimental to polysaccharide
performance because of thair shear-stability solution
cha~acteristics ~Maerker, J. M., Soc. Pet. En~. J., 259
II-311 (1975)].
The stabilizing influence of the amines is not
a ~traight forward as presented flbove. Yor example, some
stabilizers at 250 ppm scavenge dissolved oxygen, but
no~able solution ~iscosity improvements are not always
36.
11,408
~C1~7056
obser~ed. Significant viscosity ~mproY~ments are obserYed
at 50Q ppm with ~mines which readily scavenge dissolYed
o~ygen at 250 ppm, and ~iscosity stabilities approxim~ting
mobility control buffer requirements are observed over a
br~ad temperature range at 1000 ppm. The relationships
~ appear to be qualitatively exponentiali little added
stability is observed at a 2000 ppm concentration levels.
I~ also is observed that some amines, e.g. tetrapropylene-
pentamlne, hexapropyleneheptamine, etc. scavenge dissolved
oxygen (to ~ 1 ppm) slowly and are not as effective
stabilizer~ even at 1000 ppm concentrations. Subsequent
studies indicate other important contribution~ of amine
stabilizers to the attainment of long-term aqueous
solution viscosities.
Generally, amines are sbserved to be effective in
sequestering the activity of transitio~ metal ions in solu-
tion. ~or example, in solutions wherein the dissol~ed oxygen
conte~t has been lowered (to ca. 1 ppm) by nitrogen purging,
ferric ion at concentrations abo~e 5 ppm accelerates
(Figure 9) the rate of viscosity loss in HEC solutions;
ferrous ion ~above 0.5 ppm concentrations - Figure lO)
~re even more tetrimental to polymes stability. However,
at a HEHA concentration of 250 ppm, both iron valence states
to ~e expec~ed in aqueous solution~ are sequessered thereby
el~min~tfng their degradation acti~itieg at high concen~ra-
t~on levels.
The success of the amines also are due in part to
their abilit~ to protect water soluble polymers in solution
056 11,408
from degradation by ~he more reactive oxygen seavengers,
i.e. dithionite, ~ulfite, bisulfite, hydrazine, etc., in
the presence of trace amounts of oxygen.~ The ability of
the amines to moderate the degradative activity of primary
oxygen scavengers can be observed in studies utilizing
hytrazine ~Figure 11). Hydrazine is very effective in
tegrading PAMC ~Figure 4) and HEC (Figure 11) in aqueous
Eolution. However, investigations denoted a stabil-
izing influence of HEHA in moderating the activity of
hydrazine. Although the percent retained v~scosities were
60mewhat erratic in preliminary studies (Figure ll), syner-
gistic effects over certain component ratios and amounts
were observed, particularly with respect ts the use of
either "stabilizing" component alone. Subsequent studies
of HEHA/d~thionite com~inations provided similar synergistic
stabilit~es ~n both HEC and PAMC solutions.
The moderating influence of the RmineS on the
more reactive primary oxygen scavengers can be seen in
application of the formulations to polymer-preaddition
solutions (Table II and Figure 12). It is well-recognized
in the art of polymer waterflooding that addition of an
oxygen ~oavenger, e.g. dithionite, sulfite, etc., to a
thickened solution with traces of dissolved oxygen will
result in rapid degradation of the solubiLized W-S polymer.
Specifically it is taught that "it is imperative that
hydrosulfite (i.e. dithionite) be added to ~ater before
11,408
1~?~7~6
polymer ~s added" (Knlght ~upra) ~nd "it is best, however,
to incorporate the hydrosulfite additive prior to the addi-
tion of the polymeric additive" (Pye, U.S. 3,343,601).
These aspects of mobility control buffer technolo~y
~ are confirmed by the data in Table II. To minimize solution
viscosity losses, the current art practices the addition of
a reactive oxygen scavenger to aqueous solutions prior to
water ~oluble polymer addition, ~n an amount anticipating,
with a slight excess, the concentration of oxygen to be re-
introduced with polymer dis~olution. The problem of mini-
mizing oxygen reintroduction and redox degradation of the
water-soluble polymer being dissolved is ever present and 8
serious deficiency of the practiced art.
