CA1097056A - Treatment of water thickened systems - Google Patents

Abstract

~STR~CS
r ~ lc ~nY ntlo~ 1~ conc-rn-d ~th t~- tr ae~Qnt of ~t-r c~to~ to ~hlch ~r~ provl~d ~-t-r-~lu~l~
pol~ucrlc ~ t~r~ h-~ln~ th- c-p-bll~ty o~ l~cr--~ln~
th ~*~co-lt~ of ~ t-r ln ~hlch th-~ rc pro~idcd In p~rtleul~r, tbc lnY ntlon 1- conc~rn-t u~th provldl~
a ~ l~nc ~ol~ e~n- or ~n ~lkonol-~ln- ln ~n qucow r~to~ to uhlch b - b~n proY~& d ~-tcr-~olu~l-, po~-n~rlc Y~t-rl-l ~hich ~ncr~ t~Q vlccocit~ o thc ~gu~ou~ ~dl~

Description

11,4~8 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.

' ~ ' ' : ', ~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or more of the original wells or by means of entirely new wells and the o~l in the reservoir is displaced toward and withdrawn from one or m~re of the other rema~ning wells.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.

~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 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, (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 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 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.

Claims (20)

11,408 WHAT IS CLAIMED IS:

1. The composition comprising a solution of water and 2 water-soluble polymeric thickening agent in which the agent is present in an amount sufficient to increase the viscosity of the water the improvement which comprises providing in such solution between about 0.0001 to about 1.0 weight per cent of the solution of one of an alkylenepolyamine, an elkanolamine, an alicyclic polyamine, or a mixture of them.

2. In the process to effect enhanced recovery of oil from a subterranean reservoir with an aqueous driving medium whose viscosity has been increased by providing 2 water-soluble polymeric mobility control agent to the medium, the improvement which comprises providing an amine in the medium in the reservoir in an amount of between about 0.0001 to about 1.0 weight per cent of the medium, which amine is one of an alkylene polyamine, an alkanol amine, an alicyclic polyamine, or a mixture of two or more of them.

3. The process of claim 2 wherein the medium contains sulfite or dithionite oxygen scavenger.

4. The process of claim 3 wherein the oxygen scavenger is added to the medium after addition of the mobility control agent and the amine.

53.

11,408

5. The process of claim 2 wherein the amine is a polyalkylene polyamine.

6. The process of claim 2 wherein the amine is an alkanol amine.

7. The process of claim 2 wherein the amine is an alicyclic amine.

8. The process of claim 2 wherein the amine is of mixture two or more of a polyalkylene polyamine, an alkanol amine and an alicyclic amine.

9. The process of claim 3 wherein the recovery is being effected under anaerobic conditions.

10. The process of claim 2 wherein the amine is a triethylene pentamine.

11. me process of claim 2 wherein the amine is hexaethylene heptamine.

12. me process of claim 2 wherein the amine is diethylene triamine.

13. me process of claim 2 wherein the amine is tetraethylenepentamine.

14. The process of claim 2 wherein the amine is poly(ethyleneimine).

54.

11,408

15. The process of claim 2 wherein the amine is triethanolamine and the mobility agent is a poly-acrylamide.

16. The process of claim 2 wherein the mobility control agent is hydroxyethyl cellulose.

17. The process of claim 2 wherein the mobility control agent is a water-soluble polymeric carbohydrate.

18. The process of claim 17 wherein the carbo-hydrate is a polysaccharide.

19. The process of claim 18 wherein the poly-saccharide is xanthomonas compestris.

20. The process of claim 18 wherein the poly-saccharide is a guar gum.

55.