One of the positive aspects of the current inven-
t~on is the moderating effect of the amines on primary oxygen
~cavengers. m is observation permits preadditions of the
water ~oluble polymer without significant later degradation
when the primary Qcavengers are added ~n a premixed slurry
or solution with the amines. Comparative performances at
22.22C (72F) and 57.22C ~135 F), of preaddition 801u-
tions prepared at ambient temperatures, are illustrated in
Figures 12 and 13, respecti~ely. The perfonmance capability
of am~ to eliminate or minimize the viQCosity losses of
water-~oluble polymer aqueous solutions i~ defined in
~igure 12, i.e. those which effect at least 60% viscosity
retention after 24 hours with less than 30% viscosity loss
during the following 10 days. The product of ~election
56 11,408
o~o~ s~
c ,~ B ~ v
P.. ~ ~ 0 ~ S.l ,XO 3
~ o ~1 8 ~ ~ oo "Do~ ~ ~
c ~ o s~
c~ ~1 ~~
o~ ~ @~ o~Dc ~ ~
o ~ ~
~ C
i~ ~v ~ ~ , p
~ ~ E~ I ~o O
cn ~g~ 3
~~ ~ ~ ~ ~ r` ~ u~ O C~ O ~ E
P~ ~C ~ C ' ~
~0 O q ~
~ 97Q56 ll,408
would be dependent upon economic factors and upon the
care taken to exclude the contaminants influencing thi^k-
ener degradation. The preferred materials of thls inven-
_ tion are defined by the same criteria, but under more
strenuous conditions, i.e. 57.22C. (135F), solution
temperatures (Fi~ure 13).
Pre-addition of water-soluble polymers posses-
sing ~ood dispersing characteristics in substantially
neutral pH solutions facilitates good dissolution of such
materials, with less applied shear to solubilize the
Polymer. Better dissolution with many types of water-
~oluble polymers generally means fewer gel gtructures
in solution and less strenuous criteria for filtration
of the thickened solutions.
In an effort to affect lower cost formulations,
other components can be considered for achieving aqueous
water-soluble polymer solution viscosity stabilities.
Calcium oxide and sodium dithionite in combination appear
to improve long-term solution viscosity stabilities, pre-
sumably via pH and oxygen control, but this improvement
may ~e effected by the presence of ferrous ion ~Figure 14).
Implementation of the mixed formulation with tetraethylene-
pentamine (TEPA) significantly improves solution viscosities
(pro3ectet 58~ retained viscosity at 3 years). However, a
dithionite formulation employed with a higher TEPA
level is effective in achieving ~ery high stabilities
[pro~ected 74% retained at 3 years, 57.22C. (135F.), see
Fig, 14)~- These data and those noted with the same
11,408
~U97~56
formulations a~ 195F. (Fîg. 15~ denote the importance of
lnteractions between dissolved oxygen, transition metal
ions and te~perature ~n stabilizing solution viscosities,
and of the importance of the stabilizer in dealing with
-~ the variables in a concerted manner.
The amount of the amines required eo achieve
optimum aqueous water-soluble polymer solution viscosity
stability i8 dependent upon the interactions discussed
abov~. As such, the amou~t of the amine is dependent upon
-the dissolved oxygen concentration and the means employed
to achieve that level. For example, in large-scale water-
floods,aqueous solutions are often deaerated by gas strip-
ping or vacuum deaeration techniques tCarlberg, B. L.,
Soc~ Pet. Eng. Paper No. 6096). If a technique of this
nature is employed, the oxygen concentration of the aqueous
~olution to which the water-soluble polymer ~s to be added
will be low. Essentially only the oxygen re-introduced
through polymer dissolut~on will be present. Therefore,
~ess amine will be required than would be necessary in
~maller field-trial polymer flooding wherein it is often
more economical to deoxygenate aqueous solutions by purely
chemical methods. The latter approach requires the use of
larger quantities of a primary oxygen scavenger and thus
will require higher concentrations of the amines to achieve
the proper activity moderation, ~h~ch in part is also
dependent upon the total amount of dissolved oxygen and
transition metal ions present after dissolution of the
42.
1~9~5~ 11,408
water-soluble polymer. mese effects are illustrated in
Figure 16, wherein dithionite is employed as the primary
oxygen 8 cavenger.
In special tests employing high concentra-
~ tion dithionite studies, it was noted that ~pproxi-
mately 70 to 90 ppm of soduum dithionite tepleted
smbient aqueous solutions of dissolved oxygen. In the
studies illustrated in Figure 16, initlal oxygen concen-
trations of 5.6, 2.9, 0.4 and 1.1 were achieved with
increasing dithion~te and HEHA concentrations, respect-
ivel~. These discrepancies with respect to the non-
thickened concentration studies are associated with re-
introduced oxygen levels during polymer dissolution.
Projected ~hree-year aqueous solution viscosity stabil-
ities are 48, 54, 58 and 69 percen~ respectively.
HEHA, containing comparatively high initial oxygen
concentra~ions (5.6 ppm), is capable of outperforming
Rminoethylpiperazine ~olutions with a lower initial
oxygen level, i.e., 2.4 ppm.
Similar observations are observed w~en sulf~e
i8 u~ed ~t high concentrationQ as the primary oxygen
scavenger CFigure 17). Independent s~udies in non-
th~ckened solutions indieate a level of 150 ppm of sodium
43.
lC!9~56 11, 408
sulfite is required to deplete ambient aqueous s31utions
of dissolved oxygen Projected three-year stabilities of
70 &nd 60% viscosity retention are observed using the high
concentration sulfite ~nion amine mixed for~ulation approach.
When the sulfite mixtures are complemented ~y psior
nitrogen purging to lower the initial tissolved oxygen
content, lower stabilities are obtained approximating the
lower dithionite/HEHA mixed formulation projected stabil-
ities at a three-year period. These comparative studies
highlight the synergistic relationship wherein greater
stabilities are observed with certain compositional ratios
of primary to amine sta~ilizers than are obtained by using
either type of stabilizer separately.
As suggested in earlier screening comparisons,
some amines perform better than others. Comparative tif-
ferences between two effective amine stabilizers are
evitent in Figure 18 ~n s~stems where~n sulfite is employed
as the pr~mary oxygen scavenger, and in dithionite composi-
tions wherein the ~olution had been previously purged with
nitrogen. Although HEHA was observed to be a more efficient
oxygen ~cavenger, TEPA implemented better solution viscosity
stabilities at elevated temperatures, and these earlier
differences are reflected in Fi~ure 18. This may be due
to more efficient coordinating efficiency, i.e.,greater
equivalent reactivi~y per mole, consistent wieh stereo-
chemical restrictions of the various components to sequester
transition matal ions or ~ome other mechanistic feature
44.
~37~56 11,408
peculiar to the structural aspects of the lower moLecular
weight material. In these latter ~tudies, the use of non-
transition metal oxides, as lower-cose pH control reagents,
are effective, in part, in stabilizing water-Roluble
-~ polymer aqueous solution viscositie~ against primary oxygen
scavenger degradation of polymer viscosities in the presence
of trace amounts o f oxygen. However, as indicated earlier
they are not as effective a~ the amine approach even with-
out the intentional contamination of solutions wlth ferrous
ion.
me performance of the amines ~n minimizing solu-
tion viscosity losses is dependent upon the parameters
discussed above and upon the water-soluble poly~er used as
the mobility control agent. Comparative differences of
acrylamide/acrylic acid (PAMC) and hydroxyethyl cellulose
(HEC) with tetraethylene pentamine (TEPA) and triethanola-
mine (TEOA) are illustrated in Figure 19. As reflected in
earlier graphs TEOA is less forgiving of trace amounts of
cxygen in ~ dithionite environment. Interac~ing with these
~ariables is possibly the higher iron content in the B C
~olution because of the higher concen~rations used in fresh
wat~r solutions. The interaction of these variables with
te~perature is very important and care with higher
amine concentrations must be employed at higher solution
temperatures.
While not wishing to be bound by any theory or
explanation, it is believed that the method of employing
56
11,408
the amines alone or in combination with lower-eost primary
oxygen ~cavengers and/or lower-cost solutlon pH control
reagents is an effective means of obtaining long-term
solution water-solubl~-~ polymer viscoRities because of the
unique, concerted modes by which the ~mines effectively
negate the various mechanisms of polymer decomposition in
solution. me amines are effect~ve in removing residual
solution oxygen levels, introduced during polymer dis-
solution, effectively sequestering transition metal ions
fr~m coordinating with residu21 oxygen levels to
~ccelerate polymer degradation and in maintaining alkaline
pH solutions to inhibit biological degradation under aerobic
conditions. In addition, the amines are effective ~n
moderating the activity of primary oxygen scavengers in
the presence of dis~olved oxygen. Various components
employed to mainta~n pH ~olution control or scavenged
oxygen are effective in part in ob~aining some degree of
solution ~iscositY stability, particularly at lower
~olution temperature; however, the amines ~re more effect-
2~ ive ~nd far more forgi~ing of mischarges or mishandling of
solutions. Surprisingl~,it ~s observed that the amines,
in combination with primary oxygen scavengers and/or
solution pH control reagents, prov~de formulations for
obtaining greater long-term stability than observed through
utilization of the indi~idual co~ponents.
4~.
7C~5~ 11,408
EXPERrMENTAL PROOEDURE
me synthetic water-soluble polymers evaluated in
this study were acrylamide/acrylic acid copolymers (Pusher ~ i
700 - Dow ~hemical~ Polymer 835 - Calgon Corp.), poly-
(ethylene oxide) (POLYOX -WSR 301, Union Carbide Corp ) and
~ laboratory synthesized acrylic ~cid/acrylate ester ter-
polymer. Water-soluble carbohydrates, e.g. polysacchar-
ides (Jansson, et al., ~r ohydrate Res. 45, 275 tl975))
synthesized by Xanthomonas Compestris micro-organisms
(Xanflood-Kelco Corp., Galaxy-General Mills Corp.)
hydroxypropyl guar gum (Jaguar ~ HP-l, Celanese Corp.),
carboxymethyl~ellulose (Cellulose Gum~37H4., Hercules Corp.)
and hydroxyethyl cellulose (CELLOSIZE ~ QPlOOM, Union
Carbide Corp.) were also examined. All water-soluble
polymers were dissolved with stirring in aqueous solutions,
in amounts sufficient to achieve 90 centipoise (cps)
~iQCosity solutions in fresh, 6aline (3 weight percent
~odium chloride) and in saline ~olutions also containing
0.3 weight percent magnesium sulfate, calcium chloride, or
othar divalent non-transition metal salt. The rate of
~olution viscositv losæ was observed to be independent of
the amount of water-soluble polymer employed in prior
studies for several thickeners; therefore, solution vis-
cositles of 90 cps were selected for study to achieve
maximum measurement sen~itivity with a Brookfield Model
LVT Synchro-lectric Viscometer with UL adapter, operated
at a spindle speed of 6 rpm. I~e amount5 of water-soluble
1 U9 7~ S6 1l,408
polymers employed in the various aqueous solutions ~o
~chieve a 90 cps 801ut~on viscosity are recorded in
Table III. - i
_ TABLE III
AMOUNT OE W-S POLYMER REQUIR~D TO OB~AIN
90 cps SOLUTION VISCOSITY
WEIGHT PERCENT~
WATER-SOLUBLE FRESH SALINESALINE WATER
POLYMER WATER WATERWITH 0.3% DIVALENT
10 - _ ~ ION SALT
Pusher~ - 700 0.11 0.55 0.55
Polymer 835 0.09
Xanflood~ 0.17 0.19
Galaxy ~ 0.14 0.17
Jaguar~HP-l O.33
Cellulose Gum @~H4 0,70
OE LL~SIZE lOOM 0,33 0 33 0 33
Polyox~ WSR-301
b) Viscositles measured at 6 rpm spindle speed,
22.22C., (72F.) with Model LVT Brookfield ViQcometer
with UL adapter.
me polymers were dissolved in oxygen saturated
~ca. 8.5 ppm~ water or in aqueous solutions which had been
previously yurged with nitrogen containing 5 ppm.oxygen
~o that aqueous solutions with approximately lpp~o~yg~n could
be obtained. Aqueous 801ution disQolved oxygen concentra-
tions were measured in a nitrogen atmosphere with a YSI
48.
11,40~
7'~J56
Model 54A Oxygen Meter and ~olution pHs were monitored
with a Beckman Zeromatic p~ Meter.
In a given series of study, a speclfic quantity
(325 ml) of solution was charged to a pres~ure bottle
with a 350 ml capacity and c~pped. These procedures were
conducted in a nitrogen a~mosphere if the studies were
related to low oxygen investigations. Independent studies
wherein the glass containers were coated with the amines
indicated that the viscosity losses noted with time were
not the result of surface interactions between solution
polymers and components on the surface of the glass. The
containers in a given series were placed in an automated
temperature control bath and removed at the time intervals
reflected ~n the illustrations noted in this disclosure.
Upon removal, the container was cooled in a 22.22C.
t72F.) bath until a proportional temperature control
regulator indicated equilibrium had been reached; then the
solution parameters cited above were measured. The 801u-
tion was then discarded.
In ~he polymer-preaddition studies, the water was
nitrogen purged to lower the dissolved oxygen content to
~pproximately 1 ppm. me polymer was then dissol~ed under
a nitrogen abmosphere with stirring. Generally the dis-
~olved oxygen content of the thickened solution increased
despi~e attempts to avoid this occurrence. Under such cir-
cumstances the original desired oxygen concentration
(ca. 1 ppm) was ~chieved through additional nitrogen
49.
-- , .
11,408
1t~97~)56
purging; foaming of the thickened solut~ons creates a
difficult Qeyuence, but the procedure was effective. The
primary scavenger, i.e sodium dithionite, ~odium sulfite
etc., were added under a nitrogen atmo3phere ~Q solution
~ or slurry form wi~h the additive be~ng evaluated.
All additives were employed in terms of weight
percent, based on the total solution quantity employed.
Examples of the additives employed are: ferric chloride,
anhydrous, and (e~hylene di~itrilo)-tetraacetic acid, tetra
sodium salt, hydroxylamine hydrochloride and hexamethylene
diamine, ~odium tripolyphosphate, purified; calcium oxide,
powder, magnesium sulfate, anhydrous, and ferrous chloride
CFecl2-4H2o~; magnesium oxide, powder, and calcium sulfate,
powder, ethylene glycoL triethylene glycol, N-methyl-
morpholine, etc.; see the data mentioned zbove.
Noted among the family of the amines u~eful in
the pract~ce of th~s in~ention is an alicyclic amine
product such as aminoethylpiperazine, imidazolene, tri-
~zollne, hexahydro-1,3,5, triazine, etc., whic~ can be used
ef~ectively to achieve the ob~ects of this invention under
certain wellbore simulated conditions. The most effective
alicyclic compounds generally follow the ease with which
the functionalities of the alicycllc, And any appendiced
~liphatic functionalities, can form "five and BiX membered
rings" with the components whose activity i6 to be
...moderated or sequestered. me primary tests defining the
50.
~ 109~7~6 11, 408
j~o~ C~ U~
~1 ~ ,
9~ ]
E~ ~1 o o~
Y~
Z cn n
~ ¦ C¦ -
~'
~1 o
u _ 9 ~ 9
9 ` ~
1a~97~5~; 11,408
performance capability of amine additi~res
haYe been cited above in Table I and secondary tests
associ~:ted with iigures 9, 10 end Table I.
